Well wall stabilizer for fractured formation well drilling as well as preparation method and application of well wall stabilizer

Abstract

The invention relates to a borehole stabilizer for fractured formation drilling and a preparation method and application thereof, and belongs to the technical field of oil exploitation drilling. The borehole wall stabilizer is prepared by polymerizing an anionic monomer methacrylic acid, a cationic monomer dimethyl diallyl ammonium chloride, a nonionic monomer vinyl acetate and an organic silicon monomer vinyltriethoxysilane. Wherein the cationic group and the anionic group are adsorbed on the negatively charged crystal layer surface or the positively charged crystal layer section of the hard brittle mud shale through the electrostatic adsorption effect, and the ester group in the nonionic group and the-Si-OH group on the crystal layer surface of the hard brittle mud shale form stronger hydrogen bond adsorption; and the organic silicon group-Si-OH and the-Si-OH group on the surface of the hard brittle mudstone crystal layer form strong chemical bond (-Si-O-Si-) adsorption. The borehole wall stabilizer can form a relatively strong adsorption coating on the surface of hard and brittle shale, and has a good borehole wall stabilizing effect.

Description

Technical Field

[0001] This invention relates to a wellbore stabilizer for drilling in fractured formations, its preparation method, and its application, belonging to the field of oil drilling technology. Background Technology

[0002] As the exploration and development of complex oil and gas is accelerated both domestically and internationally, drilling depths are gradually increasing, and the complexity of the drilling layers is also gradually rising. Among them, fractured formations have long been a major concern as complex geological bodies in drilling engineering, and safe drilling of them is a major challenge in the drilling field.

[0003] Due to the unique characteristics of fractured formations, over 90% of wellbore instability issues during drilling occur in fractured formations. Fractured formations are characterized by wellbore instability due to wellbore development of microfractures and their hardness and brittleness, making them highly susceptible to wellbore collapse, rockfall, stuck pipe, and other complex downhole situations and accidents. Collapses in deep fractured formations may differ from those in the upper formations. Under the high temperature and pressure at the bottom of the well, the rock in deep formations may experience capillary water absorption, generating high expansion pressure that leads to collapse. To prevent wellbore collapse, methods such as increasing slurry density, inhibiting formation hydration and expansion, and enhancing drilling fluid plugging properties are commonly employed. Pluging and anti-collapse materials, primarily composed of asphalt and modified asphalt, have been developed and have shown some effectiveness in actual drilling. However, due to limited systematic research on the effectiveness of plugging and preventing collapse in fractured formations, certain technical bottlenecks remain. Drilling problems involving collapse and stuck pipe still occur frequently, indicating a lack of fundamental solutions. Therefore, in-depth research is urgently needed to improve the efficiency of drilling fluid in plugging fractured rocks, enhance cementation effectiveness, reduce filtrate penetration and hydration effects of drilling fluid, further improve the support efficiency of the drilling fluid column, and mitigate the risk of collapse in fractured rocks. Summary of the Invention

[0004] The first objective of this invention is to provide a wellbore stabilizer for drilling in fractured formations, in order to address the problem that the wellbore stabilization effect in fractured formations in the prior art needs to be improved.

[0005] The second objective of this invention is to provide a method for preparing a wellbore stabilizer for drilling in fractured formations, in order to address the problem that the wellbore stabilization effect in fractured formations needs to be improved in the prior art.

[0006] The third objective of this invention is to provide an application of a wellbore stabilizer in water-based drilling fluids to address the problem that the wellbore stabilization effect in fractured formations needs improvement in the prior art.

[0007] To achieve the above objectives, the technical solution of the wellbore stabilizer for drilling in fractured formations in this invention is as follows:

[0008] A wellbore stabilizer for drilling in fractured formations, wherein the wellbore stabilizer is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate and vinyltriethoxysilane; wherein the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate and vinyltriethoxysilane is (5-10):(2-4):(7-14):(2-4).

[0009] The beneficial effects of the above technical solution are as follows: The wellbore stabilizer for drilling in fractured formations of the present invention is an anionic, cationic, and nonionic multi-component copolymer, polymerized from anionic monomer methacrylic acid, cationic monomer dimethyl diallyl chloride, nonionic monomer vinyl acetate, and organosilicon monomer vinyltriethoxysilane. The cationic and anionic groups can quickly adsorb onto the negatively charged crystalline surface or positively charged crystalline fracture surface of hard and brittle shale through electrostatic adsorption. The ester groups in the nonionic groups can form a strong hydrogen bond adsorption with the -Si-OH groups on the crystalline surface of hard and brittle shale. Under certain temperature and pressure conditions, the organosilicon groups -Si-OH can form a strong chemical bond (-Si-O-Si-) adsorption with the -Si-OH groups on the crystalline surface of hard and brittle shale. Because the wellbore stabilizer for drilling in fractured formations of the present invention is a high-molecular polymer, it can form a strong "adsorption coating" on the surface of hard and brittle shale, thus exhibiting excellent wellbore stabilization properties.

[0010] To achieve the above objectives, the technical solution of the present invention for preparing a wellbore stabilizer for drilling in fractured formations is as follows:

[0011] A method for preparing a wellbore stabilizer for drilling in fractured formations involves dissolving methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane in water, adjusting the pH to 7-8 with KOH, and then carrying out a polymerization reaction under the action of an initiator.

[0012] The beneficial effects of the above technical solution are as follows: the preparation method of the wellbore stabilizer for drilling in fractured formations according to the present invention is simple to operate, has a wide range of raw material sources, and a high conversion rate, which can effectively reduce the production cost of the product while ensuring wellbore stability. Furthermore, potassium ions can be embedded in the six-membered rings formed by silicon-oxygen tetrahedra on the surface of hard and brittle shale crystal layers, forming a strong electrostatic attraction that dehydrates and compresses the interlayers of shale crystals.

[0013] As a further improvement, the amount of initiator used is 0.009 to 0.015 g per 50 to 100 mmol of the methacrylic acid.

[0014] As a further improvement, the initiator is ammonium persulfate and sodium bisulfite.

[0015] As a further improvement, the mass ratio of ammonium persulfate to sodium bisulfite is 1:(1-2).

[0016] As a further improvement, for every 50–100 mmol of the methacrylic acid, the amount of water used is 80 g.

[0017] As a further improvement, the reaction is carried out at a temperature of 55–75°C for 4–6 hours.

[0018] The beneficial effect of the above technical solution is that the reaction under the above conditions can effectively control the molecular weight of the wellbore stabilizer and obtain a product with better results.

[0019] To achieve the above objectives, the technical solution for the application of a wellbore stabilizer in water-based drilling fluids according to the present invention is as follows:

[0020] Application of a wellbore stabilizer in water-based drilling fluids.

[0021] The beneficial effects of the above technical solution are as follows: When the wellbore stabilizer of the present invention is added to the drilling fluid, it can improve the inhibition and cementing properties of the drilling fluid, resulting in a water-based drilling fluid with anti-collapse properties. The present invention demonstrates, through basic performance testing of the drilling fluid with the added wellbore stabilizer, that the addition of the wellbore stabilizer does not affect the basic performance indicators of the drilling fluid, such as rheological properties and friction. Through tests of anti-swelling rate, radial expansion, underwater overlap shear strength evaluation, and uniaxial compressive strength testing of rock samples, the present invention demonstrates that, compared with existing commercially available wellbore stabilizers, the wellbore stabilizer of the present invention has advantages such as better wellbore stability and stronger temperature resistance. Furthermore, the raw materials are readily available, and the production cost is lower, making it suitable for stabilizing the wellbore in oil drilling in fractured formations, and it has broad application prospects.

[0022] As a further improvement, the wellbore stabilizer has a mass concentration of 0.5% to 5% in the drilling fluid.

[0023] The beneficial effects of the above technical solution are that adding wellbore stabilizer to the drilling fluid within the above-mentioned mass concentration range can achieve good results while reducing production costs to a certain extent. Detailed Implementation

[0024] This invention relates to a wellbore stabilizer for drilling in fractured formations. The wellbore stabilizer is an anionic, cationic, and nonionic multi-component copolymer, polymerized from anionic monomer methacrylic acid, cationic monomer dimethyl diallylamine chloride, nonionic monomer vinyl acetate, and organosilicon monomer vinyltriethoxysilane. The cationic and anionic groups can quickly adsorb onto the negatively charged crystal surface or positively charged crystal fracture surface of hard, brittle shale through electrostatic adsorption. The nonionic ester groups can form a strong hydrogen bond adsorption with the -Si-OH groups on the surface of hard, brittle shale crystals. Under certain temperature and pressure conditions, the organosilicon -Si-OH groups can form a strong chemical bond (-Si-O-Si-) adsorption with the -Si-OH groups on the surface of hard, brittle shale crystals. Potassium ions can embed into the six-membered rings formed by silicon-oxygen tetrahedra on the surface of hard and brittle shale crystal layers, forming a strong electrostatic attraction that dehydrates and compresses the shale crystal layers. In addition, since this wall-stabilizing agent is a high-molecular polymer, it can form a strong "adsorption coating" on the surface of hard and brittle shale, thus having a good effect on stabilizing the wellbore.

[0025] The present invention will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used are all commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0026] Unless otherwise specified, the experimental procedures described in the following embodiments are conventional procedures in the art.

[0027] Unless otherwise specified, the raw materials used in the following embodiments are all conventional commercial products in the art.

[0028] I. Specific Embodiments of the Wellbore Stabilizer for Drilling in Fractured Formations and its Preparation Method of the Present Invention

[0029] Example 1

[0030] The wellbore stabilizer for drilling in fractured formations in this embodiment is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane; the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane is 8:2:12:2; the initiator is ammonium persulfate and sodium bisulfite. The specific preparation method is as follows:

[0031] Weigh 80 mmol of methacrylic acid and 20 mmol of dimethyl diallylamine chloride and dissolve them completely in 80 mL of distilled water to obtain a mixed solution. Weigh 120 mmol of vinyl acetate and 20 mmol of vinyltriethoxysilane and add them to the mixed solution. Slowly add 40% KOH solution to adjust the pH to 7-8. Then slowly purge nitrogen gas into the solution in the flask for 30 minutes. Then add 3 mL of 0.3 wt% initiator solution (the mass ratio of ammonium persulfate to sodium bisulfite in the initiator is 1:1) to initiate polymerization. The reactor is kept at 55°C for 4 hours. After the reaction, a viscous gel-like sample is obtained. After drying and pulverizing, a powdered wellbore stabilizer for formation drilling is obtained.

[0032] Example 2

[0033] This embodiment describes a wellbore stabilizer for drilling in fractured formations. The wellbore stabilizer is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane. The molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane is 6:2:8:2. The initiator is ammonium persulfate and sodium bisulfite. The specific preparation method is as follows:

[0034] 60 mmol of methacrylic acid and 20 mmol of dimethyl diallylamine chloride were weighed and completely dissolved in 80 mL of distilled water to obtain a mixed solution. 80 mmol of vinyl acetate and 20 mmol of vinyltriethoxysilane were weighed and added to the mixed solution. A 40% KOH solution was slowly added dropwise to adjust the pH to 7-8. Nitrogen gas was then slowly introduced into the solution in the flask for 30 minutes. Then, 3 mL of a 0.3 wt% initiator solution (the mass ratio of ammonium persulfate to sodium bisulfite in the initiator was 1:1.25) was added to initiate polymerization. The reactor was kept at 60 °C for 4.5 h. After the reaction, a viscous gel-like sample was obtained. After drying and pulverizing, a powdered wellbore stabilizer for formation drilling was obtained.

[0035] Example 3

[0036] The wellbore stabilizer for drilling in fractured formations in this embodiment is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane; the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane is 10:2:14:2; the initiator is ammonium persulfate and sodium bisulfite. The specific preparation method is as follows:

[0037] 100 mmol of methacrylic acid and 20 mmol of dimethyl diallylamine chloride were weighed and completely dissolved in 80 mL of distilled water to obtain a mixed solution. 140 mmol of vinyl acetate and 20 mmol of vinyltriethoxysilane were weighed and added to the mixed solution. The solution was then slowly added dropwise with a 40% KOH solution to adjust the pH to 7-8. Nitrogen gas was then slowly introduced into the solution in the flask for 30 minutes. 5 mL of a 0.3 wt% initiator solution (with a mass ratio of ammonium persulfate to sodium bisulfite of 1:1.5) was added to initiate polymerization. The reactor was kept at 70 °C for 5 hours. After the reaction, a viscous gel-like sample was obtained. After drying and pulverizing, a powdered wellbore stabilizer for formation drilling was obtained.

[0038] Example 4

[0039] The wellbore stabilizer for drilling in fractured formations in this embodiment is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane; the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane is 5:2:7:2; the initiator is ammonium persulfate and sodium bisulfite. The specific preparation method is as follows:

[0040] Weigh 50 mmol of methacrylic acid and 20 mmol of dimethyl diallylamine chloride and dissolve them completely in 80 mL of distilled water to obtain a mixed solution. Weigh 70 mmol of vinyl acetate and 20 mmol of vinyltriethoxysilane and add them to the mixed solution. Slowly add 40% KOH solution to adjust the pH to 7-8. Then slowly purge nitrogen gas into the solution in the flask for 30 minutes. Then add 5 mL of 0.3 wt% initiator solution (the mass ratio of ammonium persulfate to sodium bisulfite in the initiator is 1:2) to initiate polymerization. The reactor is kept at 75°C for 6 hours. After the reaction, a viscous gel-like sample is obtained. After drying and pulverizing, a powdered wellbore stabilizer for formation drilling is obtained.

[0041] II. Comparative Example

[0042] Comparative Example 1

[0043] The wellbore stabilizer in this comparative example is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and acrylamide; the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and acrylamide is 8:2:12:2; the initiator is ammonium persulfate and sodium bisulfite. The specific preparation method is as described in Example 1.

[0044] Comparative Example 2

[0045] The wellbore stabilizer in this comparative example is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane; the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane is 2:8:5:6; the initiator is ammonium persulfate and sodium bisulfite. The specific preparation method is as described in Example 1.

[0046] Comparative Example 3

[0047] The wellbore stabilizer in this comparative example is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane; the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate, and vinyltriethoxysilane is 4:8:4:8; the initiator is ammonium persulfate and sodium bisulfite. The specific preparation method is as described in Example 1.

[0048] III. Experimental Example: Application of Borehole Stabilizers in Drilling Fluids for Drilling in Fragmented Formations

[0049] The present invention tests the performance of the wellbore stabilizer for drilling in fractured formations according to Example 1. Other examples have the same or similar performance as Example 1.

[0050] Experimental Example 1

[0051] This experimental example tests the anti-swelling rate of wellbore stabilizers used in drilling in fractured formations. The specific implementation procedure is as follows:

[0052] Test method: Weigh 2g of dried bentonite; add it to test tubes containing 20mL of kerosene, distilled water, and the experimental sample solution respectively, and shake well; soak in a water bath at 40℃ for 8 hours; centrifuge at 2000-3000 rpm for 5 minutes; the volume of clay in kerosene is V0, and the volume of clay in distilled water is V1 (the volume of the expanded bentonite can be directly read from the centrifuge). The volumes of clay in the experimental sample solution are V2, V3, V4, etc.

[0053] Calculate the expansion rate:

[0054]

[0055] Expansion prevention rate:

[0056]

[0057] The results of the anti-swelling rate test are shown in Table 1. The data analysis in Table 1 shows that the wellbore stabilizer with a mass concentration of 0.5% for fractured formations has the strongest inhibitory effect, and its anti-swelling rate can reach 90% as measured by centrifugation.

[0058] Table 1 Evaluation of the anti-swelling properties of wellbore stabilizers

[0059]

[0060] Experiment Example 2

[0061] This experimental example uses an indoor radial expansion test method to preliminarily explore the wellbore stabilization performance of wellbore stabilizers for drilling in fractured formations, and compares them with some commonly used shale stabilizers. The specific implementation operation is as follows:

[0062] The rock sample was dried at 105℃±3℃, pulverized, and passed through a 200-mesh sieve. 1.00 g of the rock powder was weighed and placed in a 20.0 mm diameter iron ring, then pressed under a constant pressure of 20.0 MPa for 3 minutes to form a regular mud cake. During the experiment, the small mud cake was placed in the test liquid, and the expansion diameter d of the small mud cake at different times was observed. The radial expansion rate L was calculated. W The experimental results are shown in Table 2.

[0063] Table 2 Results of 24h Radial Expansion Test

[0064]

[0065] Note: (1) " / " indicates that the water condition is used as a reference standard to compare the effects of other stabilizers.

[0066] (2) The expansion diameter d is measured using a standard ruler and compass; Lw = (d-20) / 20.

[0067] Table 5 shows that, at the same concentration, the radial expansion rate of the small mud cake after soaking in the wellbore stabilizer for drilling in this fractured formation for 24 hours was significantly lower than that of some common polymer-based shale stabilizers, such as FA-367, PHPA (partially hydrolyzed polyacrylamide for drilling fluids), and KPAM. Compared to water, the radial expansion rate was reduced by 56.4%.

[0068] Experimental Example 3

[0069] According to the standards "Determination of Tensile Shear Strength of Adhesives" (GB7124-1986) and "Determination of Chemical Resistance of Adhesives" (GB / T13353-92), an aqueous solution of wellbore stabilizer was applied to the single lap surface of the lapped specimen (fractured formation rock cuttings). The lapped specimen was then pressed at 5 MPa for 2 hours, followed by curing in air / water at 50°C for 24 hours. A longitudinal tensile shear force was then applied to the single lap surface of the specimen to test the maximum load the specimen could withstand in air and water. The average shear stress on the lap surface is the actual lap shear strength. Table 3 shows the lap shear strength test results after the application of different chemical wall-stabilizing agents.

[0070] Table 3. Test of overlap shear strength after application of different chemical wellbore stabilizers.

[0071]

[0072] The results showed that wellbore stabilizers for drilling in fractured formations, FA-367, KPAM, and SAS (sulfonated bitumen) had high lap shear strength in air, while wellbore stabilizers for drilling in fractured formations had high lap shear strength in water, reaching 0.206 MPa, while the others had relatively low strength.

[0073] Experiment Example 4

[0074] Rock samples from well J58P47 in Hangjinqi were soaked in well wall stabilizer solutions of different concentrations for 4 hours, carefully removed, and air-dried at room temperature. They were then placed on a triaxial mechanical testing machine to test their compressive strength. The results are shown in Table 4.

[0075] Table 4. Compressive strength of rock samples treated with different wellbore stabilizers

[0076]

[0077]

[0078] Table 4 shows that the uniaxial compressive strength of the dry rock sample was 11.6 MPa, which decreased to 5.71 MPa after soaking in water, a decrease of nearly 50%. Different wellbore stabilizers improved the compressive strength of the rock samples to varying degrees. The effect was most significant after treatment with a 3% wellbore stabilizer for fractured formations, achieving a compressive strength of 8.47 MPa. This indicates that wellbore stabilizers for fractured formations can effectively improve the compressive strength of rock samples after contact with water.

[0079] Experimental Example 5

[0080] This experiment evaluates the basic performance of a water-based drilling fluid containing a wellbore stabilizer for drilling in fractured formations. The specific implementation is as follows: The basic formula is: 100mL water + 4g bentonite + 3g sulfonated lignite resin + 2g sulfonated asphalt + 0.1g FA367 + 0.5g xy-27 + 3g hydrolyzed sodium polyacrylonitrile + 3g ultrafine calcium carbonate + 2g elastic graphite + 2g wellbore stabilizer for drilling in fractured formations. The basic performance is shown in Table 5.

[0081] Table 5. Basic Performance Evaluation of Water-Based Drilling Fluids

[0082]

[0083] As can be seen from Table 5, the mud cake of the water-based drilling fluid with added wellbore stabilizer for drilling in fractured formations is smoother and denser than that of the drilling fluid without added stabilizer. The API filtration loss and high-temperature and high-pressure filtration loss are also smaller, and the friction coefficient is also smaller. Therefore, the water-based drilling fluid with added wellbore stabilizer for drilling in fractured formations prepared in Example X has better performance and can better enhance wellbore stability.

[0084] Experimental Example 6

[0085] This experimental example evaluates the hot roll recovery rate of a water-based drilling fluid with added wellbore stabilizers for drilling in fragmented formations. The specific implementation procedure is as follows:

[0086] Three drilling fluid systems were selected, and rock cuttings from fractured formations in the Wushen Banner Oilfield of Inner Mongolia were used to conduct a shale rolling recovery rate evaluation test (the experimental conditions were rolling at 120℃ for 24 hours). The experimental results are shown in Table 6.

[0087] Table 6 Evaluation of Drilling Fluid Hot Rolling Recovery Rate

[0088]

[0089]

[0090] Note: Common water-based drilling fluid formula: 100mL water: 4g bentonite + 3g sulfonated lignite resin + 2g sulfonated pitch + 0.1g FA367 + 0.5g xy-27 + 3g hydrolyzed polyacrylonitrile sodium salt + 3g ultrafine calcium carbonate;

[0091] Oil-based drilling fluid formulation: 100mL base fluid (oil-water ratio 5# white oil: 20% CaCl2 aqueous solution = 80:20) + 2.5g main emulsifier + 1.5g auxiliary emulsifier HMCOAT + 1.5g wetting agent + 2g CaO + 3g organic clay + 2.5g filtration loss reducer + 0.5g flow pattern modifier.

[0092] As shown in Table 6, the heat recovery rate of water-based drilling fluid with added fractured formation wellbore stabilizer is similar to that of oil-based drilling fluid, but significantly higher than that of ordinary drilling fluid. Therefore, the fractured formation wellbore stabilizer has good temperature resistance and can continue to enhance the wellbore under high temperature conditions.

[0093] Experimental Example 7

[0094] This experimental example evaluates the temperature resistance of water-based drilling fluids containing wellbore stabilizers for drilling in fractured formations. The specific implementation method is as follows:

[0095] Ordinary water-based drilling fluids of different densities were prepared (formulation as described in Experiment 3), and then a wellbore stabilizer for drilling fractured formations with a mass concentration of 5% was added to evaluate their temperature resistance performance. The results are shown in Table 7.

[0096] Table 7 Temperature resistance properties of water-based drilling fluids

[0097]

[0098] Note: Hot rolling aging test conditions: 200℃, 16h.

[0099] As can be seen from Table 7, the performance parameters of ordinary water-based drilling fluids of different densities did not change much before and after aging, indicating that the drilling fluid with added wellbore stabilizer for drilling in fractured formations has good temperature resistance.

[0100] Experimental Example 8

[0101] This experiment compares the performance of the wellbore stabilizers in Example 1 and Comparative Examples 1-3. The anti-swelling rate testing process is as described in Example 1, the hot rolling recovery rate testing process is as described in Example 3, the uniaxial compressive strength testing process is as described in Example 7, and the water-based drilling fluid formulation is as described in Example 2. Specific results are shown in Table 8. Table 8 shows that the mud cake from Example 1 is smooth and dense, with a hot rolling recovery rate of 80.9% and a uniaxial compressive strength of 8.47 MPa, demonstrating a significant improvement in performance compared to the comparative examples.

[0102] Table 8 Comparative Performance Comparison

[0103]

[0104] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A wellbore stabilizer for drilling in fractured formations, characterized in that: The wellbore stabilizer is polymerized from methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate and vinyltriethoxysilane; the molar ratio of methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate and vinyltriethoxysilane is (5-10):(2-4):(7-14):(2-4).

2. A method for preparing a wellbore stabilizer for drilling in fractured formations as described in claim 1, characterized in that: Methacrylic acid, dimethyl diallyl ammonium chloride, vinyl acetate and vinyltriethoxysilane are dissolved in water, and the pH is adjusted to 7-8 with KOH before polymerization is carried out in the presence of an initiator.

3. The method for preparing the wellbore stabilizer for drilling in fractured formations according to claim 2, characterized in that: For every 50–100 mmol of the methacrylic acid, the amount of initiator is 0.009–0.015 g.

4. The method for preparing the wellbore stabilizer for drilling in fractured formations according to claim 3, characterized in that: The initiator is ammonium persulfate and sodium bisulfite.

5. The method for preparing the wellbore stabilizer for drilling in fractured formations according to claim 4, characterized in that: The mass ratio of ammonium persulfate to sodium bisulfite is 1:(1-2).

6. The method for preparing the wellbore stabilizer for drilling in fractured formations according to claim 2, characterized in that: For every 50-100 mmol of the methacrylic acid, the amount of water used is 80 g.

7. The method for preparing the wellbore stabilizer for drilling in fractured formations according to any one of claims 2 to 6, characterized in that: The reaction is carried out at a temperature of 55–75°C for 4–6 hours.

8. The application of the wellbore stabilizer as described in claim 1 in water-based drilling fluids.

9. The application of the wellbore stabilizer according to claim 8 in water-based drilling fluid, characterized in that: The wellbore stabilizer has a mass concentration of 0.5% to 5% in the drilling fluid.

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