U.S. patent application number 12/673867 was filed with the patent office on 2011-04-21 for diverting agents for water shut off.
This patent application is currently assigned to M-I LLC. Invention is credited to Clark Harrison, Mark Luyster, LaTosha Moore, Bethicia B. Prasek, Raymond D. Ravitz.
Application Number | 20110088902 12/673867 |
Document ID | / |
Family ID | 40378908 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110088902 |
Kind Code |
A1 |
Harrison; Clark ; et
al. |
April 21, 2011 |
DIVERTING AGENTS FOR WATER SHUT OFF
Abstract
A method of retarding the flow of water in a subterranean
formation that includes injecting a gelling pill into the
formation, the gelling pill comprising: brine; a crosslinkable
polymer; and a crosslinkant; and allowing the crosslinkable polymer
to crosslink to form a gel in the subterranean formation is
disclosed. A water absorbing polymer is optionally included.
Inventors: |
Harrison; Clark; (Cypress,
TX) ; Luyster; Mark; (Houston, TX) ; Moore;
LaTosha; (Richmond, TX) ; Prasek; Bethicia B.;
(The Woodlands, TX) ; Ravitz; Raymond D.;
(Houston, TX) |
Assignee: |
M-I LLC
Houston
TX
|
Family ID: |
40378908 |
Appl. No.: |
12/673867 |
Filed: |
August 11, 2008 |
PCT Filed: |
August 11, 2008 |
PCT NO: |
PCT/US08/72775 |
371 Date: |
May 27, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60956516 |
Aug 17, 2007 |
|
|
|
Current U.S.
Class: |
166/300 |
Current CPC
Class: |
C09K 8/512 20130101 |
Class at
Publication: |
166/300 |
International
Class: |
E21B 43/22 20060101
E21B043/22 |
Claims
1. A method of retarding the flow of water in a subterranean
formation, comprising: injecting a gelling pill into the formation,
the gelling pill comprising: brine; a crosslinkable polymer; and a
crosslinkant; and allowing the crosslinkable polymer to crosslink
to form a gel in the subterranean formation.
2. The method of claim 1, wherein the gelling pill, when gelled,
retards water flow therethrough.
3. The method of claim 1, further comprising: producing oil from
the subterranean formation.
4. The method of claim 1, further comprising: injecting a driving
fluid into the subterranean formation.
5. The method of claim 1, wherein the gelling pill further
comprises a crosslink initiator.
6. The method of claim 1, wherein the crosslinkable polymer
comprises at least one of xanthan, guar, hydroxyalkylguar,
carboxyalkylhydroxyalkylguar, scleroglucan, wellan, gellan, and
diutan.
7. The method of claim 6, wherein the crosslinkable polymer
comprises xanthan gum.
8. The method of claim 1, wherein the crosslinkant comprises at
least one of boron, calcium, zinc, titanium, and zirconium.
9. The method of claim 8, wherein the crosslinkant comprises solid
borates of alkali metals and/or alkaline earth metals.
10. The method of claim 9, further comprising: allowing the solid
borates to permeate into the formation.
11. The method of claim 1, wherein the gelling pill further
comprises a water absorbing polymer.
12. The method of claim 10, wherein the water absorbing polymer
comprises crosslinked polyacrylamide, polyacrylate, or copolymers
thereof.
13. A method of retarding the flow of water in a subterranean
formation, comprising: introducing an effective amount of a gelling
pill into flow channels in the formation, the gelling pill
comprising: brine; a crosslinkable polymer; a crosslinkant; and a
water absorbing polymer allowing the water absorbing polymer to
permeate a region of the formation surrounding the flow channels;
and allowing the crosslinkable polymer to crosslink to form a gel
in the flow channel in the formation.
14. The method of claim 13, wherein the gelling pill, when gelled,
retards water flow therethrough.
15. The method of claim 13, further comprising: producing oil from
the subterranean formation.
16. The method of claim 13, further comprising: injecting a driving
fluid into the subterranean formation.
17. The method of claim 13, wherein the water absorbing polymer
absorbs water that flows into the region of the formation
surrounding the flow channels having the gel formed therein.
18. The method of claim 13, wherein the gelling pill further
comprises a crosslink initiator.
19. The method of claim 13, wherein the crosslinkable polymer
comprises at least one of xanthan, guar, hydroxyalkylguar,
carboxyalkylhydroxyalkylguar, scleroglucan, wellan, gellan, and
diutan.
20. The method of claim 19, wherein the crosslinkable polymer
comprises xanthan gum.
21. The method of claim 13, wherein the crosslinkant comprises at
least one of boron, calcium, zinc, titanium, and zirconium.
22. The method of claim 21, wherein the crosslinkant comprises
solid borates of alkali metals and/or alkaline earth metals.
23. The method of claim 13, wherein the water absorbing polymer
comprises crosslinked polyacrylamide, polyacrylate, or copolymers
thereof.
24. A method of retarding the flow of water in a subterranean
formation, comprising: injecting a gelling pill into flow channels
in the formation, the gelling pill comprising: brine; a
crosslinkable xanthan gum; and borate crosslinkant solids; and
allowing the borate crosslinkant solids to permeate a region of the
formation surrounding the flow channels; and triggering
crosslinking between the xanthan gum and borate crosslink with
magnesium oxide to form a gel in the subterranean formation.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments disclosed herein relate generally to methods and
compositions for retarding or inhibiting the flow of water in a
subterranean formation.
[0003] 2. Background Art
[0004] Hydrocarbons accumulated within a subterranean
hydrocarbon-bearing formation are recovered or produced therefrom
through production wells drilled into the subterranean formation.
When production of hydrocarbons slows, one or more injection wells
may be drilled into the formation, into which fluid may be injected
to enhance production by displacing or sweeping hydrocarbons
through the formation so that they may be produced from production
well(s). One type of such recovery operation uses field water or
field brine as the injection fluid, which is referred to as a
waterflood. Fluids injected later can be referred to as driving
fluids. Although water is the most common, injection and drive
fluids can include gaseous fluids such as steam, carbon dioxide,
and the like.
[0005] While conventional waterflooding is generally the most cost
effective method for obtaining additional hydrocarbons from a
reservoir, it has a number of shortcomings. Foremost among these
shortcomings is excess water and decreased oil production in some
of the offset producing wells in the field and not in others, which
results in increased production costs and reduced oil production
rate. In many instances, poor performance is thought to be a result
of water moving rapidly through high permeability channels or
through natural or induced fractures. Induced fractures are often
the result of over-pressuring the formation at some point. In other
instances, water breakthrough may be related to permeability
contrasts between different layers, which may or may not be in
vertical communication in the reservoir.
[0006] Additionally, in some extreme cases, the waterflood
channeling continues until a water breakthrough occurs such that
large quantities of water drive fluid may channel directly from the
injection well to a production well. This phenomenon most often
occurs in heterogeneous reservoirs. When this occurs, not only are
large volumes of water produced, which in and of itself is
problematic, but also the fluid flow between the injection well and
the production well likely bypasses pockets of oil.
[0007] Accordingly, there exists a continuing need for improvements
in diverting agents and plugs to reduce or prevent water flow
through a formation.
SUMMARY OF INVENTION
[0008] In one aspect, embodiments disclosed herein relate to a
method of retarding the flow of water in a subterranean formation
that includes injecting a gelling pill into the formation, the
gelling pill comprising: brine; a crosslinkable polymer; and a
crosslinkant; and allowing the crosslinkable polymer to crosslink
to form a gel in the subterranean formation.
[0009] In another aspect, embodiments disclosed herein relate to a
method of retarding the flow of water in a subterranean formation
that includes introducing an effective amount of a gelling pill
into flow channels in the formation, the gelling pill comprising:
brine; a crosslinkable polymer; a crosslinkant; and a water
absorbing polymer allowing the water absorbing polymer to permeate
a region of the formation surrounding the flow channels; and
allowing the crosslinkable polymer to crosslink to form a gel in
the flow channel in the formation.
[0010] In yet another aspect, embodiment disclosed herein relate to
a method of retarding the flow of water in a subterranean formation
that includes injecting a gelling pill into flow channels in the
formation, the gelling pill comprising: brine; a crosslinkable
xanthan gum; and borate crosslinkant solids; and allowing the
borate crosslinkant solids to permeate a region of the formation
surrounding the flow channels; and triggering crosslinking between
the xanthan gum and borate crosslink with magnesium oxide to form a
gel in the subterranean formation.
[0011] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
DETAILED DESCRIPTION
[0012] In one aspect, embodiments disclosed herein relate to
methods and diverting agents for retarding or inhibiting the flow
of water through a region of a subterranean formation. As described
above, during production operations, it is often desirable to
retard or inhibit the flow of water through a particular region of
a formation by adjusting its permeability. Such treatments/agents
used are frequently referred to in the art as diverting
treatments/agents as they divert a flow path of the fluid. The
diverting agent of the present disclosure may be a hardened gel or
plug of a crosslinked polymer formed in a formation, such as along
a flow channel in the formation. To form such a diverting plug in
situ, a gelling pill comprising a crosslinkable polymer and
crosslinkant may be emplaced downhole. The gelling pills of the
present disclosure also include a water absorbing polymer
therein.
[0013] Crosslinked Polymer
[0014] The crosslinkable polymer of the present disclosure may be
selected from any such polymers well known in the art.
Representative polymers include various hydratable polysaccharides
or polysaccharide derivatives such as xanthan gum, guar gum,
hydroxyalkylguar, hydroxyalkylcellulose,
carboxyalkylhydroxyalkylguar, wellan gum, gellan gum, diutan,
scleroglucan, succinoglucan, various celluloses, biopolymers, and
the like. The amount of crosslinkable polymer may vary; however,
suitable amounts may range from 0.5 to 5 lb/bbl, depending on
various factors such as the particular application, viscosity,
etc.
[0015] In a particular embodiment, the crosslinkable polymer is
preferably a xanthomonas gum (xanthan gum). Xanthomonas gum is a
widely used viscosifier and suspending agent in a variety of
fluids, which can be made by the fermentation of carbohydrate with
bacteria of the genus Xanthomonas.
[0016] As a crosslinkant, any suitable crosslinking ion, metal
containing species, or mixture of such ions and species may be
employed. Accordingly, as used herein, the term "crosslinked" is
understood to include crosslinking attributable to certain ions or
metal containing species, such as borate ion. The crosslinking ions
or species may be provided, as indicated, by dissolving into the
solution compounds containing the appropriate ions/metals, or by
other means. In a particular embodiment, the crosslinking ion is
provided in a compound which only partial or sparingly partial
solubility. Exemplary ions or metal containing species include
those of boron, calcium, zinc, zirconium, and titanium, supplied
from compounds such as boric acid, sodium borates, boron oxide,
zirconium oxide, and titanium oxide. One of ordinary skill in the
art would appreciate that depending on the conditions present when
the crosslinkable polymer and crosslinkant are combined,
crosslinking may be virtually immediate or may be delayed by means
known in the art to allow for mixing and pumping of the gelling
pill through surface equipment to be formed downhole in situ.
[0017] Such compounds may be provided as solid materials, and may
have a broad size range. For example, in various embodiments,
crosslinkant solids may range from 0.1 nm to 100 microns in size.
One of ordinary skill in the art would appreciate that a particular
size range may be selected depending on the particular application.
For example, if it is desirable for the solids to permeate into the
formation, smaller sized solids may be desirable. Further, the
concentration of added crosslinkant may be dependent on factors
such as the temperature, the amount of crosslinkable polymer
employed, the firmness of the gel desired, and presence of water
absorbing polymers (described below) and may range from up to 75
ppb (preferably up to 50, 30, or 25 ppb in various other
embodiments) when water absorbing polymers are added to the pill
and from up to 200 ppb (preferably up to 150, 100, or 50 ppb in
various other embodiments). For example, when a pill is formed with
the addition of the water absorbing polymers described below, to
allow for the polymers to absorb any water (and swell), the formed
gel should have sufficient flexibility for such phenomenon to
occur. In such a situation, a lower amount of crosslinkant may be
desirable. However, when no water absorbing polymers are included,
greater amounts of crosslinkant materials may be desirable to form
a firmer gel.
[0018] In a particular embodiment, hydrated borates of alkali
metals and/or alkaline earth metals, such as sodium borates,
calcium borates, and sodium calcium borates may be used as the
crosslinkant. Ulexite, NaCaB.sub.5O.sub.9.8H.sub.2O, and
probertite, NaCaB.sub.5O.sub.9.5H.sub.2O, are representative
hydrated alkali metal alkaline earth metal borates. Colemenite,
Ca.sub.2B.sub.6O.sub.11.5H.sub.2O, is a representative alkaline
earth metal borate. Use of borates in such a manner is described in
U.S. Pat. No. 4,620,596, which is incorporated herein by
reference.
[0019] When crosslinking xantham gum with a borate, a pH of at
least 8, and a pH ranging from 8 to 13 and 9 to 12 in particular
embodiments is necessary to initiate crosslinking. Thus, the
addition of a crosslink initiator that will trigger the
crosslinking may be used to allow for control of the gellation of
the pill. Such control may allow for sufficient delay in the
crosslinking so that the gelling pill may emplaced in a target zone
and permeate the formation to any necessary extent prior to
hardening/formation of the gel. In the embodiment where xanthan and
borate are used to form the crosslinked polymer of the present
disclosure, a crosslink initiator such as magnesium oxide,
potassium hydroxide, etc that will raise the pH to trigger
crosslinking may be used. DI-BALANCE.TM., which is commercially
available from TBC-Brinadd (Houston, Tex.) is an example of an
inorganic oxide that may be used as a crosslink initiator in the
embodiments disclosed herein. Further, one of ordinary skill in the
art would also appreciate that other compounds such as lime,
caustic soda, alkyl, aryl, and alkaryl amines, and calcium
chloride. However, one of ordinary skill in the art would
appreciate that some of these compounds may cause rapid setting and
their use may be tailored depending on the application (e.g., when
using small pills with fast pumping rates). Conversely, various
alkyl, aryl, and alkaryl amines may be less soluble in the
remainder of the pill and would therefore be slow to release their
pH-increasing chemistry, resulting in a slow setting. Alternative
slow-release crosslinking initiators would be obvious to one
skilled in the art.
[0020] Depending on the conditions necessary for crosslinking to
occur, one of ordinary skill in the art would appreciate that
buffering agent(s) may also be used to affect the pH of the gelling
pill to allow for greater control over crosslinking/gellation.
Thus, the combination of a weak acid and its salts may be employed,
including, for example, the corresponding acid and ammonium and
alkali metal phosphates, carbonates, bicarbonates,
sesquicarbonates, acetates, or mixtures thereof. Ammonium,
potassium, and sodium carbonates, bicarbonates, sesquicarbonates
and hydrogen phosphates are preferred as buffer salt components.
However, one of ordinary skill in the art would appreciate that
other compounds may be used, such as for example, diethanolamine.
Proportioning of the buffer components of the combinations to
achieve the desired pH is well within the ambit of those skilled in
the art. The amount of buffer used may be an effective amount,
i.e., an amount sufficient to maintain the desired pH, given the
additives and other components of the pill, which may range, for
example, up to 50 pounds per 1000 gallons of fluid. Further, in a
particular embodiment, acceleration or retardation of crosslinking
may be achieved with the addition of calcium chloride or magnesium
chloride, respectively. One of ordinary skill in the art would
appreciate that use of an accelerant such as calcium chloride may
find particular use in a cold temperature environment.
[0021] Water Absorbing Polymer
[0022] The water absorbing polymer may include crosslinked
polyacrylamide, polyacrylate, or copolymers thereof. Particularly,
the water absorbing polymer may include a copolymer of
polyacrylamide that may be crosslinked internally via amide groups
or an additional crosslinking agent, or two strands of sodium
polyacrylate crosslinked with bis(acrylamide). The amount of water
swellable polymer may vary; however, in a particular embodiment, a
suitable amount may range from 0 to 30 lb/bbl.
[0023] In other embodiments, the water absorbing polymer may
include carboxylate containing polymers such as polyacrylates,
polyaspartates, and polylacetates, sulfonate containing polymers,
quaternary or cationic amine containing polymers such as
polyallylamine or polyethyleneimine, and polyacrylamide, polyvinyl
alcohol gels, and polyurethane gels. Water absorbing polymers and
the process for making such polymers suitable for embodiments of
the present disclosure, include those described in U.S. Pat. Nos.
4,618,631, 4,698,404, 4,755,560, 6,222,091, 6,376,072, and
6,750,262, which are herein incorporated by reference in their
entirety. Some of these various water absorbing polymers have had
specific application in the disposable diaper and agricultural
water retention industries because of their ability to absorb up to
400 times their weight in water.
[0024] The absorbance capacity of the water absorbing polymers may
be explained by the matrix-like structure of dry water absorbing
polymer particle. The dry polymer may contain charged species
within the matrix, such that the ionization of the polymer will
cause the matrix network to open and create cavities that may
absorb water by capillary action. Water absorbed into the polymer
may be retained by hydrogen bonds that form between the charged
species and the water. The actual mechanism for water absorbance
and retention may vary based on the structure of a particular water
absorbing polymer. For example, sodium polyacrylate, in the dry
powdered state, contains a coiled backbone, lined with carboxyl
groups. When exposed to an aqueous solution, the carboxyl groups
dissociate into negatively charged carboxylate ions, which may
repel one another along the polymer chain.
[0025] The repelling carboxylate ions thereby widen the polymer
coils and allow water to move into contact with inner carboxyl
groups, further continuing the widening or swelling of the polymer.
Water is retained within the polymer due to hydrogen bonding
between the water and the carboxylate ions on the polymer.
Polyacrylamide, another water absorbing polymer, is structurally
similar to polyacrylate but substitutes amide groups for the
carboxyl groups on the polymer backbone. Free, unlinked amide
groups, because they contain --NH.sub.2 groups, can form hydrogen
bonds with water. Further, because of the crosslinking that exists
in these water absorbing polymers, the water absorbing polymers
remain insoluble in an aqueous solution.
[0026] In specific embodiments, gelling pills employ POLYSWELL.TM.,
available from M-I LLC (Houston, Tex.), which is an anionic
acrylamide based copolymer formulation, as the water absorbing
polymer component of the gelling pill.
[0027] Base Fluid
[0028] To prevent premature swelling of the water absorbing
polymers of the present disclosure, an aqueous base fluid other
than fresh water may be used. Such base fluids may include an
aqueous fluid such as fresh water, sea water, a brine containing
organic and/or inorganic dissolved salts, liquids containing
water-miscible organic compounds and combinations thereof and
similar compounds that should be known to one of skill in the art.
However, one of ordinary skill in the art would appreciate that the
selection of the base fluid may depend, for example, on the
hydration of the crosslinkable polymer and/or the presence of a
water absorbing polymer, so as to allow for hydration of the
crosslinkable polymer yet minimize the amount of water absorbance
by the water absorbing polymer prior to placement in the
formation.
[0029] Brines suitable for use as the base fluid of the pills
disclosed herein according to various embodiments of the present
disclosure may include seawater, aqueous solutions wherein the salt
concentration is less than that of sea water, or aqueous solutions
wherein the salt concentration is greater than that of sea water.
The salinity of seawater may range from about 1 percent to about
4.2 percent salt by weight based on total volume of seawater. The
solutions, depending on the source of the seawater, typically
contain metal salts, such as but not limited to, transition metal
salts, alkali metal salts, alkaline earth metal salts, and mixtures
thereof. Exemplary salts include halides of zinc, calcium, and
mixtures thereof. For example, the solution can include zinc
halide, such as zinc bromide or zinc chloride or both, optionally
in combination with calcium bromide or calcium chloride or both.
Salts that may be found in seawater include, but are not limited
to, sodium, calcium, aluminum, magnesium, potassium, strontium, and
lithium salts of chlorides, bromides, carbonates, iodides,
chlorates, bromates, formates, sulfates, silicates, phosphates,
nitrates, oxides, and fluorides. Salts that may be incorporated in
a given brine include any one or more of those present in natural
seawater or any other organic or inorganic dissolved salts.
Additionally, brines that may be used in the drilling fluids
disclosed herein may be natural or synthetic, with synthetic brines
tending to be much simpler in constitution. In one embodiment, the
density of the drilling fluid may be controlled by increasing the
salt concentration in the brine (up to saturation). In a particular
embodiment, a brine may include halide or carboxylate salts of
mono- or divalent cations of metals, such as cesium, potassium,
calcium, zinc, and/or sodium. The brine solution can include the
salts in conventional amounts, generally ranging from about 1% to
about 80%, and preferably from about 20% to about 60%, based on the
total weight of the solution, although as the skilled artisan will
appreciate, amounts outside of this range can be used as well. In a
particular embodiment, the brine may be a NaCl or KCl brine.
[0030] Aging Temperature
[0031] In various embodiments, the gel mechanism may be temperature
dependent.
[0032] Thus, some gelling pills may preferentially cure at elevated
temperatures such as about 60 to 100.degree. C., while yet others
may cure at higher temperatures such as 100-200.degree. C. However,
one of ordinary skill in the art would appreciate that, in various
embodiments, the reaction temperature may determine the amount of
time required for gel formation.
[0033] Time Required for Gel Formation
[0034] Embodiments of the gels disclosed herein may be formed by
mixing a crosslinkable polymer, crosslinkant, and an optional
crosslinking initiators. In some embodiments, a gel may form
immediately upon mixing the components. In other embodiments, a gel
may form within 1 minute of mixing; within 5 minutes of mixing in
other embodiments; within 30 minutes of mixing in other
embodiments. In some embodiments, a gel may form within 1 hour of
mixing; within 8 hours in other embodiments; within 16 hours in
other embodiments; within 80 hours in other embodiments; within 120
hours in yet other embodiments.
[0035] Gel Viscosity
[0036] In some embodiments, the pill may initially have a viscosity
greater than water (for pumping purposes) yet low enough that the
pill may effectively penetrate voids, small pores, and crevices,
such as encountered in fine sands, coarse silts, and other
formations. In other embodiments, the viscosity may be varied to
obtain a desired degree of flow sufficient for decreasing the flow
of water through or increasing the load-bearing capacity of a
formation. The viscosity of the solution may be varied by
increasing or decreasing the amount of base fluid relative to the
polymer components, by employing other viscosifying agents, or by
other techniques common in the art.
[0037] Gel Hardness
[0038] The reaction of the crosslinkable polymer and crosslinkant
may produce gels having a consistency ranging from a viscous sludge
to a hard gel. In some embodiments, the reaction of the two
components may result in a soft gel. In other embodiments, the
reaction may result in a firm gel and in a hard gel in yet other
embodiments. The hardness of the gel is the force necessary to
break the gel structure, which may be quantified by measuring the
force required for a needle to penetrate the crosslinked structure.
Hardness is a measure of the ability of the gel to resist to an
established degree the penetration of a weighted test needle.
[0039] Hardness may be measured by using a Brookfield QTS-25
Texture Analysis Instrument. This instrument consists of a probe of
changeable design that is connected to a load cell. The probe may
be driven into a test sample at specific speeds or loads to measure
the following parameters or properties of a sample: springiness,
adhesiveness, curing, breaking strength, fracturability, peel
strength, hardness, cohesiveness, relaxation, recovery, tensile
strength burst point, and spreadability. The hardness may be
measured by driving a 4 mm diameter, cylindrical, flat faced probe
into the gel sample at a constant speed of 30 mm per minute. When
the probe is in contact with the gel, a force is applied to the
probe due to the resistance of the gel structure until it fails,
which is recorded via the load cell and computer software. As the
probe travels through the sample, the force on the probe and the
depth of penetration are measured. The force on the probe may be
recorded at various depths of penetration, such as 20, 25, and 30
mm, providing an indication of the gel's overall hardness.
[0040] In some embodiments, the resulting gel may have a hardness
value from 10 to 100000 gram-force. In other embodiments, the
resulting gel may be a soft elastic gel having a hardness value in
the range from 10 to 100 gram-force. In other embodiments, the
resulting gel may be a firm gel having a hardness value from 100 to
500 gram-force. In other embodiments, the resulting gel may range
from hard to tough, having a hardness value from 500 to 100000
gram-force; from 1500 to 75000 gram-force in other embodiments;
from 2500 to 50000 gram-force in yet other embodiments; from 5000
to 30000 gram-force in yet other embodiments.
[0041] With respect to the variables listed above (i.e.
temperature, time, etc.), those having ordinary skill in light of
the disclosure will appreciate that, by using the present
disclosure as a guide, properties may be tailored as desired.
[0042] Methods of Use
[0043] In accordance with various embodiments of the present
disclosure, the various components of the gelling pill may be added
simultaneously or in any combination separately to mix the polymer
and crosslinkant within the formation to generate the gel in situ.
Regardless of the order of emplacement, the gelling pill components
will preferentially travel to the more permeable zones within the
formation and gel, rendering these zones less permeable to
subsequent fluid flow.
[0044] As stated above, the gelling pills and gels produced
therefrom may find particular use as profile modification agents in
enhanced oil recovery operations using injection of driving fluids
such as water or other fluids to increase oil production. In
particular, the pills may be useful for decreasing the permeability
of selected portions of underground formations prior to or during
secondary or tertiary recovery operations and also for water shut
off treatments in producing wells or in communications between
injection and producing wells.
[0045] For example, in an enhanced oil recovery operation, when a
conventional waterflood or gas drive is performed and the drive
fluid brakes through into the production well in excessive amounts,
a gelling pill of the present disclosure may be pumped down the
injection well and into the formation in any suitable manner and in
any suitable amount, and for any desired length of time sufficient
to obtain the desired in-depth penetration, gel formation and
consequent permeability reduction in the high permeability zones
(or flow channels) of the formation.
[0046] Such treatments may find particular use in rehabilitating a
formation through which a conduit or flow channel connecting an
injection well and producing well has been formed, such as
naturally or induced fractures through the formation. By pumping a
pill of the present disclosure into the conduit or flow channel,
the crosslinkable polymer may crosslink to form a gelled plug.
Without being bound to any particular mechanism, it is theorized
that for pills consisting essentially of crosslinkable polymers and
crosslinkants (without any water absorbing polymers), crosslinkant
solids may be sufficiently small to invade or permeate the
formation, which would result in a formed plug that has not only
filled a conduit or flow channel, but has also stretched into the
surrounding formation. Following gelling of the pill, the formation
becomes part of the pill, providing added stability to the plug and
formation, and reducing or preventing the likelihood of the plug
being washed out.
[0047] It is also theorized for pills possessing water absorbing
polymers therein that following the formation of the gelled plug,
any additional water (either formation water or injected water)
that comes into contact with the pill will be absorbed by the water
absorbing polymer. It is further theorized that such absorbance
will cause swelling of the polymer, pushing the pill further into
the formation and formation lattice, and may provide additional
stability to the particular area.
[0048] Alternatively, the formation may be treated prior to
carrying out the fluid drive secondary recovery operations. This
may be particularly applicable where there is good knowledge of the
nature of the formation. Thus, in a formation where the oil-bearing
strata are interspersed with more permeable porous strata which
contain no oil or an insufficient amount of oil to make secondary
recovery operations economical, but which more permeable strata
would still act as a thief zone, the formations may be treated in
accordance with the embodiments of the present disclosure prior to
initiating the fluid drive operation.
[0049] In still another embodiment, the pills may be applied to
producing wells, either oil wells or gas wells, where there is a
more porous nonhydrocarbon-bearing strata adjacent the
hydrocarbon-bearing strata. For example, such a condition can exist
where there is water sand adjacent the hydrocarbon-bearing sand and
the water intrudes into the borehole and interferes with the
production of hydrocarbons. In such instances, the formation may be
treated in accordance with the present disclosure to shut off the
flow of water. The method of carrying out such a water shutoff
treatment is substantially the same as described above in
connection with fluid drive operations. It is also within the scope
of the invention to carry out the gel injection techniques of the
present disclosure periodically or intermittently, as needed,
during the course of a fluid drive secondary operation, or during
the production of oil from a producing well.
[0050] In all of the above operations, the injection of the gelling
pill of the present disclosure may be carried out in any
conventional manner. Gels injected in accordance with the present
disclosure may be prepared in advance, stored in suitable tanks,
and then pumped into the well; or said gels may be formed in a
conduit leading to the injection well, or in the tubing in the well
itself, and then injected into the formation, or may be formed in
situ. If desired, selected portions of the formation may be
isolated mechanically, as by the use of packers, and other means
known to the art, for treatment in accordance with the present
disclosure. Further, spacer slugs as known in the art, such as a
NaCl or KCl slug, may be used to lead and/or follow the gelling
pill slug, or may be used to separate gel components when emplacing
the components sequentially.
[0051] Further, as the crosslinking and gel formation of the
present disclosure are pH dependent, should any placed pill need to
be removed, etc., an acidizing treatment may allow for the removal
of the plug formed downhole.
[0052] Exemplary Formulations
[0053] One formulation for one example of gelling pill that may be
used is shown below in Table 1. FLOVIS.RTM. PLUS (a xantham gum)
and POLYSWELL.TM. (an anionic acrylamide based copolymer) are
available from M-I LLC (Houston, Tex.). DI-BALANCE.TM. (magnesium
oxide) is available from TBC-Brinadd (Houston, Tex.). The pill is
formulated by adding the FLOVIS.RTM. PLUS, ulexite (borate ore),
and DI-BALANCE.TM. together in the NaCl brine, followed by the
addition of the POLYSWELL.TM., and allowing the pill to set up.
TABLE-US-00001 TABLE 1 10.0 PPG NaCl bbl 0.915 FLO-VIS .RTM. PLUS
grams 1.0 Ulexite (fine ground) grams 25.0 DI-BALANCE grams 12.0
POLYSWELL .TM. grams 21.0 (ultra fine dry)
[0054] Another formulation for a gelling pill that may be used is
shown below in Table 2. FLOVIS.RTM. PLUS (a xantham gum) and
POLYSWELL.TM. (an anionic acrylamide based copolymer) are all
available from M-I LLC (Houston, Tex.). DI-BALANCE.TM. (magnesium
oxide) is available from TBC-Brinadd (Houston, Tex.). The pill is
formulated by adding the FLOVIS.RTM. PLUS, ulexite (borate ore),
and DI-BALANCE.TM. together in the NaCl brine, followed by the
addition of the POLYSWELL.TM., and allowing the pill to set up.
TABLE-US-00002 TABLE 2 10.0 PPG NaCl bbl 0.915 FLO-VIS .RTM. PLUS
grams 2.0 Ulexite (fine ground) grams 25.0 DI-BALANCE .TM. grams
12.0 POLYSWELL .TM. grams 14.0 (ultra fine dry)
[0055] Yet another formulation for a gelling pill that may be used
is shown below in Table 3. FLOVIS.RTM. PLUS (a xantham gum) is
available from M-I LLC (Houston, Tex.). DI-BALANCE.TM. (magnesium
oxide) is available from TBC-Brinadd (Houston, Tex.).
TABLE-US-00003 TABLE 3 Fresh water bbl 0.92 FLO-VIS .RTM. PLUS ppb
3.0 Ulexite (fine ground) ppb 50 Evaporated NaCl ppb 18.0
DI-BALANCE .TM. ppb 12.0 Dry CaCl.sub.2 ppb 25.0
[0056] Advantageously, embodiments of the present disclosure for at
least one of the following. Modifying the fluid flow profile of the
formation in the ways described above may provide a substantial
decrease in the volume ratio of water:oil produced from the
formation at production wells, thereby improving the overall oil
recovery and economics of the operation. Moreover, the pill
compositions of the present disclosure may provide a more permanent
solution to troubling issues with water production. In particular,
in addition to providing a diversion for immediate water flow,
problems associated with subsequent water flows that have typically
caused erosion of the formation and washing away of conventional
diverting plugs may be minimized by the absorbance of such later
appearing water by components within the originally placed
pill.
[0057] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *