Scleroglucan microgels, grafted scleroglucan microgels, methods of making the same, and use in water-based drilling fluids

Abstract

The present application provides a scleroglucan microgel, a grafted scleroglucan microgel, a preparation method thereof and an application thereof in a water-based drilling fluid. The method for preparing the scleroglucan microgel comprises the following steps: 1) dissolving scleroglucan and a crosslinking agent in an aqueous alkali solution to obtain an aqueous phase; 2) dissolving an emulsifier in an organic solvent to obtain an oil phase; 3) mixing and emulsifying the aqueous phase and the oil phase to obtain an emulsion; 4) allowing the emulsion to react to obtain a reaction product; and 5) performing demulsification, first precipitation with a first precipitant, first washing with a first washing agent and first drying on the reaction product to obtain the scleroglucan microgel.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemicals, specifically to a sclerosan microgel and a grafted sclerosan microgel. Background Technology

[0002] In oil and gas drilling, wellbore instability in shale formations has always been a major technical challenge, with approximately 90% of wellbore instability incidents occurring in shale formations. As oil and gas drilling in my country gradually expands into deeper formations and shale gas, wellbore instability has become increasingly prominent, severely impacting the smooth progress of exploration and development. Shale formations have high clay mineral content and well-developed micro- and nano-scale pores. The intrusion of water-based fluids easily causes hydration and expansion of clay minerals, leading to the extension and propagation of micro-fractures, resulting in wellbore instability phenomena such as well collapse, necking, and rockfall. Oil-based drilling fluids are often used to alleviate wellbore instability; however, they are costly, have poor environmental performance, and present significant challenges in harmless disposal. Especially with increasingly stringent environmental regulations in my country, their large-scale use is restricted. Therefore, developing water-based drilling fluid plugging materials to effectively seal the nano- and micro-scale pores in shale is a crucial means to prevent drilling fluid filtrate intrusion, inhibit formation pressure transmission, and thus improve wellbore stability.

[0003] Currently, inorganic rigid particles, bituminous compounds, and polymeric alcohol-based plugging agents are commonly used in water-based drilling fluids. Shale formations are predominantly composed of micro- and nano-sized pores. Conventional inorganic rigid particles (such as calcium carbonate) have large particle sizes, making it difficult to form a plug within these pores. Bituminous plugging agents rely on their high-temperature softening and deformation capabilities to form a plug; however, they have poor environmental friendliness and can negatively impact drilling fluid formation. Polymeric alcohol-based plugging agents can hydrophobize at certain temperatures, forming micro- and nano-emulsions to plug micro-fractures, but their plugging strength is relatively low. Therefore, there is an urgent need to develop a drilling fluid plugging agent that is both environmentally friendly and highly efficient in micro- and nano-sized plugging to address wellbore instability in shale formations. Summary of the Invention

[0004] One aspect of the present invention provides a method for preparing sclerodextrin microgels, comprising the following steps:

[0005] 1) Dissolve the dextran and cross-linking agent in an alkaline aqueous solution to obtain an alkaline aqueous phase;

[0006] 2) Dissolve the emulsifier in an organic solvent to obtain the oil phase;

[0007] 3) Mix and emulsify the aqueous phase and the oil phase to obtain an emulsion;

[0008] 4) React the emulsion to obtain the reaction product;

[0009] 5) The reaction product is demulsified, precipitated with a first precipitant, washed with a first detergent, and dried to obtain the hard dextran microgel.

[0010] In one specific embodiment, the molecular weight of the sclerosan is 6 to 10 kDa.

[0011] In one specific embodiment, the crosslinking agent is ethylene glycol diglycidyl ether and / or epichlorohydrin.

[0012] In one specific embodiment, the emulsifier is Span 80 and / or Tween 80.

[0013] In one specific embodiment, the emulsifier is Span 80 and Tween 80 in a mass ratio of (1-3):1.

[0014] In one specific embodiment, the organic solvent is at least one selected from liquid paraffin, n-hexane, and cyclohexane.

[0015] In one specific embodiment, the precipitant is methanol and / or ethanol.

[0016] In one specific embodiment, the detergent used for the first washing is water.

[0017] In one specific embodiment, in step 4), the reaction occurs at a temperature of 60°C to 70°C for a duration of 5 to 6 hours.

[0018] In one specific embodiment, in step 5), the temperature of the first drying is 40°C to 50°C, and the drying time is 5 to 8 hours.

[0019] In one specific embodiment, the mass ratio of the sclerosotan to the crosslinking agent is 1:(0.7-1.2).

[0020] In one specific embodiment, the mass / volume ratio of the sclerosan to the aqueous solution of the alkali is 1:(67-100).

[0021] In one specific embodiment, the concentration of the alkali in the aqueous solution is 0.1 to 0.5 mol / L.

[0022] In one specific embodiment, the mass / volume ratio of the emulsifier to the organic solvent is (0.02-0.05):1.

[0023] In one specific embodiment, the volume ratio of the aqueous phase to the oil phase is 3:7 to 1:1.

[0024] In one specific embodiment, the volume ratio of the reaction product to the precipitant is 1:1 to 1:10.

[0025] The second aspect of this invention provides a method for preparing grafted sclerodeon microgels, comprising the following steps:

[0026] I) Disperse the sclerodecane microgel prepared by the method according to any one of the present invention in water to obtain a dispersion;

[0027] II) After deoxygenating the dispersion, the temperature is raised, and then an initiator is added for pre-initiation to obtain a pre-initiated solution;

[0028] III) Add the first grafting monomer and the second grafting monomer to the pre-initiating solution, and obtain the reaction product after the reaction.

[0029] IV) The reaction product was precipitated with a second precipitant to obtain a precipitated product;

[0030] V) The precipitate is washed with a second detergent, dried, and ground to obtain the grafted glucan microgel.

[0031] In one specific embodiment, the initiator is ammonium persulfate and / or potassium persulfate.

[0032] In one specific embodiment, the first grafting monomer is at least one of N-isopropylacrylamide, N-tert-butylacrylamide, and N,N-diethylacrylamide.

[0033] In one specific embodiment, the second grafting monomer is methacryloyloxyethyltrimethylammonium chloride and / or dimethyldiallylammonium chloride.

[0034] In one specific embodiment, the second precipitant is methanol and / or ethanol.

[0035] In one specific embodiment, the second detergent is water.

[0036] In one specific embodiment, the ratio of the total mass of the first grafted monomer and the second grafted monomer to the mass of the hard dextran microgel is (3-5):1.

[0037] In one specific embodiment, the molar ratio of the first grafting monomer to the second grafting monomer is (7-9):1.

[0038] In one specific embodiment, the amount of the initiator is 0.675% to 1% of the total mass of the first graft monomer and the second graft monomer.

[0039] In one specific embodiment, the volume ratio of the reaction product to the second precipitant is 1:1 to 1:10.

[0040] In one specific embodiment, in step II), the temperature is raised to 65°C to 70°C; the pre-initiation time is 5 min to 10 min.

[0041] In one specific embodiment, in step III), the reaction temperature is 65°C to 70°C, and the reaction time is 4h to 5h.

[0042] In one specific embodiment, in step V), the temperature of the first drying is 40°C to 50°C, and the drying time is 5 to 8 hours.

[0043] The third invention provides a composition comprising drilling fluid and the grafted sclerodeum microgel prepared by the method as described in any one of the second inventions.

[0044] The fourth invention provides the application of the grafted dextran microgel prepared by the method according to any one of the second invention or the composition described in the third invention for pore sealing; particularly for the application in the sealing of micro and nanopores in shale.

[0045] The beneficial effects of this invention are:

[0046] The grafted sclerodecanol microgel particles prepared in this invention exhibit temperature-sensitive and reversible size characteristics. Specifically, when dispersed in a liquid medium at room temperature (25°C), their average particle size is between 120 and 230 nm, placing them at the micro-nano scale, which is beneficial for their entry into the micro-nano pores of shale. When the medium is heated by the formation temperature to reach the response temperature of 65°C, the micro-nano particles, upon entering the micro-nano pores of shale, transform into larger deformable supramolecular aggregates, thereby forming a rapid and effective adaptive seal for the pores and improving the sealing performance of the drilling fluid. Furthermore, the interaction between the grafted sclerodecanol microgel and bentonite can improve the quality of the mud cake, further demonstrating the beneficial effect of the grafted sclerodecanol microgel on improving the sealing performance of drilling fluid. Moreover, sealing experiments have confirmed that it can adaptively form a tight sealing layer in micropores at temperatures above 65°C, achieving a core sealing rate of over 94%. Detailed Implementation

[0047] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0048] Example 1

[0049] 1) Dissolve 1g of 6kDa hard dextran and 1.2g of ethylene glycol diglycidyl ether in 100mL of 0.2mol / L sodium hydroxide aqueous solution to obtain an aqueous phase;

[0050] 2) Dissolve 3.11g of Span 80 and 1.55g of Tween 80 in 233mL of liquid paraffin to obtain the oil phase;

[0051] 3) Under stirring conditions of 300 r / min, the aqueous phase was added to the oil phase at a volume ratio of 40:60. The mixture was then subjected to high-speed shearing at 10000 r / min for 30 min and ultrasonic fine emulsification at 20 kHz and 500 W for 8 min to obtain the emulsion.

[0052] 4) Place the emulsion into the reactor, heat it to 65°C, and react for 5 hours to obtain the reaction product;

[0053] 5) Centrifuge the reaction product at 15000 r / min for 10 min to break the emulsion, add ethanol at a volume ratio of 1:1 to precipitate, then wash the precipitate repeatedly with deionized water until neutral, and finally place it in a vacuum drying oven at 50℃ for 6 h to obtain hard dextran microgel.

[0054] Example 2

[0055] 1) Dissolve 1g of 8kDa hard dextran and 1g of ethylene glycol diglycidyl ether in 83mL of 0.2mol / L sodium hydroxide aqueous solution to obtain an aqueous phase;

[0056] 2) Dissolve 1.86g Span 80 and 1.86g Tween 80 in 124mL of liquid paraffin to obtain the oil phase;

[0057] 3) Under stirring conditions of 300 r / min, the aqueous phase was added to the oil phase at a volume ratio of 40:60. The emulsion was then subjected to high-speed shearing at 10000 r / min for 40 min and ultrasonic fine emulsification at 20 kHz and 500 W for 8 min to obtain the emulsion.

[0058] 4) Place the emulsion into the reactor, heat it to 65°C, and react for 5 hours to obtain the reaction product;

[0059] 5) Centrifuge the reaction product at 15000 r / min for 10 min to break the emulsion, add ethanol at a volume ratio of 1:1 to precipitate, then wash the precipitate repeatedly with deionized water until neutral, and finally place it in a vacuum drying oven at 45℃ for 6 h to obtain hard dextran microgel.

[0060] Example 3

[0061] 1) Dissolve 1g of 10kDa hard dextran and 1g of ethylene glycol diglycidyl ether in 83mL of sodium hydroxide solution (0.2mol / L) to obtain an aqueous phase;

[0062] 2) Dissolve 2.48 g of Span 80 and 1.24 g of Tween 80 in 124 mL of n-hexane to obtain the oil phase;

[0063] 3) Under stirring conditions of 300 r / min, the aqueous phase was added to the oil phase at a volume ratio of 40:60. The mixture was then subjected to high-shear emulsifier at 10000 r / min for 30 min and ultrasonic fine emulsification at 20 kHz and 500 W for 10 min to obtain the emulsion.

[0064] 4) Place the emulsion into the reactor, heat it to 60°C, and react for 5 hours to obtain the reaction product;

[0065] 5) Centrifuge the reaction product at 15000 r / min for 10 min to break the emulsion, add ethanol at a volume ratio of 1:1 to precipitate, then wash the precipitate repeatedly with deionized water until neutral, and finally place it in a vacuum drying oven at 45℃ for 6 h to obtain hard dextran microgel.

[0066] Example 4

[0067] 1) Dissolve 1g of 6kDa hard dextran and 0.7g of ethylene glycol diglycidyl ether in 67mL of 0.2mol / L sodium hydroxide aqueous solution to obtain an aqueous phase;

[0068] 2) Dissolve 2.51g of Span 80 and 0.84g of Tween 80 in 67mL of cyclohexane to obtain the oil phase;

[0069] 3) Under stirring conditions of 300 r / min, the aqueous phase was added to the oil phase at a volume ratio of 40:60. The mixture was then subjected to high-shear emulsifier at 10000 r / min for 30 min and ultrasonic fine emulsification at 20 kHz and 500 W for 10 min to obtain the emulsion.

[0070] 4) Place the emulsion into the reactor, heat it to 70°C, and react for 6 hours to obtain the reaction product;

[0071] 5) Centrifuge the reaction product at 15000 r / min for 10 min to break the emulsion, add methanol at a volume ratio of 1:1 to precipitate, then wash the precipitate repeatedly with deionized water until neutral, and finally place it in a vacuum drying oven at 40℃ for 6 h to obtain hard dextran microgel.

[0072] Example 5

[0073] 1) Take 1g of the sclerosan microgel prepared in Example 1 and disperse it in 30mL of deionized water to obtain a dispersion;

[0074] 2) Purge the dispersion with nitrogen gas to remove oxygen for 30 min, raise the temperature to 65℃, add 0.05 g of ammonium persulfate for pre-initiation for 10 min, and obtain the pre-initiation solution;

[0075] 3) Add 4.15g N-isopropylacrylamide and 0.85g methacryloyloxyethyltrimethylammonium chloride to the pre-initiator solution, and react at 65℃ for 5h to obtain the reaction product;

[0076] 4) Ethanol was added to the reaction product at a volume ratio of 1:1 to precipitate the product and obtain the precipitate.

[0077] 5) The precipitate was washed 5 times with deionized water, dried under vacuum at 50°C for 6 hours, and then ground to obtain the grafted glucan microgel.

[0078] Example 6

[0079] 1) Take 1g of the sclerosan microgel prepared in Example 2 and disperse it in 25mL of deionized water to obtain a dispersion;

[0080] 2) Purge the dispersion with nitrogen gas to remove oxygen for 30 min, raise the temperature to 65℃, add 0.032 g of ammonium persulfate for 8 min to pre-initiate, and obtain the pre-initiated solution;

[0081] 3) Add 3.25g N-isopropylacrylamide and 0.75g methacryloyloxyethyltrimethylammonium chloride to the pre-initiator solution, and react at 65℃ for 5h to obtain the reaction product;

[0082] 4) Add ethanol to the reaction product to precipitate the product and obtain the precipitate.

[0083] 5) The precipitate was washed three times with deionized water, dried under vacuum at 45°C for 6 hours, and then ground to obtain the grafted glucan microgel.

[0084] Example 7

[0085] 1) Take 1g of the sclerosan microgel prepared in Example 3 and disperse it in 25mL of deionized water to obtain a dispersion;

[0086] 2) Purge the dispersion with nitrogen gas to remove oxygen for 30 min, raise the temperature to 65℃, add 0.032 g of potassium persulfate for 5 min to pre-initiate, and obtain the pre-initiated solution;

[0087] 3) Add 3.45g N-tert-butylacrylamide and 0.75g dimethyldiallylammonium chloride to the pre-initiator solution, and react at 65℃ for 4h to obtain the reaction product;

[0088] 4) Ethanol was added to the reaction product at a volume ratio of 1:1 to precipitate the product and obtain the precipitate.

[0089] 5) The precipitate was washed four times with deionized water, dried under vacuum at 45°C for 6 hours, and then ground to obtain the grafted glucan microgel.

[0090] Example 8

[0091] 1) Take 1g of the sclerosan microgel prepared in Example 4 and disperse it in 20mL of deionized water to obtain a dispersion;

[0092] 2) Purge the dispersion with nitrogen gas to remove oxygen for 30 min, heat to 70℃, add 0.027 g of potassium persulfate for 5 min to pre-initiate, and obtain the pre-initiated solution;

[0093] 3) Add 2.54 g N,N-diethylacrylamide and 0.46 g dimethyl diallyl ammonium chloride to the pre-initiator solution, and react at 70 °C for 5 h to obtain the reaction product;

[0094] 4) Add methanol to the reaction product at a volume ratio of 1:1 to precipitate the product and obtain the precipitate.

[0095] 5) The precipitate was washed four times with deionized water, dried under vacuum at 40°C for 6 hours, and then ground to obtain the grafted glucan microgel.

[0096] Performance testing

[0097] 1. Particle size test

[0098] The microgels prepared in Examples 5 to 8 were each prepared into 0.1 wt% aqueous dispersions. The hydrodynamic diameter of the microgels in each dispersion was measured at different temperatures using a nanoparticle size analyzer. The test results are shown in Table 1 below.

[0099] Table 1

[0100]

[0101] As shown in Table 1, the microgels prepared in Examples 5 to 8 have an average particle size between 120 and 230 nm at room temperature (25°C), which is at the micro-nano scale and facilitates their entry into the micro-nano pores of shale to form a seal. Upon reaching the response temperature of 65°C, they can self-assemble into supramolecular aggregates. Thus, after entering the micro-nano pores of shale, the micro-nano particles transform into larger supramolecular aggregates, rapidly forming an effective seal and improving the sealing performance of the drilling fluid.

[0102] 2. Drilling fluid performance testing

[0103] First, a 4 wt% bentonite-based slurry was prepared. Then, the microgels prepared in Examples 5 to 8 were added to each slurry to achieve a final concentration of 2 wt%. The resulting test slurries were thoroughly stirred, and their rheological filtration properties after aging at 150°C for 16 hours were evaluated according to the method in GB16783.1-2014. The test results are shown in Table 2 below.

[0104] Table 2

[0105]

[0106] As shown in Table 2, the microgels prepared in Examples 5 to 8 can effectively improve the viscosity and shear strength of bentonite-based slurries. Simultaneously, the drilling fluid filtration loss is significantly reduced after adding the microgels prepared in Examples 5 to 8, indicating that the microgels prepared in Examples 5 to 8 improve mud cake quality and enhance plugging performance through interaction with bentonite.

[0107] 3. Variable Temperature Plugging Performance Test

[0108] Using ultra-low permeability core samples to simulate micro / nano porous media, core flow experiments were conducted. The core permeability (i.e., initial permeability and post-plugging permeability) before and after injection of 2 wt% of the microgel aqueous dispersions prepared in Examples 5 to 8 was measured at different experimental temperatures. The plugging rate was calculated based on the initial permeability and post-plugging permeability to evaluate its plugging performance. The experimental results are shown in Table 3 below.

[0109] Table 3

[0110]

[0111] As can be seen from Table 3, the microgels prepared in Examples 5 to 8 under normal temperature (25℃) conditions could not form an effective sealing layer in the micropores, and the core sealing rate was only about 50%. However, when the response temperature (65℃) was reached, they could adaptively form a tight sealing layer in the micropores, and the core sealing rate reached more than 94%, thus forming a highly efficient sealing in the micro-nano pores of the core.

[0112] While the present invention has been described with reference to specific embodiments, those skilled in the art will understand that various changes can be made without departing from the true spirit and scope of the invention. Furthermore, numerous modifications can be made to the subject, spirit, and scope of the invention to suit specific situations, materials, material compositions, and methods. All such modifications are included within the scope of the claims of the present invention.

Claims

1. A method for preparing grafted sclerodecanol microgels, comprising: First, prepare the sclerodeon microgel according to the following steps: 1) Dissolve the sclerosan and crosslinking agent in an alkaline aqueous solution to obtain an alkaline aqueous phase; the mass ratio of the sclerosan to the crosslinking agent is 1:(0.7-1.2). 2) Dissolve the emulsifier in an organic solvent to obtain the oil phase; 3) The aqueous phase and the oil phase are mixed and emulsified to obtain an emulsion; the volume ratio of the aqueous phase to the oil phase is 3:7 to 1:1; 4) React the emulsion to obtain the reaction product; 5) The reaction product obtained in step 4) is demulsified, precipitated with a first precipitant, washed with a first detergent, and dried to obtain the hard dextran microgel. Then, the grafted scleroglucan microgel was prepared according to the following steps: I) The sclerodecane microgel is dispersed in water to obtain a dispersion; II) After deoxygenating the dispersion, the temperature is raised, and then an initiator is added for pre-initiation to obtain a pre-initiated solution; III) Add a first grafting monomer and a second grafting monomer to the pre-initiating solution, and obtain a reaction product after reaction; wherein, the first grafting monomer is at least one of N-isopropylacrylamide, N-tert-butylacrylamide, and N,N-diethylacrylamide; the second grafting monomer is methacryloyloxyethyltrimethylammonium chloride and / or dimethyldiallylammonium chloride; the ratio of the total mass of the first grafting monomer and the second grafting monomer to the mass of the hard dextran microgel is (3-5):1; the molar ratio of the first grafting monomer to the second grafting monomer is (7-9):1; IV) Precipitate the reaction product obtained in step III) with a second precipitant to obtain a precipitated product; V) Wash the precipitate with a second detergent, dry it, and grind it to obtain the grafted glucan microgel; The grafted sclerodactyl microgel has an average particle size between 120 and 230 nm at room temperature (25°C), and at a response temperature of 65°C, the grafted sclerodactyl microgel self-assembles to form larger deformable supramolecular aggregates.

2. The method according to claim 1, characterized in that, The molecular weight of the sclerosan is 6 to 10 kDa; and / or The crosslinking agent is ethylene glycol diglycidyl ether and / or epichlorohydrin; and / or The emulsifier is Span 80 and / or Tween 80.

3. The method according to claim 1, characterized in that, The emulsifier is Span 80 and Tween 80 in a mass ratio of (1-3):1; and / or The organic solvent is at least one selected from liquid paraffin, n-hexane, and cyclohexane; and / or The first precipitant is methanol and / or ethanol; and / or The first detergent is water.

4. The method according to claim 1, characterized in that, In step 4), the reaction occurs at a temperature of 60°C to 70°C for a time of 5 to 6 hours; and / or In step 5), the temperature of the first drying is 40°C to 50°C, and the drying time is 5 to 8 hours.

5. The method according to claim 1, characterized in that, The mass / volume ratio of the sclerosan to the aqueous solution of the alkali is 1:(67-100). The concentration of the alkali in the aqueous solution is 0.1 to 0.5 mol / L; and / or The mass / volume ratio of the emulsifier to the organic solvent is (0.02-0.05):1; and / or In step 5), the volume ratio of the reaction product to the first precipitant is 1:1 to 1:

10.

6. The method according to claim 1, characterized in that, The initiator is ammonium persulfate and / or potassium persulfate; and / or The second precipitant is methanol and / or ethanol; and / or The second detergent is water.

7. The method according to claim 1, characterized in that, The amount of the initiator is 0.675% to 1% of the total mass of the first graft monomer and the second graft monomer; and / or In step IV), the volume ratio of the reaction product to the second precipitant is 1:1 to 1:

10.

8. The method according to claim 1, characterized in that, In step II), the temperature is increased to 65°C to 70°C; the pre-initiation time is 5 min to 10 min; and / or In step III), the reaction temperature is 65°C to 70°C, and the reaction time is 4 h to 5 h; and / or In step V), the temperature of the second drying is 40°C to 50°C, and the drying time is 5 to 8 hours.

9. A composition comprising drilling fluid and the grafted dextran microgel prepared by the method according to any one of claims 1 to 8.

10. The application of the grafted dextran microgel prepared by the method according to any one of claims 1 to 8 or the composition according to claim 9 in pore sealing.

11. The application of the grafted dextran microgel prepared by the method according to any one of claims 1 to 8 or the composition according to claim 9 in the sealing of micro- and nano-pores in shale.

Images