A film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid and its preparation method and application

Abstract

The application provides a film-forming and chelating bifunctional polymer treatment agent for a water-based drilling fluid and a preparation method and application thereof, and belongs to the technical field of oil and gas drilling engineering. The preparation method of the treatment agent comprises the following steps: adding an epoxy group-containing monomer into an amino carboxylate aqueous solution and performing reaction; after the reaction is completed, purification treatment is performed to obtain a chelating functional monomer; the anionic monomer, the amide monomer, the stability monomer, the cationic monomer and the chelating functional monomer are added into water, and stirring is uniformly performed to obtain a monomer solution; the pH of the monomer solution is adjusted to 6-8, nitrogen gas is used for oxygen removal, an initiator is added, and reaction is performed; after the reaction is completed, sedimentation, washing and drying are performed to obtain the treatment agent. The treatment agent can complex Ca 2+ contaminated ions, improve the high salinity fluid pollution resistance of the drilling fluid, and form a protective film layer on the surface of a coal rock borehole wall and inside microcracks, thereby stably playing a role of stabilizing the borehole wall.

Description

Technical Field

[0001] This invention relates to a film-forming and chelating bifunctional polymer treatment agent for water-based drilling fluids, its preparation method and application, belonging to the field of oil and gas drilling engineering technology. Background Technology

[0002] In recent years, breakthroughs have been made in coalbed methane exploration and development, making it an important area for increasing natural gas reserves and production. Deep coalbed methane is predominantly in a free state, and unconventional technologies such as horizontal wells, multi-stage fracturing, and well network coordinated development are typically used to achieve reservoir stimulation and production enhancement. With increasing well density, decreasing horizontal well spacing, and continuously expanding fracturing scale and stimulation volume, the complexity of reservoir fracture systems has significantly increased. Increased fracture propagation and connectivity make wellbores with low cementation strength and fragile structures in coalbed methane and adjacent formations more susceptible to filtrate intrusion and fracture propagation, further exacerbating fracturing interference from adjacent wells. (Ca-bearing...) 2+ SO4 2- Fe 2+ / Fe 3+ Mn 2+ High-mineralized fluids containing contaminating ions can seep into adjacent wells during drilling along fractures and connecting channels, posing a dual challenge to drilling deep coal and rock reservoirs: wellbore instability and high-mineralization contamination.

[0003] To address drilling fluid contamination caused by the intrusion of highly salinized fluids, a common method is to add sodium carbonate, sodium silicate, or polymeric calcium removers containing carboxyl / sulfonic acid groups to the drilling fluid, thereby reducing the calcium content. 2+ Precipitation of metal ions can mitigate their adverse effects on the rheology, filtration, and stability of drilling fluids; however, this method is highly susceptible to causing secondary damage to the drilling fluid. Chinese patent document CN108165242A discloses a calcium remover for drilling, which uses a multi-component copolymer treatment agent containing functional groups such as carboxyl and sulfonic acid groups to remove infiltrated calcium ions. 2+ Multi-site interaction and structural regulation can synergistically improve calcium contamination resistance and system stability. However, this method mainly relies on the multi-site adsorption or weak coordination between anionic sites and metal ions, resulting in limited selectivity for the recognition and complexation of contaminating ions. Different cations easily compete for limited active sites, inducing bridging flocculation or polymer conformational changes, leading to a significant decrease in calcium removal efficiency.

[0004] Therefore, in order to address the problem of high-salinity fluid intrusion caused by calcium ion penetration when encountering salt-gypsum layers during oil and gas drilling, there is an urgent need to develop a treatment agent that can effectively improve the drilling fluid's resistance to high-salinity fluid contamination. To this end, this invention is proposed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, particularly the dual problems of fracture development and high-salinity fluid crosstalk encountered in deep coal and gas development, this invention provides a film-forming and chelating bifunctional polymer treatment agent for water-based drilling fluids, along with its preparation method and application. The treatment agent of this invention can not only treat water-based drilling fluids containing Ca... 2+ It effectively complexes the main pollutant ions, improving the drilling fluid's ability to resist high-mineralization fluid contamination. Moreover, it can form a continuous, dense, and somewhat flexible protective film on the surface of coal and rock well walls and inside micro-fractures, synergistically playing a role in stabilizing the well wall.

[0006] The technical solution of the present invention is as follows: A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluids includes the following steps: (1) Add an epoxy-containing monomer to an aqueous solution of aminocarboxylate and react; after the reaction is completed, purify the product to obtain a chelating functional monomer. (2) Add the anionic monomer, amide monomer, stable monomer, cationic monomer and the chelating functional monomer obtained in step (1) to water, stir evenly to obtain a monomer solution; adjust the pH of the monomer solution to 6~8, remove oxygen by passing nitrogen gas, add an initiator and carry out the reaction; after the reaction is completed, after precipitation, washing and drying, a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid is obtained.

[0007] According to a preferred embodiment of the present invention, the aminocarboxylate in step (1) is one of the following: sodium or potassium salt of iminodiacetic acid, sodium or potassium salt of iminodisuccinic acid, sodium or potassium salt of ethylenediaminetriacetic acid, or sodium or potassium salt of ethylenediaminedisuccinic acid; the ratio of the number of moles of aminocarboxylate to the volume of water in the aqueous solution of the aminocarboxylate is 1 mol: 0.5~1.5 L.

[0008] According to a preferred embodiment of the present invention, the aqueous solution of the aminocarboxylic acid salt in step (1) is obtained by adding an aminocarboxylic acid compound to water, followed by adding an alkali for neutralization treatment; or by dissolving the aminocarboxylic acid salt in water; more preferably, the aminocarboxylic acid compound is iminodiacetic acid, iminodisuccinic acid, ethylenediaminetriacetic acid, or ethylenediaminedisuccinic acid, the molar ratio of the aminocarboxylic acid compound to the volume of water is 1 mol: 0.5~1.5 L, the alkali is sodium hydroxide or potassium hydroxide, the molar ratio of the alkali to the carboxyl group in the aminocarboxylic acid compound is 1:1, the neutralization treatment temperature is 18~24℃, and the neutralization treatment time is 25~30 min.

[0009] According to a preferred embodiment of the present invention, the epoxy-containing monomer in step (1) is one or more of glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether; the molar ratio of the epoxy-containing monomer to the aminocarboxylate is 1~1.2:1.

[0010] According to a preferred embodiment of the present invention, the temperature of the reaction in step (1) is 60~70°C and the reaction time is 1~2h.

[0011] According to a preferred embodiment of the present invention, the purification process in step (1) is as follows: the obtained reaction solution is poured into acetone for precipitation, then filtered to obtain a precipitate, wherein the volume ratio of acetone to the molar number of aminocarboxylate is 3~8L:1mol; the precipitate obtained by filtration is dissolved in water, and then acetone is added for precipitation, followed by filtration, and the water dissolution-acetone precipitation-filtration steps are repeated 1~3 times, wherein the volume ratio of water used for dissolution to the molar number of aminocarboxylate is 0.5~5L:1mol each time, and the volume of acetone used for acetone precipitation each time is 3~8 times the volume of water used for dissolution; finally, the obtained precipitate is vacuum dried at 40~60℃ to constant weight.

[0012] According to a preferred embodiment of the present invention, the anionic monomer in step (2) is one or more of 2-acrylamide-2-methylpropanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, sodium vinylsulfonate or sodium styrenesulfonate.

[0013] According to a preferred embodiment of the present invention, the amide monomer in step (2) is one or more of acrylamide, methacrylamide, and N,N-dimethylacrylamide.

[0014] According to a preferred embodiment of the present invention, the stabilizing monomer in step (2) is one or more of N-vinylpyrrolidone, N-vinylcaprolactam, and acrylomorpholine.

[0015] According to a preferred embodiment of the present invention, the cationic monomer in step (2) is one or more of diallyl dimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, and acryloyloxyethyl trimethyl ammonium chloride.

[0016] According to a preferred embodiment of the present invention, in step (2), the monomer solution comprises the following molar amounts of monomers: 35-45 parts of anionic monomer, 15-25 parts of amide monomer, 10-20 parts of stable monomer, 5-12 parts of cationic monomer, and 10-18 parts of chelating functional monomer; more preferably, the monomer solution comprises the following molar amounts of monomers: 40 parts of anionic monomer, 20 parts of amide monomer, 15 parts of stable monomer, 10 parts of cationic monomer, and 15 parts of chelating functional monomer.

[0017] According to a preferred embodiment of the present invention, the total mass concentration of anionic monomers, amide monomers, stable monomers, cationic monomers and chelating functional monomers in the monomer solution in step (2) is 15-35%.

[0018] According to a preferred embodiment of the present invention, in step (2), the pH of the monomer solution is adjusted to 6-8 using an aqueous sodium hydroxide solution with a concentration of 20-30 wt%.

[0019] According to a preferred embodiment of the present invention, in step (2), the time for nitrogen deoxygenation is 20-40 min.

[0020] According to a preferred embodiment of the present invention, the initiator in step (2) is ammonium persulfate or potassium persulfate; the mass of the initiator is 0.5 to 3.0% of the total mass of the anionic monomer, amide monomer, stable monomer, cationic monomer and chelating functional monomer.

[0021] According to a preferred embodiment of the present invention, the temperature of the reaction in step (2) is 55~75℃, more preferably 65℃; and the reaction time is 4~8h, more preferably 6h.

[0022] According to a preferred embodiment of the present invention, the precipitation step in step (2) involves adding the reaction solution to a precipitating agent for precipitation. The precipitating agent is anhydrous ethanol and / or acetone, more preferably a mixed solvent of anhydrous ethanol and acetone, wherein the volume ratio of anhydrous ethanol to acetone in the mixed solvent is 0.5 to 3:1; and the volume ratio of the precipitating agent to the reaction solution is 3 to 8:1, more preferably 4 to 6:1.

[0023] According to a preferred embodiment of the present invention, the washing in step (2) is washing with anhydrous ethanol or acetone 1 to 3 times; the drying is vacuum drying at 40 to 60°C to constant weight.

[0024] The present invention also provides a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluids, which is prepared by the above preparation method.

[0025] According to the present invention, the application of the above-mentioned film-forming and chelating bifunctional polymer treatment agent for water-based drilling fluids in the drilling and completion process of deep coal and gas reservoirs is specifically described as follows: the film-forming and chelating bifunctional polymer treatment agent for water-based drilling fluids is added to the drilling fluid or completion fluid at a ratio of 0.5 to 2.0% relative to the mass of the drilling fluid or completion fluid; wherein the deep coal and gas reservoir is Ca 2+ The present invention targets medium- and low-temperature deep coal-gas reservoirs with pollution concentrations ≤25000 mg / L, pH values ​​of 4-6, coal and rock organic matter content ≥5%, fracture width ≤20 μm, temperatures of 60-120℃, and depths of 2000-4000 m. The treatment agent of this invention achieves treatment of Ca-containing gas reservoirs through chelation and film-forming plugging. 2+It effectively complexes or stabilizes the main pollutant ions, while forming a continuous, dense, and flexible protective film layer on the surface of the coal and rock well wall and inside the micro-cracks, thus playing a synergistic role in stabilizing the well wall.

[0026] The technical features and beneficial effects of this invention are as follows: This invention addresses the dual challenges of fracture development and high-mineralization fluid crosstalk arising from unique deep coal and gas development methods. It provides a film-forming and chelating dual-functional polymer treatment agent for water-based drilling fluids. The treatment agent is prepared via copolymerization using anionic monomers, amide monomers, stabilizing monomers, cationic monomers, and chelating functional monomers (anionic monomers). The anionic monomers enhance the copolymer's hydration properties, salt tolerance, and system stability; the amide monomers improve its flexibility and water solubility; the stabilizing monomers (cyclic amides or vinyl lactam monomers) improve the copolymer's segmental stability; the cationic monomers enhance the copolymer's adsorption and film-forming effects on wellbore walls, clay particles, and mud cake surfaces; and the chelating functional monomers impart complexing ability to the copolymer for metal ions such as calcium ions. By introducing the chelating functional monomer into a water-soluble amphoteric copolymer backbone, the resulting polymer simultaneously possesses metal ion complexation, interfacial adsorption film formation, and filtration reduction functions. Specifically, the chelating functional unit can complex calcium ions with calcium ions. 2+ By effectively complexing or stabilizing contaminant ions, the damage to the rheology, filtration, and stability of drilling fluid caused by the intrusion of high-salinity fluids is mitigated. The cationic functional unit enhances polymer adsorption on the wellbore, clay particles, and mud cake surfaces, and, under the action of amide and cyclic amide or vinyl lactam units, promotes polymer chain propagation and film formation, creating a continuous and dense protective layer on the wellbore surface and within microfractures. This reduces filtrate intrusion, enhances the plugging effect, and improves wellbore stability. The anionic unit further improves the polymer's hydration, salt tolerance, and system stability, thereby achieving a synergistic effect of anti-fouling, film-forming plugging, wellbore stabilization, and reservoir protection. Compared with existing treatment agents, this invention has the following advantages: 1. This invention adopts a technical route that combines chelating functional monomers with water-soluble amphoteric copolymer framework, so that the resulting film-forming-chelating bifunctional polymer treatment agent has the functions of metal ion complexation, interfacial adsorption and film formation to reduce filtration loss, thus realizing the integration of anti-calcium fouling and film-forming blocking functions in the same polymer molecule.

[0027] 2. In this invention, chelation antifouling and film-forming blocking form a synergistic relationship of "fluid phase regulation - interface blocking" in space, and a progressive mechanism of "first complexation to stabilize the liquid, then adsorption to form a film, and then continuous wall stabilization" in time. The chelation functional unit preferentially targets Ca... 2+The contaminant ions are complexed or stabilized to reduce their adverse effects on the dispersion state of the drilling fluid system, polymer chain conformation, and mud cake structure. Subsequently, the cationic unit enhances the adsorption of the polymer on the coal and rock well wall, clay particles, and mud cake surface, while the amide unit and cyclic amide or vinyl lactam unit promote chain segment spreading and film formation, forming a continuous and dense protective layer on the well wall surface and inside microcracks. This further inhibits filtrate intrusion and high-mineralization fluid migration, thereby achieving a dynamic synergy between chelation anti-fouling and film formation and plugging.

[0028] 3. The treatment agent of the present invention can effectively reduce the problems of flocculation, rheological abnormalities, and increased filtration loss in drilling fluid systems under high calcium pollution conditions. It can also form a continuous and dense adsorption layer or barrier layer on the well wall and mud cake surface, reduce filtrate intrusion, and enhance well wall stability and reservoir protection. Attached Figure Description

[0029] Figure 1 The infrared spectrum of the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid prepared in Example 1. Detailed Implementation

[0030] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited to the embodiments described below.

[0031] In addition, the experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0032] Unless otherwise specified, the term "parts" in the embodiments refers to molar parts.

[0033] Example 1 A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluids includes the following steps: (1) Add 0.3 mol iminodiacetic acid to 300 mL of deionized water, add 0.60 mol potassium hydroxide under stirring, and neutralize at 20 °C for 30 min to obtain a dipotassium salt solution of iminodiacetic acid; (2) Add 0.30 mol glycidyl methacrylate to the solution obtained in step (1) for 30 min. After the addition is completed, stir the reaction at 65 °C for 1 h. After the reaction is completed, pour the obtained reaction solution into 1700 mL of acetone for precipitation for 10 min, filter, dissolve the obtained precipitate in 300 mL of deionized water, add 1500 mL of acetone for precipitation for 10 min, filter, dissolve the filtered precipitate in 300 mL of deionized water, add 1500 mL of acetone for precipitation for 10 min, filter, and finally vacuum dry the obtained precipitate at 50 °C to constant weight to obtain the chelated functional monomer. (3) Add 40 parts of 2-acrylamide-2-methylpropanesulfonic acid, 20 parts of N,N-dimethylacrylamide, 15 parts of N-vinylpyrrolidone, 10 parts of diallyl dimethylammonium chloride, and 15 parts of the chelating functional monomer obtained in step (2) to deionized water to prepare a monomer solution. The total mass concentration of the monomer in the monomer solution is 25%. Adjust the pH of the monomer solution to 6.8 using a 25wt% sodium hydroxide aqueous solution. After purging nitrogen gas to remove oxygen for 30 min, add ammonium persulfate as an initiator. The mass of the initiator is 1.5% of the total mass of the monomer. Heat to 65℃ and keep the reaction at that temperature for 6 h to obtain a reaction solution. The total mass of the monomer is the sum of the masses of 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone, diallyl dimethylammonium chloride, and the chelating functional monomer. (4) The reaction solution obtained in step (3) is added to anhydrous ethanol / acetone mixed solvent (the volume ratio of anhydrous ethanol to acetone in the mixed solvent is 2:1) for precipitation for 15 min. The volume ratio of the mixed solvent to the volume of the reaction solution is 5:1. Then, the mixture is filtered, and the precipitate obtained by filtration is washed twice with anhydrous ethanol. The precipitate obtained by washing is dried under vacuum at 50°C to constant weight to obtain a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid.

[0034] The infrared spectrum of the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid prepared in this embodiment is shown below. Figure 1 As shown, by Figure 1 It can be seen that at 3400cm -1 A broad absorption peak appears nearby, which can be attributed to the stretching vibrations of the hydroxyl group (OH) and the amide group (NH); 2950 cm⁻¹ -1 The nearby absorption peaks correspond to the CH stretching vibrations of -CH2- and -CH3 in the polymer backbone and side chains; 1720 cm⁻¹ -1 The nearby absorption peak can be attributed to the stretching vibration of the C=O group in the chelating functional monomer, indicating that the ester group structure derived from glycidyl methacrylate has been introduced into the polymer; 1640 cm⁻¹ -1 The strong absorption peaks nearby can be attributed to the superimposed absorption of the amide carbonyl groups in 2-acrylamido-2-methylpropanesulfonic acid and N,N-dimethylacrylamide, and the lactam carbonyl groups in N-vinylpyrrolidone; 1450 cm⁻¹ -1 The nearby absorption peaks are mainly related to the bending vibrations of -CH2- and -CH3 and the quaternary ammonium salt structure of diallyl dimethyl ammonium chloride; 1190 cm⁻¹ -1 The nearby absorption peak can be attributed to the S=O / SO stretching vibration of the sulfonic acid group in 2-acrylamido-2-methylpropanesulfonic acid, and may also be superimposed with the CO and CN vibrations; 1050 cm⁻¹ -1 The nearby absorption peaks can be attributed to CN and CN. +The presence of SO-related vibrations further indicates the existence of quaternary ammonium salt units and sulfonic acid group structures in the system; due to the presence of amide carbonyl groups, lactam carbonyl groups, and carboxylate COO groups... - And the moisture absorption peak is at 1600-1650 cm⁻¹ -1 The regions may overlap, thus exhibiting strong superimposed absorption peaks. The aforementioned characteristic peaks indicate that 2-acrylamido-2-methylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone, diallyldimethylammonium chloride, and chelating functional monomers have all been introduced into the polymer structure.

[0035] Example 2 A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid is as described in Example 1, except that the amount of each monomer in step (3) is as follows: 45 parts of 2-acrylamide-2-methylpropanesulfonic acid, 25 parts of N,N-dimethylacrylamide, 20 parts of N-vinylpyrrolidone, 12 parts of diallyl dimethylammonium chloride, and 18 parts of the chelating functional monomer obtained in step (2).

[0036] Example 3 A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid is as described in Example 1, except that the amount of each monomer in step (3) is as follows: 35 parts of 2-acrylamide-2-methylpropanesulfonic acid, 15 parts of N,N-dimethylacrylamide, 10 parts of N-vinylpyrrolidone, 5 parts of diallyl dimethylammonium chloride, and 10 parts of the chelating functional monomer obtained in step (2).

[0037] Example 4 A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid is described in Example 1, except that in step (1), tetrasodium iminodisuccinate is added to 300mL of deionized water and stirred evenly to obtain a tetrasodium iminodisuccinate solution.

[0038] Example 5 A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluids is described in Example 1, except that allyl glycidyl ether is used instead of glycidyl methacrylate in step (2).

[0039] Example 6 A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid is as described in Example 1, except that the types and amounts of each monomer in step (3) are as follows: 40 parts of 2-acrylamide-2-methylpropanesulfonic acid, 20 parts of acrylamide, 15 parts of N-vinylcaprolactam, 10 parts of methacryloyloxyethyltrimethylammonium chloride, and 15 parts of the chelating functional monomer obtained in step (2).

[0040] Comparative Example 1 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that the reaction temperature in step (3) is 45°C.

[0041] Comparative Example 2 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that the reaction time in step (3) is 2 hours.

[0042] Comparative Example 3 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that the chelating functional monomer in step (2) is 5 parts.

[0043] Comparative Example 4 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that diallyl dimethyl ammonium chloride is not added in step (3).

[0044] Comparative Example 5 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that the pH of the monomer solution in step (3) is adjusted to 9.

[0045] Comparative Example 6 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that the chelating functional monomer in step (2) is 25 parts.

[0046] Comparative Example 7 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that N,N-dimethylacrylamide is not added in step (3).

[0047] Comparative Example 8 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that N-vinylpyrrolidone is not added in step (3).

[0048] Comparative Example 9 A method for preparing a polymer treatment agent for water-based drilling fluid is described in Example 1, except that in step (3), the chelating functional monomer is replaced with an equimolar amount of hydroxyethyl methacrylate.

[0049] Test case The polymer treatment agents prepared in the examples and comparative examples were subjected to the following tests.

[0050] Test 1 To test the effect of the polymer treatment agent synthesized in this invention when added to drilling fluid, its compatibility with the drilling fluid system and its anti-fouling performance were tested.

[0051] Preparation of drilling fluid-based slurry: Under stirring conditions, add 8g of sodium-based bentonite to 400mL of water, then add 6% anhydrous sodium carbonate by weight of bentonite. Set the speed to 3000r / min and stir for 30 minutes to fully hydrate the slurry. Let it stand for 24 hours to form a stable colloid, which is the 2% sodium-based bentonite drilling fluid-based slurry. The slurry used in each group of experiments was prepared in this way.

[0052] Preparation of drilling fluid system: Place 400 mL of drilling fluid base slurry on a high-speed stirrer, set the initial speed to 3000 r / min, and then add 4 g of low viscosity polyanionic cellulose (viscosity of 2 wt% aqueous solution at 25℃ ≤40 mPa·s), 8 g of sulfonated lignite, 4 g of white pitch, 0.8 g of xanthan gum, 12 g of ultrafine calcium carbonate (particle size of 2~5 μm), and finally add 220 g of barite. After each addition of a reagent, increase the speed by 400 r / min, and finally stir at 5000 r / min for 30 min to obtain the drilling fluid system.

[0053] Preparation of test samples: Add 8g of the polymer treatment agent prepared in the examples or comparative examples to 400mL of drilling fluid system, stir evenly, and then add calcium chloride to the system to reduce the Ca content. 2+ The pollution concentration was 25000 mg / L, and test samples were obtained. A portion of the samples were directly tested, and the remaining samples were heated at 80°C for 16 hours and then cooled to room temperature for later use. A sample without the treatment agent of this invention was set as a blank control.

[0054] The performance of the product before and after hot rolling at 80°C for 16 hours under calcium contamination conditions was tested using a six-speed viscometer and an API filtration meter. The results are shown in Table 1.

[0055] Table 1. Compatibility and salt resistance tests of polymer treatment agents and drilling fluid systems.

[0056]

[0057] As can be seen from Table 1, at 25000 mg / L Ca 2+ Under contaminated conditions, the rheological properties of drilling fluid without the treatment agent of this invention decreased significantly after being hot-rolled at 80°C for 16 hours, while the API filtration loss increased significantly, indicating that high concentrations of Ca... 2+Contamination can severely damage the colloidal stability and filtration loss control of drilling fluid systems. After adding the film-forming and chelating bifunctional polymer treatment agent of this invention, the drilling fluid systems in Examples 1-6 all exhibited good rheological retention and filtration loss reduction effects. In contrast, although Comparative Examples 1-9 showed some improvement compared to the blank drilling fluid, the rheological parameters decreased more significantly after hot rolling, API filtration loss increased, and the overall performance was significantly lower than the examples. These results indicate that suitable polymerization temperature, polymerization time, pH conditions, chelating functional monomer dosage, and the synergistic introduction of hydrophilic amide monomers, stabilizing monomers, and cationic monomers are crucial for improving the treatment agent's performance in high-Ca environments. 2+ Rheological stability and filtration control under contaminated conditions play a crucial role; insufficient or excessive chelating functional monomers, their substitution by non-chelating monomers, and the removal of cationic monomers, hydrophilic amide monomers, or stabilizing monomers all weaken the polymer's resistance to Ca. 2+ It has a stabilizing effect on pollution and a film-forming effect to reduce filtration loss.

[0058] Test 2 To test the plugging performance of the polymer treatment agent synthesized in this invention when added to drilling fluid, the plugging performance of the treatment agent in sand bed medium was tested.

[0059] Preparation of drilling fluid-based slurry: Under stirring conditions, add 8g of sodium-based bentonite to 400mL of water, then add 6% anhydrous sodium carbonate by weight of bentonite. Set the speed to 3000r / min and stir for 30 minutes to fully hydrate the slurry. Let it stand for 24 hours to form a stable colloid, which is the 2% sodium-based bentonite drilling fluid-based slurry. The slurry used in each group of experiments was prepared in this way.

[0060] Preparation of test samples: Add 8g of the polymer treatment agent prepared in the examples or comparative examples to 400mL of drilling fluid-based slurry, stir evenly, and then add calcium chloride to adjust the Ca content in the system. 2+ The contamination concentration was 25000 mg / L. The sample was then hot-rolled at 80°C for 16 hours, cooled to room temperature, and used as a test sample. A sample without the treatment agent of this invention was also provided as a blank control.

[0061] 25000 mg / L Ca was tested using a sand bed plugging instrument. 2+ The sealing performance under contaminated conditions, at 80℃, and after 16 hours of hot rolling was tested. 100-mesh quartz sand was filled into the sand bed tube to simulate a coal and rock reservoir with a pore distribution of about 150 μm. The test was conducted at 0.69 MPa for 30 minutes, and the invasion depth of each sample in the sand bed was recorded. The results are shown in Table 2.

[0062] Table 2. Sand bed plugging performance test of polymer treatment agent

[0063] The results of this test indicate that at 25000 mg / L Ca 2+ Under contaminated conditions, the penetration depth of the base slurry without the treatment agent of this invention increased to 13.2 cm within 30 minutes, indicating that the blank base slurry continuously penetrated the sand bed medium and was unable to form a stable and effective sealing layer at the pores and throats of the sand bed, resulting in weak sealing ability. After adding the film-forming and chelating bifunctional polymer treatment agent of this invention, the penetration depth of Examples 1-6 within 30 minutes was significantly lower than that of the blank base slurry, indicating that the treatment agent of this invention can effectively reduce the degree of penetration of drilling fluid in the sand bed medium and improve the sand bed sealing performance of the system. In contrast, although Comparative Examples 1-9 showed some improvement compared to the blank base slurry, their overall sand bed sealing performance was lower than that of the Example Group. Among them, the sealing performance of the treatment agents obtained by Comparative Examples 1 and 2 decreased due to deviations in polymerization temperature or polymerization time from the preferred conditions; the sealing performance of the treatment agents obtained by Comparative Examples 3 and 6 decreased due to excessively low or high dosage of chelating functional monomers. 2+ The stabilizing effect of the contamination system was weakened; Comparative Examples 4, 7, and 8, due to the lack of cationic monomers, amide monomers, or stabilizing monomers, respectively, resulted in reduced adsorption, spreading, and film-forming abilities of the polymers on the sand bed surface and at the pore throats; Comparative Example 9, using a non-chelating monomer to replace the chelating functional monomer, failed to fully utilize the synergistic effect of chelation stabilization and film-forming blocking, thus resulting in a relatively large penetration depth at 30 min. These results indicate that the chelating functional unit, cationic unit, amide unit, and stabilizing unit in the treatment agent of this invention have a synergistic effect, enabling the stabilization of Ca... 2+ The stable control of contaminant ions and their adsorption and film-forming effect on the surface and throat of the sand bed form a relatively dense sealing layer, thereby effectively inhibiting the continuous intrusion of drilling fluid into the porous medium and improving the sealing performance of drilling fluid in sand beds under high calcium contamination conditions.

[0064] Test 3 To test the inhibitory effect of the film-forming-chelating bifunctional polymer treatment agent solution synthesized in this invention on the hydration and dispersion of coal and rock cuttings, a comparative experiment was conducted on the rolling recovery of the single agent solution and the recovery with clean water.

[0065] Coal and rock samples that passed through a 10-mesh sieve and were retained on a 20-mesh sieve were dried in an 80℃ oven for 12 hours before use. Approximately 20g of coal and rock sample was weighed from each group and recorded as the initial mass before recovery. The test solution was prepared as follows: 12g of the polymer treatment agent prepared in the examples or comparative examples was weighed and added to 400mL of water. The mixture was stirred on a high-speed (3000r / min) stirrer for 30 minutes to obtain each test sample; another 400mL of water was used as a blank control group. The weighed coal and rock samples were placed in aging tanks containing each test sample and aged by rolling at 120℃ for 16 hours. After rolling, the coal and rock samples were filtered through a 40-mesh sieve and rinsed three times with water. The recovered coal and rock samples were then dried in an 80℃ oven for 12 hours, weighed, and recorded as the recovered mass. Coal and rock sample recovery rate (%) = (mass of recovered coal and rock sample / mass of coal and rock sample before recovery) × 100%.

[0066] Table 3 Comparison of experimental results between rolling recovery of treatment agent solution and water recovery

[0067] As shown in Table 3, the recovery rate of coal and rock fragments in the clear water group was low, indicating that coal and rock cuttings are prone to hydration and dispersion under rolling aging conditions at 120℃. After adding the single-agent solution of the film-forming-chelating bifunctional polymer treatment agent of this invention, the recovery rates of coal and rock fragments in Examples 1-6 were significantly improved. In contrast, the recovery rates of Comparative Examples 1-9 were generally lower than those of Examples 1-6, indicating that the change in conditions weakened the inhibitory effect of the obtained polymer on coal and rock cuttings. The above results indicate that the film-forming-chelating bifunctional polymer treatment agent of this invention can improve the rolling recovery rate of coal and rock cuttings and inhibit coal and rock hydration and dispersion through the synergistic effects of chelation stabilization, interfacial adsorption, and film-forming protection, thereby contributing to improved wellbore stability.

Claims

1. A method for preparing a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluids, characterized in that, The steps include the following: (1) Add an epoxy-containing monomer to an aqueous solution of an aminocarboxylate and react; after the reaction is completed, purify the solution to obtain a chelating functional monomer; the aminocarboxylate is one of the sodium or potassium salt of iminodiacetic acid or the sodium or potassium salt of iminodisuccinic acid; the epoxy-containing monomer is glycidyl methacrylate; the molar ratio of the epoxy-containing monomer to the aminocarboxylate is 1~1.2:1; (2) Add the anionic monomer, amide monomer, stabilizing monomer, cationic monomer, and the chelating functional monomer obtained in step (1) to water, stir evenly to obtain a monomer solution; adjust the pH of the monomer solution to 6-8, remove oxygen by purging with nitrogen, add an initiator, and carry out the reaction; after the reaction is completed, precipitate, wash, and dry to obtain a film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid; the anionic monomer is one or more of 2-acrylamide-2-methylpropanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, vinyl sulfonic acid, sodium vinyl sulfonate, or sodium styrene sulfonate; the amide monomer is one or more of acrylamide, methacrylamide, and N,N-dimethylacrylamide; the stabilizing monomer is N-vinylpyrrolidone, N- The reaction mixture comprises one or more of vinylcaprolactam and acrylomorpholine; the cationic monomer is one or more of diallyl dimethyl ammonium chloride, methacryloyloxyethyl trimethyl ammonium chloride, and acryloyloxyethyl trimethyl ammonium chloride; the monomer solution comprises the following molar amounts of monomers: 35-45 parts of anionic monomer, 15-25 parts of amide monomer, 10-20 parts of stable monomer, 5-12 parts of cationic monomer, and 10-18 parts of chelating functional monomer; the initiator is ammonium persulfate or potassium persulfate, and the mass of the initiator is 0.5-3.0% of the total mass of the anionic monomer, amide monomer, stable monomer, cationic monomer, and chelating functional monomer; the reaction temperature is 55-75℃, and the reaction time is 4-8 h.

2. The method for preparing the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid according to claim 1, characterized in that, In step (1), the ratio of the number of moles of aminocarboxylate to the volume of water in the aqueous solution of aminocarboxylate is 1 mol: 0.5~1.5 L; The aminocarboxylic acid salt aqueous solution is obtained by adding an aminocarboxylic acid compound to water, followed by neutralization with an alkali; or by dissolving an aminocarboxylic acid salt in water; the aminocarboxylic acid compound is iminodiacetic acid or iminodisuccinic acid, the molar ratio of the aminocarboxylic acid compound to the volume of water is 1 mol: 0.5~1.5 L, the alkali is sodium hydroxide or potassium hydroxide, the molar ratio of the alkali to the carboxyl group in the aminocarboxylic acid compound is 1:1, the neutralization temperature is 18~24℃, and the neutralization time is 25~30 min.

3. The method for preparing the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid according to claim 1, characterized in that, The reaction temperature in step (1) is 60~70℃ and the reaction time is 1~2h.

4. The method for preparing the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid according to claim 1, characterized in that, The purification process described in step (1) is as follows: the obtained reaction solution is poured into acetone for precipitation, then filtered to obtain the precipitate. The volume ratio of acetone to the molar number of aminocarboxylate is 3~8L:1mol. Dissolve the precipitate obtained by filtration in water, then add acetone to precipitate it, and then filter it. Repeat the water dissolution-acetone precipitation-filtration steps 1 to 3 times. Each time, the ratio of the volume of water used for dissolution to the molar number of aminocarboxylate is 0.5 to 5 L: 1 mol, and the volume of acetone used for each acetone precipitation is 3 to 8 times the volume of water used for dissolution. Finally, the precipitate is vacuum dried at 40 to 60 °C to constant weight.

5. The method for preparing the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid according to claim 1, characterized in that, In step (2), the monomer solution contains the following molar amounts of monomers: 40 parts of anionic monomer, 20 parts of amide monomer, 15 parts of stable monomer, 10 parts of cationic monomer, and 15 parts of chelating functional monomer. The total mass concentration of anionic monomers, amide monomers, stable monomers, cationic monomers, and chelating functional monomers in the monomer solution is 15-35%.

6. The method for preparing the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid according to claim 1, characterized in that, In step (2), the pH of the monomer solution is adjusted to 6-8 using a sodium hydroxide aqueous solution with a concentration of 20-30 wt%; nitrogen gas is passed through for 20-40 min to remove oxygen.

7. The method for preparing the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid according to claim 1, characterized in that, The precipitation step in step (2) involves adding the reaction solution to a precipitating agent for precipitation. The precipitating agent is anhydrous ethanol and / or acetone, and the volume ratio of the precipitating agent to the reaction solution is 3~8:

1. The washing step involves washing with anhydrous ethanol or acetone 1~3 times. The drying step involves vacuum drying at 40~60℃ to constant weight.

8. The method for preparing the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluid according to claim 7, characterized in that, The precipitant is a mixed solvent of anhydrous ethanol and acetone, wherein the volume ratio of anhydrous ethanol to acetone in the mixed solvent is 0.5 to 3:

1.

9. A film-forming and chelating bifunctional polymer treatment agent for water-based drilling fluids, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluids according to claim 9 in the drilling and completion process of deep coal and gas reservoirs, characterized in that, The specific application method is as follows: Add the film-forming-chelating bifunctional polymer treatment agent for water-based drilling fluids to the drilling fluid or completion fluid at a ratio of 0.5~2.0% relative to the mass of the drilling fluid or completion fluid; the deep coal gas reservoir is Ca... 2+ Medium- and low-temperature deep coal and gas reservoirs with pollution concentration ≤25000mg / L, pH 4~6, coal and rock organic matter content ≥5%, fracture width ≤20μm, temperature 60~120℃, and depth 2000~4000m.

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