3,079,336 United States Patent Office Patented Feb. 26, 1963 2 Furthermore, it does not normally displace as much oil 3,079,336 ALCOHOLS EN CON UNCTION WITH WATER in the portions of the reservoir which it contacts as it THECKENERS FOR A SECONDARY RECOVERY theoretically is capable of doing. PROCESS The fingering tendency of a waterflood is usually ex Paul L. Stright, Buffalo, N.Y., and Albin F. Turbak, New plained by the fact that oil reservoirs possess regions and Providence, N.J., assignors to Jersey Production Re strata that have different permeabilities. The water flows search Company, a corporation of Delaware more rapidly through those regions and strata having a No Drawing. Filed Mar. 22, 1960, Ser. No. 16,663 greater relative permeability to water than in other por 7 Claims. (C. 252-8.55) tions of the reservoir. Waterflooding often completely O misses substantial portions of the reservoir. The net The present invention is broadly concerned with a result is an inefficient oil displacement action on the part secondary recovery operation or process for obtaining oil of the water. from subterranean reservoirs. The invention is more At this point, it should be noted that crude oils vary particularly directed to a secondary recovery procedure greatly in viscosity-some being as low as 1 or 2 cps. wherein a fluid such as water is employed as a driving 15 and some ranging up to 1,000 cps. or even more. It has medium and wherein various types of water thickening been established that waterflooding performs less satis agents are utilized to increase the viscosity of the water so factorily with viscous crude oils than with relatively non as to prevent fingering in the oil reservoir. The invention viscous oils. In other words, the fingering and bypassing particularly is directed toward the use of alcohols in con tendencies of the water drive are more or less directly junction with these water thickening agents in order to related to the ratio of the viscosity of the reservoir oil to improve thermal stability. A particularly desirable process the viscosity of the aqueous driving medium. comprises the use of alcohols such as methanol in con Also of interest at this point is a mathematical relation junction with thickening agents selected from the class ship that has been developed in recent years to help ex of vinyl aromatic maleic anhydride copolymers. plain the behavior of fluids flowing through porous media In the recovery of oil from subterranean reservoirs, 25 such as oil reservoirs. When this equation is applied to a there have been substantial advances in primary recovery techniques so as to substantially increase the recovery flooding operation or the like within an oil reservoir, it of oil. However, an appreciable quantity of the oil re reads as follows: mains in the reservoir after termination of the primary Mo -is rtsK recovery methods. In general, it is estimated that only 30 M o Ko about 10 to 30% of the oil can be economically recovered by primary recovery techniques. A greater amount may where be recovered by other secondary techniques, such as repres Mo is the mobility of the oil to the reservoir in question suring treatments following the primary method. Me is the mobility of the flooding medium to the reservoir Thus, there exists a great interest in secondary recovery in question methods. Secondary recovery is the recovery of additional uo is the viscosity of the driven oil quantities of oil from a reservoir after it is no longer pe is the viscosity of the flooding medium economical to recover oil by primary recovery methods. K is the relative permeability of the reservoir toward the For example, a secondary operation may be conducted by flooding medium in the presence of residual oil drilling one or more injection wells into a permeable oil, 40 Ko is the relative permeability of the reservoir toward bearing formation within suitable proximity to a produc the oil in the presence of connate water ing well or wells which are drilled into this same permeable This equation is perhaps best explained by stating that oil bearing formation. Injection of liquids or gases when the mobility ratio of oil to the driving fluid within through the injection well is generally effective in increas the reservoir is equal to one, the oil and driving fluid ing the oil production from the producing well or wells. move through the reservoir with equal ease. Substan This technique of secondary recovery enables the recovery 45 tially equilibrium proportions of driving fluid and oil re of substantially more oil than can be produced by primary main within the reservoir as soon as the driving fluid recovery methods. has passed therethrough. Expressed otherwise, the mo As pointed out, the use of a number of secondary re bility ratio term affords a measure of the volume of driv covery procedures for removing oil from subterranean 50 ing fluid and the amount of time that is required to re oil reservoirs are well known in the petroleum industry. duce the oil content of the reservoir to an ultimate equili It is the function of such procedures to make possible the brium value. For example, a given volume of driving recovery of oil from reservoirs after primary production fluid operated at a mobility ratio of one or greater will methods are uneconomical. In general, all secondary re displace a markedly greater volume of oil from a reser covery procedures employ a driving medium such as a 55 voir than will an equal volume of driving fluid. operating liquid or gas for displacing additional oil from a reservoir. at a mobility ratio of less than one. - The displacing medium, usually a fluid, is injected in a Several procedures have been suggested to date for im reservoir as by means of one or more of the original wells proving the mechanics of waterflooding procedures par or by means of entirely new wells; and the oil in the ticularly with the view to reducing the degree of fingering reservoir is displaced toward and withdrawn from other and bypassing. One suggestion has been to increase the remaining wells. 60 viscosity of the water drive relative to the oil by incor Due partially to its ready availability in many regions, porating water soluble viscous agents within the water. water has been extensively employed as a driving medium Materials that have been suggested for this purpose in in secondary oil recovery programs. clude a wide variety of naturally occurring gums, sugars While conventional waterflooding is effective in obtain and polymers. While these materials are effective to an ing additional oil from subterranean oil reservoirs, it has 65 extent in increasing the viscosity of flood water, they a number of shortcomings which detract seriously from its are also characterized by serious disadvantages. For ex value. Foremost among these shortcomings is a tendency ample, some of the materials have a tendency to plug for of flood water to "finger' through a reservoir and to by mations; some are relatively unstable; and some have rela pass substantial portions of the reservoir. In other words, 70 tively little thickening effect. Additionally many of these a water drive has a less than perfect "sweep efficiency" in materials are quite expensive and their use is not feasible that it does not contact all portions of the reservoir. from the standpoint of economics. 3,079,336 3. 4. Accordingly, it is an object of this invention to provide EXAMPLE 2. an improved type of displacement process in which a The following data were obtained from a 0.3% solution marked increase in the viscosity of the driving fluid may of a sulfonated 3 polystyrene in reservoir water. One be readily attained. It is also an object of the invention percent methanol by volume was added. The solutions to provide a viscous "waterflooding' process in which the were aged at 212 F. in the presence of a nitrogen atmos increased viscosity of the flood water is attained inexpen phere. sively. It is still a further object of the invention to use a driving fluid whose viscosity is stable. This is attained Percent, Wiscosity by the utilization of alcohols in conjunction with water Methanol Initial Retained. After thickening agents. Low molecular weight, water soluble O N.B. 458 Added Wiscositya alcohols, such as methyl alcohol, ethyl-alcohol, isopropyl 3% Hours 27 Hours alcohol, n-propyl alcohol, and the like, are desirable. The process of the present invention may be more 23------No------.9. 57 42 readily understood by the following examples illustrating 23-2------Yes------9. 2. embodiments of the same. a Brookfield viscosity, cp., 60° C., 30r.p.m., U.L. adapter. From the foregoing, it is apparent that the viscosity EXAMPLE 1. retention of sulfonated polystyrene solutions is greatly A styrene-maleic anhydride copolymer 1 and a half improved by the addition of methanol.

EXAMPLE 3 Effect of Methanol on Thermal Stability of Polymer Solutions Percent Viscosity Retained. After N.B. Methano. Initial Refluxing (Eiours) Polyner Ref. Conc, a Added b Wis 458 . . eosity o 2 48 96 240 336 672

Polyacrylic Acid (R.V. = 18.5). 23-5 O 5.2 68 23-f 0. 15. 9. Styrene-Methacrylic Acid Co 25-2 0. 2. 43. polymer (1:2). 25-3 0. 12.3 130 d822 Polyethylene oxide (Polyox30). 28-7 4.0 3. 238 142 e O Percent by weight in reservoir water. AddedBrookfield. 19% Viscosity by volune (cp., absolute 60°C.,30r.p.m., methanol, U.L. Adapter). Gel precipitated from both solutions before 120 hours Aging data is for 60 C. in oven, rather than at reflux temperature. Polymer precipitates from refluxing Solution. methyl ester derivative of that copolymer were each dis From the foregoing, it is apparent that the viscosity solved in reservoir water and NaOH. These solutions retention of polymer solutions, containing polymers of (0.5%) were each divided into two portions, and 1% widely varying types, is improved by the addition of by volume methanol was added to one portion and not 45 methanol. the other. These solutions were then tested for viscosity The invention is broadly concerned with the use of retention, while refluxing at 212 F. in a nitrogen atmos alcohols, particularly, low molecular weight alcohols for phere. The.. data below demonstrate the increased viscos the stabilization of viscosity of thickened polymer solu ity retention obtained when methanol was present. tions for use in a secondary water flooding operation. 50 Generally, the alcohols are mono-hydroxy alcohols where in the number of carbon atoms is in the range from about Percent Viscosity Methano Initia . Retained. After 1 to 6. The alcohols are used in a concentration by Compound Added Vigi weight in the range from 0.1 to 5.0%, preferably, in the lity a range from 0.1 to 1.0%. Particularly desirable alcohols 24 Hours 264Hours 55 are, for example, methanol and isopropanol. 7.2 42 22 The alcohols are employed in conjunction with water 7.3 59 4 thickening agents which generally are of the carboxylic 4.3 154 58 acid type polymer. Other satisfactory polymers, for ex 4.3 86 15 ample, polyethylene oxides, polyvinylaromatic sulfonates, 60 polyacrylic and polymethacrylic acids and derivatives, Measured with Brookfield visconnetter-U.L. adapter at 30r.p.m. and polyvinyl alcohols, are made more stable by the ad This increased viscosity retention was also observed dition of alcohols. (1) when methanol was added during the preparation of As pointed out heretofore, satisfactory compounds are the reservoir water solution of the polymers, and (2) copolymers of vinyl aromatics and maleic anhydride. when methanol was added after the solution had been 65 These compounds are produced by copolymerizing vinyl refluxed for 24 hours. From the above, it is apparent that the methanol sub aromatics, such as styrene, vinyl toluene, vinyl naphtha stantially improved the viscosity retention of the water lene and the like with maleic anhydride. These mate thickening agent. rials are obtained in high molecular weights by using azo 70 bis-isobutyronitrile as catalyst, and polymerizing at low A styrene maleic anhydride copolymer having a molecular temperatures, such as 30- 60° C. Other catalysts can weight in excess of 200,000. be used, such as benzoyl peroxide and cumene hydro . Reservoir waters 40 liters of water, contains 2.2 grams peroxide. The viscosity of aqueous solutions have im sodium bicarbonate, 4.28 grams sodium sulfate, 5.52 grams magnesium chloride,356 grams calcium chloride, 36.5 grams sodium chloride snd 2.05 grams aluminun. sodium sulfate A sulfonated polystyrene polymer having a molecular (Al2(SO4)3Na2SO4.24H2O). 75 weight in excess of about 200,000. 3,079,886 5 6. proved salt sensitivity and heat stability as compared to Copolymers claimed in this invention can be described other polyelectrolytes. by the following general structural formula: Specific vinyl aromatics exemplifying monomers that may be copolymerized with maleic anhydride are as fol lows: styrene, vinyl toluene, c-methyl styrene, p-chloro styrene, dichlorostyrene, vinylnaphthalene, trans-stilbene, ca,c-diphenylethylene, iso-allylbenzene, vinylcarbazole and (i)(i), vinyl ferrocene. Y l The styrene was copolymerized with maleic anhydride in methyl ethyl ketone at 60° C. using 0.036 gram of O azo-bis-isobutyronitriie as catalyst per mole of monomers. X The copolymer was precipitated from methyl ethyl ke where R and R are hydrogen, alkyl or aryl. tone solution with methanol, and then hydrolyzed by dis X=H, alkyl such as ethyl or methyl, Cl, CHO, CsN, solving in dilute aqueous sodium hydroxide. OH, SOH and COH. The molecular weights of the polymers of the present 5 Y-OH, ONa, ONH4, NH2 or any other group imparting invention should be in excess of about 100,000. In gen water solubility. If Y-OH, part of the group may eral, preferred polymers should be above about 500,000, be OR where R=an alkyl group such as methyl or preferably, above 1,000,000. The molecular weights may ethyl as long as water solubility is maintained. be as high as 3,000,000 to 5,000,000, or up to 10,000,000 n-degree of copolymerization and equals at least 50 and and higher. When a polymer has a molecular weight in 20 may be as high as 100,000 or more. the range from 500,000 to 1,000,000, it should be used in a/bs the ratio of the monomers in the polymer and may the concentration of less than about 1% by volume, cover the entire range composition range as long as preferably, in the range from 0.1 to 0.5% by volume. A the product is water soluble. Polymers below 0.5/1 desirable concentration is 0.2% by weight. are believed to have little interest. Other satisfactory thickening agents for use in con 25 junction with the alcohols of the present invention are Specific compounds falling in the above-identified class copolymers of: are copolymers of acrylic acid and styrene, acrylic acid and methyl styrene (vinyl toluene), methacrylic acid and (1) Acrylic acids styrene and methacrylic acid and methyl styrene (vinyl (2) Low molecular weight aliphatic olefins 30 toluene). C-C olefins Other satisfactory polymers are copolymers of maleic Copolymers of acrylic acids or substituted acrylic acids anhydride and vinyl aromatics in conjunction with al with low molecular weight aliphatic olefins or substituted cohol adducts. A particular polymer of this category low molecular weight aliphatic olefins. comprises a copolymer of maleic anhydride and styrene The class of polymers claimed in this invention are 35 in conjunction with an alcohol adduct of methanol, prepared by copolymerizing an acrylic type acid with a ethanol and isopropanol. mono-olefin. The mono-olefin can be propylene, ethyl A particular type of water thickening agent for use in ene, isobutylene, and may be represented by the following conjunction with the alcohols of the present invention formula: are Sulfonated polymers. Compounds have the follow 40 ing structural formula: R

--- R C=CH, wherein R and R' represent hydrogen or alkyl groups. 45 The alkyl group may contain from 1 to 10 carbon atoms and preferably 1 to 6 carbon atoms. The acrylic type acid may be acrylic acid, or methacrylic acid and may be represented by the following structural formula: where: R represents H, CH3 or a group for which the Hammett function is known or readily determinable. (See Physical Organic Chemistry by J. Hine, published by Wiley and Company, New York.) (X) represents the degree of polymerization and has wherein R' represents either hydrogen or an alkyl group values such that the molecular weight of the resulting containing from 1 to 10 carbon atoms. Y represents a polymer is greater than 100,000. water solubilizing group as, for example, OH, ONa, ONH Mb represents a cationic salt component and may be and NH2. If the group comprises a hydroxy group, this NaeK9, LiCB, NH9, CHNH69, CH5NH35, may be substituted in part by OR, as long as water solu 60 CHNH39, CHNH9, CHNH9 bility remains. The resulting polymer is represented by the following formula: Y N(B Es or other ammonium derivatives. wherein the a to b ratio is not greater than 4:1, and pref The relative substituent position of R to -SOeMe erably, wherein the a to b ratio is about 1:1, and wherein 70 to the styryl group is considered to be non-limiting except n is of a value to give the desired molecular weights as by reason of ease of preparation. Thus, for example, described herein. in the case of polyvinyl toluene sulfonate prepared by Other satisfactory polymers are copolymers of acrylic polymerization of a mixed ortho and para vinyl toluene acid as, for example, methacrylic acid in conjunction with monomer, as is generally commercially supplied, the sul a vinyl aromatic, such as styrene and vinyl toluene. 75 fonate would enter respective positions along the chain 8,079,886 7 8 in accordance with the generally well established rules of compound having a molecular weight in the range from organic chemistry; each position being determined by the about 200,000 to 5,000,000 and from about 40 to 5% relative positions already occupied on the aromatic of an aliphatic alcohol having 1 to 6 carbon atoms per nucleus by the polymer backbone and the methyl group. molecule, said organic thickening compound being se In the case of polystyrene, the sulfonate would enter lected from the group consisting of (1) a copolymer of ortho and para to the position linked to the polymer back maleic anhydride and a vinyl aromatic, (2) a copolymer bone. of acrylic acid and a low molecular weight olefin, (3) a As pointed out heretofore, these polymers should have copolymer of acrylic acid and a vinyl aromatic, (4) a molecular weights above 500,000, preferably, above Sulfonated polyvinyl aromatic, (5) a polymer of ethylene 1,000,000. The molecular weights may be as high as 10 oxide, and (6) polyacrylic acid. 3,000,000 or up to 10,000,000. The polymer is used in 2. A process as defined by claim 1 wherein said organic a concentration of less than 1% by volume based upon thickening compound is a copolymer of maleic anhydride the volume of water, preferably, in a concentration of and a vinyl aromatic, and wherein said alcohol is se 0.1 to 0.5 weight percent. A desirable concentration is lected from the group consisting of methanol and iso about 0.2. weight percent. The concentration of the al propanol. cohol employed is in the range from 0.01% by volume 3. A process as defined by claim 1 wherein said organic to 5% by volume. A preferred concentration for the al thickening compound is a copolymer of acrylic acid and cohol is in the range from 0.1 to 1.0% by volume. a low molecular weight olefin. Other valuable products which can be stabilized by the 4.- A process as defined by claim 1 wherein said or addition of alcohol are the polymers and adducts of ethyl 20 ganic thickening compound is a copolymer of acrylic ene oxide. Polyethylene oxide has the structure: acid and a vinyl aromatic. 5. A process as defined by claim 1 wherein said organic thickening compound is a sulfonated polyvinyl aromatic. where x has values such as to give molecular weights in 6. A process as defined by claim 1 wherein said or excess of 100,000. ganic thickening compound is a polymer of ethylene As adducts of ethylene oxide, included are the ethoxyla oxide. tion products of polyxinyl alcohol and of polyacrylamide. 7. A process as defined by claim 1 wherein said organic These can be prepared by procedures set forth in U.S. thickening compound is polyacrylic acid. Patent No. 1,971,662. While the present application is primarily concerned 30 References Cited in the file of this patent with increasing the stability of these polymers in a Sec ondary recovery operation, it is to be understood that UNITED STATES PATENTS the general technique may be utilied to stabilize this class 2,262,428 Leitz ------Nov. 11, 1941 of polymers when used in any type of process or operation. 2,267,548 Berl ------Dec. 23, 1941 What is claimed is: 2,327,017 Chamberlain ------Aug. 17, 1943 1. An improved process for recovering oil from an oil 2,341,500 Detling ------Feb. 8, 1944 reservoir which comprises flowing through said reservoir 2,808,109 Kirk ------Oct. 1, 1957 from an input well toward an output well a flood water 2,827,964 Sandiford et al. ------Mar. 25, 1958 which has been increased in viscosity by incorporating 2,842,492 Engelhardt et al. ------July 8, 1958 therein from about 40 to 1% of an organic thickening 40