A filtrate reducer for water-based drilling fluid and its preparation method and application

Abstract

The application relates to a filtrate reducer for a water-based drilling fluid and a preparation method and application thereof. The filtrate reducer is polymerized by N, N-diethyl acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, dimethyl diallyl ammonium chloride, N-vinyl caprolactam and allyl alcohol polyoxyethylene ether, can effectively reduce water loss in fresh water drilling fluid, salt water drilling fluid and saturated salt water drilling fluid, has a smaller influence on the rheological property of the drilling fluid, can resist 2% divalent salt in a drilling fluid basic system, is particularly suitable for high-temperature deep wells and super deep wells, and can meet the needs of the drilling fluid of the high-temperature deep wells and the super deep wells.

Description

Technical Field

[0001] This application relates to the field of drilling fluid treatment agents for petroleum exploration and development, and in particular to a filtration loss reducer for water-based drilling fluids, its preparation method, and its application. Background Technology

[0002] Deep formations are characterized by high temperature, high pressure, and complex geological conditions, placing higher demands on the performance and maintenance of drilling fluids. Temperature and salt resistance have become significant challenges for drilling fluids. Drilling fluid treatment agents undergo high-temperature degradation, cross-linking, and desorption at high temperatures, leading to a severe decline in drilling fluid performance. Drilling fluid failure can easily cause serious safety accidents such as stuck pipe, lost circulation, and blowouts, increasing drilling costs, damaging oil and gas reservoirs, and significantly impacting deep oil and gas development. Oil-based drilling fluids, due to their excellent thermal stability, salt resistance, and lubricity, have proven to be the preferred drilling fluid for deep and ultra-deep wells. However, oil-based drilling fluids also have disadvantages such as high drilling costs and high risks. Therefore, to overcome the adverse effects of high temperature and salt contamination on the performance of drilling fluids in deep and ultra-deep wells, the development of new high-temperature and salt-resistant filtration reduction agents is imperative. While existing filtration reduction agents have good high-temperature resistance, their salt resistance is poor and they cannot adapt to salt-saturated environments. Summary of the Invention

[0003] This application provides a filtration loss reducer for water-based drilling fluids, its preparation method, and its application, in order to solve the problem of filtration loss reducers failing in high-temperature, salt-saturated environments in related technologies.

[0004] Based on the above findings, this application provides the following technical solution:

[0005] In a first aspect, this application provides a filtration loss reducer for water-based drilling fluids, having the following structural formula:

[0006]

[0007] Where m is 60–90, n is 30–60, x is 30–45, y is 23–30, z is 1–3, k is 10–60, and the weight-average molecular weight of the filtration loss reducing agent is 2.34 × 10⁻⁶. 5 ~5.76×10 5 .

[0008] Secondly, this application provides a method for preparing a filtration loss reducer for water-based drilling fluids, comprising a free radical micelle polymerization step, wherein the following monomers are polymerized in an aqueous solution: N,N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallyl ammonium chloride, N-vinylcaprolactam, allyl alcohol polyoxyethylene ether, an initiator, and an inorganic base; wherein the molar ratio of the monomers N,N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallyl ammonium chloride, and N-vinylcaprolactam is (4-6):(2-4):(2-3):(1.5-2), and the allyl alcohol polyoxyethylene ether is 0.5 mol% to 2 mol% of the total monomers.

[0009] In conjunction with the second aspect of this application, in some embodiments, the free radical micelle polymerization step includes: dissolving 2-acrylamido-2-methylpropanesulfonic acid in water and adjusting the pH to neutral or slightly alkaline; then sequentially adding N,N-diethylacrylamide, dimethyl diallyl ammonium chloride, N-vinylcaprolactam, and allyl alcohol polyoxyethylene ether, mixing thoroughly and heating, then adding an initiator, reacting under anaerobic conditions, purifying, and obtaining a filtration reducer for water-based drilling fluids.

[0010] In conjunction with the second aspect of this application, in some embodiments, the temperature of the free radical micelle polymerization step is 55~68°C.

[0011] In conjunction with the second aspect of this application, in some embodiments, the total concentration of the monomer is 30wt%±2wt%, and the concentration of the initiator is 0.6wt%±0.02wt%. Preferably, the initiator is azobisisobutyronitrile.

[0012] In conjunction with the second aspect of this application, in some embodiments, the pH of the aqueous solution is 7-10, and the polymerization reaction time is 4-6 hours.

[0013] Thirdly, this application provides the application of the above-mentioned filtration loss reducer for water-based drilling fluids in the field of water-based drilling fluids.

[0014] Fourthly, this application provides a water-based drilling fluid, including the aforementioned filtration loss reducer for water-based drilling fluids.

[0015] In conjunction with the fourth aspect of this application, in some embodiments, the water-based drilling fluid further includes: 0wt% to 36wt% NaCl, and / or, 1wt% to 3wt% CaCl2.

[0016] In conjunction with the fourth aspect of this application, in some embodiments, the water-based drilling fluid further comprises one or more of bentonite, flow pattern modifier, high-temperature plugging agent, lubricant, potassium chloride, nano-silica, and barite.

[0017] Compared with the prior art, this application has at least the following beneficial effects:

[0018] (1) The N,N-diethylacrylamide in the filtrate loss reducer molecule provided in this application contains carbon-carbon double bonds and amide groups, which are prone to polymerization reactions to form hydrolysis-resistant and high-performance polymers. Under the impetus of the two ethyl groups, a hyperconjugated system is formed between nitrogen, carbonyl, and double bonds, which has good thermal stability. The strong anionic sulfonic acid group has good temperature resistance, salt resistance, and divalent ion tolerance, and the amide group makes it hydrolytically stable. The quaternary ammonium salt provides a cationic group with strong and stable adsorption capacity, which copolymerizes to form a strong and stable five-membered ring molecular bond, enhances the rigidity of the molecular chain, and improves the temperature resistance. The introduction of a novel temperature-resistant amide ring with strong hydrophilicity can adsorb onto the surface of clay particles to form a thick and tough hydration film, reducing filtrate loss. This application also introduces side-chain macromolecular alcohol polyoxyethylene ether monomers to give full play to their steric hindrance effect and further improve the filtrate loss reduction effect.

[0019] (2) The filtration loss reducer provided in this application has strong adsorption and hydration properties in the quaternary ammonium cationic group and nonionic amide group contained in the main chain, and good temperature and salt resistance properties in the sulfonic acid group. The seven-membered lactam ring and the generated five-membered ring improve the rigidity of the molecule. The comb-like polymer of the macromolecular side chain can significantly improve the fluidity and filtration loss reduction of cement paste by inducing better steric hindrance. The multifunctional groups have synergistic effects, and the filtration loss reduction effect is obvious in the saturated salt environment with high temperature resistance.

[0020] (3) The water-based drilling fluid provided in this application can withstand salt to salt saturation at 220℃, which is superior to existing similar water-based drilling fluids. The fluid loss reducing agent of this application can effectively reduce fluid loss in freshwater drilling fluid, brine drilling fluid and saturated brine drilling fluid, and has little impact on the rheological properties of drilling fluid. It can also withstand 2% divalent salt in the drilling fluid base system, and is particularly suitable for high temperature deep wells and ultra-deep wells, which can meet the needs of high temperature deep wells and ultra-deep well drilling fluids. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 : Schematic diagram of the preparation of the filtration loss reducing agent in the embodiments of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value, or combined with other lower or upper limits, to form a range not explicitly stated.

[0025] It should be noted that, in the description of this application, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more. Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0026] In the description of this application, the terms "any embodiment / mode," "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment / mode or example, which are included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0027] In this application, the test methods for the following terms are specified in GB / T 16783.1-2014 "Field Testing of Drilling Fluids for the Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids" and the American Petroleum Institute (API) standard (APIRP13B 1, 2009):

[0028] API Filtration Loss Measurement: The filtrate seeping from the drilling fluid was collected for 30 minutes under low temperature (room temperature) and low pressure (AP = 0.69 MPa) conditions using an API filtration loss meter to obtain the API filtration loss (FL) of the drilling fluid. API (), the unit is mL.

[0029] High-temperature and high-pressure filtration loss: refers to the filtration loss of drilling fluid under specific high temperature and high pressure conditions. After the drilling fluid has aged, the high-temperature and high-pressure filtration loss (FL) of the drilling fluid is measured using a high-temperature and high-pressure filtration loss meter under high temperature (set temperature) and high pressure (set pressure) conditions. HTHP The test time was 30 min, and the final filtration loss was 30 min multiplied by 2, in mL.

[0030] Apparent viscosity, also known as effective viscosity or apparent viscosity, is the ratio of shear stress to velocity gradient of drilling fluid under a certain velocity gradient. It is denoted by "AV" and the unit is mPa·s (millipascals per second).

[0031] Plastic viscosity: When drilling fluid flows in laminar flow, the sum of various internal frictional forces between solid particles, between solid particles and liquid molecules, and between liquid molecules in the drilling fluid is called the plastic viscosity of the drilling fluid, represented by "PV", and the unit is mPa·s (millipascals-seconds) or cP (centipoises), 1 mPa·s = lcP.

[0032] Dynamic shear stress: The dynamic shear stress of drilling fluid reflects the magnitude of the interaction force between clay particles and polymer molecules when the drilling fluid is in laminar flow, that is, the strength of the network structure formed inside the drilling fluid. It is represented by "YP" or "T" and the unit is Pa (Pa).

[0033] in:

[0034] AV = 1 / 2 × Φ 600

[0035] PV=Φ 600 -Φ 300

[0036] YP = 1 / 2 × (Φ) 300 -PV)

[0037] Drilling fluid aging treatment: The drilling fluid samples were aged at temperatures of 180℃, 200℃, and 220℃ for 16 hours.

[0038] Performance test after aging: After aging, cool to room temperature and stir for 30 minutes at 10000~12000 r / min, and measure the filtration loss.

[0039] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. These embodiments can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0040] Filtration reducer:

[0041] The filtration loss reducer for water-based drilling fluids provided in this application has the following structural formula:

[0042]

[0043] Where m is 60–90, n is 30–60, x is 30–45, y is 23–30, z is 1–3, k is 10–60, and the weight-average molecular weight of the filtration loss reducing agent is 2.34 × 10⁻⁶. 5 ~5.76×10 5 .

[0044] Preparation method:

[0045] The method for preparing a filtration loss reducer for water-based drilling fluids provided in this application includes a free radical micelle polymerization step, in which the following monomers are polymerized in an aqueous solution: N,N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallyl ammonium chloride, N-vinylcaprolactam, allyl alcohol polyoxyethylene ether, an initiator, and an inorganic base; wherein the molar ratio of the monomers N,N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallyl ammonium chloride, and N-vinylcaprolactam is (4-6):(2-4):(2-3):(1.5-2), and the allyl alcohol polyoxyethylene ether is 0.5 mol% to 2 mol% of the total monomers.

[0046] In some embodiments, the free radical micelle polymerization step includes: dissolving 2-acrylamido-2-methylpropanesulfonic acid in water and adjusting the pH to neutral or slightly alkaline; then sequentially adding N,N-diethylacrylamide, dimethyl diallyl ammonium chloride, N-vinylcaprolactam, and allyl alcohol polyoxyethylene ether, mixing thoroughly and heating, then adding an initiator, reacting under anaerobic conditions, and purifying to obtain a filtration loss reducer for water-based drilling fluids.

[0047] In some embodiments, the total concentration of monomers is 30wt%±2wt%, and the concentration of initiator is 0.6wt%±0.02wt%.

[0048] In some embodiments, the pH of the aqueous solution is 7-10, and the polymerization reaction time is 4-6 hours.

[0049] In some embodiments, the purified material was vacuum dried at 80°C for 24 h.

[0050] application:

[0051] The aforementioned filtration loss reducer is suitable for preparing water-based drilling fluids. This application provides a water-based drilling fluid including the aforementioned filtration loss reducer for water-based drilling fluids.

[0052] In some embodiments, the water-based drilling fluid further includes: 0wt%~36wt% NaCl, and / or, 1wt%~3wt% CaCl2.

[0053] In some embodiments of this application, the water-based drilling fluid further comprises one or more of bentonite, flow pattern modifier, high-temperature plugging agent, lubricant, potassium chloride, nano-silica, and barite.

[0054] The above-mentioned water-based drilling fluid is suitable for drilling operations in high-temperature and high-salt environments, especially in saturated salt environments with a temperature of 220℃.

[0055] Example

[0056] The technical solution of this application is described in detail below through examples. Unless otherwise specified, the raw materials, equipment, or solvents used are all common raw materials, equipment, or solvents on the market. Unless otherwise specified, the raw materials with the same name used in the following examples and comparative examples are the same raw materials. Flow modifier, high-temperature plugging agent, and barite were purchased from CNPC Engineering Technology Research Institute; Huai'an clay was purchased from Hebei Huai'an Xinyuan Chemical (Bentonite) Co., Ltd.; lubricant and nano-silica sodium chloride were purchased from Shandong Deshunyuan; and monovalent / divalent salts were purchased from Sinopharm Group.

[0057] The method for preparing the filtration loss reducer in this embodiment includes the following steps:

[0058] Example 1:

[0059] 9.60 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 7 using 20 mol / L NaOH solution. 11.79 g of N,N-diethylacrylamide, 7.55 g of dimethyldiallylammonium chloride, 4.84 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 60 °C, an initiator was added, and the reaction was continued for 5 h. After the reaction was completed, the mixture was washed, precipitated, and filtered with anhydrous ethanol-acetone. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtrate loss reducer A1.

[0060] Example 2:

[0061] 11.70 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 8 using 20 mol / L NaOH solution. 11.97 g of N,N-diethylacrylamide, 6.09 g of dimethyldiallylammonium chloride, 5.24 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 65 °C, an initiator was added, and the reaction was continued for 5 h. After the reaction was completed, the mixture was washed, precipitated, and filtered with anhydrous ethanol-acetone. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtrate loss reducer A2.

[0062] Example 3:

[0063] 9.39 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 9 using 20 mol / L NaOH solution. 11.52 g of N,N-diethylacrylamide, 4.88 g of dimethyldiallylammonium chloride, 4.20 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution in sequence. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 60 °C, an initiator was added, and the reaction was continued for 5 h. After the reaction was completed, the mixture was washed with anhydrous ethanol-acetone, precipitated, and filtered. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtrate loss reducer A3.

[0064] Example 4:

[0065] 14.11 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 9 using 20 mol / L NaOH solution. 8.66 g of N,N-diethylacrylamide, 5.50 g of dimethyldiallylammonium chloride, 4.74 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 55 °C, an initiator was added, and the reaction was continued for 6 h. After the reaction was completed, the mixture was washed, precipitated, and filtered with anhydrous ethanol-acetone. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtration loss reducer A4.

[0066] Example 5:

[0067] 13.44 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 7 using 20 mol / L NaOH solution. 10.31 g of N,N-diethylacrylamide, 7.86 g of dimethyldiallylammonium chloride, 3.39 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution in sequence. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 60 °C, an initiator was added, and the reaction was continued for 5 h. After the reaction was completed, the mixture was washed with anhydrous ethanol-acetone, precipitated, and filtered. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain the filtrate loss reducer A5.

[0068] Example 6:

[0069] 7.97 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 8 using 20 mol / L NaOH solution. 14.67 g of N,N-diethylacrylamide, 9.33 g of dimethyldiallylammonium chloride, 4.01 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 65 °C, an initiator was added, and the reaction was continued for 4 h. After the reaction was completed, the mixture was washed with anhydrous ethanol-acetone, precipitated, and filtered. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtration loss reducer A6.

[0070] Comparative Example 1:

[0071] 20.85 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 7 using 20 mol / L NaOH solution. 6.39 g of N,N-diethylacrylamide, 5.42 g of dimethyldiallylammonium chloride, 2.33 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 60 °C, an initiator was added, and the reaction was continued for 4 h. After the reaction was completed, the mixture was washed with anhydrous ethanol-acetone, precipitated, and filtered. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtrate loss reducer B1.

[0072] Comparative Example 2:

[0073] 8.64 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 8 using 20 mol / L NaOH solution. 7.07 g of N,N-diethylacrylamide, 13.48 g of dimethyldiallylammonium chloride, 5.80 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 55 °C, an initiator was added, and the reaction was continued for 5 h. After the reaction was completed, the mixture was washed with anhydrous ethanol-acetone, precipitated, and filtered. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtrate loss reducer B2.

[0074] Comparative Example 3:

[0075] 16.02 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 9 using 20 mol / L NaOH solution. 9.83 g of N,N-diethylacrylamide, 4.99 g of dimethyldiallylammonium chloride, 2.15 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 60 °C, an initiator was added, and the reaction was continued for 5 h. After the reaction was completed, the mixture was washed, precipitated, and filtered with anhydrous ethanol-acetone. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtrate loss reducer B3.

[0076] Comparative Example 4:

[0077] 9.60 g of 2-acrylamido-2-methylpropanesulfonic acid monomer was weighed and dissolved in deionized water. The pH of the solution was adjusted to 11 using 20 mol / L NaOH solution. 11.79 g of N,N-diethylacrylamide, 7.55 g of dimethyldiallylammonium chloride, 4.84 g of N-vinylcaprolactam, and 1 mol% allyl alcohol polyoxyethylene ether were added to the solution sequentially. After stirring evenly, the mixture was poured into a three-necked flask and stirred at 30 °C under nitrogen purging for 30 min. Then, the temperature was raised to 65 °C, an initiator was added, and the reaction was continued for 5 h. After the reaction was completed, the mixture was washed, precipitated, and filtered with anhydrous ethanol-acetone. After vacuum drying at 80 °C for 24 h, the mixture was pulverized to obtain filtrate loss reducer B4.

[0078] Verification Example 1: Drilling Fluid Preparation

[0079] Preparation of base slurry: Slowly add 16g bentonite and 0.56g sodium carbonate to 400mL distilled water, stir thoroughly, and age at room temperature for 24h to prepare base slurry.

[0080] Freshwater drilling fluid preparation: Add a filtration loss reducer to 400 mL of base slurry and stir for 20 min at 10000~12000 r / min to obtain freshwater drilling fluid.

[0081] Saltwater drilling fluid: Add 0~36wt% NaCl to 400mL of base slurry, and after complete dissolution, add 4g of filtration loss reducer. Stir for 20min at 10000~12000r / min to obtain saltwater drilling fluid.

[0082] Drilling fluid base system: 2% base slurry + 1.5% filtration loss reducer + 2% flow pattern modifier + 3% KCl + 2% high temperature plugging agent + 2% nano calcium carbonate + 3% lubricant + barite.

[0083] Verification Example 2: Evaluation of the Effect of Filtration Loss Reducing Agent

[0084] The filtration loss reducers prepared in the examples and comparative examples were added to the base slurry at 2 wt% to obtain freshwater drilling fluid. The API filtration loss results of the freshwater drilling fluid before and after aging are shown in Table 1.

[0085] Table 1

[0086]

[0087] According to the experimental results, the filtration loss reducing agent prepared in this application has a good filtration loss reducing effect. After the prepared freshwater drilling fluid is aged at 180°C for 16 hours, the API filtration loss is <5mL. In contrast, the filtration loss reducing agent prepared in the comparative example shows a poor filtration loss reducing effect. After aging, the API filtration loss of the prepared freshwater drilling fluid is >12mL.

[0088] Verification Example 3: Temperature Resistance Test of Filtration Loss Reducer

[0089] This verification example uses the filtration loss reducer A2 prepared in Example 2 of this application as a representative. It was added to the base slurry at a dosage of 1 wt% to prepare a freshwater drilling fluid to evaluate the temperature resistance of the filtration loss reducer prepared in this application. The rheological and filtration loss test results of the freshwater drilling fluid before and after aging are shown in Table 2.

[0090] Table 2

[0091]

[0092] As shown in Table 2, the freshwater drilling fluid maintained good filtration loss reduction effect after aging at 220℃. This is because the amide groups and strong anionic sulfonic acid groups contained in the polymer molecules have excellent temperature resistance. At the same time, the copolymerization produces stable five-membered ring internal bonds to enhance the rigidity of the molecular chain, and the synergistic effect further improves the temperature resistance. The cationic groups and lactam rings have strong and stable adsorption capacity, adsorbing on the surface of clay particles to form a thick and tough hydration film, reducing filtration loss. The side-chain macromolecular monomers give full play to their steric hindrance effect, further improving the filtration loss reduction effect.

[0093] Verification Example 4: Salt resistance test of filtration loss reducer

[0094] This verification example uses the filtration loss reducer A2 prepared in Example 2 of this application as a representative. It was added to the base slurry at a dosage of 1 wt%, along with a certain amount of sodium chloride, to prepare a brine drilling fluid to evaluate the temperature and salt resistance of the filtration loss reducer prepared in this application. The rheological and filtration loss test results of the brine drilling fluid before and after aging are shown in Table 3.

[0095] Table 3

[0096]

[0097] As shown in Table 3, the brine drilling fluid maintained good filtration loss reduction effect after aging at 220℃. With the increase of salt concentration, the apparent viscosity of the drilling fluid showed a decreasing trend, and the apparent viscosity was still >20 mPa·s in saturated salt. The API filtration loss showed an increasing trend with the increase of salt concentration. This is because the addition of salt will destroy the filtration loss reduction effect of the polymer, but the filtration loss is <10 mL in saturated salt environment.

[0098] In summary, the filtration loss reducer prepared in this application exhibits excellent resistance to saturated salts. This is because the polymer molecules contain strong anionic sulfonic acid groups, which improve salt resistance and tolerance to divalent ions. The polymer also contains both quaternary ammonium cationic groups and anionic sulfonic acid groups, and the presence of zwitterions gives it salt-responsive characteristics. With the addition of electrolyte salts, the molecular chains expand and the hydrodynamic dimensions increase, forming a regular and dense spatial network structure, which further enhances the salt resistance and filtration loss reduction effect.

[0099] Verification Example 5: Compatibility Test of Filtration Loss Reduction Agent System

[0100] This verification example uses the filtration loss reducer A2 prepared in Example 2 of this application as a representative. A drilling fluid base system was prepared with an addition amount of 1 wt% to evaluate the filtration loss reducer's resistance to temperature, saturated salt, and 2 wt% divalent salt. The rheological and filtration loss test results of the drilling fluid base system before and after aging are shown in Table 4.

[0101] Table 4

[0102]

[0103] Experimental results show that the filtration loss reducer prepared in the embodiments of this application has good compatibility in drilling fluid base systems, and has good resistance to temperature, saturated salt, and 2wt% divalent salt, and has broad application prospects.

[0104] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a filtration loss reducer for water-based drilling fluids, characterized in that, The process includes a free radical micellar polymerization step, which comprises: dissolving 2-acrylamido-2-methylpropanesulfonic acid in water, adjusting the pH to 7-10 with an inorganic base; then sequentially adding N,N-diethylacrylamide, dimethyldiallyl ammonium chloride, N-vinylcaprolactam, and allyl alcohol polyoxyethylene ether, mixing thoroughly, heating, adding an initiator, reacting under anaerobic conditions, purifying, and obtaining a filtration reducer for water-based drilling fluids; wherein the molar ratio of N,N-diethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, dimethyldiallyl ammonium chloride, and N-vinylcaprolactam monomers is (4-6):(2-4):(2-3):(1.5-2), and allyl alcohol polyoxyethylene ether is 0.5 mol% to 2 mol of the total monomers.

2. The method for preparing the filtration loss reducer for water-based drilling fluid according to claim 1, characterized in that: The temperature for the free radical micelle polymerization step is 55~68℃.

3. The method for preparing the filtration loss reducer for water-based drilling fluid according to claim 1, characterized in that: The total monomer concentration was 30wt%±2wt%, and the initiator concentration was 0.6wt%±0.02wt%.

4. The method for preparing the filtration loss reducer for water-based drilling fluid according to claim 3, characterized in that: The polymerization reaction takes 4 to 6 hours.

5. The application of the filtration loss reducer for water-based drilling fluid prepared by the method of any one of claims 1 to 4 in the field of water-based drilling fluid.

6. A water-based drilling fluid comprising the filtration loss reducer for water-based drilling fluid prepared by the method for preparing the filtration loss reducer for water-based drilling fluid according to any one of claims 1 to 4.

7. The water-based drilling fluid according to claim 6, characterized in that: The water-based drilling fluid also includes: 0wt%~36wt% NaCl, and / or, 1wt%~3wt% CaCl2.

8. The water-based drilling fluid according to claim 6, characterized in that: The water-based drilling fluid also contains one or more of the following: bentonite, flow pattern modifier, high-temperature plugging agent, lubricant, potassium chloride, nano-silica, and barite.

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