CA1092797A - Method for controlling permeability of subterranean formations - Google Patents
Method for controlling permeability of subterranean formationsInfo
- Publication number
- CA1092797A CA1092797A CA291,282A CA291282A CA1092797A CA 1092797 A CA1092797 A CA 1092797A CA 291282 A CA291282 A CA 291282A CA 1092797 A CA1092797 A CA 1092797A
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- Prior art keywords
- polymer
- water
- fluid
- microgels
- hydrocarbon
- Prior art date
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Abstract
ABSTRACT OF THE DISCLOSURE
In the recovery of hydrocarbon materials from subterrancan formations, the simultaneous production of loss of other fluids such as water is inhibited by the selective introduction into the subterranean porous structure of discrete spheroidal microgels of a water--swollen or water-swellable, crosslinked polymer such as crosslinked polyacrylamide.
In the recovery of hydrocarbon materials from subterrancan formations, the simultaneous production of loss of other fluids such as water is inhibited by the selective introduction into the subterranean porous structure of discrete spheroidal microgels of a water--swollen or water-swellable, crosslinked polymer such as crosslinked polyacrylamide.
Description
lOg~797 This invention relates to methods for the pro-duction of hydrocarbon materials such as oil and natural -gas by the recovery of such hydrocarbon materials from sub-terranean oil bearing reservoirs.
One of the more significant problems attendant -to the recovery of hydrocarbon materials from subterranean ---formations is the concommitant recovery of undesirable fluids such as water. Such recovered water can be brine native to the formation or it can be injection water em-ployed in enhanced oil recovery treatments being applied to the reservoir. Whatever the source, there is an upper -limit beyond which water production can no longer be - -~
tolerated and its further entry into the producing well - --bore must be reduced. In addition other fluids such as natural gas are sometimes undesirable particularly when such fluids exceed the upper limits of gas:oil ratio desired for most efficient recovery of the hydrocarbons. -.. . .:: .. ~
As is well known, many oil reservoirs comprise layers or zones of porous rock which can vary in perme-ability from less than 10 millidarcies to more than 1000 `
millidarcies. Regardless of whether the~undesired fluid~ `
is a natural drive fluid or one coming from an enhanced oil recovery operation, there is a real tendency for -the drive fluid to channel along or through the more permeable zones of the formation. Such channeling, often called fingering, generally hinders or prevents the recovery of oil from less permeable zones. For example, the more permeable zones, after oil has been largely -displaced therefrom, function as thief zones which permit ---the drive fluid to channel directly into the production -or recovery well. - ;
1~,379-F -1-X I ,, ... . . .
10~7g7 Among the prior solutions to the problem of --undesirable fluid entry into the production well is the ~
placement of a solid plug of a material such as cement -within the formation. Unfortunately, such solid plugs often inhibit the use of drive fluids to assist in forcing _-~
desired hydrocarbon material from the formation into the producing or recovery well bore. In addition the use -_ of such solid plugs invariably results in the permanent -_ _ loss of desired fluids. Further, should the undesirable fluids seep by or otherwise bypass such solid plugs, the plug cannot shift position to block such seepage or other - _ changes in flow pattern of the undesired fluid.
In order to overcome the deficiencies associated with the use of solid plugs, it has been a common practice to modify the mobility of the driving fluid by pumping a : ~
highly viscous fluid into the oil bearing formation. An ~
illustration of this technique is the incorporation of a --partially hydrolyzed polyacrylamide in an aqueous drive fluid such as described in U.S. Patent No. 3,039,529. ~_ While the recovery of hydrocarbon by employing such -_-techniques is measurably enhanced, substantial quantities -~
of polymers must be added to the drive fluid in order to maintain the desired high viscosity. Moreover in --cases of highly porous subterranean structures which _--are proximate to oil bearing formations of relatively ~ ~
low permeability, substantial quantities of the unde~
sirable drive fluid are often recovered. -More recently, as disclosed in U.S. Patent ; -Nos. 3,780,806 and 3,785,437, it has been a practice to attempt to plug some of the more porous formations by 18,379-F -2-~' .
10~;~7~7 ..
- .
introducing a water soluble polymer into the highly porous structure and crosslinking the polymer in situ to form a water-insoluble gel. Alternatively, as disclosed in U.S.
Patent No. 3,921,733, attempts have been made to pump a -partially gelled polymer into a porous formation ahead of the drive f~uid. All of these procedures suffer from handling problems characteristic of two component systems comprising a polymer and a crosslinking agent. For example, most of the ~-procedures involve the addition of a dry polymer to an aqueous medium at the well site which gives rise to difficulties in solubilizing the polymer. More importantly, it is difficult to control the gelation characterisitics of the polymer as needed to insure effective control of formation permeability.
In view of the deficiencies of prior art methods for controlling permeability in subterranean structures as needed -for recovery of hydrocarbon materials, it would be highly :desirable to provide an improved oil recovery method which essentially eliminates many of the problems characteristic of the aforementioned in situ gelation techniques.
The present invention provides such an improved ~:
oil recovery method whereby the fluid permeability of a ~-subterranean geological formation is modified, preferably to restrict the passage of fluids (particularly aqueous fluids) .-therethrough. Alternatively, such modification of the fluid permeability of ~he formation can be expressed as controlling the mobility of fluids in the fo mation. In the practice --of this invention, the desired control of fluid mobility -is achieved by introducing into the subterranean formation, preferably via a well bore, a fluid medium containing dis-crete, spheroidal microgels of a water-swellable or ---water-swollen, crosslinked polymer in an amount sufficient to control the mobility of fluids in the subterranean formation. ~-. . .
, 18,379-F - 3 -:' , ~
10~;~79'7 '~.
The microgels have partly or totally water-swollen diameters which are generally within the range from 0.5 to 200 micrometers and are very useful in treatment of porous subterranean strata that are commonly found in --hydrocarbon bearing formations. The m~rogels when dispersed .,,,,~
in water or other aqueous media exist as discrete, spheroidal, water-swollen particles which can be separated from the aqueous media by filtration or other similar technique.
The fluid medium containing the microgels is most -advantageously low in viscosity and therefore much more easily pumped into the desired porous formation than are conventional high viscosity water-soluble polymers or partially -gelled polymers used hereinbefore. This advantageous -property is believed to be due to the discrete, spheroidal characteristics of the microgels as well as to their relatively controlled particle size and crosslinked character.
These characteristics enable the microgels to penetrate deeply into the pores of the porous structure to be restricted or plugged. Surprisingly, the microgels are not readily displaced even when the direction of liquid flow in the subterranean structure is reversed.
Accordingly, the improved method of the present invention is most advantageously employed in enhanced oil recovery operations wherein a drive fluid is introduced through a bore hole in the earth into a porous subterranean ~
formation penetrated by said bore hole thereby driving oil from oil bearing structures toward a producing well. In ---addition such fluid media containing the microgels are usefully employed as the fluid in well drilling operations, E
as packer fluids in well completion operations and as ---~
mobility control fluids in other enhanced oil recovery operations. Methods using such media in drilling operations, in well completion operations, and as friction reduction aids in normal water flooding operations as well as in '~:
- 18,379-F - 4 -'' X
109;~797 ~'~
fracturing processes are additional aspects of the invention. .-~.
It is further observed that fluid media containing the micro- :.
.......
gels are very useful in the treatment of subterranean .-:
structures containing substantial amounts of salt water or brine which normally hinder or prevent the gelation reactions required in in situ gelation procedures. ~:
The present invention particularly resides in a .....
hydrocarbon recovery method wherein a production well penetrates --a porous subterranean formation having at least a hydro-carbon-bearing stratum and adjacent thereto at least one ~.:
stratum bearing an aqueous fluid, comprising the steps of ~
introducing into the subterranean formation via the production ...
well bore a fluid medium containing discreteJ spheroidal .....
microgels of a water-swellable or water-swollen, crosslinked ......
polymer of an ethylenically unsaturated water-soluble monomer(s) ...
in an amount sufficient to reduce the fluid permeability of the ..
porous formation, and wherein said microgels are in at least a partially water-swollen state with diameters in the range from 0.5 to 200 micrometers, said polymer being crosslinked ....
with from S to 200 weight parts of a copolymerizable poly- ...
ethylenic monomer per million parts of the total monomers of ~
the polymer thereby controlling the flow of the aqueous ~.-.
fluid into the well bore. E:
The present invention also reside in an enhanced ,--oil recovery method .in which an aqueous drive fluid is injected through an injection well bore into a hydrocarbon-bearing nonfractured formation having hydrocarbon-deficient and hydrocarbon-rich zones to drive hydrocarbon from the formation ..
to a recovery well, the improvement wherein an aqueous fluid ~
medium containing discrete, spheroidal microgels of a water--swellable or water-swollen, crosslinked polymer of ethylenically -`..
unsaturated water-soluble monomer(s) is introduced through ... :.
the injection well bore into the formation in an amount sufficient to reduce the aqueous fluid permeability of the : :
.. ..
.......
18,379-F ~ 5 ~
.
.
.
-5a- 109~797 porous formation, said microgels in at least a partially water-swollen sta~e having diameters in the range from about 0.5 to about 200 micrometers, thereby restricting the passage of the drive fluid into hydrocarbon-deficient zones of the formation but not substantially impeding the passage of the drive fluid through hydrocarbon-rich zones of the formation.
Reference is hereby also made to a copending Application No. 291,355, filed November 21, 1977 claiming an invention by M. L. Zweigle et al. for a composition which comprises discrete, spheroidal microgels of a water-swellable or water-swollen polymer of water-soluble ethylenically i~ unsaturated monomer, said polymer being sufficiently cross-linked to enable the microgels to remain discrete and retain spheroidal shape upon being dispersed in an ~ aqueous fluid medium, said microgels in at least a partially F~'~ water-swollen state having diameters in the range from 0.5 to 200 micrometers.
The application also claims a method for thickening ` 20 an aqueous medium to obtain a composition having the properties of a viscous short solution and being resistant to viscosity degradation under conditions of high shear which comprises the step of thoroughly dispersing in said medium from 0.1 to 2 percent by weight of microbeads of a water-insoluble, ^~ 25 water-swellable polymer of a water-soluble vinyl monomer -~ or mixture of water-soluble vinyl monomers, cross-linked with a difunctional cross-linking agent copolymerizable with said monomer or monomers, said microbeads having - diameters of from 0.2 to 4 microns in the dry state and having a gel capacity of at least about 10 grams per gram :
~ 379-F -5a-.
.. .
~ -5b- 109~797 in aqueous 0.27 molar sodium chloride solution, said cross--linking agent being present in an amount from 50 to 1000 parts by weight of cross-linking agent per million parts of vinyl monomer or monomers in the polymer.
The microgels which are essential to the practice of the present invention are generally characterized as discrete, well defined spheroids that are water-swellable and/or water-swollen. In their water-swollen or at least partially water-swollen state, the microgels comprise water and a crosslinked polymer of a water-soluble ethyleni-cally unsaturated monomer. Perhaps one of the most signi-ficant characterisitics of the microgels is their ability . to absorb substantial proportions of water. In their partially or totally water-swollen state, the ,.
.:
~ /
' ' .
. .
' ' 18,~ 9-F -5b-lQ9;~797 , par~ic1e si (~; o~ Lll~ ~li r~J~ a~ n(Je from a}~out 0.5 to ahout ~Oo n-llc ~ ers, pr~:f~Ya~]y rroln ab~ut 1 to abollt 10 micrometcri. In ~'ae cl~y state, the rnicroyels , ~ exist as microbeads h.-vincJ diarn~Lers cJenerally less than about 20 microMeters, preferably less than about 1 ~ micrometer. In their partially water-swollen (pre-inversion) s state, the rnicrogels are water--swellable and contain at ~ least abou' 30 weight percent of crosslinked polyrner and I up to about 70 weight percent of water. In their totally water-swollen state, the microgels contain up to about 99.9 weight percent of water and as little as about 0.1 weight percent of crosslinked polymer. The microgels, when , dispersed in a fluid aqueous medium such as water, can be subjected to substantial amounts of high shear, e.g., >500,000 sec 1, which is characteristic of the pumping actlon existing in many enhan~eu oii reco-~ery operation~
without undergoing substantial degradation, i.e., loss of particle size or capacity to hold water (often called gel ~ capacity).
¦- 20 Ethylenically unsaturated monomers suitable t for use in preparing the microgels are those which are ~ sufficiently water-soluble to form at least 5 weight ¦ percent solutions when dissolved in water and which ~ readily undergo addition polymerization to form polymers which are at least inherently water dispersible and ~, preferably water~soluble. By "inherently water dis-, s persible", it is meant that the polymer when contacted with an aqueous medium will disperse therein without the aid of surfactants to form a colloidal dispersion of ~ 30 the polymer in the aqueous medium. Exemplary rnonomers :' 1~,31~-F ~6-109;~797 L
include the ~ater-soluhle etl~ylenically unsaturat~d amides sucll as acrylaInide, mctllacrylanlicle and fumaramide;
N-substituted ethylenically unsaturated amides SUCIl a5 N-isopropylacrylamide, I~-t-butylacrylamide and ~-rnethylol-~s 5 acrylamide and N-substituted-(N'-dialkylaninoalkyl)-aerylamides, e.g., N-(dimethylaminomethyl)acrylamide and N-(diethylaminomethyl)methacrylamide and quaternized derivatives thereof, e.g., N-(trimethylammoniwnmethyl)-aerylamide ehloride; ethylenically unsaturated earboxylie aeids such as aerylie acid, methaerylic aeid, itaconic aeid, fumarie aeid and the like; ethylenically unsaturated quaternary ~mmonium eompounds sueh as vinylbenzyltrimethyl-~ ammonium ehloride; sulfoalky~ esters of earboxylie aeids a~-' such as 2-sulfoethyl methacrylate and the alkali metal and ammonium salts thereof; aminoalkyl esters of unsaturated earboxylie acids sueh as ~-aminoethyl methaelyla~es vlrlyl ~ aryl sulfonates sueh as vinylbenzene sulfonates ineluding - the alkali metal and ammonium salts thereof and the like.
Of the foregoing water-soluble monomers, aerylamide, methaerylamide and eombinations thereof with aerylie aeid or methaerylie aeid are preferred, with j aerylamide and eombinations thereof with up to 70 weight t pereent of aerylie aeid being more preferred. Most i preferred are the eopolyrners of aerylam~de with from s 25 about 5 to about 40, espeeially from about 15 to about 30, weight pereent of aerylie aeid. The partiele size of the mierogels of these most preferred eopolymers is more easily eontrolled than are the aeid-free eopolymers.
For example~ the adclition of polyvalent metal ions such as calciwll, magnesium and the like to aqueous composition~
.
18,379-F _7_ ~09;~7~7 containin~ the micro-Jels reduces thc p~rticle si~es of microgcls hy ~ hi.gh]y prcdicta~le amount.
In prefcrred embodiments, it i~. desirable that the total monomer mixture contain a relatively sl.lall proportion of a copolymerizable polyethylenic monomer.
Such proportion is advantageously an amount sufficient ' to crosslink the polymer, thereby converting the polymer to a non-linear polymeri.c microgel without appreciably ~: reducing water swellability charactcristics of the polymer. Exemplary suitable comonomeric crosslinking agents include divinylarylsulfonates such as divinylben-zenesulfonate, d.iethylenically unsaturated diesters : including alkylene glycol diacrylates and dimethacrylates ~' ~uch as ethylene glycol diacrylate, ethylene glycol methacrylate and propylene glycol diacrylate; ethyleni-cally unsaturated esters of ethyienicaliy ul~sd~uLated carboxylic acids such as allyl acrylate; diethylenically unsaturated ethers such as diallyl ethylene glycol ether, divinyl ether, diallyl ether, divinyl ether of ethylene ~ 20 glycol, divinyl ether of diethylene glycol, divinyl ether t'~ of triethylene glycol; N,N'-alkylidene-bis(ethylenically unsaturated amides) such as N,N'-methylene-bis~acrylamide), N,N'-methylene-bis(methacrylamide), and other lower alkylidene-bis(ethylenically unsaturated amides) wherein r.~ 25 . the alkylidene group has from 1 to 4 carbons. When a "' 'f i crosslinking comonomer is the means employed to provide the necessary crosslinking, any amount of such cross-. linking agent in the monomer mixture is suitable provided that i.t is sufficient to crosslink the polymer to form ~ ~ .
, .
18,379-F -8-''' ' , .......
g ,~
a discrete, spheroidal, water-swellable microgel as defined ~
herein. Preferably, however, good results have been achieved :-when the crosslinking agent is employed in concentrations from 5 to 200, more preferably from 10 to 100 parts, by -~
weight of crosslinking agent per million weight parts of total monomer. ,--The microgels are advantageously prepared by microdisperse solution polymerization techniques, e.g., ~ -the water-in-oil polymerization method described in U.S.
Patent No. 3,284,393. In the practice of this method, -a water-in-oil emulsifying agent is dissolved in the oil ::
phase while a free radical initiator, when one is used, --is dissolved in the oil or monomer (aqueous) phase, ~;
depending on whether an oil or water-soluble initiator is used. An aqueous solution of monomer or mixed monomer~
~ or a monomer per se is added to the oil phase with agitation i until the monomer phase is emulsified in the oil phase. ;
i` In cases where a crosslinking comonomer is employed, the crosslinking comonomer is added along with the other monomer - -;
to the oil phase. The reaction is initiated by purging :
the reaction medium of inhibitory oxygen and contnued with -agitation until conversion is substantially complete.
The product obtained has the general appearance of a poly- ~-meric latex. When it is desirable to recover the microgel -in essentially dry form, the polymer microgel is readily -separated from the reaction medium by adding a flocculating -~- agent and filtering and then washing and drying the microgel. -~
Alternatively, and preferably, the water-in-oil emulsion ~- reaction ._ ..
f~ ........
f ~ , '.. . ~
,' . .
....
' :. :.
18.379-F - 9 -?. ' ': .
109~7~7 produ~: is ;uit~ ly enll~loycd as the fluid medium containing ~' the micro(Jels.
~ suitable, but less preferred, metnod for preparing the microgels is a microsuspension method wherein aqueous solutions of the monomers are suspended in an oil phase and then subjected to conditions of free radical suspension polymerization. In such method the concentration of rnonomer in the aqueous solution can be varied over a wide range, for examp]e, from about 5 to about 80 weight percent of monomer in the aqueous solution, preferably from about 20 to about 40 weight percent. The j~ choice of a particular monomer concentration depends ; in large part upon the particular monomer being employed as well as the polymerization temperature. The ratio ~ 15 of the agueous solution of monomer to the oil phase is '~33 also widely variable, advantageously from about 5 to t~ about 75 weight parts of aqueous phase to correspondingly;~ from about 95 to about 25 weight parts of oil phase.
The suspending agent suitably employed as a solid or , 20 liquid substance having a low hydrophile-lipophile l~ balance, i.e., preponderantly hydrophobic. Exemplary -j~ suitable suspending agents are described in U.S. Patent No. 2,982,749. A preferred suspending agent is an organic polymer which, while predominantly hydrophobic, has hydrophilic substituents such as amine, sulfone, sulfonate, carboxy, and the like. The suspending agent '3 ~hould be employed in an amount sufficient to assure j the desired particle size of the resultant microgel, preferably from about ~.~ to ahout 1 weight ~ercent, based on the weight of the aqueous phase. Exemplary '' .
.
18,37g~F -10-109;~7~7 preferred suspending agents include silanized silica, ethyl cellulose and the like. In order to insure that ~-microgels having the desired particle size are obtained, it is often desirable to subject the water-in-oil sus-pension to high rates of shear.
In either process, the oil phase can be any inert hydrophobic liquid which (1) does not take part in the polymerization reaction and (2) can bP separated -readily from the polymeric product. Of such liquids the - -~
hydrocarbons and chlorin'ated hydrocarbons such as toluene, xylene, o-dichlorobenzene, ethyl benzene, liquid paraffins ; having from 8 to 12 carbons, monochlorobenzene, propylene dichloride, carbon ~etrachloride, l,l,l-trichloroethane, tetrachloroethylene, methylene chloride, etc., are --advantageously employed, with liquid paraffins; toluene, xylene and the chlorinated hydrocarbons being preferred.
Polymerization initiators suitably employed in either the suspension or emulsion polymerization tech- ---niques include peroxygen catalysts such as t-butylhydro-peroxide, dimethanesulfonyl peroxide and redox systems -~
such as t-butyl hydroperoxide or alkali metal or ammonium persulfates in combination with usual reducing agents --such as sulfide or bisulfide. Alternatively, any free ; radical generating means can be suitably employed, for example, those generated in situ by ultraviolet or X-rays ---and the like. --In addition to the employment of a crosslinking ` monomer as a means for forming the desired polyme~
microgel, other crosslinking techniques are also suitable.
For example, the polymer in dispersed particulate form .
18,379-F -11-X
'~ - ~ . .
1C~9;~797 may be crosslinked subsequent to polymerization by treat- -ment with a chemical crosslinking agent for the polymer -such as bleach or similar alkali metal hypohalite or -aldehydes such as formaldehyde and dialdehyde, e.g., glyoxal, when the polymer is one bearing pendant amide - -groups. ~-In addition, it is sometimes desirable to convert the polymer microgel to a product that has substituted cationic character such as the N-amino-methyl form (Mannich form) of polyacrylamide, or to a -- -polycation such as the quaternized derivative of the -Mannich derivative of polyacrylamide. For example, in - -the preparation of polymer having cationic characteristics, -- -f the polymer microgel may be reacted with formaldehyde and ~; 15 an amine to produce the polymer in a manner as disclosed ,~ in U.S. Patent No. 3,539,535. The polycation may be --' formed by reacting the microgel of the Mannich deriva-tive of polyacrylamide with an alkyl halide and thereby quaternize the amine nitrogen, for example, as described `
in the procedure in U.S. Patent No. 3,897,333. Also it `
may be desirable to hydrolyze some of the amide moieties of acrylamide polymer microgels to acid form by treatment with a hydrolyzing agent such as sodium hydroxide. - `
In the practice of employing the aforementioned -microgels in a process for recovering oil from a sub~
terranean formatioh, it is desirable to disperse the microgel in a fluid medium, preferably water or a water- --in-oil emulsion, such that the resulting dispersion is --reasonably stable. The concentration of the microgel in the fluid medium is suitably any concentration that ef-............
18,379-F - -12-- X
., .
. .. . : -109;~797 fects the desired control of the permeability of the treated formation before excessive amounts of the fluid medium pass into the producing well or out of the porous structure being treated as the case may be. In order to minimize the viscosity of the fluid medium containing the microgel and thereby reduce the amount of energy required to pump the fluid medium into the subterranean formation, it is desirable to dilute the microgel in the fluid medium as much as possible prior to its introduction into the well bore or porous structure. In preferred embodi-ments utilized for fluid mobility control in enhanced oil recovery, it is desirable that the concentration of the microgel in the fluid medium be in the range from 100 to ~ 50,000 ppm of dry polymer based on the total weight of j~ 15 the fluid medium, more preferably from 250 to 10,000 ppm, most preferably from 250 to 5,000 ppm.
While the particle size of the microgel is not particularly critical, it is found that the microgels are ~- most advantageously employed in porous structures that are generally free of large fractures or vugs that are more than 10 times the diameter of the swollen microgel and preferably is free of vugs that are more than 5 times ` in size than the diameter of the swollen microgel. In the most preferred embodiments, it is desirable to employ microgels having diameters that are from one-third to the same size as the average pore size of the porous subterranean formation. In selecting a microgel, it should be understood that it is the particle size that the microgel will possess in the .
18,379-F -13-'~ .
,s`
,. : . . -109;~797 porous subterranean structure to be treated that is significant. Accordingly, the gel capacity of the microgel, i.e., its ability to absorb the aqueous medium native to the subterranean formation to be modified, is a significant factor in determining which microgels will --most beneficially control the permeability of a particular -; subterranean structure. For example, it is observed that the unswollen microgels can sometimes absorb as much as 5 to 10 times as much water when dispersed in deionized --water as they ~ill absorb when they are dispersed in a - - -salt solution similar to the brines that exist in many oil-bearing subterranean formations. For example, a partially swollen microgel (30 percent polymer solids) prepared with 30 ppm methylene bisacrylamide based on total monomer and having an average diameter of about 1 micrometer can increase to a water swollen microgel having an average diameter of about 5 micrometers when fully --diluted with deionized water whereas it can only increase to a water swollen microgel having an average diameter of 3.8 micrometers when fully diluted with 0.7 molar aqueous solution of sodium chloride. --The fluid medium used to carry the microgels - -into the subterranean formation is suitably any fluid medium which does not substantially inhibit the water swelling characteristics of the microgels. Most commonly, --~
the fluid medium is an aqueous liquid which may contain a variety of other ingredients such as salts, surfactants, bases such as caustic and other additaments commonly- -~
employed in the drive fluid of enhanced oil recovery=--`
operations. In addition to water and other suitable 18,379-F -14-10~i~75'7 liqui~ tiC~ iluid ~lcdium may cornprise alcohc,l~, O~-CJll~iC acicls, c~]ycols and ~ost often watcr--in-oil erlulsionc. whereiI. the microgels reside in the aqueous phase of s~lch emulsions. In such emulsions, the oil phase can be generally hydrocarbon, halohydrocarbon or similar water in~iscible organic fluids. Of the foregoing fluid media, water is preferred.
As indicated hereinbefore, the aforementioned fluid medium containing the r~icrogels is particularly useful in fluid drive operations for the enhanced re-covery of oil. The microgels are particularly ef-fectivc for decreasin~ the mobility of the drive fluid, such as water or other fluids, or decreasing the perme-ability of nonfractured porous formations prior t~ or i5 during enhanced oil recovery operations which involve the use of fluid drive. Such microgels are also ùseful for .' .~
water shutoff treatments in production wells. In such processes, the fluid medium containing the microgels can be injected into the formation prior to or subsequent to the injection of another fluid.
In another embodiment of the invention, a conventional water flood or gas drive is carried out in a conventional manner until the drive fluid breaks through into the production well in excessive amounts.
¦ 25 At such time the microgels dispersed in the fluid medium are then pumped into the well through which the drive fluid is being supplied and into the porous formation n any suitable manner, in any suitable amount, and for any desired period of time sufficient to obtain the desired in-depth penetration and decrease in the mobility , . . .
18,379-F -15-,......... . .
109;~797 of the drive fluid. Injection of the microgels in this manner will plug the thief zone adjacent to oil-bearing strata. At this point, the water or brine flood can be --restarted to force oil from the oil-bearing strata.
In yet another embodiment, the microgels can be applied to producing wells, (including oil wells or gas wells), where there is an unstable, nonhydrocarbon- --bearing strata adjacent to the hydrocarbon-bearing-strata. -~
For example, if a water-bearing sand is adjacent to the h~dro~
carbon-bearing sand and the water intrudes into the bore ---hole thereby interfering with the production of hydrocarbon, ~~~
~ the formation can be treated with microgels to shut off -'! the flow of water. The method of treatment in this case ~ -'~ is essentially the same as described in connection with the fluid drive operations.
In any of the above-described embodiments -of the invention, a slug of an ungelled polymer can ; sometimes be advantageously injected into the formation prior to ths injection of microgels in the manner generally described in U.S. Patent No. 3,039,529. The initial injection of water-soluble (linear) polymer often satisfies ; the absorption requirements of the formation and also -aids in reducing face plugging if this is a problem. --; It is also within the scope of this invention : --to inject the microgel into the subterranean formation periodically or intermittently, as needed, during the course of a fluid drive operation or during the production ^ of oil or gas from a producing well. In all of the --foregoing operations, the injection of the fluid medium containing the microgels can be carried out in any -18,379-F -16-~g . .. , ~
10~;~797 cenventiona:L m~7nller. It is one of the particular advan-ta;~c o t~ re_ien~ invention that the microgels dis-persed in a liquid may be stored for substantial periods of time and then pumped into the subterranean forrnation as desired.
In addition to the aforementioned enhanced oil recovery applications, the microgels dispersed in ~3~? ~ the fluid medium may be employed as drilling fluids or -~ in combination therewith in the drilling of wells in anymanner known to the art for the use of drilling fluids.
As is known to the artisan skilled in well drilling, drilling fluids are employed to remove cuttings and to maintain pressure in the wel~ to prevent blowout. The ~j~ use of microgels in drilling fluids minimizes the loss of drilling fluid via penetration of subterranean strata ` -~-~
~- near the well. While the microgels can be en~ployed ;7~ ~` ~ alone as the drilling fluid, it is often desirable to include weighting agents such as barium carbonate, barium -~ sulfate, amGrphous silica and the like as well as linear , ~ ~
~ 20 water-soluble polymers such as polyacrylamide or derivatives l ~ thereof such as the cationic Mannich derivatives or quaternized Mannich derivatives in the drilling fluids c~taining the microgels. If desired, other additives compatible with the microgels can also be included in the drilling fluid, e.g., clays such as bentonite and atta-pulgite, fluid loss agents, and the like. In the selec-tion of such additives for the use in a particular , ~ ; .
drilling fluid, care should be taken to avoid materials which are not compatih]e ~ith the microgels. As for ~,.
.. . .
18,379-F -17-!.- ....
9;~797 com~inin~; th(~ c; ~-iit:h t~ i(LocJels~ ~ny con-ventio~ l mar~n~r toc ~r~ i(J dri]ling ~lui(1s for t.}liS
purpos~ are sui ~c3 t)l~ r~over, these mic~ogels are suitably emplo~c(-l in eit}lcr the lli~3h solids or lo~ solids drillin~ fluids known to thc oil indllstry.
The following examples are given to illustrate the invention and should not be us~d ~o limit its scope.
Unless otherwise indicated all parts and percentages are by weight.
Example 1 A. Preparation of the Microgels ?
To an oil phase consisting of ingredients as listed hereinafter is added an aqueous solution of monomers as also described hereinafter with agitation until the monomer phase is emulsified in the oil phase.
Ingredients Amount, gra~s ; Aqueous Phase Acrylamide 134.4 Acrylic acid 33.6 Sodium hydroxide 28.75 Deionized water 403.25 Methylene-bis-acrylamide 0.0047 (28 ppm) DETPA* 0.168 (1000 ppm) t-butyl hydroperoxide -0.0420 (250 ppm) Sodium bisulfite 0.0218 (130 ppm) Oil Phase ~j Deodorized kerosene 240.3 ~ Isopropanolamide of oleic acid 16.8 1, *Pentasodium salt of diethvlenetriamine-pentaacetic acid 18,379-F -18-. .
109;~797 I~l for~ g tlle emulsioll, the ak,reJ~ tiol~-d aqueous phase (less tlle t-butyl hydro~jero,idc ancl soc!ium bisulfite) is mixed with the oil ~hase usin~ controlled high shear, i.e., 30 scconds in a ~aring ~endor or Eppenbach Homogenizer. The resulting emulsion is placed in a reactor which is purged for 1 hour with N2. The t-butyl hydroperoxide (20 percent a~ueous solution emulsified in oil at a weight ratio of ~3 oil to 5 water) is added to the reactor in a single shot. The sodium bisulfite (2 percent aqueous solution emulsified in oil at a weight ratio of ~3 oil:S water) is added ;` portionwise to the reactor in 10-ppm increments until polymerization of the monomers is completed. After - polymerization, the temperature is increased to 60C
for 2 hours. In a dispersion of the water-swellable microgels in deionized water containing ~0 percent polymer, it is observed that the mean particle diameter of the water-swollen microgels is about one micrometer.
B. Water Fermeability Reduction Tests The ability of the microgels to control perme-ability of porous subterranean formations is determined ;; using a series of Berea sandstone cores according to - the following test procedure. In most of the core samples (2.54 cm length x 2.54 cm diameter), the pore volume is from 2.8 to 3.2 ml and the pore size is from about 14 to 16 micrometers. The initial core permeability is determined by pressuring an aqueous solution of NaCl (4~) through the core in forward and reversc directions. The afore-mentioncd microgels are diluted to 0.02% solids bv adding deionized water and injected into the core sample at 10 psig.
18,379-F -19-,~.. , ~ . ............................ .
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The micro(Jc~ :i.njectic~ ., fol:lowed wi ~h a brine flow in tllc for~ L,I .~n(l reve~se ~irection to estal-lish the permcabili.-ty reducti<)ll. The differential pressure during the brine ~]ow is then increased in 20 psi increments to 60 psi. After each illcremental increase, 50 ml of brine is passed through tlle core sample and the flow rate is : determined. The pressure is then returned to the original test pressure of 10 psig and a final brine flow rate is determined after the sample stabilizes (flow rate becomes constant). Comparison of initial and final brine flow rates establish the permeability reduction resulting from the microgel treatment of the core sample. The results for this sample (Sample No. 1) are recorded in Table I.
` For the purposes of comparison, several ~ 15 water-soluble (noncrosslinked) acrylamide/acrylic acid copolymers (Sample Nos. Cl-C5) are simiIarly ~: tested for.water diverting capability. The results of --~ these tests are similarly reported in Table I.
:~ Example 2 Following the general procedure for prep æ ing acrylamide/acxylic acid copolymer microgels as speci-fied in Example 1, microgels are prepared using amounts of methylenebis(acrylamide) ranging from 7 to 200 parts , per million instead of the 28 parts per million employed .. 25 . in Example 1. Also runs are carried out using polyacryl-amide microgels wherein the carboxyl moiety is varied from 5 to 40 mole percent. The resulting microgels.are sirnilarly tested for their water diverting capability by th~ proce(lure set forth in Example 1 and the results for the salaples (Sample Nos. 2-7) are similarly recorded in ; Tab].e I.
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;'-10~797 As evid~llced by t~l~ data in Table I, the fluid micro~l composit.ions of the pres2nt invention exert a generally greater control of the permeability of porou.s core samples (fluid mobility control) at lower viscosities than do compositions containing linear polymer.
.' Example 3 ~ To illustrate the effect of microgel particle ;, . size on the ability of the microgel to control fluid mobility in a core samplQ of a given pore size, three core tests are carried out using synthetic core s,~mples each having an average pore size of 24-26 micrometers : and microgels having different average diameters as ; .~; -. ~ ~ specified in Table II. The polymer of each of the micro-; gel samples is an acrylamide/acrylic acid (80/20) copolymer . ``~ 15 which has been crosslinked with 14 ppm of methylene ;~$, bis(acrylamiae). The microgels are injPc~ed into the core samples under a pressure of 10 psi. The treated core samples are tested for permeability in the forward direction and the results are recorded in Table II.
~- 20 TABLE II
~ ~ Micro~el Par~ticle Size, ~m j~ P~ 7~b~3~ Permeability (1) Run Swollen Water Swollen Initial, Treated, No70% H2O 98~ H2 _ md md ~` 2 5 15 5350 49 '~
;~ ~ (1) Same as (4j in Table I
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1~9;~797 I;JIi].c Ia;~- ~e. ' j)li)v~ e grcatcst rc~uction in pcrmc.lj.iJity, i.~ ot~ t~ o. 2 provi(1cs the most effcctivc perl,le;ll~il.it-.y cor)t:rol without a sub!itantial increase in the energy to pwlip the r,licrogels into the S core sample. Accordingly, it is generally more preferred to employ microgels haVillC3 water-swollen diameters that are from about one-third to about the .same size as the a.erage pore size of the formdtion bei~g treated.
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18,379-F -2~-?
One of the more significant problems attendant -to the recovery of hydrocarbon materials from subterranean ---formations is the concommitant recovery of undesirable fluids such as water. Such recovered water can be brine native to the formation or it can be injection water em-ployed in enhanced oil recovery treatments being applied to the reservoir. Whatever the source, there is an upper -limit beyond which water production can no longer be - -~
tolerated and its further entry into the producing well - --bore must be reduced. In addition other fluids such as natural gas are sometimes undesirable particularly when such fluids exceed the upper limits of gas:oil ratio desired for most efficient recovery of the hydrocarbons. -.. . .:: .. ~
As is well known, many oil reservoirs comprise layers or zones of porous rock which can vary in perme-ability from less than 10 millidarcies to more than 1000 `
millidarcies. Regardless of whether the~undesired fluid~ `
is a natural drive fluid or one coming from an enhanced oil recovery operation, there is a real tendency for -the drive fluid to channel along or through the more permeable zones of the formation. Such channeling, often called fingering, generally hinders or prevents the recovery of oil from less permeable zones. For example, the more permeable zones, after oil has been largely -displaced therefrom, function as thief zones which permit ---the drive fluid to channel directly into the production -or recovery well. - ;
1~,379-F -1-X I ,, ... . . .
10~7g7 Among the prior solutions to the problem of --undesirable fluid entry into the production well is the ~
placement of a solid plug of a material such as cement -within the formation. Unfortunately, such solid plugs often inhibit the use of drive fluids to assist in forcing _-~
desired hydrocarbon material from the formation into the producing or recovery well bore. In addition the use -_ of such solid plugs invariably results in the permanent -_ _ loss of desired fluids. Further, should the undesirable fluids seep by or otherwise bypass such solid plugs, the plug cannot shift position to block such seepage or other - _ changes in flow pattern of the undesired fluid.
In order to overcome the deficiencies associated with the use of solid plugs, it has been a common practice to modify the mobility of the driving fluid by pumping a : ~
highly viscous fluid into the oil bearing formation. An ~
illustration of this technique is the incorporation of a --partially hydrolyzed polyacrylamide in an aqueous drive fluid such as described in U.S. Patent No. 3,039,529. ~_ While the recovery of hydrocarbon by employing such -_-techniques is measurably enhanced, substantial quantities -~
of polymers must be added to the drive fluid in order to maintain the desired high viscosity. Moreover in --cases of highly porous subterranean structures which _--are proximate to oil bearing formations of relatively ~ ~
low permeability, substantial quantities of the unde~
sirable drive fluid are often recovered. -More recently, as disclosed in U.S. Patent ; -Nos. 3,780,806 and 3,785,437, it has been a practice to attempt to plug some of the more porous formations by 18,379-F -2-~' .
10~;~7~7 ..
- .
introducing a water soluble polymer into the highly porous structure and crosslinking the polymer in situ to form a water-insoluble gel. Alternatively, as disclosed in U.S.
Patent No. 3,921,733, attempts have been made to pump a -partially gelled polymer into a porous formation ahead of the drive f~uid. All of these procedures suffer from handling problems characteristic of two component systems comprising a polymer and a crosslinking agent. For example, most of the ~-procedures involve the addition of a dry polymer to an aqueous medium at the well site which gives rise to difficulties in solubilizing the polymer. More importantly, it is difficult to control the gelation characterisitics of the polymer as needed to insure effective control of formation permeability.
In view of the deficiencies of prior art methods for controlling permeability in subterranean structures as needed -for recovery of hydrocarbon materials, it would be highly :desirable to provide an improved oil recovery method which essentially eliminates many of the problems characteristic of the aforementioned in situ gelation techniques.
The present invention provides such an improved ~:
oil recovery method whereby the fluid permeability of a ~-subterranean geological formation is modified, preferably to restrict the passage of fluids (particularly aqueous fluids) .-therethrough. Alternatively, such modification of the fluid permeability of ~he formation can be expressed as controlling the mobility of fluids in the fo mation. In the practice --of this invention, the desired control of fluid mobility -is achieved by introducing into the subterranean formation, preferably via a well bore, a fluid medium containing dis-crete, spheroidal microgels of a water-swellable or ---water-swollen, crosslinked polymer in an amount sufficient to control the mobility of fluids in the subterranean formation. ~-. . .
, 18,379-F - 3 -:' , ~
10~;~79'7 '~.
The microgels have partly or totally water-swollen diameters which are generally within the range from 0.5 to 200 micrometers and are very useful in treatment of porous subterranean strata that are commonly found in --hydrocarbon bearing formations. The m~rogels when dispersed .,,,,~
in water or other aqueous media exist as discrete, spheroidal, water-swollen particles which can be separated from the aqueous media by filtration or other similar technique.
The fluid medium containing the microgels is most -advantageously low in viscosity and therefore much more easily pumped into the desired porous formation than are conventional high viscosity water-soluble polymers or partially -gelled polymers used hereinbefore. This advantageous -property is believed to be due to the discrete, spheroidal characteristics of the microgels as well as to their relatively controlled particle size and crosslinked character.
These characteristics enable the microgels to penetrate deeply into the pores of the porous structure to be restricted or plugged. Surprisingly, the microgels are not readily displaced even when the direction of liquid flow in the subterranean structure is reversed.
Accordingly, the improved method of the present invention is most advantageously employed in enhanced oil recovery operations wherein a drive fluid is introduced through a bore hole in the earth into a porous subterranean ~
formation penetrated by said bore hole thereby driving oil from oil bearing structures toward a producing well. In ---addition such fluid media containing the microgels are usefully employed as the fluid in well drilling operations, E
as packer fluids in well completion operations and as ---~
mobility control fluids in other enhanced oil recovery operations. Methods using such media in drilling operations, in well completion operations, and as friction reduction aids in normal water flooding operations as well as in '~:
- 18,379-F - 4 -'' X
109;~797 ~'~
fracturing processes are additional aspects of the invention. .-~.
It is further observed that fluid media containing the micro- :.
.......
gels are very useful in the treatment of subterranean .-:
structures containing substantial amounts of salt water or brine which normally hinder or prevent the gelation reactions required in in situ gelation procedures. ~:
The present invention particularly resides in a .....
hydrocarbon recovery method wherein a production well penetrates --a porous subterranean formation having at least a hydro-carbon-bearing stratum and adjacent thereto at least one ~.:
stratum bearing an aqueous fluid, comprising the steps of ~
introducing into the subterranean formation via the production ...
well bore a fluid medium containing discreteJ spheroidal .....
microgels of a water-swellable or water-swollen, crosslinked ......
polymer of an ethylenically unsaturated water-soluble monomer(s) ...
in an amount sufficient to reduce the fluid permeability of the ..
porous formation, and wherein said microgels are in at least a partially water-swollen state with diameters in the range from 0.5 to 200 micrometers, said polymer being crosslinked ....
with from S to 200 weight parts of a copolymerizable poly- ...
ethylenic monomer per million parts of the total monomers of ~
the polymer thereby controlling the flow of the aqueous ~.-.
fluid into the well bore. E:
The present invention also reside in an enhanced ,--oil recovery method .in which an aqueous drive fluid is injected through an injection well bore into a hydrocarbon-bearing nonfractured formation having hydrocarbon-deficient and hydrocarbon-rich zones to drive hydrocarbon from the formation ..
to a recovery well, the improvement wherein an aqueous fluid ~
medium containing discrete, spheroidal microgels of a water--swellable or water-swollen, crosslinked polymer of ethylenically -`..
unsaturated water-soluble monomer(s) is introduced through ... :.
the injection well bore into the formation in an amount sufficient to reduce the aqueous fluid permeability of the : :
.. ..
.......
18,379-F ~ 5 ~
.
.
.
-5a- 109~797 porous formation, said microgels in at least a partially water-swollen sta~e having diameters in the range from about 0.5 to about 200 micrometers, thereby restricting the passage of the drive fluid into hydrocarbon-deficient zones of the formation but not substantially impeding the passage of the drive fluid through hydrocarbon-rich zones of the formation.
Reference is hereby also made to a copending Application No. 291,355, filed November 21, 1977 claiming an invention by M. L. Zweigle et al. for a composition which comprises discrete, spheroidal microgels of a water-swellable or water-swollen polymer of water-soluble ethylenically i~ unsaturated monomer, said polymer being sufficiently cross-linked to enable the microgels to remain discrete and retain spheroidal shape upon being dispersed in an ~ aqueous fluid medium, said microgels in at least a partially F~'~ water-swollen state having diameters in the range from 0.5 to 200 micrometers.
The application also claims a method for thickening ` 20 an aqueous medium to obtain a composition having the properties of a viscous short solution and being resistant to viscosity degradation under conditions of high shear which comprises the step of thoroughly dispersing in said medium from 0.1 to 2 percent by weight of microbeads of a water-insoluble, ^~ 25 water-swellable polymer of a water-soluble vinyl monomer -~ or mixture of water-soluble vinyl monomers, cross-linked with a difunctional cross-linking agent copolymerizable with said monomer or monomers, said microbeads having - diameters of from 0.2 to 4 microns in the dry state and having a gel capacity of at least about 10 grams per gram :
~ 379-F -5a-.
.. .
~ -5b- 109~797 in aqueous 0.27 molar sodium chloride solution, said cross--linking agent being present in an amount from 50 to 1000 parts by weight of cross-linking agent per million parts of vinyl monomer or monomers in the polymer.
The microgels which are essential to the practice of the present invention are generally characterized as discrete, well defined spheroids that are water-swellable and/or water-swollen. In their water-swollen or at least partially water-swollen state, the microgels comprise water and a crosslinked polymer of a water-soluble ethyleni-cally unsaturated monomer. Perhaps one of the most signi-ficant characterisitics of the microgels is their ability . to absorb substantial proportions of water. In their partially or totally water-swollen state, the ,.
.:
~ /
' ' .
. .
' ' 18,~ 9-F -5b-lQ9;~797 , par~ic1e si (~; o~ Lll~ ~li r~J~ a~ n(Je from a}~out 0.5 to ahout ~Oo n-llc ~ ers, pr~:f~Ya~]y rroln ab~ut 1 to abollt 10 micrometcri. In ~'ae cl~y state, the rnicroyels , ~ exist as microbeads h.-vincJ diarn~Lers cJenerally less than about 20 microMeters, preferably less than about 1 ~ micrometer. In their partially water-swollen (pre-inversion) s state, the rnicrogels are water--swellable and contain at ~ least abou' 30 weight percent of crosslinked polyrner and I up to about 70 weight percent of water. In their totally water-swollen state, the microgels contain up to about 99.9 weight percent of water and as little as about 0.1 weight percent of crosslinked polymer. The microgels, when , dispersed in a fluid aqueous medium such as water, can be subjected to substantial amounts of high shear, e.g., >500,000 sec 1, which is characteristic of the pumping actlon existing in many enhan~eu oii reco-~ery operation~
without undergoing substantial degradation, i.e., loss of particle size or capacity to hold water (often called gel ~ capacity).
¦- 20 Ethylenically unsaturated monomers suitable t for use in preparing the microgels are those which are ~ sufficiently water-soluble to form at least 5 weight ¦ percent solutions when dissolved in water and which ~ readily undergo addition polymerization to form polymers which are at least inherently water dispersible and ~, preferably water~soluble. By "inherently water dis-, s persible", it is meant that the polymer when contacted with an aqueous medium will disperse therein without the aid of surfactants to form a colloidal dispersion of ~ 30 the polymer in the aqueous medium. Exemplary rnonomers :' 1~,31~-F ~6-109;~797 L
include the ~ater-soluhle etl~ylenically unsaturat~d amides sucll as acrylaInide, mctllacrylanlicle and fumaramide;
N-substituted ethylenically unsaturated amides SUCIl a5 N-isopropylacrylamide, I~-t-butylacrylamide and ~-rnethylol-~s 5 acrylamide and N-substituted-(N'-dialkylaninoalkyl)-aerylamides, e.g., N-(dimethylaminomethyl)acrylamide and N-(diethylaminomethyl)methacrylamide and quaternized derivatives thereof, e.g., N-(trimethylammoniwnmethyl)-aerylamide ehloride; ethylenically unsaturated earboxylie aeids such as aerylie acid, methaerylic aeid, itaconic aeid, fumarie aeid and the like; ethylenically unsaturated quaternary ~mmonium eompounds sueh as vinylbenzyltrimethyl-~ ammonium ehloride; sulfoalky~ esters of earboxylie aeids a~-' such as 2-sulfoethyl methacrylate and the alkali metal and ammonium salts thereof; aminoalkyl esters of unsaturated earboxylie acids sueh as ~-aminoethyl methaelyla~es vlrlyl ~ aryl sulfonates sueh as vinylbenzene sulfonates ineluding - the alkali metal and ammonium salts thereof and the like.
Of the foregoing water-soluble monomers, aerylamide, methaerylamide and eombinations thereof with aerylie aeid or methaerylie aeid are preferred, with j aerylamide and eombinations thereof with up to 70 weight t pereent of aerylie aeid being more preferred. Most i preferred are the eopolyrners of aerylam~de with from s 25 about 5 to about 40, espeeially from about 15 to about 30, weight pereent of aerylie aeid. The partiele size of the mierogels of these most preferred eopolymers is more easily eontrolled than are the aeid-free eopolymers.
For example~ the adclition of polyvalent metal ions such as calciwll, magnesium and the like to aqueous composition~
.
18,379-F _7_ ~09;~7~7 containin~ the micro-Jels reduces thc p~rticle si~es of microgcls hy ~ hi.gh]y prcdicta~le amount.
In prefcrred embodiments, it i~. desirable that the total monomer mixture contain a relatively sl.lall proportion of a copolymerizable polyethylenic monomer.
Such proportion is advantageously an amount sufficient ' to crosslink the polymer, thereby converting the polymer to a non-linear polymeri.c microgel without appreciably ~: reducing water swellability charactcristics of the polymer. Exemplary suitable comonomeric crosslinking agents include divinylarylsulfonates such as divinylben-zenesulfonate, d.iethylenically unsaturated diesters : including alkylene glycol diacrylates and dimethacrylates ~' ~uch as ethylene glycol diacrylate, ethylene glycol methacrylate and propylene glycol diacrylate; ethyleni-cally unsaturated esters of ethyienicaliy ul~sd~uLated carboxylic acids such as allyl acrylate; diethylenically unsaturated ethers such as diallyl ethylene glycol ether, divinyl ether, diallyl ether, divinyl ether of ethylene ~ 20 glycol, divinyl ether of diethylene glycol, divinyl ether t'~ of triethylene glycol; N,N'-alkylidene-bis(ethylenically unsaturated amides) such as N,N'-methylene-bis~acrylamide), N,N'-methylene-bis(methacrylamide), and other lower alkylidene-bis(ethylenically unsaturated amides) wherein r.~ 25 . the alkylidene group has from 1 to 4 carbons. When a "' 'f i crosslinking comonomer is the means employed to provide the necessary crosslinking, any amount of such cross-. linking agent in the monomer mixture is suitable provided that i.t is sufficient to crosslink the polymer to form ~ ~ .
, .
18,379-F -8-''' ' , .......
g ,~
a discrete, spheroidal, water-swellable microgel as defined ~
herein. Preferably, however, good results have been achieved :-when the crosslinking agent is employed in concentrations from 5 to 200, more preferably from 10 to 100 parts, by -~
weight of crosslinking agent per million weight parts of total monomer. ,--The microgels are advantageously prepared by microdisperse solution polymerization techniques, e.g., ~ -the water-in-oil polymerization method described in U.S.
Patent No. 3,284,393. In the practice of this method, -a water-in-oil emulsifying agent is dissolved in the oil ::
phase while a free radical initiator, when one is used, --is dissolved in the oil or monomer (aqueous) phase, ~;
depending on whether an oil or water-soluble initiator is used. An aqueous solution of monomer or mixed monomer~
~ or a monomer per se is added to the oil phase with agitation i until the monomer phase is emulsified in the oil phase. ;
i` In cases where a crosslinking comonomer is employed, the crosslinking comonomer is added along with the other monomer - -;
to the oil phase. The reaction is initiated by purging :
the reaction medium of inhibitory oxygen and contnued with -agitation until conversion is substantially complete.
The product obtained has the general appearance of a poly- ~-meric latex. When it is desirable to recover the microgel -in essentially dry form, the polymer microgel is readily -separated from the reaction medium by adding a flocculating -~- agent and filtering and then washing and drying the microgel. -~
Alternatively, and preferably, the water-in-oil emulsion ~- reaction ._ ..
f~ ........
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,' . .
....
' :. :.
18.379-F - 9 -?. ' ': .
109~7~7 produ~: is ;uit~ ly enll~loycd as the fluid medium containing ~' the micro(Jels.
~ suitable, but less preferred, metnod for preparing the microgels is a microsuspension method wherein aqueous solutions of the monomers are suspended in an oil phase and then subjected to conditions of free radical suspension polymerization. In such method the concentration of rnonomer in the aqueous solution can be varied over a wide range, for examp]e, from about 5 to about 80 weight percent of monomer in the aqueous solution, preferably from about 20 to about 40 weight percent. The j~ choice of a particular monomer concentration depends ; in large part upon the particular monomer being employed as well as the polymerization temperature. The ratio ~ 15 of the agueous solution of monomer to the oil phase is '~33 also widely variable, advantageously from about 5 to t~ about 75 weight parts of aqueous phase to correspondingly;~ from about 95 to about 25 weight parts of oil phase.
The suspending agent suitably employed as a solid or , 20 liquid substance having a low hydrophile-lipophile l~ balance, i.e., preponderantly hydrophobic. Exemplary -j~ suitable suspending agents are described in U.S. Patent No. 2,982,749. A preferred suspending agent is an organic polymer which, while predominantly hydrophobic, has hydrophilic substituents such as amine, sulfone, sulfonate, carboxy, and the like. The suspending agent '3 ~hould be employed in an amount sufficient to assure j the desired particle size of the resultant microgel, preferably from about ~.~ to ahout 1 weight ~ercent, based on the weight of the aqueous phase. Exemplary '' .
.
18,37g~F -10-109;~7~7 preferred suspending agents include silanized silica, ethyl cellulose and the like. In order to insure that ~-microgels having the desired particle size are obtained, it is often desirable to subject the water-in-oil sus-pension to high rates of shear.
In either process, the oil phase can be any inert hydrophobic liquid which (1) does not take part in the polymerization reaction and (2) can bP separated -readily from the polymeric product. Of such liquids the - -~
hydrocarbons and chlorin'ated hydrocarbons such as toluene, xylene, o-dichlorobenzene, ethyl benzene, liquid paraffins ; having from 8 to 12 carbons, monochlorobenzene, propylene dichloride, carbon ~etrachloride, l,l,l-trichloroethane, tetrachloroethylene, methylene chloride, etc., are --advantageously employed, with liquid paraffins; toluene, xylene and the chlorinated hydrocarbons being preferred.
Polymerization initiators suitably employed in either the suspension or emulsion polymerization tech- ---niques include peroxygen catalysts such as t-butylhydro-peroxide, dimethanesulfonyl peroxide and redox systems -~
such as t-butyl hydroperoxide or alkali metal or ammonium persulfates in combination with usual reducing agents --such as sulfide or bisulfide. Alternatively, any free ; radical generating means can be suitably employed, for example, those generated in situ by ultraviolet or X-rays ---and the like. --In addition to the employment of a crosslinking ` monomer as a means for forming the desired polyme~
microgel, other crosslinking techniques are also suitable.
For example, the polymer in dispersed particulate form .
18,379-F -11-X
'~ - ~ . .
1C~9;~797 may be crosslinked subsequent to polymerization by treat- -ment with a chemical crosslinking agent for the polymer -such as bleach or similar alkali metal hypohalite or -aldehydes such as formaldehyde and dialdehyde, e.g., glyoxal, when the polymer is one bearing pendant amide - -groups. ~-In addition, it is sometimes desirable to convert the polymer microgel to a product that has substituted cationic character such as the N-amino-methyl form (Mannich form) of polyacrylamide, or to a -- -polycation such as the quaternized derivative of the -Mannich derivative of polyacrylamide. For example, in - -the preparation of polymer having cationic characteristics, -- -f the polymer microgel may be reacted with formaldehyde and ~; 15 an amine to produce the polymer in a manner as disclosed ,~ in U.S. Patent No. 3,539,535. The polycation may be --' formed by reacting the microgel of the Mannich deriva-tive of polyacrylamide with an alkyl halide and thereby quaternize the amine nitrogen, for example, as described `
in the procedure in U.S. Patent No. 3,897,333. Also it `
may be desirable to hydrolyze some of the amide moieties of acrylamide polymer microgels to acid form by treatment with a hydrolyzing agent such as sodium hydroxide. - `
In the practice of employing the aforementioned -microgels in a process for recovering oil from a sub~
terranean formatioh, it is desirable to disperse the microgel in a fluid medium, preferably water or a water- --in-oil emulsion, such that the resulting dispersion is --reasonably stable. The concentration of the microgel in the fluid medium is suitably any concentration that ef-............
18,379-F - -12-- X
., .
. .. . : -109;~797 fects the desired control of the permeability of the treated formation before excessive amounts of the fluid medium pass into the producing well or out of the porous structure being treated as the case may be. In order to minimize the viscosity of the fluid medium containing the microgel and thereby reduce the amount of energy required to pump the fluid medium into the subterranean formation, it is desirable to dilute the microgel in the fluid medium as much as possible prior to its introduction into the well bore or porous structure. In preferred embodi-ments utilized for fluid mobility control in enhanced oil recovery, it is desirable that the concentration of the microgel in the fluid medium be in the range from 100 to ~ 50,000 ppm of dry polymer based on the total weight of j~ 15 the fluid medium, more preferably from 250 to 10,000 ppm, most preferably from 250 to 5,000 ppm.
While the particle size of the microgel is not particularly critical, it is found that the microgels are ~- most advantageously employed in porous structures that are generally free of large fractures or vugs that are more than 10 times the diameter of the swollen microgel and preferably is free of vugs that are more than 5 times ` in size than the diameter of the swollen microgel. In the most preferred embodiments, it is desirable to employ microgels having diameters that are from one-third to the same size as the average pore size of the porous subterranean formation. In selecting a microgel, it should be understood that it is the particle size that the microgel will possess in the .
18,379-F -13-'~ .
,s`
,. : . . -109;~797 porous subterranean structure to be treated that is significant. Accordingly, the gel capacity of the microgel, i.e., its ability to absorb the aqueous medium native to the subterranean formation to be modified, is a significant factor in determining which microgels will --most beneficially control the permeability of a particular -; subterranean structure. For example, it is observed that the unswollen microgels can sometimes absorb as much as 5 to 10 times as much water when dispersed in deionized --water as they ~ill absorb when they are dispersed in a - - -salt solution similar to the brines that exist in many oil-bearing subterranean formations. For example, a partially swollen microgel (30 percent polymer solids) prepared with 30 ppm methylene bisacrylamide based on total monomer and having an average diameter of about 1 micrometer can increase to a water swollen microgel having an average diameter of about 5 micrometers when fully --diluted with deionized water whereas it can only increase to a water swollen microgel having an average diameter of 3.8 micrometers when fully diluted with 0.7 molar aqueous solution of sodium chloride. --The fluid medium used to carry the microgels - -into the subterranean formation is suitably any fluid medium which does not substantially inhibit the water swelling characteristics of the microgels. Most commonly, --~
the fluid medium is an aqueous liquid which may contain a variety of other ingredients such as salts, surfactants, bases such as caustic and other additaments commonly- -~
employed in the drive fluid of enhanced oil recovery=--`
operations. In addition to water and other suitable 18,379-F -14-10~i~75'7 liqui~ tiC~ iluid ~lcdium may cornprise alcohc,l~, O~-CJll~iC acicls, c~]ycols and ~ost often watcr--in-oil erlulsionc. whereiI. the microgels reside in the aqueous phase of s~lch emulsions. In such emulsions, the oil phase can be generally hydrocarbon, halohydrocarbon or similar water in~iscible organic fluids. Of the foregoing fluid media, water is preferred.
As indicated hereinbefore, the aforementioned fluid medium containing the r~icrogels is particularly useful in fluid drive operations for the enhanced re-covery of oil. The microgels are particularly ef-fectivc for decreasin~ the mobility of the drive fluid, such as water or other fluids, or decreasing the perme-ability of nonfractured porous formations prior t~ or i5 during enhanced oil recovery operations which involve the use of fluid drive. Such microgels are also ùseful for .' .~
water shutoff treatments in production wells. In such processes, the fluid medium containing the microgels can be injected into the formation prior to or subsequent to the injection of another fluid.
In another embodiment of the invention, a conventional water flood or gas drive is carried out in a conventional manner until the drive fluid breaks through into the production well in excessive amounts.
¦ 25 At such time the microgels dispersed in the fluid medium are then pumped into the well through which the drive fluid is being supplied and into the porous formation n any suitable manner, in any suitable amount, and for any desired period of time sufficient to obtain the desired in-depth penetration and decrease in the mobility , . . .
18,379-F -15-,......... . .
109;~797 of the drive fluid. Injection of the microgels in this manner will plug the thief zone adjacent to oil-bearing strata. At this point, the water or brine flood can be --restarted to force oil from the oil-bearing strata.
In yet another embodiment, the microgels can be applied to producing wells, (including oil wells or gas wells), where there is an unstable, nonhydrocarbon- --bearing strata adjacent to the hydrocarbon-bearing-strata. -~
For example, if a water-bearing sand is adjacent to the h~dro~
carbon-bearing sand and the water intrudes into the bore ---hole thereby interfering with the production of hydrocarbon, ~~~
~ the formation can be treated with microgels to shut off -'! the flow of water. The method of treatment in this case ~ -'~ is essentially the same as described in connection with the fluid drive operations.
In any of the above-described embodiments -of the invention, a slug of an ungelled polymer can ; sometimes be advantageously injected into the formation prior to ths injection of microgels in the manner generally described in U.S. Patent No. 3,039,529. The initial injection of water-soluble (linear) polymer often satisfies ; the absorption requirements of the formation and also -aids in reducing face plugging if this is a problem. --; It is also within the scope of this invention : --to inject the microgel into the subterranean formation periodically or intermittently, as needed, during the course of a fluid drive operation or during the production ^ of oil or gas from a producing well. In all of the --foregoing operations, the injection of the fluid medium containing the microgels can be carried out in any -18,379-F -16-~g . .. , ~
10~;~797 cenventiona:L m~7nller. It is one of the particular advan-ta;~c o t~ re_ien~ invention that the microgels dis-persed in a liquid may be stored for substantial periods of time and then pumped into the subterranean forrnation as desired.
In addition to the aforementioned enhanced oil recovery applications, the microgels dispersed in ~3~? ~ the fluid medium may be employed as drilling fluids or -~ in combination therewith in the drilling of wells in anymanner known to the art for the use of drilling fluids.
As is known to the artisan skilled in well drilling, drilling fluids are employed to remove cuttings and to maintain pressure in the wel~ to prevent blowout. The ~j~ use of microgels in drilling fluids minimizes the loss of drilling fluid via penetration of subterranean strata ` -~-~
~- near the well. While the microgels can be en~ployed ;7~ ~` ~ alone as the drilling fluid, it is often desirable to include weighting agents such as barium carbonate, barium -~ sulfate, amGrphous silica and the like as well as linear , ~ ~
~ 20 water-soluble polymers such as polyacrylamide or derivatives l ~ thereof such as the cationic Mannich derivatives or quaternized Mannich derivatives in the drilling fluids c~taining the microgels. If desired, other additives compatible with the microgels can also be included in the drilling fluid, e.g., clays such as bentonite and atta-pulgite, fluid loss agents, and the like. In the selec-tion of such additives for the use in a particular , ~ ; .
drilling fluid, care should be taken to avoid materials which are not compatih]e ~ith the microgels. As for ~,.
.. . .
18,379-F -17-!.- ....
9;~797 com~inin~; th(~ c; ~-iit:h t~ i(LocJels~ ~ny con-ventio~ l mar~n~r toc ~r~ i(J dri]ling ~lui(1s for t.}liS
purpos~ are sui ~c3 t)l~ r~over, these mic~ogels are suitably emplo~c(-l in eit}lcr the lli~3h solids or lo~ solids drillin~ fluids known to thc oil indllstry.
The following examples are given to illustrate the invention and should not be us~d ~o limit its scope.
Unless otherwise indicated all parts and percentages are by weight.
Example 1 A. Preparation of the Microgels ?
To an oil phase consisting of ingredients as listed hereinafter is added an aqueous solution of monomers as also described hereinafter with agitation until the monomer phase is emulsified in the oil phase.
Ingredients Amount, gra~s ; Aqueous Phase Acrylamide 134.4 Acrylic acid 33.6 Sodium hydroxide 28.75 Deionized water 403.25 Methylene-bis-acrylamide 0.0047 (28 ppm) DETPA* 0.168 (1000 ppm) t-butyl hydroperoxide -0.0420 (250 ppm) Sodium bisulfite 0.0218 (130 ppm) Oil Phase ~j Deodorized kerosene 240.3 ~ Isopropanolamide of oleic acid 16.8 1, *Pentasodium salt of diethvlenetriamine-pentaacetic acid 18,379-F -18-. .
109;~797 I~l for~ g tlle emulsioll, the ak,reJ~ tiol~-d aqueous phase (less tlle t-butyl hydro~jero,idc ancl soc!ium bisulfite) is mixed with the oil ~hase usin~ controlled high shear, i.e., 30 scconds in a ~aring ~endor or Eppenbach Homogenizer. The resulting emulsion is placed in a reactor which is purged for 1 hour with N2. The t-butyl hydroperoxide (20 percent a~ueous solution emulsified in oil at a weight ratio of ~3 oil to 5 water) is added to the reactor in a single shot. The sodium bisulfite (2 percent aqueous solution emulsified in oil at a weight ratio of ~3 oil:S water) is added ;` portionwise to the reactor in 10-ppm increments until polymerization of the monomers is completed. After - polymerization, the temperature is increased to 60C
for 2 hours. In a dispersion of the water-swellable microgels in deionized water containing ~0 percent polymer, it is observed that the mean particle diameter of the water-swollen microgels is about one micrometer.
B. Water Fermeability Reduction Tests The ability of the microgels to control perme-ability of porous subterranean formations is determined ;; using a series of Berea sandstone cores according to - the following test procedure. In most of the core samples (2.54 cm length x 2.54 cm diameter), the pore volume is from 2.8 to 3.2 ml and the pore size is from about 14 to 16 micrometers. The initial core permeability is determined by pressuring an aqueous solution of NaCl (4~) through the core in forward and reversc directions. The afore-mentioncd microgels are diluted to 0.02% solids bv adding deionized water and injected into the core sample at 10 psig.
18,379-F -19-,~.. , ~ . ............................ .
: . , - ~ -' ,: :
1()~;~7~
The micro(Jc~ :i.njectic~ ., fol:lowed wi ~h a brine flow in tllc for~ L,I .~n(l reve~se ~irection to estal-lish the permcabili.-ty reducti<)ll. The differential pressure during the brine ~]ow is then increased in 20 psi increments to 60 psi. After each illcremental increase, 50 ml of brine is passed through tlle core sample and the flow rate is : determined. The pressure is then returned to the original test pressure of 10 psig and a final brine flow rate is determined after the sample stabilizes (flow rate becomes constant). Comparison of initial and final brine flow rates establish the permeability reduction resulting from the microgel treatment of the core sample. The results for this sample (Sample No. 1) are recorded in Table I.
` For the purposes of comparison, several ~ 15 water-soluble (noncrosslinked) acrylamide/acrylic acid copolymers (Sample Nos. Cl-C5) are simiIarly ~: tested for.water diverting capability. The results of --~ these tests are similarly reported in Table I.
:~ Example 2 Following the general procedure for prep æ ing acrylamide/acxylic acid copolymer microgels as speci-fied in Example 1, microgels are prepared using amounts of methylenebis(acrylamide) ranging from 7 to 200 parts , per million instead of the 28 parts per million employed .. 25 . in Example 1. Also runs are carried out using polyacryl-amide microgels wherein the carboxyl moiety is varied from 5 to 40 mole percent. The resulting microgels.are sirnilarly tested for their water diverting capability by th~ proce(lure set forth in Example 1 and the results for the salaples (Sample Nos. 2-7) are similarly recorded in ; Tab].e I.
18,379-F -20-. ~ . , 109~797 a) t~o ).. ,~ ~ ~ n o aJ
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18, 3 79-F' -22-.~ .. . . . ~ .
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.
;'-10~797 As evid~llced by t~l~ data in Table I, the fluid micro~l composit.ions of the pres2nt invention exert a generally greater control of the permeability of porou.s core samples (fluid mobility control) at lower viscosities than do compositions containing linear polymer.
.' Example 3 ~ To illustrate the effect of microgel particle ;, . size on the ability of the microgel to control fluid mobility in a core samplQ of a given pore size, three core tests are carried out using synthetic core s,~mples each having an average pore size of 24-26 micrometers : and microgels having different average diameters as ; .~; -. ~ ~ specified in Table II. The polymer of each of the micro-; gel samples is an acrylamide/acrylic acid (80/20) copolymer . ``~ 15 which has been crosslinked with 14 ppm of methylene ;~$, bis(acrylamiae). The microgels are injPc~ed into the core samples under a pressure of 10 psi. The treated core samples are tested for permeability in the forward direction and the results are recorded in Table II.
~- 20 TABLE II
~ ~ Micro~el Par~ticle Size, ~m j~ P~ 7~b~3~ Permeability (1) Run Swollen Water Swollen Initial, Treated, No70% H2O 98~ H2 _ md md ~` 2 5 15 5350 49 '~
;~ ~ (1) Same as (4j in Table I
.~ .`~
. . .
lt.,~' . . .
J
.1~. -, .
18,379-F -23-, ' ' ' . .
, , ' .
1~9;~797 I;JIi].c Ia;~- ~e. ' j)li)v~ e grcatcst rc~uction in pcrmc.lj.iJity, i.~ ot~ t~ o. 2 provi(1cs the most effcctivc perl,le;ll~il.it-.y cor)t:rol without a sub!itantial increase in the energy to pwlip the r,licrogels into the S core sample. Accordingly, it is generally more preferred to employ microgels haVillC3 water-swollen diameters that are from about one-third to about the .same size as the a.erage pore size of the formdtion bei~g treated.
.j ' ' , .
., .
18,379-F -2~-?
Claims (11)
1. A hydrocarbon recovery method wherein a production well penetrates a porous subterranean formation having at least a hydrocarbon-bearing stratum and adjacent thereto at least one stratum bearing an aqueous fluid, comprising the steps of introducing into the subterranean formation via the production well bore a fluid medium containing discrete, spheroidal microgels of a water-swellable or water-swollen, crosslinked polymer of an ethylenically unsaturated water-soluble monomer (s) in an amount sufficient to reduce the fluid permeability of the porous formation, and wherein said microgels are in at least a partially water-swollen state with diameters in the range from 0.5 to 200 micrometers, said polymer being crosslinked with from 5 to 200 weight parts of a copolymerizable polyethylenic monomer per million parts of the total monomers of the polymer thereby controlling the flow of the aqueous fluid into the well bore.
2. The method of Claim 1 wherein the corsslinked polymer is an .alpha.,.beta.-ethylenically unsaturated amide polymer or a polymer of an N-substituted-(N'-dialkylaminoalkyl) derivative of said amide or a polymer of a quaternized derivative of said N-substituted derivative.
3. The method of Claim 1 or 2 wherein the con-centration of microgel in the fluid medium is from 250 to 10,000 parts of crosslinked polymer calculated on a dry weight basis to a million weight parts of the fluid medium.
4. The method of Claim 1 wherein the crosslinked polymer is an acrylamide polymer crosslinked with from 5 to 200 weight parts of an N,N'-alkylidene-bis(ethylenically unsaturated amide) per millions parts of total monomer of the polymer.
5. The method of Claim 1 wherein the crosslinked polymer is an acrylamide polymer containing from 5 to 40 weight percent of polymerizing acrylic acid and crosslinked with from 10 to 100 weight parts of an N,N'-alkylidene--bis(ethylenically unsaturated amide) per million parts of total monomer of the polymer.
6. The method of Claim 1 wherein the water-soluble ethylenically unsaturated monomer is selected from the group .alpha.,.beta.-ethylenically unsaturated amides, N-substituted-(N'--dialkylaminoalkyl)acrylamides and their quaternized derivatives, ethylenically unsaturated carboxylic acids, ethylenically unsaturated quaternary ammonium compounds, sulfoalkyl esters of unsaturated carboxylic acids, amino-alkyl esters of unsaturated carboxylic acids and vinyl-aryl sulfonates.
7. The method of Claim 1 wherein the hydrocarbon bearing stratum is a gaseous hydrocarbon bearing stratum.
8. A well drilling method wherein a drilling fluid is injected into a borehole in the earth during the drilling of the borehole, the improvement which comprises injecting as the drilling fluid the fluid medium of Claim 1 in an amount sufficient to reduce the loss of the drilling fluid via penetration of porous subterranean strata proximate to the borehole.
9. In an enhanced oil recovery method in which an aqueous drive fluid is injected through an injection well bore into a hydrocarbon-bearing nonfractured formation having hydrocarbon-deficient and hydrocarbon-rich zones to drive hydrocarbon from the formation to a recovery well, the im-provement wherein an aqueous fluid medium containin discrete, spheroidal microgels of a water-swellable or water-swollen, crosslinked polymer of ethylenically unsaturated water-soluble monomer(s) is introduced through the injection well bore into the formation in an amount sufficient to reduce the aqueous fluid permeability of the porous formation, said microgels in at least a partially water-swollen state having diameters in the range from about 0.5 to about 200 micrometers, thereby restricting the passage of the drive fluid into hydrocarbon-deficient zones of the formation but not substantially impeding the passage of the drive fluid through hydrocarbon-rich zones of the formation.
10. The improvement of Claim 7 or Claim 8 wherein the polymer is crosslinked with from about 5 to about 200 weight parts of copolymerizable polyethylenic monomer per million parts of total monomer of the polymer.
11. The improvement of Claim 9 wherein the polymer is a polymer of acrylamide.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA291,282A CA1092797A (en) | 1977-11-21 | 1977-11-21 | Method for controlling permeability of subterranean formations |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA291,282A CA1092797A (en) | 1977-11-21 | 1977-11-21 | Method for controlling permeability of subterranean formations |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1092797A true CA1092797A (en) | 1981-01-06 |
Family
ID=4110078
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA291,282A Expired CA1092797A (en) | 1977-11-21 | 1977-11-21 | Method for controlling permeability of subterranean formations |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1092797A (en) |
-
1977
- 1977-11-21 CA CA291,282A patent/CA1092797A/en not_active Expired
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