GB2078280A - Drilling fluid composition - Google Patents

Abstract

A water-based drilling fluid composition comprises an aqueous dispersion of a clay material containing an effective dispersing amount of a modified lignosulfonate which is obtained by graft polymerization of from 5 to 30 weight percent of an acrylic compound with the lignosulfonate. The grafted lignosulfonate has an average molecular weight of less than 80,000. The drilling fluid may also contain a phosphate, a particular metal or both.

Description

SPECIFICATION Drilling fluid composition This invention pertains to a drilling fluid composition. More particularly, it pertains to a drilling fluid composition comprising a graft copolymer of lignosulfonate and an acrylic compound such as to render the copolymer especially useful in drilling fluids.

Water-based drilling fluids have been widely used to drill subterranean wells such as oil and gas wells.

These drilling fluids are often referred to as "drilling muds" because they comprise an aqueous dispersion of clay material. Such dispersions are thixotropic and it was found that certain lignosulfonates improved the properties thereof and such lignosulfonates came to be called "thinners" since, among other things, they function to reduce the effective viscosity of the drilling fluid under drilling conditions. The history and function of such drilling fluids is described in more detail in U. S. Patent No. 2,935,473. This patent discloses and claims a major innovation in lignosulfonate thinners, namely the use of certain metal salts of lignosulfonate wherein the metals are chromium, aluminum, iron, copper, or a combination thereof, which salts may be or may not be oxidized.Of the metal lignosulfonate salts disclosed in the above patent, the chromium salt has been most effective so that the chromium salt or salts of chromium mixed with other metals have been in the past mainly used. In addition to better thinning properties of the chromium salt, the thermal stability of drilling fluids containing the chromium salt is considerably improved over drilling fluids containing lignosulfonates of other metals. Recently, however, the use of chromium is being discouraged in view of the unknown environmental and pollution effects. Also, the availability of oil and gas at readily accessible locations has diminished and it has become necessary to drill wells to deeper levels. As the drilling depth increases, the temperature to which the drilling fluids are subjected increases so that thermal stability of the drilling fluid is becoming a more important consideration.

It is therefore, an object of one embodiment of the present invention to provide a drilling fluid composition which can be chrome-free.

Another object of one embodiment of the present invention is to provide a modified lignosulfonate drilling fluid additive which may be free of heavy metals which may be used in many respects as a replacement of the presently used chromium lignosulfonate-containing drilling fluid compositions.

Afurther object is to provide a drilling fluid composition having an enhanced thermal stability and which may be effectively used in drilling wells at temperatures above 250"F.

Another object is to provide a drilling fluid composition having an enhanced thermal stability and which is effective in muds such as seawater muds and gypsum-containing drilling fluids.

Another object is to provide an improved drilling fluid additive.

The above and other objects are obtained by this invention which comprises using an effective dispersing amount of a reaction product of lignosulfonate and an acrylic compound, such as acrylic acid, acrylonitrile, acrylamide, and other acrylic acid derivatives such as esters of one or two carbon atoms of acrylic acid in an aqueous drilling fluid composition containing clay material. The grafted product of lignosulfonate and the acrylic compound is prepared by reacting lignosulfonate with from 5 to 30 percent of the acrylic compound using a free radial initiator to obtain a reaction product having an average molecular weight not exceeding about 80,000. The drilling fluid composition has good thermal stability generally exceeding the present day chromium-containing drilling fluid additives in most mud systems.In gypsum-containing and some other muds where a small addition of a phosphate or polyphosphate and other additives such as particular heavy metal cations may be added to enhance the effectiveness of acrylic acid grafted lignosulfonate products.

The reaction or polymerization of the acrylic compound with the lignosulfonate is effected using conventional grafting techniques of polymerizing vinyl monomers to polymers with free radical type reactions. The reaction is preferably carried out by reaction of the acrylic compound with the lignosulfonate in an aqueous medium. In carrying out the reaction with free radical generation, an association of the acrylic compound with the lignosulfonate is obtained characteristic of graft type copolymers. Preferably, free radical initiators such as benzoyl peroxide, alpha-azobisisobutyronitrile, cumene hydroperoxide, and other free radical initiators, such as hydrogen peroxide-metal redox system, may be used. With the latter initiators, generally lignosulfonate as obtained contains sufficient amount of iron so that additions of metal do not have to be made.

Lignosulfonates obtained from any source may be used for the polymerization with the acrylic compound.

Lignins are polymeric substances composed of substituted aromatics found in plant and vegetable tissue associated with cellulose and other plant constituents. In the pulp and paper industry, lignin-containing materials such as wood, straw, corn stalks, bagasse, and other vegetable and plant tissues are processed to recover the cellulose or pulp. The residual pulping liquors containing the lignin as by-products are, thus, one of the main sources of lignins. While there is some variation in the chemical structure of lignin, depending upon the plant from which lignin is obtained, place where the plant is grown, and also upon the method used in recovery or isolation of the lignin from the plant tissue, the basic structure and properties of the lignins are similar, all containing an aromatic nucleus through which the reaction may possibly be affected.Thus, lignins obtained by any method or from any source may be used in this reaction as long as the lignin is in a form which may at least be partially soluble in a solvent in which it may be grafted with the acrylic compound to form the product of this invention.

Since the lignins separated from the plant may be chemicaliy altered somewhat from that found in the plant, the term "lignins", as used herein, means the lignin products which are obtained upon separation from the cellulose or recovered from the plant. In the suifite pulping process, the lignocellulosic material is digested with a sulfurous acid-metal bisulfite solution resulting in the sulfonation of the lignins. In other methods of the recovery or separation of the lignins from the plant, the lignins may not be sulfonated but may be chemically altered somewhat in some other manner. For example, in residual pulping liquors obtained in the sulfate and other alkaline pulping processes, the lignins are present as alkaline metal salts disolved in the alkaline aqueous liquor. "Hydrolysis lignin" is obtained from the hydrolysis of lignocellulosic materials found in the plant.The lignin obtained by hydrolysis or by an alkaline pulping process may be sulfonated as well as spent sulfite liquor being further sulfonated. Also, the lignin products such as a residual pulping liquor may be subjected to various treatments such as, for example, acid, alkaline or heat treatment or reacted with other chemicals which may further alter somewhat the lignin constituents. The lignins remain operative as long as the treatment is not so severe as to destroy the basic aromatic polymeric structure.

The residual pulping liquors, or the lignin-containing product obtained in the separation or recovery of lignins from the plant, will generally contain lignins of various molecular weights varying from less than 1,000 to over 100,000. A weight average molecular weight of these lignins is generally in the range of 10,000 to 15,000. These liquors also may contain other constituents besides the lignins. For example, in the sulfite pulping process, the spent sulfite liquor contains lignosulfonates which may be present as salts of cations, such as magnesium, calcium, ammonium, sodium and other cations which may have been present during the sulfonation of the lignin.The spent sulfite liquor generally contains only about 40 to 60 weight percent on an oven-dried basis of lignosulfonates with the remainder being carbohydrates and other organic and inorganic constituents dissolved in the liquor. Lignin products obtained by other pulping processes may likewise contain other materials such as carbohydrates, degradation products of carbohydrates, and resinous materials which are separated from the lignocellulosic materials with the lignin. Lignin obtained by hydrolysis of lignocellulosic materials may not contain the carbohydrates but may contain resinous-type materials as well as other materials which are not removed by the hydrolysis. It is not necessary to separate the lignin-containing constituents from the other constituents.The lignin product as obtained containing all of the constituents may be used as such or subjected to different treatments such as alkaline, acid, or heat treatments as well as reacted with chemicals to modify or remove some of the non-lignin constituents prior to the polymerization reaction. Some reaction of the acrylic compound with the non-lignin constituents may be obtained, but the presence of the products of reaction of these constituents is not of sufficient importance to warrant their removal before or after the polymerization.They are generally of lower molecular weight materials and can be easily removed from the final lignosulfonate-acrylic graft copolymer after reaction if desired using methods, such as dialysis, gel permeation chromatography, chemical precipitation and extraction, or other methods well known in the art for the fractionation and recovery of high molecular weight organic water-soluble polymers from lower molecular weight materials. The lignin materials may also be separated from the non-lignin constituents and fractionated into fractions of various molecular weights prior to reaction with the acrylate monomer.

The acrylic compound which is preferably used for the preparation of the lignosulfonate graft polymer is acrylic acid. Derivatives of acrylic acid such as acrylonitrile and acrylamide may also be used by themselves or in mixtures with acrylic acid. Drilling fluids prepared with the lignosulfonate-acrylic compound products have improved thermal stabiiities over chromium lignosulfonates but are not effective in muds such as gypsum-containing muds without the addition of phosphate.When a mixture of acrylic acid and another acrylic compound is used in preparation of the graft copolymer, the amount of the acrylic acid employed in the mixture generally is from about 10 to 90%, preferably 60 to 40%, but may be widely varied as long as the mixture, when grafted upon the lignosulfonate, is water soluble or upon alkaline hydrolysis becomes water soluble.

While the reaction of the lignin with the acrylic compound using free radical initiators is preferably carried out in an aqueous medium, other solvents such as alkanols having from 1 to 4 carbon atoms, acetone, dioxane, ethylene glycol, formamide, dimethylformamide, dimethylsulfoxide, and others may be used.

Preferably the solvents which are water miscible and which can be used in mixture with water are preferred.

In some of the reactions, the presence of an alcohol, such as methanol, may enhance the reaction of the acrylic compound with the lignin molecuie. However, it is not necessary to use an aqueous medium. The copolymerization of the lignosulfonate with the acrylic compound may be carried out in other media in which the reactants are at least partially soluble. For example, the medium used may be such that the lignin is only partially soluble, swelling in the medium, or a medium in which the lignosulfonate-acrylic copolymer will precipitate upon formation. The products obtained may vary somewhat depending upon the particular reaction employed for the polymerization of the lignin with the acrylic compound. For example, the number and molecular weight of the acrylic side chains grafted to the lignosulfonate backbone presumably may differ when the reaction is carried out using a peroxide or chemical free radical initiator in place of irradiation as well as when particular acrylic compounds are used.

The lignosulfonate is copolymerized with from 5 to 30 weight percent of the acrylic compound, preferably with from 10 to about 20 percent. The amount of initiator used is generally such that when the reaction is relatively completed the average molecular weight of the lignosulfonate graft polymer with the acrylic compound will not exceed about 80,000. With the higher amounts of acrylic compounds, for example, the amount of initiator used may have to be more closely controlled to complete the graft polymerization without obtaining excessive cross-linking between the lignosulfonate units to give a product of excess molecular weight. At the desired molecular weights, the copolymer is generally readily water soluble and, thus, may be used as the drilling fluid additive. Preferably a copolymer having an average molecular weight in the range of 20,000 to 60,000 is preferred.The graft polymerization is generally carried out under acid conditions using a pH below 6, preferably at a pH between 3 and 4. The amount of acrylic compound used may be varied depending upon the properties desired in the final product. For drilling fluids which may be subjected to normal temperatures, from 5 to 10 percent of acrylic acid will result in an effective thinner.

Usually from 10 to 15 percent of the acrylic compound is used for the polymerization. The product thus obtained generally gives good thermal stability which will exceed that of a chrome lignosulfonate. It is about as effective as a thinner as a chrome lignosulfonate in seawater muds and in gyp muds with the addition of other additives. With higher amounts of the acrylic compound copolymerized with lignosulfonates, generally further improvements in thermal stability are obtained, e.g., at drilling temperatures approaching 475"F, 20% and greater of the acrylic compound would be used which would give a thinner which is considerably more effective for high-temperature muds than the presently used chrome lignosulfonate. For these high temperatures, generally the alkali metal salts, preferably sodium or potassium salts, of the copolymer are used.The presence of heavy metal cations, such as iron, for example, has a negative effect on thermal stability, so if the heavy metal is used for the high temperatures it is usually used in limited amounts only.

In determining the molecular weight of the graft copolymer of lignosulfonate and the acrylic compound, the agar gel diffusion method, as described by J. Moacanin, H. Nelson, E. Back, V. F. Felicetta and J. L.

McCarthy in the Journal of the American Chemical Society 81, 2054 (1959), is used.

The phosphate compound used to improve performance of the copolymers, for example, in a gypsum or seawater drilling fluid may be any water-soluble phosphoric acid or condensed phosphoric acid compound or salt, such as an ortho-, meta-, or polyphosphate salt. Most commonly, an ammonium or alkali metal phosphate salt is used such as ammonium or alkali metal orthophosphate, hexametaphosphate, tripolyphosphate, or pyrophosphate. Sodium orthophosphate or metaphosphate is preferably used due to their availability and cost. The phosphate may be added to the drilling fluid at any time or in any form. It may be simply added to the drilling fluid when it is prepared or it may be intermixed with the lignosulfonateacrylic compound copolymer prior to addition.Generally after preparation of the reaction product of lignosulfonate and the acrylic compound, the phosphate may be added to the reaction mixture at the end of the polymerization and dried to obtain a uniformly mixed dry product. This also simplifies preparation of the drilling fluid in the field by requiring only the addition of the mixture instead of mixing the individual components in proper proportions in the field. The amount of the phosphate used is generally in an amount, expressed as phosphorous, of from 0.5 to about 5 weight percent of the reaction product. Preferably the phosphate content is generally maintained in the range of from about 1 to 3%, with the phosphate usually being in the lower range when the heavy metals are used in conjunction with the phosphate.

Generally, the addition of the phosphate enhances the thermal stability of the lignosulfonate-acrylate copolymer and the effectiveness of the product in the presence of salt and gypsum contamination. The presence of or the partial conversion of the lignosulfonate-acrylate copolymerto heavy metals, such as iron, zinc, manganese, titanium, copper, and chromium, generally in limited amounts, greatly improves the dispersing and thinning properties of drilling fluids which are contaminated or treated with non-swelling low-yield clays, shales, and other clay contaminants as may be encountered in drilling through various formations. Iron and some of the other cations may have a negative effect on thermal stability at high temperatures, while the presence of the phosphate may have a negative effect in the presence of certain non-swelling clays or shales.Thus, the amount of the heavy metal cations and phosphate used may be varied with respect to the particular drilling fluid used and the particular contaminations encountered. For certain drilling fluids where thermal stability and stability to contamination against gypsum and salt are desired, phosphate by itself may be used, while in other systems where clay and shale contamination is encountered the heavy metal may be used only. Generally, the heavy metal is added in an amount of at least 0.6 weight percent, based upon the weight of the copolymer or reaction product. The amount of the metal may be increased to 10% or more, but generally the amount used is limited to 5 weight percent. Preferably, the amount is in the range of 1.5 to 3.5 percent.At the preferred metal concentrations, the additive is still sufficiently thermally stable and with the addition of phosphate, effective for most drilling fluid systems and contaminants which may be encountered in drilling operations. Of the heavy metals, iron is preferred.

The heavy metal, as a water-soluble compound, may be intermixed with the phosphate-treated polymer as an aqueous solution or intermixed dry with the polymer and the phosphate. For convenience, the metal compound may be added to the copolymer after the condensation or polymerization and prior to or after the phosphate addition, if the phosphate is added. Other methods of adding heavy metal and phosphate to the polymer may be used as long as the conditions are such that the metal is not rapidly precipitated out as an insoluble phosphate salt. When the metal compound is added to a solution of the polymer containing phosphate, possibly some of the metal may become associated with the phosphate to form a fine insoluble phosphate salt which remains dispersed in the mixture. After setting for some time, some gel can be obtained upon centrifugation which is believed to be the insoluble phosphate salt with occluded polymer. Without the presence of metals forming insoluble phosphates, the gels have not been noted.

In preparation of the drilling fluid composition, the methods and procedures conventionally used for preparation of these compositions with other additives are normally followed. The copolymer is added in a sufficient amount to effectively disperse the clay and other constituents in the drilling fluid and can be widely varied, similar to the variations presently employed with the chrome-containing drilling fluid additives, depending upon the formations being drilled and the depth of the well. The additives may be used with weighting materials, water loss agents and also with other additives such as, for example, phosphate or polyphosphate in particular contaminated muds.

The following examples further illustrate the invention.

Example I A number of runs were made where a fermented calcium-based spent sulfite liquor was reacted in the presence of hydrogen peroxide with acrylic acid, acrylonitrile, and a mixture of the two. The products obtained were then used as drilling mud additives and tested for thermal stability.

The lignosulfonate used was a calcium-based fermented spent sulfite liquor which had been diluted to about 42% solids concentration. To the spent sulfite liquor containing 100 grams solids, 10 grams of acrylic acid were intermixed with the spent sulfite liquor solution and then 5 grams of hydrogen peroxide were slowly added as a 35% aqueous solution. The mixture was then heated for 3 to 4 hours on a hot water bath at a temperature in the range of 70 to 750C with occasional stirring. After the reaction, the sample was cooled, centrifuged or filtered and freeze dried.

In a process similar to that described above, other samples were prepared where, instead of acrylic acid, the spent sulfite liquor containing 100 grams solids was reacted with 10 grams of acrylonitrile and with a mixture of 5 grams each of acrylonitrile and acrylic acid.

The freeze dried products were then used as drilling fluid additives and tested for thermal stability at 425"F.

The following procedure was used for the thermal stability test for this and the following Examples. The sample in a specific amount was mixed into a fresh water mud and the mixture hot rolled at 150"F for 20 hours at a pH of about 9.5. After the hot rolling, the sample was cooled and barium sulfate as a weighing agent was added in an amount to give a density of 16 pounds per gallon. The mixture was then mixed and hot rolled again for an additional 20 hours at 150"F at a pH of about 9.5. After the second hot rolling, the sample was placed in a sealed metal container and heated at 425"F for 22 hours. After heating, the sample was colled and a sheartest and mud tests similar to API standard test procedures for drilling fluids were made.

The results obtained are shown in Table I below compared to a control which was a commercial ferrochrome lignosulfonate drilling fluid additive sold under the trademark of Q-BROXIN.

Example II A fermented calcium-based liquor was base exchanged to the sodium base by addition of sodium sulfate to precipitate the calcium as calcium sulfate which was then removed by filtration. To 3,666 grams of the base-exchanged liquor having a solids concentration of 44.9% were added to 164.6 grams of acrylic acid which was about 10% of the spent sulfite liquor solids. To this mixture, 58.8 grams of 35% hydrogen peroxide were then added which represented about 1.25 weight percent of the spent sulfite liquor solids. The liquor as obtained contained about 80-100 ppm of iron so that no additional iron was added. The mixture was heated for approximately 3 to 4 hours on a hot water bath at a temperature in the range of 70 to 80"C.

After the reaction 164.6 grams of sodium hexametaphosphate dissolved in water were added to the product.

After mixing, the product was at a pH of 3.9. The sample was spray dried and tested for thermal stability at 425"F at 15 pounds per barrel of additive and in gypsum and seawater containing muds. The results obtained as compared to a control are shown below. The control was a commercial ferrochrome lignosulfonate described in Example I.

Example 111 A sodium-based spent sulfite liquor prepared as described in Example II was reacted with 15,20 and 25% of acrylic acid. In the first run made, the sodium lignosulfonate solution in an amount of 221 grams TABLE I Thermal Stability Test at 425 F at 15#/bbl Acrylic %acrylic Graft Compound Shear PH IG 600 300 PV Y 10G Acrylic Acid 10% 323 8.0 1.0 46.5 23.5 23.0 0.5 12 Acrylonitrile 10% 800 8.2 4.0 63.5 36.5 27.0 9.5 82 Acrylic Acid 5% 592 8.2 2.5 58.0 32.0 26.0 6.0 56 Acrylonitrile 5% Control 1083 8.0 5.0 130.0 73.5 56.5 17.0 75 TABLE II Type of Amount of Additive Mud Additive Shear PH IG 600 300 PV Y 10G Lignosulfonate Acrylic Acid Seawater 3#/bbl --- 8.3 8.0 37.5 28.0 9.5 18.5 38.0 Control " 3#/bbl --- 8.4 6.0 28.5 19.0 9.5 9.5 18.0 Lignosulfonate Acrylic Acid Gypsum 6#;/bbl --- 8.3 1.0 34.5 19.0 15.5 3.5 3.0 Control " 6#/bbl --- 8.2 1.0 28.5 16.0 12.5 3.5 8.0 Thermal Stability Test at 425 F Lignosulfonate Acrylic Acid 15#/bbl 387 8.5 3.5 112.5 66.0 46.5 19.5 6.0 Control 15#/bbl 2150 too thick to test containing 45.2% solids was diluted with 50 grams of water and then 15 grams of acrylic acid were added.

After addition of the acrylic acid, 3.6 grams of 35% hydrogen peroxide were added and the sample was heated for about 3 to 4 hours on a hot water bath at 70 to 80 C. The pH of the reaction mixture was 3.8.

Similar to the procedure described above, two additional runs were made where 20 grams and 25 grams, respectively, of acrylic acid were used instead of the 15 grams above. The samples after preparation were cooled and a portion of each of the samples was freeze dried and tested in an amount of 3 pounds per barrel as additives for seawater drilling fluid and for thermal stability at 424"F at 15 pounds per barrel of additive.

The results obtained are shown in the Table below. A commercial ferrochrome lignosulfonate as noted above was used as the control for the seawater drilling fluid.

The following Examples further illustrate the invention.

Example IV A run was made where a lignosulfonate was reacted with 5% acrylic acid after which various amounts of sodium hexametaphosphate were added and the product as a dispersant in gypsum-containing drilling fluids.

A fermented calcium-based spent sulfite liquor was base exchanged to a sodium base by addition of sodium sulfate and precipitating the calcium as calcium sulfate. To 519 grams of the base exchanged spent sulfite liquor solution having a concentration of 48.2%, 12.5 grams of acrylic acid were added with 3.1 grams of 35% solution of hydrogen TABLE Ill Seawater Drilling Fluid at 3#lbbl of Additive Amount of Acrylic Acid Run Reacted, % Shear PH IG 600 300 PV Y 10G 1 15 --- 8.0 15.0 39.5 29.5 10.0 19.5 43.0 2 20 --- 8.0 7.5 36.5 26.5 10.0 16.5 38.0 3 25 --- 8.2 11.0 32.0 23.0 9.0 14.0 37.0 Control --- --- 8.2 6.0 31.0 21.0 10.0 11.0 18.0 Thermal Stability Test at 425"F at 25#;1bbl 1 15 353 7.3 4.0 130.0 78.0 52.0 26.0 19.0 2 20 198 7.8 3.5 119.0 72.0 47.0 25.0 12.0 3 25 148 7.8 3.5 113.0 67.5 45.5 22.0 7.5 peroxide. The hydrogen peroxide was diluted with approximately an equal amount of water prior to addition. After mixing, the reaction mixture was digested on a boiling water bath for about 1 hour with occasional mixing. The reacted mixture was cooled and diluted to about 40% solids concentration. The product was then divided into increments of about 50 grams each of the original spent sulfite liquor solids.

To three of the increments, 5,7.5, and 2.5 grams, respectively, of sodium hexametaphosphate were added which represented 2.9, 4.2, and 7 weight percent of phosphorous based on the copolymer, and after mixing the products were spray dried. An increment was spray dried without the addition of the phosphate.

The four samples obtained above were tested in a gypsum-containing drilling fluid at an amount of 6 pounds per barrel and compared to results obtained against a control which was a commercial ferrochrome lignosulfonate sold under the trademark of Q-BROXIN. The gypsum-containing drilling fluid was obtained by adding 6 pounds per barrel of calcium sulfate (1/2 hydrate) to a fresh water drilling fluid. The tests made were similar to API standard test procedures for drilling fluids. The results obtained are shown in the Table below.

TABLE IV Phosphorous Run % IG PV Y 10G WL 1 0 7.0 7.0 16.0 21.5 15.5 2 2.9 1.0 10.0 3.5 13.0 9.4 3 4.2 1.0 11.0 1.5 2.0 9.8 4 7.0 1.0 11.5 2.5 6.0 9.4 Control --- 1.0 10.5 3.5 5.0 11.4 Example V A run similar to that described in Example IV was made where the base exchanged spent sulfite liquor was reacted with 15 weight percent acrylic acid in the presence of 3 weight percent of hydrogen peroxide, based upon the spent sulfite liquor solids. After preparation of the product, the reaction mixture was divided into five increments so that each increment contained approximately 50 grams of the original SSL solids. To one increment no phosphate was added but to the others different phosphoric acid and sodium hydroxide were added in proper proportions to obtain a pH of about 3.4.The increments were then spray dried and tested in gypsum and seawater-containing muds and a thermal stability test at 350'was also made. The phosphate salts were added in an amount equal to about 2.5 weight percent of the phosphorous, based upon the copolymer. In the tests made, the additive was used in an amount of 6 pounds per barrel for the gyp mud test, 3 pounds per barrel for the seawater drilling fluid, and the thermal tests were made using 8 pounds per barrel of the additive.

The following procedure was used for the thermal stability test. The sample in a specific amount was mixed into a fresh water mud and the mixture hot rolled at 150"F for 20 hours at a pH of about 9.5. After the hot rolling, the sample was cooled and barium sulfate as a weighting agent was added in an amount to give a density of 16 pounds per gallon. The mixture was then mixed and hot rolled again for an additional 20 hours at 150do at a pH of about 9.5. After the second hot rolling, the sample was placed in a sealed metal container and heated at 350"F for 22 hours. After heating, the sample was cooled and a shear test and mud tests similar to API standard test procedures for drilling fluids were made.

The results obtained are shown in Table V below compared to a control which was a commercial ferrochrome lignosulfonate drilling fluid additive as noted in Example IV.

Example VI A sodium-based spent sulfite liquor similar to that described in Example IV was reacted with 25 weight percent acrylic acid in the presence of 1.7 weight percent of hydrogen peroxide in a procedure similar to that described in Example IV. To twd increments of the reaction mixture, each representing about 50 grams of the original spent sulfite liquor reacted, phosphoric acid was added in an amount to represent 1.5 weight percent phosphorous in one increment and 2.2% phosphorous in the second, based upon the copolymer. Sodium hydroxide was also added in proper proportion to maintain the reaction mixtures at a pH of about 3. The products were tested in gypsum and seawater-containing muds and also for thermal stability at 475"F for 22 hours using the procedure described in Example V.The additive was used in an amount of 6 pounds per barrel in gyp mud, 3 pounds per barrel in seawater mud, and 15 pounds per barrel for the thermal stability test.

The results obtained are shown in the Table below where a ferrochrome lignosulfonate noted in Example IV was used as a control for the gypsum and seawater drilling fluid, and for high temperature stability tests at 475"F, a special chrome lignosulfonate prepared according to U.S.

TABLE V Phosphate Gypsum Mud Seawater Mud Run Added IG PV Y 10G IG PV Y 10G 1 No Phosphate 18.0 8.0 26.0 35.0 8.0 10.5 16.0 44.0 2 Sodium 1.0 10.5 2.0 3.0 6.5 9.0 9.0 24.0 Hexametaphosphate 3 Sodium 1.0 11.0 2.0 2.0 6.0 9.5 9.0 24.0 Pyrophosphate 4 Sodium 1.0 10.0 1.5 1.5 3.0 8.5 8.5 23.0 Tripolyphosphate 5 Phosphoric Acid- 1.0 11.0 2.0 1.5 5.0 9.5 9.5 22.0 Sodium Hydroxide Control ---- 1.0 10.0 2.5 4.0 6.5 9.0 9.5 15.0 Thermal Stability Test at 350 F Shear IG PV Y 10G 1 No Phosphate 139 2.0 24.0 3.0 7.0 2 Sodium 227 2.0 34.5 5.0 3.0 Hexametaphosphate 3 Sodium 195 2.0 37.0 5.0 3.0 Pyrophosphate 4 Sodium 185 2.0 36.5 5.5 3.0 Tripolyphosphate 5 Phosphoric Acid- 168 2.0 37.0 4.5 3.0 Sodium Hydroxide Control ---- 166 13.0 25.0 24.0 51.0 TABLE VI Gypsum Mud Seawater Mud Run IG PV Y 10G WL IG PV Y 10G 1 1.0 15.5 3.0 3.0 7.4 4.0 8.0 8.0 23.0 2 1.0 16.5 3.5 2.5 7.2 3.0 9.0 7.5 22.0 Control 1.0 13.5 3.0 5.0 10.6 5.5 9.0 9.0 15.5 Thermal Stability Test at 475"F Shear IG PV Y 10G WL 1 353 7.0 43.0 36.0 76.0 6.6 2 273 4.0 40.5 22.5 24.0 6.0 Control 380 3.0 47.0 8.0 10.0 10.2 Patent No. 3,686,119 for use at high temperatures was used for the control.

Example VII Acrylamide in an amount of 10 grams was dissolved in 50 grams of water and added to 197 grams of a fermented spent sulfite liquor having a concentration of 50.8% solids. The fermented liquor was a calcium-based liquor. After addition of the acrylamide, 10.2 grams of 48.8% hydrogen peroxide were added and the sample was heated to about 75" while being stirred. The reaction became exothermic and the sample was maintained at a temperature of 75 to 85" for one hour, after which ferric sulfate dissolved in water was added and the sample heated for an additional hour at about 75"C to convert the product to an iron salt containing about 9% iron. The reaction mixture was at a pH of 3.1. The sample was cooled and filtered and the filtrate was freeze dried and a portion tested as a drilling mud additive in gyp mud and for thermal stability at 350"F for 22 hours at 12 pounds per barrel of additive. The procedure used for the thermal stability test was similar to that described in Example V. The results obtained as compared to a ferrochrome lignosulfonate control are shown in Table VII below.

Example VIII A product was prepared where different water-soluble metal compounds were added to a reaction product of lignosulfonate and acrylic acid and the product tested in a drilling fluid containing non-swellable or contaminating clays.

TABLE VII Type Drilling Additive Run Fluid #/bbl Shear PH IG 600 300 PV Y 10G Lignosulfonate- Gypsum 6 --- 8.2 1.0 30.5 17.5 13.0 4.5 12.0 Acrylamide Control " 6 --- 8.1 1.0 24.5 13.5 11.0 2.5 4.0 Thermal Stability Test at 350 F Lignosulfonate- 12 155 8.0 2.5 72.0 37.0 35.0 2.0 2.0 Control 12 143 8.3 2.5 74.0 39.0 35.0 4.0 6.5 A series of samples was prepared where a sodium-base spent sulfite liquor was reacted with 13% of acrylic acid using iron-hydrogen peroxide as the free radical initiator. After the polymerization of the acrylic acid with the lignosulfonate, manganese sulfate was added to the reaction mixture, and the mixture heated for 30 minutes at about 95". The pH was then raised to 3 with sodium hydroxide and a portion of the product was spray dried.

The procedure similar to that above was repeated except that in place of manganese sulfate, zinc sulfate, copper sulfate, chromium sulfate, iron sulfate were added, respectively. Also a sample was prepared using titanium sulfate which was dissolved in strong sulfuric acid solution. After the addition of the titanium sulfate, the solution was neutralized with calcium hydroxide and the calcium sulfate filtered off. The clarified solution was then maintained at 95" for 30 minutes prior to spray drying.

The products above were evaluated by using the products as additives in a fresh water drilling fluid which had been contaminated with calcium-base non-swelling bentonite clays. The drilling fluid was prepared by mixing high-yield and low-yield bentonites of the type conventionally used in preparation of drilling fluids in an amount to represent clay solids in the drilling fluid of about 8.4 percent. The non-swelling clays were added in an amount of about 2.6% to obtain a drilling fluid which contains about 11% solids. The additives were added to the above drilling fluid in an amount of 4 pounds per barrel and the mixture hot rolled at 150oF for about 20 hours. The additives were also tested with and without phosphate in a gypsum contaminated drilling fluid where 6 pounds per barrel of gypsum were added to a fresh water mud.The additives were added to the drilling fluid in an amount of 6 pounds per barrel. The results obtained are shown in Table VIII where the results were compared to using a lignosulfonate-acrylic acid copolymer as a sodium base without the presence of the heavy metals.

Example IX A series of samples of a lignosulfonate-acrylic acid copolymer containing 13% acrylic acid was tested with phosphate, heavy metal, and with a mixture of phosphate and heavy metal in the clay contaminated mud system of Example VIII wherein additional contamination was added in an amount of 5 pounds per barrel of salt and 2 pounds per barrel of gypsum. The additives were used in an amount of 5 pounds per barrel. The constituents of the additives and the results obtained are shown in Table IX below.

Example X A series of additives of a copolymer obtained by reacting lignosulfonate with 13 weight percent acrylic acid was also tested with phosphate, heavy metal, and both metal and phosphate for thermal stability at 400"F in a drilling fluid similar to that described in Example V. The procedure used for the thermal test was similar to that described in Example V, except that the barium sulfate was added at the beginning of the test so the sample was hot rolled only once at 150"F before being placed in the sealed metal container for aging at 400"F for 22 hours. The additive was used in an amount of 12 pounds per barrel for the test. The constituents of the additives and the results obtained are shown in Table X below.

TABLE VIII Clay Contaminated Gypsum Contaminated Drilling Fluid Drilling Fluid Amt. of Amt. of Metal, Phosphorous, Run Metal Wt.% IG PV Y 10G Wt.% IG PV Y 10G 0 22.0 10.0 26.0 45.0 1 Mn 2.5 0.5 12.0 4.0 1.5 1.4 0.5 12.0 0 9.0 0 1.5 11.0 13.0 27.0 2 Zn 2.9 0.5 14.0 3.0 2.5 1.4 1.0 10.5 2.0 5.0 0 0.5 15.5 1.0 14.0 3 Cu 2.8 0.5 13.5 3.0 3.0 1.4 0.5 10.5 6.5 17.0 0 0.5 10.0 8.0 11.0 4 Cr 2.3 1.5 14.0 7.0 2.5 1.4 4.0 11.5 10.0 22.0 0 8.0 11.0 20.0 26.0 5 Ti 2.1 0.5 15.0 4.0 2.0 1.4 1.5 9.5 7.0 16.0 0 1.5 14.0 19.0 37.0 6 Fe 2.5 0.5 14.5 3.5 1.5 1.4 0.5 10.5 2.0 6.0 0 16.0 --- --- 37.0 7 Control 0 1.5 15.5 6.5 15.0 1.4 2.5 12.5 16.0 37.0 TABLE IX Gypsum, Salt and Clay Contaminated Amt. of Amt. of Iron, Phosphorous, Run Wt. % Wt. % IG PV Y 10G Control O 0 18.0 11.0 50.0 80.0 1 0 1.4 10.0 18.0 19.0 89.0 2 1.0 0 19.0 20.0 32.0 71.0 3 10.0 0 8.0 20S0 25.0 90.0 4 1.5 1.4 1.5 17.0 10.0 50.0 5 2.5 1.4 1.5 15.0 9.0 36.0 6 3.5 1.4 1.0 18.0 7.0 22.0 TABLE X Thermal Stability Test @ 400"F Amt. of Amt. of Iron, Phosphorous, Shear Run Wt. % Wt. % #/100 Ft2 IG PV Y 10G Control O 0 125 1.5 37.5 7.5 2.5 1 0 1.4 50 1.5 38.0 4.0 2.0 2 2.5 0 190 1.5 41.0 4.0 5.0 3 10.0 0 360 3.0 31.0 23.0 67 4 1.5 1.4 115 2.0 38.0 9.0 2.5 5 2.5 1.4 125 1.5 38.5 6.5 1.5 6 3.5 1.4 125 1.5 41.0 5.0 3.5

Claims (8)

1. Awater-based drilling fluid comprising a suspension of clay material and an effective dispersing amount of a water-soluble reaction product of lignosulfonate and an acrylic compound comprising one or more acrylic compounds such as acrylic acid, acrylonitrile, acrylamide, and esters of acrylic acid with C1 or C2 alcohols, said reaction product being prepared by reacting lignosulfonate with from 5 to 30 weight percent of acrylic compound using a free radical initiator, said reaction product having an average molecular weight not exceeding about 80,000.

2. A composition according to claim 1 wherein the acrylic compound is acrylic acid.

3. A composition according to claim 2 wherein the acrylic acid is reacted with the lignosulfonate in an amount of from 10 to 15 percent.

4. A composition according to claim 1 wherein the lignosulfonate is reacted with the acrylic compound until said reaction product has an average molecular weight in the range of 20,000 to 60,000.

5. A composition according to claim 1 containing a water-soluble phosphate compound in an amount, expressed as phosphorous, in the range of from 0.5 to 5 weight percent of the reaction product.

6. A composition according to claim 1 or claim 5 containing a water-soluble compound of a metal selected from iron, titanium, manganese, zinc, copper, and chromium, said metal compound being combined with the reaction product in an amount such that at least 0.6 weight percent of the metal, based upon the reaction product, is present.

7. A process of drilling a well comprising circulating in the well, while drilling, a drilling fluid composition of claim 1,5or6.

8. A water-based drilling fluid composition according to claim 1 and substantially as herein described with reference to the examples.