Method of plugging subterranean zone

Abstract: A subterranean zone having a temperature above 76°C (170°F) is plugged by introducing into the zone an aqueous solution of a polymerizable monomer, a polymerization initiator and a high temperature polymerization inhibitor, and allowing the polymerizable monomer to polymerize to form a sealing or plugging gel.

Description: This invention relates to a method of plugging a subterranean zone having a temperature above about 76°C. Sealing compositions have heretofore been utilized in subterranean well completion and remedial operations. For example, sealing compositions have been used in well completion operations whereby casings and liners are sealed in well bores. In performing such operations, a sealing composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a casing string or liner disposed therein. The sealing composition is permitted to gel or set in the annular space thereby forming an annular sealing mass therein. In remedial operations carried out in wells, sealing compositions are used to seal holes or cracks in casings and liners and in the sealing masses maintaining the casings and liners in well bores. Oil and gas wells very often produce water in addition to the desired hydrocarbons. If the ratio of water produced to hydrocarbons produced by a well is relatively low, the produced water can be separated from the hydrocarbons and disposed of in a manner which does not make the operation of the well uneconomical. However, if uncontrolled large quantities of water are produced in addition to hydrocarbons by a well, the cost of pumping, handling, storing and disposing of the produced water often makes the continuing operation of the well uneconomical. Polymeric compositions which form polymerized and crosslinked impermeable masses have been developed and used heretofore in well completion and remedial operations. For example, polymeric compositions have heretofore been used to reduce or terminate the flow of water from a subterranean zone penetrated by a well. Such compositions are introduced into a subterranean water producing zone and caused to polymerize and crosslink therein whereby a stable gel which reduces or terminates the water flow from the zone is formed therein. United States Patents Nos. 3,334,689 issued August 8, 1967 and 3,490,533 issued January 20, 1970, both to McLaughlin, disclose polymerizable monomer solutions containing a polymerization catalyst for injection into subterranean zones. The solutions polymerize and are crosslinked in the zones to form stable gels which reduce the water permeabilities of the zones and decrease or terminate the flow of water therefrom. United States Patents Nos. 5,335,726 issued on August 9, 1994 and 5,358,051 issued October 25, 1994, both to Rodrigues, disclose methods of forming polymeric gels in subterranean zones to reduce or shut off the flow of water therefrom wherein a monomer is polymerized in the formation in the presence of a crosslinker by an initiator selected from certain azo compounds. Also, the use of hydroxy unsaturated carbonyl monomers is disclosed. The aqueous solutions of monomer or monomer and crosslinker and a polymerization initiator have heretofore been pumped as low viscosity solutions into subterranean zones in which completion or remedial procedures are to be conducted. The low viscosity solutions polymerize after placement which results in the formation of sealing gels in the zones. The polymerization of the monomer utilized is not initiated by the polymerization initiators heretofore used and/or does not proceed at an appreciable rate until oxygen-induced polymerization inhibition is overcome. That is, a polymeric solution contains dissolved oxygen which inhibits the polymerization of the monomer in the solution until all of the oxygen is consumed. The time required for the initiator to react with the oxygen present in the solution is known as the "induction period." The induction period enables placement of the polymeric solution in the zone to be sealed or plugged before polymerization of the solution prevents its flow into the zone. While various polymerization initiators such as persulfates, peroxides and azo compounds have been utilized heretofore, azo compounds are generally preferred for the reason that they are less likely to cause premature gelation. Persulfates and peroxides are subject to premature oxidation-reduction activation when they contact certain reductants such as metal ions which are commonly encountered in well tubular goods and the like. GB2226066 provides compositions containing unsaturated monomers capable of forming hydrogels in an aqueous medium in which gelling is delayed. These compositions comprise, in addition to water and at least one said monomer, a polymerization initiator in the form of a water-soluble or water-dispersible organic peroxide having a half-life of at least 10 hours at 60°C, and a polymerization inhibitor consisting of an alkali metal or ammonium salt of N-nitrosophenylhydroxylamine used in combination with an aminocarboxylic acid in acidic or basic form. In performing a completion or remedial operation using a polymeric composition in a subterranean zone which exists at a high temperature, i.e. a temperature above about 170°F (76°C), azo polymerization initiators relatively rapidly decompose and generate free radicals which react with oxygen at a rate such that the oxygen is consumed in too short a time. That is, the oxygen in the polymeric composition is consumed too fast whereby the polymeric composition often can not be pumped into the desired subterranean zone prior to the gelation of the polymeric composition taking place. Thus, there is a need for improved polymeric compositions and methods for performing well completion and remedial operations at high temperatures whereby the induction periods of the polymeric compositions can be economically lengthened. The present invention provides a method of sealing or plugging a subterranean zone having a temperature above 170°F (76°C), which method comprises the steps of introducing into said zone an aqueous solution of a polymerizable monomer, an azo polymerization initiator and a polymerization inhibitor which functions in the absence of oxygen to extend the induction period of said solution selected from phenothiazine, N-nitrosophenylhydroxylamine, or a salt thereof, which is present in said aqueous solution in an amount of from 0.001% to 0.1% by weight of said solution; and allowing said polymerizable monomer to polymerize in said zone to form a sealing or plugging gel therein. The improved polymeric compositions of the present invention for use in high temperature well applications are basically comprised of water, a polymerizable monomer, an azo polymerisation initiator and a polymerization inhibitor which functions in the absence of oxygen to extend the induction period of the composition. The polymerisation inhibitor is preferably selected from the group of phenothiazine and N-nitrosophenylhydroxylamine and its salts. The present invention provides an improved method of carrying out well completion and remedial operations at high temperatures including reducing the undesirable flow of water from high temperature subterranean zones, i.e. zones having a temperature above about 170°F (76°C). The performance of well completion or remedial operations in high temperature wells utilizing polymeric compositions is difficult. For example, the uncontrolled and undesirable flow of water from high temperature subterranean zones is often encountered in deep onshore wells. The temperatures involved are often in the range of from about 170°F to about 250°F (about 76° to 121°) and have heretofore made treatments for reducing or terminating the flow of water difficult or impossible. That is, when a polymeric composition containing an azo compound initiator is utilized in such a high temperature zone, the azo compound initiator rapidly decomposes and forms free radicals which react with oxygen at a high rate. This, in turn, causes the oxygen to be quickly consumed whereby gelation takes place too rapidly and the polymeric composition can not be pumped for a long enough time to place it in the desired subterranean zone. This problem is solved by the present invention which provides improved methods and compositions for carrying out well completion and remedial operations at high temperatures such as terminating undesirable subterranean water flows whereby the pumping time of the polymeric composition is extended by including a polymerization inhibitor in the composition. The polymeric compositions for performing well completion and remedial operations at temperatures about 170°F (76°C) are basically comprised of water, a polymerizable monomer, an azo polymerization initiator and a polymerization inhibitor which functions in the absence of oxygen to extend the induction period of the composition. The water used to form the polymeric compositions of this invention can be from any source provided it does not contain an excess of compounds that adversely affect other components in the compositions. For example, the water can be fresh water, seawater, brine or water containing various concentrations of one or more salts. The water is generally present in a polymeric composition of this invention in an amount in the range of from about 70% to about 95% by weight of the composition. A variety of water soluble polymerizable monomers can be utilized in the polymeric compositions. Examples of such monomers include acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-methacrylamido-2-methyl propane sulfonic acid, 2-acrylamido-2-methyl propane sulfonic acid, N,N-dimethylacrylamide, vinyl sulfonic acid, N,N-dimethylaminoethylmethacrylate, 2-triethylammoniumethyl methacrylate chloride, N,N-dimethylaminopropylmethacrylamide, methacrylamide, methacrylamidopropyl trimethylammonium chloride, N-vinyl pyrrolidone, vinylphosphonic acid and methacryloyloxyethyl trimethylammonium sulfate and mixtures thereof. Additional more preferred monomers include hydroxyethylacrylate, hydroxymethylacrylate, hydroxyethylmethacrylate, N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, polyethylene and polypropylene glycol acrylate and methacrylate and mixtures thereof. Of these, hydroxyethylacrylate is most preferred. The polymerizable monomer or monomers are combined with the polymeric compositions in a general amount in the range of from about 5% to about 20% by weight of the compositions. Preferably, the polymerizable monomer or monomers are present in an amount in the range of from about 10% to about 15% by weight of the compositions, most preferably in an amount of about 15%. The above monomers are often used in combination with crosslinking multifunctional vinyl monomers such as glycerol dimethacrylate and diacrylate, ethoxylated and propoxylated glycerol dimethacrylate and diacrylate, ethoxylated and propoxylated trimethacrylate and triacrylate, ethoxylated and propoxylated trimethylolpropane trimethacrylate and triacrylate, ethoxylated and propoxylated pentaerythritol di, tri and tetra methacrylate and acrylate, methylene-bis-acrylamide and methacrylamide, polyethylene and polypropylene glycol dimethacrylate and diacrylate, allylmethacrylate and acrylate and mixtures thereof. When used, the crosslinking monomers are included in the polymeric compositions in an amount in the range of from about 0.005% to about 0.5% by weight of the compositions. Azo polymerization initiators are used in the present invention. Azo polymerization initiators generally include those of the formula: R 1 -N=N-R 2 wherein: R 2 is the same as R 1 or R 3 is -CH 3 or -C≡N , R 4 is (CH 2 )COOH or -CH 3 , R 5 is =N-, =NH or =O , and when R 2 is R 3 is -C≡N and R 4 is -CH 3 . .Azo polymerization initiators within the scope of the above formula are temperature activated at various temperatures and are not activated by oxidation-reduction mechanisms. The term "activation temperature" is used herein to mean that temperature at which half the molar amount of a compound converts to free radicals in a period of 10 hours. As will be understood by those skilled in the art, a particular azo polymerization initiator can be selected from the above group for use in a polymeric composition of this invention provided it has an activation temperature equal to or slightly less than the temperature of the subterranean zone to be sealed. Further, since the azo compounds are not activated by oxidation-reduction mechanisms, the reducing metals commonly encountered in pumping equipment and tubular goods of wells do not cause premature gelation of the polymeric composition. Examples of preferred azo compounds for use in accordance with this invention in high temperature applications are 1-[(1-cyano-1-methylethyl)azo] formamide, azodicarbonamide and 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]. The most preferred high temperature azo polymerization initiator is 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]. The activation temperatures of such initiators are 219°F (104°C), 189°F (87°C) and 187°F (86°C), respectively. The quantity of azo initiator employed is an amount in the range of from about 0.005% to about 0.15% by weight of the polymeric composition. Examples of the polymerization inhibitors which can be utilized in accordance with this invention in polymeric compositions used in high temperature applications are phenothiazine and N-nitrosophenylhydroxylamine and its salts. The inhibitors function in the absence of oxygen to increase the induction period and therefore the pumping time of the polymeric compositions. The most preferred such inhibitor is the ammonium salt of N-nitrosophenylhydroxylamine. The polymerization inhibitor used is included in the polymeric compositions of this invention in an amount in the range of from about 0.001% to about 0.1% by weight of the compositions. In carrying out the methods of this invention for sealing or plugging a subterranean zone having a high temperature above about 170°F (76°C), a polymeric composition of the invention is introduced into the zone, i.e. an aqueous solution of a polymerizable monomer, an azo polymerization initiator and a polymerization inhibitor which functions in the absence of oxygen to extend the induction period of the composition. Thereafter, the polymerizable monomer in the composition is allowed to polymerize in the zone thereby forming a sealing or plugging gel therein. In order to further illustrate the polymeric compositions and methods of this invention, the following Example is given by way of illustration only. Example 1 Four test polymeric compositions were each prepared by dissolving 5.4 grams of potassium chloride and 0.72 gram of a borate pH buffer (used to slow monomer hydrolysis at high temperatures) in 259 millilitres of water. 41 millilitres of hydroxyethylacrylate monomer and 0.18 gram of N,N'-methylenebisacrylamide crosslinking monomer were then added and dissolved in each composition. The composition was divided into four test portions. A high temperature polymerization inhibitor comprised of 3% by weight ammonium N-nitrosophenylhydroxylamine dissolved in water was then added to three of the four test compositions in varying amounts and 0.072 gram of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl) propionamide] polymerization initiator was added to each composition. The test compositions were tested for gelation times at a temperature of 200°F (93°C). Each test portion of polymeric composition was prepared with stirring at the test temperature and transferred to a 300ml high pressure glass bottle containing a marble and having a back pressure of 50 psig held thereon. The glass bottle was completely filled with the composition and capped in a manner so as not to trap any air inside the bottle. Each bottle was placed in a water bath at the test temperature and checked at 15 minute intervals for gelation. That is, when the marble remained stationary or moved very slowly as the bottle was inverted, the formation of a gel was indicated. The results of these tests are given in Table I below. Gelation Time Tests Polymerization Inhibitor Concentration milligrams/liter Gelation Time, Hours 0 2.25 50 3.5 75 4.0 100 5.25 From Table I, it can be seen that the polymeric compositions of the present invention have extended gelation times at high temperatures in the absence of oxygen.

Claims: A method of sealing or plugging a subterranean zone having a temperature above 170°F (76°C), which method comprises the steps of introducing into said zone an aqueous solution of a polymerizable monomer, an azo polymerization initiator and a polymerization inhibitor which functions in the absence of oxygen to extend the induction period of said solution selected from phenothiazine, N-nitrosophenylhydroxylamine, or a salt thereof, which is present in said aqueous solution in an amount of from 0.001% to 0.1% by weight of said solution; and allowing said polymerizable monomer to polymerize in said zone to form a sealing or plugging gel therein. A method according to claim 1, wherein the polymerizable monomer is acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-methacrylamido-2-methyl propane sulfonic acid, 2-acrylamido-2-methyl propane sulfonic acid, N,N-dimethylacrylamide, vinyl sulfonic acid, N,N-dimethylaminoethylmethacrylate, 2-triethylammoniumethylmethacrylate chloride, N,N-dimethylaminopropylmethacrylamide, methacrylamidopropyl trimethylammonium chloride, N-vinyl pyrrolidone, vinyl phosphonic acid or methacryloyloxyethyl trimethylammonium sulfate or any mixture of two or more thereof. A method according to claim 1 or 2, wherein the polymerizable monomer is present in the aqueous solution in an amount of from 5% to 20% by weight of the solution. A method according to claim 1, wherein the polymerizable monomer is N-hydroxymethylacrylamide, hydroxyethylacrylate, hydroxyethylmethacrylamide or N-hydroxymethylmethacrylamide, or any mixture of two or more thereof. A method according to claim 4, wherein the polymerizable monomer is present in the aqueous solution in an amount of from 5% to 20% by weight of said solution. A method according to any of claims 1 to 5, wherein said aqueous solution further comprises a crosslinking multi-functional vinyl monomer selected from glycerol dimethacrylate or diacrylate, ethoxylated or propoxylated glycerol dimethacrylate or diacrylate, ethoxylated or propoxylated glycerol trimethacrylate or triacrylate, ethoxylated or propoxylated trimethylolpropane trimethacrylate or triacrylate, ethoxylated or propoxylated pentaerythritol di, tri or tetra methacrylate or acrylate, methylene-bis-acrylamide or methacrylamide, polyethylene or polypropylene glycol dimethacrylate or diacrylate, allylmethacrylate or acrylate, or any mixture of two or more thereof. A method according to claim 6, wherein the crosslinking monomer is present in the aqueous solution in an amount of from 0.005% to 0.5% by weight of said solution. A method according to any of claims 1 to 7, wherein said azo polymerization initiator is 1-[(1-cyano-1-methylethyl)azo]formamide, azodicarbonamide or 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide]. A method according to any of claims 1 to 8, wherein said azo polymerization initiator is present in the aqueous solution in an amount of from 0.005% to 0.15% by weight of said solution.

Inventors: FROST KEITH A, FUNKHOUSER GARY P, FROST, KEITH A., FUNKHOUSER, GARY P.
Applicants: HALLIBURTON ENERGY SERV INC, HALLIBURTON ENERGY SERVICES, INC.
Application year: 1998
Main classification: E21B33
IPC codes: C09K8