A silicate water-based drilling fluid specially used for coalbed methane wells and its application

Abstract

The present invention relates to the field of oilfield chemical technology for oil and gas drilling engineering, and in particular to a silicate water-based drilling fluid for coalbed methane wells and its application. Calculated by mass, the raw materials of the silicate water-based drilling fluid for coalbed methane wells include: 100 parts of water, 1-3 parts of bentonite, 1-5 parts of pH regulator, 3-5 parts of silicate, 2-4 parts of silicate stabilizer, 0.1-0.15 parts of viscosity enhancer, 2-4 parts of fluid loss reducer, 3-5 parts of auxiliary inhibitor, 1-2 parts of activator, 2-4 parts of plugging agent and 2-4 parts of lubricant. The silicate water-based drilling fluid for coalbed methane wells of the present invention has good rheological properties, fluid loss properties, plugging properties and lubrication properties in a low temperature environment, and is more suitable for coalbed methane well drilling operations.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry for oil and gas drilling engineering, and in particular to a silicate water-based drilling fluid special for coalbed methane wells and application thereof. Background Art

[0002] As an important unconventional natural gas resource, coalbed methane has gradually attracted widespread attention due to its advantages of low pollution and high energy efficiency. In the drilling process of coalbed methane wells, due to the high brittleness of coal rock and poor lithology, the development of cleats and cracks, the wellbore collapse is very likely to occur during the drilling process, causing downhole accidents, resulting in long drilling cycles, increased costs, and failure to reach the target well depth. Drilling fluid is the most important fluid in the drilling process. In addition to carrying cuttings and lubricating the drill bit, its biggest function is to maintain the stability of the wellbore. Although oil-based drilling fluid has excellent performance, its high cost and environmental problems limit its application in coalbed methane drilling. In coalbed methane drilling, polymer drilling fluid system is generally used. This system has the characteristics of good rheology and low filtration loss. It has been widely used in coalbed methane drilling, but this system does not completely solve the problem of wellbore collapse in coal seams. With the continuous extension of the horizontal section of coalbed methane drilling and the development of deep coalbed methane, the problem of wellbore collapse in coal seams has become more prominent.

[0003] In order to deal with the above problems, researchers are committed to developing new water-based drilling fluid systems, among which silicate water-based drilling fluids have attracted the attention of researchers due to their unique chemical and physical properties. The gelation properties of silicates can form a stable barrier on the formation well wall and in the cracks, thus providing good well wall stability.

[0004] Currently, there are few studies specifically targeting coalbed methane on the silicate water-based drilling fluid system. Although the silicate system is recognized as the best water-based drilling fluid for preventing wellbore collapse, it has not become the mainstream water-based drilling fluid for preventing wellbore collapse. The main reason is that the system stability of the silicate system and wellbore collapse are a complex contradiction that has not been effectively resolved.

[0005] Therefore, a silicate water-based drilling fluid specially used for coalbed methane wells is provided, which can improve its plugging and anti-collapse effect while ensuring the stability of the silicate water-based drilling fluid system, so as to solve the problem of wellbore collapse during coalbed methane drilling, which is of great significance to the field of oilfield chemical technology in oil and gas drilling engineering. Summary of the invention

[0006] Based on the above content, the present invention provides a silicate water-based drilling fluid for coalbed methane wells and its application. The drilling fluid has the characteristics of low cost, good stability, environmental friendliness and strong plugging and anti-collapse, and can realize safe, environmentally friendly, economical and efficient drilling operations of coalbed methane.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention is a silicate water-based drilling fluid specially used for coalbed methane wells, wherein the raw materials include, by weight: 100 parts of water, 1-3 parts of bentonite, 1-5 parts of pH regulator, 3-5 parts of silicate, 2-4 parts of silicate stabilizer, 0.1-0.15 parts of viscosity enhancer, 2-4 parts of fluid loss reducer, 3-5 parts of auxiliary inhibitor, 1-2 parts of activator, 2-4 parts of plugging agent and 2-4 parts of lubricant;

[0009] In terms of mass fraction, the pH regulator is a mixture of 40 to 60 parts of sodium hydroxide and 40 to 60 parts of potassium hydroxide; the silicate is sodium silicate and / or potassium silicate; and the modulus of the silicate is 2.85 to 3.40.

[0010] A second technical solution of the present invention is an application of the above-mentioned silicate water-based drilling fluid specially used for coalbed methane wells in coalbed methane drilling projects.

[0011] The present invention discloses the following technical effects:

[0012] The silicate water-based drilling fluid for coalbed methane wells of the present invention has strong alkalinity under the action of a pH regulator, and under the synergistic action of a silicate stabilizer, can ensure the stability of silicate, and then ensure the stability of the drilling fluid. The silicate water-based drilling fluid for coalbed methane wells of the present invention has good rheological properties, filtration properties, plugging properties, and lubrication properties under low temperature environments, and is more suitable for coalbed methane well drilling operations.

[0013] The silicate water-based drilling fluid specially used for coalbed methane wells of the present invention has excellent plugging and anti-collapse performance, and it mainly realizes the rapid prevention of coalbed collapse through the following three aspects: first, after the silicate component enters the pores and microcracks of the coal rock formation along with the filtrate, it chemically reacts with the humic acid component in the coal seam to form a high-strength gel, which forms a cementing effect on the coal rock (similar to the manufacture of briquette); second, the silicate reacts with the mineral components such as calcium, magnesium, iron, and aluminum of the coal gangue in the coal seam to form a precipitate, thereby plugging the pores and microcracks, preventing the filtrate from continuing to penetrate deep, and increasing the pressure bearing strength to prevent collapse; third, after the activator provided in the drilling fluid enters the formation along with the filtrate, it will quickly consume alkali through a hydrolysis reaction, promote the silicate itself to form a gel, and combine with the above two formation factors to jointly form cementation and plugging of the coal seam cleats and cracks, thereby ensuring the stability of the well wall.

[0014] The silicate water-based drilling fluid specially used for coalbed methane wells of the present invention has a pH value greater than 11, a filtration loss of ≤4.0 mL, a plugging percolation volume of ≤8.2 mL, a friction coefficient of less than 0.1, and a coal rock strength attenuation rate of ≤25%, thereby providing a guarantee for safe and efficient drilling operations in coalbed methane wells. DETAILED DESCRIPTION

[0015] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0016] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0017] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0018] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0019] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0020] The "parts" described in the present invention, unless otherwise specified, all represent parts by mass.

[0021] The first aspect of the present invention provides a silicate water-based drilling fluid specially used for coalbed methane wells. The raw materials include, by weight, 100 parts of water, 1 to 3 parts of bentonite, 1 to 5 parts of pH regulator, 3 to 5 parts of silicate, 2 to 4 parts of silicate stabilizer, 0.1 to 0.15 parts of viscosity enhancer, 2 to 4 parts of filtration reducer, 3 to 5 parts of auxiliary inhibitor, 1 to 2 parts of activator, 2 to 4 parts of plugging agent and 2 to 4 parts of lubricant.

[0022] The bentonite used in the specific embodiment of the present invention is the bentonite commonly used in the drilling industry and is obtained through commercial channels.

[0023] The water used in the specific embodiments of the present invention, unless otherwise specified, is fresh water.

[0024] In some embodiments of the present invention, the raw material further comprises barite; the added amount of the barite is 0-50% of the mass of the water.

[0025] In some embodiments of the present invention, the pH adjuster is a mixture of 40-60 parts of sodium hydroxide and 40-60 parts of potassium hydroxide, by mass.

[0026] Sodium hydroxide can provide a strong alkaline environment for the system. On the one hand, it ensures the stability of silicates. On the other hand, each component raw material can play its maximum role in an alkaline environment. In addition, it can also prevent acidic substances from corroding drill tools. In addition to the above functions, potassium hydroxide can also provide free potassium ions and use the embedding effect of potassium ions to improve the performance of drilling fluid in inhibiting clay hydration.

[0027] In some embodiments of the present invention, the silicate is sodium silicate and / or potassium silicate; the modulus of the silicate is 2.85-3.40.

[0028] Silicates penetrate into the pores and microcracks in the coal seams and form high-strength gels by chemical reactions with humic acid contained in the coal seams, which is beneficial for cementing the well wall and thus preventing collapse and block falling. Furthermore, the coal seams contain a large amount of coal gangue, which contains minerals such as calcium, magnesium, iron, and aluminum, which can also react with silicates to form precipitates or gels, thereby sealing the pores or microcracks and stabilizing the well wall.

[0029] In some embodiments of the present invention, the silicate stabilizer is a mixture of 40-60 parts of sodium citrate and 40-60 parts of potassium citrate, by mass.

[0030] On the one hand, silicate stabilizers can further provide sodium and potassium ions to strengthen inhibition; on the other hand, sodium citrate and potassium citrate both have good antiseptic effects, which are helpful in preventing problems such as spoilage of natural materials such as starch. In addition, citrate can complex calcium and magnesium ions in water, which is beneficial to the stability of silicate and auxiliary inhibitors in the system.

[0031] In some embodiments of the present invention, the viscosity increasing agent is a mixture of 30-40 parts of xanthan gum, 30-40 parts of sclerotium gum and 20-40 parts of welan gum, calculated by weight.

[0032] Xanthan gum, sclerotium gum and welan gum are all microbial polysaccharide polymers, which are also well soluble in cold water and can play a role in viscosity increase under low temperature conditions, significantly improving the shear thinning properties of drilling fluids, which is conducive to suspending and carrying cuttings and improving the cleaning effect of wellbore. In addition, these biopolymers are naturally non-toxic, environmentally friendly, biodegradable and renewable, which is conducive to reducing environmental pollution.

[0033] In some embodiments of the present invention, the fluid loss reducer is a mixture of 10 to 20 parts of pregelatinized corn starch, 10 to 20 parts of pregelatinized potato starch, 10 to 20 parts of pregelatinized cassava starch and 40 to 70 parts of modified lignin, calculated by weight.

[0034] In some embodiments of the present invention, the method for preparing the modified lignin comprises the following steps:

[0035] Step 1, adding 3-aminopropyltriethoxysilane to an ethanol aqueous solution for hydrolysis reaction; after the hydrolysis reaction is completed, adding lignin for reaction to obtain an intermediate product;

[0036] Step 2: adding the intermediate product and 1-ethyl-(3-dimethylaminopropyl)carbodiimide to a mixture of adipic anhydride and N,N-dimethylformamide to react under an inert atmosphere to obtain the modified lignin.

[0037] In some embodiments of the present invention, in step 1, the volume concentration of the ethanol aqueous solution is 90%; the mass ratio of the ethanol aqueous solution to the 3-aminopropyltriethoxysilane is 200:(1-3); the mass ratio of the 3-aminopropyltriethoxysilane to the lignin is (1-3):(15-20); the temperature of the hydrolysis reaction is 60°C and the time is 4 hours; the temperature of adding lignin for reaction is 70-80°C and the time is 10 hours; the reaction is carried out under stirring; after the addition of lignin for reaction is completed, the steps of cooling, removing the solvent by reduced pressure distillation, washing, vacuum drying and crushing are also included;

[0038] In some embodiments of the present invention, in step 2, the mass ratio of the lignin to the adipic anhydride is (15-20): (6-9); the mass ratio of the adipic anhydride to the N,N-dimethylformamide is (6-9): 150; the mass ratio of the lignin to the 1-ethyl-(3-dimethylaminopropyl)carbodiimide is (15-20): (0.5-1.0); the inert atmosphere is a nitrogen atmosphere; the reaction temperature is 80-90°C and the reaction time is 6 hours. After the reaction is completed, the steps of cooling, vacuum distillation to remove the remaining solvent, vacuum filtration after washing, vacuum drying and crushing are also included in sequence.

[0039] In the present invention, the fluid loss reducer is composed of pregelatinized starch and modified lignin. Among them, the pregelatinized starch is obtained by physical modification of natural starch, and has the non-toxic, biodegradable and renewable characteristics of natural starch, which is beneficial to protecting the ecological environment. In addition, the pregelatinized starch can play a role in cold water and has a fluid loss reduction effect. The prepared modified lignin contains hydrophobic groups such as aromatic groups, ester groups, and alkyl groups and hydrophilic groups such as carboxyl groups, amide groups, and hydroxyl groups, and has amphiphilic properties, which is conducive to adsorption in coal rock pores and microcracks and forming a hydrophobic film, thereby preventing further water intrusion, and the fluid loss reduction effect is significant.

[0040] The reason for choosing pregelatinized corn starch, pregelatinized potato starch and pregelatinized cassava starch for mixing is that each single starch has its own advantages and disadvantages, and the mixture is beneficial to take advantage of their strengths and overcome their weaknesses and avoid their respective shortcomings.

[0041] In some embodiments of the present invention, the auxiliary inhibitor is a mixture of 60-80 parts of potassium sulfate and 20-40 parts of sodium sulfate, calculated by weight.

[0042] The potassium and sodium ions in the auxiliary inhibitors can inhibit the hydration of clay minerals in the formation, while the sulfate ions can react with high-valent ions such as calcium, magnesium, iron, and aluminum contained in the formation to form precipitates, thereby blocking micropores and microcracks.

[0043] In some embodiments of the present invention, the activator is a mixture of 40-60 parts of polylactic acid, 20-30 parts of polyhydroxybutyrate and 20-30 parts of polybutylene succinate, by weight.

[0044] In the present invention, the activator mainly accelerates the consumption of alkali by generating organic acid through hydrolysis reaction, thereby promoting silicate to form gel, thereby playing an activation role. Since the content of the activator is not high, in the strong alkaline environment generated by the high-concentration pH regulator, its consumption of alkali will not cause silicate to form gel and affect the stability of the drilling fluid; but after the activator enters the micropores and microcracks of the formation with the filtrate, under the premise of no alkaline substance to supplement the alkalinity, the organic acid generated by its hydrolysis reaction will accelerate the consumption of the alkalinity in the environment, and then promote the silicate that also enters the formation to accelerate the formation of gel, which is conducive to quickly strengthening the coal seam well wall and effectively preventing coal rock collapse.

[0045] In some embodiments of the present invention, the plugging agent is a mixture of 30-40 parts of potassium humate, 10-20 parts of potassium fulvic acid, 30-40 parts of sodium humate and 10-20 parts of sodium fulvic acid, by mass.

[0046] The lubricant is a mixture of 30 to 40 parts of polyoxyethylene ether, 30 to 40 parts of polyether siloxane, 5 to 10 parts of polyoxyethylene linolenate and 15 to 30 parts of ricinoleic acid diethanolamide in parts by mass.

[0047] The special silicate water-based drilling fluid for coalbed methane wells of the present invention can be prepared by conventional preparation methods, for example, various raw materials are mixed evenly according to mass fractions to obtain the special silicate water-based drilling fluid for coalbed methane wells.

[0048] The second aspect of the present invention provides an application of the above-mentioned silicate water-based drilling fluid dedicated for coalbed methane wells in coalbed methane drilling projects.

[0049] Unless otherwise specified, the raw materials used in the embodiments of the present invention can be obtained through commercial sources.

[0050] The specific gravity of the barite used in the embodiment of the present invention is 4.2 g / cm 3 , the average particle size is 20μm.

[0051] The present invention is further described below by way of examples. Example 1

[0052] A silicate water-based drilling fluid specially used for coalbed methane wells, the raw material composition is as follows by weight:

[0053] Water: 100 parts

[0054] Bentonite: 1 part

[0055] pH adjuster: 1 part

[0056] Silicate: 3 parts

[0057] Silicate stabilizer: 2 parts

[0058] Thickener: 0.1 part

[0059] Fluid loss reducer: 2 parts

[0060] Auxiliary inhibitor: 3 parts

[0061] Activator: 1 part

[0062] Blocking agent: 2 parts

[0063] Lubricant: 2 parts

[0064] Barite: 0 parts.

[0065] Wherein, the pH adjuster is a mixture of 40 parts of sodium hydroxide and 60 parts of potassium hydroxide by mass.

[0066] The silicate is sodium silicate with a modulus of 2.85.

[0067] The silicate stabilizer is a mixture of 40 parts of sodium citrate and 60 parts of potassium citrate by mass.

[0068] The viscosity enhancer is a mixture of 30 parts of xanthan gum, 30 parts of sclerotium gum and 40 parts of welan gum by mass.

[0069] The fluid loss reducer is a mixture of 10 parts of pregelatinized corn starch, 10 parts of pregelatinized potato starch, 10 parts of pregelatinized cassava starch and 70 parts of modified lignin by weight;

[0070] The preparation method of the modified lignin mentioned above comprises the following steps:

[0071] First, 200 parts of 90% ethanol aqueous solution were added to a three-necked flask, and then 1 part of 3-aminopropyltriethoxysilane (APTES) was slowly added under stirring conditions, the temperature was raised to 60°C, and the hydrolysis reaction was carried out for 4 hours; then 15 parts of lignin were added, the temperature was raised to 70°C, and the reaction was carried out under stirring conditions for 10 hours; after the reaction was completed, the heating was stopped and the mixture was allowed to cool, the solvent was removed by reduced pressure distillation, and the mixture was washed with anhydrous ethanol for multiple times, and then vacuum dried and crushed to obtain an intermediate product;

[0072] Secondly, 6 parts of adipic anhydride (ADAn) and 150 parts of N,N-dimethylformamide (DMF) were added to a three-necked flask, and then nitrogen was introduced to deoxygenate under stirring conditions, and then the intermediate product in the above step and 0.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were added. After the addition was completed, nitrogen was introduced again to deoxygenate, and the temperature was slowly raised to 80°C. After reacting for 6 hours, the heating was stopped and the product was allowed to cool. The remaining solvent was removed by reduced pressure distillation, and the mixture was washed several times with a dilute alkaline solution, vacuum filtered, vacuum dried and crushed. The obtained dark brown powder was the target product, modified lignin.

[0073] The auxiliary inhibitor is a mixture of 60 parts of potassium sulfate and 40 parts of sodium sulfate by mass.

[0074] The activator is a mixture of 40 parts of polylactic acid, 30 parts of polyhydroxybutyrate and 30 parts of polybutylene succinate by mass.

[0075] The plugging agent is a mixture of 30 parts of potassium humate, 10 parts of potassium humate, 40 parts of sodium humate and 20 parts of sodium humate, by mass.

[0076] The lubricant is a mixture of 30 parts of polyoxyethylene ether, 30 parts of polyether siloxane, 10 parts of polyoxyethylene linolenate and 30 parts of ricinoleic acid diethanolamide, based on mass parts.

[0077] The drilling fluid density prepared in this example is 1.05 g / cm 3 , the hot rolling temperature of the drilling fluid is 30℃. Example 2

[0078] A silicate water-based drilling fluid specially used for coalbed methane wells, the raw material composition is as follows by weight:

[0079] Water: 100 parts,

[0080] Bentonite: 2 parts

[0081] pH adjuster: 3 parts

[0082] Silicate: 4 parts

[0083] Silicate stabilizer: 3 parts

[0084] Thickener: 0.125 parts

[0085] Fluid loss reducer: 3 parts

[0086] Auxiliary inhibitor: 4 parts

[0087] Activator: 1.5 parts

[0088] Blocking agent: 3 parts

[0089] Lubricant: 3 parts

[0090] Barite: 7 parts.

[0091] Wherein, the pH adjuster is a mixture of 50 parts of sodium hydroxide and 50 parts of potassium hydroxide by mass.

[0092] The silicate is potassium silicate with a modulus of 3.10.

[0093] The silicate stabilizer is a mixture of 50 parts of sodium citrate and 50 parts of potassium citrate by mass.

[0094] The viscosity enhancer is a mixture of 35 parts of xanthan gum, 35 parts of sclerotium gum and 30 parts of welan gum by mass.

[0095] The fluid loss reducer is a mixture of 15 parts of pregelatinized corn starch, 15 parts of pregelatinized potato starch, 15 parts of pregelatinized cassava starch and 55 parts of modified lignin by weight;

[0096] The preparation method of the modified lignin mentioned above comprises the following steps:

[0097] First, 200 parts of 90% ethanol aqueous solution were added to a three-necked flask, and then 2 parts of 3-aminopropyltriethoxysilane (APTES) were slowly added under stirring conditions, the temperature was raised to 60°C, and the hydrolysis reaction was carried out for 4 hours; then 17.5 parts of lignin were added, the temperature was raised to 75°C, and the reaction was carried out under stirring conditions for 10 hours; after the reaction was completed, the heating was stopped and the mixture was allowed to cool, the solvent was removed by reduced pressure distillation, and the mixture was washed with anhydrous ethanol for multiple times, and then vacuum dried and crushed to obtain an intermediate product;

[0098] Secondly, 7.5 parts of adipic anhydride (ADAn) and 150 parts of N,N-dimethylformamide (DMF) were added to a three-necked flask, and then nitrogen was introduced to deoxygenate under stirring conditions, and then the intermediate product in the above step and 0.75 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were added. After the addition was completed, nitrogen was introduced again to deoxygenate, and the temperature was slowly raised to 85°C. After reacting for 6 hours, the heating was stopped and the product was allowed to cool. The remaining solvent was removed by reduced pressure distillation, and the mixture was washed several times with a dilute alkaline solution, vacuum filtered, vacuum dried and crushed. The obtained dark brown powder was the target product, modified lignin.

[0099] The auxiliary inhibitor is a mixture of 70 parts of potassium sulfate and 30 parts of sodium sulfate by mass.

[0100] The activator is a mixture of 50 parts of polylactic acid, 25 parts of polyhydroxybutyrate and 25 parts of polybutylene succinate by mass.

[0101] The plugging agent is a mixture of 35 parts of potassium humate, 15 parts of potassium humate, 35 parts of sodium humate and 15 parts of sodium humate, in terms of mass.

[0102] The lubricant is a mixture of 35 parts of polyoxyethylene ether, 35 parts of polyether siloxane, 7.5 parts of polyoxyethylene linolenate and 22.5 parts of ricinoleic acid diethanolamide, based on mass parts.

[0103] The drilling fluid density prepared in this example is 1.1 g / cm 3 , the hot rolling temperature of the drilling fluid is 40℃. Example 3

[0104] A silicate water-based drilling fluid specially used for coalbed methane wells, which is composed of the following components by weight:

[0105] Water: 100 parts

[0106] Bentonite: 3 parts

[0107] pH adjuster: 5 parts

[0108] Silicate: 5 parts

[0109] Silicate stabilizer: 4 parts

[0110] Thickener: 0.15 parts

[0111] Fluid loss reducer: 4 parts

[0112] Auxiliary inhibitor: 5 parts

[0113] Activator: 2 parts

[0114] Blocking agent: 4 parts

[0115] Lubricant: 4 parts

[0116] Barite: 25 parts.

[0117] Wherein, the pH adjuster is a mixture of 60 parts of sodium hydroxide and 40 parts of potassium hydroxide by mass.

[0118] The silicate is a mixture of 40 parts of sodium silicate and 60 parts of potassium silicate by mass, and the modulus is 3.40.

[0119] The silicate stabilizer is a mixture of 60 parts of sodium citrate and 40 parts of potassium citrate by mass.

[0120] The viscosity enhancer is a mixture of 40 parts of xanthan gum, 40 parts of sclerotium gum and 20 parts of welan gum by mass.

[0121] The fluid loss reducer is a mixture of 20 parts of pregelatinized corn starch, 20 parts of pregelatinized potato starch, 20 parts of pregelatinized cassava starch and 40 parts of modified lignin by weight;

[0122] The preparation method of the modified lignin mentioned above comprises the following steps:

[0123] First, 200 parts of 90% ethanol aqueous solution were added to a three-necked flask, and then 3 parts of 3-aminopropyltriethoxysilane (APTES) were slowly added under stirring conditions, the temperature was raised to 60°C, and the hydrolysis reaction was carried out for 4 hours; then 20 parts of lignin were added, the temperature was raised to 80°C, and the reaction was carried out under stirring conditions for 10 hours; after the reaction was completed, the heating was stopped and the mixture was allowed to cool, the solvent was removed by reduced pressure distillation, and the mixture was washed with anhydrous ethanol for multiple times, and then vacuum dried and crushed to obtain an intermediate product;

[0124] Secondly, 9 parts of adipic anhydride (ADAn) and 150 parts of N,N-dimethylformamide (DMF) were added to a three-necked flask, and then nitrogen was introduced to deoxygenate under stirring conditions, and then the intermediate product in the above step and 1.0 part of 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were added. After the addition was completed, nitrogen was introduced again to deoxygenate, and the temperature was slowly raised to 90°C. After reacting for 6 hours, the heating was stopped and the product was allowed to cool. The remaining solvent was removed by reduced pressure distillation, and the mixture was washed several times with a dilute alkaline solution, vacuum filtered, vacuum dried and crushed. The obtained dark brown powder was the target product, modified lignin.

[0125] The auxiliary inhibitor is a mixture of 80 parts of potassium sulfate and 20 parts of sodium sulfate by mass.

[0126] The activator is a mixture of 60 parts of polylactic acid, 20 parts of polyhydroxybutyrate and 20 parts of polybutylene succinate by mass.

[0127] The plugging agent is a mixture of 40 parts of potassium humate, 20 parts of potassium humate, 30 parts of sodium humate and 10 parts of sodium humate, in terms of mass.

[0128] The lubricant is a mixture of 40 parts of polyoxyethylene ether, 40 parts of polyether siloxane, 5 parts of polyoxyethylene linolenate and 15 parts of ricinoleic acid diethanolamide, based on mass parts.

[0129] The drilling fluid density prepared in this example is 1.2 g / cm 3 , the hot rolling temperature of the drilling fluid is 50℃. Example 4

[0130] A silicate water-based drilling fluid specially used for coalbed methane wells, which is composed of the following components by weight:

[0131] Water: 100 parts

[0132] Bentonite: 2 parts

[0133] pH adjuster: 1.5 parts

[0134] Silicate: 3 parts

[0135] Silicate stabilizer: 3 parts

[0136] Thickener: 0.11 parts

[0137] Fluid loss reducer: 3 parts

[0138] Auxiliary inhibitor: 3 parts

[0139] Activator: 1 part

[0140] Blocking agent: 3 parts

[0141] Lubricant: 3 parts

[0142] Barite: 38 parts.

[0143] Wherein, the pH adjuster is a mixture of 45 parts of sodium hydroxide and 55 parts of potassium hydroxide by mass.

[0144] The silicate is a mixture of 50 parts sodium silicate and 50 parts potassium silicate by mass, and has a modulus of 3.00.

[0145] The silicate stabilizer is a mixture of 55 parts of sodium citrate and 45 parts of potassium citrate by mass.

[0146] The viscosity enhancer is a mixture of 40 parts of xanthan gum, 30 parts of sclerotium gum and 30 parts of welan gum by mass.

[0147] The fluid loss reducer is a mixture of 10 parts of pregelatinized corn starch, 15 parts of pregelatinized potato starch, 15 parts of pregelatinized cassava starch and 60 parts of modified lignin by weight;

[0148] The preparation method of the modified lignin comprises the following steps:

[0149] First, 200 parts of 90% ethanol aqueous solution were added to a three-necked flask, and then 2.5 parts of 3-aminopropyltriethoxysilane (APTES) were slowly added under stirring conditions, the temperature was raised to 60°C, and the hydrolysis reaction was carried out for 4 hours; then 18.5 parts of lignin were added, the temperature was raised to 73°C, and the reaction was carried out under stirring conditions for 10 hours; after the reaction was completed, the heating was stopped and the mixture was allowed to cool, the solvent was removed by reduced pressure distillation, and the mixture was washed with anhydrous ethanol for multiple times, and then vacuum dried and crushed to obtain an intermediate product;

[0150] Secondly, 8 parts of adipic anhydride (ADAn) and 150 parts of N,N-dimethylformamide (DMF) were added to a three-necked flask, and then nitrogen was introduced to deoxygenate under stirring conditions, and then the intermediate product in the above step and 0.9 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were added. After the addition was completed, nitrogen was introduced again to deoxygenate, and the temperature was slowly raised to 88°C. After reacting for 6 hours, the heating was stopped and the product was allowed to cool. The remaining solvent was removed by reduced pressure distillation, and after multiple washings with a dilute alkaline solution, vacuum filtration, vacuum drying and pulverization were performed, and the obtained dark brown powder was the target product.

[0151] The auxiliary inhibitor is a mixture of 75 parts of potassium sulfate and 25 parts of sodium sulfate by mass.

[0152] The activator is a mixture of 55 parts of polylactic acid, 25 parts of polyhydroxybutyrate and 20 parts of polybutylene succinate by mass.

[0153] The plugging agent is a mixture of 30 parts of potassium humate, 20 parts of potassium humate, 30 parts of sodium humate and 20 parts of sodium humate, in terms of mass.

[0154] The lubricant is a mixture of 30 parts of polyoxyethylene ether, 40 parts of polyether siloxane, 5 parts of polyoxyethylene linolenate and 25 parts of ricinoleic acid diethanolamide, based on mass parts.

[0155] The drilling fluid density prepared in this example is 1.3 g / cm 3 , the hot rolling temperature of the drilling fluid is 60℃. Example 5

[0156] A silicate water-based drilling fluid specially used for coalbed methane wells, the raw material composition is as follows by weight:

[0157] Water: 100 parts

[0158] Bentonite: 2 parts

[0159] pH adjuster: 2 parts

[0160] Silicate: 5 parts

[0161] Silicate stabilizer: 3 parts

[0162] Thickener: 0.1 part

[0163] Fluid loss reducer: 3 parts

[0164] Auxiliary inhibitor: 5 parts

[0165] Activator: 1.5 parts

[0166] Blocking agent: 4 parts

[0167] Lubricant: 4 parts

[0168] Barite: 50 parts.

[0169] Wherein, the pH adjuster is a mixture of 45 parts of sodium hydroxide and 55 parts of potassium hydroxide by mass.

[0170] The silicate is a mixture of 60 parts of sodium silicate and 40 parts of potassium silicate by mass, and the modulus is 3.20.

[0171] The silicate stabilizer is a mixture of 55 parts of sodium citrate and 45 parts of potassium citrate by mass.

[0172] The viscosity enhancer is a mixture of 30 parts of xanthan gum, 40 parts of sclerotium gum and 30 parts of welan gum by mass.

[0173] The fluid loss reducer is a mixture of 15 parts of pregelatinized corn starch, 10 parts of pregelatinized potato starch, 10 parts of pregelatinized cassava starch and 65 parts of modified lignin by weight;

[0174] The preparation method of the modified lignin mentioned above comprises the following steps:

[0175] First, 200 parts of 90% ethanol aqueous solution were added to a three-necked flask, and then 1.5 parts of 3-aminopropyltriethoxysilane (APTES) were slowly added under stirring conditions, the temperature was raised to 60°C, and the hydrolysis reaction was carried out for 4 hours; then 16 parts of lignin were added, the temperature was raised to 77°C, and the reaction was carried out under stirring conditions for 10 hours; after the reaction was completed, the heating was stopped and the mixture was allowed to cool, the solvent was removed by reduced pressure distillation, and the mixture was washed with anhydrous ethanol for multiple times, and then vacuum dried and crushed to obtain an intermediate product;

[0176] Secondly, 6.5 parts of adipic anhydride (ADAn) and 150 parts of N,N-dimethylformamide (DMF) were added to a three-necked flask, and then nitrogen was introduced under stirring to deoxygenate, and then the intermediate product in the above step and 0.7 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were added. After the addition was completed, nitrogen was introduced again to deoxygenate, and the temperature was slowly raised to 82°C. After reacting for 6 hours, the heating was stopped and the product was allowed to cool. The remaining solvent was removed by reduced pressure distillation, and the mixture was washed several times with a dilute alkali solution, vacuum filtered, vacuum dried and crushed. The obtained dark brown powder was the target product, modified lignin.

[0177] The auxiliary inhibitor is a mixture of 65 parts of potassium sulfate and 35 parts of sodium sulfate by mass.

[0178] The activator is a mixture of 45 parts of polylactic acid, 30 parts of polyhydroxybutyrate and 25 parts of polybutylene succinate by mass.

[0179] The plugging agent is a mixture of 40 parts of potassium humate, 10 parts of potassium humate, 40 parts of sodium humate and 10 parts of sodium humate, in terms of mass.

[0180] The lubricant is a mixture of 30 parts of polyoxyethylene ether, 40 parts of polyether siloxane, 10 parts of polyoxyethylene linolenate and 20 parts of ricinoleic acid diethanolamide, based on mass parts.

[0181] The drilling fluid density prepared in this example is 1.4 g / cm 3 , the hot rolling temperature of the drilling fluid is 70℃. Comparative Example 1

[0182] The polymer potassium chloride water-based drilling fluid commonly used on site is composed of 100 parts of fresh water, 3 parts of bentonite, 0.5 parts of pH adjuster (the mass ratio of sodium hydroxide and sodium carbonate is 1:1), 5 parts of potassium chloride, 0.3 parts of zwitterionic polymer strong coating agent, 0.3 parts of high viscosity carboxymethyl cellulose, 3 parts of lignite resin, 3 parts of modified vegetable oil and 25 parts of barite.

[0183] The drilling fluid density prepared in this comparative example is 1.2 g / cm 3 , the hot rolling temperature of the drilling fluid is 50℃.

[0184] The drilling fluids prepared in the above examples and comparative examples were evaluated according to GB / T16783.1-2014 "Field Test of Drilling Fluids in the Petroleum and Natural Gas Industry Part 1: Water-Based Drilling Fluids". The results are shown in Table 1.

[0185] Table 1 Comprehensive properties of drilling fluid

[0186] .

[0187] Note:

[0188] ρ: drilling fluid density, g / cm 3

[0189] T: Drilling fluid aging temperature, °C

[0190] t: Drilling fluid rolling aging time, h

[0191] PV: drilling fluid plastic viscosity, mPa·s

[0192] YP: Drilling fluid dynamic shear force, Pa

[0193] YP / PV: Dynamic plastic ratio, Pa / mPa·s

[0194] Φ3: Six-speed rotary viscometer 3-turn reading, dimensionless

[0195] API: Drilling fluid medium pressure loss (0.7MPa, room temperature, 30min), mL

[0196] PPT: Drilling fluid permeate loss (6.9MPa, T, 30min), mL

[0197] pH: pH value of drilling fluid filtrate, dimensionless

[0198] EP: Extreme pressure friction coefficient, dimensionless

[0199] CRS: Coal rock strength decay rate (3.5MPa, T, 72h), %

[0200] It can be seen from Examples 1 to 5 that the silicate water-based drilling fluid for coalbed methane wells has a density of 1.05 to 1.40 g / cm 3 range, the temperature is in the range of 30~70℃, and after 72 hours of aging, they all have good rheological properties, filtration control performance, plugging performance, lubrication performance and anti-collapse performance. It can be seen from Example 3 and Comparative Example 1 that compared with the commonly used polymer potassium chloride water-based drilling fluid on site, the silicate water-based drilling fluid dedicated to coalbed methane has lower plastic viscosity and higher dynamic shear force, showing better suspension rock carrying performance; and the API filtration control performance and PPT plugging performance are better. The most critical thing is that the silicate water-based drilling fluid dedicated to coalbed methane wells performs better in anti-collapse performance, and the strength attenuation rate of coal rock after high-pressure immersion for 72 hours does not exceed 25%; while for the commonly used polymer potassium chloride water-based drilling fluid on site, the coal rock is completely broken after being immersed in it for the same time, and the strength attenuation is 100%.

[0201] The five groups of embodiments of the silicate water-based drilling fluid specially used for coalbed methane wells of the present invention, after aging for 72 hours at different densities and different temperatures: the pH is all greater than 11, and the silicate remains stable; the rheological properties are good, and the dynamic plastic ratio is generally higher than 0.70, showing good suspension rock carrying performance; the API filtration loss is low, generally not exceeding 4.0 mL; the PPT plugging performance is excellent, which is beneficial to reducing the penetration of filtrate into the formation and preventing the well wall from becoming unstable; the friction coefficient is not higher than 0.1, and the lubrication performance is good, which is beneficial to reducing the friction torque and increasing the mechanical drilling speed; the coal rock strength attenuation rate does not exceed 25%, and the anti-collapse effect is significant, which is beneficial to stabilizing the coal rock well wall and ensuring safe and efficient drilling operations of coalbed methane wells.

[0202] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A silicate water-based drilling fluid for coalbed methane wells, characterized in that: The raw materials include, by weight: 100 parts of water, 1-3 parts of bentonite, 1-5 parts of pH regulator, 3-5 parts of silicate, 2-4 parts of silicate stabilizer, 0.1-0.15 parts of viscosity enhancer, 2-4 parts of fluid loss reducer, 3-5 parts of auxiliary inhibitor, 1-2 parts of activator, 2-4 parts of plugging agent and 2-4 parts of lubricant; The pH regulator is a mixture of 40 to 60 parts of sodium hydroxide and 40 to 60 parts of potassium hydroxide by mass; the silicate is sodium silicate and / or potassium silicate; the modulus of the silicate is 2.85 to 3.40; The silicate stabilizer is a mixture of 40 to 60 parts of sodium citrate and 40 to 60 parts of potassium citrate by weight; The viscosity enhancer is a mixture of 30-40 parts of xanthan gum, 30-40 parts of sclerotium gum and 20-40 parts of welan gum in parts by mass; The fluid loss reducer is a mixture of 10 to 20 parts of pregelatinized corn starch, 10 to 20 parts of pregelatinized potato starch, 10 to 20 parts of pregelatinized cassava starch and 40 to 70 parts of modified lignin in parts by mass; The preparation method of the modified lignin comprises the following steps: Step 1, adding 3-aminopropyltriethoxysilane to an ethanol aqueous solution for hydrolysis reaction; after the hydrolysis reaction is completed, adding lignin for reaction to obtain an intermediate product; Step 2, adding the intermediate product and 1-ethyl-(3-dimethylaminopropyl)carbodiimide to a mixture of adipic anhydride and N,N-dimethylformamide to react under an inert atmosphere to obtain the modified lignin; In step 1, the mass ratio of the ethanol aqueous solution to the 3-aminopropyltriethoxysilane is 200:(1-3); the mass ratio of the 3-aminopropyltriethoxysilane to the lignin is (1-3):(15-20); the temperature of the hydrolysis reaction is 60°C and the time is 4 hours; the temperature of the reaction with the addition of lignin is 70-80°C and the time is 10 hours; In step 2, the mass ratio of the lignin to the adipic anhydride is (15-20): (6-9); the mass ratio of the adipic anhydride to the N,N-dimethylformamide is (6-9): 150; the mass ratio of the lignin to the 1-ethyl-(3-dimethylaminopropyl)carbodiimide is (15-20): (0.5-1.0); the inert atmosphere is a nitrogen atmosphere; the reaction temperature is 80-90° C., and the reaction time is 6 hours; The auxiliary inhibitor is a mixture of 60-80 parts of potassium sulfate and 20-40 parts of sodium sulfate by mass; In terms of weight, the activator is a mixture of 40 to 60 parts of polylactic acid, 20 to 30 parts of polyhydroxybutyrate and 20 to 30 parts of polybutylene succinate.

2. The silicate water-based drilling fluid for coalbed methane wells according to claim 1, characterized in that: The raw materials also include barite; the added amount of the barite is 0-50% of the mass of the water.

3. The silicate water-based drilling fluid for coalbed methane wells according to claim 1, characterized in that: The plugging agent is a mixture of 30-40 parts of potassium humate, 10-20 parts of potassium humate, 30-40 parts of sodium humate and 10-20 parts of sodium humate by mass. The lubricant is a mixture of 30 to 40 parts of polyoxyethylene ether, 30 to 40 parts of polyether siloxane, 5 to 10 parts of polyoxyethylene linolenate and 15 to 30 parts of ricinoleic acid diethanolamide in parts by mass.

4. Application of the silicate water-based drilling fluid for coalbed methane wells as claimed in any one of claims 1 to 3 in coalbed methane drilling projects.