U.S. patent application number 12/163263 was filed with the patent office on 2008-10-16 for downhole servicing compositions having high thermal conductivities and methods of using the same.
This patent application is currently assigned to Halliburton Energy Services, Inc.. Invention is credited to Gary W. Matula, Toby N. McClain.
Application Number | 20080251755 12/163263 |
Document ID | / |
Family ID | 38353777 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080251755 |
Kind Code |
A1 |
Matula; Gary W. ; et
al. |
October 16, 2008 |
Downhole servicing compositions having high thermal conductivities
and methods of using the same
Abstract
A downhole servicing composition comprising from about 15
percent to about 80 percent by weight of a clay, and from about 10
percent to about 75 percent by weight of a carbon source is
disclosed. The invention includes a downhole servicing composition
comprising from about 15 percent to about 45 percent by weight of a
first clay, from about 15 percent to about 45 percent by weight of
a second clay, from about 10 percent to about 35 percent by weight
of a filler, and from about 10 percent to about 75 percent by
weight of a carbon source. The invention also includes a downhole
servicing composition comprising an aqueous base and from about 10
percent to about 75 percent by weight of flaked graphite, wherein
the downhole servicing composition has a thermal conductivity not
less than about 0.8 BTU/hr-ft-.degree. F.
Inventors: |
Matula; Gary W.; (Houston,
TX) ; McClain; Toby N.; (Kingwood, TX) |
Correspondence
Address: |
CRAIG W. RODDY;HALLIBURTON ENERGY SERVICES
P.O. BOX 1431
DUNCAN
OK
73536-0440
US
|
Assignee: |
Halliburton Energy Services,
Inc.
Houston
TX
|
Family ID: |
38353777 |
Appl. No.: |
12/163263 |
Filed: |
June 27, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11422277 |
Jun 5, 2006 |
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12163263 |
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10767690 |
Jan 29, 2004 |
7067004 |
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11422277 |
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11099023 |
Apr 5, 2005 |
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10767690 |
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Current U.S.
Class: |
252/71 |
Current CPC
Class: |
C04B 28/105 20130101;
C04B 28/10 20130101; C09K 8/16 20130101; C04B 28/105 20130101; Y10S
106/04 20130101; C04B 28/10 20130101; C09K 8/46 20130101; C04B
24/2641 20130101; C04B 24/18 20130101; C04B 14/104 20130101; C04B
14/024 20130101; C04B 14/06 20130101; C04B 14/022 20130101; C04B
24/003 20130101; C04B 14/047 20130101; C04B 14/22 20130101; C04B
22/16 20130101; C04B 14/104 20130101; C04B 14/104 20130101; C04B
14/104 20130101; C04B 14/06 20130101 |
Class at
Publication: |
252/71 |
International
Class: |
C09K 5/00 20060101
C09K005/00 |
Claims
1. A downhole servicing composition comprising: from about 15
percent to about 80 percent by weight of a clay, and from about 10
percent to about 75 percent by weight of flaked graphite.
2. The downhole servicing composition of claim 1 wherein the clay
is sodium bentonite, calcium bentonite, or combinations
thereof.
3. The downhole servicing composition of claim 1 wherein the clay
is sodium bentonite.
4. The downhole servicing composition of claim 1 further comprising
from about 10 to about 35 percent by weight of filler selected from
the group consisting of silica flour, silica fume, fly ash,
pozzolan, sand, barite, zeolites, powdered glass, or combinations
thereof.
5. The downhole servicing composition of claim 2 further comprising
from about 10 to about 35 percent by weight of filler selected from
the group consisting of silica flour, silica fume, sand, or
combinations thereof.
6. The downhole servicing composition of claim 3 further comprising
from about 10 to about 35 percent by weight of filler selected from
the group consisting of silica flour, silica fume, sand, or
combinations thereof.
7. The downhole servicing composition of claim 3 further comprising
from about 10 to about 35 percent by weight silica flour as
filler.
8. The downhole servicing composition of claim 1 further
comprising: up to about 2 percent by weight of an alkaline earth
metal oxide or an alkaline earth metal hydroxide selected from the
group consisting of magnesium oxide, strontium oxide, calcium
hydroxide, barium hydroxide, or combinations thereof.
9. The downhole servicing composition of claim 6 further
comprising: up to about 2 percent by weight of magnesium oxide.
10. The downhole servicing composition of claim 1 further
comprising: from about 2 percent to about 10 percent by weight of a
dispersant selected from the group consisting of ammonium
lignosulfonate salt, a metal lignosulfonate salt, a phosphate, a
polyphosphate, an organophosphate, a phosphonate, a tannin,
leonardite, a polyacrylate, or combinations thereof.
11. The downhole servicing composition of claim 6 further
comprising: from about 2 percent to about 10 percent by weight of
polyphosphate as a dispersant.
12. The downhole servicing composition of claim 9 further
comprising: from about 2 percent to about 10 percent by weight of
polyphosphate as a dispersant.
13. The downhole servicing composition of claim 1 further
comprising water to form a slurry.
14. The downhole servicing composition of claim 1 wherein the
downhole servicing composition has a thermal conductivity not less
than about 0.8 BTU/hr-ft-.degree. F. upon placement and setting in
a wellbore.
15. The downhole servicing composition of claim 7, further
comprising water to form a slurry and wherein the dry components
are present in an amount not exceeding about 50 percent by weight
of the slurry.
16. A downhole servicing composition comprising: an aqueous base
and from about 10 percent to about 75 percent by weight of flaked
graphite, wherein the downhole servicing composition has a thermal
conductivity not less than about 0.8 BTU/hr-ft-.degree. F. upon
placement and setting in a wellbore.
17. The downhole servicing composition of claim 16 wherein the
downhole servicing composition is substantially free of sand.
18. The downhole servicing composition of claim 16 wherein the
downhole servicing composition has a hydraulic conductivity of from
about 5.times.10.sup.-9 cm/s to about 1.times.10.sup.-7 cm/s.
19. The downhole servicing composition of claim 16 further
comprising from about 10 to about 35 percent by weight of filler
selected from the group consisting of silica flour, silica fume, or
combinations thereof
20. The downhole servicing composition of claim 19 further
comprising from about 15 percent to about 80 percent by weight of
sodium bentonite.
21. A downhole servicing composition comprising: from about 15
percent to about 80 percent by weight of sodium bentonite, and from
about 10 percent to about 75 percent by weight of a carbon source
selected from the group consisting of petroleum coke, pitch coke,
tar coke, powdered carbon, flaked graphite, amorphous carbon, vein
carbon, crystalline carbon, synthetic carbon, or combinations
thereof.
22. The downhole servicing composition of claim 21 wherein the
carbon source is flaked graphite and wherein the downhole servicing
composition has a thermal conductivity not less than about 0.8
BTU/hr-ft-.degree. F. upon placement and setting in a wellbore.
23. The downhole servicing composition of claim 22 further
comprising from about 10 to about 35 percent by weight of filler
selected from the group consisting of silica flour, silica fume,
sand, or combinations thereof.
24. A downhole servicing composition consisting essentially of:
from about 15 percent to about 80 percent by weight of sodium
bentonite; from about 10 percent to about 75 percent by weight of
flaked graphite; from about 10 to about 35 percent by weight of
filler selected from the group consisting of silica flour, silica
fume, sand, or combinations thereof; optionally up to about 2
percent by weight of magnesium oxide; optionally from about 2
percent to about 10 percent by weight of polyphosphate as a
dispersant; and water to form a slurry.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation application claiming priority to U.S.
patent application Ser. No. 11/422,277, filed Jun. 5, 2006, now
published as U.S. Patent Publication 2006-0243166 A1, and entitled
"Downhole Servicing Compositions Having High Thermal Conductivities
and Methods of Using the Same," which claims priority to U.S.
patent application Ser. No. 10/767,690 filed Jan. 29, 2004, now
issued as U.S. Pat. No. 7,067,004, and U.S. patent application Ser.
No. 11/099,023 filed Apr. 5, 2005, now published as U.S. Patent
Publication 2005-0205834 A1, which are incorporated by reference as
if reproduced in their entirety.
FIELD OF THE INVENTION
[0002] This invention generally relates to thermally conductive
downhole servicing compositions. More specifically, the invention
relates to grout compositions having relatively high thermal
conductivities and low hydraulic conductivities and methods of
using the same to install a heat transfer loop in the earth.
[0003] This invention also relates to fluids having high thermal
conductivity or low thermal resistivity and their use underground.
More particularly, this invention relates to products and methods
for dissipating heat underground, particularly heat associated with
buried high voltage power lines and other buried electrical
transmission and distribution equipment such as cables.
BACKGROUND OF THE INVENTION
[0004] Heat transfer loops are often placed in the earth to provide
for the heating and cooling of residential and commercial spaces.
Since ground temperatures are generally similar to room
temperatures in buildings, the use of such heat transfer loops can
be cost effective alternatives to conventional heating and cooling
systems. The installation of such heat transfer loops involves
inserting a continuous loop of pipe connected to a heat pump unit
into a hole or series of holes in the earth to act as a heat
exchanger. A thermally conductive grout is then placed in the hole
between the pipe wall and the earth. A heat transfer fluid can be
circulated through the underground heat transfer loop to allow heat
to be transferred between the earth and the fluid via conduction
through the grout and the pipe wall. When the system is operating
in a heating mode, a relatively cool heat transfer fluid is
circulated through the heat transfer loop to allow heat to be
transferred from the warmer earth into the fluid. Similarly, when
the system is operating in a cooling mode, a relatively warm heat
transfer fluid is circulated through the heat transfer loop to
allow heat to be transferred from the fluid to the cooler earth.
Thus, the earth can serve as both a heat supplier and a heat
sink.
[0005] The efficiency of the heat transfer loop is affected by the
grout employed to provide a heat exchange pathway and a seal from
the surface of the earth down through the hole. The grout needs to
have a relatively high thermal conductivity to ensure that heat is
readily transferred between the heat transfer fluid and the earth.
Further, the grout may form a seal that is substantially
impermeable to fluids that could leak into and contaminate ground
water penetrated by the hole in which it resides. Even if the
fluids do not penetrate the ground water, a seal is still
desirable. The hydraulic conductivity, which measures the rate of
movement of fluid (i.e., distance/time) through the grout, is thus
desirably low. Moreover, the grout needs to have a relatively low
viscosity to allow for its placement in the space between the heat
transfer loop and the earth, thereby displacing any drilling fluid
residing therein. In an attempt to achieve such properties, two
types of grouts containing sand to enhance their thermal
conductivity, i.e., bentonite-based grout and cement-based grout,
have been developed that are extremely labor intensive to prepare.
In particular, conventional grouts often require several hundred
pounds of sand to render them suitably thermally conductive.
Unfortunately, the thermal conductivity that may be achieved by
these conventional grouts is limited by the amount of sand that can
be incorporated into and properly suspended in the grout. Also, the
preparation of such grouts is inflexible in that the concentrations
of the components and the mixing procedures must be precise to
avoid problems in the field. Further, cement-based grout has the
limitation of being very expensive.
[0006] A need therefore exists for an improved grout for use in
sealing a heat transfer loop to the earth. It is desirable for the
grout to have a higher thermal conductivity and a lower hydraulic
conductivity than conventional grouts while at the same time being
relatively easy and inexpensive to prepare. It is also desirable
for the grout to have some flexibility in the way it can be
prepared.
[0007] Increasingly, electrical equipment such as high voltage
transmission and distribution power lines are being installed (or
buried) underground, for safety, ecological, aesthetic, and/or
operational reasons. For example, the advantages of buried power
lines in tropical regions, where above ground lines are vulnerable
to high winds and rains due to tropical storms and hurricanes, are
readily apparent. However, the capabilities of such installations
are limited by the ability of the installations to dissipate heat
generated by the flow of electrical power through the equipment. If
the thermal resistivity of the environment surrounding the buried
equipment is unsatisfactorily high, the heat generated during
functioning of the equipment can cause an increase in the
temperature of the equipment beyond tolerable limits resulting over
time in the premature failure or destruction of the equipment. At
the very least, the equipment's life expectancy is decreased, which
is an economic disadvantage.
[0008] Currently, cable is installed by either digging a trench and
backfilling around the cable with a thermally conductive material,
or drilling a bore hole, pulling the cable through the bore hole,
and placing a thermally conductive material around this cable. The
industry typically addresses dissipation of heat around buried
power lines in one of two basic ways, both of which involve placing
a thermally conductive material around the outside of power line
cable (whether or not the cable is strung through a carrier pipe).
One way uses bentonite grout to which sand may be added to increase
thermal conductivity. The other way uses a cement or similar
cementitious material containing sand to provide thermal
enhancement. The thermally conductive material is typically
installed by either digging a trench and backfilling around the
cable with the thermally conductive material or by drilling a bore
(hole) and then pulling the cable through the bore containing the
thermal enhancement material.
[0009] Without sand, bentonite grout does not have high thermal
conductivity properties. Typical thermal conductivity values for
bentonite grouts range from about 0.4 to about 0.6
BTU/hr-ft-.degree. F. The addition of sand of an appropriate size
can increase such thermal conductivity to a range of about 1.0 to
about 1.2 BTU/hr-ft-.degree. F. However, the sand can cause
placement problems and high pump pressures when positioning as the
thermally conductive grout. In horizontal heat loops, high pump
pressures can lead to a "frac out" situation where the material
induces fractures in the soil through which the material can break
through to the surface. Use of cement grout can magnify such
problems. Use of sand can also lead to excessive friction,
prematurely wearing out pumps and their various parts. For example,
in the case of a pipe bundle containing cables, such friction from
sand can result in pulling forces that can exceed the strength of
the bundle causing the bundle to separate during installation.
Backfilling soil with sand added after the pipe installation might
be used to avoid such installation friction but backfilling may not
always be possible or effective for the full length of the
installation. Further, additional wear caused by the sand to pumps
and pump parts remains a concern.
SUMMARY OF THE INVENTION
[0010] In one aspect, the invention includes a downhole servicing
composition comprising from about 15 percent to about 80 percent by
weight of a clay, and from about 10 percent to about 75 percent by
weight of a carbon source. In one embodiment, the downhole
servicing composition further comprises up to about 2 percent by
weight of an alkaline earth metal oxide or an alkaline earth metal
hydroxide. The alkaline earth metal oxide or earth metal hydroxide
may be magnesium oxide, strontium oxide, calcium hydroxide, barium
hydroxide, or combinations thereof. In another embodiment, the
downhole servicing composition further comprises from about 2
percent to about 10 percent by weight of a dispersant. The
dispersant may be ammonium lignosulfonate salt, a metal
lignosulfonate salt, a phosphate, a polyphosphate, an
organophosphate, a phosphonate, a tannin, leonardite, a
polyacrylate, or combinations thereof. In yet another embodiment,
the downhole servicing composition further comprises water. The
downhole servicing composition may have a thermal conductivity not
less than about 0.8 BTU/hr-ft-.degree. F. when the dry components
are present in an amount not exceeding about 50 percent by weight
of the slurry. Optionally, the downhole servicing composition has a
thermal conductivity not less than about 0.8 BTU/hr-ft-.degree.
F.
[0011] In a second aspect, the invention includes a downhole
servicing composition comprising from about 15 percent to about 45
percent by weight of a first clay, from about 15 percent to about
45 percent by weight of a second clay, from about 10 percent to
about 35 percent by weight of a filler, and from about 10 percent
to about 75 percent by weight of a carbon source.
[0012] In one embodiment, the first clay has a first swelling rate,
and the second clay has a second swelling rate less than the first
swelling rate. The first clay may be sodium bentonite,
montmorillonite, beidellite, nontronite, hectorite, samonite,
smectite, or combinations thereof, while the second clay may be
calcium bentonite. In another embodiment, the filler is silica
flour, silica fume, fly ash, pozzolan, sand, barite, zeolites,
powdered glass, or combinations thereof. The downhole servicing
composition may be substantially free of water. The carbon source
may be petroleum coke, pitch coke, tar coke, powdered carbon,
flaked graphite, amorphous carbon, vein carbon, crystalline carbon,
synthetic carbon, or combinations thereof.
[0013] In a third aspect, the invention includes a downhole
servicing composition comprising an aqueous base and from about 10
percent to about 75 percent by weight of flaked graphite, wherein
the downhole servicing composition has a thermal conductivity not
less than about 0.8 BTU/hr-ft-.degree. F. In one embodiment, the
downhole servicing composition is substantially free of sand. In
another embodiment, the downhole servicing composition has a
hydraulic conductivity of from about 5.times.10.sup.-9 cm/s to
about 1.times.10.sup.-7 cm/s. The invention includes a grout
comprising the downhole servicing composition and a drilling fluid
comprising the downhole servicing composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Downhole servicing slurries having an improved thermal
conductivity of greater than about 0.8 BTU/hr-ft-.degree. F. may be
employed to install a conduit in one or more holes in the earth. As
used herein, "downhole servicing composition" refers to a fluid
that is placed into or circulated through a wellbore or trench to
enhance or improve the properties of the wellbore or trench. The
term downhole servicing composition expressly includes grouts,
cements, and drilling fluids. Their high thermal conductivities and
relatively low hydraulic conductivities give them the ability to
form very good thermally conductive seals around the conduit. As
used herein, "conduit" refers to a material through which fluid or
a current may flow, wherein the conduit may be hollow to allow the
passage of fluid therethrough or solid to allow the flow of current
therethrough. The conduit may be, for example, a heat transfer loop
or a grounding rod. It is understood that the earth may be exposed
or it may be covered by water such as sea or ocean water.
[0015] As will be described in more detail later, the grout
slurries may be formed by combining a grout composition that is
preferably a one-sack product with water. As used herein, "one-sack
product" refers to a form of the grout composition in which its
components are combined together in a single container such as a
sack, allowing the grout composition to be easily transported to an
on-site location where it will be used to form a grout slurry. The
resulting grout slurries can be pumped into the hole in the earth
and allowed to set in the space between the walls of the conduit
and the earth. The solids content (i.e., the amount of the grout
composition) in the grout slurries can be varied to achieve a
desirable thermal conductivity therein and need not be very high to
achieve desirable properties in the slurry. An exemplary grout
slurry exhibits a relatively high thermal conductivity, a
relatively low hydraulic conductivity after setting, and a
relatively low pumping viscosity when the amount of the grout
composition present in the grout slurry is in the range of from
about 35% to about 50% by weight of the grout slurry, alternatively
from about 35% to about 45% by weight of the grout slurry.
[0016] Grout compositions that may be used to form such grout
slurries contain components that enhance the various properties of
the slurries. In an embodiment, grout compositions comprising
sodium bentonite, calcium bentonite, a silica material, a carbon
source, an alkaline earth metal oxide, and a dispersant may be used
to install a conduit in a hole in the earth. The specific
concentrations of the components in the grout compositions are as
follows: calcium bentonite present in an amount of from about 15%
to about 45%; sodium bentonite present in an amount of from about
15% to about 45%; a silica material present in an amount of from
about 10% to about 35%; and a carbon source present in an amount of
from about 10% to about 75%; optionally an alkaline earth metal
oxide present in an amount of from about 0% to about 2%; and
optionally a dispersant present in an amount of from about 2% to
about 10%, all percentages (%'s) being by weight of the grout
compositions.
[0017] Sodium bentonite is a water-swellable clay in which the
principal exchangeable cation is a sodium ion. Its use in the grout
compositions serves to enhance the viscosity of the grout slurries
such that the solid particles contained therein can be transported
to a desired location. The sodium bentonite also contributes to the
low hydraulic conductivity of the grout slurries and thus enhances
the ability of the slurries to form a good seal between the heat
transfer loop and the earth. Examples of suitable sodium bentonite
clays include Wyoming sodium bentonite, Western sodium bentonite,
and combinations thereof. The sodium bentonite used in the grout
compositions preferably has a 30-mesh grind size, but other grind
sizes of the sodium bentonite may also be used. In alternative
embodiments, the sodium bentonite may be supplemented by or
substituted with other types of swellable clays known in the art
such as montmorillonite, beidellite, nontronite, hectorite,
samonite, smectite, or combinations thereof.
[0018] Calcium bentonite is a clay in which the principal
exchangeable cation is a calcium ion. It has a much slower
hydration or swelling rate and degree of swelling than sodium
bentonite and thus provides for improved control over the placement
of the grout slurries. Various grind sizes of the calcium bentonite
may be used, with a 200-mesh grind size being preferred.
[0019] The carbon source serves to improve the thermal conductivity
of the grout slurries. Examples of suitable carbon sources include
desulfurized petroleum coke, powdered carbon, flaked graphite, and
combinations thereof, with flaked graphite being preferred.
Desulfurized petroleum coke is described in U.S. Pat. No.
4,291,008, which is incorporated by reference herein in its
entirety. Powdered carbon is an amorphous carbon having a particle
size generally less than about 0.8 mm. Flaked graphite is a form of
graphite present in gray cast iron that appears in the
microstructure as an elongated, curved inclusion. Due to its
relatively low resistivity and thin shape, it can become interlaced
between the other types of particles in the grout slurries to form
a conductive path in the slurries. Other examples of suitable
carbons source include pitch coke, tar coke, amorphous carbon, vein
carbon, crystalline carbon, synthetic carbon, or combinations
thereof.
[0020] The silica material acts as a filler and contributes to the
good hydraulic conductivity and thermal conductivity exhibited by
the grout slurries. The silica material is preferably silica flour,
which is a finely ground silica generally having a particle size of
less than or equal to about 40 microns. Examples of other suitable
silica materials include condensed silica fume. Condensed silica
fume is a by-product of the manufacture of silicon or ferrosilicon,
which involves subjecting quartz (when silicon is produced) or
quartz and an iron-bearing material (when ferrosilicon is produced)
to reduction with coke or coal and wood chips in a furnace. A
gaseous suboxide of silicon forms, and a portion of the gaseous
suboxide escapes into the atmosphere where it reacts with oxygen
and condenses to form the glassy microscopic particles known as
condensed silica fume. The particle size of condensed silica fume
is generally smaller than about 1 micron. In addition, other inert
fillers may be used, such as sand, barite, zeolites, powdered
glass, and combinations thereof.
[0021] The alkaline earth metal oxide or alkaline earth metal
hydroxide improves the set strength of the grout slurries and the
hydraulic conductivity of the slurries. Various alkaline earth
metal oxides can be employed in the grout compositions, including
magnesium oxide, strontium oxide, or combinations thereof. The
preferred alkaline earth metal oxide is magnesium oxide. Examples
of suitable alkaline earth metal hydroxides include calcium
hydroxide, barium hydroxide, and combinations thereof.
[0022] In addition, various dispersants or thinners suitable for
use with the other components in the grout compositions can be
employed. Examples of suitable dispersants include ammonium
lignosulfonate salt, metal lignosulfonate salts, phosphates,
polyphosphates, organophosphates, phosphonates, tannins,
leonardite, polyacrylates having a molecular weight less than about
10,000, and combinations thereof. A preferred dispersant is sodium
acid pyrophosphate (SAPP). When the finer sodium bentonite grind
sizes are used, the concentration of the SAPP used in conjunction
with the sodium bentonite is near the upper limit of the previously
mentioned SAPP concentration range.
[0023] The grout compositions may further include additional
additives as deemed appropriate by one skilled in the art. Suitable
additives would bring about desired results without adversely
affecting other components in the grouting composition or the
properties thereof.
[0024] In an embodiment, the grout compositions comprise a first
clay such as sodium bentonite present in an amount of from about
15% to about 45%, alternatively from about 15% to about 20%; a
second clay such as calcium bentonite present in an amount of from
about 15% to about 45%, alternatively from about 15% to about 20%;
a filler such as silica material present in an amount of from about
10% to about 35%, alternatively from about 10% to about 20%; a
carbon source present in an amount of from about 10% to about 75%,
alternatively from about 40% to about 50%; an alkaline earth metal
oxide or alkaline earth metal hydroxide present in an amount up to
about 2%, alternatively from about 0.5% to about 1%; and a
dispersant present in an amount of from about 2% to about 10%,
alternatively from about 4% to about 7%, all by weight of the grout
compositions. In a preferred embodiment, the grout compositions
comprise calcium bentonite present in an amount of about 17.5%,
sodium bentonite present in an amount of about 17.5%, a silica
material present in an amount of about 14.5%, a carbon source
present in an amount of about 45%, an alkaline earth metal oxide
present in an amount of about 0.5%, and a dispersant present in an
amount of about 5%, all by weight of the grout compositions.
[0025] The grout compositions may be made by combining all of the
components in any order and thoroughly mixing the components in a
manner known to one skilled in the art. In a preferred embodiment,
the grout compositions are manufactured off-site and then shipped
as a one-sack product to the location where it is to be used to
install an underground conduit.
[0026] Methods of installing a conduit in a hole in the earth
comprise placing the conduit in the hole in the earth, mixing one
of the foregoing grout compositions, which may be a one-sack
product, with water to form a grout slurry, and placing the grout
slurry in the hole adjacent to the conduit. The hole in the earth
may be a borehole that has been drilled in the earth to a depth
sufficient to hold the conduit therein. The grout slurry may be
pumped into the space between the conduit and the walls of the hole
until the space is filled with the slurry. After the placement of
the grout slurry, it is allowed to set, thus forming a thermally
conductive seal between the conduit and the earth. The water
utilized in the grout slurry can be water from any source provided
that it does not adversely affect the components or properties of
the slurry and that it would not contaminate nearby soil.
Preferably, fresh water in an amount sufficient to form a pumpable
slurry is mixed with the grout composition. The water and the grout
composition may be mixed to form the grout slurry using a standard
mixing device such as a grouter or other similarly functioning
device. The grout slurry preferably comprises from about 35% to
about 45% of the grout composition by weight of the grout slurry
and a balance of the water.
[0027] The set grout slurry seals the conduit within the hole in
the earth and acts as a heat transfer medium between the conduit
and the earth. In one embodiment, the conduit may be a heat
transfer loop through which a heat transfer fluid flows. Heat may
be transferred between the earth and the heat transfer fluid via
the set grout slurry and the walls of the heat transfer loop for
the purpose of heating and/or cooling a space such as a building
located above the surface of the earth.
[0028] In another embodiment, the conduit may be a grounding rod
used to protect structures such as television towers and radio
antennas from lightning strikes. The grounding rod may extend from
the top of such structure down to the set grout slurry, which has a
relatively low resistivity. As such, if lightning strikes the
grounding rod, the current created by the lightning may pass
through the grounding rod and the set grout slurry to the
ground.
[0029] After the grout slurry has set, it exhibits excellent
properties that allow it to be used in the manner described above.
The thermal conductivity, k, of the grout slurry varies depending
on the particular concentration of the grout composition (i.e., the
solids) in the slurry, with the thermal conductivity increasing as
the grout composition increases. The grout slurry can be prepared
inexpensively since the amount of the grout composition needed
relative to the amount of water is relatively low. Further, less
labor is required to prepare the grout slurry such that several
holes in the earth can be filled more quickly. Based on
measurements taken using a thermal conductivity meter made in-house
at Halliburton Energy Services, Inc. (hereinafter a "Baroid thermal
conductivity meter"), the grout slurry has a high thermal
conductivity of, for example, greater than or equal to about 0.8
BTU/hr-ft-.degree. F., greater than or equal to about 0.9
BTU/hr-ft-.degree. F., greater than or equal to about 1.0
BTU/hr-ft-.degree. F., greater than or equal to about 1.1
BTU/hr-ft-.degree. F., greater than or equal to about 1.2
BTU/hr-ft-.degree. F., greater than or equal to about 1.3
BTU/hr-ft-.degree. F., greater than or equal to about 1.4
BTU/hr-ft-.degree. F., greater than or equal to about 1.5
BTU/hr-ft-.degree. F., or greater than or equal to about 1.6
BTU/hr-ft-.degree. F. In addition, the grout slurry has a low
hydraulic conductivity, K, of from about 5.times.10.sup.-9 cm/s to
about 1.times.10.sup.-7 cm/s. While the thermal conductivity of the
grout slurry indicates its ability to transfer heat, the hydraulic
conductivity of the grout slurry indicates its resistance to fluids
and thus measures its sealing ability. The lower the hydraulic
conductivity of the set grout slurry, the better the seal it forms.
As such, fluids are less likely to leak through the grout slurry
from the surface into sub-surface ground water or wet soil. The
grout slurry thus acts as a barrier to prevent contamination of
such ground water or soil. Further, fluids such as oil, gas, and
water in subterranean formations or zones are less likely to pass
into other subterranean zones via the grout slurry. Details
regarding the manner in which the thermal conductivity and the
hydraulic conductivity can be determined are provided in the
examples below.
[0030] The grout slurry also has a good working time, i.e., the
time period between when it is prepared and when its viscosity is
insufficient to allow it to be displaced into a space. For example,
its working time may range from about 15 minutes to about 30
minutes. Furthermore, for a grout slurry comprising less than or
equal to about 40% solids (i.e., grout composition) by weight of
the slurry, the viscosity of the grout slurry is less than about
600 centipoise (cp) as measured using a FANN 35A rotational
viscometer with a 5.times. torsion spring at 300 rpm. As such, the
grout slurry can be pumped into the hole in the earth using, e.g.,
a grouter, without having to use relatively high pump pressures.
The grout slurry also exhibits a good set strength, which is also
referred to as the shear strength. For example, the set strength
typically is greater than or equal about 2,000 lbs/100 ft.sup.2 for
a grout slurry comprising 35% solids, greater than or equal to
about 3,000 lbs/100 ft.sup.2 for a grout slurry comprising 40%
solids, and greater than or equal to about 4,000 lbs/100 ft.sup.2
for a grout slurry comprising 45% solids, all % solids being by
weight of the grout slurry. In addition, the grout slurry
experiences minimal or no subsidence after placement. Moreover, it
is believed that the grout slurry is environmentally friendly such
that there is no need to be concerned that it could contaminate
drinking water.
[0031] In an embodiment, the grout slurry may be placed in and
allowed to set in a series of holes through which a continuous heat
transfer loop, e.g., piping, has been run. The greater the number
of holes, the more surface area of earth is exposed for heat
transfer. Due to the higher thermal conductivity of the grout
slurry described herein, less holes may be required to achieve the
same amount of heat transfer as compared to using a conventional
grout slurry. Therefore, the cost of a heat transfer system, which
comprises holes in the earth and a heat transfer loop passing from
a heat pump through the holes and back to the heat pump, may be
lowered by using the grout slurry described herein to seal the
holes. In an embodiment of the present invention, a highly
thermally conductive fluid (or a fluid having low resistivity) is
placed around buried or underground electrical equipment, such as,
for example, high voltage power lines, to dissipate heat given off
by the equipment in operation. Such heat dissipation allows more
efficient flow of electricity through the equipment. The increased
heat dissipation away from the high voltage cable allows the cable
to operate more efficiently by allowing increased amounts of
electricity to flow through the cable. The increased heat
dissipation also prolongs the life of the cable. Further, such
dissipation helps keep the heat within operational design
limitations for the equipment and thus does not contribute to or
cause excess wear of the equipment.
[0032] Any aqueous based drilling fluid suitable for trenchless
drilling or for digging or excavating trenches is believed suitable
for use as the base of the fluid product of the invention, provided
the drilling fluid is capable of suspending flaked graphite and
preferably is capable of gelling to a consistency ranging from that
commonly found in pudding to that commonly found in peanut butter.
Aqueous bentonitic drilling fluids are most preferred. Also
preferably the drilling fluid base and the fluid product of the
invention will not contain compounds that provide high resistivity
or low thermal conductivity characteristics to the fluid. The fluid
product should be pumpable and substantially free of sand. Silica
flour, preferably about 200 mesh material, may be added as a
supplemental thermal enhancement material as well as to assist in
achieving a low hydraulic conductivity. The use of silica flour
also contributes to the final set of the product. Silica flour may
also assist in achieving low hydraulic conductivity, a separate
parameter not generally affected by thermal enhancement. Such
silica flour lacks the abrasiveness and density of sand and thus
affords utility in a drilling fluid not practicable with sand.
Graphite is added to the fluid to improve the fluid's thermal
conductivity properties. Preferably the graphite is flaked. The
specific amount of graphite added dictates the amount or degree of
the resulting thermally conductive properties, and such
relationship affords significant flexibility to the fluid. For
example, to achieve a thermal conductivity of about 1.0
BTU/hr-ft-.degree. F., about 145 pounds of flaked graphite per 100
gallons of aqueous drilling fluid would typically be needed.
However, thermal conductivities of about 1.6 to about 1.7
BTU/hr-ft-.degree. F. or higher are achievable when adding flaked
graphite to aqueous drilling fluid. The graphite may be added to
aqueous fluid already prepared or being used for drilling in the
field, or the fluid may be originally prepared to include the
graphite.
[0033] The fluid should remain pumpable upon addition of the
graphite and under subterranean conditions, at least for a time
sufficient to allow or to facilitate placement of the fluid in the
borehole being drilled or the trench being dug or filled or in a
pipe being filled. The fluid may optionally comprise a gellant or
equivalent component(s) to turn the fluid into a semi-solid or
solid following such placement.
[0034] To fully appreciate the benefits of the invention, the fluid
product of the invention is placed adjacent or proximate to the
electrical equipment and preferably between the equipment and the
soil covering or burying the equipment for dissipation of heat from
the equipment during operation or use of the equipment. When the
equipment comprises power lines, the lines may be encased in pipe
or not, as the invention is effective in providing a thermally
conductive environment in either situation.
[0035] According to one method of the invention, electrical
equipment is installed by trenchless drilling, wherein a hole for
receiving the equipment is drilled employing the fluid product of
the invention. The fluid product of the invention may be used in
drilling all or a portion of the hole. In one embodiment, a typical
or traditional bentonitic drilling fluid may be used for drilling a
horizontal borehole and just prior to pulling pipe and/or cable
into the bore, the bentonitic drilling fluid is either replaced
with the fluid of the invention or effectively made into the
drilling fluid of the present invention by adding graphite thereto.
During and after such drilling with the fluid of the invention, at
least some of said fluid and particularly some graphite in said
fluid deposits on the sides of said borehole and/or otherwise
remains in said borehole. The electrical equipment, one or more
high voltage power lines for example, is pulled through the
borehole for positioning underground. The graphite provides an
additional benefit of some lubrication for said pulling or
installation of the electrical equipment. The amount of graphite
included in the fluid depends on the thermal conductivity
(resistivity) desired, as discussed above. Optionally, the fluid
product of the invention remaining in the borehole may increase in
viscosity, and may also harden, or transform to a solid or
semi-solid.
[0036] During another method of the invention, electrical equipment
is installed by drilling or excavating a trench, positioning the
equipment in the trench, and then covering the equipment and/or
backfilling the trench with soil. In this method, the fluid product
of the invention may be used as a drilling fluid in excavating the
trench and/or may be flowed in the trench after it is dug and
preferably before the equipment is positioned in the trench.
Additionally, or alternatively, the product of the invention may be
added to the soil for use in the backfilling of the trench (after
the equipment is positioned in the trench). Thus, in at least one
such point in the installation, the fluid product of the invention
is included so that it is adjacent to the equipment to facilitate
dissipation of heat during use of the equipment.
[0037] In another method of the invention, the fluid product of the
invention is flowed into and/or through the inside or interior of a
protective covering for the equipment, such as inside pipe encasing
power lines or cable for example, preferably before the pipe is
installed underground. During such flow, at least some of said
fluid and particularly some graphite in said fluid deposits on the
sides of said equipment and/or protective covering of said
equipment. Preferably, the underground installation of the
equipment will be conducted by trenchless drilling using the fluid
product of the invention.
EXAMPLES
[0038] The invention having been generally described, the following
examples are given as particular embodiments of the invention and
to demonstrate the practice and advantages hereof. It is understood
that the examples are given by way of illustration and are not
intended to limit the specification or the claims to follow in any
manner.
Example 1
[0039] Three samples of a grout composition were prepared that
contained 17.5% 30-mesh sodium bentonite, 17.5% 200-mesh calcium
bentonite, 0.5% magnesium oxide, 5% sodium acid pyrophosphate,
14.5% silica flour, and 45% flaked graphite, all by weight of the
grout composition. The three samples were added to different
amounts of fresh water while blending over a 30-second period,
followed by blending the resulting mixtures for an additional 90
seconds, thereby forming three grout slurries containing 35%, 40%,
and 45% of the grout composition, respectively. This blending was
performed using a LAB MASTER G3UO5R mixer commercially available
from Lightnin Mixer Co. The thermal conductivity of each grout
slurry was measured using the Baroid thermal conductivity meter
(TCM) in accordance with the following procedure. The communication
box of the TCM was electrically coupled to a computer and to the
thermal conductivity device of the TCM. Then 400 mL of the grout
slurry was poured into the thermal conductivity device up to a
level directly below a sensor at the top of the device. A cap was
next placed on the thermal conductivity device, and the power of
the communication box was turned on. The TCM program was then run
on the computer. The heater of the TCM was turned on using the
computer. Data collection began immediately after the heater was
turned on. The TCM readings were allowed to stabilize, and such
readings were taken for about 6 hours or more after stabilization
had been achieved. The readings were then saved into an EXCEL
spreadsheet upon test completion. The thermal conductivity measured
for each grout slurry sample is shown in Table 1 below.
TABLE-US-00001 TABLE 1 Amount of Grout Composition in the Thermal
Conductivity, Grout Slurry, % by weight of the slurry
BTU/hr-ft-.degree. F. 35% 1.1 40% 1.3 45% 1.6
Example 2
[0040] The hydraulic conductivity of a grout slurry sample (the
IDP-357 slurry) made as described in this application and two
control grout slurry samples (the IDP-232 slurry and the BAROTHERM
slurry) were tested using the following procedure. Each grout
slurry sample was prepared by adding the appropriate amount of the
dry grout composition (188.5 grams for the 35% solids sample,
233.33 grams for the 40% solids sample, and 286.4 grams for the 45%
solids sample) to 350 mL deionized water over a period of 30
seconds, followed by mixing the dry grout composition with the
water for 1 minute after completing the addition of the dry grout
composition. The LAB MASTER G3UO5R mixer set at 1,000 rpm was used
for this mixing. The grout slurry was then immediately poured into
a filter press cell containing 1/4 inch of fine sand. The grout
slurry was allowed to set for 4 hours, and then deionized water was
poured on top of the set grout slurry. The filter press was
subsequently sealed and allowed to set overnight. The filter press
was then pressurized to 10 psi, and the filtrate was collected. The
amount of filtrate collected was measured and used in the following
formula to determine the hydraulic conductivity:
K = ( 5.08 P * 47.38 ) * ( Q t ) ##EQU00001##
where K=hydraulic conductivity in cm/s, Q=filtrate collected in mL,
t=time interval in seconds, and P=pressure factor, which converts
air pressure into an equivalent pressure exerted by a column of
water. The thermal conductivity of each grout sample was also
tested in the manner described in Example 1. Table 2 below gives
the hydraulic conductivity and the thermal conductivity of each
sample tested. The hydraulic conductivity values and the thermal
conductivity values for two other controls are also provided in
Table 2.
TABLE-US-00002 TABLE 2 Grout Slurry & Amount of Hydraulic
Thermal Solids in the Slurry, % by Conductivity, Conductivity,
weight of the slurry cm/s BTU/hr-ft-.degree. F. IDP-232, 63.5%
solids 6.9 .times. 10.sup.-6 0.977 (control).sup.1 BAROTHERM, 70.4%
6 .times. 10.sup.-8 0.95 solids (control).sup.2 THERMAL GROUT
<6.9 .times. 10.sup.-8 1.0 LITE, 65.1% solids (control).sup.3
THERMAL GROUT <6.9 .times. 10.sup.-8 1.2 SELECT, 70.4% solids
(control).sup.3 MIX 111 (control).sup.4 .sup. 1 .times. 10.sup.-16
1.4 THERM-EX, 67% solids 6 .times. 10.sup.-8 1.05 (control).sup.5
GEOTHERMAL GROUT, 5 .times. 10.sup.-8 1.2 68.3% solids
(control).sup.6 IDP-357, 45% solids.sup.7 5 .times. 10.sup.-9 1.65
.sup.1The IDP-232 grout is described in U.S. Pat. No. 6,258,160,
which is incorporated by reference herein. Its data is from testing
conducted internally by the Industrial Drilling Products (IDP)
laboratory. .sup.2The BAROTHERM grout is commercially available
from Halliburton Energy Services, Inc. Its data is from testing
conducted internally by the Industrial Drilling Products (IDP)
laboratory. .sup.3The THERMAL GROUT LITE and SELECT grout are
commercially available from GeoPro, Inc. Their data is from
published literature by GeoPro, Inc. .sup.4The formulation for the
MIX 111 grout was made available to the public by the U.S.
Department of Energy's Brookhaven National Laboratory. The MIX 111
grout is described in U.S. Pat. No. 6,251,179, which is
incorporated by reference herein. Its data is taken from Brookhaven
National Laboratory's web site located at www.bnl.gov/est/ghpfp.htm
and entitled "Thermally Conductive Cementitious Grouts for
Geothermal Heat Pumps." .sup.5The THERM-EX grout is commercially
available from WYO-BEN, Inc. Its data is from published literature
by WYO-BEN, Inc. .sup.6The GEOTHERMAL GROUT is commercially
available from Colloid Environmental Technologies Co. (CETCO). Its
data is from published literature by CETCO. .sup.7The IDP-357 grout
data is from testing conducted internally by the IDP
laboratory.
[0041] Based on the results shown in Table 2, the grout slurry of
the present application, i.e., the IDP-357 grout, exhibited a much
higher thermal conductivity than the control grout slurries.
Further, its hydraulic conductivity was lower than all of the
control grout slurries except the MIX 111 grout slurry. As such,
the grout slurry of the present application is recommended for use
in installing a conduit such as a heat transfer loop in one or more
holes in the earth.
Example 3
[0042] Laboratory tests were conducted to test and demonstrate the
invention. In the tests, thermal conductivity was measured using
the Baroid IDP Thermal Conductivity Meter available from Baroid
Fluid Services, a Halliburton Company, in Houston, Tex. Examples of
the ability of flaked graphite additions to increase the thermal
conductivity of a base slurry containing varying amounts of
graphite follow in Table 3.
TABLE-US-00003 TABLE 3 THERMAL AQUEOUS BENTONITE FLUID CONDUCTIVITY
Base without flaked graphite TC - 0.4 BTU/hr-ft-.degree. F. Base
with 130 lb flaked TC - 0.8 BTU/hr-ft-.degree. F. graphite/100 gal
Base with 145 lb flaked TC - 0.95 BTU/hr-ft-.degree. F.
graphite/100 gal Premixed with 35% solids TC - 0.9
BTU/hr-ft-.degree. F. Premixed with 40% solids TC - 1.3
BTU/hr-ft-.degree. F. Premixed with 45% solids TC - 1.6
BTU/hr-ft-.degree. F.
Any of the above compositions may be pre-mixed one bag
products.
[0043] While preferred embodiments of the invention have been shown
and described, modifications thereof can be made by one skilled in
the art without departing from the spirit and teachings of the
invention. The embodiments described herein are exemplary only, and
are not intended to be limiting. Many variations and modifications
of the invention disclosed herein are possible and are within the
scope of the invention. Use of the term "optionally" with respect
to any element of a claim is intended to mean that the subject
element is required, or alternatively, is not required. Both
alternatives are intended to be within the scope of the claim.
[0044] Accordingly, the scope of protection is not limited by the
description set out above but is only limited by the claims which
follow, that scope including all equivalents of the subject matter
of the claims. Each and every claim is incorporated into the
specification as an embodiment of the present invention. Thus, the
claims are a further description and are an addition to the
preferred embodiments of the present invention. The discussion of a
reference in the Description of Related Art is not an admission
that it is prior art to the present invention, especially any
reference that may have a publication date after the priority date
of this application. The disclosures of all patents, patent
applications, and publications cited herein are hereby incorporated
by reference, to the extent that they provide exemplary, procedural
or other details supplementary to those set forth herein.
* * * * *
References