U.S. patent application number 11/353913 was filed with the patent office on 2007-08-16 for hydraulic fracturing methods using cross-linking composition comprising delay agent.
Invention is credited to Donald Edward Putzig.
Application Number | 20070187102 11/353913 |
Document ID | / |
Family ID | 38367154 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070187102 |
Kind Code |
A1 |
Putzig; Donald Edward |
August 16, 2007 |
Hydraulic fracturing methods using cross-linking composition
comprising delay agent
Abstract
A method for hydraulically fracturing a subterranean formation
comprises introducing into the formation a cross-linking
composition which comprises (a) an aqueous liquid, (b) a pH buffer,
(c) a cross-linkable organic polymer, (d) a cross-linking agent
which comprises an organic titanate, an organic zirconate, or
combinations thereof, and (e) a delay agent which is a
hydroxyalkylaminocarboxylic acid. The method can be used over a
wide range of pH conditions.
Inventors: |
Putzig; Donald Edward;
(Newark, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
38367154 |
Appl. No.: |
11/353913 |
Filed: |
February 14, 2006 |
Current U.S.
Class: |
166/300 ;
166/308.5; 507/903; 507/924 |
Current CPC
Class: |
C09K 8/685 20130101 |
Class at
Publication: |
166/300 ;
166/308.5; 507/903; 507/924 |
International
Class: |
E21B 43/26 20060101
E21B043/26 |
Claims
1. A method for fracturing a subterranean formation which comprises
introducing into said formation a cross-linking composition at a
flow rate and pressure sufficient to create, reopen and/or extend a
fracture in said formation, wherein said composition comprises (a)
an aqueous liquid, (b) a pH buffer, (c) a cross-linkable organic
polymer, (d) a cross-linking agent which comprises an organic
titanate, an organic zirconate, or combinations thereof, and (e) a
delay agent which is a hydroxyalkylaminocarboxylic acid.
2. The method of claim 1 wherein the cross-linkable organic polymer
is a solvatable polysaccharide selected from gums, gum derivatives,
and cellulose derivatives.
3. The method of claim 2 wherein the delay agent is selected from
the group consisting of bishydroxyethylglycine,
bishydroxymethylglycine, bishydroxypropylglycine,
bishydroxyisopropylglycine, bishydroxybutylglycine,
monohydroxyethylglycine, monohydroxymethylglycine and their alkali
metal salts.
4. The method of claim 3 wherein the delay agent is
bishydroxyethylglycine.
5. The method of claim 3 wherein the cross-linking agent is an
organic zirconium complex selected from the group consisting of
zirconium .alpha.-hydroxycarboxylic acid salt, zirconium polyol
complexes, zirconium alkanol amine complexes, zirconium
hydroxyalkylated alkylenediamine complexes, and combinations
thereof.
6. The method of claim 3 wherein the cross-linking agent is an
organic titanium complex selected from the group consisting of
titanium .alpha.-hydroxycarboxylic acid salt, titanium polyol
complexes, titanium alkanol amine complexes, and combinations
thereof.
7. A method for fracturing a subterranean formation which comprises
(a) preparing a base gel by mixing an aqueous liquid with a
cross-linkable organic polymer; (b) preparing a delayed
cross-linking composition by mixing a cross-linking agent which
comprises an organic titanate, an organic zirconate, or
combinations thereof with a delay agent which is a
hydroxyalkylaminocarboxylic acid; wherein a pH buffer is added to
the base gel, the delayed cross-linking composition or both; (c)
contacting the base gel with the delayed cross-linking composition;
(d) permitting the base gel and the cross-linking agent to react
after a controllable amount of time to form a cross-linked aqueous
gel; and (e) introducing the cross-linked gel into the formation at
a flow rate and pressure sufficient to create, reopen, and/or
extend a fracture in the formation.
8. The method of claim 7 wherein the subterranean formation is
penetrated by a wellbore and wherein said contacting step (c)
occurs in the wellbore.
9. The method of claim 8 wherein the delay agent is
bishydroxyethylglycine.
10. The method of claim 9 wherein the cross-linking agent is an
organic zirconium complex selected from the group consisting of
zirconium .alpha.-hydroxycarboxylic acid salt, zirconium polyol
complexes, zirconium alkanol amine complexes, zirconium
hydroxyalkylated alkylenediamine complexes, and combinations
thereof.
11. The method of claim 9 wherein the cross-linking agent is an
organic titanium complex selected from the group consisting of
titanium .alpha.-hydroxycarboxylic acid salt, titanium polyol
complexes, titanium alkanol amine complexes, and combinations
thereof.
12. A method for fracturing a subterranean formation which
comprises: (a) preparing a base gel by mixing an aqueous liquid
with a cross-linkable organic polymer and a delay agent which is a
hydroxyalkylaminocarboxylic acid; (b) contacting the base gel with
a cross-linking agent which comprises an organic titanate, an
organic zirconate, or combinations thereof; wherein a pH buffer is
admixed with the base gel, the cross-linking agent or both, prior
to contacting; (c) permitting the base gel and the cross-linking
agent to react after a controllable amount of time to form a
cross-linked aqueous gel; and (d) introducing the cross-linked gel
into the formation at a flow rate and pressure sufficient to
create, reopen, and/or extend a fracture in the formation.
13. The method of claim 12 wherein the subterranean formation is
penetrated by a wellbore and wherein said contacting step (b)
occurs in the wellbore.
14. The method of claim 13 wherein the delay agent is
bishydroxyethylglycine.
15. The method of claim 14 wherein the cross-linking agent is an
organic zirconium complex selected from the group consisting of
zirconium .alpha.-hydroxycarboxylic acid salt, zirconium polyol
complexes, zirconium alkanol amine complexes, zirconium
hydroxyalkylated alkylenediamine complexes, and combinations
thereof.
16. The method of claim 14 wherein the cross-linking agent is an
organic titanium complex selected from the group consisting of
titanium .alpha.-hydroxycarboxylic acid salt, titanium polyol
complexes, titanium alkanol amine complexes, and combinations
thereof.
17. A method for hydraulically fracturing a subterranean formation
penetrated by a wellbore which comprises: (a) preparing a base gel
by mixing an aqueous liquid with a cross-linkable polymer; (b)
introducing the base gel into the wellbore; (c) simultaneously with
or sequentially after, introducing the base gel into the wellbore,
introducing a cross-linking agent which comprises an organic
titanate, an organic zirconate, or combinations thereof into the
wellbore; wherein a pH buffer and a delay agent which is a
hydroxyalkylaminocarboxylic acid are independently admixed with the
base gel, the cross-linking agent or both prior to introducing the
base gel and the cross-linking agent into the wellbore; (d)
permitting the base gel and the cross-linking agent to react after
a controllable period of time to form a cross-linked aqueous gel;
and (e) introducing the cross-linked gel into the formation from
the wellbore at a flow rate and pressure sufficient to create,
reopen, and/or extend a fracture in the formation.
18. The method of claim 17 wherein the delay agent is
bishydroxyethylglycine.
19. The method of claim 18 wherein the cross-linking agent is an
organic zirconium complex selected from the group consisting of
zirconium .alpha.-hydroxycarboxylic acid salt, zirconium polyol
complexes, zirconium alkanol amine complexes, zirconium
hydroxyalkylated alkylenediamine complexes, and combinations
thereof.
20. The method of claim 18 wherein the cross-linking agent is an
organic titanium complex selected from the group consisting of
titanium .alpha.-hydroxycarboxylic acid salt, titanium polyol
complexes, titanium alkanol amine complexes, and combinations
thereof.
21. The method of claim 1, 7, 12, or 17 further comprising
introducing a cross-linking composition comprising (a) an aqueous
liquid, (b) a pH buffer, (c) a cross-linkable organic polymer, (d)
a cross-linking agent which comprises an organic titanate, an
organic zirconate, or combinations thereof, (e) a delay agent which
is a hydroxyalkylaminocarboxylic acid and (f) proppant, into the
fracture.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the field of oil well fracturing
using a cross-linking composition. The cross-linking composition
comprises a cross-linking agent which is a zirconium or titanium
complex or mixtures thereof, a cross-linkable organic polymer and a
delay agent.
BACKGROUND OF THE INVENTION
[0002] The production of oil and natural gas from an underground
well (subterranean formation) can be stimulated by a technique
called hydraulic fracturing, in which a viscous fluid composition
(fracturing fluid) containing a suspended proppant (e.g., sand,
bauxite) is introduced into an oil or gas well via a conduit, such
as tubing or casing, at a flow rate and a pressure which create,
reopen and/or extend a fracture into the oil- or gas-containing
formation. The proppant is carried into the fracture by the fluid
composition and prevents closure of the formation after pressure is
released. Leak-off of the fluid composition into the formation is
limited by the fluid viscosity of the composition. Fluid viscosity
also permits suspension of the proppant in the composition during
the fracturing operation. Cross-linking agents, such as borates,
titanates or zirconates are usually incorporated into the
composition to control viscosity.
[0003] Normally, less than one third of available oil is extracted
from a well after it has been fractured before production rates
decrease to a point at which recovery becomes uneconomical.
Enhanced recovery of oil from such subterranean formations
frequently involves attempting to displace the remaining crude oil
with a driving fluid, e.g., gas, water, brine, steam, polymer
solution, foam, or micellar solution. Ideally, such techniques
(commonly called flooding techniques) provide a bank of oil of
substantial depth being driven into a producing well; however, in
practice this is frequently not the case. Oil-bearing strata are
usually heterogeneous, some parts of them being more permeable than
others. As a consequence, channeling frequently occurs, so that the
driving fluid flows preferentially through zones depleted of oil
(so-called "thief zones") rather than through those parts of the
strata which contain sufficient oil to make oil-recovery operations
profitable.
[0004] Difficulties in oil recovery due to high permeability of
zones may be corrected by injecting an aqueous solution of an
organic polymer and a cross-linking agent into certain subterranean
formations under conditions where the polymer will be cross-linked
to produce a gel, thus reducing the permeability of such
subterranean formations to driving fluid (gas, water, etc.).
Polysaccharide- or partially hydrolyzed polyacrylamide-based fluids
cross-linked with certain aluminum, titanium, zirconium and
boron-based compounds are also used in these enhanced oil recovery
applications.
[0005] Cross-linked fluids or gels, whether for fracturing a
subterranean formation or for reducing permeability of a
subterranean formation, are now being used in hotter, deeper wells
under a variety of pH conditions, where rates of cross-linking with
known cross-linking compositions may be unacceptable. Rather than
developing new cross-linking agents for these new conditions, the
oil well service companies may add delay agents that effectively
delay the cross-linking of a particular metal cross-linking agent
under these conditions.
[0006] A number of patents disclose the use of various delay agents
in combination with particular cross-linking agents for which they
are effective. These patents typically specify adding one or more
ingredients to a cross-linking composition or specify particular
operating conditions, such as a narrow range of pH. There are only
a limited number of disclosed delay agents suitable for titanium
and zirconium cross-linking agents. Thus, use of delay agents with
titanium and zirconium cross-linking agents has limited flexibility
for use by the oil well service companies to stimulate or enhance
recovery of oil or gas from a well or other subterranean
formation.
[0007] There is a need for a more effective method for delaying the
action of titanium and zirconium cross-linking agents in oil
recovery applications, such as hydraulic fracturing and plugging
permeable zones and leaks. There is also a need to be able to
control rate of cross-linking in oil recovery applications so that
a range of cross-linking rates and may be achieved under a range of
pH conditions with a single cross-linking composition. The present
invention meets these needs.
SUMMARY OF THE INVENTION
[0008] This invention provides a method for hydraulically
fracturing a subterranean formation which comprises using a
cross-linking composition which comprises (a) an aqueous liquid,
(b) a pH buffer, (c) a cross-linkable organic polymer, (d) a
cross-linking agent which comprises an organic titanate, an organic
zirconate, or combinations thereof, and (e) a delay agent which is
a hydroxyalkylaminocarboxylic acid. The composition can be used
over a wide range of pH, especially pH 3-12. Preferably the
cross-linkable organic polymer is a solvatable polysaccharide. The
preferred delay agent is bishydroxyethylglycine.
[0009] This method comprises introducing the composition into a
subterranean formation at a flow rate and pressure sufficient to
create, reopen and/or extend a fracture in the formation. The
components of the cross-linking composition may be mixed prior to
introducing them into the formation or the components can be
introduced and permitted to react in the formation after a
controllable period of time.
[0010] The present invention provides methods for effective
delaying the action of titanium and zirconium cross-linking agents
in oil field applications. Surprisingly, a range of temperature, pH
and other conditions can be tolerated and delay times controlled to
provide flexibility by adjusting relative amounts of components,
including cross-linking agent and delay agents.
DETAILED DESCRIPTION OF THE INVENTION
[0011] This invention provides methods for use of a cross-linking
composition, especially wherein the rate of cross-linking of a
cross-linkable organic polymer is delayed. These methods are useful
in oil well applications such as hydraulic fracturing and plugging
of permeable zones.
[0012] The cross-linking composition comprises (a) an aqueous
liquid; (b) a pH buffer; (c) a cross-linkable organic polymer; (d)
a cross-linking agent which comprises an organic titanate, an
organic zirconate, or combinations thereof; and (e) a delay agent
which is a hydroxyalkylaminocarboxylic acid. The composition may
further comprise proppants, stabilizers, breakers, organic
solvents, and the like.
[0013] The aqueous liquid may be water, a mixture of water and an
alcohol, such as aqueous methanol or aqueous ethanol, or an aqueous
solution comprising additional components. For example, an aqueous
solution may comprise a clay stabilizer. Clay stabilizers include,
for example, hydrochloric acid and chloride salts, such as,
tetramethylammonium chloride (TMAC) or potassium chloride. Aqueous
solutions comprising clay stabilizers may comprise, for example,
0.05 to 0.5 weight % of the stabilizer, based on the total weight
of the cross-linking composition.
[0014] The composition is useful over a wide range of pH. A pH
buffer is added to the composition to control pH. The composition
may comprise a pH buffer which is acidic, neutral or basic. The pH
buffer is generally capable of controlling the pH from about pH 3
to about pH 12. For example, in a composition for use at pH of
about 4-5, an acetic acid-based buffer can be used. In a
composition for use at a pH of 5-7, a fumaric acid-based buffer or
a sodium diacetate-based buffer can be used. In a composition for
use at a pH of 7-8.5, a sodium bicarbonate-based buffer can be
used. In a composition for use at a pH of 9-12, a sodium carbonate
or sodium hydroxide-based buffer can be used. Other suitable pH
buffers can be used, as are known to those skilled in the art.
[0015] Examples of suitable cross-linkable organic polymers include
solvatable polysaccharides, polyacrylamides and
polymethacrylamides. Preferably the organic polymer is a solvatable
polysaccharides and is selected from the group consisting of gums,
gum derivatives and cellulose derivatives. Gums include guar gum
and locust bean gum, as well as other galactomannan and glucomannan
gums, such as those derived from sennas, Brazilwood, tera, honey
locust, karaya gum and the like. Gum derivatives include
hydroxyethylguar (HEG), hydroxypropylguar (HPG),
carboxyethylhydroxyethylguar (CEHEG),
carboxymethylhydroxypropylguar (CMHPG), carboxymethyl guar (CMG),
and the like. Cellulose derivatives include those containing
carboxyl groups, such as carboxymethylcellulose (CMC),
carboxymethylhydroxyethylcellulose (CMHEC), and the like. The
solvatable polysaccharides can be used individually or in
combination; usually, however, a single material is used. Guar
derivatives and cellulose derivatives are preferred, such as, HPG,
CMC and CMHPG. HPG is generally more preferred based upon its
commercial availability and desirable properties. However, CMC and
CMHPG may be more preferred in cross-linking compositions when the
pH of the composition is less than 6.0 or higher than 9.0, or when
the permeability of the formation is such that one wishes to keep
the residual solids at a low level to prevent damage to the
formation.
[0016] The cross-linkable polymer is normally blended with a
solvent such as water or mixed water/organic solvent or with the
aqueous liquid as described above to form an uncross-linked gel.
Organic solvents that may be used include alcohols, glycols,
polyols, and hydrocarbons such as diesel. As an example, the
polymer may be blended with water, a water/alcohol mixture (e.g.,
where the alcohol is methanol or ethanol), or an aqueous solution
comprising a clay stabilizer).
[0017] The cross-linking agent comprises an organic titanium
complex, an organic zirconium complex or a combination thereof.
[0018] Suitable organic zirconium complexes for use in the
composition of this invention include but are not limited to
zirconium .alpha.-hydroxycarboxylic acid salt, zirconium polyol
complexes, zirconium alkanol amine complexes, zirconium
hydroxyalkylated alkylenediamine complexes, and combinations
thereof. Examples of useful zirconium complexes include zirconium
diethanolamine complex, zirconium triethanolamine complex,
zirconium lactate, zirconium ethylene glycolate, zirconium
acetylacetonate, zirconium ammonium lactate, zirconium
diethanolamine lactate, zirconium triethanolamine lactate,
zirconium diisopropylamine lactate, zirconium sodium lactate salts,
zirconium glycerol complex, zirconium sorbitol complex, zirconium
hydroxyalkylated ethylenediamine complexes, or combinations
thereof.
[0019] The preferred zirconium complexes are zirconium polyol
complexes and zirconium alkanol amine complexes. Polyols include
glycerol, erythritol, threitol, ribitol, arabinitol, xylitol,
allitol, altritol, sorbitol, mannitol, dulcitol, iditol, perseitol,
and the like. Alkanol amines include those corresponding to the
formula R'--N--CH.sub.2--CH(OH)R'').sub.2 wherein R' is hydrogen or
--CH.sub.2--CH(OH)R'' and R'' is hydrogen, methyl or ethyl. A more
preferred zirconium complex is zirconium tetra-triethanolamine
complex, which is available commercially from E. I. du Pont de
Nemours and Company, Wilmington, Del., as Tyzor.RTM. TEAZ organic
zirconate.
[0020] Suitable organic titanium complexes for use in the
composition of this invention include but are not limited to
titanium .alpha.-hydroxycarboxylic acid salt, titanium polyol
complexes, titanium alkanol amine complexes, and combinations
thereof. Examples of useful titanium complexes include titanium
diethanolamine complex, titanium triethanolamine complex, titanium
lactate, titanium ethylene glycolate, titanium acetylacetonate,
titanium ammonium lactate, titanium diethanolamine lactate,
titanium triethanolamine lactate, titanium diisopropylamine
lactate, titanium sodium lactate salts, titanium sorbitol
complexes, and combinations thereof.
[0021] The preferred titanium complexes are titanium alkanol amine
complexes. Suitable alkanol amines are those described hereinabove.
A more preferred titanium complex is titanium tetra-triethanolamine
complex, which is available commercially from E. I. du Pont de
Nemours and Company, Wilmington, Del. as Tyzor.RTM. TE organic
titanate.
[0022] The cross-linking agent is generally used as a solution or
suspension in an organic, aqueous or mixed aqueous/organic solvent.
Organic solvents are typically alcohols, such as ethanol,
n-propanol, i-propanol, and the like. For example, the
cross-linking agent can be used as a solution in the aqueous
liquid. The concentration of the cross-linking agent can vary and
is typically from 0.01 to 1.0 weight %, based on the total weight
of the cross-linking composition. The preferred concentration is
0.1 to 0.5 weight %, based on the total weight of the
composition.
[0023] The delay agent is a hydroxyalkylaminocarboxylic acid.
Preferably, the delay agent is selected from the group consisting
of bishydroxyethylglycine, bishydroxymethylglycine,
bishydroxypropylglycine, bishydroxyisopropylglycine,
bishydroxybutylglycine, monohydroxyethylglycine,
monohydroxymethylglycine and their alkali metal salts. More
preferably the hydroxyalkylaminocarboxylic acid is
bishydroxyethylglycine.
[0024] The delay agents are commercially available and/or may be
prepared by processes described in the literature. For example,
bishydroxyethylglycine suitable for this invention may be made by a
number of processes described in the literature (see,
Kromov-Borisov and Remizov, in Zhur. Obshchei Khim., 1953, 23, 598;
Gump, et al., in J. Org. Chem., 1959, 24, 712-14).
Bishydroxyethylglycine is also available commercially and sold
under the generic name of "bicine".
[0025] The delay agent is typically used as an aqueous solution.
The concentration of delay agent in the solution may vary and is
typically from 0.1-75% by weight. The preferred concentration is
10-30 weight %, based on the total weight of the solution.
[0026] The composition may comprise optional components, including
those which are common additives for oil field applications. Thus,
the composition may further comprise one or more of proppants,
friction reducers, bactericides, hydrocarbons, chemical breakers,
stabilizers, surfactants, formation control agents, and the like.
Proppants include sand, bauxite, glass beads, nylon pellets,
aluminum pellets and similar materials. Friction reducers include
polyacrylamides. Hydrocarbons include diesel oil. Chemical breakers
break the cross-linked polymer (gel) in a controlled manner and
include enzymes, alkali metal persulfate, ammonium persulfate.
Stabilizers include methanol, alkali metal thiosulfate, ammonium
thiosulfate. Stabilizers may also include clay stabilizers such as
hydrochloric acid and chloride salts, for example,
tetramethylammonium chloride (TMAC) or potassium chloride.
[0027] The composition may also further comprise as optional
components, a complexing agent or a polyfunctional organic
compound, such as one or more of hydroxycarboxylic acid,
aminocarboxylic acid, alkanolamine (hydroxyalkylamines,
hydroxyalkyl alkylenediamines, polyhydroxyl compounds, sodium
carbonate, and sodium bicarbonate. Hydroxycarboxylic acid includes
polyhydroxylcarboxylic acid, hydroxy monocarboxylic acid,
.alpha.-hydroxycarboxylic acid. Polyhydroxyl compounds include
polyols and polyhydroxylcarboxylic acids.
[0028] Each component is present in the composition in an amount
sufficient to achieve the desired cross-linking performance based
on the individual components, desired delay in cross-linking time,
temperature and other conditions present in the formation being
fractured or permeable zone being plugged. Aqueous liquid is added
in an amount sufficient to render the composition active for
cross-linking the cross-linkable polymer by the cross-linking agent
in the presence of the delay agent. The pH buffer is added in an
amount sufficient to maintain pH of the composition in the desired
pH range.
[0029] The amounts of cross-linkable polymer and the cross-linking
agent may vary. One uses small but effective amounts, each of which
will vary with the circumstances, e.g., the type of subterranean
formation, the depth at which the method (e.g., fluid fracturing,
permeable zone plugging or leak plugging) is to be performed, as
well as temperature and pH, among other conditions. Generally one
uses as small an amount of each as will provide the viscosity level
necessary to effect the desired result, i.e., fracturing of the
subterranean formation, or plugging of permeable zones or leaks in
order to promote adequate recovery of oil or gas from a
subterranean formation.
[0030] The amount of delay agent is dependent on the extent to
which the rate of cross-linking is desired to be delayed. Typically
the ratio of the delay agent to cross-linking agent, on a weight
basis, is 0.001:1 to 100:1 of delay agent to cross-linking agent.
Preferably when the delay agent is bishydroxyethylglycine, this
ratio is 0.1-10:1 of delay agent to cross-linking agent. Within
these broad ranges, the amount of delay agent selected for use is
dependent on the type and amount of cross-linking agent being used,
the temperature of the formation being fractured or permeable zone
being plugged and the delay in cross-link time desired. As the
weight ratio of delay agent to cross-linking agent is increased,
the rate of cross-linking, i.e., gel formation is reduced or
cross-link time is increased. At higher ratios of delay agent to
cross-linking agent, higher temperature may be needed to initiate
cross-linking. The maximum viscosity of the final gel decreases as
cross-link times are increased. By controlling the rate of
cross-linking of the polymer by the use of a delay agent in
combination with a single cross-linking agent over the variety of
pH and temperature conditions experienced in the field, one can
minimize premature cross-linking on the surface and subsequent
viscosity loss due to shear degradation.
[0031] The composition of this invention may be produced by mixing
the aqueous liquid, pH buffer, organic polymer, cross-linking agent
and delay agent, along with any optional components in any order.
For example, in a particular application in the oil field, the
components may be introduced into a subterranean formation as
separate streams, or two or more of the components may be premixed
and introduced into the formation as a combined stream, or all
components may be premixed and introduced as a single stream.
Preferably, the cross-linkable polymer is not premixed with the
cross-linking agent. When these two components are premixed, they
are premixed just prior to the use of the composition, that is,
introducing the mixture into a subterranean formation, for example,
for hydraulic fracturing or plugging of subterranean permeable
zones or leaks. Advantageously, the components may be mixed in
different combinations, and more advantageously, the components may
be mixed just prior to use to enable easy variation and adjustment
of the cross-linking rate.
[0032] The compositions of this invention provide advantages over
those of the prior art when used in methods for hydraulic
fracturing or plugging of subterranean zones or leaks. The
compositions can be modified to provide a range of cross-linking
rates with a single cross-linking agent. The compositions can be
used at both high and low pH. The compositions can be used at high
temperatures at acceptable rates. The compositions can be used with
fluids containing a high level of brine. Thus, the compositions can
be used in hot subterranean formations, including those at greater
depths in oil and gas wells. The compositions provide excellent
performance in hydraulic fracturing and for selectively plugging
permeable zones and leaks in subterranean formations.
[0033] The present invention further provides methods of using the
cross-linking composition of this invention. In a hydraulic
fracturing method of this invention, one or more fractures is
created, reopened, and/or extended in an oil- or gas-containing
subterranean. Thus, this invention provides a method for fracturing
a subterranean formation which comprises introducing into said
formation a cross-linking composition at a flow rate and pressure
sufficient to create, reopen and/or extend a fracture in said
formation, wherein said composition comprises (a) an aqueous
liquid, (b) a pH buffer, (c) a cross-linkable organic polymer, (d)
a cross-linking agent which comprises an organic titanate, an
organic zirconate, or combinations thereof, and (e) a delay agent
which is a hydroxyalkylaminocarboxylic acid.
[0034] In a first embodiment of the method for hydraulically
fracturing a subterranean formation, the cross-linkable organic
polymer and the cross-linking agent are contacted prior to their
introduction into the subterranean formation, such that the polymer
and cross-linking agent react to form a cross-linked aqueous gel,
which gel is then introduced into the formation.
[0035] In one example of the first embodiment of the hydraulic
fracturing method, a base gel is prepared by mixing an aqueous
liquid with a cross-linkable organic polymer and a delayed
cross-linking composition is prepared by mixing a cross-linking
agent which comprises an organic titanate, an organic zirconate, or
combinations thereof, with a delay agent which is a
hydroxyalkylaminocarboxylic acid. A pH buffer is added to the base
gel, the delayed cross-linking composition, or both. In this
embodiment, more specifically, the method for hydraulically
fracturing a subterranean formation comprises (a) preparing a base
gel; (b) preparing a delayed cross-linking composition; (c)
contacting the base gel with the delayed cross-linking composition;
(d) permitting the base gel and the cross-linking agent to react
after a controllable amount of time to form a cross-linked aqueous
gel; and (e) introducing the cross-linked gel into the formation at
a flow rate and pressure sufficient to create, reopen, and/or
extend a fracture in the formation.
[0036] In a second example of the first embodiment, a base gel is
prepared by mixing an aqueous liquid with a cross-linkable polymer
and a delay agent which is a hydroxyalkylaminocarboxylic acid. In
this embodiment, the method for hydraulically fracturing a
subterranean formation comprises (a) preparing a base gel; (b)
contacting the base gel with a cross-linking agent which comprises
an organic titanate, an organic zirconate, or combinations thereof;
(c) permitting the base gel and the cross-linking agent to react
after a controllable amount of time to form a cross-linked aqueous
gel; and (d) introducing the cross-linked gel into the formation at
a flow rate and pressure sufficient to create, reopen, and/or
extend a fracture in the formation. In this second embodiment, a pH
buffer is admixed with the base gel, the cross-linking agent, or
both, prior to contacting the base gel with the cross-linking
agent.
[0037] In a modification of this first embodiment, the subterranean
formation may be penetrated by a wellbore, such that contacting the
base gel with the cross-linking agent occurs in the wellbore and
the cross-linked aqueous gel is introduced into the formation from
the wellbore at a flow rate and pressure sufficient to create,
reopen and/or extend a fracture in the formation.
[0038] In a second embodiment, components of a cross-linking
composition are introduced separately, either sequentially or
simultaneously, into a subterranean formation such that
cross-linking occurs within the subterranean formation. The method
of this embodiment for hydraulically fracturing a subterranean
formation penetrated by a wellbore comprises (a) preparing a base
gel by mixing an aqueous liquid with a cross-linkable polymer; (b)
introducing the base gel into the wellbore; (c) simultaneously with
or sequentially after, introducing the base gel into the wellbore,
introducing a cross-linking agent which comprises an organic
titanate, an organic zirconate, or combinations thereof into the
wellbore; wherein a pH buffer and a delay agent which is a
hydroxyalkylaminocarboxylic acid are independently admixed with the
base gel, the cross-linking agent or both prior to introducing the
base gel and the cross-linking agent into the wellbore; (d)
permitting the base gel and the cross-linking agent to react after
a controllable period of time to form a cross-linked aqueous gel;
and (e) introducing the cross-linked gel into the formation from
the wellbore at a flow rate and pressure sufficient to create,
reopen, and/or extend a fracture in the formation.
[0039] Upon creation of a fracture or fractures, the method may
further comprise introducing a cross-linking composition comprising
(a) an aqueous liquid, (b) a pH buffer, (c) a cross-linkable
organic polymer, (d) a cross-linking agent which comprises an
organic titanate, an organic zirconate, or combinations thereof,
(e) a delay agent which is a hydroxyalkylaminocarboxylic acid and
(f) proppant, into the fracture or fractures. This second
introduction of a cross-linking composition is preferably performed
in the event the cross-linking composition used to create the
fracture or fractures did not comprise proppant. The cross-linking
composition may subsequently be recovered from the formation.
[0040] In the method for fracturing a subterranean formation,
satisfactory gels can generally be made by using the cross-linkable
organic polymer in amounts up to about 1.2 weight % and the
cross-linking agent in amounts up to about 1.0 weight %, both
percentages being based on the weight of the aqueous liquid.
Preferably, from about 0.25 to about 0.75 weight % of the
cross-linkable organic polymer is used and from about 0.05 to about
0.50 weight % of the cross-linking agent is used, both percentages
being based on the weight of the aqueous liquid.
[0041] In another method of this invention, the composition of this
invention is used to plug a permeable zone or leak in a
subterranean formation. This method comprises introducing a
cross-linking composition (or cross-linked gel) into the permeable
zone or leak.
[0042] More specifically, the method of plugging a permeable zone
or a leak in a subterranean formation comprises introducing into
said zone or said leak, a cross-linking composition comprising (a)
an aqueous liquid, (b) a pH buffer, (c) a cross-linkable organic
polymer, (d) a cross-linking agent which comprises an organic
titanate, an organic zirconate, or combinations thereof, and (e) a
delay agent which is a hydroxyalkylaminocarboxylic acid.
[0043] In a first embodiment of the method for plugging a permeable
zone or a leak in a subterranean formation, the cross-linkable
organic polymer and the cross-linking agent are contacted prior to
their introduction into the subterranean formation, such that the
polymer and cross-linking agent react to form a cross-linked
aqueous gel, which gel is then introduced into the formation.
[0044] In one example of the first embodiment of the plugging a
permeable zone or a leak in a subterranean formation method, a base
gel is prepared by mixing an aqueous liquid with a cross-linkable
organic polymer and a delayed cross-linking composition is prepared
by mixing a cross-linking agent which comprises an organic
titanate, an organic zirconate, or combinations thereof, with a
delay agent which is a hydroxyalkylaminocarboxylic acid. A pH
buffer is added to the base gel, the delayed cross-linking
composition, or both. In this embodiment, more specifically, the
method comprises (a) preparing the base gel; (b) preparing a
delayed cross-linking composition; (c) contacting the base gel with
the delayed cross-linking composition; (d) permitting the base gel
and the cross-linking agent to react after a controllable amount of
time to form a cross-linked aqueous gel; and (e) introducing the
cross-linked gel into the permeable zone or leak.
[0045] In a second example of the first embodiment, a base gel is
prepared by mixing an aqueous liquid with a cross-linkable polymer
and a delay agent which is a hydroxyalkylaminocarboxylic acid. In
this embodiment, the method for plugging a permeable zone or leak
comprises (a) preparing the base gel; (b) contacting the base gel
with a cross-linking agent which comprises an organic titanate, an
organic zirconate, or combinations thereof; (d) permitting the base
gel and the cross-linking agent to react after a controllable
amount of time to form a cross-linked aqueous gel; and (e)
introducing the cross-linked gel into the permeable zone or leak.
In this second embodiment, a pH buffer is added to the base gel or
admixed with cross-linking agent.
[0046] In a second embodiment, components of a cross-linking
composition are introduced separately into a permeable zone or leak
in a subterranean formation such that cross-linking occurs within
the subterranean formation. The method of this embodiment comprises
(a) preparing a base gel by mixing an aqueous liquid with a
cross-linkable polymer; (b) introducing the base gel into the
permeable zone or leak; (c) simultaneously with or sequentially
after, introducing the base gel into the permeable zone or leak,
introducing a cross-linking agent which comprises an organic
titanate, an organic zirconate, or combinations thereof into
permeable zone or leak; wherein a pH buffer and a delay agent which
is a hydroxyalkylaminocarboxylic acid are independently admixed
with the base gel, the cross-linking agent or both prior to
introduction of the base gel and the cross-linking agent into the
permeable zone or leak; and (d) permitting the base gel and the
cross-linking agent to react after a controllable period of time to
form a cross-linked aqueous gel to plug the permeable zone or
leak.
[0047] In a method for plugging permeable zones or leaks in
subterranean formations, one generally uses about 0.25 to 1.2
weight % of a cross-linkable organic polymer, preferably 0.40 to
0.75 weight %, and 0.01 to 1.0 weight % of a cross-linking agent,
preferably 0.05 to 0.50 weight %, all percentages being based on
the weight of the aqueous liquid.
EXAMPLES
Methods
Preparation of a Base Gel
[0048] One liter of tap water was added to a Waring blender jar
equipped with a three bladed paddle stirrer. Agitation was started
and 3.6 g of a solvatable polysaccharide polymer was added,
followed by a clay stabilizer (tetramethylammonium chloride) and a
buffer selected to adjust the pH to 4.0-7.0 to provide a solution.
The rate of agitation was adjusted to maintain a slight vortex at
the top of the solution and agitation continued for 30 minutes,
which produced a "30 lb/1000 gallon" base gel. After 30 minutes,
the pH of the base gel was adjusted to the desired final pH with
(1) an acetic acid-based buffer for pH 4-5; (2) a fumaric acid or
sodium diacetate-based buffer for pH 5-7; (3) a sodium
bicarbonate-based buffer for pH 7-8.5; or (4) a sodium carbonate or
sodium hydroxide-based buffer for pH 9-11. Agitation was stopped
and the base gel allowed to sit for 30 minutes.
[0049] Alternatively, for a "20 lb/1000" gallon base gel, 2.4 g of
polymer was added to one liter of tap water. For a "60 lb/1000"
gallon base gel, 7.2 g of polymer was added to one liter of tap
water.
Vortex Closure Test:
[0050] A 250 ml portion of base gel was measured into a clean
Waring blender jar. Agitation was started and the rate adjusted to
create a vortex exposing the blade nut. The setting on the Variac
controlling the blender speed was recorded and kept constant for
all tests for reproducibility. An amount of cross-linking agent was
injected into the edge of the vortex of the agitated base gel and a
stopwatch immediately started, which set time=0. When the viscosity
of the gel increased sufficiently to allow the fluid to cover the
nut on the blade of the blender jar and the vortex remained closed,
the time was recorded. This time, that is the difference between
the time the stopwatch started and the time the vortex remained
closed, is the vortex closure time. If the vortex had not closed
within 10 minutes, the test was discontinued and a vortex closure
time of greater than 10 minutes was recorded. The beginning and
final pH of the cross-linked gel were also recorded as pHb and pHf,
respectively. Such vortex closure tests provide a means for
obtaining a reasonably good estimate of the time required to
complete cross-linking of the polymer by the cross-linking agent.
Complete closure of the vortex indicates a substantial degree of
cross-linking.
[0051] The test was repeated using the same base gel and
cross-linking agent. However, a specified amount of
bishydroxyethylglycine delay agent was injected immediately
following the injection of the cross-linking agent. The vortex
closure time was recorded in a similar fashion. Results for the
cross-linking compositions are provided below.
[0052] Note 1: 0.2% by weight of the total composition of
tetramethyl ammonium chloride was used as clay stabilizer.
[0053] Note 2: A 30 lb/1000 gallon carboxymethylcellulose (CMC)
base gel, prepared in 1 gal/1000 gal of 50% TMAC solution in water
was used to measure the vortex closure times at pH 4.
[0054] Note 3: A 20 lb/1000 gal carboxymethylcellulose (CMC) base
gel, prepared in 1 gal/1000 gal of 50% TMAC solution in water was
used to measure the vortex closure times at pH 5.
[0055] Note 4: A 60 lb/1000 gal carboxymethylhydroxypropylguar
(CMHPG) base gel was used to measure the vortex closure times at pH
10.
Example 1
[0056] Sodium chloroacetate (237 g) was added to 422 g of tap water
in a 2-liter flask equipped with a dropping funnel, thermocouple,
condenser and nitrogen bubbler. Agitation was started and heat
applied to dissolve the sodium chloroacetate. After the sodium
chloroacetate dissolved, 218 g of diethanolamine (99%) were added,
and the reaction mass heated to reflux and held there for 10 hours.
On cooling the solution was diluted with 510 g of water to give a
clear, water white solution containing 24% bishydroxyethylglycine.
The product of Example 1 was evaluated as a delay agent with each
of the products of Examples 2-5 and Comparative Example D.
Example 2
[0057] A 500-ml flask, equipped with a thermocouple, dropping
funnel, nitrogen bleed and condenser, was charged with 313.7 g of
zirconium tetra-triethanolamine complex, available from E. I. du
Pont de Nemours and Company, Wilmington, Del. Agitation was started
and a mixture of 20.9 g of glycerol and 20.9 g of water were added.
The solution was agitated for 2 hours at 60.degree. C. to give 355
g of an orange solution containing 11.6% Zr. Table 1A provides
results using the product of Example 2 in the Vortex Closure
Test.
Example 3
[0058] A 500-ml flask, equipped with a thermocouple, dropping
funnel, nitrogen bleed and condenser, was charged with 313.7 g of
zirconium tetra-triethanolamine complex. Agitation was started and
the following were added: 132.6 g of Quadrol.RTM.
tetrakis(2-hydroxypropyl)ethylenediamine, available from BASF
Corp., and a mixture of 42 g of glycerol and 42 g of water. The
solution was agitated for 2 hours at 60.degree. C. to give 530 g of
an orange solution containing 7.8% Zr. Table 1B provides results
using the product of Example 3 in the Vortex Closure Test.
Comparative Example A
[0059] A 1000-ml flask equipped with agitator, a condenser, a
dropping funnel, a thermocouple and a nitrogen bleed was charged
with 352 g (0.799 mol) of tetra-n-propylzirconate. Agitation was
started and 230.8 g (0.83 mol) of hydroxyethyl
tris-(2-hydroxypropyl)ethylenediamine were added. The reaction mass
was heated to 60.degree. C. and held there for 2 hours. After the
hold period the reaction mass was cooled to room temperature to
yield a viscous, clear yellow liquid containing 12.3% Zr. Table 1C
provides results using the product of Comparative Example A in the
Vortex Closure Test.
Comparative Example B
[0060] A 1000-ml flask equipped with agitator, a condenser, a
dropping funnel, a thermocouple and a nitrogen bleed, was charged
with 364 g (0.826 mol) of tetra-n-propylzirconate. Agitation was
started and 493.4 g (3.3 mol) of triethanolamine were added. The
reaction mass was heated to 60.degree. C. and held there for 2
hours. After the hold period, a 20 mm Hg vacuum was applied to
remove the n-propanol liberated in the reaction. The reaction mass
was then cooled to room temperature to yield a viscous, clear
yellow liquid containing 13.2% Zr. Table 1C provides results using
the product of Comparative Example B in the Vortex Closure
Test.
Comparative Example C
[0061] A 1000-ml flask equipped with agitator, a condenser, a
dropping funnel, a thermocouple and a nitrogen bleed, was charged
with 368.6 g (0.609 mol) of zirconium oxychloride, dissolved as 30%
aqueous solution. Agitation was started and 40 g (0.83 mol) of
water were added. Next, 181.3 g (1.77 mol) of 85% lactic acid were
rapidly added under high speed agitation, while temperature was
maintained at 20-30.degree. C. The reaction mass was stirred an
additional hour at 20-30.degree. C. and then neutralized to pH
6.7-7.3 with 25% aqueous sodium hydroxide solution. The reaction
mass was then heated to 80.degree. C. and held there for 4 hours.
After the hold period the reaction mass was cooled to room
temperature to yield a clear, pale yellow liquid containing 5.4%
Zr. Table 1C provides results using the product of Comparative
Example C in the Vortex Closure Test. TABLE-US-00001 TABLE 1A
Vortex Vortex Conc Closure Closure Cross- (ml/ Time Time linking
1000 Conc (ml/ (min:sec) (min:sec) Agent ml) Delay Agent 1000 ml)
pH 4 pH 5 Example 2 0.35 none 0 1:10 Example 2 0.35 Example 1 1
2:05 Example 2 0.35 glycerol (70%) 1 1:22 Example 2 0.35 sorbitol
(70%) 1 1:04 Example 2 0.70 Example 1 1 2:39 Example 2 0.70 none 0
0:59 Example 2 0.70 glycerol (70%) 1 2:01 Example 2 0.70 sorbitol
(70%) 1 1:05
[0062] TABLE-US-00002 TABLE 1B Vortex Vortex Conc Closure Closure
Cross- (ml/ Time Time linking 1000 Conc (ml/ (min:sec) (min:sec)
Agent ml) Delay Agent 1000 ml) pH 4 pH 5 Example 3 0.50 None 0 1:14
Example 3 0.50 Example 1 1 3:03 Example 3 0.50 glycerol (70%) 1
1:42 Example 3 0.50 sorbitol (70%) 1 1:18 Example 3 1.0 None 1:23
Example 3 1.0 Example 1 1 4:49 Example 3 1.0 glycerol (70%) 1 2:39
Example 3 1.0 sorbitol (70%) 1 1:33 Example 3 0.50 Example 1 0 3:50
Example 3 0.50 Example 1 0.5 7:45 Example 3 0.50 Example 1 1 >10
Example 3 0.75 Example 1 0 1:44 Example 3 0.75 Example 1 0.5 5:29
Example 3 0.75 Example 1 1 >10
[0063] TABLE-US-00003 TABLE 1C Vortex Vortex Closure Closure Time
Time Cross-linking Conc (ml/ Delay Conc (ml/ (min:sec) (min:sec)
Agent 1000 ml) Agent 1000 ml) pH 4 pH 5 Comp. Ex. A. 0.4 None --
0:02 0:23 Comp. Ex. B 0.08 None -- >10 Comp. Ex. B 0.12 none --
0:32 Comp. Ex. C 0.20 None -- 6:17 Comp. Ex. C 0.28 None --
>10
[0064] Tables 1A-1C provide the evaluation results for the vortex
closure times when using cross-linking compositions comprising
different delay agents, including compositions comprising the
products of Examples 1 and 2 and of Comparative Examples A, B and
C, at pH 4 and at pH 5. From Tables 1A-1C, it can be seen that
bishydroxyethylglycine is a much more effective delay agent at pH 4
and pH 5 than glycerol and sorbitol, which are delay agents
disclosed in the prior art.
[0065] Table 1B illustrates the effect of increasing the delay
agent concentration on rate of cross-linking. That is, higher
amounts of delay agent increase rate of cross-linking.
[0066] In order to meet the performance requirements for use in a
low pH fracturing fluid cross-link times at either pH 4 or pH 5
should typically be within a period of time of 2 seconds to 5
minutes. The vortex closure times of Comparative Examples, which
lack the bishydroxyethylglycine delay agent are outside of this
time period.
Comparative Example D
[0067] The effect of various delay agents in combination with a
boron compound, boric acid, as a cross-linking agent were
determined using the Vortex Closure Test as described above.
Equimolar amounts of delay agent and boric acid (0.15 g) were added
to a 30 lb/100 gallon CMHPG base gel in which pH was adjusted to
about pH 12 using sodium hydroxide. The vortex closure times in
minutes are provided in Table 2. TABLE-US-00004 TABLE 2 Rate of
Cross-linking of Boric Acid with Bishydroxyethylglycine Vortex
Closure Delay Agent (amount added) Time (min.) pHb pHf No Delay
Agent 0:48 12.90 12.59 Sodium Glutamate (0.75 g) 6:13 12.90 12.57
Sorbitol (0.85 g) >10 12.95 12.58 Example 1 (2.67 g) 0:53 12.95
12.60 Example 1 (5.37 g) 0:37 12.97 12.58
[0068] As can be seen from Table 2, use of the composition of
Example 1, bishydroxyethylglycine, is a poor delay agent for the
boron cross-linking agent. The vortex closure time when using boric
acid as a cross-linking agent is substantially the same with or
without addition of bishydroxyethylglycine. In contrast, other
known delay agents (sodium glutamate and sorbitol) are effective at
increasing the vortex closure time when used with the boron
cross-linking agent.
Example 4
[0069] A 500-ml flask, equipped with a thermocouple, dropping
funnel, nitrogen bleed and condenser, was charged with 313.7 g of
zirconium tetra-triethanolamine complex. Agitation was started and
the following were added to the flask: 132.6 g of Quadrol.RTM.
tetrakis(2-hydroxypropyl)ethylenediamine and a mixture of 42 g of
glycerol and 21 g of water. The solution was agitated for 2 hours
at 60.degree. C. to give 509 g of an orange solution containing
8.1% Zr.
[0070] The product was evaluated in the Vortex Closure Time test
along with a commercially available zirconate cross-linking agent,
zirconium tetra-triethanolamine complex, available from E. I. du
Pont de Nemours and Company, Wilmington, Del. Each cross-linking
agent was used in an equimolar amount. A 60 lb/1000 gal CMHPG base
gel prepared as described above under Preparation of a Base Gel was
used. Sodium hydroxide was used to provide a pH of 10. A test was
performed in the absence and then in the presence of
bishydroxyethylglycine, the product of Example 1. TABLE-US-00005
TABLE 3 Conc. Cross- Vortex linking Conc. Closure Agent Example 1
Time Cross-linking Agent ml/1000 ml ml/1000 ml (min.) pHb pHf
Example 4 1.08 0 7:24 10.00 10.04 Example 4 1.08 0.25 >10 10.00
9.80 Zirconium tetra- 0.68 0 1:52 10.00 10.00 triethanolamine
complex Zirconium tetra- 0.68 0.25 8:47 10.00 9.84 triethanolamine
complex
[0071] Table 3 shows that bishydroxyethylglycine is very effective
at pH 10 in delaying the rate by cross-linking of zirconate
complexes such as the zirconium complex prepared in Example 4 or a
commercial zirconium cross-linking agent, zirconium
tetra-triethanolamine complex.
Example 5
[0072] Two commercially available titanium cross-linking agents,
titanium triethanolamine complex (available as Tyzor.RTM. TE
organic titanate) and titanium ammonium lactate (available as
Tyzor.RTM. LA organic titanate), both from E. I. du Pont de Nemours
and Company, Wilmington, Del., were evaluated in the Vortex Closure
Time test. Each cross-linking agent was used in an amount of 0.52
ml per 1000 ml of solution of the 60 lb/1000 gal CMHPG prepared as
described above under Preparation of a Base Gel. Sodium hydroxide
was used to provide a pH of 10. A test was performed in the absence
and then in the presence of bishydroxyethylglycine, the product of
Example 1. TABLE-US-00006 TABLE 4 Conc. Example 1 Vortex Closure
Cross-linking Agent (ml/1000 ml) Time (min.) Titanium
triethanolamine complex 0 1:06 Titanium triethanolamine complex
0.25 4:12 Titanium ammonium lactate 0 4:01 Titanium ammonium
lactate 0.25 >10
[0073] Table 4 shows that bishydroxyethylglycine is very effective
at pH 10 in delaying the rate of cross-linking by titanate
complexes.
* * * * *