MXPA96006059A - Composition and process for the treatment of an underground formation containing hydrocarb - Google Patents

Abstract

The present invention relates to a composition comprising effective proportions of: (1) a carboxylate-containing polymer, (2) a multivalent metal compound which comprises a cation and an anion wherein the cation is selected from the group consisting of zirconium , titanium and combinations thereof, and the anion is selected from the group consisting of fluoride, carbonate, chloride, citrate, amine and combinations of any two or more thereof, (3) a liquid that is selected from the group consisting of of pure water, tap water, solutions or suspensions of salts, and combinations of any two or more thereof, and (4) a pH reducing agent that is selected from the group consisting of carbon dioxide, dioxide-generating compounds, carbon, weak acids, esters and combinations of any two or more thereof, wherein the composition does not contain an agent that retards gelation and the ratio is effective to form a n gel from the composition

Description

COMPOSITION ¥ PROCESS FOR THE TREATMENT OF A UNDERGROUND FORMATION CONTAINING HYDROCARBONS FIELD OF THE INVENTION The present invention relates to a composition and a process that are useful, for example, for altering the permeability and correcting the problems of suction or formation of water cones of underground formations possessing hydrocarbons.

BACKGROUND OF THE INVENTION It is well known to those skilled in the art that gelled or crosslinked water soluble polymers are useful in the improved recovery of oil and other operations in oil fields. These have been used to alter the permeability of underground formations, in order to improve the effectiveness of flood operations with water. In general, the polymers together with an appropriate crosslinking system are injected into an aqueous solution within the formation. The polymers are then permeated inside and gelled in regions that have the highest water permeability. REF: 23550 Due to environmental problems, as well as the cost for the disposal of a produced brine that is defined as brine co-produced with oil or gas, and is frequently contaminated with oil or gas, or both, it may be desirable to use the brine produced as the aqueous solution used for the appropriate polymers and crosslinking systems. The use of the produced brines eliminates not only the cost associated with the acquisition and pretreatment of fresh water for use as the aqueous solution, but also the cost of disposal for the brine produced. Most of the brines produced are known to be hard brines, for example, those having a bivalent cation concentration greater than 1000 ppm. Although a chromium salt can be used (III) which is not as toxic as a chromium salt (VI), as a crosslinking agent, this is not an environmentally desirable compound, and its use may require additional costs to ensure the integrity of the injection wells, to avoid contamination of groundwater sources. Other multivalent metal compounds such as zirconium, titanium, ferric or aluminum compounds, or combinations of any two or more thereof, have been used to produce gels with water soluble polymers, synthetics, or natural polymers for various operations in oil fields such as, for example, permeability corrections and water occlusion for deposits. Usually these metal ions crosslink gellable polymers through the interaction with the carboxylate groups of the polymer molecules. In general, the gellable polymers used, such as, for example, polyacrylamide, are high molecular weight and contain high degrees of hydrolysis, for example, they contain 10-30 mol% of carboxylate groups. However, these polymers containing carboxylate groups of high molecular weight and / or high mole percent, gel almost instantaneously in the presence of the multivalent metal compounds described above. Such rapid rate of gelling makes the application of the gelling compositions containing these polymers and multivalent metal compounds, not useful in many applications in oil fields such as, for example, reductions of the occlusion and permeability with water. In addition, the resulting gels typically suffer from the strong phenomenon of syneresis in most brines in oil fields.

Many processes have been developed to retard the gelation of the gelling compositions, by the addition of a gelation retarding agent to the gelling compositions. However, a gelling retarding agent is not cheap and a gelling retarding agent often adds appreciable costs to the operation in the oil fields. Therefore, a more environmentally appropriate process using a gelling composition, which. can form stable gels in a liquid such as, for example, brines produced for shallow well drilling as well as in depth treatments, and which does not require a gelling retarding agent, is highly desirable.

BRIEF DESCRIPTION OF THE INVENTION An object of the invention is to provide a composition and a process useful for altering the permeability of hydrocarbon-bearing formations. Still another object of the invention is to provide a composition and a process for altering the permeability of hydrocarbon-forming formations by the use of a gelling composition that is environmentally suitable for use in oil field operations. A further object of the invention is to provide a composition and a process for altering the permeability of the hydrocarbon-forming formation, wherein the composition does not require a gelling retarding agent. A further objective of the invention is to provide a process for the treatment in well drilling, employing a gelling composition that is environmentally suitable for operations in oil fields. An advantage of the invention is that the process of the invention does not employ a gelling retarding agent, achieves even the alteration of permeability of the formations or other applications in oil fields. Yet another advantage of the invention is that in general the gelation of the composition can be accelerated by the addition of a pH decreasing agent. Other objects, features and advantages will become more apparent as the invention is more fully described hereinafter. According to a first embodiment of the present invention, there is provided a composition that can be used to improve the recovery of hydrocarbons. The composition comprises a water soluble polymer, a crosslinking agent and a liquid, and does not contain a gelling retarding agent. According to a second embodiment of the present invention, there is provided a process for the formation treatment having hydrocarbons, which comprises the injection into the formation, of a gelling composition comprising a water soluble polymer, a crosslinking agent. , and a liquid wherein the gelling composition forms gels when injected into the formation.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graphical representation of the strength or strength of the gel, of the gels formed, as a function of aging time at 49 ° C (120 ° F) in 2% potassium chloride solution in the presence of ( i) or absence (A) of carbon dioxide. Figure 2 is the same as Figure 1, except that distilled water was used in place of 2% potassium chloride. The concentration of the copolymer was 5,000 mg / l (ppm) and that of the crosslinking agent, ammonium-zirconium carbonate measured as zirconium cation, was 750 ppm. See Example II for details.

DETAILED DESCRIPTION OF THE INVENTION According to the first embodiment of the present invention, there is provided a composition that can be used for the treatment of a hydrocarbon-forming formation and comprises, or consists essentially of, or consists of a water-soluble polymer, a cross-linking agent and a liquid. In general, the water soluble polymer contains a functional group such as the carboxylate group which is crosslinkable with a metal cation and is present in an aqueous solution containing a liquid. The most frequently used water-soluble polymers are carboxylate-containing polymers. The term "liquid" used herein is interchangeable with "water" and generically refers to, unless otherwise indicated, pure water, regular tap water, a solution or suspension wherein the solution or suspension They contain a variety of salts. A typical solution is a brine produced. The term "hydrocarbon" denotes any hydrocarbons that may or may not be oxygenated or substituted with appropriate substituents. The hydrocarbon may contain minor components such as, for example, sulfur. The currently preferred hydrocarbons are crude oil and natural gas. The treatment includes, but is not limited to, alteration of permeability, correction of suction or formation of water cones, occlusion by water, gas occlusion, and zone abandonment. The brine produced is defined as the brine co-produced with petroleum or natural gas, or both, which is generally a hard brine, for example, containing at least 1,000 ppm of Ca + 2, Ba + 2, Mgr2, or Sr + 2, or combinations thereof. A brine produced generally contains high salinity from about 1% by weight to about 30% of total dissolved solids. A produced brine is contaminated in general with oil or natural gas, or both. The gellable polymer generally gels well in produced brines having a salinity of from about 0.3% to about 25%. The term "carboxylate-containing polymer" used herein refers to, unless otherwise indicated, a polymer that contains at least one free carboxylic group or a carboxylate group, in which the carboxylic acid proton is substituted with an ammonium radical, an alkali metal, an alkaline earth metal, or combinations of any two or more thereof. According to the present invention, the term "retarding agent" denotes a chemical or mixture of chemicals that retard the gelation rate or rate. A retarding agent useful for retarding the gelation rate is in general a carboxylic acid and salts thereof, which may contain one or more hydroxyl groups. A commonly known retarding agent can also be an amine having more than one functional group, and it contains one or more hydroxyl groups, and the zirconium or titanium portion of the zirconium or titanium compounds described above can be chelated. The term "retarding agent" can be interchangeable with "chelating agent", or "sequestering agent" or "gelling retarding agent". According to the present invention, the molecular weight of the water-soluble polymers is generally at least about 10,000 and less than about 25,000,000, preferably less than about 20,000,000. The mole percent of the carboxylate group in the carboxylate-containing polymers is generally in the range of about 0.01 or less than about 45, preferably about 0.1 to less than about 25, more preferably about 0.1 to less than about 15, still more preferably from about 0.1 to less than about 10, and most preferably from 0.2 to 10 mol%. According to the present invention, the gelation rate is defined as the rate at which the gel particles are formed. At the start of the gelling these particles are sufficiently small so that the gelling solution still flows, but these particles can be detected from the apparent flow characterization caused by the change in apparent viscosity. The small particles grow to form larger granules, over time, and they become strong enough to hold fluids within their structures, which restricts the characterization of the free flow of the gelling solution and thus develops tongue length. The gelation rate is generally greater than about 1 hour, preferably greater than about 2 hours, more preferably greater than about 3 hours, still more preferably greater than about 4 hours, and most preferably greater than 10 hours. In general, no appreciable gel strength is observed, as defined in Example I, until a tongue length can be measured. The carboxylate-containing polymers suitable for the use of this invention are those capable of gelling in the presence of a crosslinking agent such as, for example, a multivalent metal compound. Polymers suitable for use in this invention, for example, those capable of gelling in the presence of a crosslinking agent, include, but are not limited to, biopolysaccharides, cellulose ethers, and polymers containing acrylamide. Suitable cellulose ethers are described in U.S. Patent No. 3,727,688 (incorporated by reference herein). Particularly preferred cellulose ethers include carboxymethylhydroxyethylcellulose (CMHEC) and carboxymethylcellulose (CMC) for their ready availability. Suitable biopolysaccharides are described in U.S. Patent No. 4,068,714 (incorporated by reference herein). Particularly preferred is polysaccharide B-1459 and xanthan gums which are biopolysaccharides produced by the action of the bacterium Xan thomonas campestris. This biopolysaccharide is commercially available in various grades under the tradename "KELZAN®" (Kelco Company, San Diego Ca) and "FLOCON" 4800 (Pfizer, Groton, CT) and these are readily available. Suitable acrylamide-containing polymers that also contain protruding carboxylate groups are described in US Patent No. 3,749,172 (incorporated by reference herein). Particularly preferred are the so-called partially hydrolyzed polyacrylamides, which have outstanding carboxylate groups through which crosslinking can take place. The thermally stable carboxylate-containing acrylamide polymers, such as polyacrylamides; copolymers of N-vinyl-2-pyrrolidone and acrylamide; terpolymers of sodium-2-acrylamido-2-methylpropanesulfonate, acrylamide and N-vinyl-2-pyrrolidone; and copolymers of sodium-2-acrylamido-2-methylpropanesulfonate and acrylamide; and combinations of any two or more thereof, are particularly preferred for applications in environments of high salinity at elevated temperatures, for stability. Selected carboxylate-containing terpolymers are also useful in the present process, such as terpolymers derived from acrylamide and comonomers of N-vinyl-2-pyrrolidone with minor amounts of thermonomers such as vinyl acetate, vinylpyridine, styrene, methyl methacrylate , and other polymers containing acrylate groups. Other miscellaneous polymers, suitable for the use of the present invention, include partially hydrolyzed polyacrylonitriles, styrene acrylate and sulfonate copolymers, or combinations of any two or more of them. Presently preferred carboxylate-containing polymers are CMHEC, CMC, xanthan gum, and acrylamide-containing polymers, particularly partially hydrolyzed polyacrylamides, acrylamide-containing polymers, alkali metal or ammonium salts of acrylic acid, and polymers containing ammonium or alkali metal salts of acrylic acid, N-vinyl-2-pyrrolidone, and sodium-2-acrylamido-2-methylpropanesulfonate. The alkali metal or ammonium salts of acrylic acid are referred to herein as acrylate, as in the claims. In the process of the present invention, any crosslinking agents such as, for example, a multivalent metal compound which is substantially soluble in the liquid component of the composition, and which is capable of crosslinking the gellable polymer containing carboxylate in the formations that have hydrocarbons. The presently preferred multivalent metal compound is a metal compound selected from the group consisting of zirconium compounds, titanium compounds, aluminum compounds, iron compounds, chromium compounds, and combinations of any two or more thereof. Examples of suitable multivalent metal compounds include, but are not limited to, ammonium-zirconium carbonate, sodium-zirconium carbonate, potassium-zirconium carbonate, ammonium-zirconium fluoride, ammonium-zirconium chloride, zirconium-ammonium citrate. , zirconium chloride, tetrakis (triethanolamine) zirconate, zirconium carbonate, zirconium ammonium carbonate, ammonium titanium carbonate, titanium chloride, titanium carbonate, ammonium titanium chloride and combinations of any two or more of the same. These compounds are commercially available. The presently most preferred crosslinking agent is ammonium-zirconium carbonate. The agent for lowering the pH can be any chemical that lowers the pH of the compositions of the invention to a pH or a pH range that is appropriate for the gelation of the composition. Examples of the appropriate agent for pH decrease include, but are not limited to, carbon dioxide; or a compound that generates carbon dioxide; a weak acid such as carbonic acid, formic acid, acetic acid, propionic acid, butyric acid and phosphoric acid; esters such as ethyl formate, ethyl acetate, methyl formate, and amyl acetate; a mineral acid; and combinations of any two or more thereof. The agent to lower the pH, currently preferred is carbon dioxide because it is readily available, cheap, and relatively easy and safe to handle.

While the invention is not compromised by theory, it is believed that the agent for lowering the pH lowers the pH of the composition, such that the crosslinking metal compound dissociates to provide available cations for crosslinking. The concentration or amount of the water soluble polymer in the gelation composition can vary widely and be so suitable and convenient for the various polymers, and for the degree of gelation necessary for the particular deposits. In general, the concentration of the polymer in an aqueous solution is constituted up to a suitable strength of about 100 to 100,000 mg / l (ppm), preferably of about 200 to 70,000 ppm, and more preferably from 500 to 50,000 ppm. The concentration of the crosslinking agent used in the present invention is highly dependent on the concentrations of the polymer in the composition. Lower polymer concentrations, for example, require lower concentrations of the crosslinking agent. In addition, it has been found that for a given concentration of polymer, the increase in the concentration of the crosslinking agent generally increases substantially the gelation rate. The concentration of the slag crosslinking agent injected generally varies over a wide range from about 1 mg / 1 (ppm) to about 5,000 ppm, preferably in the range from about 1 ppm to about 3,000 ppm, and more preferably from 1 ppm to 2,000 ppm. According to the present invention, the amount of pH reducing agent required, can be any amount that can lower the pH of the composition, so that gelation can be accelerated. In general, the amount required depends on the type of crosslinking agent, as well as the water soluble polymer used in the composition, the pH reducing agent employed, and the desired gelation rate. The amount may be in the range of from about 1 ppm to about 100,000 ppm, preferably from about 1 ppm to about 50,000, ppm, and more preferably from about 1 ppm to about 20,000 ppm. The liquid component generally constitutes the rest of the composition.

The composition of the invention, although not necessary, may also contain a complexing ligand, such as a salt of a carboxylic acid. The concentration of the ligand for complex formation, if present, in the composition, also depends on the concentrations of the water soluble polymer in the composition, and the desired rate of gelation. In general, the lower the concentration of the complexing ligand, the faster the gelation rate. Any suitable methods can be used for the preparation of aqueous mixtures of the water-soluble polymers, the crosslinking agents and the liquid. Some of the polymers may require particular mixing conditions, such as the slow addition of the fine powder polymer in a vortex of stirred brine, pre-wetting with alcohol, protection of the air (oxygen) preparation of reserve solutions from rather fresh water that of salt water, as is known for such polymers. In general, a water soluble polymer is mixed with a crosslinking agent, in a liquid state. The pH reducing agent is then added to the mixture of the polymer and the crosslinking agent. The timing of addition of the pH reducing agent depends on the desired gel time. For example, the water soluble polymer may be first combined with a crosslinking agent, either in a liquid to form a mixture. A pH reducing agent is then introduced into the mixture to form a second mixture. The second mixture can then be used to form gels in an underground formation. The use of gelled polymers to alter the water permeability of underground formations, it is well known to those skilled in the art. In general, an aqueous solution containing the polymer and a cross-linking agent is pumped into the formation, so that the solution can enter the more water-swept portions of the formation and alter the water permeability by gelation. in this. According to the second embodiment of the present invention, a process is provided in which an aqueous composition comprising a crosslinking agent and a water soluble polymer is prepared, and thereafter injected into an injection or production well. . The water-soluble polymer and the cross-linking agent, both in the liquid state, can also be simultaneously injected or sequentially injected in any order. The definition and scope of the crosslinking agent and the polymer are the same as those described above. The amount of the injected aqueous gelling composition can vary widely depending on the volume of injected treatment. The amount of the gellable polymer injected is also dependent on the desired strength of the gel, just as that described for the crosslinking agent. The pH reducing agent can be added to the aqueous composition comprising a crosslinking agent and a water soluble polymer, just before the composition is injected. The pH reducing agent can also be separately injected, either before or after the injection of the composition. Alternatively, each component of the aqueous composition in a liquid can be sequentially injected, in any order. The nature of the underground formation treated is not critical to the practice of the present invention. The described gelling composition can be injected in a formation having a temperature range from about 21 ° C (70 ° F) to about 149 ° C (300 ° F), when the polymer used is a suitable gelling copolymer for the used brine at the temperature or temperatures of the deposit, in the range from about 21 ° C (70 ° F) to about 149 ° C (300 ° F) for partially hydrolyzed polyacrylamide, xanthan gum, CMC or CMHEC, preferably from about 27 ° C (80 ° F) to about 82 ° C (180 °) F), and more preferably from 27 ° C (80 ° F) to 77 ° C (170 ° F) for best results. Any means known to the person skilled in the art can be used to inject the gelling composition. The examples given below are intended to help someone of skill in the art to further understand the invention, and should not be considered as limiting.

EXAMPLE I The purpose of this example is to illustrate the gelation of a composition comprising a water soluble polymer, a crosslinking agent, and a brine, and to use this example as a control.

Polyacrylamide solutions (at 0.5% by weight) were prepared by mixing sufficient amount of the polymer in a synthetic brine that included 2% potassium chloride. Subsequently, 20 ml samples of each polymer solution were placed in two bottles. Each vial was then loaded with ammonium-zirconium carbonate to a final concentration of 750 ppm (mg / 1) measured as the Zr ion. The flasks were placed vertically in test tube racks and then placed in ovens heated to and maintained at 49 ° C (120 ° F). Periodically, ampules were removed from the oven and the mechanical strength of the gels was determined. As the cross-linking developed, small granule microgels began to appear, for example, a very light gel formed. Then there was continuous growth of microgels to a globule, called a light gel. Then, larger gel masses appeared, called a partial gel, followed by the development of stronger gels with measurable tongue lengths. The tongue lengths were measured by placing each bottle horizontally, allowing the gelling composition to flow to its equilibrium position, and then measuring the length of the formed tongue. As the gelation progressed over time, stronger gels and shorter tongue lengths were developed. The resistance of the gel is expressed mathematically as Percent Gel Strength = (AL-TL) x 100 / AL where AL is equal to the length of the vial (in centimeters), typically 22.5 cm, and TL is equal to the tongue length of the gel measured in centimeters, from the point at which the gel makes contact with the entire circumference of the tube to the furthest point to which the gel has spread. In this way, the strongest gels could have a gel strength of 100%, and the weaker gels could have a gel strength of 0.

EXAMPLE II This example illustrates the gelation of the compositions of the present invention. The abbreviations used in Figure 1 and Figure 2 are: NG, not gel; VSG, very light gel; SG light gel; T, thick (solution); VT, very thick (solution) and PG, partial gel.

The runs were carried out using the procedure described in Example I. The data on the gelation of the polyacrylamides with 750 ppm of ammonium-zirconium carbonate in the presence and absence of C02, are presented in Figure 1, which show that a solution of 5000 ppm of polyacrylamides "OFXC-1163" (commercially available from American Cynamide, hydrolysis of about 8% and molecular weight of 14,000,000-18,000,000), in 2% potassium chloride, did not produce a measurable gel with ammonium carbonate -circonium in the absence of C02 even after six months of aging at 49 ° C (120 ° F). This mixture only produced a light gel (SG) after approximately one day of aging, and the resulting gel gradually deteriorated with further aging to a thick solution (T). However, the same solution produced a gel within a few seconds of exposure to 30 cm3 of CO2. The resulting gels that lost approximately 25% of their resistance in six months of aging, could be suitable for shallow well treatments. The mechanism by which gelation occurs was probably due to the pH change in the presence of CO ?, which made the zirconium cation available for cross-linking in this brine. Figure 2 shows the results of gelation for a similar mixture, as described above for Figure 1, except that the solvent used was distilled water instead of 2% potassium chloride solution. In the absence of C02, no measurable gel was produced until after 3.5 hours of aging at 49 ° C (120 ° F). This was a sufficient period of time to inject the gelling mixture into its tarzone before the CO 2 injection and the immediate formation of the gel. The results of the two waters in the absence of C02, indicate that the gelation rate decreased substantially with the salinity of the water used. Without wishing to be compromised by theory, this may be due to the lower solubility of ammonium-zirconium carbonate in the presence of dissolved salts. It should be noted that the use of distilled water as a solvent for gel treatments of the wells is highly unlikely, and the tests were only performed to evaluate the limits of this invention. The results shown in the previous examples clearly demonstrate that the present invention is well adapted to carry out the objectives and achieve the ends and advantages mentioned, as well as those inherent in the present. While modifications may be made by those skilled in the art, such modifications are encompassed within the spirit of the present invention, as defined by the description and the claims.

It is noted that in relation to this date, the best known method, by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (13)

1. A composition for the treatment of an underground formation having hydrocarbons, characterized in that the composition comprises effective proportions of: (1) a water-soluble polymer, which comprises at least one functional group that can be cross-linked with a multivalent metal compound, (2) a multivalent metal compound, and (3) a liquid, wherein said composition contains a gelling retarding agent and said ratio is effective to form a gel from said composition.

2. A composition according to claim 1, further characterized in that it comprises a pH reducing agent, which is carbon dioxide, a compound that generates carbon dioxide, a weak acid, an ester, or a combination of any two or more of said agents.

3. A composition according to claim 2, characterized in that the pH reducing agent is carbon dioxide, carbonic acid, formic acid, acetic acid, propionic acid, butyric acid, phosphoric acid, ethyl formate, ethyl acetate, methyl formate , amyl acetate, or a combination of any two or more of said agents.

4. A composition according to any one of claims 1 to 3, characterized in that the polymer is a biopolysaccharide, a cellulose ether, an acrylamide-based polymer, an acrylonitrile-based polymer, a sulfonate-based polymer, or a combination of any two or more of said polymers.

5. A composition according to claim 4, characterized in that the polymer is an acrylamide-based polymer containing carboxylate groups.

6. A composition according to claim 5, characterized in that the polymer is a polyacrylamide, for example, a partially hydrolyzed polyacrylamide.

7. A composition according to any of the preceding claims, characterized in that the multivalent metal compound is a zirconium compound, a titanium compound, or a combination of any two or more of said compounds.

8. A composition according to claim 7, characterized in that the multivalent metal compound is ammonium-zirconium carbonate, sodium-zirconium carbonate, potassium-zirconium carbonate, ammonium-zirconium fluoride, ammonium-zirconium chloride, zirconium citrate -ammonium, zirconium chloride, tetrakis (triethanolamine) zirconate, zirconium carbonate, zirconium ammonium carbonate, ammonium-titanium carbonate, titanium chloride, titanium carbonate, ammonium-titanium chloride, or a combination of any two or more of said compounds.

9. A composition according to any of the preceding claims, characterized in that the liquid is water, a solution, a suspension, or a combination of any two or more of said liquids.

10. A composition according to claim 9, characterized in that the liquid is a solution containing 2% potassium chloride.

11. A composition according to any of the preceding claims, characterized in that the water-soluble polymer is present in the range of 500 to 50,000 ppm of said composition, the multivalent metal compound is present in the range of about 1 to 2,000 ppm of the composition , and the pH reducing agent is present in the range of 1 to 20,000 ppm of the composition.

. 12. A process for the treatment of a formation having hydrocarbons, characterized the process because it comprises injecting into a subterranean formation a composition according to any of the preceding claims.

13. A process according to claim 12, characterized in that it comprises (A) the injection into the underground formation,. of the composition comprising the water soluble polymer, the multivalent metal compound, and the liquid; and after this (B) the pH reducing agent is injected into the formation