U.S. patent application number 15/811041 was filed with the patent office on 2018-08-02 for methods and compositions for the controlled crosslinking and viscosifying of well servicing fluids utilizing mixed borate hydrocarbon-based suspensions.
The applicant listed for this patent is TUCC Technology, LLC. Invention is credited to James W. Dobson, JR., Kimberly A. Pierce.
Application Number | 20180215994 15/811041 |
Document ID | / |
Family ID | 50024348 |
Filed Date | 2018-08-02 |
United States Patent
Application |
20180215994 |
Kind Code |
A1 |
Dobson, JR.; James W. ; et
al. |
August 2, 2018 |
Methods and Compositions for the Controlled Crosslinking and
Viscosifying of Well Servicing Fluids Utilizing Mixed Borate
Hydrocarbon-Based Suspensions
Abstract
Disclosed are treating fluid compositions for use in
subterranean workover and hydrocarbon recovery operations, as well
as methods of treating subterranean formations penetrated by a
wellbore utilizing the treating fluid. The treating fluid
compositions contain a first, aqueous liquid, and a crosslinkable
organic polymer that is at least partly soluble in the liquid. The
treating fluid further contains a borate crosslinking agent
solution containing a primary, un-refined borate and a secondary,
refined borate, the borate solution being present as a crosslinking
agent upon addition to the first fluid admixture so as to crosslink
the organic polymer and increase the viscosity and/or accelerate
the crosslink time of the treating fluid.
Inventors: |
Dobson, JR.; James W.;
(Houston, TX) ; Pierce; Kimberly A.; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TUCC Technology, LLC |
Houston |
TX |
US |
|
|
Family ID: |
50024348 |
Appl. No.: |
15/811041 |
Filed: |
November 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13938220 |
Jul 9, 2013 |
9816025 |
|
|
15811041 |
|
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61669282 |
Jul 9, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 8/685 20130101;
C09K 8/90 20130101; E21B 43/267 20130101; C09K 2208/26 20130101;
E21B 43/26 20130101 |
International
Class: |
C09K 8/68 20060101
C09K008/68; E21B 43/26 20060101 E21B043/26; E21B 43/267 20060101
E21B043/267; C09K 8/90 20060101 C09K008/90 |
Claims
1. A treating fluid composition comprising: a polymer solution,
comprising: an aqueous fluid; a crosslinkable organic polymer
having a solubility in the aqueous fluid; a viscosifier; and an
alkaline buffer; and a borate crosslinking composition, comprising:
a low-aromatic content hydrocarbon fluid; an un-refined borate
crosslinking agent; and a refined borate crosslinking agent,
wherein the treating fluid composition has a pH of greater than pH
8.
2. The treating fluid composition of claim 1, wherein the aqueous
fluid comprises substantially any aqueous fluid that does not
adversely react with the constituents of the treating fluid, the
subterranean formation, and the fluids present therein.
3. The treating fluid composition of claim 1, wherein the aqueous
fluid is selected from the group consisting of fresh water, natural
brines, and artificial brines.
4. The treating fluid composition of claim 3, wherein the
artificial brines are selected from the group consisting of
potassium halide solutions, sodium halide solutions, and cesium
halide solutions.
5. The treating fluid composition of claim 1, wherein the
crosslinkable, organic polymer is guar or guar derivatives,
galactomannan gum, cellulose, hydroxyethylcellulose, hydroxypropyl
cellulose, carboxymethylcellulose, carboxymethylhydroxyethyl
cellulose, xanthan gum, diutan, scleroglucan, carrageenan,
polyacrylamide, and polyacrylate.
6. The treating fluid composition of claim 1, wherein the alkaline
buffer comprises alkaline compounds.
7. The treating fluid composition of claim 6, wherein the alkaline
compounds comprise one or more selected from the group consisting
of ammonium, alkali metal (Group 1) hydroxides, carbonates and
bicarbonates, and alkaline earth metal (Group 2) hydroxides,
carbonates, and bicarbonates.
8. The treating fluid composition of claim 6, wherein the alkaline
compounds are selected from the group consisting of sodium
hydroxide, sodium carbonate, sodium bicarbonate, potassium
hydroxide, potassium carbonate, and potassium bicarbonate.
9. The treating fluid composition of claim 1, wherein the
un-refined borate crosslinking agent contains about 5 wt. % or more
of boron.
10. The treating fluid composition of claim 1, wherein the
un-refined borate crosslinking agent is selected from the group
consisting of ulexite, colemanite, probertite, and mixtures
thereof.
11. The treating fluid composition of claim 1, wherein the refined
borate crosslinking agent is a metal octaborate material.
12. The treating fluid composition of claim 11, wherein the metal
octaborate is disodium octaborate tetrahydrate.
13. The treating fluid composition of claim 1, wherein the
low-aromatic content hydrocarbon fluid has less than about 0.5%
aromatics.
14. The treating fluid composition of claim 1, wherein the
low-aromatic content hydrocarbon fluid is a hydrotreated light
petroleum distillate with a CCS kinematic viscosity of less than
about 2 cSt at 40.degree. F.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Non-Provisional
patent application Ser. No. 13/938,220, filed Jul. 9, 2013 (now
U.S. Pat. No. 9,816,025), which is a non-provisional of U.S.
Provisional Patent Application Ser. No. 61/669,282, filed Jul. 9,
2012. Priority is claimed to these applications, and they are
incorporated herein by reference in their entireties.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO APPENDIX
[0003] Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0004] The inventions disclosed and taught herein relate generally
to well treatment fluid compositions and methods, and more
specifically are related to compositions, systems and methods for
controlling crosslinking reaction times in subterranean well
treatment fluids.
2. Description of the Related Art
[0005] Concentrated suspensions of borate-containing crosslinking
agents for preparing crosslinked fracturing fluids have been
exemplified in the patent literature, including U.S. Pat. No.
4,619,776, U.S. Pat. No. 5,488,083, U.S. Pat. No. 5,565,513, U.S.
Pat. No. 6,225,264, and U.S. Pat. No. 6,251,838.
[0006] U.S. Pat. No. 6,936,575, U.S. Pat. No. 7,018,956, and U.S.
Patent Publication No. 2010/0048429 A1 describe the use of
sparingly-soluble borates, such as alkaline earth metal borates, or
alkali metal alkaline earth metal borates, which are suspended in
aqueous-based solutions to control crosslinking times in organic
polymer-containing fracturing fluids.
[0007] However, in the aforementioned patent documents, which
generally focus on the use of a single, borate-ion containing
mineral incorporated in hydrocarbon-based suspensions, crosslinking
times greater than about 12 minutes are generated, and often cannot
be accelerated beyond a certain point utilizing any of the yet
disclosed technology or techniques. In view of this, there is a
need for compositions, systems, and methods for providing more
precise control of delays over the crosslinking reaction of
borate-containing treatment fluids, particularly aqueous-based
subterranean formation treatment fluids, such as fracturing
fluids.
[0008] The inventions disclosed and taught herein are directed to
improved compositions, methods, and associated systems for the
controlled crosslinking of well servicing fluids.
BRIEF SUMMARY OF THE INVENTION
[0009] The present disclosure relates to methods and compositions
for use in subterranean operations. More particularly, in certain
embodiments, the present disclosure relates to methods and
compositions related to methods of increasing the viscosity or
accelerating the crosslink time of a subterranean treatment fluid
with a boron-containing composition that contains both un-refined
and refined borates, the two types of borate materials being
unequivalent.
[0010] In accordance with embodiments of the present disclosure, a
method of controlling the crosslinking reaction and enhancing the
viscosity of an aqueous fracturing fluid for fracturing a
subterranean formation is described, the method comprising blending
an aqueous fluid and a hydratable polymer that is capable of
gelling in the presence of borate ions together for a period of
time sufficient to form a base fluid; aging the base fluid for a
period of time sufficient to render the polymer molecules in the
base fluid to be at least partially hydrated; admixing an alkaline
buffer in an amount sufficient to adjust the pH of the hydrated
base fluid to a pH in the range from about pH 8 to about pH 12;
combining a primary crosslinking agent capable of furnishing borate
ions and a secondary crosslinking agent capable of furnishing
borate ions in a suspension fluid so as to generate a crosslinking
suspension; and adding the crosslinking suspension to the hydrated
base fluid to crosslink the hydrated base fluid.
[0011] In accordance with further embodiments of the present
disclosure, a composition is described, the composition comprising
a fracturing fluid comprising a base fluid and a boron-containing
crosslinking suspension, wherein the base fluid comprises an
aqueous fluid, and an organic polymer that is capable of being
crosslinked and having solubility in the aqueous fluid; and wherein
the boron-containing crosslinking suspension comprises a suspension
fluid; a primary crosslinking agent; and a secondary crosslinking
agent.
[0012] In yet another embodiment of the present disclosure, a
composition is described, the composition comprising a first
liquid; an organic polymer that is capable of being crosslinked and
having a solubility in the first liquid; and a borate crosslinking
suspension composition comprising a second liquid; a primary
crosslinking agent; and a secondary crosslinking agent. In
accordance with aspects of this embodiment, the first fluid is
unequivalent to the second liquid, and is an aqueous fluid which
comprises substantially any aqueous fluid that does not adversely
react with the constituents of the composition, subterranean
formations, or fluids present therein. In accordance with this
aspect, the aqueous fluid is selected from the group consisting of
fresh water, natural brines, and artificial brines, wherein the
artificial brines are selected from the group consisting of
potassium halide solutions, sodium halide solutions, and cesium
halide solutions. In further accordance with aspects of this
embodiment, the organic polymer that is capable of being
crosslinked is selected from the group consisting of guar or guar
derivatives, galactomannan gum, cellulose, hydroxyethylcellulose,
hydroxypropyl cellulose, carboxymethylcellulose,
carboxymethylhydroxyethyl cellulose, xanthan gum, diutan,
scleroglucan, carrageenan, polyacrylamide, and polyacrylate. In
further accordance with aspects of this embodiment, the second
liquid comprises a low-aromatic content hydrocarbon fluid, such as
a hydrotreated light petroleum distillate.
[0013] An a further embodiment of the present disclosure, a
treating fluid composition is described, the treating fluid
comprising a polymer solution and a borate crosslinking
composition, wherein the polymer solution comprises an aqueous
fluid; a crosslinkable organic polymer having a solubility in the
aqueous fluid; a viscosifier; and an alkaline buffer. The borate
crosslinking composition, comprises a low-aromatic content
hydrocarbon fluid; an un-refined borate crosslinking agent; and a
refined borate crosslinking agent, wherein the treating fluid
composition has a pH of greater than pH 8. In accordance with
aspects of this embodiment, the refined borate crosslinking agent
is not the same as the unrefined borate crosslinking agent.
[0014] In accordance with still further embodiments of the present
disclosure, a method for formulating a boron-containing fracturing
fluid having a pH greater than about 8 is described, the method
comprising the steps of placing an aqueous fluid into a suitable
mixing device; adding or contacting the aqueous fluid with a
natural hydratable polymer to the mixture in an amount ranging from
about 10 lb/1,000 gal to about 100 lb/1,000 gal of the aqueous
fluid; mixing the mixture for a first predetermined period of time;
adding or contacting the mixture with an alkaline buffer to the
mixture in an amount sufficient to raise the pH of the mixture to a
pH greater than about pH 8; mixing the mixture for a second
predetermined period of time; adding to the mixture a
boron-containing crosslinking suspension containing an un-refined
borate crosslinking agent and a refined borate crosslinking agent
in a solution, suspension, or slurry comprising at least one
low-aromatic content hydrocarbon fluid; and, mixing the admixture
until gelation occurs, thereby producing the fracturing fluid. In
accordance with aspects of this embodiment, the aqueous fluid
comprises substantially any aqueous fluid that does not adversely
react with the constituents of the composition, subterranean
formations, or fluids present therein. In accordance with this
aspect, the aqueous fluid is selected from the group consisting of
fresh water, natural brines, and artificial brines.
[0015] In accordance with further embodiments of the present
disclosure, methods of hydraulically fracturing a subterranean
formation penetrated by a borehole are described, the methods
comprising the steps of preparing an aqueous based borate
crosslinked guar fracturing fluid having a pH from about 8 to about
12, comprising: a polymer solution comprising: an aqueous fluid, a
natural, hydratable polymer, and an alkaline buffer; and a
boron-containing crosslinking suspension containing an un-refined
borate crosslinking agent and a refined borate crosslinking agent
in a low-aromatic, low-viscosity hydrocarbon fluid; pumping the
fracturing fluid into the subterranean formation zone via the well
bore; and permitting the fracturing fluid to gel after having
substantially traversed the well bore or after having entered the
subterranean formation, thereby causing hydraulic fracturing of the
subterranean formation. The method may optionally further comprise
the steps of adding proppants to the fracturing fluid, and
utilizing the fracturing fluid to disperse the proppants throughout
the subterranean formation. In further aspects of this embodiment,
the method may further comprise the step of adding a breaker to the
fracturing fluid to permit the removal of the fracturing fluid from
the subterranean formation.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0016] The following figures form part of the present specification
and are included to further demonstrate certain aspects of the
present invention. The invention may be better understood by
reference to one or more of these figures in combination with the
detailed description of specific embodiments presented herein.
[0017] FIG. 1 illustrates a general production flow chart for the
manufacture of disodium octaborate tetrahydrate (DOT).
[0018] FIG. 2 illustrates the physical characteristics of a milled
borax decahydrate sample after the compaction test of Example
2.
[0019] FIG. 3 illustrates the physical characteristics of a DOT
sample after the compaction test of Example 2.
[0020] FIG. 4 illustrates an exemplary viscosity plot over time of
the test of Example 3.
[0021] FIG. 5 illustrates a viscosity plot over time of various
guar compositions at 100 sec.sup.-1 and 200.degree. F.
[0022] FIG. 6 illustrates an exemplary viscosity plot over time of
the test of Example 6.
[0023] While the inventions disclosed herein are susceptible to
various modifications and alternative forms, only a few specific
embodiments have been shown by way of example in the drawings and
are described in detail below. The figures and detailed
descriptions of these specific embodiments are not intended to
limit the breadth or scope of the inventive concepts or the
appended claims in any manner. Rather, the figures and detailed
written descriptions are provided to illustrate the inventive
concepts to a person of ordinary skill in the art and to enable
such person to make and use the inventive concepts.
Definitions
[0024] The following definitions are provided in order to aid those
skilled in the art in understanding the detailed description of the
present invention.
[0025] The term "alkali metal", as used herein, refers to the
series of elements comprising Group 1 of the Periodic Table of the
Elements.
[0026] The term "alkaline earth metal", as used herein, refers to
the series of elements comprising Group 2 of the Periodic Table of
the Elements, wherein Group 1 and Group 2 are the Periodic Table
classifications according to the International Union of Pure and
Applied Chemistry, (2002).
[0027] The term "aged" or "aging", as used herein, refers to an
additional period of time that a solution of polymers as described
herein stands, the time being sufficient for the polymer molecules
to open and extend (also referred to as "activation"), thereby
exposing ionic sites of the polymer molecules to the water.
[0028] The term "dry powder", as used herein, includes any
composition which is dry and flowable such as, for example,
granules, flakes, spheroids, and other forms which can be readily
prepared and when added to an appropriate liquid and mixed give the
desired liquid solution or suspension.
[0029] The term "hydrotreated" or "hydrotreating", as used herein,
refers to a catalytic process, usually carried out in the presence
of free hydrogen, in which the primary purpose is the removal of
various metal contaminants, such as arsenic, aluminum, and cobalt;
heteroatoms, such as sulfur and nitrogen; oxygenates; or aromatics
from a hydrocarbon feed stock.
[0030] Kinematic viscosity, or "KV" as used herein, refers to the
measurement of the resistance to flow of a fluid under gravity.
Many lubricating base oils, finished lubricants and compositions
made from them, and the correct operation of equipment depends upon
the appropriate viscosity of the fluid being used. Kinematic
viscosity is determined by ASTM D 445-01. The results are reported
in centistokes (cSt), at the temperature indicated (e.g.,
40.degree. C. or 100.degree. C.), for example as K.sub.V40 for a
kinematic viscosity at 40.degree. C. The kinematic viscosities of
the low-viscosity base oils of this invention are between about 1
cSt and about 20 cSt, preferably between about 1.5 cSt and about 12
cSt, including values and ranges within these ranges, such as
between about 1.5 cSt and about 6 cSt.
[0031] As used herein, the terms "low aromatic content" or "low
aromatic base oil" means that the oil contains less than about 10%
aromatics; that is, that this component of the fluid will have an
aromatic content in volume percent of less than about 10%, and
preferably less than about 5%.
[0032] The term "suspension" as used herein indicates a mixture in
which a liquid medium contains dispersed small particles of solid
material that are substantially not solubilized (insoluble) in the
liquid medium. The mixture typically contains a substantially
uniform distribution of solute and particulate matter throughout
the liquid medium, or carrier.
[0033] The term "solution" as used herein indicates a uniform
mixture of at the molecular or ionic level of one or more solutes
in a liquid solvent.
[0034] As used herein, the term "oil-in-water emulsion" is used as
a generic term for a mixture of two substantially immiscible phases
wherein an oil (dispersed phase) is dispersed in an aqueous
solution (the continuous phase).
[0035] As used herein, the term "emulsion" means a two-phase system
consisting of two completely immiscible liquids, one being
dispersed as fine globules in the other including colloidal
dispersions of a third dissimilar solid such as wax. As used
herein, the term "inverse emulsion" means a water-in-oil emulsion
where water is the discontinuous phase and the hydrocarbon is in
actual contact with the work surface. In select embodiments,
inversion is achieved by the slow addition of water to the emulsion
during the cool down phase of manufacture. As the water
concentration is increased, the emulsion slowly becomes more
viscous and finally reaches the inversion point, which is
accompanied by rapid thinning of the system. Additional water may
be added to adjust the viscosity. Inverted emulsion techniques
provide for higher stability by promoting finer particle size and
distribution.
[0036] As used herein, the term "un-refined borate" refers to
borates that are exposed to one or more mechanical actions,
including crushing, soaking, washing, sizing, and/or micronizing,
but does not include any chemical refinement or processing
steps.
[0037] The term "refined borate(s)" as used herein refers to
borates that have been subjected to one or more chemical and
mechanical processing steps, including crushing, dissolving,
settling, crystallizing, filtering, and drying.
[0038] The terms "borate", and "boron-containing material", are
used interchangeably herein, and refer to salts or esters of boric
acid, including boron-containing minerals (those minerals that
contain a borate anion group, BO.sub.3.sup.-, and borate units that
are polymerized, resulting in B.sub.2O.sub.4, B.sub.2O.sub.5,
B.sub.3O.sub.6, as well as other, anions) and materials, and their
salts.
[0039] The term "well treatment fluid" or "well treating fluid", as
used herein, refers to drilling, stimulation, completion, and
workover fluids for use in hydrocarbon recovery operations from
subterranean formations. Such fluids specifically include, but are
not restricted to, hydraulic fracturing fluids.
DETAILED DESCRIPTION
[0040] The Figures described above and the written description of
specific structures and functions below are not presented to limit
the scope of what Applicants have invented or the scope of the
appended claims. Rather, the Figures and written description are
provided to teach any person skilled in the art to make and use the
inventions for which patent protection is sought. Those skilled in
the art will appreciate that not all features of a commercial
embodiment of the inventions are described or shown for the sake of
clarity and understanding. Persons of skill in this art will also
appreciate that the development of an actual commercial embodiment
incorporating aspects of the present inventions will require
numerous implementation-specific decisions to achieve the
developer's ultimate goal for the commercial embodiment. Such
implementation-specific decisions may include, and likely are not
limited to, compliance with system-related, business-related,
government-related and other constraints, which may vary by
specific implementation, location and from time to time. While a
developer's efforts might be complex and time-consuming in an
absolute sense, such efforts would be, nevertheless, a routine
undertaking for those of skill in this art having benefit of this
disclosure. It must be understood that the inventions disclosed and
taught herein are susceptible to numerous and various modifications
and alternative forms. Lastly, the use of a singular term, such as,
but not limited to, "a," is not intended as limiting of the number
of items. Also, the use of relational terms, such as, but not
limited to, "top," "bottom," "left," "right," "upper," "lower,"
"down," "up," "side," and the like are used in the written
description for clarity in specific reference to the Figures and
are not intended to limit the scope of the invention or the
appended claims.
[0041] Applicants have created compositions for use in the
controlled crosslinking of well servicing or treatment fluids that
include a crosslinkable organic polymer, wherein the compositions
include a primary crosslinking agent that is capable of increasing
the viscosity of the treating fluid by crosslinking the organic
polymer, and a secondary crosslinking agent/modifier that can
accelerate the crosslinking time generated by the primary
crosslinking agent. The combination of boron-containing
crosslinking agents is used in crosslinking a hydratable or
crosslinkable organic polymer for forming a crosslinked, gelled
fluid.
[0042] The treating fluids described herein are an admixture of a
first fluid formed from an aqueous fluid and one or more
water-soluble (or at least partially soluble) organic polymers, and
a second fluid containing a first and second boron-containing
crosslinking agents in a low-viscosity and/or low-aromatic content
base oil. The first and second boron-containing crosslinking
agents, equivalently referred to herein as the primary and second
crosslinking agents, are un-refined and refined borates,
respectively, and in select aspects are not equivalent borate
compounds. Preferably, the primary and secondary (un-refined and
refined) borates are present in the second fluid in a ratio (in
weight percent, wt. %) ranging from about 30:0.1 to about 50:20,
inclusive, including ranges from about 40:0.1 to about 45:10, and
from about 40:0.1 to about 50:5.
[0043] The typical crosslinkable or hydratable organic polymers,
sometimes referred to equivalently herein as "gelling agents" or
"solvatable polymers", that may be included in the treatment fluids
and systems described herein, particularly aqueous fluids and
systems, and that may be used in connection with the presently
disclosed inventions, typically comprise biopolymers, synthetic
polymers, or a combination thereof, wherein the `gelling agents` or
crosslinkable organic polymers are at least slightly soluble in
water (wherein slightly soluble means having a solubility of at
least about 0.01 kg/m.sup.3) and may be considered to be hydratable
(hydratable polymers). Without limitation, these crosslinkable
organic polymers may serve to increase the viscosity of the
treatment fluid during application. A variety of gelling agents can
be used in conjunction with the methods and compositions of the
present inventions, including, but not limited to, hydratable
polymers that contain one or more functional groups such as
hydroxyl, cis-hydroxyl, carboxylic acids, derivatives of carboxylic
acids, sulfate, sulfonate, phosphate, phosphonate, amino, or amide.
The gelling agents may also be biopolymers comprising natural,
modified and derivatized polysaccharides, and derivatives thereof
that contain one or more of the monosaccharide units selected from
the group consisting of galactose, mannose, glucoside, glucose,
xylose, arabinose, fructose, glucuronic acid, or pyranosyl
sulfate.
[0044] Suitable gelling agents, or crosslinkable organic polymers,
which may be used in accordance with the present disclosure
include, but are not limited to, guar, guar derivatives (such as
carboxyalkyl guar or hydroxyalkylated guar), hydroxypropyl guar
(HPG), carboxymethyl guar (CMG), hydroxyethyl guar (HEC),
hydroxybutyl guar (HBG), cellulose, carboxymethyl cellulose (CMC),
carboxymethyl hydroxyethyl cellulose (CMHEC), hydroxyethylcellulose
(HEC), carboxymethylhydroxypropyl guar (CMHPG), other derivatives
of guar gum, xanthan, galactomannan gums and gums comprising
galactomannans, cellulose, and other cellulose derivatives,
derivatives thereof, and combinations thereof, such as various
carboxyalkylcellulose ethers, such as carboxyethylcellulose; mixed
ethers such as carboxyalkylethers; hydroxyalkylcelluloses such as
hydroxypropylcellulose; alkylhydroxyalkylcelluloses such as
methylhydroxypropylcellulose; alkylcelluloses such as
methylcellulose, ethylcellulose and propylcellulose;
alkylcarboxyalkylcelluloses such as ethylcarboxymethylcellulose;
alkylalkylcelluloses such as methylethylcellulose;
hydroxyalkylalkylcelluloses such as hydroxypropylmethylcellulose;
biopolymers such as xanthan, diutan, and scleroglucan; combinations
thereof, and the like. Preferably, in accordance with one
non-limiting embodiment of the present disclosure, the gelling
agent is guar, hydroxypropyl guar (HPG), or
carboxymethylhydroxypropyl guar (CMHPG), alone or in
combination.
[0045] It is sometimes preferred that the hydratable organic
polymer, such as guar or hydroxyalkylated guar, has a molecular
weight ranging from about 1 million to about 3 million. The
carboxyl content of the hydratable polysaccharides is typically
expressed as the `Degree of Substitution` (DS), and the DS of the
carboxylated guar is typically in the range of from about 0.08 to
about 0.18. The hydroxypropyl content of the hydroxyalkylated guar,
expressed as Molar Substitution (defined as the number of moles of
hydroxyalkyl groups per mole of anhydroglucose), is typically in
the range of from about 0.25 to about 0.6. Further preferred as the
hydratable organic polymer in certain aspects of the invention
include those polymers available from a number of commercial
sources (e.g., Baker Hughes) as GW-3 (highly refined guar gum),
GW-4 (guar), GW-2 (guar), "GW45" (CMG), "GW32" (HPG) and "GW38"
(CMHPG). Slurried counterparts of these hydratable organic polymers
may also be used and are available from a variety of commercial
sources, under a variety of names, such as "GLFC-5" (a high-yield
guar gum, GW-3 slurried in mineral oil), "GLFC2" (HPG), "GLFC2B"
(HPG), "GLFC3" (CMPHG), "GLFC3B" (CMHPG), "XLFC2" (HPG), "XLFC2B"
(HPG), "XLFC3" (CMPHG), "XLFC3B" (CMHPG), "VSP1" (CMG), and "VSP2"
(CMG).
[0046] Non-limiting examples of suitable synthetic polymers include
acrylamide polymers, vinyl sulfonates, and the like. An acrylamide
polymer maybe a polymer or copolymer of acrylamide useful as, e.g.,
a friction reducing agent for slickwater fracturing treatments.
Even though these acrylamide polymers are often called
"polyacrylamide", many are actually copolymers of acrylamide and
one or more other chemical species. The main consequence is to give
the "modified" polyacrylamide some ionic character. The
polyacrylamide may also be used as a homopolymer. As used herein,
the expression "polyacrylamide" is meant to encompass acrylamide
homopolymers and copolymers, or any suitable synthetic form of
polyacrylamide. As used herein, "homopolymers" are those polymers
containing less than about 0.1% by weight of other co-monomers.
Combinations or mixtures of homopolymers and copolymers may be used
as well. The copolymers may include two or more different
co-monomers and may be random or block copolymers. The co-monomers
may include, for example, sodium acrylate. The polyacrylamide
polymers and copolymers useful for the invention may include those
having a number-average molecular weight (M.sub.n) or a
weight-average molecular weight (M.sub.w) of from about 1000, or
lower, to about 20 million, or above, with from about 1 million to
about 5 million being typical. Typically, the amount of hydratable
polymer, or gelling agent, employed can vary widely, but can be
preferably in the range of about 15 to about 50, or about 20 to
about 30, pounds per 1,000 gallons of aqueous liquid medium (e.g.,
water) in the fluid. In at least some aspects of the present
disclosure, the amount of liquid medium is preferably minimized to
employ the least amount possible while still achieving the desired
level of polymer hydration.
[0047] Additional natural polymers suitable for use as
crosslinkable organic polymers/gelling agents in accordance with
the present disclosure include, but are not limited to, locust bean
gum, tara (Cesalpinia spinosa lin) gum, konjac (Amorphophallus
konjac) gum, starch, cellulose, karaya gum, xanthan gum, tragacanth
gum, arabic gum, ghatti gum, tamarind gum, carrageenan and
derivatives thereof. Additionally, synthetic polymers and
copolymers that contain any of the above-mentioned functional
groups may also be used. Non-limiting examples of such synthetic
polymers include, but are not limited to, polyacrylate,
polymethacrylate (also known as PMMA, poly(methyl methacrylate)),
polyacrylamide (poly(2-prop-enamide)), polyvinyl alcohol (PVA),
styrene maleic anhydride (SMA), methylvinyl ether copolymers, and
polyvinylpyrrolidone (PVP).
[0048] Generally speaking, the amount of a hydratable,
crosslinkable organic polymer that may be included in a treatment
fluid for use in conjunction with the present disclosure depends on
the viscosity of the resultant treatment fluid desired. Thus, the
amount to include will be an amount effective to achieve a desired
viscosity effect. In certain exemplary embodiments of the present
inventions, the gelling agent may be present in the treatment fluid
in an amount in the range of from about 0.1% to about 60% by weight
of the treatment fluid. In other exemplary embodiments, the gelling
agent may be present in the range of from about 0.1% to about 20%
by weight of the treatment fluid. In general, however, the amount
of crosslinkable organic polymer included in the well treatment
fluids described herein is not particularly critical so long as the
viscosity of the fluid is sufficiently high to keep the proppant
particles or other additives suspended therein during the fluid
injecting step into the subterranean formation. Thus, depending on
the specific application of the treatment fluid, the crosslinkable
organic polymer may be added to the aqueous base fluid in
concentrations ranging from about 15 to 60 pounds per thousand
gallons (lb/1,000 gal.; "pptg") by volume of the total aqueous
fluid (1.8 to 7.2 kg/m.sup.3). In a further non-limiting range for
the present inventions, the concentration may range from about 20
lb/1,000 gal. (2.4 kg/m.sup.3) to about 40 lb/1,000 gal. (4.8
kg/m.sup.3). In further, non-restrictive aspects of the present
disclosure, the crosslinkable organic polymer/gelling agent present
in the aqueous base fluid may range from about 25 lb/1,000 gal.
(about 3 kg/m.sup.3) to about 40 lb/1,000 gal. (about 4.8
kg/m.sup.3) of total fluid. One skilled in the art, with the
benefit of this disclosure, will recognize the appropriate gelling
agent and amount of the gelling agent to use for a particular
application. Preferably, in accordance with one aspect of the
present disclosure, the fluid composition or well treatment system
will contain from about 1.2 kg/m.sup.3 (0.075 lb/ft.sup.3) to about
12 kg/m.sup.3 (0.75 lb/ft.sup.3) of the gelling agent/crosslinkable
organic polymer, most preferably from about 2.4 kg/m.sup.3 (0.15
lb/ft.sup.3) to about 7.2 kg/m.sup.3 (0.45 lb/ft.sup.3).
[0049] The base fluid of the well treatment fluids, particularly in
the first aqueous solution that includes a crosslinkable organic
polymer, that may be used in conjunction with the compositions and
methods of these inventions preferably comprise an aqueous-based
fluid, although they may optionally also further comprise an
oil-based fluid, or an emulsion as appropriate. The aqueous
(water)-based fluid may be from any source provided that it does
not contain compounds that may adversely affect other components in
the treatment fluid. The base fluid may comprise a fluid from a
natural or synthetic source. In certain exemplary embodiments of
the present inventions, an aqueous-based fluid may comprise fresh
water or salt water depending upon the particular density of the
composition required. The term "salt water" as used herein may
include unsaturated salt water or saturated salt water "brine
systems", such as a NaCl, or KCl brine, as well as heavy brines
including CaCl.sub.2, CaBr.sub.2, NaBr, KBr, ZnBr.sub.2, ZnCl2,
ZnBr.sub.2/CaBr.sub.2, ZnBr.sub.2/KBr, sodium formate
(NaCO.sub.2H), cesium formate (CsCO.sub.2H), and potassium formate
(KCO.sub.2H). The brine systems suitable for use herein may
comprise from about 1% to about 75% by weight of an appropriate
salt, including about 3 wt. %, about 5 wt. %, about 10 wt. %, about
15 wt. %, about 20 wt. %, about 25 wt. %, about 30 wt. %, about 35
wt. %, about 40 wt. %, about 45 wt. %, about 50 wt. %, about 55 wt.
%, about 60 wt. %, about 65 wt. %, about 70 wt. %, and about 75 wt.
% salt, without limitation, as well as concentrations falling
between any two of these values, such as from about 21 wt. % to
about 66 wt. % salt, inclusive. Generally speaking, the base fluid
will be present in the well treatment fluid in an amount in the
range of from about 2% to about 99.5% by weight. In other exemplary
embodiments, the base fluid may be present in the well treatment
fluid in an amount in the range of from about 70% to about 99% by
weight. Depending upon the desired viscosity of the treatment
fluid, more or less of the base fluid may be included, as
appropriate. One of ordinary skill in the art, with the benefit of
this disclosure, will recognize an appropriate base fluid and the
appropriate amount to use for a chosen application.
[0050] In accordance with exemplary methods of the present
disclosure, an aqueous fracturing fluid, as a non-limiting example,
is first prepared by blending one or more crosslinkable organic
polymers into a liquid, which may be a hydrocarbon, such as light
distillate, or water, or an aqueous base fluid, depending on the
particular subterranean well being treated. The aqueous base fluid
may be, for example, water, brine (e.g., a NaCl or KCl brine),
aqueous-based foams or water-alcohol mixtures. The brine base fluid
may be any brine, conventional or to be developed which serves as a
suitable media for the various components. As a matter of
convenience, in many cases the brine base fluid may be the brine
available at the site used in the completion fluid, for a
non-limiting example.
[0051] Any suitable mixing apparatus may be used for this
procedure. In the case of batch mixing, the crosslinkable organic
polymer, such as guar or a guar derivative, and the aqueous fluid
are blended for a period of time sufficient to form a gelled or
viscosified solution. The organic polymer that is useful in the
present inventions is preferably any of the hydratable or
solvatable polysaccharides, as described herein above, and in
particular those hydratable polysaccharides which are capable of
gelling in the presence of a crosslinking agent to form a gelled
base fluid. The most preferred hydratable polymers for the present
inventions are guar gums, carboxymethyl hydroxypropyl guar and
hydroxypropyl guar, as well as combinations thereof. In other
embodiments of the present disclosure, the crosslinkable organic
polymer, or gelling agent, may be depolymerized, as necessary. The
term "depolymerized," as used herein, generally refers to a
decrease in the molecular weight of the gelling agent.
Depolymerized polymers are described in U.S. Pat. No. 6,488,091,
the relevant disclosure of which is incorporated herein by
reference as appropriate.
[0052] In addition to the aqueous base fluid and
hydratable/crosslinkable organic polymer, the treatment fluid of
the present disclosure comprises a crosslinking composition, which
is used to crosslink the hydratable organic polymer and create a
crosslinked, viscosified and gelled treatment fluid. In accordance
with the instant disclosure, the crosslinking composition comprises
a primary boron-containing material, which is an un-refined borate
crosslinking agent, and a secondary boron-containing material,
which is a refined borate crosslinking agent, wherein the secondary
material, which is a refined borate crosslinking agent, is not the
same as the primary boron-containing agent.
[0053] The distinction between the primary and secondary
boron-containing materials for use in the current compositions and
methods is linked to the type of processing that the borate
material has undergone prior to use in these compositions. As
indicated above, such processing can yield a product that is termed
"refined" or "un-refined." The processing for each of the
commercially available un-refined borate minerals is a
comparatively simple procedure, involving largely coarse,
mechanical operations. The desire for good purity, low costs, high
recovery and efficiency has led to often complex operational
variations involving both chemical and mechanical operations so as
to produce highly beneficiated, refined borates. The general
processing technology for un-refined (alkaline earth metal borates
and/or alkali metal alkaline earth metal borates) and refined
borates (borax, boric acid, or disodium octaborate tetrahydrate) is
discussed in detail below.
[0054] A. Un-Refined Borates.
[0055] Un-refined borates are those borates that are exposed to one
(or more) of the following mechanical actions, and that do not
include any chemical refinement in their processing, prior to use.
Typical processes that are included in the processing of un-refined
borates include crushing operations, soaking, washing, sizing,
and/or micronizing. During a typical crushing operation, borate ore
from a mine is crushed and resized into rock pieces 8 inches or
less. Following the crushing operation, the rock is delivered to a
water-filled pit and left for 16-24 hours in a soaking process.
Intermittently during the soaking, the material is turned to loosen
clay from the surface of the ore. During the washing process, the
product is then transferred into a rotary drum and is washed with
high pressure water to remove additional clay from the ore. At the
end of the rotary drum is a 25 millimeter screen for separating the
ore in the sizing operation. The larger material goes directly to a
sorting belt and the particles having a size below 25 millimeters
enters a spiral classifier. The ore below 3 millimeters is then
separated and the coarse fraction is returned to the sorting belt
which is transporting the material larger than 25 millimeters. The
product size at this stage ranges from approximately 3 millimeters
to 150 millimeters. Finally, the product enters the micronizing
stage, wherein the sized borate ore is crushed and hammer milled to
a particle size less than 2,800 microns. These particles are then
processed through a rotary dryer to a moisture level of less than
7%, milled, and air classified to a particle size ranging from
about 0.15 microns to about 120 microns.
[0056] B. Refined Borates.
[0057] Refined borates generally include those borates that are
exposed to both chemical and mechanical steps prior to use. Typical
processes that are included in the processing of refined borates
include crushing, dissolving, settling, crystallizing, filtering,
and drying. In the crushing step of the process, borate ore from
the mine is crushed before refining. Crushers reduce the ore to
approximately one-inch pieces, increasing the surface area of the
ore, which makes the refining process more efficient. In the
subsequent dissolving step, the crushed ore is mixed with hot water
to create a "liquor" which is a combination of borates and water.
The borates dissolve in the hot water, while screens remove
insoluble material such as rocks, sand and other solids, thus
forming a saturated borate solution. Additionally, the hot water
solution can optionally be reacted with sulfuric acid if boric acid
is to be manufactured. In the settling process step, the saturated
borate solution is pumped into large settling tanks called
thickeners. As the rock and clay mixture is heavier, it settles in
the bottom of the thickener, leaving borates dissolved in the
liquor. A crystallizing step is next. The liquor is transported to
tanks called crystallizers, where the solution slowly cools. The
cooling forces the borates to crystallize and come out of solution,
forming a slurry of borate crystals and water. The slurry is poured
over special filters and washed to ensure purity in the filter
process step. Water from the filtering process is typically drawn
away by a vacuum located beneath the filters. At the drying step,
the damp borate crystals are removed from the filters and
transported to rotating dryers where hot air is used to finish the
crystal drying process. Typical particle size ranges for the dried,
refined borate are from about 5 microns to about 1,900 microns. The
large particle size of these refined borates is too course to be
suspended in liquid, and they cannot be micronized, due to
compaction issues. The compaction test results detailed herein
(Example 2) demonstrates that some refined borates, such as borax
decahydrate, cannot be milled/air classified to a fine particle
size (0.7 microns-100 microns), packaged, and palletized. Internal
particle moisture exposed after the milling process results in
agglomeration and compaction of particles during storage, rendering
the product unusable in a blended suspension. Boric acid cannot be
sized due to agglomeration of the particles into an unusable hard
mass (FIG. 2) during the milling process.
[0058] C. Borate Crosslinking Systems.
[0059] In accordance with the present disclosure, the viscosifying
well treatment fluids described herein comprise two general
components, a first fluid system comprising the guar- or other
crosslinkable organic polymer in a suitable base fluid, and a
second fluid system, equivalently referred to herein as a borate
crosslinking solution, suspension or emulsion, comprising a primary
crosslinking agent and a secondary crosslinking agent in an
appropriate fluid, particularly a low-aromatic and/or low-viscosity
base oil or hydrocarbon-based fluid, or the equivalent. After (or
during) preparation, the first and second fluid systems are admixed
to generate the well treating compositions of the present
disclosure. Exemplary, non-limiting low-aromatic or low-viscosity
base oils include, without limitation, hydrotreated light petroleum
distillates which are insoluble in water and have boiling points at
or above about 200.degree. C. (about 392.degree. F.), such as those
hydrotreated light petroleum distillates sold under the trade names
LVT.RTM.-200 (Calumet Penreco, LLC, Indianapolis, Ind.), which has
a boiling point above 400.degree. F., or CONOSOL.RTM. C-200
(Penreco, Houston, Tex.), which has a boiling point of
221.1-287.8.degree. C. (430-550.degree. F.).
[0060] In one embodiment, the low aromatic and/or low-viscosity
base fluid for the borate crosslinking solution, suspension, or
emulsion is a mineral or vegetable oil having a kinematic viscosity
(K.sub.V100) from about 3, or about 3.5, or about 4 up to about 15,
or to about 11, or to about 10, or to about 9 centistokes at
100.degree. C. Useful mineral oils include 40, 100, 150, 200 and
300 neutral mineral oils. Nonlimiting examples of specific liquid
hydrocarbons which may be used as the base fluid for the borate
crosslinking solution also include Exxon ESCAID.RTM. 110 (a
petroleum distillate comprising 20% aromatics, 56.6% paraffins and
23.4% naphthenes available commercially from ESSO), Total HDF 200,
Conoco LVT.RTM. oil (a mineral oil with the viscosity of 1.8
centistokes at 40.degree. C., available from Conoco Oil Company),
Conoco LVT.RTM. 200 (a mineral oil with a kinematic viscosity of
2.1 centistokes at 40.degree. C. and less than 0.5% aromatic
content, available from Conoco Oil Company), and Calumet LVT.RTM.
200 (a hydrotreated, light petroleum distillate/base oil fluid with
a kinematic viscosity of about 2.1 cSt at 40.degree. C. and less
than 0.5% aromatic content, available from Calumet Penreco,
LLC).
[0061] Although not necessary the second fluid system compositions
(the borate crosslinking fluid system) may also contain commercial
clays such as bentonite, attapulgite, sepiolite, and the like. In
one embodiment, the compositions may also include an organophilic
clay. Organophilic clays are clays, such as montmorillonite,
hectorite, saponite, attapulgite and illite, that have absorbed
amine salts. These clays may optionally be converted from
water-yielding (e.g., present in the brine phase of the emulsion)
to oil-yielding (e.g., present in the liquid oil phase) clays by
the absorption of amine salts. Organophilic clays are preferably
oil-wettable and are dispersed in the oil phase to produce
viscosity and gel properties. Montmorillonite, bentonite and
attapulgite are preferred, with montmorillonite more preferred.
Water and methanol may optionally be used to activate the
organophilic clay. The organophilic clay, when included, is present
in the second fluid system in an amount from about 1, or about 2 up
to about 16 pounds per barrel (ppb), or to about 10 pounds per
barrel (ppb), or to about 8 ppb. Exemplary, commercially available
organophilic clays suitable for use with the compositions described
herein include CLAYTONE.RTM. IMG 400, available from Southern Clay
Products, Inc., Gonzalez, Tex., U.S.A., or BENTONE.RTM. 38
Organoclay (a commercial hectorite-based product, available form a
number of suppliers).
[0062] While any suitable boron-containing crosslinking agent may
be used as the primary crosslinking agent in the crosslinking
composition, it is particularly preferred in accordance with the
present disclosure that the crosslinking agent is an un-refined
borate. Generally, in accordance with the present disclosure, the
un-refined borate crosslinking agent may be any material that
supplies and/or releases borate ions in solution, and that has been
processed using one or more of the mechanical means discussed
above. Exemplary un-refined borates suitable for use as
crosslinkers in the compositions in accordance with the present
disclosure include, but are not limited to, alkali metal borates,
alkali metal-alkaline earth metal borates, and the alkaline earth
metal borates, as well as other suitable boron containing minerals
and ores that are un-refined. In accordance with certain aspects of
the present disclosure, the concentration of the un-refined borate
crosslinking agent described herein ranges from about from about
0.01 kg/m.sup.3 to about 10 kg/m.sup.3, preferably from about 0.1
kg/m.sup.3 to about 5 kg/m.sup.3, and more preferably from about
0.25 kg/m.sup.3 to about 2.5 kg/m.sup.3 in the well treatment
fluid.
[0063] Boron-containing minerals suitable for use as the primary,
un-refined borate crosslinking agent in accordance with the present
disclosure are those ores that are un-refined and that contain
approximately 5 wt. % or more boron, including both
naturally-occurring and synthetic boron-containing minerals and
ores. Exemplary naturally-occurring, boron-containing minerals and
ores suitable for use herein include but are not limited to
colemanite (Ca.sub.2B.sub.6O.sub.11-5H.sub.2O), frolovite
Ca.sub.2B.sub.4O.sub.8-7H.sub.2O, ginorite
(Ca.sub.2B.sub.14O.sub.23-8H.sub.2O), gowerite
(CaB.sub.6O.sub.10-5H.sub.2O), howlite
(Ca.sub.4B.sub.10O.sub.23Si.sub.2-5H.sub.2O), hydroboracite
(CaMgB.sub.6O.sub.11-6H.sub.2O), inderborite
(CaMgB.sub.6O.sub.11-11H.sub.2O), inderite
(Mg.sub.2B.sub.6O.sub.11-15H.sub.2O), inyoite
(Ca.sub.2B.sub.6O.sub.11-13H.sub.2O), kaliborite (Heintzite)
(KMg.sub.2B.sub.11O.sub.19-9H.sub.2O), kernite (rasorite)
(Na.sub.2B.sub.4O.sub.7-4H.sub.2O), kumakovite
(MgB.sub.3O.sub.3(OH.sub.5-15H.sub.2O), meyerhofferite
(Ca.sub.2B.sub.6O.sub.11-7H.sub.2O), nobleite
(CaB.sub.6O.sub.10-4H.sub.2O), pandermite
(Ca.sub.4B.sub.10O.sub.19-7H.sub.2O), patemoite
(MgB.sub.2O.sub.13-4H.sub.2O), pinnoite
(MgB.sub.2O.sub.4-3H.sub.2O), priceite
(Ca.sub.4B.sub.10O.sub.19-7H.sub.2O), preobrazhenskite
(Mg.sub.3B.sub.10O.sub.18-4.5H.sub.2O), (probertite
NaCaB.sub.5O.sub.9-5H.sub.2O), tertschite
(Ca.sub.4B.sub.10O.sub.19-20H.sub.2O), tincalconite
(Na.sub.2B.sub.4O.sub.7-5H.sub.2O), tunellite
(SrB.sub.6O.sub.10-4H.sub.2O), ulexite
(Na.sub.2Ca.sub.2B.sub.10O.sub.18-16H.sub.2O), and veatchite
Sr.sub.4B.sub.22O.sub.37-7H.sub.2O, as well as any of the Class
V-26 Dana Classification borates, hydrated borates containing
hydroxyl or halogen, as described and referenced in Gaines, R. V.,
et al. [Dana's New Mineralogy, John Wiley & Sons, Inc., NY,
(1997)], or the class V/G, V/H, V/J or V/K borates according to the
Strunz classification system [Hugo Strunz; Ernest Nickel: Strunz
Mineralogical Tables, Ninth Edition, Stuttgart: Schweizerbart,
(2001)]. Any of these may be hydrated and have variable amounts of
water of hydration, including but not limited to tetrahydrates,
hemihydrates, sesquihydrates, and pentahydrates. Further, in
accordance with some aspects of the present disclosure, it is
preferred that the primary, un-refined borates be borates
containing at least 3 boron atoms per molecule, including but not
limited to, triborates, tetraborates, pentaborates, hexaborates,
heptaborates, decaborates, and the like. In accordance with one
aspect of the present disclosure, the preferred primary
crosslinking agent is an un-refined borate selected from the group
consisting of ulexite, colemanite, probertite, and mixtures
thereof.
[0064] Synthetic un-refined borates which may be used as primary
crosslinking agents in accordance with the presently disclosed well
treatment fluids and associated methods include, but are not
limited to, nobleite and gowerite, all of which may be prepared
according to known procedures. However, while synthetic un-refined
borates may be used as the primary crosslinking agents in the
compositions and well treatment fluids described herein,
naturally-occurring un-refined borates are preferred. This is due,
in part, to the fact that although the synthetic compositions have
the potential of being of higher purity than the
naturally-occurring materials since they lack the mineral
impurities found in naturally occurring specimens, they are
generally relatively low in available borate content by
comparison.
[0065] The primary boron-containing crosslinking agent is
preferably present in the crosslinking composition in an amount
ranging from about 10 wt. % to about 60 wt. %, inclusive,
preferably in an amount ranging from about 15 wt. % to about 55 wt.
% (inclusive), and preferably is present in an amount ranging from
about 40 wt. % to about 50 wt. %, inclusive.
[0066] The secondary boron-containing crosslinking agent, in
accordance with the present disclosure, is not equivalent to (with
respect to the boron-content) the primary boron-containing
crosslinking agent, is a refined borate material, and further is
preferably an octaborate alkaline salt. Suitable octaborate
alkaline salts for use as the secondary boron-containing
cross-linking agent include, but are not limited to, dipotassium
calcium octaborate dodecahydrate
(K.sub.2O.CaO.4B.sub.2O.sub.3.12H.sub.2O), potassium strontium
tetraborate decahydrate
(K.sub.2Sr[B.sub.4O.sub.5(OH).sub.4].sub.2.10H.sub.2O(cr)),
rubidium calcium octaborate dodecahydrate
(Rb.sub.2Ca[B.sub.4O.sub.5(OH).sub.4].sub.2.8H.sub.2O), and
disodium octaborate tetrahydrate (DOT)
(Na.sub.2B.sub.8O.sub.13.4H.sub.2O). Preferably, the secondary
boron-containing crosslinking agent is disodium octaborate
tetrahydrate (DOT), such as ETIDOT-67.RTM. or AQUABOR.RTM., both
available from American Borate Company (Virginia Beach, Va.)),
having the molecular formula Na.sub.2B.sub.8O.sub.13-4H.sub.2O and
containing 67.5% (min) B.sub.2O.sub.3 and 15.0% (min)
Na.sub.2O.sub.3.
[0067] The disodium octaborate material, such as disodium
octaborate tetrahydrate (DOT), and similar octaborate materials
suitable for use as the secondary boron-containing crosslinking
agent in the instant compositions, is considered refined due to the
unique production process. As can be seen from FIG. 1, the
production process for refined DOT combines granular boric acid
(H.sub.3BO.sub.3/B.sub.2O.sub.3=56.25%-56.32%) and borax
decahydrate
(Na.sub.2B.sub.4O.sub.7.10H.sub.2O/B.sub.2O.sub.3=36.47%-37.2%) in
water at the ratio of 39.34 wt. % boric acid and 60.66 wt. % borax
decahydrate. The DOT forms through the following, empirical
chemical reaction:
Na.sub.2O.2B.sub.2O.sub.3.10H.sub.2O+4H.sub.3BO.sub.3.fwdarw.Na.sub.2O.4-
B.sub.2O.sub.3.4H.sub.2O+12H.sub.2O
[0068] As shown with continued reference to the general process
scheme of FIG. 1, the process starts with boric acid and borax
decahydrate being fed from feed silos to a solution tank, where
they are admixed together with water. From the initial mixing tank,
the solution is pumped to a middle mixing tank through a horizontal
filter assembly, and then to a final mixing tank. Thereafter, the
concentrated solution of disodium octaborate tetrahydrate (DOT) is
homogenized, filtered, and maintained at a temperature of about
98.degree. C. (208.4.degree. F.). The mixture then passes through a
high-speed atomizer (.about.10,000 rotations per minute) as it
enters a spray dryer, where it is dispersed at very high speed
against pressurized hot air (380.degree. C.; 716.degree. F.). Fine,
dry particles of DOT are formed and subsequently separated in
cyclones, producing a finished product (99.9% minimum purity) with
a particle size ranging from about 1 micron (.quadrature.m) to
about 200 microns with a chemical composition of Na.sub.2O (at
least about 14.7%), B.sub.2O.sub.3 (at least about 67.1%), and
H.sub.2O (18.2%). The inherent fine particle size distribution of
the DOT requires no micronizing, and the simulated compaction test
of Example 2, and the associated FIG. 3, demonstrates the
free-flowing characteristics of this refined borate.
[0069] In accordance with the present disclosure, the secondary,
refined boron-containing crosslinking agent is present in the
crosslinking composition in an amount ranging from about 0.1 wt. %
to about 10.0 wt. %, inclusive, and more preferably in an amount
ranging from about 0.5 wt. % to about 4 wt. %, inclusive. In
accordance with other aspects of the present disclosure, the
primary boron-containing crosslinking agent is present in an amount
(wt. %) relative to the amount (wt. %) of the secondary
boron-containing agent in a ratio of from about 70:0.1 to about
17:1, inclusive.
[0070] Preferably, the primary and secondary (un-refined and
refined) borates are present in the second fluid in a ratio (in
weight percent, wt. %) ranging from about 30:0.1 to about 50:20,
inclusive, including ranges from about 40:0.1 to about 45:10, and
from about 40:0.1 to about 50:5. Additional exemplary ranges
include wt. % ranges of primary-to-secondary borates in the second
fluid from about 40:0.5 to about 45:5, and from about 42:0.1 to
about 44:2.5.
[0071] In yet another embodiment of the present disclosure, fluids
for treating (including fracturing and hydraulic fracturing)
subterranean formations may be prepared using the compositions
described herein. In particular, delayed crosslinking fracturing
fluid systems comprising a borate system prepared in accordance
with the instantly disclosed processes may be prepared, wherein the
fluid or system is prepared by a process comprising the steps of
(a) providing an aqueous mixture of one or more hydrated
galactomannan gums or related compounds, such as guar or
hydroxypropyl guar (HPG); and (b) adding to the aqueous mixture a
cross-linking composition for crosslinking the hydrated
galactomannan gum or related compound at the environmental
conditions of the subterranean formation, wherein the crosslinking
composition comprises a borate system comprising a primary,
un-refined boron-containing mineral or material (such as an
un-refined borate), and a secondary, refined boron-containing
mineral or material (such as a refined borate). The use of the
two-part borate system of the present disclosure provides a
crosslinking composition that exhibits a stabilized crosslink time
as the boron content following the initial crosslink, the stability
in crosslink time being determined by a Vortex Closure Test. Such a
well treating fluid or fluid system may further comprise process
steps of pumping the aqueous mixture of the hydrated galactomannan
gum or equivalent and the (boron-releasing) cross-linking
composition into a subterranean formation through a wellbore at
fracturing pressures, and then crosslinking the hydrated
galactomannan gum or related compound with borate ions released by
the crosslinking composition at the conditions of the subterranean
formation.
[0072] The well treatment fluid systems described herein may also
further include one or more components suitable for modification of
the rheological and/or chemical properties of the fluid. The well
treating fluid or fluid system, particularly if the fluid is a
fracturing fluid, may also typically have incorporated therein a
breaker for the gelled fluid which can be any of the type commonly
employed in the art for borate crosslinked guar based fluids,
including enzymatic breakers as well as soluble (e.g., oxidants
such as ammonium persulfate or peroxide) and limited solubility
breakers.
[0073] In addition, such fluids can also contain other conventional
additives common to the well service industry such as surfactants,
corrosion inhibitors, and the like, as well as proppants. Propping
agents are typically added to the base fluid prior to the addition
of the crosslinking agent, although this is not necessary for
purposes of the present disclosure. Propping agents suitable for
use with fracturing fluids of the present disclosure include, but
are not limited to, quartz sand grains, glass and ceramic beads,
walnut shell fragments and other nut- or seed-based proppants,
aluminum pellets, nylon pellets, and the like, any of which may be
coated or non-coated. The propping agents are normally used in
concentrations between about 1 to 8 pounds per gallon of fracturing
fluid composition but higher or lower concentrations can be used as
required.
[0074] The instant cross-linking compositions further comprise one
or more buffering or pH control additives, such as potassium
carbonate, magnesium carbonate, potassium hydroxide, sodium
hydroxide, sodium phosphate, sodium hydrogen phosphate, boric
acid-sodium hydroxide, citric acid-sodium hydroxide, boric
acid-borax, sodium bicarbonate, ammonium salts, sodium salts,
potassium salts, dibasic phosphate, tribasic phosphate, calcium
oxide, magnesium oxide, zinc oxide, or other similar buffering
agents, in an amount ranging from 0.1 wt. % to about 1 wt. %,
inclusive. The buffering agents, when included, are effective to
provide a pH for the well treating or fracturing fluid system in a
range from about pH 8.0 to about pH 12.0, inclusive, including in a
range from about pH 9.5 to about pH 11.7, and in a pH range from
about pH 9.8 to about pH 11.5, inclusive.
[0075] The compositions may further include one or more clay
viscosifiers, and further optionally clay stabilizers, the latter
of which have a variety of functions, including acting to aid in
the prevention of clay minerals in the reservoir rock expanding on
contact with water and plugging the reservoir, by stabilizing clay
particles in the fluid. Exemplary clay viscosifiers suitable for
use with the compositions of the present disclosure include, but
are not limited to, clays of varying shapes and sizes (such as
minute, plate-like, tube-like, and/or fiber-like particles having a
large surface area), such as clay minerals of the montmorillonite
(smectite) group, including montmorillonite, saponite, nontronite,
hectorite, and sauconite; clay minerals of the kaolin group such as
kaolinite, nacrite, dickite, and halloysite; clay minerals of the
hydrousmica group, such as hydrobiotite, glauconite, illite and
bramallite; clay minerals of the chlorite group, such as chlorite
and chamosite; clay minerals not belonging to the above groups,
such as vermiculite, attapulgite, and sepiolite; and mixed-layer
varieties of such minerals. Exemplary clay stabilizers which may be
used with the compositions of described herein include
chloride-free clay stabilizers, such as amines, neutralized amines,
and quaternary polyamines, as well as mixtures thereof. An
exemplary clay stabilizer is CLAY TREAT-3C.TM., a clay stabilizer
substitute for potassium chloride, available from Baker Hughes,
Inc. (Houston, Tex.).
[0076] The compositions of the present disclosure may further
contain a number of optionally-included additives, as appropriate
or desired, such optional additives including, but not limited to,
suspending agents/anti-settling agents, stabilizers, deflocculants,
breakers, chelators, non-emulsifiers, fluid loss additives,
biocides, weighting agents, wetting agents, lubricants, friction
reducers, pH control agents, oxygen scavengers, surfactants, fines
stabilizers, metal chelators, metal complexors, antioxidants,
polymer stabilizers, freezing point depressants, scale inhibitors,
scale dissolvers, shale stabilizing agents, corrosion inhibitors,
wax inhibitors, wax dissolvers, asphaltene precipitation
inhibitors, waterflow inhibitors, sand consolidation chemicals,
leak-off control agents, permeability modifiers, micro-organisms,
viscoelastic fluids, gases, foaming agents, and combinations
thereof, such that none of the optionally-included additives
adversely react or effect the other constituents of these
inventions.
[0077] Various breaking agents may also be used with the methods
and compositions of the present disclosure in order to reduce or
"break" the gel of the fluid, including but not necessarily limited
to enzymes, oxidizers, polyols, aminocarboxylic acids, and the
like, along with gel breaker aids. One of ordinary skill in the art
will recognize the appropriate type of additive useful for a
particular subterranean treatment operation. Further, all such
optional additives may be included as needed, provided that they do
not disrupt the structure, stability, mechanism of controlled
delay, or subsequent degradability of the crosslinked gels at the
end of their use.
[0078] The compositions may also include one or more alkyl
carbonates, alkyl glutamates, alkyl glycols, alkyl glycol ethers,
alkyl glucosides, alkyl pyrrolidones, alkyl sarcosinates, alkyl
succinates, alkyl sorbitans, as well as sugar alcohols,
monosacchardies, and disaccharides as biodegradable, non-toxic
additives which may serve to stabilize, solubilize (e.g., acting as
a solvent or co-solvent), help delay crosslink, demulsify, and/or
chelate the compositions to which they are added. Examples of
suitable alkyl carbonates include, but are not limited to, ethylene
carbonate, propylene carbonate, glycerine carbonate, diethyl
carbonate, and butylene carbonate, as well as combinations thereof.
Suitable saccharides include, but are not necessarily limited to
glucoses, mannose, galactose, fructose, lactose, and the like, and
suitable sugar alcohols include, but are not necessarily limited to
sorbitol, xylitol, mannitol, and the like, and mixtures thereof.
For example, and without limitation, the composition that comprises
the first and second (unrefined and refined) borate crosslinking
agents may further include one or more such biodegradable
additives, particularly an alkyl carbonate.
[0079] In accordance with some embodiments, the compositions may
further include one or more surfactants selected from the group
consisting of cationic, anionic, zwitterionic, amphoteric,
nonionic, and combinations thereof. Without limitation, suitable
surfactants for use herein include those surfactants described in
U.S. Pat. No. 7,150,322 (Szymanski, et al., issued Dec. 19, 2006),
U.S. Pat. No. 5,566,760 (Harris, issued Oct. 22, 1996), and U.S.
Pat. No. 6,966,379 (Chatterji, et al, issued Nov. 22, 2005), The
surfactant may be a soap-like molecules containing a long
hydrophobic paraffin chain with a hydrophilic end group.
Surfactants include cationic, anionic, nonionic or amphoteric
compounds such as for example, betaines, sulfated or sulfonated
alkoxylates, alkyl quarternary amines, alkoxylated linear alcohols,
alkyl sulfonates, alkyl aryl sulfonates, C.sub.10-C.sub.20
alkyldiphenyl ether sulfonates, and the like, and any combination
thereof. Examples of suitable surfactants include polyethylene
glycols, ethers of alkylated phenol, sodium dodecylsulfate, alpha
olefin sulfonates such as sodium dodecane sulfonate and trimethyl
hexadecyl ammonium bromide. The surfactant may include or consist
of one or more nonionic surfactant. Preferred nonionic surfactants
have a generally low hydrophile-lipophile balance ("HLB") values.
Commercially available nonionic surfactants include, but are not
limited to, ENVIROGEM.TM. AE01, ENVIROGEM.TM. AE02, and
ENVIROGEM.TM. AE03 available from Air Products and Chemicals, Inc.,
of Allentown, Pa., and RHODOCLEAN.TM. HP, available from Rhodia
Inc. of Cranbury, N.J. The surfactant may include a tertiary alkyl
amine ethoxylates. Nonlimiting examples of amphoteric surfactants
that may be used include lauryl amine oxide, a mixture of lauryl
amine oxide and myristylamine oxide, cocoamine oxide, lauryl
betaine, oleyl betaine, cocoamido propyl betaine, or combinations
thereof. Other suitable, exemplary surfactants for use herein
include, without limitation, those surfactants available from
Conlen SurfactantTechnology, Conroe, Tex. (USA). The amount of
surfactant used, when included, can range from about 1 wt. % to
about 5 wt. %, inclusive, including from about 2.0 wt. % to about
3.0 wt. %, inclusive.
[0080] According to a further embodiment, the crosslinking agents
release calcium ion. Calcium in particular can interact with the
viscosifying agent added to increase the crosslinker viscosity by
forming a network. This undesirable effect can be reduced by adding
one or more chelating agents able to complex with the calcium
ion.
[0081] The chelating agent may be a metal, alkali metal, or alkali
earth metal (e.g. calcium) complexing agent such as sodium citrate,
citric acid, malic acid, lactic acid, tartaric acid, phtalic acid,
benzoic acid, ethylenediaminetetraacetic acid (EDTA),
dimethylethylenediaminotetraacetic acid (DMEDTA),
cyclohexyldiaminotetraacetic acid (CDTA) and mixtures thereof. The
chelating agent, when included in a composition, is present in the
solution in an amount between about 0.001% to about 20%) by weight,
or between about 0.01% to about 15% by weight, or between about
0.5%) to about 10%>by weight.
[0082] Other and further embodiments utilizing one or more aspects
of the inventions described above can be devised without departing
from the spirit of the Applicants' inventions. Further, the various
methods and embodiments of the well treatment fluids and
application methods described herein can be included in combination
with each other to produce variations of the disclosed methods and
embodiments. Discussion of singular elements can include plural
elements and vice-versa.
[0083] The following examples are included to demonstrate preferred
embodiments of the invention. It should be appreciated by those of
skill in the art that the techniques disclosed in the examples
which follow represent techniques discovered by the inventor(s) to
function well in the practice of the invention, and thus can be
considered to constitute preferred modes for its practice. However,
those of skill in the art should, in light of the present
disclosure, appreciate that many changes can be made in the
specific embodiments which are disclosed and still obtain a like or
similar result without departing from the scope of the
invention.
EXAMPLES
Example 1: Sample Preparation
[0084] Experiments were performed on a series of compositions to
determine the effect of a mixture of un-refined and refined
borates, as a borate source in a crosslinking composition, on a
fluid viscosified with a crosslinkable polymer. The viscous fluids
were prepared by mixing 250 mL of Houston, Tex. tap water, 2.5 mL
of guar slurry containing 40 lb/1,000 gal of guar (GLFC-5,
available from Baker Hughes, Houston, Tex.), and 0.25 mL (1
gal/1,000 gal) of clay stabilizer for 10 minutes in a Waring
blender. The pH of the solutions were then adjusted to 11.3 with
potassium hydroxide (KOH). The guar mixtures had initial
viscosities at 511 sec.sup.-1 from 38 cP-40 cP at 24.degree. C.
(75.2.degree. F.), as measured on a FANN.RTM. Model 35A viscometer
(available from the FANN Instrument Company, Houston, Tex.).
[0085] General Preparation of Crosslinking Suspensions.
[0086] Base slurries were prepared by combining LVT-200 (available
from Calumet Specialty Partners, L.P., Indianapolis, Ind.) at
concentrations from 49.8%-52.0% by weight, 9.5 g of Claytone
IMG-400 (available from Southern Clay Products, Gonzales, Tex.),
1.0 mL of propylene carbonate, and 4.0 mL of CST-7605D surfactant
(available from Conlen Surfactant Technology, Conroe, Tex.), 175 g
of ulexite (available from American Borate Company, Virginia Beach,
Va.), and 0%-2.5% by weight EDITOT-67.RTM. (disodium octaborate
tetrahydrate), available from American Borate Company, Virginia
Beach, Va. The components were admixed and used in the crosslink
time tests described herein.
[0087] Preparation of TBC-X315 Borate Crosslinking Solution.
[0088] A first crosslinking solution containing a primary
(un-refined) and secondary (refined) borate was prepared as
follows. A mixture of 249.29 mL LVT-200 (Calumet Specialty
Partners, L.P., Indianapolis, Ind.), Claytone IMG 400 (9.5 g,
available from Southern Clay Products, Gonzales, Tex.), propylene
carbonate (1 mL), 4.0 mL of CST-7605 surfactant (Conlen Surfactant
Technology, Conroe, Tex.), 175 g of ulexite (Ulexite-15, available
from American Borate Company, Virginia Beach, Va.), and 2.5 g. of
ETIDOT-67 (disodium octaborate tetrahydrate, DOT, available from
American Borate Company, Virginia Beach, Va.) were admixed and then
used directly in the viscosity tests described herein.
[0089] Preparation of TBC-X318 Borate Crosslinking Solution.
[0090] A second crosslinking solution containing a primary
(un-refined) and secondary (refined) borate was prepared as
follows, generating a solution with a higher ratio of
refined-to-un-refined borate than in the first crosslinking
solution. A mixture of 242.47 mL LVT-200 (Calumet Specialty
Partners, L.P., Indianapolis, Ind.), Claytone IMG 400 (9.5 g,
available from Southern Clay Products, Gonzales, Tex.), propylene
carbonate (1 mL), 4.0 mL of CST-7605 surfactant (Conlen Surfactant
Technology, Conroe, Tex.), 175 g of ulexite (Ulexite-15, available
from American Borate Company, Virginia Beach, Va.), and 10.0 g. of
ETIDOT-67 (disodium octaborate tetrahydrate, DOT, available from
American Borate Company, Virginia Beach, Va.) were admixed and then
used directly in the viscosity tests described herein.
[0091] Details of these exemplary compositions, as well as a blank
containing only an un-refined borate, ulexite, are presented in
Table A, below.
TABLE-US-00001 TABLE A Exemplary Formulations. Formulation Blank
TBC-X315 TBC-X318 Component 350 (mL) 42 gal. 350 (mL) 42 gal. 350
(mL) 42 gal. LVT-200 251.56 mL 30.19 249.29 mL 29.91 242.47 mL
29.10 gal. Claytone IMG 9.5 g 9.5 lb. 9.5 g 9.5 lb. 9.5 g 9.5 lb.
400 Propylene 1.0 mL 0.12 gal. 1.0 mL 0.12 gal. 1.0 mL 0.12 gal.
carbonate CST-7605 (dry) 4.0 mL 0.48 gal. 4.0 mL 0.48 gal. 4.0 mL
0.48 gal. Ulexite 15 175 g 175 lb 175 g 175 lb. 175 g 175 lb
ETIDOT-67 -- -- 2.5 g 2.5 lb. 10.0 g 10 lb. Total Wt..sup.1 9.406
9.419 9.467 % by Wt. of un- 44.30 wt. %:0 44.24:0.64 44.02:2.51
refined to refined borate .sup.1Total weight of barrel.
Example 2: Comparison of Compacting Tendencies
[0092] The compacting tendencies of exemplary refined borates,
borax decahydrate (milled particle size distribution of D10-10
microns, D50-30 microns, D90-63 microns), and disodium octaborate
tetrahydrate (DOT produced particle size distribution of D10-7
microns, D50-27 microns, D90-92 microns), such as described in
Example 1, were compared using the following testing method:
[0093] Seventeen gram samples of borate powder, borax decahydrate,
or DOT, were placed on a filter pad in the chamber of a stainless
steel test cylinder. The powders were compressed by inserting a
metal plunger into the cylinder, placing the cylinder on a Carver
hydraulic press, and applying 1,000 psi of pressure for 5 seconds.
The samples were then removed from the press and the cylinder, and
aged at atmospheric conditions, approximately 25.degree. C.
(77.degree. F.) for a period of 24 hours. Pressure was then applied
(with fingers) to determine the hardness and free-flowing
characteristics of the compacted borate. The results of these tests
are shown in FIG. 2 and FIG. 3. Notably, the borax decahydrate
(FIG. 2) is solidified into a pellet suggesting that this
particular compound would be un-suitable for use in the borate
suspensions of the present invention. The disodium octaborate
tetrahydrate (DOT) product (FIG. 3) exhibits a distinctly different
characteristic, that of a free-flowing powder, making it very
attractive for use in the currently described compositions.
Example 3: Crosslinking Evaluation Procedure
[0094] The degree of cross-linking of several of the
boron-containing compositions prepared as described herein was
determined using standard methods, as described, for example, in
U.S. Pat. No. 7,018,956. In general, to conduct the crosslinking
tests a guar solution was prepared as previously explained, and the
mixing speed of the blender motor was adjusted using a rheostat
(e.g., a Variac voltage controller) to form a vortex in the guar
solution so that the acorn nut (the blender blade bolt) and a small
area of the blade, that surrounds the acorn nut in the bottom of
the blender jar was fully exposed, yet not so high as to entrain
significant amounts of air in the guar solution. While maintaining
mixing at this speed, 0.5 mL (2 gal/1,000 gal) of boron-containing
crosslinking additive was added to the guar solution to effect
crosslinking. Upon addition of the entire boron-containing material
sample to the guar solution, a timer was simultaneously started.
The crosslinking rate is expressed by two different time
recordings: vortex closure (T.sub.1) and static top (T.sub.2).
T.sub.1 is defined herein as the time that has elapsed between the
time that the crosslinking additive is added and the time when the
acorn nut in the blender jar becomes fully covered by fluid.
T.sub.2 is defined as the time that has elapsed between the time
that the crosslinking additive/boron-containing material is added
and the time when the top surface of the fluid in the blended jar
has stopped rolling/moving and becomes substantially static. Those
of ordinary skill in the art of evaluating fracturing fluids will
quickly recognize the fundamental tenants of evaluating such fluids
in the manner described in these Examples, although individual
testing practices and procedures may vary from those described
herein.
[0095] In an initial experiment, a crosslink time comparison for
both un-refined borate and un-refined borate/refined borate
combinations, in hydrocarbon suspensions, were evaluated. The
results of these tests are shown in Table B.1, below.
TABLE-US-00002 TABLE B.1 Crosslink Time Comparison. Crosslink Time,
min:sec Composition (grams) Vortex Closure Change Static Top Change
Un-refined.sup.1 Refined.sup.2 (VC) (%) (ST) (%) 175 0 9:59 --
11:40 -- 185 0 8:45 12.4 10:26 10.6 175 0.5 7:20 26.5 8:36 26.3 175
1.5 6:48 31.9 7:46 33.4 .sup. 200.sup.3 0 6:04 39.2 7:08 38.9 175
2.5 3:22 66.3 4:12 64.0 175 5.0 2:29 75.1 2:56 74.9 175 7.5 2:11
78.1 2:32 78.3 175 10.0 1:14 87.6 1:26 87.7 .sup.1Ulexite, particle
size D.sub.50 of 15 microns. .sup.2Disodium octaborate tetrahydrate
(DOT), particle size D.sub.50 of 27 microns. .sup.3Maximum
concentration allowable to prevent suspension gelation.
[0096] As can be seen from this table, the results of this Example
demonstrate the ability of the compositions described herein to
produce dramatic changes in crosslink times of well treatment
fluids. Table A illustrates that incremental increases of DOT
combined with ulexite will progressively accelerate crosslink
times, and that a composition containing 175 g of ulexite with 10 g
of DOT can vary the crosslink time (as measured by static top test)
about 87.7% from a composition which only contains 175 g of
ulexite.
TABLE-US-00003 Crosslink Time Comparison for Ulexite (un-refined
borate) and a secondary, boron-containing crosslink modifier.
Composition (grams) Crosslink Time, min:sec Un-refined Secondary
Vortex Closure Change Static Top Change borate.sup.1 borate (VC)
(%) (ST) (%) 200 .sup. 0 12:50 -- 14:15 -- 190 10.sup.2 9:02 29.6
7:41 46.1 190 10.sup.3 8:20 35.1 10:02 29.6 190 10.sup.4 4:53 61.9
5:38 60.5 190 10.sup.5 4:31 64.8 5:21 62.5 190 10.sup.6 2:54 77.4
3:29 75.6 .sup.1Ulexite D.sub.50-15 microns, un-dried; IA-35.
.sup.210-molar borax. .sup.3Dried ulexite, D.sub.50 - 15 microns.
.sup.4Disodium octaborate tetrahydrate. .sup.55-molar borax.
.sup.6boric acid.
Example 4: Viscosity Comparison of Refined and Un-Refined Borate
Combinations
[0097] Tests were performed to compare the viscosities generated by
a crosslinking suspension containing un-refined borate (blank), and
crosslinking suspensions formulated with un-refined borate and
various concentrations of refined borate, using the guar mixture
and crosslinking evaluation procedure described in Example 2. The
boron-containing crosslinking additives utilized in the
crosslinking procedure were TBC-X315 and TBC-X318 whose
compositions are described herein. The viscosities of the
crosslinked fluids were conducted on a Grace M5600 rheometer
(available from Grace Instrument Company, Houston, Tex.) for 2
hr:10 min, at a temperature of 110.degree. C. (230.degree. F.), and
400 psi of pressure. The results are shown in Table C, below.
TABLE-US-00004 TABLE C Viscosity Comparison. Viscosity @ 100
sec.sup.-1, cP TBC- Value Blank.sup.2 TBC-X315.sup.3 % Change.sup.1
X318.sup.4 % Change.sup.1 Average 914.7 1,317.5 44.0 1,348.6 47.4
Max./Peak 1,295.9 2,218.4 71.2 1,937.9 49.5 Min. after 687.5 921.4
34.0 1,048.6 52.5 Peak .sup.1Percent change, relative to the blank.
.sup.2The blank contains 175 g. ulexite, having a particle size
D.sub.50 of 15 microns. .sup.3Prepared as per Example 1, containing
175 g. ulexite and 2.5 g. disodium octaborate tetrahydrate (DOT),
having a particle size, D.sub.50 of 27 microns). .sup.4Prepared as
per Example 1, containing 175 g. ulexite and 10 g of disodium
octaborate tetrahydrate (DOT).
[0098] The results of Example 3 illustrate the ability of the
compositions described herein to produce substantial changes in the
viscosity of well treatment fluids. Table B shows that a
composition containing 175 g of ulexite with 2.5 g-10 g of DOT will
increase the average viscosity by 44.0%-47.4%, the maximum/peak
viscosity by 49.5%-71.2%, and the minimum viscosity recorded after
the maximum/peak viscosity by 34.0%-52.5% above the composition
(blank) which contains only 175 g of ulexite. The results of these
comparisons, over a 2 hr:10 min test time, are shown graphically in
FIG. 4.
Example 5. Guar Concentration Comparison
[0099] Tests were conducted to examine the viscosities produced by
a crosslinking suspension containing un-refined and refined borates
with various concentrations of guar. The viscous fluids were
prepared by mixing 250 mL of Houston, Tex. tap water, 0.813
mL-1.563 mL of guar slurry containing 13 lb/1,000 gal-25 lb/1,000
gal of guar (GLFC-5, available from Baker Hughes, Houston, Tex.),
and 0.25 mL (1 gal/1,000 gal) of clay stabilizer for 10 minutes in
a Waring blender. The pH of the solutions were then adjusted to
11.7 with potassium hydroxide (KOH). The guar mixtures had initial
viscosities at 511 sec.sup.-1 from 11 cP-23 cP at 24.degree. C.
(75.2.degree. F.), as measured by a FANN.RTM. Model 35A viscometer
(available from FANN Instrument Company, Houston, Tex.). The
crosslinking evaluation procedure as described in Example 2 was
followed with TBC-X315, at a concentration of 0.75 mL (3 gal/1,000
gal), utilized as the boron-containing crosslinking additive. The
viscosities of the crosslinked fluid were conducted on a Grace
M5600 rheometer (available from Grace Instrument Company, Houston,
Tex.) for 2 hr:10 min, at a temperature of 93.degree. C.
(199.4.degree. F.), and 400 psi of pressure. The results of these
comparisons are shown graphically in FIG. 5.
Example 6: Viscosity Comparison of Un-Refined and Refined Borate
Combinations Using a Reduced Guar Concentration
[0100] A test with a reduced guar concentration (15 lb/1,000 gal)
was performed as described in Example 4 to compare the viscosities
generated by a crosslinking suspension containing un-refined borate
(blank) and TBC-X315 which is formulated with both un-refined and
refined borates, as described in Example 3.
TABLE-US-00005 TABLE D Reduced Guar Concentration Viscosity
Comparison. Viscosity @ 100 sec.sup.-1, cP Value Blank.sup.2
TBC-X315.sup.3 % Change.sup.1 Average 127.2 173.8 36.6 Max./Peak
167.7 209.8 25.1 Min. after Peak 109.4 161.8 47.9 .sup.1Percent
change, relative to the blank. .sup.2The blank contains 175 g
ulexite, particle size D50 of 15 microns. .sup.3Prepared as per
Example 3, containing 175 g ulexite and 2.5 g disodium octaborate
tetrahydrate (DOT), particle size D50 of 27 microns.
[0101] The results of Example 6 demonstrate the ability of the
compositions described herein to produce dramatic changes in the
viscosity of well treatment fluids, even with very low guar
concentrations. Table D shows that a composition containing 175 g
of ulexite with 2.5 g of DOT increases the average viscosity by
36.6%, the maximum/peak viscosity by 25.1%, and the minimum
viscosity recorded after the maximum/peak viscosity by 47.9% above
the composition (blank) which contains only 175 g of ulexite. The
results of these comparisons, over a 2 hr: 10 min test time, are
shown graphically in FIG. 6.
[0102] Other and further embodiments utilizing one or more aspects
of the inventions described above can be devised without departing
from the spirit of Applicant's invention. For example, two or more
different borate materials can be used as primary crosslinking
agents in combination with the secondary crosslinking agent.
Further, the various methods and embodiments of the methods of
treating subterranean formations can be included in combination
with each other to produce variations of the disclosed methods and
embodiments. Discussion of singular elements can include plural
elements and vice-versa.
[0103] The order of steps can occur in a variety of sequences
unless otherwise specifically limited. The various steps described
herein can be combined with other steps, interlineated with the
stated steps, and/or split into multiple steps. Similarly, elements
have been described functionally and can be embodied as separate
components or can be combined into components having multiple
functions.
[0104] The inventions have been described in the context of
preferred and other embodiments and not every embodiment of the
invention has been described. Obvious modifications and alterations
to the described embodiments are available to those of ordinary
skill in the art. The disclosed and undisclosed embodiments are not
intended to limit or restrict the scope or applicability of the
invention conceived of by the Applicants, but rather, in conformity
with the patent laws, Applicants intend to fully protect all such
modifications and improvements that come within the scope or range
of equivalent of the following claims.
* * * * *