Wellbore stabilizer for marine natural gas hydrate formation and preparation method and application thereof

Abstract

The present invention belongs to the technical field of water-based drilling fluid treatment agents for marine natural gas hydrate drilling, and relates to a marine natural gas hydrate formation well wall stabilizer and a preparation method and application. The marine natural gas hydrate formation well wall stabilizer is prepared by free radical copolymerization of tannic acid, dimethyldiallylammonium chloride, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide. The marine natural gas hydrate formation well wall stabilizer described in the present invention can effectively cement muddy loose sandstone clay mineral particles, adhere to cyclopentane hydrate particles, improve the low-temperature rheology of the drilling fluid, improve the stability of the hydrate reservoir and the wellbore, and ensure the safe and smooth progress of the hydrate drilling project; the well wall stabilizer has good wall solidification and inhibition, can effectively improve the wall solidification performance of the artificial hydrate core skeleton, has certain salt resistance and biodegradation rate, and has good environmental protection effect.

Description

Technical Field

[0001] The invention belongs to the technical field of water-based drilling fluid treatment agents for offshore natural gas hydrate drilling, and relates to an offshore natural gas hydrate formation well wall stabilizer and a preparation method and application thereof. Background Art

[0002] The stability of the wellbore in the natural gas hydrate reservoir is crucial for the safe and efficient exploration and development of hydrates, and mechanical-chemical coupling is the key to solving the problem of wellbore instability. Using a wellbore stabilizer with underwater bonding properties to construct a wellbore strengthening water-based drilling fluid can effectively enhance the wellbore stability in the muddy fine silt sand formation in the sea area.

[0003] The existing technology has not been able to improve the bonding strength between clay minerals and sandstone particles, has not been able to enhance the cohesion between hydrate particles and between hydrates and rock mineral particles, and has not been able to improve the structural stability of the hydrate particles themselves. It has not yet effectively solved the problem of wellbore instability in natural gas hydrate reservoirs and cannot meet the needs of safe and efficient drilling of natural gas hydrates.

[0004] Therefore, developing a drilling fluid additive that can improve the bonding strength between clay minerals and sandstone particles and enhance the cohesion between hydrate particles and between hydrates and rock mineral particles is one of the key technologies to ensure the stability of wellbore and safe and efficient drilling and production of natural gas hydrate reservoirs in offshore areas, and is worthy of further study. Summary of the invention

[0005] The purpose of the present invention is to provide a marine natural gas hydrate formation wellbore stabilizer and its preparation method and application in view of the shortcomings of the existing drilling fluid wellbore stabilizer technology. The wellbore stabilizer of the present invention can effectively cement clay mineral particles, effectively inhibit the hydration, dispersion and expansion of clay mineral particles, and can effectively bind hydrate particles, which is beneficial to enhance the wellbore stability of hydrate mud fine silt reservoir and improve the safety during hydrate drilling and production.

[0006] The sea area natural gas hydrate formation well wall stabilizer of the present invention is prepared by free radical copolymerization of tannic acid, dimethyl diallyl ammonium chloride, 2-acrylamide-2-methylpropane sulfonic acid and acrylamide; it comprises the following raw materials by mass: 1-10 parts of tannic acid, 5-50 parts of dimethyl diallyl ammonium chloride, 2-20 parts of 2-acrylamide-2-methylpropane sulfonic acid, 5-50 parts of acrylamide, 0.2-2 parts of initiator. Preferably, 1-5 parts of tannic acid, 5-30 parts of dimethyl diallyl ammonium chloride, 2-10 parts of 2-acrylamide-2-methylpropane sulfonic acid, 5-30 parts of acrylamide, and 0.2-1.5 parts of initiator. The initiator is potassium persulfate.

[0007] In the present invention, tannic acid not only provides bionic mussel adhesion, but also forms a strong adhesion layer between fine sand and muddy particles for the special strata of weakly cemented fine sand and muddy hydrate encountered during drilling, effectively slowing down the sand production rate of the wellbore and the risk of well wall peeling. Tannic acid improves the overall adhesion of the well wall at a specific content.

[0008] The addition of acrylamide increases the length and strength of the molecular chain, significantly enhancing the adsorption performance and compressive resistance of the wellbore stabilizer. In drilling fluid, acrylamide can form a polymer chain with a higher molecular weight, which produces a tighter cross-linked structure with other components, thereby improving the pressure bearing capacity and stability of the wellbore. The ratio of dimethyldiallylammonium chloride and acrylamide directly affects the cross-linking degree of the polymer network, thereby enhancing the wellbore's anti-collapse ability.

[0009] In the present invention, the AMPS anion monomer is introduced, and the sulfonic acid group provided in the polymer synthesis can significantly enhance the salt resistance of the well wall stabilizer. The reasons are as follows: (1) Strong electron-withdrawing effect: The sulfonic acid group completely dissociates into sulfonate ions and hydrogen ions in aqueous solution, wherein the sulfonate ions have a strong electron-withdrawing effect, so that the sulfonic acid group can form a stable ion pair with the cations in the solution, while reducing the influence of other cations on the polymer structure. (2) Electrostatic repulsion: Since the sulfonic acid group carries a negative charge, electrostatic repulsion will be generated between multiple sulfonic acid groups, thereby resisting the molecular chain contraction or aggregation caused by salt ions. Even in the high-salt environment of the sea, the sulfonic acid group can still maintain the extension and dispersion of the molecular chain through electrostatic repulsion, thereby preventing the polymer from precipitating or losing solubility. Therefore, the well wall stabilizer can have the ability to cement clay mineral particles and inhibit clay hydration and dispersion in both fresh water and 3.5% NaCl aqueous solution.

[0010] The well wall stabilizer described in the present invention is a brown transparent liquid, which is always in liquid state in an underwater environment and can adhere to mineral particles in water. It is an underwater binder and shale inhibitor. It uses the phenolic hydroxyl group with super strong underwater adhesion ability and the ionic bond formed by strong adsorption to have the ability to bind reservoir mineral particles and inhibit clay hydration and dispersion in an underwater environment. The use of the raw materials and proportions described in the present invention not only achieves the effect of sand control and collapse prevention, but also has the ability to adapt to marine drilling environments such as high pressure resistance and salt resistance.

[0011] The well wall stabilizer of the present invention is a copolymer initiated by free radicals.

[0012] The preparation method of the above-mentioned natural gas hydrate reservoir drilling fluid well wall stabilizer is: tannic acid, dimethyldiallylammonium chloride, 2-acrylamido-2-methylpropanesulfonic acid, acrylamide and initiator are fully dissolved in deionized water respectively, mixed evenly, and under the protection of inert gas, the initiator is added, and the well wall stabilizer is obtained through reaction and drying.

[0013] The specific steps are:

[0014] (1) Mix tannic acid and deionized water and adjust the pH value to 7.5 to obtain a tannic acid aqueous solution;

[0015] In this process, the pH value of tannic acid is adjusted to 7.5, which can: (a) improve solubility: tannic acid is more easily dissociated under alkaline conditions to form negatively charged phenol oxide ions, thereby enhancing water solubility and facilitating dissolution; (b) reduce self-condensation reactions: under alkaline conditions, the hydroxyl groups of tannic acid are partially deprotonated, inhibiting their self-condensation or oxidation reactions with other functional groups, thereby maintaining their activity and structural integrity.

[0016] (2) mixing 2-acrylamide-2-methylpropane sulfonic acid with deionized water and adjusting the pH value to 7.0 to obtain an aqueous solution of 2-acrylamide-2-methylpropane sulfonic acid;

[0017] During this process, the pH value of 2-acrylamido-2-methylpropanesulfonic acid was adjusted to 7.0, which can: (a) maintain stability and electrical neutrality: AMPS is relatively stable at neutral pH, and its sulfonic acid group is not easy to dissociate under neutral conditions, which can keep the structure and properties of the monomer unchanged; (b) avoid side reactions: AMPS may cause self-polymerization or other side reactions under acidic or alkaline conditions. A neutral environment can reduce this risk and ensure that it maintains high activity in the reaction system.

[0018] (3) Dimethyldiallyl ammonium chloride and acrylamide are mixed with deionized water to obtain a dimethyldiallyl ammonium chloride aqueous solution and an acrylamide aqueous solution.

[0019] (4) In a protective gas atmosphere and under stirring conditions, the tannic acid aqueous solution, 2-acrylamido-2-methylpropanesulfonic acid aqueous solution, dimethyldiallylammonium chloride aqueous solution and acrylamide aqueous solution are mixed evenly, the temperature is raised to 60°C, an initiator is added, the mixture is stirred and reacted at 70°C-80°C for 7-8h, and then dried to obtain a marine natural gas hydrate formation well wall stabilizer.

[0020] Preferably, the mass fraction of tannic acid in the tannic acid aqueous solution is 1-10%; the mass fraction of 2-acrylamido-2-methylpropanesulfonic acid in the 2-acrylamido-2-methylpropanesulfonic acid aqueous solution is 1-10%; the mass fraction of dimethyldiallylammonium chloride in the dimethyldiallylammonium chloride aqueous solution is 1-30%; and the mass fraction of acrylamide in the acrylamide aqueous solution is 1-30%.

[0021] Preferably, in terms of mass ratio, tannic acid: dimethyldiallylammonium chloride: 2-acrylamido-2-methylpropanesulfonic acid: acrylamide is 3.5:28:7:28.

[0022] Preferably, the mixing temperature of the tannic acid aqueous solution, the dimethyldiallylammonium chloride aqueous solution, the 2-acrylamido-2-methylpropanesulfonic acid aqueous solution and the acrylamide aqueous solution is 15-25° C.; the mixing is carried out under stirring conditions, the stirring rate is 150-250 rpm, and the stirring time is 15-30 minutes.

[0023] Preferably, the protective gas is nitrogen or argon.

[0024] Preferably, the initiator is potassium persulfate.

[0025] Preferably, the mass of the initiator is 0.1%-1.5% of the total mass of tannic acid, dimethyldiallylammonium chloride, 2-acrylamido-2-methylpropanesulfonic acid and acrylamide, preferably 0.5%-1.5%.

[0026] Preferably, the initiator is added when the reaction temperature reaches 60°C; the stirring reaction temperature is 70-85°C, the stirring rate is 200-350rpm, and the stirring reaction time is 7-8h; ethanol is used for washing; the drying time is 36-48h, and the drying temperature is 70-90°C.

[0027] The above-mentioned natural gas hydrate reservoir drilling fluid wellbore stabilizer can be applied to weakly cemented natural gas hydrate reservoir drilling fluid to enhance the bonding strength between clay mineral particles in muddy fine silt reservoir, inhibit clay hydration dispersion and expansion, and bond hydrate particles. It not only achieves the effect of sand prevention and collapse prevention, but also has the ability to adapt to marine drilling environment such as high pressure resistance and salt resistance.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The tannic acid added in the present invention is a bionic material that simulates the function of mussel adhesive protein; tannic acid is rich in phenolic hydroxyl groups, which can be tightly combined with the surface of hydrate particles through hydrogen bonding under wet conditions to form an adhesion layer on the surface of hydrate particles, and can adsorb clay mineral particles in a water environment and cement muddy fine silt sand formations.

[0030] 2. The wellbore stabilizer of the present invention adopts a variety of monomers such as acrylamide, dimethyldiallylammonium chloride, 2-acrylamido-2-methylpropanesulfonic acid, etc. The polymer chain formed by these components contains hydrophilic groups such as hydroxyl groups, amide groups, ammonium ions, etc., which further enhance the adhesion to the hydrate particles; these hydrophilic groups can not only form hydrogen bonds with water molecules on the surface of the hydrate particles, but also improve the adhesion effect through electrostatic adsorption, so that the wellbore stabilizer can be firmly attached to the hydrate particles.

[0031] 3. The natural gas hydrate reservoir well wall stabilizer provided by the present invention introduces sulfonic acid groups to make it salt-resistant and able to have the ability to fix the wall in the marine environment.

[0032] 4. The natural gas hydrate reservoir wellbore stabilizer provided by the present invention has excellent wall-fixing performance and inhibitory properties, and can adhere to hydrate particles without the need for compounding with other shale inhibitors; moreover, the wellbore stabilizer has good wall-fixing and inhibitory properties in both fresh water and 3.5% NaCl aqueous solution.

[0033] 5. The method for preparing a wellbore stabilizer for a natural gas hydrate reservoir provided by the present invention is simple, can be completed in just one step, has low cost, and has a wide range of synthetic raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The appearance morphology of the natural gas hydrate artificial core skeleton immersed in deionized water, polyether solution (a shale inhibitor), the well wall stabilizer aqueous solution prepared in Example 1, the well wall stabilizer aqueous solution prepared in Example 2, and the well wall stabilizer aqueous solution prepared in Example 3;

[0035] Figure 2 It is a linear expansion height diagram of the artificial core in deionized water, polyether solution, the well wall stabilizer aqueous solution prepared in Example 1 and the well wall stabilizer aqueous solution prepared in Example 5. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0037] Meanwhile, the experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents, materials and equipment described are all commercially available unless otherwise specified.

[0038] Tannic acid: analytical grade, 96%, Beijing Inokai Technology Co., Ltd.;

[0039] Dimethyldiallylammonium chloride: analytical grade, 60%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0040] 2-Acrylamide-2-methylpropanesulfonic acid: analytical grade, 99%, Beijing Inokai Technology Co., Ltd.;

[0041] Acrylamide: analytical grade, 98%, Beijing Inokai Technology Co., Ltd.;

[0042] Sodium hydroxide: analytical grade, 98%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0043] Potassium persulfate: analytical grade, 99%, Beijing Inokai Technology Co., Ltd.

[0044] Example 1

[0045] The natural gas hydrate reservoir drilling fluid well wall stabilizer is prepared by including the following raw materials in parts by weight: 3.5g of tannic acid, 28g of dimethyldiallylammonium chloride, 7g of 2-acrylamido-2-methylpropanesulfonic acid, 28g of acrylamide, and 0.67g of initiator.

[0046] The specific preparation steps are:

[0047] (1) 3.5 g of tannic acid and 70 g of deionized water were mixed at 20° C. using NaOH to adjust the pH to 7.5, and stirred at a stirring rate of 150 r / min for 20 minutes to obtain a tannic acid aqueous solution;

[0048] (2) 28 g of dimethyldiallyl ammonium chloride and 70 g of deionized water were uniformly mixed, and stirred for 20 minutes at a stirring rate of 150 r / min and a temperature of 20° C. to obtain a dimethyldiallyl ammonium chloride aqueous solution;

[0049] (3) 7 g of 2-acrylamide-2-methylpropanesulfonic acid and 70 g of deionized water were uniformly mixed, the pH was adjusted to 7 using NaOH under ice bath conditions, and the mixture was stirred for 20 minutes at a stirring rate of 150 r / min to obtain an aqueous solution of 2-acrylamide-2-methylpropanesulfonic acid;

[0050] (4) 28 g of acrylamide and 70 g of deionized water were uniformly mixed, and stirred for 20 minutes at a stirring rate of 150 r / min and a temperature of 20° C. to obtain an acrylamide aqueous solution;

[0051] (5) Under a protective gas atmosphere and stirring conditions, the solutions obtained in steps (1) to (4) were added sequentially into a 500 mL three-necked flask, placed in a constant temperature water bath, and stirred at 20° C. for 15 minutes at a stirring rate of 250 rpm to obtain a monomer mixed solution;

[0052] (6) The temperature was raised to 60°C, and 0.67 g of potassium persulfate initiator was added to the three-necked flask. After the addition was completed, the mixture was kept warm for 7 hours at a stirring rate of 250 r / min, a temperature of 70°C, and nitrogen. After the reaction was completed, the mixture was dried in an electric constant temperature blast drying oven at 80°C for 48 hours to obtain a well wall stabilizer.

[0053] Example 2

[0054] The well wall stabilizer for natural gas hydrate formations in the sea area is prepared by including the following raw materials in parts by weight: 1.75g ​​of tannic acid, 28g of dimethyldiallylammonium chloride, 7g of 2-acrylamido-2-methylpropanesulfonic acid, 28g of acrylamide, and 0.33g of initiator.

[0055] The specific preparation steps are:

[0056] (1) 1.75 g of tannic acid and 70 g of deionized water were mixed at 20° C. using NaOH to adjust the pH to 7.5, and stirred at a stirring rate of 150 r / min for 20 minutes to obtain a tannic acid aqueous solution;

[0057] (2) 28 g of dimethyldiallyl ammonium chloride and 70 g of deionized water were uniformly mixed, and stirred for 20 minutes at a stirring rate of 150 r / min and a temperature of 20° C. to obtain a dimethyldiallyl ammonium chloride aqueous solution;

[0058] (3) 7 g of 2-acrylamide-2-methylpropanesulfonic acid and 70 g of deionized water were uniformly mixed, the pH was adjusted to 7 using NaOH under ice bath conditions, and the mixture was stirred for 20 minutes at a stirring rate of 150 r / min to obtain an aqueous solution of 2-acrylamide-2-methylpropanesulfonic acid;

[0059] (4) 28 g of acrylamide and 70 g of deionized water were uniformly mixed, and stirred for 20 minutes at a stirring rate of 150 r / min and a temperature of 20° C. to obtain an acrylamide aqueous solution;

[0060] (5) Under a protective gas atmosphere and stirring conditions, the solutions obtained in steps (1) to (4) were added sequentially into a 500 mL three-necked flask, placed in a constant temperature water bath, and stirred at 20° C. for 20 minutes at a stirring rate of 250 rpm to obtain a monomer mixed solution;

[0061] (6) The temperature was raised to 60°C, and 0.33 g of potassium persulfate initiator was added to the three-necked flask. After the addition was completed, the mixture was kept warm for 7 hours at a stirring rate of 350 r / min, a temperature of 85°C, and nitrogen. After the reaction was completed, the mixture was dried in an electric constant temperature blast drying oven at 80°C for 48 hours to obtain a well wall stabilizer.

[0062] Example 3

[0063] The well wall stabilizer for natural gas hydrate formations in the sea area is prepared by including the following raw materials in parts by weight: 7g of tannic acid, 28g of dimethyldiallylammonium chloride, 3.5g of 2-acrylamido-2-methylpropanesulfonic acid, 28g of acrylamide, and 0.67g of initiator.

[0064] The specific preparation steps are:

[0065] (1) 7 g of tannic acid and 70 g of deionized water were mixed at 20° C. using NaOH to adjust the pH to 7.5, and stirred at a stirring rate of 150 r / min for 20 minutes to obtain a tannic acid aqueous solution;

[0066] (2) 28 g of dimethyldiallyl ammonium chloride and 70 g of deionized water were uniformly mixed, and stirred for 20 minutes at a stirring rate of 150 r / min and a temperature of 20° C. to obtain a dimethyldiallyl ammonium chloride aqueous solution;

[0067] (3) 3.5 g of 2-acrylamide-2-methylpropanesulfonic acid was uniformly mixed with 70 g of deionized water, the pH was adjusted to 7 using NaOH in an ice bath, and the mixture was stirred for 20 minutes at a stirring rate of 150 r / min to obtain an aqueous solution of 2-acrylamide-2-methylpropanesulfonic acid;

[0068] (4) 28 g of acrylamide and 70 g of deionized water were uniformly mixed, and stirred for 20 minutes at a stirring rate of 150 r / min and a temperature of 20° C. to obtain an acrylamide aqueous solution;

[0069] (5) Under a protective gas atmosphere and stirring conditions, the solutions obtained in steps (1) to (4) were added sequentially into a 500 mL three-necked flask, placed in a constant temperature water bath, and stirred at 20° C. for 30 minutes at a stirring rate of 150 rpm to obtain a monomer mixed solution;

[0070] (6) The temperature was raised to 60°C, and 0.67 g of potassium persulfate initiator was added to the three-necked flask. After the addition was completed, the mixture was stirred at a rate of 200 r / min, the temperature was 70°C, and the reaction was carried out under nitrogen for 8 hours. After the reaction was completed, the mixture was dried in an electric constant temperature blast drying oven at 80°C for 48 hours to obtain a well wall stabilizer.

[0071] Example 4

[0072] A method for preparing a marine natural gas hydrate formation wellbore stabilizer is as described in Example 1, except that the amount of tannic acid used is 1.5 g; the other steps and conditions are consistent with those in Example 1.

[0073] Example 5

[0074] A method for preparing a marine natural gas hydrate formation wellbore stabilizer is as described in Example 1, except that the amount of tannic acid used is 2.5 g; the other steps and conditions are consistent with those in Example 1.

[0075] Example 6

[0076] A method for preparing a marine natural gas hydrate formation wellbore stabilizer is as described in Example 1, except that the amount of tannic acid used is 7 g; the other steps and conditions are consistent with those in Example 1.

[0077] Example 7

[0078] A method for preparing a marine natural gas hydrate formation wellbore stabilizer is as described in Example 1, except that the amount of initiator used is 1.33 g; the other steps and conditions are consistent with Example 1.

[0079] Comparative Example 1

[0080] Prepare 400mL of drilling fluid system, the formula of the drilling fluid system is: seawater + 5% KCl + 0.8% PAC (filtration reducer) + 0.1% XC (xanthan gum) + 3% white asphalt (plugging agent) + 5% CaCO3 (plugging agent) + 1% AL (hydrate decomposition inhibitor) + 1% polyvinyl pyrrolidone (PVP) + 3% hollow glass microspheres.

[0081] Test Example 1

[0082] Prepare 400 mL of drilling fluid system, the formula of the drilling fluid system is: seawater + 5% KCl + 0.8% PAC (filtration reducer) + 0.1% XC (xanthan gum) + 3% white asphalt (plugging agent) + 5% CaCO3 (plugging agent) + 1% AL (hydrate decomposition inhibitor) + 1% polyvinyl pyrrolidone (PVP) + 3% hollow glass microspheres + 2% wellbore stabilizer prepared in Example 1, the prepared drilling fluid density is 1.03 g / cm 3 .

[0083] The prepared drilling fluid was subjected to low temperature and high pressure rheological and conventional performance tests to evaluate the compatibility of the wellbore stabilizer in the water-based drilling fluid. The low temperature and high pressure rheological parameters and API filtration loss of the drilling fluids prepared in Comparative Example 1 and Example 1 were tested using an ultra-low temperature and ultra-low speed static gel rheometer, and the results are shown in Table 1.

[0084] Table 1 Rheological filtration test of the drilling fluids prepared in Example 1 and Comparative Example 1

[0085] .

[0086] It can be seen from Table 1 that under the influence of the wellbore stabilizer of the present invention, the apparent viscosity of the drilling fluid increases slightly, the dynamic shear force is significantly improved, and the filtration loss is reduced, so that the drilling fluid has good rheological properties, and the wellbore stabilizer has good compatibility with other treatment agents of the drilling fluid.

[0087] Test Example 2

[0088] The wall-fixing performance of the well wall stabilizers prepared in Example 1, Example 2 and Example 3 was tested and compared with deionized water and polyether solution.

[0089] The specific test steps are as follows:

[0090] Core Soak Test:

[0091] At 5° C., the natural gas hydrate artificial core skeleton was immersed in deionized water, polyether solution (a shale inhibitor) or 2% aqueous solution of the wellbore stabilizer prepared in Example 1, Example 2 and Example 3 for 24 hours, and the appearance of the artificial core skeleton was observed.

[0092] observe Figure 1 It can be concluded that a large number of clay mineral particles fell off and disintegrated in the core skeleton in the deionized water and polyether solution; the core did not foam and disperse in the well wall stabilizer solution of Example 1, and the core shape was still intact;

[0093] A small amount of clay mineral particles fell off and disintegrated in the well wall stabilizer aqueous solution prepared in Example 2 and Example 3, but it still did not affect the use. Compared with other solutions, the well wall stabilizer solution of the present invention showed superiority in maintaining the integrity of the core structure.

[0094] Linear expansion test:

[0095] The linear expansion test can quantitatively evaluate the ability of the wellbore stabilizer to inhibit hydration expansion. The specific test steps are as follows: at room temperature, the artificial core is immersed in deionized water, 1% polyether aqueous solution, 1% wellbore stabilizer aqueous solution prepared in Example 1, or 1% wellbore stabilizer aqueous solution prepared in Example 5, and the artificial core is monitored for 16 hours at room temperature and pressure using a shale dual-channel expansion instrument. The results are as follows: Figure 2 shown.

[0096] Depend on Figure 2 It can be concluded that compared with deionized water and polyether solution, the well wall stabilizers in Example 1 and Example 5 significantly reduced the swelling height of clay. Among them, the swelling heights of deionized water, polyether, Example 5 and Example 1 are 3.49 mm, 2.99 mm, 1.57 mm and 1.3 mm, respectively. This is because the cations and hydrogen atoms in the well wall stabilizer described in the present invention and the negative charges on the surface of the clay mineral produce strong chemical adsorption due to electrostatic and hydrogen bonding, so that ionic bonds and hydrogen bonds are formed between the polymer and the clay mineral particles, thereby better inhibiting the hydration of the clay particles.

[0097] Core compressive strength test:

[0098] The core compressive strength test was conducted by placing the natural gas hydrate artificial standard core skeleton in a beaker at 5°C, and soaking the core in clean water and the wellbore stabilizer aqueous solution prepared in Examples 1-6 for 24 hours. Then, the core compressive strength was tested at room temperature using a dynamic rock strength evaluation system, and the results are shown in Table 2:

[0099] Table 2

[0100] .

[0101] It can be seen from Table 2 that the well wall stabilizer of the present invention improves the compressive strength of the core. By analyzing the failure load-deformation of the core, it can be seen from the deformation data that the artificial core, after being treated with the well wall stabilizer aqueous solution prepared by the present invention, shows higher compressive strength and lower deformation, that is, the core can resist pressure more effectively without breaking or deforming. This is because the well wall stabilizer enhances the bonding force between particles by chemical adsorption with the core particles, reduces the hydration of clay, and thus improves the overall stability and compressive resistance of the core. Among them, after the artificial core is treated with the well wall stabilizer aqueous solution prepared in Example 1, the deformation is the smallest when the peak strength reaches 1.93 MPa, which is only 0.296 mm.

Claims

1. A marine natural gas hydrate formation wellbore stabilizer, characterized in that: The method comprises the following raw materials in parts by weight: 1-10 parts of tannic acid, 5-50 parts of dimethyldiallylammonium chloride, 2-20 parts of 2-acrylamido-2-methylpropanesulfonic acid, 5-50 parts of acrylamide, and 0.2-2 parts of an initiator; The specific preparation steps are: (1) Mix tannic acid and deionized water and adjust the pH value to 7.5 to obtain a tannic acid aqueous solution; (2) mixing 2-acrylamide-2-methylpropane sulfonic acid with deionized water and adjusting the pH value to 7.0 to obtain an aqueous solution of 2-acrylamide-2-methylpropane sulfonic acid; (3) mixing dimethyldiallyl ammonium chloride and acrylamide with deionized water respectively to obtain a dimethyldiallyl ammonium chloride aqueous solution and an acrylamide aqueous solution; (4) In a protective gas atmosphere and under stirring conditions, the tannic acid aqueous solution, 2-acrylamido-2-methylpropanesulfonic acid aqueous solution, dimethyldiallylammonium chloride aqueous solution and acrylamide aqueous solution are mixed evenly, the temperature is raised to 60°C, an initiator is added, the mixture is stirred and reacted at 70°C-80°C for 7-8h, and then dried to obtain a marine natural gas hydrate formation well wall stabilizer.

2. The marine natural gas hydrate formation wellbore stabilizer according to claim 1, characterized in that: The method is prepared by comprising the following raw materials in parts by weight: 1-5 parts of tannic acid, 5-30 parts of dimethyldiallylammonium chloride, 2-10 parts of 2-acrylamide-2-methylpropanesulfonic acid, 5-30 parts of acrylamide and 0.2-1.5 parts of initiator.

3. The marine natural gas hydrate formation wellbore stabilizer according to claim 1, characterized in that: The initiator is potassium persulfate.

4. The marine natural gas hydrate formation wellbore stabilizer according to claim 1, characterized in that: The mass fraction of tannic acid in the tannic acid aqueous solution is 1-10%.

5. The marine natural gas hydrate formation wellbore stabilizer according to claim 1, characterized in that: In the aqueous solution of 2-acrylamide-2-methylpropanesulfonic acid, the mass fraction of 2-acrylamide-2-methylpropanesulfonic acid is 1-10%.

6. The marine natural gas hydrate formation wellbore stabilizer according to claim 1, characterized in that: The mass fraction of dimethyldiallylammonium chloride in the dimethyldiallylammonium chloride aqueous solution is 1-30%.

7. The marine natural gas hydrate formation wellbore stabilizer according to claim 1, characterized in that: The mass fraction of acrylamide in the acrylamide aqueous solution is 1-30%.

8. The marine natural gas hydrate formation wellbore stabilizer according to claim 1, characterized in that: In step (4), the stirring rate is 250-350 rpm, the drying time is 36-48 h, and the drying temperature is 70-90° C.

9. Use of the offshore natural gas hydrate formation wellbore stabilizer according to any one of claims 1 to 8 in drilling fluid for weakly cemented natural gas hydrate reservoirs.

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