MXPA00009087A - Compositions and processes for oil field applications - Google Patents

Abstract

A composition and a process for treating a subterranean formation are disclosed. The process comprises injecting into the subterranean formation a composition which comprises a polymer, a crosslinking agent, a liquid, optionally a clay, and further optionally a weighting agent wherein the polymer forms a gel in the formation, in the presence of the crosslinking agent.

Description

COMPOSITIONS AND PROCESSES FOR APPLICATIONS IN OIL FIELDS FIELD OF THE INVENTION The present invention relates to a composition and a process useful for operations in oil fields.

BACKGROUND OF THE INVENTION During drilling operations, large flow channels such as fractures, cracks and voids around the borehole, whether induced or natural, can cause various problems during drilling or completion operations. Such problems can include the substantial loss of fluids from the sounding. Any of these results in the loss of the hydrostatic head, with the subsequent potential for loss of well control. This can also lead to damage to the production capacity of the oil and gas zones, when these channels represent a portion of the drainage pattern.

REF. : 123265 Various methods could be used in the attempt to control the loss of drilling fluid from these channels, fractures, cracks or voids. For example, the incorporation of solids such as paper, mica flakes and / or fabric fibers into the drilling fluid has been utilized. However, these methods are not always effective because solids can be lost in these channels. Therefore, there is a growing need to develop a process to control the loss of drilling fluids. One such process is to employ a mud gel as described later in this invention. Such a process can crosslink either on the surface, during placement or without a composition of gelling. In many applications, the placement of a gel may be sufficient to prevent further invasion by drilling fluids. In some case, however, hydraulic forces can lead to dehydration, channeling or even extrusion, of a gel. This could be due to the relatively large surface area of the gel, which is exposed to the drilling fluids, and to the relatively small surface area, within the channels, fractures, cracks or voids, which is available for adhesion. This situation can be corrected by the incorporation of solids such as, for example, sand, calcium carbonate and lost circulation materials, commercially available, into the gel. Such incorporation can effectively create a porous matrix within the channel, thereby dramatically increasing the surface area for adhesion and reducing the cross-sectional area of the exposed gel. Similarly, fractures may also occur in an injection well, a production well, or both. It may also be employed a similar process. In order to correct the sweep profile found in fractured deposits, large volumes of gellable polymeric solutions can be used to plug the fractures. The effectiveness of these treatments is sometimes adversely affected by the hydraulic failure of the gel near the sounding. Again, the incorporation of sand or other suitable solid, such as an artificial matrix within the fracture, can also greatly improve the mechanical properties of the gel plug, probably by reducing the surface area exposed in the gel and increasing the adhesive capabilities of the gel . The destabilization of the seabed is commonly found while drilling in some areas on the high seas. As the hole progresses down through the sediment, the circulation of the drilling fluid will sometimes wash the unconsolidated sediment around the borehole. In extreme cases, but not uncommon, a channel can develop that diverts the whole sounding. It has been reported that underwater cameras recorded large piles of sediment, displaced from the well, which were deposited by the circulating drilling fluid. This weakening of the seabed causes considerable problems due to the proximity of the drilling platform. Even after the drilling operation is completed and the casing is adjusted, these sediments poorly until completely unconsolidated can impose serious problems. Although a very rigid structure could be used around the borehole, such as a resinous system, such a structure can not provide the necessary protection, especially at low temperature near the seabed, which could be as cold as 35 ° C.

Again, there is an increasing need to develop a process for the stabilization of such an unconsolidated settlement. Problems were also encountered during the drilling of a sub-saline well. One of the problems encountered is a very unstable matrix with high fluid pressure that releases gas to the drill rod. This requires interruption of drilling and separation of the gas, due to safety problems. A gelation system with very low molecular weight polyacrylamide and a crosslinking agent can be injected into the unstable matrix described above and hardened on site to block further release of the gas into the borehole. Another problem frequently encountered during the drilling of a sub-saline well is the presence of fractures that cause loss of circulation and interrupt the drilling process. A "mud gel" composition, as described hereinafter, produced with a mud containing clays such as bentonite and filler such as barite, containing dissolved polymer and a crosslinking agent such as Chromium propionate in its composition.

In drilling wells, a drilling fluid is generally circulated down the drill string and reinforces the ring between the drill string and the drilling face. A chain of casing or coating is then cemented into the borehole. However, it has been widely reported that there are numerous annular leaks through cement. Such oil and gas leaks through cement contaminate the bottom water causing additional environmental problems. A gas leak through the cement out of the well surface can also represent a dangerous condition. Therefore, a process to prevent such annular leaks through cement needs to be developed.

BRIEF DESCRIPTION OF THE INVENTION An object of the invention is to provide a process for the consolidation of sand in an underground formation. Also, an object of the invention is to provide a process for plugging an annular flow of gas, oil, water or combinations of two or more thereof through the defects in the cement in a production well. Another object of the invention is to provide a process for the treatment of a subterranean formation at low temperature by the use of a gelation composition. Yet another object of the invention is to provide a process for the prevention of drilling fluid loss. A further object of the invention is to provide a process for plugging fractures in the underground formation, with a gelling composition. A further object of the invention is to provide a process for the treatment of sounding using a gelation composition that is suitable for low temperature operations. Yet another objective of this invention is to develop integrity in the sediments surrounding the sounding, by placing a gelling composition in the formation. Another objective of the invention is to develop a process that is to place the gel periodically during the drilling operation, in order to prevent these problems from occurring or recurring. Other objects, features and advantages will become more apparent as the invention is more fully described in the following.

According to a first embodiment of the present invention, there is provided a composition that can be used in a water-based fluid, for applications in an underground formation, comprising a clay, a gelling mixture, a liquid and optionally an agent of charge wherein the gelation mixture comprises a polymer and a crosslinking agent. According to a second embodiment of the invention, a process that can be used in the drilling of an underground formation is provided. The process involves the injection of a composition into an underground formation during the drilling operation, wherein the composition can be the same as that described in the first embodiment of the invention. According to a third embodiment, a process is provided for the settlement of unconsolidated sediments in an underground formation, or around the surface of a sounding in a low temperature environment. The process may comprise, consist essentially of, or consist of, the injection "of a composition into the formation, wherein the formation may be the same as that described in the first embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of gel strength, of gels formed by a gelation composition as a function of maturation or aging time at 54 ° C (130 ° F) in 26% by weight of sodium chloride brine without pH adjustment. Figure 2 is the same as Figure 1, except that the pH of the gelation composition was adjusted to 9.0. Figure 3 is the same as Figure 1, except that the pH of the gelation composition was adjusted to 10.5. Figure 4 illustrates the effect of pH on the stability ratio of the gels produced. Figure 5 shows the gel strength as a function of the maturation time for the polymer at 2-4% by weight in a gelation composition. Figure 6 illustrates the gel strength of the mud gel versus the ripening time. Figure 7 shows the gel strength of a mud gel formed using chromium acetate as a crosslinking agent. Figure 8 also illustrates the gel strength of a mud gel formed using chromium propionate. Figure 9 illustrates the gel strength of the mud gels formed using chromium propionate at different concentrations of chromium. Figure 10 illustrates the gelation of 2.07 kg / liter (17.3 pounds) per gallon of a drilling mud with variant amount of polymer and 500 ppm by weight of chromium as chromium propionate. In these figures, the gels were formed from a low molecular weight polyacrylamide of about 300,000 to 500,000, a chromium acetate or chromium propionate (obtained from Drilling Specialties Company, Bartlesville, Okla.) As a crosslinking agent, and a brine The concentrations of the polymer and the crosslinking agent, measured as chromium, are shown in the Figures.

DETAILED DESCRIPTION OF THE INVENTION The term "hydrocarbon" denotes any hydrocarbons that may or may not be oxygenated or substituted with appropriate substituents. The hydrocarbon may also contain minor components such as, for example, sulfur. The currently preferred hydrocarbons are crude oil and gas. An application in the oil field includes, but is not limited to, drilling, completion of drilling, production of hydrocarbons, alteration of permeability, correction of water cone formation, water occlusion, gas occlusion, abandonment of the area and combinations of any two or more thereof. According to the first embodiment of the invention, a composition that can be used in an oil field application is provided. The composition may comprise, consist essentially of, or consist of a clay, a gelling mixture and optionally a bulking agent. The clay useful in the invention can be any clay, as long as the clay can viscosify a fluid based on water or petroleum. Examples of suitable clays include, but are not limited to, kaolinite, halloysite, vermiculite, chlorite, atapulguite, smectite, montmorilloni ta, illite, saconite, sepiolite, paligorski ta, Fuller's earth, and combinations of any two or more of them. The currently preferred clay is montmorillonite clay. The currently most preferred clay is sodium montmorillonite, which is also known as bentonite. Based on the total weight percentage of the composition, the clay may be present in the composition in the range of about 0.25% by weight to about 30% by weight, preferably about 0.5% by weight to about 25% by weight, and more preferably 1% by weight to 20% by weight. Any known filler that can be suspended in the composition can be used in the present invention. Examples of suitable fillers include, but are not limited to, barite, hematite, calcium carbonate, galena, or combinations of any two or more thereof. The currently preferred filler is barite because it is readily available and effective. The bulking agent may be present in the composition in the range of about 5 to about 30, preferably about 8 to about 25, and most preferably 1.2 to 2.4 kg / liter (10 to 20 pounds) per gallon.

According to the invention, any gelation mixture that can gel a clay-containing composition can be employed. In general, a gelling composition comprises, consists essentially of, or consists of, a polymer and a cross-linking agent. Any polymers that can form a mud gel as when employed in the presence of a clay, a filler and a crosslinking agent, can be used in the composition of the present invention. The presently preferred polymer is a carboxylate-containing polymer that can be cross-linked with a metal-multivalent compound. The term "carboxylate-containing polymer" used herein refers, unless otherwise indicated, to 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. As used herein, the term "copolymer" includes copolymer, terpolymer or tetrapolymers.

According to the present invention, the molecular weight of the carboxylate-containing polymers can generally be about 10,000 and less than about 30,000,000, preferably less than about 25,000,000, and most preferably less than about 20,000,000. The mole percent (%) of the carboxylate group is generally in the range of about 0.01 to less than about 30, preferably about 0.01 to less than about 20, and most preferably about 0.1 to about 10. However, if the molecular weight of a suitable polymer is about 1,000,000 or less, the molar percentage of the carboxylate group can be in the range of about 0.01 to about 10%, preferably about 0.01 to about 10%, more preferably about 0.1 to about 5% and most preferably 0.1 to 1%. According to the present invention, the gelation rate or rate is defined as the rate at which the gel particles are formed. At the beginning of the gelation these particles are sufficiently small, so that the gelation solution still flows, but these particles can be detected from the apparent flow characterization caused by the change in apparent viscosity. Small particles develop to larger granules over time, and become sufficiently strong to retain fluids within their structures, which restricts the free-flowing characterization of the gelling solution and thus develops the length of language. The desired gelation speed varies depending on the application. The applications illustrated in the present invention include, but are not limited to, plugging fractures or channels, preventing the loss of circulation fluids, blocking the release of gas during drilling, or combinations of any two or more of the same. The gel time is generally less than about 6 hours, preferably about 4 hours, more preferably about 3 hours, and most preferably 2 hours or shorter. In general, appreciable gel strength is not observed, as defined in Example I hereinafter, until a tongue length can be measured.

For example, if a leakage of drilling fluid is detected, it is desirable to prevent such loss as soon as possible, and therefore, requires a gelling speed as short as possible, but still long enough that it can travel towards the fracture, for example, before the composition of the invention becomes gel. The carboxylate-containing polymers, suitable for use in this invention, are those capable of gelling in the presence of a crosslinking agent such as, for example, a multi-alloy 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. Pat. No. 3,727,688 (incorporated by reference herein). Particularly preferred cellulose ethers include carboxymethylhydroxyethylcellulose (CMHEC) and carboxymethylcellulose (CMC) for its easy availability.

Biopolysaccharides are described in U.S. Patent No. 4,068,714 (incorporated herein by reference). Particularly preferred is polysaccharide B-1459 and xanthan gums which are biopolysaccharides produced by the action of the Xan thomon a s farmer s bacteria. This biopolysaccharide is commercially available in various grades under the trade names "KELZAN®" (Kelco Company, Los Angeles, CA), "FLOCON" 4800 (Pfizer, Groton, CT), and "FLOWZAN" (Drilling Specialties Company, Bart lesville, Oklahoma), and they are readily available. Suitable acrylamide-containing polymers which also contain protruding carboxylate groups are described in U.S. 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 polyacrylamides can be hydrolyzed in general under an underground formation condition, to produce some crosslinkable carboxylate groups, and thus can also be used in the present invention. The thermally stable carboxylate-containing acrylamide polymers, the partially hydrolyzed polyacrylamide, such as the copolymers of N-vinyl-2-pyrrolidone and acrylamide; copolymers of sodium 2-acrylamido-2-methylpropanesulfonate, acrylamide and N-vinyl-2-pyrrolidone; copolymers of N-vinyl-2-pyrrolidone and acrylamide, and sodium acrylate, copolymers of acrylamide, sodium 2-acrylamido-2-methylpropropanesulfonate and sodium acrylate; and copolymers of sodium 2-acrylamido-2-methylpropansul fonate and acrylamide; copolymers of sodium 2-acrylamido-2-methylpropansul fonate, acrylamide, and sodium acrylate; copolymers of sodium 2-acrylamido-2-methylpropropansul fonate, acrylamide, N-vinyl-2-pyrrolidone, and sodium acrylate; they are particularly preferred for applications in environments of high salinity at elevated temperatures, for stability. Selected carboxylate-containing copolymers are also useful in the present process, such as copolymers derived from acrylamide, which is partially hydrolyzed to acrylate, and comonomers of N-vinyl-2-pyrrolidone with minor amounts of thermonomers such as sodium acetate. vinyl, vinylpyridine, styrene, methyl methacrylate, and other polymers containing acrylate groups. In general, suitable polymers contain some carboxylate group if polymers are used to crosslink with multivalent cations such as Cr cations, Zr cations, Ti cations, Fe cations, Al cations, or combinations of any two or more thereof. Any polymer that can be used to crosslink with an organic crosslinking agent can also be used in the present invention. An organic crosslinking agent may include, but is not limited to, phenol and formaldehyde or precursors thereof, or furfuryl alcohol and formaldehyde, or an aminobenzoic acid and formaldehyde, or combinations of any two or more thereof. Formaldehyde precursors such as, for example, hexameth and lens can be, and are more preferably, used in place of formaldehyde. The more detailed description of such crosslinking agents can be found in U.S. Patent Nos. 5,399,269 and 5,480,933, the descriptions of which are incorporated by reference herein. Other miscellaneous polymers suitable for use in the present invention include partially hydrolyzed polyacrylonitriles, styrene acrylate and sulfonate copolymers, or combinations of any two or more thereof. Although any crosslinkable and gellable polymers can be used in the present invention, the presently preferred polymers are carboxylate-containing polymers which include CMHEC, CMC, xanthan gum, polymers containing acrylamide or combinations of any two or more thereof. Current and particularly preferred polymers are partially hydrolyzed polyacrylamides, polymers containing acrylamide, alkali metal or ammonium salts of acrylic acid, and polymers containing ammonium or alkali metal salts of acrylic acid, N-vinyl-2-pyrrole suitable , and sodium 2-acrylamido-2-methylpropanesulfonate. The ammonium or alkali metal salts of acrylic acid are referred to herein as acrylate, as in the claims.

Any crosslinking agents, such as, for example, a metal compound or tivalent, which are capable of crosslinking the gellable carboxylate-containing polymer in an underground formation can be used in the process of the present invention. The presently preferred multivalent metal compound is a metal compound selected from the group consisting of a zirconium compound complexed, a titanium compound complexed and mixtures thereof. Examples of suitable multivalent metal compounds include, but are not limited to, zirconium citrate, zirconium complex of hydroxyethylglycine, ammonium zirconium fluoride, zirconium 2-methexanoate, zirconium acetate, zirconium tartrate, zirconium malonate, zirconium propionate, zirconium neodecanoate, zirconium acetylacetonate, tetrakis (triethanolamine) z irconate, zirconium carbonate, ammonium zirconium carbonate, zirconium ammonium carbonate, zirconium lactate, titanium acetylacetonate, titanium ethylacetoacetate, titanium citrate, triethanolamine titanium, ammonium titanium lactate, aluminum citrate, chromium nitrate, chromium chloride, chromium citrate, chromium acetate, chromium propionate or combinations of any two or more thereof. The presently most preferred crosslinking agent is chromium chloride, chromium propionate, chromium acetate, zirconium lactate, zirconium citrate, tetrakis (triethanolamine) zirconate, zirconium complex of hydroxyethylglycine, zirconium tartrate, zirconium malonate, propionate of zirconium or combinations of any two or more thereof. These compounds are commercially available. According to the present invention, the crosslinking agent can also contain a complexing ligand if necessary, to further delay the gelation rate, so that the composition can reach the desired sites in an underground formation before it is formed. gelify completely. The complexing ligand, useful for the present invention, for retarding the rate of gelation is generally a carboxylic acid containing one or more hydroxyl groups and salts thereof. The complex forming ligand can also be an amine having more than one functional group and containing one or more hydroxyl groups, and the zirconium or titanium portion of the zirconium or titanium compounds described above can be chelated. Examples of suitable complexing ligands include, but are not limited to, hydroxyethylglycine, acetic acid, sodium acetate, ammonium acetate, potassium acetate, lactic acid, ammonium lactate, sodium lactate, potassium lactate, citric acid. , ammonium citrate, potassium citrate, sodium citrate, isocitric acid, ammonium isocitrate, potassium isocitrate, sodium isocitrate, malic acid, ammonium malate, potassium malate, sodium malate, tartaric acid, ammonium tartrate, potassium tartrate, sodium tartrate, triethanolamine, malonic acid, ammonium malonate, potassium malonate, sodium malonate and combinations of any two or more thereof. The presently preferred complex forming ligands are citric acid, lactic acid, tartaric acid, and salts thereof, triethanolamine and hydroxyethylglycine, because of their ready availability and low cost. "The concentration or amount of the carboxylate-containing polymer in the gelation composition it can be in a wide range and be so suitable and convenient for the various polymers, and for the degree of gelation necessary for a particular formation condition.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 / liter (ppm), preferably about 200 to 70,000 ppm, and more preferably 1,000 to 50,000 ppm .. Any of the methods suitable for the preparation of an aqueous mixture of the gellable polymer can be used. of polymers may require particular mixing conditions, such as slow addition of the fine powder polymer in a turbine of stirred brine, pre-wetting with alcohol, protection against air (oxygen), preparation of reserve solutions from fresh water instead of salt, as is known for such polymers . The concentration of the crosslinking agent used in the present invention depends to a large extent on the desired gel time. This may also depend on the polymer concentrations in the composition, the operating conditions or the depth of the desired site in a formation. For example, if it is desirable for a gelling mixture to gel in 2 hours, the concentration of a crosslinking agent must be higher than that for the gelation to be completed in 4 hours. In addition, it has been found that for a given concentration of polymer, the increase in the concentration of the crosslinking agent generally substantially increases the rate of gelation. The concentration of the crosslinking agent in the injected plug generally varies over the broad range of about 1 mg / l (ppm) to about 20,000 ppm, preferably in the range of about 1 ppm to about 10,000 ppm, and most preferably 1 ppm up to 5,000 ppm. The concentration of the complexing ligand, 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 complex-forming ligand, the faster the gelling rate.

The liquid component in general constitutes the remainder of the composition of the invention. According to the present invention, the term "liquid" used herein is interchangeable with "water" and in general refers to, unless otherwise indicated, pure water, regular tap water, a solution or suspension wherein the solution or suspension contains a variety of salts. A brine produced, which is defined as the brine co-produced with oil or gas, when it is a liquid that can be used. A brine produced in general is a mature salt, for example, containing 1,000 ppm of Ca + 2, Ba + 2, Mg + 2, or Sr + 2, or combinations of two or more thereof. A brine produced generally comprises high salinity of about 1% by weight to about 30% of the total dissolved solids. A brine produced is generally contaminated with oil or gas, or both. The gellable polymer generally gels well in produced brines having a salinity of about 0.3% to about 27%. The composition of the present invention, before it is injected into the underground formation, can be an aqueous solution, a suspension comprising undissolved solids, gas or petroleum, or combinations of two or more thereof. After mixing the components of the composition, the composition may be substantially free of gelling, in the form of microgels, of bulk gels, or combinations of any two or more thereof, which may be flowing or may travel to a desired site in an underground formation. However, once the composition completes gelation, the composition becomes gels that do not flow. According to the present invention, the composition of the present invention may contain total solids (dissolved and undissolved) in the range of about 30 by weight, preferably about 50% by weight, and more preferably 55% by weight, up to about 90 % in weigh. The density of the composition may be in the range of about 1 to about 3.5, preferably about 1.5 to about 3 or about 2 to about 3, and most preferably about 2.5 to 3 g / ml. According to the second embodiment of the present invention, a composition comprising, consisting essentially of, or consisting of a clay, a crosslinking agent, a gellable polymer, a liquid and optionally a bulking agent, is injected into a underground formation. The definition and range of clay, filler, crosslinking agent, polymer, and liquid are the same as those described above. The amount of the injected composition can vary widely depending on the treatment required or desired. In general, the process, for example, the injection of the composition, is carried out when there is any sign of loss of drilling fluid during the drilling operation, to prevent the loss of drilling fluid; or when there is an increase in the gas fluid pressure in the drill rod, for the treatment of an unstable matrix in an underground formation; or there is an increase in unconsolidated sediments as shown by a higher rate of unconsolidated sediment production. The nature of the underground formation is not critical to the practice of the process of the present invention. The composition described can be injected into a formation having a temperature range from about 2 ° C (35 ° F) to about 149 ° C (300 ° F) when the polymer used is a suitable gelling copolymer for the brine used the temperature or temperatures of the reservoir in the range of about 2 ° C (35 ° F) to about 149 ° C (300 ° F) for partially hydrolyzed polyacrylamide, xanthan gum, CMC, or CMHEC, or combination of any two or more from the same. However, to maintain the integrity of unconsolidated marine sediments, the temperature is preferably from about 2 ° C (35 ° F) to about 52 ° C (125 ° F), preferably about 2 ° F (45 ° F) to about 24 ° F (75 ° F) at about 18 ° C (65 ° F), and most preferably at 16 ° C (60 ° F). Any means known to a person skilled in the art such as, for example, pumps, can be used to inject the composition and the polymer solution. It is intended that the examples provided below, later in the present, help a person skilled 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 (2% by weight) were prepared by mixing a sufficient amount of the polymer in a brine containing 26% by weight of the sodium chloride. Then 20 ml samples of each polymer solution were placed in three bottles. Each bottle was then loaded with a crosslinking agent. The bottles were placed upright in the test tube racks and then placed in ovens heated to and maintained at 54 ° C (130 ° F). Periodically, the bottles 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. The development of the microgels continued until the formation of globules, called light gel, occurred. Then, larger gel masses appeared, called partial gel, followed by the development of stronger gels with measurable tongue lengths. The tongue lengths were measured by placing each vial horizontally, allowing the gelation 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 of Gel Resistance = (AL-TL) x 100 / AL where AL is equal to the length of the ampoule (22.5 centimeters), and TL is equal to the length of the tongue of the gel, measured in centimeters from the point at which the gel makes contact with the entire circumference of the tube to the fullest point distant to which the gel has spread. Thus, the strongest gels would have a gel strength of 100% and the weakest gels would have a gel strength of 0.

First, the use of chromium propionate and chromium acetate to crosslink "ALCOFLOOD 254S" (obtained from Allied Colloids, Inc., Suffolk, Virginia, which has < 4% hydrolysis) was evaluated with a low molecular weight polyacrylamide (300,000 to 500,000) dissolved in saturated sodium chloride solution at various pH levels. In general, the gelation rate with chromium acetate is higher than that with chromium propionate. Figure 1 shows a graph of 2.0% "ALCOFLOOD 254S" in 26% sodium chloride solution without pH adjustment (pH = 6.7) with varying levels of chromium propionate concentrations. It is clear from this graph that the gelation rate was a function of the Cr (III) concentration. However, the gel made only with 100 ppm, Cr level, was weak and degraded within a month of maturation. Gels produced with 250 and 500 ppm Cr have survived for approximately 100 days of maturation at 54 ° C (130 ° F). Figures 2 and 3 show similar results for the gelation of 2.0% "ALCOFLOOD 254S" in 26% sodium chloride solutions, with pH adjustments at 9.0 and 10.5.

Figure 4 summarizes the effect of pH on the speed and stability of the gels produced with 2.0% "ALCOFLOOD 254S" and 250 ppm Cr (III) in 26% sodium chloride solution of three pH levels. These results indicate a small dependence of gel properties in the pH range of 6.7 (unadjusted) to 10.5. Figure 5 shows a graph of gel strength versus maturation time for "ALCOFLOOD 254S" solutions at various concentrations in 26.0% sodium chloride solutions, (pH = 10.5) with chromium propionate (250 ppm CR ). The gelling speed was faster with higher polymer levels. A small drop in gel strength was unexpected with further maturation for gels prepared with 4% polymer. The control tests were also carried out with 2% "ALCOFLOOD 254S" in 26.0% sodium chloride solution (pH = 10.5) and chromium propionate (500 ppm Cr). Berea witness plugs (obtained from Cleveland Quarries, Amherst, Ohio) 12. 7 to 14.9 cm in length and 2.54 cm in diameter were treated with approximately 10-16 pore volumes of the gelation solution at 54 ° C (130 ° F). The controls used in these tests varied in water permeability from 277 mD to 669 mD. After injection of the gelation solution, each control was temporarily closed for a period of time sufficient for the gels to harden before they would be subjected to a flow of nitrogen in the opposite direction, in which the solution of the solution was injected. gelation The first control that was temporarily closed for 24 hours, required 70.32 kg / cm2 (1000 psi) of nitrogen to break through. The second control, which was temporarily closed for 2 hours, required 5.98 kg / cm2 (85 psi) of nitrogen to break through. The third control that was temporarily closed for 3 hours required 23.91 kg / cm2 (340 psi) of nitrogen while the fourth control that was temporarily closed for four hours, did not break through, even though the differential pressure reached 140.65 kg / cm2 ( 2000 psi).

EXAMPLE II This is a simulated example that illustrates the process to stabilize unconsolidated sand on a seabed. The process was carried out through t "placing a 250 ml sample of a base fluid (such as tap water, 2% potassium chloride, seawater, or combinations thereof) in a mixer. The pH of the mixed fluid was adjusted as necessary, using dilute hydrochloric acid or sodium hydroxide. After this, the appropriate amount of polymer was added to the fluid and stirred until dissolved. A 10 ml sample of the test fluid was removed, using a syringe and placed in a glass jar (15 mm by 135 mm), which has a screw cap. A suitable amount of a crosslinking agent was added in the form of a dilute aqueous solution. The lid was placed on the bottle, it was shaken, and then the bottle was placed on a shelf. The samples were either stored on a laboratory bench (22 ° C (75 ° F)), placed in an oven at 38 ° C (100 ° F), or placed in a cold water bath (4-10 ° C) (40-50 ° F)). The gel resistance measurement was performed periodically to determine the progress of the gelation process. The gel strength was measured using the formula described in Example I.

The data shown in Table I demonstrate the practicality of controlling the gel time by varying the polymer concentration for a molecular weight of about 3 million polyacrylamide having 10% hydrolysis. Table 1 also shows that the gelation was complete (100% gel strength) in as little as 30 minutes at a low temperature of 24 ° C (75 ° F).

Table II represents the results for a system similar to Table I, conducted at a lower temperature (10 ° C (50 ° F)). These results indicate a lower gelation rate at a lower temperature. The data in Table III below demonstrate the utility of controlling the rate of gelation by limiting the availability of the crosslinking sites (carboxylic acid groups). For this terpolymer of acrylamide, sodium 2-acrylamido-2-methylpropanesulfonate and sodium acrylate, the reduction of the acrylate groups (degree of hydrolysis) increased the delay in gelation.

Table IV demonstrates the use of a metal salt for rapid gelation, as required for drilling purposes, and metal complexes for very slow gelation, as required for deep consolidation of unconsolidated marine sediments where the Deep penetration of the treatment fluid is necessary.

The data in Table V also demonstrate the use of a metal salt for rapid gelation, as required for drilling purposes, and metal complexes for very slow gelation, as required for deep consolidation in unconsolidated marine sediments. where deep penetration of the treatment fluid is necessary. a Cr + J was supplied to the solution either as salt (chromium chloride), or complexed with a carboxylic acid (chromium acetate).

Chromic chloride samples crosslinked within 5 minutes • The CMC has a molecular weight of approximately 500,000, with a degree of substitution of approximately 1.2 The results shown in the above examples indicate that for polymers of lower molecular weight (< 1, 000, 000) the degree of hydrolysis can be from 0.1 to about 10% to produce acceptable gels with a crosslinking agent. For higher molecular weight polymers (> 1, 000, 000) a low degree of hydrolysis is preferred.

EXAMPLE III This example illustrates a mud gel composition comprising a clay, a liquid, and a gelation mixture. The mud gels for fracture treatments were prepared by using a typical drilling mud. Table VI below shows the composition of the drilling mud used to form the mud gels.

The addition of "ALCOFLOOD 254S" was the last step in the preparation of the mud. The sludge was allowed to mature overnight (16 hours) at 54 ° C (130 ° F) to ensure complete hydration of the polymer, prior to the addition of a cross-linking agent containing chromium. Maturation may be as short as about 5 minutes, preferably about 10 minutes, and most preferably 1 hour, and may be as long as about 30 hours, preferably about 25 hours, and most preferably 20 hours. After adding sufficient amount of cross-linking agent and suitable mixing, samples of aliquots of 20 ml of this gelling slurry were placed in flasks and matured at room temperature as well as at 54 ° C (130 ° F) and 77 ° C ( 170 ° F). At various time intervals, the tongue length of the mud gel was measured. Figure 6 shows a graph of gel strength versus time for a mud gel made with chromium propionate (494 ppm Cr) at these temperatures. While the gelation rate at 54 ° C (130 ° F) and 77 ° C (170 ° F) was clearly rapid, the gelation rate at room temperature was slow. This system required up to one day of maturation to produce a measurable gel at room temperature. Figure 7 shows a similar graph for mud gels produced with chromium acetate, under similar conditions. Comparing Figures 6 and 7 it is shown that the gelation rate was faster with the chromium acetate than the chromium propionate under identical conditions. Figure 8 shows a graph of gel strength versus time for mud gels produced with chromium propionate at 247 ppm chromium (from chromium propionate) at three temperatures. The gelation rate was slightly lower than the mud gels made with chromium propionate at a level of 494 ppm Cr (III). Figure 9 shows a similar graph for mud gels made with chromium propionate at 75 ppm, 125 ppm and 250 ppm Cr (III). As this graph indicates, the syneresis of these gels was related to the amount of Cr concentration. Figure 10 shows a plot of the gel strength versus the maturation time at 54 ° C (130 ° C) for the gels of sludge produced with chromium propionate at 500 ppm Cr (III) and 1.5% at 3.0% "ALCOFLOOD 254S". This graph shows the dependence of the syneresis of the gel on the amount of polymer present. The mud gels produced in this study were rubber type gels with higher resistances as the polymer content increased. However, the viscosity of the gelling sludge before curing also increases with the polymer content and may be the limiting factor for the higher concentrations. To produce a mud gel with sufficient strength and stability, the appropriate amount of polymer and the level of crosslinking agent had to be used.

Several control tests were performed to block induced fractures in Berea cores or nuclei. The Berea witnesses (length of 15.24 cm (6 inches) diameter 2.54 cm (1 inch) were divided along their lengths and reintegrated together with a spacer material stretched along the edges on both sides. glued together with epoxy resin The fracture widths of these tests were in the range of 0.5 mm to 0.8 mm Each control was placed in the control holder after the resin was cured.The control was then saturated with chloride solution of sodium at 26% and its permeability was measured.The control was then heated to 54 ° C (130 ° F.) Approximately 150-200 ml of a gelling solution containing 2.0% (by volume) was injected into the control ) of "ALCOFLOOD 254S" and chromium propionate at 500 ppm Cr. The sample of the control effluents and the injected solutions matured at 54 ° C (130 ° F) and produced good mud gels. in witnesses where and 28-gauge copper wires were used as the spacer. The tests in container made with strips of placement of different materials, in solutions of mud of gelling before maturation, showed that the copper wire was not a good choice since the mud gel did not adhere to it. While other metallic strips initially adhered to the mud gel, these did lose their adhesion with the additional maturation. Strips of "Teflon®" and "Marlex®" adhered perfectly to the mud gel. A Berea control piece placed in the gelling sludge solution also adhered very strongly to the mud gel. These results indicate that the resulting mud gels blocked the fractures. The results shown in the above examples also 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 specification and the claims.

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

Claims (39)

RE IVINDICACIES Having described the invention as above, the content of the following claims is claimed as property:

1. A composition comprising a clay, a polymer, a crosslinking agent, and a liquid, characterized in that the clay, the polymer, the crosslinking agent and the liquid are each present in the composition in an effective amount to form a gel; the composition contains a total of solids (dissolved and undissolved) in the range of about 30 to about 90% by weight.

2. A composition according to claim 1, further characterized in that it comprises a bulking agent.

3. A composition according to claim 1, characterized in that the clay is selected from the group consisting of kaolinite, halloisite, vermiculite, chlorite, atapulguite, smectite, montmorillonite, illite, saconite, sepiolite, paligorskite, Fuller's earth, and combinations of any two or more of them.

4. A composition according to claim 1, characterized in that the clay is bentonite.

5. A composition according to claim 1, characterized in that the polymer is selected from the group consisting of biopolysaccharides, cellulose ethers, polymers containing acrylamide, copolymers of acrylate and styrene sulfonate, partially hydrolyzed polyacrylonitrile, polyacrylate and combinations of any two or more of them.

6. A composition according to claim 1, characterized in that the polymer contains an effective mole percentage of carboxylate groups for crosslinking with the crosslinking agent, and because it is selected from the group consisting of polyacrylamide, partially hydrolyzed polyacrylamides, acrylamide copolymers and N -vinyl-2-pyrrolidone, copolymers of acrylamide, acrylate and N-vinyl-2-pyrrolidone, copolymers of acrylate and styrene sulfonate, copolymers of acrylamide and sodium 2-acrylamido-2-methylpropanesulfonate, copolymers of acrylamide, acrylate and sodium acrylamido-2-methylpropanesulfonate, copolymers of acrylamide, N-vinyl-2-pyrrolidone and sodium 2-acrylamido-2-methylpropansulfonate, copolymers of acrylamide, acrylate, N-vinyl-2-pyrrolidone and 2-acrylamido-2 sodium-methylpropansulfonate, copolymers of acrylamide, sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate, carboxymethylcellulose, carboxymethylhydroxyethylcellulose, xa gum and combinations of any two or more thereof.

7. A composition according to claim 1, characterized in that the polymer contains a carboxylate group in the range of about 0.01 to about 30 mol%.

8. A composition according to claim 1, characterized in that the polymer contains a carboxylate group in the range from about 0.1 to about 10.0 mol%.

9. A composition according to claim 1, characterized in that the composition is prepared by the combination of the clay, the polymer, the crosslinking agent and the liquid.

10. A composition according to claim 2, characterized in that the bulking agent is selected from the group consisting of barite, hematite, calcium carbonate, galena and combinations of any two or more thereof.

11. A composition according to claim 1, characterized in that the gelling time of the composition is less than about 6 hours.

12. A composition according to claim 1, characterized in that the gelling time of the composition is less than about 3 hours.

13. A composition according to claim 2, characterized in that the density of the composition is in the range of about 1 to about 3.5 g / ml.

14. A composition according to claim 2, characterized in that the density of the composition is in the range of about 2.2 to about 3.0 g / ml.

15. A composition, characterized in that it comprises: a clay selected from the group consisting of kaolinite, halloysite, vermiculite, chlorite, atapulguite, smectite, montmorillonite, illite, saconite, sepiolite, paligorski ta, Fuller's earth, and combinations of any two or more of the same; a carboxylate-containing polymer having a molecular weight in the range of about 10,000 to about 30,000,000 selected from the group consisting of biopolysaccharides, cellulose ethers, polymers containing acrylamide, copolymers of acrylate and styrene sulfonate, partially hydrolyzed polyacrylonitrile, and combinations of any two or more thereof; a crosslinking agent selected from the group consisting of chromium acetate, chromium propionate, chromium chloride, chromium nitrate, zirconium complex of hydroxyethylglycine, ammonium-zirconium fluoride, zirconium 2-ethylhexanoate, zirconium acetate, decanoate zirconium, zirconium acetylacetonate, tetrakis (triethanolamine) zirconate, zirconium carbonate, ammonium zirconium carbonate, zirconyl ammonium carbonate, zirconium citrate, zirconium lactate, zirconium tartrate, zirconium malonate, zirconium propionate, acetylacetonate titanium, titanium ethylacetoacetate, titanium citrate, titanium triethanolamine, ammonium titanium lactate, aluminum citrate, and combinations of any two or more thereof; and a liquid; wherein the polymer is present in the composition in the range of about 100 to about 100,000 mg / L and the crosslinking agent is present in the composition in the range of about 1 to about 5,000 mg / L.

16. A composition according to claim 15, characterized in that the polymer is selected from the group consisting of partially hydrolyzed polyacrylamides, copolymers of acrylamide and N-vinyl-2-pyrrolidone, copolymers of acrylamide, acrylate and N-vinyl-2-pyrrolidone, copolymers of acrylate and styrene sulfonate, copolymers of acrylamide and sodium 2-acrylamido-2-methylpropropanesulfonate, copolymers of acrylamide, acrylate and sodium 2-acrylamido-2-methylpropanesulfonate, copolymers of acrylamide, N-vinyl-2-pyrrolidone and sodium 2-acrylamido-2-methylpropansulfonate, copolymers of acrylamide, acrylate, N-vinyl-2-pyrrole idone and sodium 2-acrylamido-2-methylpropanesulfonate copolymers of acrylamide, sodium acrylate and 2-acrylamido-2-met lpropansul sodium fonate, carboxymethylcellulose, carboxymethylhydroxyethylcellulose, xanthan gum, and combinations of any two or more thereof; the polymer has a molecular weight in the range of 10,000 to 20,000,000, contains a carboxylate group in the range of about 0.1 to about 10 mol%, and is present in the composition in the range of 1,000 to 50,000 mg / l; and the crosslinking agent is selected from the group consisting of chromium acetate, chromium propionate, chromium chloride, chromium nitrate, and combinations thereof, and is present in the composition in the range of 1 to 2,000 mg / l. .

17. A composition according to claim 16, characterized in that the polymer is selected from the group consisting of partially hydrolyzed polyacrylamides, copolymers of acrylamide, sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate, and combinations of any two or more of the same; and the crosslinking agent is zirconium lactate.

18. A process, characterized in that it comprises the injection of a mud gel composition into an underground formation, wherein the composition comprises a clay, a polymer, a crosslinking agent, and a liquid; the clay, the polymer, the crosslinking agent and the liquid are each present in an effective amount to form a gel; and the composition contains a total of solids (dissolved and undissolved) in the range of about 30 to about 90% by weight.me.

19. A process according to claim 18, characterized in that the composition further comprises a filler.

20. A process according to claim 18, characterized in that the clay is selected from the group consisting of kaolinite, halloysite, vermiculite, chlorite, atapulguite, smectite, montmorillonite, ilite, saconite, sepiolite, pal igorskite, Fuller's earth, and combinations of any two or more thereof.

21. A process according to claim 21, characterized in that the polymer is selected from the group consisting of biopolysaccharides, cellulose ethers, polymers containing acrylamide, copolymers of acrylate and styrene sulfonate, partially hydrolyzed polyacrylonitrile, polyacrylate and combinations of any two or more of them.

22. A process according to claim 19, characterized in that the bulking agent is selected from the group consisting of barite, hematite, calcium carbonate, galena and combinations of any two or more thereof.

23. A process according to claim 19, characterized in that the density of the composition is in the range of about 1 to about 3.5 g / ml.

24. A process according to claim 19, characterized in that the composition is prepared by combining the clay, the polymer, the crosslinking agent, the filler and the liquid.

25. A process, characterized in that it comprises injecting a mud gel composition into an underground formation in view of a loss of circulation or an increase in fluid or gas pressure in a drill rod, wherein the composition comprises: clay selected from the group consisting of kaolinite, halloysite, vermiculite, chlorite, atapulguite, smectite, montmorillonite, illite, saconite, sepiolite, paligorskite, Fuller's earth, and combinations of any two or more thereof; a carboxylate-containing polymer having a molecular weight in the range of about 10,000 to about 30,000,000 selected from the group consisting of biopolysaccharides, cellulose ethers, polymers containing acrylamide, copolymers of acrylate and styrene sulfonate, partially hydrolyzed polyacrylonitrile, and combinations of any two or more thereof; a crosslinking agent selected from the group consisting of chromium acetate, chromium propionate, "chromium chloride, chromium nitrate, zirconium complex of hydroxyethylglycine, ammonium-zirconium fluoride, zirconium 2-ethylhexanoate, zirconium acetate, zirconium decanoate, zirconium acetylacetonate, tetrakis (triethanolamine) zirconate, zirconium carbonate, ammonium zirconium carbonate, zirconyl ammonium carbonate, zirconium citrate, zirconium lactate, zirconium tartrate, zirconium malonate, zirconium propionate, titanium acetylacetonate, titanium ethylacetoacetate, titanium citrate, titanium triethanolamine, ammonium titanium lactate, aluminum citrate, and combinations of any two or more thereof; and a liquid; wherein the polymer is present in the composition in the range of about 100 to about 100,000 mg / L and the crosslinking agent will be present in the composition in the range of about 1 to about 5,000 mg / L.

26. A process according to claim 25, characterized in that the polymer is selected from the group consisting of partially hydrolyzed polyacrylamides, copolymers of acrylamide and N-vinyl-2-pyrrolidone, copolymers of acrylamide, acrylate and N-vinyl-2-pyrrolidone, copolymers of acrylate and styrene sulfonate, copolymers of acrylamide and sodium 2-acrylamido-2-methylpropanesulfonate, copolymers of acrylamide, acrylate and sodium 2-acrylamido-2-methylpropanesulfonate, copolymers of acrylamide, N-vini 1-2- pyrrole idone and sodium 2-acrylamido-2-methylpropansulfonate, copolymers of acrylamide, acrylate, N-vinyl-2-pyrrolidone and sodium 2-acrylamido-2-methylpropanesulfonate copolymers of acrylamide, sodium acrylate and 2-acrylamido-2- Sodium methylpropanesulfonate, carboxymethylcellulose, carboxymethylhydroxyethylcellulose, xanthan gum, and combinations of any two or more thereof; the polymer has a molecular weight in the range of 10,000 to 20,000,000, contains a carboxylate group in the range of about 0.1 to about 10 mol%, and is present in the composition in the range of 1,000 to 50,000 mg / l; and the crosslinking agent is selected from the group consisting of chromium acetate, chromium propionate, chromium chloride, chromium nitrate, and combinations thereof, and is present in the composition in the range of 1 to 2,000 mg / l.

27. A process according to claim 26, characterized in that the polymer is selected from the group consisting of partially hydrolyzed polyacrylamides, copolymers of acrylamide, sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate, and combinations of any two or more of the same; and the crosslinking agent is zirconium lactate.

28. A process, characterized in that it comprises the irjection of a composition into an underground formation in view of an increase in the unconsolidated sediments during the drilling of said formation, wherein the composition is prepared by the combination: (1) a polymer selected from the group consisting of partially hydrolyzed polyacrylamides, copolymers of acrylamide, sodium acrylate and 2-acrylamido-2-methylpropansul-fonate sodium, and combinations of any two or more thereof, wherein the polymer has a molecular weight in the range of about 10,000 to 30,000,000, has a carboxylate group in the range of about 0.1 to about 30 mol%, and is present in the composition in the range of 1,000 to 50,000 mg / l; (2) a crosslinking agent that is present in the composition in the range of 1 to 2,000 mg / l; and (3) a liquid constituting the remainder of the composition; and the composition contains a total of solids (dissolved and undissolved) in the range of about 30 to about 90% by weight.

29. A composition comprising a clay, a polymer, a crosslinking agent and a liquid, characterized in that: the clay, the polymer, the crosslinking agent and the liquid are each present in the composition in an amount effective to form a gel; the crosslinking agent is selected from the group consisting of organic crosslinking agents, multivalent metal compounds and combinations of any two or more thereof; and the multivalent metal compound is selected from the group consisting of chromium acetate, chromium propionate, chromium chloride, chromium nitrate, zirconium complex of hydroxyethylglycine, ammonium-zirconium fluoride, zirconium 2-ethylhexanoate, zirconium acetate , zirconium decanoate, zirconium acetylacetonate, tetrakis (triethanolamine) zirconate, zirconium carbonate, ammonium zirconium carbonate, zirconyl ammonium carbonate, zirconium citrate, zirconium lactate, zirconium tartrate, zirconium malonate, zirconium propionate, acetylacetonate of titanium, titanium ethylacetoacetate, titanium citrate, titanium triethanolamine, ammonium titanium lactate, aluminum citrate and combinations of any two or more thereof.

30. A composition according to claim 29, characterized in that it also comprises a filler.

31. A composition according to claim 29, characterized in that the clay is selected from the group consisting of kaolinite, halloisite, vermiculite, chlorite, atapulguite, smectite, montmorillonite, illite, saconite, sepiolite, pal igorski ta, Fuller's earth, and combinations of any two or more thereof.

32. A composition according to claim 29, characterized in that the clay is bentonite.

33. A composition according to claim 29, characterized in that the polymer is selected from the group consisting of biopolysaccharides, cellulose ethers, polymers containing acrylamide, copolymers of acrylate and styrene sulfonate, partially hydrolyzed polyacrylonitrile, polyacrylate and combinations of any two or more of them.

34. A composition according to claim 29, characterized in that the polymer contains an effective molar percentage of carboxylate groups for crosslinking with the crosslinking agent, and because it is selected from the group consisting of polyacrylamide, partially hydrolyzed polyacrylamides, acrylamide copolymers and N -vinyl-2-pyrrolidone, copolymers of acrylamide, acrylate and N-vini 1-2-pyrrolidone, copolymers of acrylate and styrene sulfonate, copolymers of acrylamide and sodium 2-acrylamido-2-methylpropansul fonate, copolymers of acrylamide, • acrylate and 2-acrylamide -2-methylpropansul fonpados of sodium, copolymers of acrylamide, N-vinyl-2-pyrrolidone and sodium 2-acrylamido-2-methylpropansulfonate, copolymers of acrylamide, acrylate, N-vinyl-2-pyrrolidone and 2-acrylamido-2- sodium methylpropansulfonate, copolymers of acrylamide, sodium acrylate and sodium 2-acrylamido-2-methylpropansul fonate, carboxymethylcellulose, carboxymethylhydroxyethylcellulose, xanthan gum and combinations of any two or more thereof.

35. A composition according to claim 29, characterized in that the polymer contains a carboxylate group in the range of about 0.01 to about 30 mol%.

36. A composition according to claim 29, characterized in that the composition is prepared by the combination of the clay, the polymer, the crosslinking agent and the liquid.

37. A composition according to claim 30, characterized in that the bulking agent is selected from the group consisting of barite, hematite, calcium carbonate, galena and combinations of any two or more thereof.

38. A composition according to claim 30, characterized in that the density of the composition is in the range of about 1 to about 3.5 g / ml.

39. A composition according to claim 30, characterized in that the composition contains a total of solids (dissolved and undissolved) in the range of about 30 to about 90% by weight.