U.S. patent application number 14/572486 was filed with the patent office on 2016-08-18 for electrically-conductive proppant and methods for making and using same.
The applicant listed for this patent is CARBO Ceramics Inc.. Invention is credited to Chad Cannan, Daniel R. Mitchell, Todd Roper, Steve Savoy.
Application Number | 20160237342 14/572486 |
Document ID | / |
Family ID | 56127823 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160237342 |
Kind Code |
A1 |
Cannan; Chad ; et
al. |
August 18, 2016 |
Electrically-Conductive Proppant and Methods for Making and Using
Same
Abstract
Electrically-conductive sintered, substantially round and
spherical particles and methods for producing such
electrically-conductive sintered, substantially round and spherical
particles from an alumina-containing raw material. Methods for
using such electrically-conductive sintered, substantially round
and spherical particles in hydraulic fracturing operations.
Inventors: |
Cannan; Chad; (Cypress,
TX) ; Roper; Todd; (Katy, TX) ; Savoy;
Steve; (Austin, TX) ; Mitchell; Daniel R.;
(Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CARBO Ceramics Inc. |
Houston |
TX |
US |
|
|
Family ID: |
56127823 |
Appl. No.: |
14/572486 |
Filed: |
December 16, 2014 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 18/1851 20130101;
C23C 18/36 20130101; C01P 2006/10 20130101; E21B 43/267 20130101;
B05D 5/12 20130101; C09K 8/805 20130101; Y10T 428/2438 20150115;
Y10T 428/2991 20150115; C23C 18/50 20130101; C23C 18/1641 20130101;
C23C 18/1639 20130101; H01B 1/02 20130101; C01P 2006/40
20130101 |
International
Class: |
C09K 8/80 20060101
C09K008/80 |
Goverment Interests
STATEMENT OF GOVERNMENTAL INTEREST
[0001] This invention was made under a CRADA (SC11/01780.00)
between CARBO Ceramics, Inc. and Sandia National Laboratories,
operated for the United States Department of Energy. The Government
has certain rights in this invention.
Claims
1. A proppant pack comprising: a plurality of particles, each said
particle, comprising a coating of an electrically-conductive metal
having a thickness of at least about 270 nm formed on the outer
surface of each said particle, wherein each particle has a specific
gravity of less than 4 and a size of about 100 mesh to about 10
mesh, wherein the pack has an electrical conductivity, and wherein
increasing a load on the pack by a factor of 5 increases the
electrical conductivity of the pack by at least 50%.
2. The proppant pack of claim 1, wherein the plurality of particles
is selected from the group consisting of sand, resin coated sand,
and sintered, substantially round and spherical particles.
3. The proppant pack of claim 2, wherein increasing the load on the
pack by a factor of 2 decreases the resistivity of the pack by
about 5% to about 25%.
4. The proppant pack of claim 1, wherein the
electrically-conductive metal has a thickness of about 500 nm to
about 1,200 nm.
5. The proppant pack of claim 1, wherein the pack has an electrical
conductivity of at least about 5 S/m.
6. The proppant pack of claim 5, wherein each said particle has a
roughness of less than 5 .mu.m.
7. The proppant pack of claim 1, wherein the
electrically-conductive metal is selected from the group consisting
of aluminum, tin, zinc, copper, silver, nickel, gold, platinum,
palladium and rhodium.
8. The proppant pack of claim 3, wherein the
electrically-conductive metal is deposited onto the outer surface
of each said particle using autocatalytic deposition.
9. The proppant pack of claim 1, wherein the proppant pack has a
resistivity of less than 0.5 ohm-cm.
10. The proppant pack of claim 1, wherein the outer surface of each
said particle comprises palladium, silver, or any combination
thereof.
11. The proppant pack of claim 1, wherein the proppant pack has a
long term fluid conductivity at 7,500 psi of at least about 100
mD-ft.
12. A method of manufacturing electrically-conductive proppant
particles, comprising: contacting a plurality of particles having a
size of about 100 mesh to about 10 mesh with an alkaline solution
having a pH greater than 8 to provide conditioned particles; and
contacting the conditioned particles with a plating solution
comprising one or more electrically-conductive metal to provide
electrically-conductive proppant particles comprising a coating of
the electrically-conductive metal having a thickness of at least
about 270 nm formed on the outer surface of each said particle,
wherein a pack of the electrically-conductive proppant particles
has an electrical conductivity, and wherein increasing a load on
the pack by a factor of 5 increases the electrical conductivity of
the pack by at least 50%.
13. The method of claim 12, further comprising: contacting the
conditioned particles with an activation solution comprising a
catalytically active material to provide activated particles,
wherein the catalytically active material comprises tin, palladium,
or silver or any combination thereof; and contacting the activated
particles with the plating solution to provide the
electrically-conductive proppant particles.
14. The method of claim 12, further comprising: contacting the
conditioned particles with a reducing agent solution to provide
activated particles, wherein the reducing agent solution comprises
sodium borohydride, sodium hypophosphite, or sodium
cyanoborohydride or any combination thereof; and contacting the
activated particles with the plating solution to provide the
electrically-conductive proppant particles.
15. The method of claim 12, wherein the plurality of particles is
selected from the group consisting of sand, resin coated sand, and
sintered, substantially round and spherical particles.
16. (canceled)
17. A method of manufacturing electrically-conductive proppant
particles, comprising: activating a plurality of sintered,
substantially round and spherical particles to provide activated
particles, wherein each of the plurality of sintered, substantially
round and spherical particles has a specific gravity of less than 4
and a size of about 100 mesh to about 10 mesh; and contacting the
activated particles with a plating solution comprising one or more
electrically-conductive metal to provide electrically-conductive
proppant particles comprising a coating of the
electrically-conductive metal having a thickness of at least about
270 nm formed on the outer surface of each said particle, wherein a
pack of the electrically-conductive proppant particles has an
electrical conductivity, and wherein increasing a load on the pack
by a factor of 5 increases the electrical conductivity of the pack
by at least 50%.
18. The method of claim 17, wherein activating the conditioned
particles comprises one of: contacting the plurality of sintered,
substantially round and spherical particles with an activation
solution comprising a catalytically active material to provide the
activated particles, wherein the catalytically active material
comprises tin, palladium, or silver or any combination thereof; or
contacting the plurality of sintered, substantially round and
spherical particles with a reducing agent solution to provide the
activated particles, wherein the reducing agent solution comprises
sodium borohydride, sodium hypophosphite, or sodium
cyanoborohydride or any combination thereof.
19. The method of claim 17, wherein the electrically-conductive
metal is selected from the group consisting of aluminum, tin, zinc,
copper, silver, nickel, gold, platinum, palladium and rhodium.
20. The method of claim 19, wherein the plating solution is an
alkaline solution comprising nickel.
21. The method of claim 20, wherein the electrically-conductive
proppant particles comprise palladium, phosphorous and nickel
deposited on the outer surfaces of the plurality of sintered,
substantially round and spherical particles.
Description
BACKGROUND
[0002] Embodiments of the present invention relate generally to
hydraulic fracturing of geological formations, and more
particularly to electromagnetic (EM) methods for detecting,
locating, and characterizing electrically-conductive proppants used
in the hydraulic fracture stimulation of gas, oil, or geothermal
reservoirs. The methods described herein involve electrically
energizing the earth at or near a fracture at the depth of the
fracture and measuring the electric and magnetic field responses at
the earth's surface or in adjacent wells/boreholes. Other
embodiments of the present invention relate to compositions and
methods for the formation of the electrically-conductive proppants
for use in the electromagnetic methods for detecting, locating and
characterizing such proppants.
[0003] In order to stimulate and more effectively produce
hydrocarbons from downhole formations, especially formations with
low porosity and/or low permeability, induced fracturing (called
"frac operations", "hydraulic fracturing", or simply "fracing") of
the hydrocarbon-bearing formations has been a commonly used
technique. In a typical frac operation, fluids are pumped downhole
under high pressure, causing the formations to fracture around the
borehole, creating high permeability conduits that promote the flow
of the hydrocarbons into the borehole. These frac operations can be
conducted in horizontal and deviated, as well as vertical,
boreholes, and in either intervals of uncased wells, or in cased
wells through perforations.
[0004] In cased boreholes in vertical wells, for example, the high
pressure fluids exit the borehole via perforations through the
casing and surrounding cement, and cause the formations to
fracture, usually in thin, generally vertical sheet-like fractures
in the deeper formations in which oil and gas are commonly found.
These induced fractures generally extend laterally a considerable
distance out from the wellbore into the surrounding formations, and
extend vertically until the fracture reaches a formation that is
not easily fractured above and/or below the desired frac interval.
The directions of maximum and minimum horizontal stress within the
formation determine the azimuthal orientation of the induced
fractures. Normally, if the fluid, sometimes called slurry, pumped
downhole does not contain solids that remain lodged in the fracture
when the fluid pressure is relaxed, then the fracture re-closes,
and most of the permeability conduit gain is lost.
[0005] These solids, called proppants, are generally composed of
sand grains or ceramic particles, and the fluid used to pump these
solids downhole is usually designed to be sufficiently viscous such
that the proppant particles remain entrained in the fluid as it
moves downhole and out into the induced fractures. Prior to
producing the fractured formations, materials called "breakers",
which are also pumped downhole in the frac fluid slurry, reduce the
viscosity of the frac fluid after a desired time delay, enabling
these fluids to be easily removed from the fractures during
production, leaving the proppant particles in place in the induced
fractures to keep them from closing and thereby substantially
precluding production fluid flow there through.
[0006] The proppants can also be placed in the induced fractures
with a low viscosity fluid in fracturing operations referred to as
"water fracs" or "slick water fracs". The fracturing fluid in water
fracs is water with little or no polymer or other additives. Water
fracs are advantageous because of the lower cost of the fluid used.
Also when using cross-linked polymers, it is essential that the
breakers be effective or the fluid cannot be recovered from the
fracture, effectively restricting flow of formation fluids. Water
fracs, because the fluid is not cross-linked, do not rely on the
effectiveness of breakers.
[0007] Commonly used proppants include naturally occurring sands,
resin coated sands, and ceramic proppants. Ceramic proppants are
typically manufactured from naturally occurring materials such as
kaolin and bauxitic clays, and offer a number of advantages
compared to sands or resin coated sands principally resulting from
the compressive strength of the manufactured ceramics and their
highly spherical particle shape.
[0008] Although induced fracturing has been a highly effective tool
in the production of hydrocarbon reservoirs, the amount of
stimulation provided by this process depends to a large extent upon
the ability to generate new fractures, or to create or extend
existing fractures, as well as the ability to maintain connection
to the fractures through appropriate placement of the proppant.
Without appropriate placement of the proppant, fractures generated
during the hydraulic fracturing can tend to close, thereby
diminishing the benefits of the hydraulic fracturing treatment.
However, reliable methods for detecting, locating and
characterizing the placement of proppant within fractures at
relatively far distances from the wellbore and thus confirming
whether or not such placement has been appropriate are not
available.
[0009] Current state of the art proppant identification techniques
are limited to relatively short distances (12 inches to 18 inches
maximum) from the wellbore. Radioactive and non-radioactive tracers
and proppants are currently used to infer the presence of proppant
in the near well bore region. A better understanding of proppant
placement in the far field regions of a hydraulic fracture is
needed.
[0010] Previous work for massive hydraulic fracture mapping is
summarized in Bartel, L. C., McCann, R. P., and Keck, L. J., Use of
potential gradients in massive hydraulic fracture mapping and
characterization, prepared for the 51st Annual Fall Technical
Conference and Exhibition of Society of Petroleum Engineers, New
Orleans, Oct. 3-6, 1976 paper SPE 6090. In this previous work, the
electric potential differences were measured between two concentric
circles of voltage electrodes around a vertical fracture well at
the earth's surface. The well was electrically energized at the top
of the well casing or at the depth of the fracture. The electrical
ground was established at a well located at a distance of
approximately one mile from the fracture well. At that time, the
fact that the grounding wire acted as a transmitting antenna was
not taken into account. The water used for the fracture process
contained potassium chloride (KCl) to enhance its electrical
conductivity and the fracture was propped using non-conducting
sand. A 1 Hz repetition rate square wave input current waveform was
used and only the voltage difference amplitudes were measured.
Voltages using an elementary theory based on current leakage from
the well casing and the fracture into a homogeneous earth were used
to produce expected responses. Comparing the field data to results
from the elementary model showed that a fracture orientation could
be inferred, however, since the model did not account for the
details of the fracture, other fracture properties could not be
determined using the elementary model.
[0011] A method of detecting, locating and characterizing the
location of the proppant as placed in a hydraulic fracture at
distances of more than several inches from the cased wellbore is
currently unavailable. Such a method for detecting, locating and
characterizing the proppant material after the proppant material is
placed in a fracture would be beneficial.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention may best be understood by referring to the
following description and accompanying drawings that are used to
illustrate embodiments of the invention. In the drawings:
[0013] FIG. 1 is a schematic illustration of a system for preparing
substantially round and spherical particles from a slurry as
described herein.
[0014] FIG. 2 is a flow chart showing steps of an electroless
coating method for electrically-conductive material onto a proppant
substrate.
[0015] FIG. 3 is another flow chart showing alternative steps of an
electroless coating method for electrically-conductive material
onto a proppant substrate.
[0016] FIG. 4 is a diagram of the geometric layout of a vertical or
deviated well in which layers of the earth having varying
electrical and mechanical properties are depicted.
[0017] FIG. 5 is a schematic of an installed horizontal wellbore
casing string traversing a hydrocarbon bearing zone with proppant
filled fractures in which layers of the earth having varying
electrical and mechanical properties are depicted.
[0018] FIG. 6 is a schematic cross-sectional illustration of a
hydraulic fracture mapping system which depicts two embodiments for
introducing electric current into a wellbore, namely energizing the
wellbore at the surface and energizing via a wireline with a sinker
bar near perforations in the wellbore.
[0019] FIG. 7 is a schematic plan illustration of a hydraulic
fracture mapping system.
[0020] FIG. 8 is a schematic perspective illustration of a
hydraulic fracture mapping system.
[0021] FIG. 9A is a schematic illustration of an electrically
insulated casing joint.
[0022] FIG. 9B is a schematic illustration of an electrically
insulated casing collar.
[0023] FIG. 10 is a schematic illustration of a test system for
measuring proppant electrical resistance.
[0024] FIG. 11 is a graph of resistivity (Ohm-cm) vs. Closure
Pressure (psi) for various proppant samples.
[0025] FIG. 12 is a graph of resistivity (Ohm-cm) vs. Closure
Pressure (psi) for mixtures of CARBOLITE 20/40 coated with aluminum
and standard ECONOPROP 20/40 samples.
[0026] FIG. 13 is a graph of resistivity (Ohm-cm) vs. Closure
Pressure (psi) for mixtures of HYDROPROP 40/80 coated with aluminum
and standard HYDROPROP 40/80 samples.
[0027] FIG. 14 is a graph of Conductivity (Siemens/m) vs. Pressure
(psi) for CARBOLITE 20/40 coated with nickel and CARBOLITE 20/40
coated with copper.
[0028] FIG. 15 is a graph of Conductivity (Siemens/m) vs. Pressure
(psi) for CARBOLITE 20/40 samples coated with varied thicknesses of
nickel.
[0029] FIG. 16 is a graph of Conductivity (Siemens/m) vs. exposure
time to frac fluid at a fixed Closure Pressure (psi) for CARBOLITE
20/40 samples coated with nickel and copper.
DETAILED DESCRIPTION
[0030] In the following description, numerous specific details are
set forth. However, it is understood that embodiments of the
invention may be practiced without these specific details. In other
instances, well-known structures and techniques have not been shown
in detail in order not to obscure the understanding of this
description.
[0031] Described herein are electromagnetic (EM) methods for
detecting, locating, and characterizing electrically -conductive
proppants used in the hydraulic fracture stimulation of gas, oil,
or geothermal reservoirs. Also described herein are
electrically-conductive sintered, substantially round and spherical
particles and methods for preparing such electrically-conductive
sintered, substantially round and spherical particles from a slurry
of an alumina-containing raw material for use as proppants in the
electromagnetic methods. The term "substantially round and
spherical" and related forms, as used herein, is defined to mean an
average ratio of minimum diameter to maximum diameter of about 0.8
or greater, or having an average sphericity value of about 0.8 or
greater compared to a Krumbein and Sloss chart.
[0032] According to embodiments of the present invention, the
electrically-conductive sintered, substantially round and spherical
particles, referred to hereinafter as "electrically-conductive
proppant" may be made from a conventional proppant such as a
ceramic proppant, resin-coated ceramic proppant, sand, resin-coated
sand, plastic beads and glass beads. Such conventional proppants
can be manufactured according to any suitable process including,
but not limited to continuous spray atomization, spray
fluidization, spray drying, or compression. Suitable conventional
proppants and methods for their manufacture are disclosed in U.S.
Pat. Nos. 4,068,718, 4,427,068, 4,440,866, 5,188,175, and
7,036,591, the entire disclosures of which are incorporated herein
by reference.
[0033] Ceramic proppants vary in properties such as apparent
specific gravity by virtue of the starting raw material and the
manufacturing process. The term "apparent specific gravity" as used
herein is the weight per unit volume (grams per cubic centimeter)
of the particles, including the internal porosity. Low density
proppants generally have an apparent specific gravity of less than
3.0 g/cm.sup.3 and are typically made from kaolin clay and other
alumina, oxide, or silicate ceramics. Intermediate density
proppants generally have an apparent specific gravity of about 3.1
to 3.4 g/cm.sup.3 and are typically made from bauxitic clay. High
strength proppants are generally made from bauxitic clays with
alumina and have an apparent specific gravity above 3.4
g/cm.sup.3.
[0034] Sintered, substantially round and spherical particles can be
prepared from a slurry of alumina-containing raw material. In
certain embodiments, the particles have an alumina content of from
about 40% by weight (wt %) to about 55 wt % . In certain other
embodiments, the sintered, substantially round and spherical
particles have an alumina content of from about 41.5 wt % to about
49 wt %.
[0035] In certain embodiments, the sintered, substantially round
and spherical particles have a bulk density of from about 1
g/cm.sup.3, about 1.15 g/cm.sup.3, about 1.25 g/cm.sup.3, or about
1.35 g/cm.sup.3 to about 1.55 g/cm.sup.3, about 1.75 g/cm.sup.3,
about 2 g/cm.sup.3, or about 2.5 g/cm.sup.3. The term "bulk
density," as used herein, refers to the weight per unit volume,
including in the volume considered, the void spaces between the
particles. In certain other embodiments, the particles have a bulk
density of from about 1.40 g/cm.sup.3 to about 1.50 g/cm.sup.3.
[0036] According to several exemplary embodiments, the
substantially round and spherical particles have any suitable
permeability and fluid conductivity in accordance with ISO 13503-5:
"Procedures for Measuring the Long-term Conductivity of Proppants,"
and expressed in terms of Darcy units, or Darcies (D). The
particles can have a long term permeability at 7,500 psi of at
least about 1 D, at least about 2 D, at least about 5 D, at least
about 10 D, at least about 20 D, at least about 40 D, at least
about 80 D, at least about 120 D, or at least about 150 D. The
particles can have a long term permeability at 12,000 psi of at
least about 1 D, at least about 2 D, at least about 3 D, at least
about 4 D, at least about 5 D, at least about 10 D, at least about
25 D, or at least about 50 D. The particles can have a long term
conductivity at 7,500 psi of at least about 100 millidarcy-feet
(mD-ft), at least about 200 mD-ft, at least about 300 mD-ft, at
least about 500 mD-ft, at least about 1,000 mD-ft, at least about
1,500 mD-ft, at least about 2,000 mD-ft, or at least about 2,500
mD-ft. For example, the particles can have a long term conductivity
at 12,000 psi of at least about 50 mD-ft, at least about 100 mD-ft,
at least about 200 mD-ft, at least about 300 mD-ft, at least about
500 mD-ft, at least about 1,000 mD-ft, or at least about 1,500
mD-ft.
[0037] In certain embodiments, the sintered, substantially round
and spherical particles have a crush strength at 10,000 psi of from
about 5% to about 8.5%, and a long-term fluid conductivity at
10,000 psi of from about 2500 mD-ft to about 3000 mD-ft. In certain
other embodiments, the sintered, substantially round and spherical
particles have a crush strength at 10,000 psi of from about 5% to
about 7.5%.
[0038] The sintered, substantially round and spherical particles
can have any suitable apparent specific gravity. In one or more
exemplary embodiments, the sintered, substantially round and
spherical particles have an apparent specific gravity of less than
5, less than 4.5, less than 4.2, less than 4, less than 3.8, less
than 3.5, or less than 3.2. In still other embodiments, the
sintered, substantially round and spherical particles have an
apparent specific gravity of from about 2.50 to about 3.00, about
2.75 to about 3.25, about 2.8 to about 3.4, about 3.0 to about 3.5,
or about 3.2 to about 3.8. The term "apparent specific gravity,"
(ASG) as used herein, refers to a number without units that is
defined to be numerically equal to the weight in grams per cubic
centimeter of volume, including void space or open porosity in
determining the volume.
[0039] The sintered, substantially round and spherical particles
can have any suitable size. According to one or more exemplary
embodiments, the substantially round and spherical particles can
have a size of at least about 100 mesh, at least about 80 mesh, at
least about 60 mesh, at least about 50 mesh, or at least about 40
mesh. For example, the substantially round and spherical particles
can have a size from about 115 mesh to about 2 mesh, about 100 mesh
to about 3 mesh, about 80 mesh to about 5 mesh, about 80 mesh to
about 10 mesh, about 60 mesh to about 12 mesh, about 50 mesh to
about 14 mesh, about 40 mesh to about 16 mesh, or about 35 mesh to
about 18 mesh. In a particular embodiment, the substantially round
and spherical particles have a size of from about 20 to about 40
U.S. Mesh.
[0040] Suitable ceramic proppants can also include proppants
manufactured according to vibration-induced dripping methods,
herein called "drip casting." Suitable drip casting methods and
proppants made therefrom are disclosed in U.S. Pat. Nos. 8,865,631
and 8,883,693, U.S. Patent Application Pub. No. 2012/0227968, and
U.S. patent application Ser. No. 14/502,483, the entire disclosures
of which are incorporated herein by reference. Proppants produced
from the drip cast methods can have a specific gravity of at least
about 2.5, at least about 2.7, at least about 3, at least about
3.3, or at least about 3.5. Proppants produced from the drip cast
methods can have a specific gravity of less than 5, less than 4.5,
or less than 4. The drip cast proppants can also have a surface
roughness of less than 5 .mu.m, less than 4 .mu.m, less than 3
.mu.m, less than 2.5 .mu.m, less than 2 .mu.m, less than 1.5 .mu.m,
or less than 1 .mu.m. In one or more exemplary embodiments, the
drip cast proppants have an average largest pore size of less than
about 25 .mu.m, less than about 20 .mu.m, less than about 18 .mu.m,
less than about 16 .mu.m, less than about 14 .mu.m, or less than
about 12 .mu.m and/or a standard deviation in pore size of less
than 6 .mu.m, less than 4 .mu.m, less than 3 .mu.m, less than 2.5
.mu.m, less than 2 .mu.m, less than 1.5 .mu.m, or less than 1
.mu.m. In one or more exemplary embodiments, the drip cast
proppants have less than 5,000, less than 4,500, less than 4,000,
less than 3,500, less than 3,000, less than 2,500, or less than
2,200 visible pores at a magnification of 500.times. per square
millimeter of proppant particulate.
[0041] The ceramic proppants, produced by the drip casting methods
or the conventional methods, can have any suitable composition. The
ceramic proppant can be or include silica and/or alumina in any
suitable amounts. According to one or more embodiments, the ceramic
proppant includes less than 80 wt %, less than 60 wt %, less than
40 wt %, less than 30 wt %, less than 20 wt %, less than 10 wt %,
or less than 5 wt % silica based on the total weight of the ceramic
proppant. According to one or more embodiments, the ceramic
proppant includes from about 0.1 wt % to about 70 wt % silica, from
about 1 wt % to about 60 wt % silica, from about 2.5 wt % to about
50 wt % silica, from about 5 wt % to about 40 wt % silica, or from
about 10 wt % to about 30 wt % silica. According to one or more
embodiments, the ceramic proppant includes at least about 30 wt %,
at least about 50 wt %, at least about 60 wt %, at least about 70
wt %, at least about 80 wt %, at least about 90 wt %, or at least
about 95 wt % alumina based on the total weight of the ceramic
proppant. According to one or more embodiments, the ceramic
proppant includes from about 30 wt % to about 99.9 wt % alumina,
from about 40 wt % to about 99 wt % alumina, from about 50 wt % to
about 97 wt % alumina, from about 60 wt % to about 95 wt % alumina,
or from about 70 wt % to about 90 wt % alumina. In one or more
embodiments, the ceramic proppant produced by the processes
disclosed herein can include alumina, bauxite, or kaolin, or any
mixture thereof. For example, the ceramic proppant can be composed
entirely of or composed essentially of alumina, bauxite, or kaolin,
or any mixture thereof. The term "kaolin" is well known in the art
and can include a raw material having an alumina content of at
least about 40 wt % on a calcined basis and a silica content of at
least about 40 wt % on a calcined basis. The term "bauxite" is well
known in the art and can be or include a raw material having an
alumina content of at least about 55 wt % on a calcined basis.
[0042] An electrically-conductive material such as a metal, a
conductive polymer, conductive carbonaceous material such as
graphene, or a conductive nanoparticle can be added at any suitable
stage in the manufacturing process of any one of these proppants to
result in proppant suitable for use according to certain
embodiments of the present invention. The electrically-conductive
material can also be added to any one of these proppants after
manufacturing of the proppants. Suitable metals include aluminum,
tin, zinc, copper, silver, nickel, gold, platinum, palladium,
rhodium and the like and can be added to result in an
electrically-conductive proppant having any suitable metal content.
The electrically-conductive proppant can have an
electrically-conductive metal concentration of about 0.01 wt %,
about 0.05 wt %, about 0.1 wt %, about 0.5 wt %, about 1 wt %,
about 2 wt %, or about 5 wt % to about 6 wt %, about 8 wt %, about
10 wt %, about 12 wt %, or about 14 wt %.
[0043] Suitable conductive polymers include
poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)
(PEDOT:PSS), polyanilines (PANI), polypyrroles (PPY) and the like
and can be added to result in an electrically-conductive proppant
having any suitable conductive polymer content. The
electrically-conductive proppant can have a conductive polymer
concentration of about 0.01 wt %, about 0.05 wt %, about 0.1 wt %,
about 0.5 wt %, about 1 wt %, about 2 wt %, or about 5 wt % to
about 6 wt %, about 8 wt %, about 10 wt %, about 12 wt %, or about
14 wt %.
[0044] Suitable PEDOT:PSS, PANI and PYY conductive polymers are
commercially available from Sigma-Aldrich. Certain specific
embodiments of processes for coating proppant with a conductive
polymer are described below in Example 2.
[0045] Suitable conducting nanoparticles include graphite,
graphene, single or double-walled carbon nanotubes, or other
material that when present in the nanoscale particle size range
exhibits sufficient electrical conductivity to permit detection in
the present invention. Such conducting nanoparticles can be added
to result in a proppant having a conducting nanoparticle content of
from about 0.01 wt %, about 0.05 wt %, about 0.1 wt %, about 0.5 wt
%, about 1 wt %, about 2 wt %, or about 5 wt % to about 6 wt %,
about 8 wt %, about 10 wt %, about 12 wt %, or about 14 wt % based
on the weight of the electrically-conductive proppant.
[0046] Ceramic proppant may also be manufactured in a manner that
creates porosity in the proppant grain. A process to manufacture a
suitable porous ceramic proppant is described in U.S. Pat. No.
7,036,591, the entire disclosure of which is incorporated herein by
reference. In this case the electrically-conductive material can be
impregnated into the pores of the proppant grains to a
concentration of about 0.01 wt %, about 0.05 wt %, about 0.1 wt %,
about 0.5 wt %, about 1 wt %, about 2 wt %, or about 5 wt % to
about 6 wt %, about 8 wt %, about 10 wt %, about 12 wt %, about 15
wt %, or about 20 wt % based on the weight of the
electrically-conductive proppant. Water soluble coatings such as
polylactic acid can be used to coat these particles to allow for
delayed/timed release of conducting nano-particles for detection at
different stages of the fracture treatment.
[0047] The ceramic proppants can have any suitable porosity. The
ceramic proppants can include an internal interconnected porosity
from about 1%, about 2%, about 4%, about 6%, about 8%, about 10%,
about 12%, or about 14% to about 18%, about 20%, about 22%, about
24%, about 26%, about 28%, about 30%, about 34%, about 38%, or
about 45% or more. In several exemplary embodiments, the internal
interconnected porosity of the ceramic proppants is from about 5 to
about 35%, about 5 to about 15%, or about 15 to about 35%.
According to several exemplary embodiments, the ceramic proppants
have any suitable average pore size. For example, the ceramic
proppant can have an average pore size from about 2 nm, about 10
nm, about 15 nm, about 55 nm, about 110 nm, about 520 nm, or about
1,100 nm to about 2,200 nm, about 5,500 nm, about 11,000 nm, about
17,000 nm, or about 25,000 nm or more in its largest dimension. For
example, the ceramic proppant can have an average pore size from
about 3 nm to about 30,000 nm, about 30 nm to about 18,000 nm,
about 200 nm to about 9,000 nm, about 350 nm to about 4,500 nm, or
about 850 nm to about 1,800 nm in its largest dimension. According
to certain embodiments described herein, the sintered,
substantially round and spherical particles are made in a
continuous process, while in other embodiments, the particles are
made in a batch process.
[0048] In one or more exemplary embodiments, the
electrically-conductive material can be added to a ceramic proppant
in its method of manufacture. Referring now to FIG. 1, an exemplary
system for implementing a continuous process for preparing
sintered, substantially round and spherical particles from a slurry
is illustrated. The exemplary system illustrated in FIG. 1 is
similar in configuration and operation to that described in U.S.
Pat. No. 4,440,866, the entire disclosure of which is incorporated
herein by reference. The operations performed by the exemplary
system illustrated in FIG. 1 can also be used to make the particles
according to a batch process, as described in Example 1 below.
[0049] In the system illustrated in FIG. 1, an alumina-containing
raw material having an alumina content of from about 40% to about
55% by weight (on a calcined basis) is passed through a shredder
105 which slices and breaks apart the raw material into small
chunks. In some embodiments, when the raw material as mined, or as
received, (referred to herein as "untreated" raw material) is of
such consistency that it can be processed as described herein
without shredding, the shredder may be bypassed. Raw material fed
through a shredder such as is illustrated in FIG. 1, is referred to
as "treated" raw material.
[0050] In certain embodiments, the shredder breaks apart and slices
the alumina-containing raw material so as to yield pieces having a
diameter of less than about five inches, although pieces having
smaller and larger diameters can be further processed into a slurry
as described herein. Shredders and numerous other devices for
slicing, chopping or comminuting the alumina-containing raw
material, as well as commercial sources for same, such as the
Gleason Foundry Company, are well -known to those of ordinary skill
in the art.
[0051] The treated or untreated alumina-containing raw material and
water are fed to a blunger 110, which has a rotating blade that
imparts a shear force to and further reduces the particle size of
the raw material to form a slurry. In a continuous process, the raw
material and water are continuously fed to the blunger. Blungers
and similar devices for making slurries of such materials, as well
as commercial sources for same are well-known to those of ordinary
skill in the art.
[0052] In certain embodiments, the electrically-conductive material
is added to the alumina-containing raw material and water in the
blunger 110 to result in an electrically-conductive material
concentration of about 0.1% to about 10.0% or about 5.0% to about
10.0% by weight of the solids content in the slurry or just prior
to the formation of pellets as described below.
[0053] A sufficient amount of water is added to the blunger 110 to
result in a slurry having a solids content in the range of from
about 40% to about 60% by weight. In certain embodiments, a
sufficient amount of water is added to the slurry such that the
solids content of the slurry is from about 45% to about 55% by
weight. In still other embodiments, a sufficient amount of water is
added to the slurry such that the solids content of the slurry is
about 50% by weight. The water added to the blunger 110 can be
fresh water or deionized water. In a continuous process for
preparing the slurry, the solids content of the slurry is
periodically analyzed and the amount of water fed to the slurry
adjusted to maintain the desired solids content. Methods for
analyzing the solids content of a slurry and adjusting a feed of
water are well-known and understood by those of ordinary skill in
the art.
[0054] In certain embodiments, a dispersant is added to the slurry
in the blunger 110 to adjust the viscosity of the slurry to a
target range as discussed further below. In other embodiments, the
viscosity of the slurry in the blunger 110 is adjusted to the
target range by the addition of a dispersant and a pH-adjusting
reagent.
[0055] A dispersant may be added to the slurry prior to the
addition of the electrically-conductive material or other
additives. In certain embodiments, the composition includes a
dispersant in an amount of from about 0.15% to about 0.30% by
weight based on the dry weight of the alumina-containing raw
material.
[0056] Exemplary materials suitable for use as a dispersant in the
compositions and methods described herein include but are not
limited to sodium polyacrylate, ammonium polyacrylate, ammonium
polymethacrylate, tetra sodium pyrophosphate, tetra potassium
pyrophosphate, polyphosphate, ammonium polyphosphate, ammonium
citrate, ferric ammonium citrate, and polyelectrolytes such as a
composition of ammonium polymethacrylate and water commercially
available from a variety of sources, such as, Kemira Chemicals
under the trade name C-211, Phoenix Chemicals, Bulk Chemical
Systems under the trade name BCS 4020 and R. T. Vanderbilt Company,
Inc. under the trade name DARVAN C. Generally, the dispersant can
be any material that will adjust the viscosity of the slurry to a
target viscosity such that the slurry can be subsequently processed
through one or more pressure nozzles of a fluidizer. In certain
embodiments, the target viscosity is less than 150 centipoises
(cps) (as determined on a Brookfield Viscometer with a #61
spindle). In other embodiments, the target viscosity is less than
100 cps.
[0057] According to embodiments in which a pH-adjusting reagent is
used, a sufficient amount of a pH-adjusting reagent is added to the
slurry to adjust the pH of the slurry to a range of from about 8 to
about 11. In certain embodiments, a sufficient amount of the
pH-adjusting reagent is added to the slurry to adjust the pH to
about 9, about 9.5, about 10 or about 10.5. The pH of the slurry
can be periodically analyzed by a pH meter, and the amount of
pH-adjusting reagent fed to the slurry adjusted to maintain a
desired pH. Methods for analyzing the pH of a slurry and adjusting
the feed of the pH-adjusting reagent are within the ability of
those of ordinary skill in the art. Exemplary materials suitable
for use as a pH-adjusting reagent in the compositions and methods
described herein include but are not limited to ammonia and sodium
carbonate.
[0058] Generally, the target viscosity of the compositions is a
viscosity that can be processed through a given type and size of
pressure nozzle in a fluidizer, without becoming clogged.
Generally, the lower the viscosity of the slurry, the more easily
it can be processed through a given fluidizer. However, the
addition of too much dispersant can cause the viscosity of the
slurry to increase to a point that it cannot be satisfactorily
processed through a given fluidizer. One of ordinary skill in the
art can determine the target viscosity for given fluidizer types
through routine experimentation.
[0059] The blunger 110 mixes the alumina-containing raw material,
electrically-conductive material, water, dispersant and
pH-adjusting reagent until a slurry is formed. The length of time
required to form a slurry is dependent on factors such as the size
of the blunger, the speed at which the blunger is operating, and
the amount of material in the blunger.
[0060] From the blunger 110, the slurry is fed to a tank 115, where
the slurry is continuously stirred, and a binder is added in an
amount of from about 0.2% to about 5.0% by weight, based on the
total dry weight of the alumina-containing raw material and the
electrically-conductive material. In certain embodiments, the
binder is added in an amount of from about 0.2% to about 3.0% by
weight based on the total dry weight of the alumina-containing raw
material and the electrically-conductive material. Suitable binders
include but are not limited to polyvinyl acetate, polyvinyl alcohol
(PVA), methylcellulose, dextrin and molasses. In certain
embodiments, the binder is PVA having a molecular weight of from
about 20,000 to 100,000 M.sub.n. "M.sub.n" represents the number
average molecular weight which is the total weight of the polymeric
molecules in a sample, divided by the total number of polymeric
molecules in that sample.
[0061] The tank 115 maintains the slurry created by the blunger
110. However, the tank 115 stirs the slurry with less agitation
than the blunger, so as to mix the binder with the slurry without
causing excessive foaming of the slurry or increasing the viscosity
of the slurry to an extent that would prevent the slurry from being
fed through the pressurized nozzles of a fluidizer.
[0062] In another embodiment, the binder can be added to the slurry
while in the blunger. In this embodiment, the blunger optionally
has variable speeds, including a high speed to achieve the high
intensity mixing for breaking down the raw material into a slurry
form, and a low speed to mix the binder with the slurry without
causing the above-mentioned excessive foaming or increase in
viscosity.
[0063] Referring again to the tank 115 illustrated in FIG. 1, the
slurry is stirred in the tank, after addition of the binder, for a
time sufficient to thoroughly mix the binder with the slurry. In
certain embodiments, the slurry is stirred in the tank for up to
about 30 minutes following the addition of binder. In other
embodiments, the slurry is stirred in the tank 115 for at least
about 30 minutes. In still other embodiments, the slurry is stirred
in the tank for more than about 30 minutes after addition of the
binder.
[0064] Tank 115 can also be a tank system comprised of one, two,
three or more tanks. Any configuration or number of tanks that
enables the thorough mixing of the binder with the slurry is
sufficient. In a continuous process, water, and one or more of
dust, oversize particles, or undersize particles from a subsequent
fluidizer or other apparatus can be added to the slurry in the tank
115.
[0065] From the tank 115, the slurry is fed to a heat exchanger
120, which heats the slurry to a temperature of from about
25.degree. C. to about 90.degree. C. From the heat exchanger 120,
the slurry is fed to a pump system 125, which feeds the slurry,
under pressure, to a fluidizer 130.
[0066] A grinding mill(s) and/or a screening system(s) (not
illustrated) can be inserted at one or more places in the system
illustrated in FIG. 1 prior to feeding the slurry to the fluidizer
to assist in breaking any larger-sized alumina-containing raw
material down to a target size suitable for feeding to the
fluidizer. In certain embodiments, the target size is less than 230
mesh. In other embodiments, the target size is less than 325 mesh,
less than 270 mesh, less than 200 mesh or less than 170 mesh. The
target size is influenced by the ability of the type and/or size of
the pressure nozzle in the subsequent fluidizer to atomize the
slurry without becoming clogged.
[0067] If a grinding system is employed, it is charged with a
grinding media suitable to assist in breaking the raw material down
to a target size suitable for subsequent feeding through one or
more pressure nozzles of a fluidizer. If a screening system is
employed, the screening system is designed to remove particles
larger than the target size from the slurry. For example, the
screening system can include one or more screens, which are
selected and positioned so as to screen the slurry to particles
that are smaller than the target size.
[0068] Referring again to FIG. 1, fluidizer 130 is of conventional
design, such as described in, for example, U.S. Pat. No. 3,533,829
and U.K. Patent No. 1,401,303. Fluidizer 130 includes at least one
atomizing nozzle 132 (three atomizing nozzles 132 being shown in
FIG. 1), which is a pressure nozzle of conventional design. In
other embodiments, one or more two-fluid nozzles are suitable. The
design of such nozzles is well -known, for example from K. Masters:
"Spray Drying Handbook", John Wiley and Sons, New York (1979).
[0069] Fluidizer 130 further includes a particle bed 134, which is
supported by a plate 136, such as a perforated, straight or
directional plate. Hot air flows through the plate 136. The
particle bed 134 comprises seeds from which green pellets of a
target size can be grown. The term "green pellets" and related
forms, as used herein, refers to substantially round and spherical
particles which have been formed from the slurry but are not
sintered. When a perforated or straight plate is used, the seeds
also serve to obtain plug flow in the fluidizer. Plug flow is a
term known to those of ordinary skill in the art, and can generally
be described as a flow pattern where very little back mixing
occurs. The seed particles are smaller than the target size for
green pellets made according to the present methods. In certain
embodiments, the seed comprises from about 5% to about 20% of the
total volume of a green pellet formed therefrom. Slurry is sprayed,
under pressure, through the atomizing nozzles 132, and the slurry
spray coats the seeds to form green pellets that are substantially
round and spherical.
[0070] External seeds can be placed on the perforated plate 136
before atomization of the slurry by the fluidizer begins. If
external seeds are used, the seeds can be prepared in a slurry
process similar to that illustrated in FIG. 1, where the seeds are
simply taken from the fluidizer at a target seed size. External
seeds can also be prepared in a high intensity mixing process such
as that described in U.S. Pat. No. 4,879,181, the entire disclosure
of which is hereby incorporated by reference.
[0071] According to certain embodiments, external seeds are made
from either a raw material having at least the same alumina content
as the raw material used to make the slurry, or from a raw material
having more or less alumina than the raw material used to make the
slurry. In certain embodiments, the slurry has an alumina content
that is at least 10%, at least 20%, or at least 30% less than that
of the seeds. In other embodiments, the external seeds have an
alumina content less than that of the slurry, such as at least 10%,
at least 20%, or at least 30% less than that of the slurry.
[0072] Alternatively, seeds for the particle bed are formed by the
atomization of the slurry, thereby providing a method by which the
slurry "self-germinates" with its own seed. According to one such
embodiment, the slurry is fed through the fluidizer 130 in the
absence of a seeded particle bed 134. The slurry droplets exiting
the nozzles 132 solidify, but are small enough initially that they
get carried out of the fluidizer 130 by air flow and caught as
"dust" (fine particles) by a dust collector 145, which may, for
instance, be an electrostatic precipitator, a cyclone, a bag
filter, a wet scrubber or a combination thereof. The dust from the
dust collector is then fed to the particle bed 134 through dust
inlet 162, where it is sprayed with slurry exiting the nozzles 132.
The dust may be recycled a sufficient number of times, until it has
grown to a point where it is too large to be carried out by the air
flow and can serve as seed. The dust can also be recycled to
another operation in the process, for example, the tank 115.
[0073] Referring again to FIG. 1, hot air is introduced to the
fluidizer 130 by means of a fan and an air heater, which are
schematically represented at 138. The velocity of the hot air
passing through the particle bed 134 is from about 0.9
meters/second to about 1.5 meters/second, and the depth of the
particle bed 134 is from about 2 centimeters to about 60
centimeters. The temperature of the hot air when introduced to the
fluidizer 130 is from about 250.degree. C. to about 650.degree. C.
The temperature of the hot air as it exits from the fluidizer 130
is less than about 250.degree. C., and in some embodiments is less
than about 100.degree. C.
[0074] The distance between the atomizing nozzles 132 and the plate
136 is optimized to avoid the formation of dust which occurs when
the nozzles 132 are too far away from the plate 126 and the
formation of irregular, coarse particles which occurs when the
nozzles 132 are too close to the plate 136. The position of the
nozzles 132 with respect to the plate 136 is adjusted on the basis
of an analysis of powder sampled from the fluidizer 130.
[0075] The green pellets formed by the fluidizer accumulate in the
particle bed 134. In a continuous process, the green pellets formed
by the fluidizer 130 are withdrawn through an outlet 140 in
response to the level of product in the particle bed 134 in the
fluidizer 130, so as to maintain a given depth in the particle bed.
A rotary valve 150 conducts green pellets withdrawn from the
fluidizer 130 to an elevator 155, which feeds the green pellets to
a screening system 160, where the green pellets are separated into
one or more fractions, for example, an oversize fraction, a product
fraction, and an undersize fraction.
[0076] The oversize fraction exiting the screening unit 160
includes those green pellets that are larger than the desired
product size. In a continuous process, the oversize green pellets
may be recycled to tank 115, where at least some of the oversize
green pellets can be broken down and blended with slurry in the
tank. Alternatively, oversize green pellets can be broken down and
recycled to the particle bed 134 in the fluidizer 130. The
undersize fraction exiting the screening system 160 includes those
green pellets that are smaller than the desired product size. In a
continuous process, these green pellets may be recycled to the
fluidizer 130, where they can be fed through an inlet 162 as seeds
or as a secondary feed to the fluidizer 130.
[0077] The product fraction exiting the screening system 160
includes those green pellets having the desired product size. These
green pellets are sent to a pre-sintering device 165, for example,
a calciner, where the green pellets are dried or calcined prior to
sintering. In certain embodiments, the green pellets are dried to a
moisture content of less than about 18% by weight, or less than
about 15% by weight, about 12% by weight, about 10% by weight,
about 5% by weight, or about 1% by weight.
[0078] After drying and/or calcining, the green pellets are fed to
a sintering device 170, in which the green pellets are sintered for
a period of time sufficient to enable recovery of sintered,
substantially round and spherical particles having one or more of a
desired apparent specific gravity, bulk density, and crush
strength. Alternatively, the pre-sintering device 165 can
eliminated if the sintering device 170 can provide sufficient
calcining and/or drying conditions (i.e., drying times and
temperatures that dry the green pellets to a target moisture
content prior to sintering), followed by sufficient sintering
conditions.
[0079] The specific time and temperature to be employed for
sintering is dependent on the starting ingredients and the desired
density for the sintered particles. In some embodiments, sintering
device 170 is a rotary kiln, operating at a temperature of from
about 1000.degree. C. to about 1600.degree. C., for a period of
time from about 5 to about 90 minutes. In certain embodiments, a
rotary kiln is operated at a temperature of about 1000.degree. C.,
about 1200.degree. C., about 1300.degree. C., about 1400.degree. C.
or about 1500.degree. C. In certain embodiments, the green pellets
have a residence time in the sintering device of from about 50
minutes to about 70 minutes, or from about 30 minutes to about 45
minutes. After the particles exit the sintering device 170, they
can be further screened for size, and tested for quality control
purposes. Inert atmosphere sintering can be used to limit or
prevent the oxidation of the electrically-conductive material.
Techniques for replacing the oxygen rich atmosphere in the
sintering device with an inert gas such as argon, nitrogen, or
helium are well -known to those of ordinary skill in the art.
Generally, oxygen is replaced with an inert gas such that 0.005%
oxygen or less remains in the sintering atmosphere.
[0080] According to certain embodiments of the present invention,
the electrically-conductive material is coated onto the proppants.
For example, the electrically-conductive material can be coated
onto ceramic proppant after the proppant particles exit sintering
device 170 and have been further screened for size, and tested for
quality control measures. The coating may be accomplished by any
coating technique well-known to those of ordinary skill in the art
such as spraying, sputtering, vacuum deposition, dip coating,
extrusion, calendaring, powder coating, transfer coating, air knife
coating, roller coating, electroless plating (such as disclosed in
U.S. Pat. Nos. 3,296,012, 4,812,202, and 3,617,343, the entire
disclosures of which are hereby incorporated by reference),
electroplating and brush coating.
[0081] According to several exemplary embodiments, the
electrically-conductive material is deposited as a coating on the
ceramic proppant or natural sands. Processes for electrolytic and
electroless coating are well-known to those of ordinary skill in
the art. For example, see U.S. Pat. No. 3,556,839, the entire
disclosure of which is hereby incorporated by reference.
[0082] According to several exemplary embodiments and in accordance
with conventional autocatalytic plating methods, a non-conductive
substrate, such as a ceramic proppant sample, is suitably cleaned
and roughened, then sensitized and activated by successive
immersions in an aqueous solution of a reducing agent and solutions
of catalytic metal such as stannous chloride and palladium chloride
and rinsing in water following each such immersion. Thereafter, the
substrate can be immersed in the plating bath heated to a
temperature of between 55-95.degree. C. The bath can include, for
example, an aqueous solution containing a salt of nickel and a
phosphorous-containing reducing agent such as sodium hypophosphite
in the presence of salts such as sodium citrate and sodium acetate,
where the pH of the solution is adjusted to a value of between 4
and 6. Those of ordinary skill in the art will understand that any
conventional electroless nickel, copper, silver or gold plating
bath solution may be utilized such as those that are commercially
available from suppliers such as Uyemura, Transene or Caswell.
After immersion for a period of about 1 to about 30 minutes, the
bath is substantially exhausted and a film of nickel ranging from
about 0.5 to about 5 microns in thickness is deposited on the
surface of the substrate.
[0083] According to several exemplary embodiments and in accordance
with conventional electroless plating methods, a non-conductive
substrate, such as a ceramic proppant sample, is suitably cleaned
and then sensitized by successive immersions in an aqueous solution
of catalytic metal and an aqueous solution of a reducing agent such
as, for example, solutions of palladium chloride and stannous
chloride, and rinsing in water following each such immersion.
Thereafter, the substrate is immersed in the plating bath
maintained at a temperature of between 25-65.degree. C. The bath
may include, for example, an aqueous solution containing a salt of
copper and an alkali metal hydroxide in the presence of one or more
salts such as potassium sodium tartrate and sodium carbonate. Those
of ordinary skill in the art will understand that any conventional
electroless nickel, copper, silver or gold plating bath solution
can be utilized such as those that are commercially available from
suppliers such as Uyemura, Transene or Caswell. After immersion for
a period of about 1 to about 30 minutes, the bath is substantially
exhausted and a film of copper ranging from about 0.5 to about 5
microns in thickness is deposited on the substrate.
[0084] The conventional autocatalytic plating methods, however, can
use acidic palladium solutions that may oxidize active metal
expressed in the native proppant surface and therefore can lead to
poor deposition of metal onto the proppant surface. It has been
found that incorporating a conditioning step into an electroless
coating method can improve the deposition of metal onto the
proppant surface.
[0085] Referring now to FIG. 2, a flow chart is depicted showing
steps of a process 200 for electroless coating of the
electrically-conductive material onto proppant utilizing a
conditioning step. In the electroless coating process 200, a supply
of proppant via line 202 can be introduced to one or more washing
units 204 where the proppant via line 202 can be contacted with a
first washing solution to remove dust and/or fines to provide a
clean proppant via line 206. The washing unit 204 can be or include
one or more tanks, one or more vessels, one or more conveyance
systems, one or more conduits, or the like. The first washing
solution can be or include an aqueous solution containing an acid
or base, such as water containing dilute acid, or an organic phase
solution, such as a liquid hydrocarbon, this washing can also be
conducted at an elevated temperature. Clean proppant via line 206
can be withdrawn from the washing unit 204 and introduced to one or
more pretreatment units 208 where the clean proppant via line 206
can be contacted with a conditioning solution. The pretreatment
unit 208 can be or include one or more tanks, one or more vessels,
one or more conveyance systems, one or more conduits, or the like.
The conditioning solution can be or include an alkaline solution to
adjust the pH of the surface of the proppant to alkaline levels
(pH>7). The alkaline solution can include one or more of an
hydroxide, ammonia, or a carbonate.
[0086] The conditioning in the pretreatment unit 108 can be further
enhanced by combining or mixing a suitable surfactant with the
conditioning solutions. Suitable surfactants can include, but are
not limited to, anionic, cationic, nonionic, and amphoteric
surfactants, or combinations thereof. According to several
exemplary embodiments, suitable surfactants include but are not
limited to saturated or unsaturated long-chain fatty acids or acid
salts, long-chain alcohols, polyalcohols, polysorbates,
dimethylpolysiloxane and polyethylhydrosiloxane. According to
several exemplary embodiments, suitable surfactants include but are
not limited to linear and branched carboxylic acids and acid salts
having from about 4 to about 30 carbon atoms, linear and branched
alkyl sulfonic acids and acid salts having from about 4 to about 30
carbon atoms, linear alkyl benzene sulfonate wherein the linear
alkyl chain includes from about 4 to about 30 carbon atoms,
sulfosuccinates, phosphates, phosphonates, phospholipids,
ethoxylated compounds, carboxylates, sulfonates and sulfates,
polyglycol ethers, amines, salts of acrylic acid, pyrophosphate and
mixtures thereof. In one or more exemplary embodiments, the
surfactant is a polysorbate, such as Tween.TM. 20 (PEG(20) sorbitan
monolaurate).
[0087] The clean proppant via line 206 can contact the conditioning
solution in the pretreatment unit 208 under any suitable conditions
to provide a conditioned proppant via line 210. Suitable conditions
can include a temperature of about 10.degree. C., about 25.degree.
C., about 30.degree. C., about 35.degree. C., about 40.degree. C.,
about 45.degree. C. to about 47.degree. C., about 50.degree. C.,
about 55.degree. C., about 60.degree. C., about 75.degree. C., or
about 100.degree. C. under a residence time of about 1 second (s),
about 5 s, about 15 s, about 25 s, about 45 s, or about 55 s to
about 65 s, about 75 s, about 100 s, about 2 minutes (min), about 5
min, or about 10 min. The conditioning solution can have a pH of at
least about 7.2, at least about 8, at least about 8.5, at least
about 9, at least about 10, at least about 11, at least about 12,
at least about 12.5, or at least about 13.
[0088] The conditioned proppant via line 210 can be withdrawn from
the pretreatment unit 208 and introduced to one or more turbidity
reduction units 212 where the conditioned proppant via line 210 can
be contacted with a second washing solution to further remove dust
and/or fines to provide a washed proppant via line 214 having a
reduced turbidity compared to the conditioned proppant via line
210. The turbidity reduction unit 212 can be or include one or more
tanks, one or more vessels, one or more conveyance systems, one or
more conduits, or the like. The second washing solution can be the
same as or similar to the first washing solution and can include an
aqueous solution, such as water, or an organic phase solution, such
as a liquid hydrocarbon. The second washing solution can also have
a sensitizer which aids the activator in the subsequent step. The
sensitizer can be any agent that reduces the activator, such as tin
chloride, sodium borohydride or sodium hypophosphite or any other
known reducing agent. In one or more exemplary embodiments, the
second washing solution does not contain the sensitizer. The
sensitizer step would be followed by another rinse step, but in
some embodiments may be omitted.
[0089] Washed proppant via line 214 can be withdrawn from the
turbidity reduction unit 212 and introduced to one or more catalyst
reduction units 216 where the washed proppant via line 214 can be
contacted with an activation solution. The activation solution can
activate the proppant by attaching catalytically active material,
such as palladium or silver, to the proppant surface. The
activation solution can be or include one or more palladium salts,
such as palladium chloride or palladium ammonium chloride, and/or
silver nitrate. The activation solution can be an aqueous phase
solution or an organic phase solution. The activation solution can
have a palladium salt concentration of about 0.1 milligrams of
Pd.sup.2+ per liter (mg/l ), about 0.5 mg/l about 1 mg/l about 5
mg/l, about 10 mg/l, or about 20 mg/l to about 30 mg/l, about 35
mg/l, about 40 mg/l, about 50 mg/l, or about 100 mg/l. The
activation solution can also contain a reducing agent, or
sensitizer. The reducing agent can be or include a tin salt, such
as stannous chloride. In one or more exemplary embodiments, the
activation solution does not contain the reducing agent.
[0090] The washed proppant via line 214 can contact the activation
solution in the catalyst reduction unit 216 under any suitable
conditions to provide an activated proppant via line 218. Suitable
conditions can include a temperature of about 20.degree. C., about
35.degree. C., about 50.degree. C., about 65.degree. C., about
75.degree. C., about 78.degree. C. to about 82.degree. C., about
85.degree. C., about 90.degree. C., about 95.degree. C., about
100.degree. C., or about 105.degree. C. under a residence time of
about 1 min, about 2 min, about 3 min, about 4 min, about 5 min, or
about 7 min to about 8 min, about 9 min, about 10 min, about 12
min, about 15 min, or about 20 min or more and/or until the bath is
substantially exhausted. The activation solution can have a pH of
about 7.1, about 7.2, about 7.4, about 7.6, or about 7.8 to about
8, about 8.5, about 9, about 9.5, about 10, about 11, about 12, or
about 13 or more.
[0091] The activated proppant via line 218 can be withdrawn from
the activation unit 216 and introduced to one or more rinse units
220 where the activated proppant via line 218 can be contacted with
a third washing solution to remove excess activation solution from
the activated proppant. The rinse unit 220 can be or include one or
more tanks, one or more vessels, one or more conveyance systems,
one or more conduits, or the like. The third washing solution can
include an aqueous solution, such as tap water or de-ionized
water.
[0092] Rinsed proppant via line 222 can be withdrawn from the rinse
unit 220 and introduced to one more metallization units 224 where
the rinsed proppant via line 222 can be subjected to metal plating.
In the metallization unit 224, the rinsed proppant via line 222 can
be immersed in a plating bath solution having a temperature of
about 20.degree. C., about 35.degree. C., about 50.degree. C.,
about 60.degree. C., or about 70.degree. C. to about 75.degree. C.,
about 80.degree. C., about 90.degree. C., about 95.degree. C.,
about 100.degree. C., about 110.degree. C., or about 120.degree. C.
or more under a residence time of about 1 min, about 2 min, about 4
min, about 8 min, about 12 min, or about 14 min to about 16 min,
about 20 min, about 25 min, about 30 min, about 45 min, or about 60
min or more and/or until the bath is substantially exhausted. After
immersion, a film of electrically-conductive material ranging from
about 10 nanometers (nm), about 50 nm, about 100 nm, about 250 nm,
or about 400 nm to about 500 nm, about 600 nm, about 700 nm, about
800 nm, about 900 nm, about 1,000 nm, or about 1,200 nm or more can
be substantially uniformly coated onto the rinsed proppant to
provide the electrically-conductive proppant.
[0093] The plating bath solution can be an aqueous solution
containing water or an organic phase solution containing one or
more hydrocarbons. The plating bath solution can be basic or acidic
and can include a metal salt, a complexing agent, a reducing agent,
and a buffer. For example, the plating bath solution can include a
salt of nickel such as nickel sulfate, nickel sulphate hexahydrate,
and nickel chloride. The complexing agent can include acetate,
succinate, aminoacetate, malonate, pyrophosphate, malate, or
citrate or any combination thereof. The reducing agent can include
sodium borohydride, dimethylamine borane, or hydrazine or any
combination thereof. The buffer can include acetic acid, propionic
acid, glutaric acid, succinic acid, or adipic acid or any
combination thereof. Those of ordinary skill in the art will
understand that any conventional electroless nickel, copper, silver
or gold plating bath solution can also be utilized such as those
that are commercially available from suppliers such as Uyemura,
Transene, Caswell, and Metal-Chem.
[0094] Additional and/or alternative steps can be employed in the
electroless plating process. Referring now to FIG. 3, a flow chart
is depicted showing steps of a process 300 for electroless coating
of the electrically-conductive material onto proppant in which
alternative activation and metal deposition steps are depicted.
Proppant particles can be subjected to alkaline conditioning 301,
which can be the same as or similar to the alkaline conditioning in
the pretreatment unit 208, to provide conditioned proppant
particles.
[0095] After being subjected to the alkaline conditioning step 301,
the conditioned proppant particles can be subjected to an
activation step 302 prior to electroless metal deposition 303. The
conditioned particles can be sensitized using a sensitizer solution
of tin(II) 304 to produce sensitized particles. After subsequent
exposure to palladium(II) activator solution 305, palladium(II) is
reduced to palladium metal (Pd.sup.2+.fwdarw.Pd.sup.0) on the
surface of the sensitized particles and tin(II) is oxidized to
tin(IV) (Sn.sup.2+.fwdarw.Sn.sup.4+). An accelerator solution 306
can be used to remove oxidized tin(IV) after exposure to
palladium(II) activator solution 305 and prior to electroless metal
deposition 303. Alternative embodiments involve a combined tin(IV)
and palladium(II) activator and sensitizer colloidal suspension 307
which can be followed by the accelerator solution 306. The
accelerator solution 306 can be an aqueous solution and can include
one or more accelerator agents including, but not limited to, one
or more organic sulfide compounds, such as
bis(sodium-sulfopropyl)disulfide, 3-mercapto-1-propanesulfonic acid
sodium salt, N,N-dimethyl-dithiocarbamyl propylsulfonic acid sodium
salt or 3-S-isothiuronium propyl sulfonate, and mixtures thereof.
Other suitable accelerator agents can include, but are not limited
to, thiourea, allylthiourea, acetylthiourea, and pyridine and the
like.
[0096] In certain embodiments, specific to proppant particle
surfaces, the alkaline conditioning can enable activation using
only the Pd activator as shown in step 308. The conditioned
particles are activated using a solution of any suitable palladium
salt, such as palladium chloride or palladium ammonium chloride, in
a concentration of from about 0.1, about 0.5, about 1, about 5,
about 10, about 15 or about 20 to about 25, about 30, about 35,
about 40, or about 50 or more milligrams Pd.sup.2+ per liter, where
the pH of the solution can be adjusted between 7 and 14 using any
suitable bases such as, for example, sodium hydroxide.
[0097] In one or more exemplary embodiments, intrinsic surface
activation 309 can be accomplished prior to electroless metal
deposition 303. In this embodiment, iron or any other suitable
metal ion incorporated into the proppant particles during firing or
sintering that are expressed at the surface of the proppant, can
serve to directly activate the particles. In one or more exemplary
embodiments, the surface of the particles is activated by soaking
the particles in a reducing agent solution, such as sodium
borohydride, sodium hypophosphite or sodium cyanoborohydride, where
this solution can be transferred directly to the electroless
plating bath with the particles still wet from the solution, or
dried onto the particles prior to electroless metal plating 303, or
rinsed completely from the particles.
[0098] Ceramic proppant particles can contain a significant amount
of oxidized iron. In one or more exemplary embodiments of intrinsic
surface activation 309, these iron moieties can be reduced to
elemental iron, or other reduced form [iron (II)] which is
catalytically active to copper, nickel and other noble metal
electroless plating solutions. By utilizing the native iron content
intrinsic to the particle, it is possible to plate onto the
particles without Pd activators. The reduction of surface iron ions
to atomic iron can occur within a sintering device, such as
sintering device 170, or subsequent to sintering, by maintaining a
reducing environment in the kiln, which is characterized by the
presence of carbon monoxide or other products of partial
combustion. Iron on the surface of the proppant particles can also
be reduced after manufacturing by exposing the surfaces of the
proppant particles to carbon monoxide or hydrogen at any suitable
temperatures such as, for example, about 200.degree. C., about
300.degree. C., about 400.degree. C., about 500.degree. C., or
about 600.degree. C. to about 750.degree. C., about 900.degree. C.,
about 1,100.degree. C., or about 1,500.degree. C.
[0099] After particle activation 302, activated proppant 310 can be
converted into electrically-conductive proppant 311 by electroless
metal deposition 303. Processes for electrolytic and electroless
coating are well-known to those of ordinary skill in the art. See,
for example, U.S. Pat. No. 3,556,839, the entire disclosure of
which is incorporated herein by reference. According to several
exemplary embodiments, and in accordance with conventional
autocatalytic or electroless plating methods, the activated
proppant sample can be coated with metal and metal alloys by
various methods.
[0100] After activation 302, the substrate can be immersed in,
submerged in, or otherwise contacted with a plating bath of the
electroless metal deposition 303 to provide the
electrically-conductive proppant 311. The plating bath can be
heated to a temperature of from about 35.degree. C., about
45.degree. C., about 55.degree. C., about 65.degree. C., or about
75.degree. C. to about 85.degree. C., about 95.degree. C., about
105.degree. C., or about 120.degree. C. or more. In one or more
embodiments, the plating bath can be or include an acidic,
nickel-containing bath with a high phosphorous content (about 5 wt
% to about 12 wt % phosphorous by weight of the resulting
nickel-phosphorous alloy film) 312. The high phosphorous content
bath can include, for example, an aqueous solution containing a
salt of nickel and a phosphorous-containing reducing agent such as
sodium hypophosphite in the presence of salts such as sodium
citrate and sodium acetate. The pH of the high phosphorous content
bath solution can be from about 2, about 3, about 3.5, about 4, or
about 4.5 to about 5, about 5.5, about 6, or about 6.5.
[0101] In one or more embodiments, the plating bath can be an
alkaline, nickel-containing bath 313 with a low phosphorous content
(about >1 wt % to about 4.9 wt % phosphorous by weight of the
resulting nickel-phosphorous alloy film). The pH of the alkaline
plating bath 313 with a low phosphorous content can be from about
7, about 7.5, about 8, about 8.5, or about 9 to about 10, about
10.5, about 11, about 12, or about 13 or more. The alkaline plating
bath 313 can chelate free nickel ions to prevent solution
reactivity with Pd, as can occur with Pd solution drag out, and
therefore offer a preferred reaction environment for high surface
area materials such as ceramic proppant. Alkaline plating solutions
can require relatively longer periods of time to plate, but can
lead to thinner, contiguous coatings with higher conductivity which
may enhance electromagnetic detection. Those of ordinary skill in
the art will understand that any conventional electroless nickel,
copper, silver or gold plating bath solution may be utilized with
any range of pH such as those that are commercially available from
suppliers such as Metal-Chem, Enthone, Uyemura, Transene or
Caswell. In one or more exemplary embodiments, the plating bath can
be or include alkaline electroless copper 314 containing
formaldehyde as a reducing agent. In one or more exemplary
embodiments, the plating bath can include electroless noble metals
315, such as silver, gold, and platinum. For example, the plating
bath can be or include a silver nitrate solution.
[0102] The electrically-conductive proppant 311 can have any
suitable film thickness of electrically-conductive material
disposed on the outer surfaces thereof. In one or more embodiments,
the film of electrically-conductive material can be from about 10
nm, about 50 nm, about 100 nm, about 250 nm, or about 400 nm to
about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900
nm, about 1,000 nm, about 1,200 nm, about 1,500 nm, about 2,500 nm,
or about 3,500 nm or more in thickness when substantially uniformly
coated onto the proppant to provide the electrically-conductive
ceramic proppant 311. In one or more exemplary embodiments, the
thickness of the substantially uniform coating of
electrically-conductive material can be from about 50 nm to about
150 nm, about 400 nm to about 600 nm, about 500 nm to about 1,200
nm, about 550 nm to about 700 nm, about 750 nm to about 1,200 nm,
or about 750 nm to about 1,000 nm.
[0103] The electrically-conductive material can also be
incorporated into a resin material. Ceramic proppant or natural
sands can be coated with the resin material containing the
electrically-conductive material such as metal clusters, metal
flake, metal shot, metal powder, metalloids, metal nanoparticles,
quantum dots, carbon nanotubes, buckminsterfullerenes, and other
suitable electrically conductive materials to provide
electrically-conductive material-containing proppant that can be
detected by electromagnetic means. Processes for resin coating
proppants and natural sands are well known to those of ordinary
skill in the art. For example, a suitable solvent coating process
is described in U.S. Pat. No. 3,929,191, to Graham et al., the
entire disclosure of which is incorporated herein by reference.
Another suitable process such as that described in U.S. Pat. No.
3,492,147 to Young et al., the entire disclosure of which is
incorporated herein by reference, involves the coating of a
particulate substrate with a liquid, uncatalyzed resin composition
characterized by its ability to extract a catalyst or curing agent
from a non-aqueous solution. Also, a suitable hot melt coating
procedure for utilizing phenol-formaldehyde novolac resins is
described in U.S. Pat. No. 4,585,064, to Graham et al., the entire
disclosure of which is incorporated herein by reference. Those of
ordinary skill in the art will be familiar with still other
suitable methods for resin coating proppants and natural sands.
[0104] The electrically-conductive proppant 311 can have any
suitable electrical conductivity. In one or more exemplary
embodiments, a pack of the electrically-conductive proppant 311 can
have an electrical conductivity of at least about 1 Siemens per
meter (S/m), at least about 5 S/m, at least about 15 S/m, at least
about 50 S/m, at least about 100 S/m, at least about 250 S/m, at
least about 500 S/m, at least about 750 S/m, at least about 1,000
S/m, at least about 1,500 S/m, or at least about 2,000 S/m. The
electrical conductivity of the pack of the electrically-conductive
proppant 311 can also be from about 10 S/m, about 50 S/m, about 100
S/m, about 500 S/m, about 1,000 S/m, or about 1,500 S/m to about
2,000 S/m, about 3,00 S/m, about 4,000 S/m, about 5,000 S/m, or
about 6,000 S/m. The pack of the electrically-conductive proppant
311 can have any suitable resistivity. In one or more exemplary
embodiments, the pack of the electrically-conductive proppant 311
can have a resistivity of less than 100 Ohm-cm, less than 80
Ohm-cm, less than 50 Ohm-cm, less than 25 Ohm-cm, less than 15
Ohm-cm, less than 5 Ohm-cm, less than 2 Ohm-cm, less than 1 Ohm-cm,
less than 0.5 Ohm-cm, or less than 0.1 Ohm-cm.
[0105] In one or more exemplary embodiments, increasing a load or
pressure onto the pack of the electrically-conductive proppant 311
by a factor of 2, a factor of 5, or a factor of 10 can increase the
electrical conductivity of the pack of the electrically-conductive
proppant 311 by at least about 50%, at least about 75%, at least
about 100%, at least about 150%, or at least about 200%. In one or
more exemplary embodiments, increasing a load or pressure onto the
pack of the electrically-conductive proppant 311 by a factor of 2,
a factor of 5, or a factor of 10 can decrease the resistivity of
the pack of the electrically-conductive proppant 311 by from about
1%, about 2%, or about 5% to about 10%, about 15%, or about
25%.
[0106] The electromagnetic methods described herein involve
electrically energizing the earth at or near a fracture at depth
and measuring the electric and magnetic responses at the earth's
surface or in adjacent wells/boreholes. The electromagnetic methods
described herein are typically used in connection with a cased
wellbore, such as well 20 shown in FIG. 4. Specifically, casing 22
extends within well 20 and well 20 extends through geological
strata 24a-24i in a manner that has three dimensional
components.
[0107] Referring now to FIG. 5, a partial cutaway view is shown
with production well 20 extending vertically downward through one
or more geological layers 24a-24i and horizontally in layer 24i.
While wells are conventionally vertical, the electromagnetic
methods described herein are not limited to use with vertical
wells. Thus, the terms "vertical" and "horizontal" are used in a
general sense in their reference to wells of various
orientations.
[0108] The preparation of production well 20 for hydraulic
fracturing typically comprises drilling a bore 26 to a desired
depth and then in some cases extending the bore 26 horizontally so
that the bore 26 has any desired degree of vertical and horizontal
components. Casing 22 is cemented 28 into well 20 to seal the bore
26 from the geological layers 24a-24i in FIG. 5. The casing 22 has
a plurality of perforations 30. The perforations 30 are shown in
FIG. 5 as being located in a horizontal portion of well 20 but
those of ordinary skill in the art will recognize that the
perforations can be located at any desired depth or horizontal
distance along the bore 26, but are typically at the location of a
hydrocarbon bearing zone in the geological layers 24, which may be
within one or more of the geological layers 24a-24j. The
hydrocarbon bearing zone may contain oil and/or gas, as well as
other fluids and materials that have fluid-like properties. The
hydrocarbon bearing zone in geological layers 24a-24j is
hydraulically fractured by pumping a fluid into casing 22 and
through perforations 30 at sufficient rates and pressures to create
fractures 32 and then incorporating into the fluid an
electrically-conductive proppant which will prop open the created
fractures 32 when the hydraulic pressure used to create the
fractures 32 is released.
[0109] The hydraulic fractures 32 shown in FIG. 5 are oriented
radially away from the metallic well casing 22. This orientation is
exemplary in nature. In practice, hydraulically-induced fractures
32 may be oriented radially as in FIG. 5, laterally or intermediate
between the two. Various orientations are exemplary and not
intended to restrict or limit the electromagnetic methods described
herein in any way.
[0110] According to certain embodiments of the electromagnetic
method of the present invention and as shown schematically in FIG.
6, electric current is carried down wellbore 20 to an energizing
point which will generally be located within 10 meters or more
(above or below) of perforations 30 in casing 22 via a seven strand
wire line insulated cable 34, such as those which are well known to
those of ordinary skill in the art and are widely commercially
available from Camesa Wire, Rochester Wire and Cable, Inc.,
WireLine Works, Novametal Group, and Quality Wireline & Cable
Inc. A sinker bar 36 connected to the wire line cable 34 contacts
or is in close proximity to the well casing 22 whereupon the well
casing 22 becomes a current line source that produces subsurface
electric and magnetic fields. These fields interact with the
fracture 32 containing electrically-conductive proppant to produce
secondary electric and magnetic fields that will be used to detect,
locate, and characterize the proppant-filled fracture 32.
[0111] According to certain embodiments of the electromagnetic
method of the present invention and as shown schematically in FIG.
6, a power control box 40 is connected to casing 22 by a cable 42
so that electric current is injected into the fracture well 20 by
directly energizing the casing 22 at the well head. In one
embodiment, the power control box 40 is connected wirelessly by a
receiver/transmitter 43 to a receiver/transmitter 39 on equipment
truck 41. Those of ordinary skill in the art will recognize that
other suitable means of carrying the current to the energizing
point may also be employed.
[0112] As shown schematically in FIGS. 6-8, a plurality of electric
and magnetic field sensors 38 will be located on the earth's
surface in a rectangular or other suitable array covering the area
around the fracture well 20 and above the anticipated fracture 32.
In one embodiment, the sensors 38 are connected wirelessly to a
receiver/transmitter 39 on equipment truck 41. The maximum
dimension of the array (aperture) in general should be at least 80
percent of the depth to the fracture zone. The sensors 38 will
measure the x, y and z component responses of the electric and
magnetic fields. It is these responses that will be used to infer
location and characterization of the electrically-conductive
proppant through comparison to numerical simulations and/or
inversion of the measured data to determine the source of the
responses. The responses of the electric and magnetic field
components will depend upon: the orientation of the fracture well
20, the orientation of the fracture 32, the electrical
conductivity, magnetic permeability, and electric permittivity of
layers 24a-24j, the electrical conductivity, magnetic permeability,
and electric permittivity of the proppant filled fracture 32, and
the volume of the proppant filled fracture 32. Moreover, the
electrical conductivity, magnetic permeability and electric
permittivity of the geological layers residing between the surface
and the target formation layers 24a-24j influence the recorded
responses. From the field-recorded responses, details of the
proppant filled fracture 32 can be determined.
[0113] In another embodiment, electric and magnetic sensors can be
located in adjacent well/boreholes.
[0114] Depending upon the conductivity of the earth surrounding the
well casing 22, the current may or may not be uniform as the
current flows back to the surface along the well casing 22.
According to both embodiments shown in FIG. 6, current leakage
occurs along wellbore 20 such as along path 50 or 52 and returns to
the electrical ground 54 which is established at the well head. As
described in U.S. patent application Ser. No. 13/206,041 filed Aug.
9, 2011 and entitled "Simulating Current Flow Through a Well Casing
and an Induced Fracture," the entire disclosure of which is
incorporated herein by reference, the well casing is represented as
a leaky transmission line in data analysis and numerical modeling.
Numerical simulations have shown that for a conducting earth
(conductivity greater than approximately 0.05 siemens per meter
(S/m)), the current will leak out into the formation, while if the
conductivity is less than approximately 0.05 S/m the current will
be more-or-less uniform along the well casing 22. As shown in FIGS.
9A and 9B, to localize the current in the well casing 22,
electrically insulating pipe joints or pipe collars may be
installed. According to the embodiment shown in FIG. 9A, an
insulating joint can be installed by coating the mating surfaces 60
and 62 of the joint with a material 64 having a high dielectric
strength, such as any one of the well-known and commercially
available plastic or resin materials which have a high dielectric
strength and which are of a tough and flexible character adapted to
adhere to the joint surfaces so as to remain in place between the
joint surfaces. As described in U.S. Pat. No. 2,940,787, the entire
disclosure of which is incorporated herein by reference, such
plastic or resin materials include epoxies, phenolics, rubber
compositions, and alkyds, and various combinations thereof.
Additional materials include polyetherimide and modified
polyphenylene oxide. According to the embodiment shown in FIG. 9B,
the mating ends 70 and 72 of the joint are engaged with an
electrically-insulated casing collar 74. The transmission line
representation is able to handle various well casing scenarios,
such as vertical only, slant wells, vertical and horizontal
sections of casing, and, single or multiple insulating gaps.
[0115] The detection, location, and characterization of the
electrically-conductive proppant in a fracture will depend upon
several factors, including but not limited to the net electrical
conductivity of the fracture, fracture volume, the electrical
conductivity, magnetic permeability, and electric permittivity of
the earth surrounding the fracture and between the fracture and
surface mounted sensors. The net electrical conductivity of the
fracture means the combination of the electrical conductivity of
the fracture, the proppant and the fluids when all are placed in
the earth minus the electrical conductivity of the earth formation
when the fracture, proppant and fluids were not present. Also, the
total electrical conductivity of the proppant filled fracture is
the combination of the electrical conductivity created by making a
fracture, plus the electrical conductivity of the new/modified
proppant plus the electrical conductivity of the fluids, plus the
electro-kinetic effects of moving fluids through a porous body such
as a proppant pack. The volume of an overly simplified fracture
with the geometric form of a plane can be determined by multiplying
the height, length, and width (i.e. gap) of the fracture. A three
dimensional (3D) finite-difference electromagnetic algorithm that
solves Maxwell's equations of electromagnetism can be used for
numerical simulations. In order for the electromagnetic response of
a proppant-filled fracture at depth to be detectable at the Earth's
surface, the net fracture conductivity multiplied by the fracture
volume within one computational cell of the finite difference (FD)
grid must be larger than approximately 100 Sm.sup.2 for a Barnett
shale-like model where the total fracture volume is approximately
38 m.sup.3. For the Barnett shale model, the depth of the fracture
is 2000 m. These requirements for the numerical simulations can be
translated to properties in a field application for formations
other than the Barnett shale.
[0116] The propagation and/or diffusion of electromagnetic (EM)
wavefields through three-dimensional (3D) geological media are
governed by Maxwell's equations of electromagnetism.
[0117] According to one embodiment of the present invention, the
measured three dimensional components of the electric and magnetic
field responses can be analyzed with imaging methods such as an
inversion algorithm based on Maxwell's equations and
electromagnetic migration and/or holography to determine proppant
pack location. Inversion of acquired data to determine proppant
pack location involves adjusting the earth model parameters,
including but not limited to the proppant location within a
fracture or fractures and the net electrical conductivity of the
fracture, to obtain the best fit to forward model calculations of
responses for an assumed earth model. As described in Bartel, L.
C., Integral wave-migration method applied to electromagnetic data,
Sandia National Laboratories, 1994, the electromagnetic integral
wave migration method utilizes Gauss's theorem where the data
obtained over an aperture is projected into the subsurface to form
an image of the proppant pack. Also, as described in Bartel, L. C.,
Application of EM Holographic Methods to Borehole Vertical Electric
Source Data to Map a Fuel Oil Spill, Sandia National Laboratories,
1993, the electromagnetic holographic method is based on the
seismic holographic method and relies on constructive and
destructive interferences where the data and the source wave form
are projected into an earth volume to form an image of the proppant
pack. Due to the long wavelengths of the low frequency
electromagnetic responses for the migration and holographic
methods, it may be necessary to transform the data into another
domain where the wavelengths are shorter. As described in Lee, K.
H., et al., A new approach to modeling the electromagnetic response
of conductive media, Geophysics, Vol. 54, No. 9 (1989), this domain
is referred to as the q-domain. Further, as described in Lee, K.
H., et al., Tomographic Imaging of Electrical Conductivity Using
Low-Frequency Electromagnetic Fields, Lawrence Berkeley Lab, 1992,
the wavelength changes when the transformation is applied.
[0118] Also, combining Maxwell's equations of electromagnetism with
constitutive relations appropriate for time-independent isotropic
media yields a system of six coupled first-order partial
differential equations referred to as the "EH" system. The name
derives from the dependent variables contained therein, namely the
electric vector E and the magnetic vector H. Coefficients in the EH
system are the three material properties, namely electrical current
conductivity, magnetic permeability, and electric permittivity. All
of these parameters can vary with 3D spatial position. The
inhomogeneous terms in the EH system represent various body sources
of electromagnetic waves, and include conduction current sources,
magnetic induction sources, and displacement current sources.
Conduction current sources, representing current flow in wires,
cables, and borehole casings, are the most commonly-used sources in
field electromagnetic data acquisition experiments.
[0119] An explicit, time-domain, finite-difference (FD) numerical
method is used to solve the EH system for the three components of
the electric vector E and the three components of the magnetic
vector H, as functions of position and time. A three-dimensional
gridded representation of the electromagnetic medium parameters,
referred to as the "earth model" is required, and can be
constructed from available geophysical logs and geological
information. A magnitude, direction, and waveform for the current
source are also input to the algorithm. The waveform can have a
pulse-like shape (as in a Gaussian pulse), or can be a repeating
square wave containing both positive and negative polarity
portions, but is not limited to these two particular options.
Execution of the numerical algorithm generates electromagnetic
responses in the form of time series recorded at receiver locations
distributed on, or within, the gridded earth model. These responses
represent the three components of the E or H vector, or their
time-derivatives.
[0120] Repeated execution of the finite-difference numerical
algorithm enables a quantitative estimate of the magnitude and
frequency-content of electromagnetic responses (measured on the
earth's surface or in nearby boreholes) to be made as important
modeling parameters are varied. For example, the depth of current
source can be changed from shallow to deep. The current source can
be localized at a point, or can be a spatially-extended
transmission line, as with an electrically charged borehole casing.
The source waveform can be broad-band or narrow-band in spectral
content. Finally, changes to the electromagnetic earth model can be
made, perhaps to assess the shielding effect of shallow conductive
layers. The goal of such a modeling campaign is to assess the
sensitivity of recorded electromagnetic data to variations in
pertinent parameters. In turn, this information is used to design
optimal field data acquisition geometries that have enhanced
potential for imaging a proppant-filled fracture at depth.
[0121] The electric and magnetic responses are scalable with the
input current magnitude. In order to obtain responses above the
background electromagnetic noise, a large current on the order of
10 to 100 amps may be required. The impedance of the electric cable
to the current contact point and the earth contact resistance will
determine the voltage that is required to obtain a desired current.
The contact resistance is expected to be small and will not
dominate the required voltage. In addition, it may be necessary to
sum many repetitions of the measured data to obtain a measurable
signal level over the noise level. In the field application and
modeling scenarios, a time-domain current source waveform can be
used. A typical time-domain waveform consists of an on time of
positive current followed by an off time followed by an on time of
negative current. In other words, + current, then off, then -
current, then off again. The repetition rate to be used would be
determined by how long the current has to be on until a
steady-state is reached or alternatively how long the energizing
current has to be off until the fields have died to nearly zero. In
this exemplary method, the measured responses would be analyzed
using both the steady-state values and the decaying fields
following the current shut-off. The advantage of analyzing the data
when the energizing current is zero (decaying fields) is that the
primary field contribution (response from the transmitting
conductor; i.e., the well casing) has been eliminated and only the
earth responses are measured. In addition, the off period of the
time domain input signal permits analysis of the direct current
electrical fields that can arise from electro-kinetic effects,
including but not limited to, flowing fluids and proppant during
the fracturing process. Fracture properties (orientation, length,
volume, height and asymmetry will be determined through inversion
of the measured data and/or a form of holographic reconstruction of
that portion of the earth (fracture) that yielded the measured
electrical responses or secondary fields. According to certain
embodiments, a pre-fracture survey will be prepared to isolate the
secondary fields due to the fracture. Those of ordinary skill in
the art will recognize that other techniques for analyzing the
recorded electromagnetic data, such as use of a pulse-like current
source waveform and full waveform inversion of observed
electromagnetic data can also be used.
[0122] A field data acquisition experiment was conducted to test
the transmission line representation of a well casing current
source. The calculated electric field and the measured electric
field are in good agreement. This test demonstrates that the
transmission line current source implementation in the 3D
finite-difference electromagnetic code gives accurate results. The
agreement, of course, depends upon an accurate model describing the
electromagnetic properties of the earth. In this field data
acquisition experiment, common electrical logs were used to
characterize the electrical properties of the earth surrounding the
test well bore and to construct the earth model.
[0123] The following examples are included to demonstrate
illustrative embodiments of the present invention. It will be
appreciated by those of ordinary skill in the art that the
techniques disclosed in these examples are merely illustrative and
are not limiting. Indeed, those of ordinary skill in the art
should, in light of the present disclosure, appreciate that many
changes can be made in the specific embodiments that are disclosed,
and still obtain a like or similar result without departing from
the spirit and scope of the invention.
EXAMPLE 1
[0124] Conventional low density and medium density ceramic
proppants which are commercially available from CARBO Ceramics Inc.
of Houston, Tex. under the trade names CARBOLITE.RTM. (CL) 20/40,
CARBOHYDROPROP.RTM. (HP or HYDROPROP) 40/80, CARBOPROP.RTM. 20/40
and CARBOPROP 40/70 were coated with thin layers of metals using RF
magnetron sputtering. Three metal targets were used for the
depositions, namely aluminum, copper and nickel. The depositions
were performed in a sputter chamber using a 200 W RF power, a
deposition pressure of 5 mTorr, and an argon background flow rate
of 90 sccm. The sputter chamber had three articulating 2 inch
target holders that can be used to coat complex shapes. The system
also had a rotating, water-cooled sample stage that was used in a
sputter-down configuration. Prior to coating the proppants,
deposition rates for the three metals were determined by sputtering
the metals onto silicon wafers and measuring the coating thickness
by scanning electron microscope (SEM) cross-sectional analysis with
a Zeiss Neon 40 SEM.
[0125] The proppants were loaded into the sputter chamber in a 12
inch diameter aluminum pan with 1 inch tall sides. Approximately
130 g of proppant was used for each coating run. This amount of
proppant provided roughly a single layer of proppant on the base of
the pan. The proppant was "stirred" during the deposition using a 6
inch long fine wire metal that was suspended above the pan and
placed into contact with the proppant in the pan. The coating
deposition times were doubled compared to what was determined from
the silicon wafer coating thickness measurements to account for
roughly coating the proppants on one side, rolling them over, and
then coating the other side. Coatings of approximately 100 nm and
approximately 500 nm were deposited on each type of proppant with
each of the three metals.
[0126] Following the coating process, the proppant was inspected
visually and by optical microscopy. The results indicated that the
proppant having a thinner coating of approximately 100 nm had a
generally non-uniform coating while the proppant with the thicker
coating of approximately 500 nm had a uniform coating.
EXAMPLE 2
[0127] Conventional low density and medium density ceramic
proppants which are commercially available from CARBO Ceramics Inc.
of Houston, Texas under the trade names CARBOLITE 20/40,
CARBOHYDROPROP 40/80, CARBOPROP 20/40 and CARBOPROP 40/70 were
sensitized and activated by immersing in a 2.0% stannous chloride
solution for about 3 minutes, rinsing in water, immersing in a
0.01% palladium chloride solution for about 3 minutes and finally
thoroughly rinsing in water.
[0128] An electroless nickel plating bath solution was prepared
that included 25 g of nickel sulphate hexahydrate, 20 g. of sodium
hypophosphate, 11 g. of sodium citrate dihydrate and 10 g. of
sodium acetate per liter of distilled water. The pH of the plating
bath was adjusted to 5 using sulfuric acid and the plating bath was
then heated to a temperature of 90.degree. C. The previously
sensititized and activated proppant samples were then added to the
bath and coated for 1-30 minutes to yield an
electrically-conductive nickel coated proppant. Following the
coating process, the coated proppant samples were inspected
visually and by optical microscopy.
EXAMPLE 3
[0129] Conventional low density and medium density ceramic
proppants which are commercially available from CARBO Ceramics,
Inc. of Houston, Tex. under the trade names CARBOLITE 20/40,
CARBOHYDROPROP 40/80, CARBOPROP 20/40 and CARBOPROP 40/70 were
sensitized and activated by immersing in a 2.0% stannous chloride
solution for about 3 minutes, rinsing in water, immersing in a
0.01% palladium chloride solution for about 3 minutes and finally
thoroughly rinsing in water.
[0130] An electroless copper plating bath solution was prepared
that included 53 g of potassium sodium tartrate, 19 g of copper
sulfate, 13 g of sodium hydroxide and 21 g of sodium carbonate per
liter of distilled water. The plating bath was then prepared by
adding 10-40 ml of formaldehyde per liter of the concentrate. The
plating bath was then heated to 45.degree. C. The previously
sensititized and activated proppants were then added to the bath
and coated for 1-30 minutes to yield an electrically-conductive
copper-coated proppant. Following the coating process, the coated
proppant samples were inspected visually and by optical
microscopy.
EXAMPLE 4
[0131] In this example, 57 grams of CARBOLITE 20/40 was immersed in
20 ml of deionized water containing 10 mg of sodium borohydride and
1 .mu.L of Tween.TM. 20 (PEG(20)sorbitan monolaurate). This mixture
was then evaporated onto the surface of the particles by drying in
an 85.degree. C. oven. These dried particles were then transferred
to a bath formed from the Caswell Electroless Nickel Plating Kit,
which is commercially available from Caswell Inc. of Lyons, N.Y.,
where plating initiated instantaneously. This example demonstrates
that the surface of the ceramic particles can be activated without
the use palladium or other precious metals. It was found that the
surface of the particles can be activated by soaking the particles
in a reducing agent solution, such as sodium borohydride or sodium
cyanoborohydride, where this solution can either be dried onto the
particles or the particles moistened with this solution can be
transferred to an electroless plating bath, both of which are
sufficient to induce plating.
EXAMPLE 5
[0132] It was found that certain ceramic mixtures used to make
proppants contain a significant amount of oxidized iron, or iron
moieties. These iron moieties can be reduced to elemental iron,
which is catalytically active to copper and nickel electroless
plating solutions. In this example, 57 grams of CARBOPROP 20/40 was
placed into an alumina boat that was inserted into a tube furnace
under an atmosphere of 5% hydrogen in argon. The temperature was
raised to 700.degree. C. over a period of two hours and the
CARBOPROP 20/40 was permitted to soak for two hours. The furnace
was permitted to cool naturally and the sample was in a condition
to be plated after removal from the furnace.
[0133] This example shows that by utilizing native iron content,
proppant particles can be plated without the need for additional
activators, such as Pd. The reduction of surface iron ions to
atomic iron can be induced near the end of a manufacturing process
by maintaining a reducing environment in a kiln, which can be
characterized by the presence of carbon monoxide or other products
of partial combustion. The iron on the surface of the proppant
particles can also be reduced after manufacturing by exposure to
carbon monoxide or hydrogen at elevated temperatures, which can be
from about 300.degree. C. to about 1100.degree. C. Finally, the
iron on the surface of the particles can be reduced by placing the
particles in a solution of a reducing agent, such as sodium
borohydride. After reduction of these surface iron sites, the
particles can be plated using electroless plating solutions.
[0134] When used as a proppant, the particles described herein can
be handled in the same manner as conventional proppants. For
example, the particles can be delivered to the well site in bags or
in bulk form along with the other materials used in fracturing
treatment. Conventional equipment and techniques can be used to
place the particles in the formation as a proppant. For example,
the particles are mixed with a fracture fluid, which is then
injected into a fracture in the formation.
EXAMPLE 6
[0135] Conventional low density ceramic proppants which are
commercially available from CARBO Ceramics Inc. of Houston, Tex.
under the trade names of CARBOLITE 20/40 and CARBOHYDROPROP 40/80
were coated with thin layers of a conductive polymer using a
planetary bench mixer with a "B" flat beater and a heating mantle.
Approximately 500 g of proppant was used for each coating run.
Coatings of 0.1% by weight and 0.4% by weight of the proppant were
prepared as shown in Table I below:
TABLE-US-00001 TABLE I 0.1% 0.4% Conductive polymer coating coating
PEDOT:PSS 42 g 167 g Obtained from Sigma-Aldrich as a 1.2% solution
in water PANI 10 g 40 g Obtained from Sigma-Aldrich in an
emeraldine base, as a 5% solution in tetrahydrofuran (THF) and
doped with a 4-dodecylbenzene sulfonic acid in a 1:1 molar ratio
PPY 10 g 40 g Obtained from Sigma-Aldrich as a doped 5% dispersion
in water
[0136] In each case, the proppant was heated to a temperature of
150-200.degree. C. in an oven and was added to a steel mixing bowl.
An adhesion promoter, such as aminopropyl triethoxy silane, an
amino-functional coupling agent, and glycidyloxypropyl trimethoxy
silane, a functional organosilane coupling agent, was added to the
heated proppant to enhance the bond between the inorganic substrate
and the organic polymer. The mixing bowl was set in an external
heating mantle to allow the heat to remain in the system as
additives were added. The "B" flat beater traveled along the side
of the wall surfaces of the mixing bowl in circular orbits at an
intermediate speed of approximately 280 rpm while the mixing bowl
stayed in place, thereby allowing complete mixing in a short time.
A typical batch schedule is shown in Table II below:
TABLE-US-00002 TABLE II Coating Schedule on Ceramics: Ingredient
Time of Addition Substrate 0 s Adhesion Promoter 7 s Conductive
Polymer 15 s End Cycle 5-10 min
[0137] Additionally, 0.1% and 0.4% coatings were made by adding
PEDOT:PSS to a phenol-formaldehyde (Novolac) coating using a
planetary mixer with "B" flat beater and a heating mantle as
described above. Approximately 500 g of proppant was used for each
coating run. For a 0.1% and 0.4% by weight coating of the proppant,
approximately 42 g and 167 g of PEDOT:PSS, respectively, were added
to 500 g of proppant with 20 g of phenol-formaldehyde (Novolac)
resin cross-linked with hexamine (13% hexamine based on
phenol-formaldehyde (Novolac) resin) with and without adhesion
promoters as mentioned above. A typical batch schedule is shown in
Table III below:
TABLE-US-00003 TABLE III Coating Schedule on Ceramics with
Phenol-Formaldehyde Resin: Ingredient Time of Addition Substrate 0
s Phenol-Formaldehyde resin 0 s Adhesion Promoter 7 s Hexamine
(cross-linker) 30 s Conductive Polymer 1.5-2 min End Cycle 5-10
min
[0138] Following the coating process, the coated proppant samples
were inspected visually and by optical microscopy.
EXAMPLE 7
[0139] The electrical conductivity of various proppant samples
prepared according to Examples 1-3 and 6 as well as uncoated
proppant samples was measured using the test device shown in FIG.
10. As shown in FIG. 10, the test system 1000 included an
insulating boron nitride die 1002, having an inside diameter of 0.5
inches and an outside diameter of 1.0 inches, disposed in a bore
1004 in a steel die 1006 in which the bore 1004 had an inside
diameter of 1.0 inches. Upper and lower steel plungers 1008 and
1010 having an outside diameter of 0.5 inches were inserted in the
upper and lower ends 1012, 1014, respectively, of the insulating
boron nitride die 1002 such that a chamber 1016 is formed between
the leading end 1018 of the upper plunger 1008, the leading end
1020 of the lower plunger 1010 and the inner wall 1022 of the boron
nitride sleeve 1002. Upper plunger 1008 was removed from the
insulating boron nitride die 1002 and proppant was loaded into the
chamber 1016 until the proppant bed 1024 reached a height of about
1 to 2 cm above the leading end 1020 of the lower plunger 1010. The
upper plunger 1008 was then reinstalled in the insulating boron
nitride die 1002 until the leading end 1018 of the upper plunger
1008 engaged the proppant 1024. A copper wire 1026 was connected to
the upper plunger 1008 and one pole of each of a current source
1028 and a voltmeter 1030. A second copper wire 1032 was connected
to the lower plunger 1010 and the other pole of each of the current
source 1028 and the voltmeter 1030. The current source can be any
suitable DC current source well-known to those of ordinary skill in
the art such as a Keithley 237 High Voltage Source Measurement Unit
in the DC current source mode and the voltmeter can be any suitable
voltmeter well known to those of ordinary skill in the art such as
a Fluke 175 True RMS Multimeter which may be used in the DC mV mode
for certain samples and in the ohmmeter mode for higher resistance
samples.
[0140] The current source was powered on and the resistance of the
test system 1000 with the proppant bed 1024 in the chamber 1016 was
then determined. The resistance of the proppant 1024 was then
measured with the Multimeter as a function of pressure using the
upper plunger 1008 and lower plunger 1010 both as electrodes and to
apply pressure to the proppant bed 1024. Specifically, R=V/I--the
resistance of the system with the plungers touching is subtracted
from the values measured with the proppant bed 1024 in the chamber
1016 and the resistivity, p=R*A/t where A is the area occupied by
the proppant bed 1024 and t is the thickness of the proppant bed
1024 between the upper plunger 1008 and the lower plunger 1010.
[0141] The results were as follows:
[0142] Electrical measurements of base proppants without the
addition of any conductive material were conducted at 100 V DC on
samples that were 50 volume % proppant in wax that were pressed
into discs nominally 1 inch in diameter and approximately 2 mm
thick. Using these values to calculate the resistivity and using
the measured resistivity for pure wax, the values below were
extrapolated by plotting log(resistivity) vs. volume fraction
proppant and extrapolating to a volume fraction of one:
[0143] CARBOPROP 40/70: 2.times.10.sup.12 Ohm-cm
[0144] CARBOPROP 20/40: 0.6.times.10.sup.12 Ohm-cm
[0145] CARBOHYDROPROP: 1.8.times.10 .sup.12 Ohm-cm
[0146] CARBOECONOPROP: 9.times.10.sup.12 Ohm-cm
[0147] It should be noted that the resistivities of the samples
measured above are very high and not suitable for detection in the
present invention.
[0148] Electrical measurements of base proppants with coatings of
aluminum in thicknesses of 100 nm and 500 nm prepared according to
Example 1, and base proppants with coatings of 0.1% or 0.4% of
poly(3,4-ethylenedioxythiophene) (PEDOT), with or without amino
silane were conducted. The results are shown in Table IV below and
FIG. 11.
TABLE-US-00004 TABLE IV Resistivity (ohm-cm) Description 0 psi 1500
psi 2500 psi 3000 psi 5000 psi Base Material-no coating/no
modification 9 .times. 10.sup.12 Not Not Not Not measured measured
measured measured CL w/0.1% PEDOT Not 1000 to 1000 to 1000 to 1000
to measured 5000 5000 5000 5000 CL w/0.1% PEDOT/amino silane Not
10,000 to 10,000 to 10,000 to Not measured 100,000 50,000 25,000
measured CL w/0.4% PEDOT Not 1000 to 1000 to 1000 to 1000 to
measured 5000 5000 5000 5000 CL w/0.4% PEDOT/amino silane Not 5000
to ~5000 ~5000 Not measured 10,000 measured CL w/100 nm Al coat Not
1,000 1,000 1,000 Not measured measured CL w/500 nm Al coat 5 to 10
~0 0.1-0 0.1-0 0.1-0 CL w/500 nm Al coat Not ~0 0.27 Not Not
measured measured measured HP w/100 nm Al coat Not >1,000,000
>1,000,000 >1,000,000 >1,000,000 measured HP w/500 nm Al
coat Not 0-1 0.30 0-1 0-1 measured
[0149] As can be seen from FIG. 11, the best results in terms of
conductivity were obtained with CARBOLITE 20/40 and CARBOHYDROPROP
40/80 having a 500 nm thick coating of aluminum.
[0150] Electrical measurements of mixtures of base proppants with
varying percentages of such base proppants with coatings of
aluminum in thicknesses of 500 nm prepared according to Example 1
were conducted. The results are shown in Tables V and VI below and
FIGS. 12-13.
[0151] Table V shows data for mixtures of CARBOLITE 20/40 with a
500 nm coating of aluminum and CARBOLITE 20/40 with no added
conductive material. For each sample shown in Table V, 3 g. of the
sample material was placed in the 0.5 inch die to provide an area
of 0.196 square inches. The applied current for each test was 5 mA
and the tests were conducted at room temperature.
TABLE-US-00005 TABLE V 80% 500 nm Al-coated CARBOLITE with 20%
CARBOLITE 20/40 Load Pressure Voltage Resistance Resistivity (lbs)
(psi) (mV) (Ohm) (Ohm-cm) 100 509 6.1 1.22 1.107 200 1019 5.6 1.12
1.016 300 1528 5.0 1.00 0.907 400 2037 4.7 0.94 0.853 500 2546 4.5
0.90 0.817 60% 500 nm Al-coated CARBOLITE with 40% CARBOLITE 20/40
Load Pressure Voltage Resistance Resistivity (lbs) (psi) (mV) (Ohm)
(Ohm-cm) 200 1019 20.0 4.00 3.630 300 1528 17.8 3.56 3.230 400 2037
17.0 3.40 3.085 500 2546 16.1 3.22 2.922 600 3056 15.8 3.16 2.867
40% 500 nm Al-coated CARBOLITE with 60% CARBOLITE 20/40 Load
Pressure Voltage Resistance Resistivity (lbs) (psi) (mV) (Ohm)
(Ohm-cm) 100 509 253 50.60 46.516 200 1019 223 44.60 41.000 300
1528 218 43.60 40.080 400 2037 226 45.20 41.552 500 2546 221 44.20
40.632
[0152] Table VI shows data for mixtures of HYDROPROP 40/80 with a
500 nm coating of aluminum and HYDROPROP 40/80 with no added
conductive material. For each sample shown in Table VI, 3 g. of the
sample material was placed in the 0.5 inch die to provide an area
of 0.196 square inches. The applied current for each test was 5 mA
and the tests were conducted at room temperature.
TABLE-US-00006 TABLE VI 80% 500 nm Al-coated HYDROPROP 40/80 with
20% HYDROPROP 40/80 Load Pressure Voltage Resistance Resistivity
(lbs) (psi) (mV) (Ohm) (Ohm-cm) 100 509 5.9 1.18 1.083 200 1019 5.3
1.06 0.973 300 1528 4.9 0.98 0.900 400 2037 4.6 0.92 0.845 500 2546
4.4 0.88 0.808 60% 500 nm Al-coated HYDROPROP 40/80 with 40%
HYDROPROP 40/80 Load Pressure Voltage Resistance Resistivity (lbs)
(psi) (mV) (Ohm) (Ohm-cm) 200 1019 17.5 3.50 3.167 300 1528 15.6
3.12 2.823 400 2037 14.5 2.90 2.624 500 2546 13.8 2.76 2.497 40%
500 nm Al-coated HYDROPROP 40/80 with 60% HYDROPROP 40/80 Load
Pressure Voltage Resistance Resistivity (lbs) (psi) (mV) (Ohm)
(Ohm-cm) 200 1019 550 110.00 99.532 300 1528 470 94.00 85.055 400
2037 406 81.20 73.473 500 2546 397 79.40 71.844
[0153] As can be seen from TABLES V and VI as well as FIGS. 12-13,
the resistivity of the proppant packs, regardless of the relative
amounts of coated or un-coated proppant, tends to decrease with
increasing closure pressure. In addition, as the relative amount of
uncoated proppant increases and the relative amount of coated
proppant decreases, the resistivity of the proppant packs increases
dramatically. Lastly, the lowest resistivity is achieved with 100%
Al-coated proppant. No mixture of coated and uncoated proppant
results in a resistivity measurement less than 100% Al-coated
proppant.
[0154] Electrical measurements of proppants with coatings of nickel
and copper were also conducted. The results are shown in TABLE VII
below and FIG. 14. TABLE VII shows data for CARBOLITE 20/40 with a
coating of nickel and CARBOLITE 20/40 with a coating of copper. For
each sample shown in TABLE VII, the sample material was placed in
the 0.5 inch die. The applied voltage for each test was 0.005V.
TABLE-US-00007 TABLE VII Ni-coated CARBOLITE 20/40 Load Pressure
Current Resistance Conductivity (lbs) (psi) (mA) (Ohm) (S/m) 100
509 5.9 0.85 766.04 200 1019 6.1 0.75 966.44 300 1528 7.4 0.68
1182.18 400 2037 7.8 0.64 1327.66 500 2546 8.1 0.62 1449.91 800
4074 8.6 0.58 1684.37 1000 5093 8.9 0.56 1847.51 Cu-coated
CARBOLITE 20/40 Load Pressure Current Resistance Conductivity (lbs)
(psi) (mA) (Ohm) (S/m) 100 509 9.3 0.54 2098.05 200 1019 10.6 0.47
3330.51 300 1528 10.9 0.46 3766.11 400 2037 11.1 0.45 4108.19 500
2546 8.1 0.45 4298.15 800 4074 11.2 0.43 4962.66 1000 5093 11.5
0.43 5222.51
[0155] Electrical measurements of proppants having coatings of
varied thicknesses of nickel were also conducted. The results are
shown in TABLE VIII below and FIG. 15. TABLE VIII shows data for
CARBOLITE 20/40 with a coating of nickel at thicknesses of 0.27
microns, 0.50 microns, 0.96 microns, 2.47 microns, and 3.91
microns. One sample in FIG. 15 became oxidized and because of this
was not sufficiently conductive for purposes of this example. For
each sample shown in TABLE VIII, the sample material was placed in
the 0.5 inch die. The applied voltage for each test was 0.01V.
TABLE-US-00008 TABLE VIII CARBOLITE 20/40 with 0.27 micron thick
Ni-coating Load Pressure Current Resistance Conductivity (lbs)
(psi) (mA) (Ohm) (S/m) 200 1019 1.0E-07 1.00E+08 3.738E-06 400 2037
0.004 2.56E+03 0.146 600 3056 0.021 4.76E+02 0.786 800 4074 0.040
2.50E+02 1.498 1000 5093 0.055 1.82E+02 2.060 CARBOLITE 20/40 with
0.50 micron thick Ni-coating Load Pressure Current Resistance
Conductivity (lbs) (psi) (mA) (Ohm) (S/m) 200 1019 0.06 1.82E+02
2.060 400 2037 0.23 4.35E+01 8.674 600 3056 0.39 2.56E+01 14.800
800 4074 0.52 1.92E+01 19.833 1000 5093 0.61 1.64E+01 23.347
CARBOLITE 20/40 with 0.96 micron thick Ni-coating Load Pressure
Current Resistance Conductivity (lbs) (psi) (mA) (Ohm) (S/m) 200
1019 2.8 3.57 117.198 400 2037 3.9 2.56 171.292 600 3056 4.5 2.22
203.110 800 4074 4.9 2.04 225.317 1000 5093 5.3 1.89 248.375
CARBOLITE 20/40 with 2.47 micron thick Ni-coating Load Pressure
Current Resistance Conductivity (lbs) (psi) (mA) (Ohm) (S/m) 200
1019 13.2 7.58E-01 994.508 400 2037 15.3 6.54E-01 1374.809 600 3056
16.3 6.13E-01 1612.612 800 4074 17.0 5.88E-01 1809.833 1000 5093
17.4 5.75E-01 1936.619 CARBOLITE 20/40 with 3.91 micron thick
Ni-coating Load Pressure Current Resistance Conductivity (lbs)
(psi) (mA) (Ohm) (S/m) 200 1019 19.5 0.513 2850.607 400 2037 20.9
0.478 3862.317 600 3056 21.5 0.465 4480.414 800 4074 21.9 0.457
4988.307 1000 5093 22.1 0.452 5279.416
[0156] Electrical measurements of proppants with coatings of nickel
and copper were also conducted as a function of KCl exposure. The
results are shown in TABLE IX below and FIG. 16. TABLE IX shows
data for CARBOLITE 20/40 with a coating of nickel and CARBOLITE
20/40 with a coating of copper. Each sample was exposed to a 2% KCl
solution having a pH of 10 and a temperature of 120.degree. C. for
0 day, 1 day, 3 days, and 7 days. For each sample shown in TABLE
IX, the sample material was placed in the 0.5 inch die under a
pressure of 3560 psi.
TABLE-US-00009 TABLE IX Ni-coated CARBOLITE Cu-coated CARBOLITE
Conductivity Conductivity Time (days) (S/m) (S/m) 0 1880 4314 1
1874 1536 3 1718 812 7 1763 1272
[0157] As can be seen from TABLE VII and FIG. 14, the copper
coating provides a greater conductivity than the conductivity
provided by the nickel. As can be seen from TABLE VIII and FIG. 15,
decreasing thicknesses of the nickel coating provide decreasing
conductivity. And as can be seen from TABLES VII and VIII as well
as FIGS. 14 and 15, the conductivity of the proppant packs,
regardless of the relative amounts of coated or un-coated proppant,
tends to increase with increasing closure pressure. Lastly,
exposure to the KCl solution greatly reduces the conductivity of
copper coated proppant, but has little noticeable effect on the
conductivity of the nickel coated proppant.
[0158] In an exemplary method of fracturing a subterranean
formation, a hydraulic fluid is injected into the formation at a
rate and pressure sufficient to open a fracture therein, and a
fluid containing sintered, substantially round and spherical
particles prepared from a slurry as described herein and having one
or more of the properties as described herein is injected into the
fracture to prop the fracture in an open condition.
[0159] The foregoing description and embodiments are intended to
illustrate the invention without limiting it thereby. It will be
understood that various modifications can be made in the invention
without departing from the spirit or scope thereof.
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