A filtration loss reducer, its preparation method, drilling fluid containing the same, and its applications.

Abstract

This invention discloses a filtration loss reducer, its preparation method, drilling fluids containing the same, and their applications. The invention uses cellulose derivatives, styrene sulfonates, diallyl ammonium salts, acrylamide monomers, and 2-acrylamido-2-methylpropanesulfonic acid as raw materials to prepare a polymeric framework matrix with certain high-temperature resistance, which is then grafted onto modified silica nanomaterials to synthesize the filtration loss reducer. The filtration loss reducer prepared by this invention is an organic / inorganic multi-component copolymer. Considering the advantages and disadvantages of organic polymers and inorganic modified nanomaterials, a water-based drilling fluid filtration loss reducer with temperature, salt, and calcium resistance is synthesized. The slurry containing this filtration loss reducer exhibits good water loss reduction, salt resistance, and calcium resistance after being hot-rolled at 230℃ and 260℃ for 16 hours, respectively.

Description

Technical Field

[0001] This invention relates to the field of drilling fluids, and more specifically to a filtration loss reducer, its preparation method, drilling fluids containing the same, and their applications. Background Technology

[0002] With the rapid growth in demand for oil and gas resources, the depth and breadth of oil and gas well drilling are constantly increasing, leading to a rise in complex oil and gas well engineering projects. While engineering technologies for deep wells, ultra-deep wells, complex structure wells, and directional horizontal wells are maturing, this also means that the geological environments encountered during drilling will become more complex. Geological conditions such as high temperature, high pressure, and high salinity make it more difficult to control the rheology, filtration performance, and lubricity of drilling fluids. Therefore, the development of corresponding high-performance treatment agents is particularly important.

[0003] Filtration loss reducers, also known as filtration control agents or fluid loss mitigators, are the most widely used treatment agents in drilling fluids. The stability of drilling fluid performance and the safe and efficient drilling process are inseparable from them. Currently, commonly used drilling fluid filtration loss reducers are mainly classified into cellulose-based, humic acid-based, acrylic acid-based, starch-based, and resin-based types. Their primary purpose is to form a dense, thin, and tough low-permeability filter cake. In recent years, widely used filtration loss reducers synthesized from monomers such as acrylates, sulfonates, and acrylamide salts can meet the requirements of high-temperature and salt-resistant deep formations at 200℃~220℃. However, due to increasingly stringent requirements for the exploration and development of ultra-deep wells, the high-temperature and calcium-resistant properties are generally poor. Therefore, there is an urgent need to develop a treatment agent that can withstand high temperatures and high calcium in deep formations to meet the performance requirements of ultra-deep drilling fluids.

[0004] Nanomaterials possess characteristics such as high temperature resistance, small particle diameter, high specific surface energy, and strong stability. By adding appropriate amounts of nanomaterials to commonly used drilling fluid filtration reducers, the fine pores in the mud cake can be blocked, making the mud cake more compact. Simultaneously, if the nanomaterials are added appropriately, they can chemically adsorb with clay particles, effectively reducing the pore radius and decreasing water loss. Currently, there is a wealth of literature on high-temperature filtration reducers, but evaluations of their effectiveness against high temperatures, calcium, and salt are scarce. For example, neither CN111909670A nor CN113150754A includes an evaluation of their calcium resistance. Summary of the Invention

[0005] The first objective of this invention is to provide a filtration loss reducer and its preparation method. This invention synthesizes a water-based drilling fluid filtration loss reducer with added nanomaterials, which can effectively reduce filtration loss and exhibits good salt and calcium resistance filtration loss reduction properties at both room temperature and high temperatures of 230°C and 260°C.

[0006] A second objective of the present invention is to provide a drilling fluid comprising the aforementioned filtration loss reducer and its application therein.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The first aspect of this invention provides a method for preparing a filtration loss reducing agent, the method comprising the following steps:

[0009] The cellulose derivative was dissolved in water to obtain solution 1;

[0010] After adding 2-acrylamido-2-methylpropanesulfonic acid to solution 1, the pH was adjusted to alkaline by adding alkaline solution; then diallyl ammonium salt, acrylamide monomer, styrene sulfonate and modified nano silica were added to obtain solution 2.

[0011] An initiator is added to the solution 2 to carry out a polymerization reaction. After the reaction is completed, the solution is dried and ground to obtain the filtrate loss reducer.

[0012] The mass ratio of the acrylamide monomer, diallyl ammonium salt, 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonate, and modified nano-silica is (1-5):(2-4):(3-6):(0.2-4):(0.2-2); preferably (2.5-3.5):(2.5-3.5):(3.5-5.5):(0.5-1.5):(0.5-1.5), further preferably (2.7-3.2):(2.7-3.2):(4.3-5.5):(0.7-1.3):(0.75-1.2), for example 2.7:3:5.5:1.2:1. Under these preferred conditions, when the copolymer is used in drilling fluid, the resulting drilling fluid exhibits superior salt and calcium resistance.

[0013] Cellulose derivatives exhibit excellent thermal stability and salt resistance. The sulfonic acid groups in 2-acrylamido-2-methylpropanesulfonic acid and styrene sulfonate exhibit strong hydration properties, forming a hydration film on the clay surface. Simultaneously, they combine with the amide groups in acrylamide monomers and diallyl ammonium salts to form multi-dimensional adsorption sites, further enhancing their affinity for cations (Ca). 2+ and Na + Adsorption and complexation are performed, and taking advantage of the steric hindrance of the benzene ring and other monomers in sodium styrene sulfonate, which makes them difficult to decompose at high temperatures, a high-temperature resistant polyanionic cellulose-based water-soluble synthetic copolymer is copolymerized. This copolymer can resist 35wt% Ca2+ after aging at 200℃. 2+ It can still resist 10wt% Na pollution even after aging at 260℃. + It exhibits a very strong ability to resist cationic contamination at high temperatures.

[0014] According to the preparation method of the present invention, preferably, the polymerization reaction is carried out at a temperature of 70-75°C for 6-12 hours.

[0015] According to the preparation method of the present invention, preferably, the cellulose derivative is one or a combination of two of carboxymethyl cellulose and polyanionic cellulose.

[0016] According to the preparation method of the present invention, preferably, the molecular weight of the cellulose derivative is 200,000 to 800,000, more preferably 300,000 to 600,000, and even more preferably 400,000 to 500,000.

[0017] According to the preparation method of the present invention, preferably, in the solution 1, the mass of the cellulose derivative accounts for 2%-3% of the mass of water, more preferably 2.3wt%-2.8wt%.

[0018] According to the preparation method of the present invention, preferably, in the solution 2, the total mass of the cellulose derivative and other monomers (acrylamide monomers, diallyl ammonium salts, 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonate and modified nano silica) accounts for about 30% to 40% of the mass of water.

[0019] According to the preparation method of the present invention, preferably, the diallyl ammonium salt is one or a combination of two or more of N,N-dimethyldiallyl ammonium chloride, N,N-dimethyldiallyl ammonium bromide, N,N-diethyldiallyl ammonium chloride, N,N-diethyldiallyl ammonium bromide, N,N-dipropyldiallyl ammonium chloride, and N,N-dipropyldiallyl ammonium bromide.

[0020] According to the preparation method of the present invention, preferably, the acrylamide monomer is one or a combination of two of N,N-dimethylacrylamide and N,N-diethylacrylamide.

[0021] According to the preparation method of the present invention, preferably, the styrene sulfonate is one or a combination of two of sodium p-styrene sulfonate and potassium p-styrene sulfonate.

[0022] According to the preparation method of the present invention, preferably, the alkaline solution is an aqueous solution of NaOH, and more preferably, an aqueous solution of NaOH is added to adjust the pH to 9-10.

[0023] According to the preparation method of the present invention, preferably, the modified nano-silica is silane coupling agent modified nano-silica, more preferably, it is vinyl silane coupling agent or methacryloyloxyethyl silane coupling agent modified nano-silica.

[0024] According to the preparation method of the present invention, preferably, the average particle size of the modified nano-silica is 20nm to 100nm, and more preferably 30nm to 80nm.

[0025] According to the preparation method of the present invention, preferably, the initiator is sodium bisulfite and ammonium persulfate. More preferably, the mass ratio of sodium bisulfite to ammonium persulfate is 1:1; even more preferably, the total amount of sodium bisulfite and ammonium persulfate added is 0.1wt% to 0.5wt% of the total mass of the reactants; preferably 0.1wt% to 0.25wt%.

[0026] According to the preparation method of the present invention, preferably, the polymerization reaction is carried out in a protective atmosphere to ensure that the polymerization reaction is carried out in an oxygen-free environment; the protective gas is selected, for example, from nitrogen, argon, etc.

[0027] According to the preparation method of the present invention, preferably, the drying temperature is 50-85°C and the drying time is 12-72 hours. More preferably, the drying temperature is 60-80°C for 6-24 hours.

[0028] In a preferred embodiment, the preparation method includes the following steps:

[0029] Weigh out the cellulose derivative and slowly add it to deionized water. Stir at high speed for 20-30 minutes to dissolve, and obtain solution 1.

[0030] 2-Acrylamido-2-methylpropanesulfonic acid (AMPS) was dissolved in solution 1 under ice bath conditions. The pH was adjusted to 9-10 with sodium hydroxide. After thorough stirring, diallyl ammonium salt, acrylamide monomer, styrene sulfonate, and modified silica were added to the solution respectively. The mixed solution was heated to 70-75°C, and a protective gas was introduced into the reaction vessel for 20-30 minutes. During the gas introduction, 0.1-0.5 wt% of initiator based on the total mass of the reactants was added. The reaction was carried out for 6-12 hours. After the reaction was completed, the product was dialyzed in deionized water. The dialyzed solution was transferred to a vacuum drying oven at 60-80°C and dried for 6-24 hours. Finally, the obtained solid was pulverized into powder to obtain the final product, the filtration loss reducer.

[0031] This invention uses cellulose derivatives, styrene sulfonates, diallyl ammonium salts, acrylamide monomers, and 2-acrylamido-2-methylpropanesulfonic acid as raw materials to prepare a polymeric framework matrix with certain high-temperature resistance, and then grafts it onto SiO2 nanomaterials treated with silane coupling agent to synthesize a filtration loss reducer. The filtration loss reducer prepared by this invention is an organic / inorganic multi-component copolymer. Taking into account the advantages and disadvantages of organic polymers and inorganic modified nanomaterials, a water-based drilling fluid filtration loss reducer with temperature, salt, and calcium resistance was synthesized. The slurry containing this filtration loss reducer exhibited good water loss reduction performance, salt resistance, and calcium resistance after being hot-rolled at 230℃ and 260℃ for 16 hours, respectively.

[0032] A second aspect of the present invention provides a filtration loss reducer prepared by the above preparation method.

[0033] A third aspect of the present invention provides a drilling fluid comprising the above-mentioned filtration loss reducing agent.

[0034] According to the drilling fluid of the present invention, preferably, the content of the filtration loss reducer is 0.5 wt% to 2 wt% based on the total mass of the drilling fluid.

[0035] The drilling fluid according to the present invention preferably further comprises water, bentonite, a thickener, an anti-collapse agent, a lubricant, calcium chloride, and sodium carbonate. More preferably, based on the total mass of the drilling fluid, the content of bentonite is 2 wt% to 4 wt%, the content of the thickener is 0.2 wt% to 0.4 wt%, the content of the anti-collapse agent is 3 wt% to 4 wt%, the content of the lubricant is 3 wt% to 4 wt%, the content of calcium chloride is 0.5 wt% to 1 wt%, and the content of sodium carbonate is 0.2 wt% to 0.4 wt%.

[0036] The fourth aspect of this invention provides the application of the above drilling fluid in oil and gas drilling, which has the following beneficial effects: it can withstand temperatures up to 230-260℃, and the filtration loss at normal temperature and pressure after aging at 230℃ and 260℃ for 16 hours is 6.5-13mL and 7.2-16.3mL, respectively, while the filtration loss at high temperature and high pressure is 16-23.8mL. At the same time, after aging at 230℃, the base slurry has the properties of resisting saturated salts and 4wt% CaCl2.

[0037] To address the problems of poor performance and easy decomposition at high temperatures in existing high-temperature filtration loss reducing agents, this invention utilizes the characteristics of small particle size, numerous micropores, large specific surface area, and high surface hydroxyl content of nano-silica particles to copolymerize with polymers to prepare a filtration loss reducing agent with good temperature resistance. This filtration loss reducing agent exhibits good temperature resistance, salt resistance, and calcium resistance within a range of room temperature and high temperatures, withstanding temperatures of 230℃~260℃ and resisting calcium... 2+ The concentration can reach 40wt%, which can meet the drilling fluid requirements of deep and high-temperature wells. Detailed Implementation

[0038] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0039] All numerical specifications in this invention (e.g., temperature, time, concentration, and weight, including ranges for each) are generally approximate values ​​that can be changed in increments of 0.1 or 1.0 (+) or (-). All numerical specifications are to be understood as being preceded by the term "about". In the following examples, unless otherwise specified, all experimental instruments and materials involved are commercially available, and room temperature refers to 25±2℃.

[0040] Experimental apparatus:

[0041] Six-speed viscometer: ZNN-D6B, Qingdao Tongchun Petroleum Instrument Co., Ltd.

[0042] Medium-pressure filter loss meter: SD6-1, Qingdao Tongchun Petroleum Instrument Co., Ltd.

[0043] High-temperature and high-pressure filter loss meter: GGS42-2A, Qingdao Tongchun Petroleum Instrument Co., Ltd.

[0044] Drying oven: DHG-9070A, Shanghai Xiyu Instrument Equipment Co., Ltd.

[0045] Crusher: BJ-400, Qingdao Tongchun Petroleum Instrument Co., Ltd.

[0046] Filtration loss performance test:

[0047] The drilling fluid filtration performance test was conducted in accordance with the API measurement procedure (American Petroleum Institute (RP13B-1 2017) and the Chinese standard SY / T16783-1997).

[0048] Example 1:

[0049] This embodiment prepares a filtration loss reducing agent A1, including the following steps:

[0050] Weigh 4.8g of low-viscosity polyanionic cellulose (LV-PAC, molecular weight 300,000-500,000), slowly add it to 200mL of deionized water, stir at high speed for 20min to dissolve, and obtain LV-PAC solution;

[0051] Under ice bath conditions of 3–5°C, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) was added to the prepared LV-PAC solution. The pH was adjusted to 10 using NaOH. Then, N,N-dimethylacrylamide (DMAA), dimethyldiallylammonium chloride (DMDAAC), sodium p-styrenesulfonate (SSS), and KH570 modified silica were added. After stirring for 10 min, the solution was poured into a 500 mL three-necked flask equipped with a reflux device. Equal masses of sodium bisulfite and ammonium persulfate solutions were added to the mixed solution, totaling 0.25% of the total monomer mass. The water bath was opened and the temperature was raised to 75°C. The mixture was stirred, and nitrogen gas was introduced into the three-necked flask for 30 min. The reaction was allowed to proceed for 8 h. The reaction time was carefully recorded. To ensure an oxygen-free process, nitrogen gas was introduced throughout the entire reaction. The obtained product was dried in a drying oven at 60°C for 24 h and then pulverized using a pulverizer to obtain a filtration loss reducer A1 with an average particle size of approximately 200 nm.

[0052] The mass ratio of N,N-dimethylacrylamide (DMAA), dimethyl diallyl ammonium chloride (DMDAAC), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium p-styrene sulfonate (SSS), and KH570 modified silica is 2.7:3:4.6:2.9:1.1, and the total mass of LV-PAC and other monomers accounts for approximately 30% of the water mass.

[0053] Example 2:

[0054] This embodiment uses a method similar to that of Example 1. The difference is that in this embodiment, the mass ratio of DMAA:DMDAAC:AMPS:SSS:KH570-SiO2 is 2.7:3:5:1:1; all other conditions are the same, and filtration loss reducer A2 is obtained.

[0055] Example 3:

[0056] This embodiment uses a method similar to that of Example 1. The difference is that in this embodiment, the mass ratio of DMAA:DMDAAC:AMPS:SSS:KH570-SiO2 is 2.7:3:4.5:1:1; all other conditions are the same, and filtration loss reducer A3 is obtained.

[0057] Example 4:

[0058] This embodiment uses a method similar to that of Example 1, except that the mass ratio of DMAA:DMDAAC:AMPS:SSS:KH570-SiO2 is 2.7:3:5.5:1.2:1; all other conditions are the same, and filtration loss reducer A4 is obtained.

[0059] Example 5:

[0060] This embodiment uses a similar method to Example 4, except that humic acid resin is used instead of polyanionic cellulose, while all other conditions are the same, to obtain filtration loss reducer B1.

[0061] Example 6:

[0062] This embodiment uses a similar method to Example 1, except that carboxymethyl cellulose is used instead of polyanionic cellulose, while all other conditions are the same, to obtain filtration loss reducer B2.

[0063] Example 7:

[0064] This embodiment uses a similar method to Example 4, except that unmodified nano-SiO2 is used instead of KH570-SiO2, while all other conditions are the same, to obtain filtration loss reducer C1.

[0065] Example 8:

[0066] This embodiment was carried out using a similar method to Example 1, except that the mass ratio of N,N-dimethylacrylamide (DMAA), dimethyl diallyl ammonium chloride (DMDAAC), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium p-styrene sulfonate (SSS), and KH570 modified silica was 2.7:3:4.6:0.9:1.5, and all other conditions were the same, resulting in filtration loss reducer C2.

[0067] Example 9:

[0068] This embodiment uses a similar method to Example 1, except that acrylamide is used instead of DMAA, while other conditions remain the same, to obtain filtration loss reducer D1.

[0069] Example 10:

[0070] This embodiment uses a similar method to Example 4, except that methacrylamide is used instead of DMAA, while other conditions remain the same, to obtain filtration loss reducer D2.

[0071] Example 11:

[0072] This embodiment was carried out using a similar method to Example 1, except that the mass ratio of N,N-dimethylacrylamide (DMAA), dimethyldiallylammonium chloride (DMDAAC), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium p-styrenesulfonate (SSS), and KH570 modified silica was 3:3:4.6:0.9:1.1, and other conditions were the same, resulting in filtration loss reducer D3.

[0073] Example 12:

[0074] This embodiment uses a similar method to Example 4, except that DMDAAC is replaced with methacryloyloxyethyltrimethylammonium chloride, while other conditions remain the same, to obtain filtration loss reducer E1.

[0075] Example 13:

[0076] This embodiment uses a similar method to Example 4, except that diethyldiallylammonium chloride is used instead of DMDAAC, while other conditions remain the same, to obtain filtration loss reducer E2.

[0077] Example 14:

[0078] This embodiment was carried out using a similar method to Example 1, except that the mass ratio of N,N-dimethylacrylamide (DMAA), dimethyl diallyl ammonium chloride (DMDAAC), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium p-styrenesulfonate (SSS), and KH570 modified silica was 2.7:3.2:4.6:0.9:1.1, and other conditions were the same, resulting in filtration loss reducer E3.

[0079] Example 15:

[0080] This embodiment was carried out using a similar method to Example 4, except that 2g of polyanionic cellulose was dissolved in a water / ethanol mixed solution with a volume ratio of 1:1, with a total volume of 200mL. At the same time, sodium p-styrene sulfonate was replaced with styrene, and other conditions were the same, to obtain filtration loss reducer F1.

[0081] Example 16:

[0082] This embodiment uses a similar method to Example 1, except that the mass ratio of N,N-dimethylacrylamide (DMAA), dimethyl diallyl ammonium chloride (DMDAAC), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium p-styrenesulfonate (SSS), and KH570 modified silica is 2.7:3:4.6:1.2:1.1, and other conditions are the same, to obtain filtration loss reducer F2.

[0083] Example 17:

[0084] This embodiment was carried out using a similar method to Example 4, except that no cellulose derivative was added; all other conditions were the same, and filtration loss reducer G1 was obtained.

[0085] Example 18:

[0086] This embodiment uses a similar method to Example 4, except that no nanomaterials are added; all other conditions are the same, and filtration loss reducer G2 is obtained.

[0087] Performance testing:

[0088] 1) After adding more than 2 wt% of the filtration loss reducer prepared in each example to the fresh water-based slurry, the filtration loss was measured after aging at 230°C for 16 h. The specific results are shown in Table 1.

[0089] Freshwater-based slurry: Water, calcium-based bentonite, and anhydrous sodium carbonate in a mass ratio of 400:16:1 were stirred at high speed for 30 minutes and then hydrated and cured at room temperature for 24 hours to obtain freshwater-based slurry.

[0090] Table 1

[0091] Example 1 A1 6.9 Example 2 A2 6.6 Example 3 A3 6.7 Example 4 A4 6.5 Example 5 B1 8.3 Example 6 B2 7.7 Example 7 C1 15.3 Example 8 C2 6.8 Example 9 D1 8.7 Example 10 D2 8.1 Example 11 D3 7.2 Example 12 E1 10 Example 13 E2 6.5 Example 14 E3 6.8 Example 15 F1 18.9 Example 16 F2 6.7 Example 17 G1 11.5 Example 18 G2 17.7

[0092] Table 1 shows that among the filtration loss reducing agents A1-A4, agent A4 has the best filtration loss reduction effect, with an API filtration loss of only 6.5 mL after aging at 230℃ for 16 hours. In contrast, agent B1 (Example 5), which uses humic acid resin instead of LV-PAC based on agent A4, has a relatively poor effect, with an API filtration loss of only 8.3 mL. However, agent G1 (Example 17, without the addition of cellulose derivatives compared to Example 4) achieved an API filtration loss of 11.5 mL, while agent G2 (Example 18, without the addition of nanomaterials compared to Example 4) achieved an API filtration loss of 17.7 mL, showing a significant increase in filtration loss. This indicates that filtration loss reducing agents without the addition of cellulose derivatives and nanomaterials have poor temperature resistance.

[0093] 2) Analysis of the effect of filtration loss reducer dosage on filtration loss reduction effect of freshwater-based slurry:

[0094] Filtration loss reducer A4 was added to freshwater-based slurry. The effect of the dosage of filtration loss reducer on filtration loss reduction of freshwater-based slurry was analyzed before and after aging at 200℃, 230℃ and 260℃ for 16 hours.

[0095] Without adding a filtration reducer, a freshwater drilling fluid B0 is obtained.

[0096] The amount of filtration loss reducer A4 added is 0.5% of the water mass in the base slurry to obtain drilling fluid B1.

[0097] The amount of filtration reducer A4 added is 1% of the water mass in the base slurry to obtain drilling fluid B2.

[0098] The amount of filtration loss reducer A4 added is 1.5% of the water mass in the base slurry to obtain drilling fluid B3.

[0099] The amount of filtration loss reducer A4 added is 2% of the water mass in the base slurry to obtain drilling fluid B4.

[0100] The amount of filtration loss reducer A4 added is 2.5% of the water mass in the base slurry to obtain drilling fluid B5.

[0101] The amount of filtration loss reducer A4 added is 3% of the water mass in the base slurry to obtain drilling fluid B6.

[0102] The effect of adding filtration loss reducer on reducing API filtration loss in freshwater-based drilling fluid was analyzed before and after aging at 200℃, 230℃, and 260℃ for 16 hours. The measurement results are shown in Table 2. Table 3 shows the filtration loss of drilling fluid B4 under high temperature and high pressure.

[0103] Table 2

[0104]

[0105] Table 3

[0106]

[0107] Table 2 shows that drilling fluid B4 exhibits the best filtration efficiency compared to drilling fluids B0-B3, with a filtration loss of 6-7.2 mL after aging. The API filtration loss of drilling fluid B4 after aging at 200℃, 230℃, and 260℃ for 16 hours was 6 mL, 6.5 mL, and 7.2 mL, respectively, compared to only 5.4 mL before aging. The change was minimal; further increasing the amount of the filtration reducer resulted in a slight decrease in API filtration loss. Therefore, the filtration reducer of this invention maintains a stable and good filtration reduction effect even after aging at high temperatures of 200℃-260℃. Furthermore, its filtration reduction performance is best at a dosage of 2 wt%.

[0108] Table 3 shows that the high-temperature and high-pressure water loss of drilling fluid B4 is 16-32.3 mL. The results indicate that the filtration loss reducer of this invention can maintain stable and relatively good filtration performance under high-temperature and high-pressure conditions.

[0109] 3) The effect of NaCl dosage on the filtration loss reduction effect of the filtration loss reducing agent:

[0110] The API filtration loss was measured before and after adding 2 wt% of filtration loss reducer A4 to brine base slurries of different concentrations and aging at 230℃ for 16 h and 260℃ for 16 h, respectively. The results are shown in Table 4.

[0111] Salt-based slurry: Water, calcium-based bentonite, and anhydrous sodium carbonate in a mass ratio of 400:16:1 were mixed with NaCl at mass fractions of 5%, 10%, 20%, 30%, and 36%, respectively. The mixture was stirred at high speed for 30 minutes and then hydrated and cured at room temperature for 24 hours to obtain different salt-based slurries.

[0112] Table 4

[0113]

[0114] As shown in Table 4, the API filtration loss after aging at 230℃ for 16 hours increased from 5.4-3.3 mL to 6.5 mL-15.2 mL compared to before aging, indicating an increase in filtration loss. After aging at 260℃ for 16 hours, the filtration loss reducer could still resist the intrusion of 10 wt% NaCl, maintaining the medium-pressure filtration loss below 20 mL. This demonstrates that the filtration loss reducer of the present invention can resist saturated salt contamination (36 wt%) after high-temperature aging at 230℃, and still maintains good salt resistance (10 wt%) after aging at 260℃.

[0115] 4) The effect of CaCl2 dosage on the filtration loss reduction effect of the filtration loss reducing agent:

[0116] The API filtration loss was measured before and after adding 2 wt% of filtration loss reducer A4 to calcium-based slurries of different concentrations and aging at 200℃ for 16 h and 230℃ for 16 h, respectively. The results are shown in Table 5.

[0117] Calcium-based slurry: Water, calcium-based bentonite, and anhydrous sodium carbonate in a mass ratio of 400:16:1 were mixed with 1wt%, 2wt%, 3wt%, 4wt%, 10wt%, 20wt%, 30wt%, and 40wt% CaCl2, respectively, and then hydrated and cured at room temperature for 24 hours to obtain different calcium-based slurries.

[0118] Table 5

[0119]

[0120] Table 5 shows that before aging, despite the continuous increase in CaCl2 content, the effect of the filtration loss reducer was significant, with the filtration loss maintained at 3.4-5.5 mL. After high-temperature aging, the effect of the filtration loss reducer weakened with increasing CaCl2 content, specifically: the filtration loss reached 18.6 mL after aging at 200℃ and 19.8 mL after aging at 230℃. Temperature and CaCl2 content affected the effectiveness of the nano-filtration loss reducer, but after aging at 200℃, the filtration loss reducer still exhibited excellent calcium resistance (40 wt%).

[0121] 5) Performance comparison of existing polymer-based filtration loss reducers

[0122] Two wt% of filtration loss reducer A4 and two similar filtration loss reducers (AH1 and AH2, synthesized according to the steps in CN110591667A and CN11113904A) were added to three parts of freshwater-based slurry. AH1 is a filtration loss reducer grafted with humic acid resin copolymer and nanomaterials. The synthesis method is as follows:

[0123] Acrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, maleic anhydride, N-vinylpyrrolidone, nanomaterials, and humic acid resin were dissolved in water in a weight ratio of 5:4:3:2:2:1:6. After adjusting the pH to 8, an initiator was added at 80°C, and the mixture was stirred for 6 hours. The resulting product was then dried and pulverized to obtain AH1. The nanomaterials were a mixture of silane coupling agent-modified nano-alumina and nano-silica, with a mass ratio of silane coupling agent, nano-alumina, and nano-silica of 1:15:45. The initiator was ammonium persulfate, added at 2 wt%.

[0124] AH2 is a filtrate loss reducer for sulfonated phenolic resin copolymers, and its synthesis method is as follows:

[0125] 10g of high molecular weight sulfonate polymer was dissolved in 100mL of water, stirred until homogeneous, and then sealed and heated at 220℃ for 4h to degrade it. The solution was then cooled to room temperature. 10g of sulfomethylphenol resin was added to the degraded polymer solution and stirred until homogeneous. 0.3g of formaldehyde was added under stirring conditions, and the mixture was stirred at room temperature for 30min. The solution was then transferred to a sealed container, purged with nitrogen, and heated to 90℃ for 4h. AH2 was obtained.

[0126] Subsequently, the medium-pressure filtration loss and the high-temperature and high-pressure filtration loss at 180℃ and 3.5MPa were measured for freshwater drilling fluids with added filtration loss reducer A4, filtration loss reducer AH1, and filtration loss reducer AH2 after aging at 230℃ for 16 hours. The amount of filtration loss reducers A6, AG1, and AG3 added was 2wt% of the water reference in the drilling fluid. The results are shown in Table 6.

[0127] Table 6

[0128] A4 6.5 21 AH1 10.7 36.5 AH2 7.8 27.4

[0129] As shown in Table 6, the nanocomposite filtration loss reducer of the present invention has a significantly superior filtration loss reduction effect after aging compared with the other two filtration loss reducers, stronger temperature resistance, and lower filtration loss.

[0130] The test results in the table above show that the nanostructured copolymer provided by this invention has excellent filtration loss reduction effect and resistance to high temperature, high salt and high calcium when used as a filtration loss reducer for drilling fluid.

[0131] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a filtration loss reducing agent, characterized in that, The preparation method includes the following steps: The cellulose derivative was dissolved in water to obtain solution 1; After adding 2-acrylamido-2-methylpropanesulfonic acid to solution 1, the pH was adjusted to alkaline by adding alkaline solution; then diallyl ammonium salt, acrylamide monomer, styrene sulfonate and modified nano silica were added to obtain solution 2. An initiator is added to the solution 2 to carry out a polymerization reaction. After the reaction is completed, the solution is dried and ground to obtain the filtrate loss reducer. The cellulose derivative is a low-viscosity polyanionic cellulose with a molecular weight of 300,000 to 500,000. The acrylamide monomer is N,N-dimethylacrylamide; The diallyl ammonium salt is N,N-dimethyldiallyl ammonium chloride or N,N-diethyldiallyl ammonium chloride; The styrene sulfonate is sodium p-styrene sulfonate; The modified nano-silica is KH570 modified silica; The mass ratio of the acrylamide monomer, diallyl ammonium salt, 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonate, and modified nano-silica is 2.7:3:5.5:1.2:

1. In solution 1, the cellulose derivative accounts for 2.3 wt% to 2.8 wt% of the water mass; in solution 2, the total mass of the cellulose derivative, acrylamide monomer, diallyl ammonium salt, 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonate and modified nano silica accounts for 30% of the water mass.

2. The preparation method according to claim 1, characterized in that, The polymerization reaction is carried out at a temperature of 70-75°C for 6-12 hours.

3. The preparation method according to claim 1, characterized in that, The modified nano-silica has an average particle size of 20 nm to 100 nm.

4. The preparation method according to claim 1, characterized in that, The modified nano-silica has an average particle size of 30nm~80nm.

5. A filtration loss reducing agent, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. A drilling fluid, characterized in that, It includes the filtration loss reducing agent as described in claim 5.

7. The drilling fluid according to claim 6, characterized in that, Based on the total mass of the drilling fluid, the content of the filtration loss reducer is 0.5wt%~2wt%.

8. The drilling fluid according to claim 7, characterized in that, The drilling fluid also contains water, bentonite, thickener, anti-collapse agent, lubricant, calcium chloride, and sodium carbonate.

9. The drilling fluid according to claim 8, characterized in that, Based on the total mass of the drilling fluid, the bentonite content is 2wt%~4wt%, the viscosity modifier content is 0.2wt%~0.4wt%, the anti-collapse agent content is 3wt%~4wt%, the lubricant content is 3wt%~4wt%, the calcium chloride content is 0.5wt%~1wt%, and the sodium carbonate content is 0.2wt%~0.4wt%.

10. The application of the drilling fluid according to any one of claims 6-9 in oil and gas drilling.

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