Preparation method of a fluid loss additive and application thereof

Abstract

The application provides a preparation method of a fluid loss additive and application thereof, and the preparation method comprises the following steps: under an acidic condition, a silane coupling agent containing a double bond is added dropwise into a graphite dispersion solution to perform a grafting reaction, a silane coupling agent modified graphite is obtained, then a crosslinking agent is added into the silane coupling agent modified graphite, the pH is adjusted to neutral, a first intermediate solution is obtained, acrylamide, a sulfonic acid monomer, a cationic monomer and a monomer containing a cyclic group are mixed, the pH is adjusted to neutral, a second intermediate solution is formed, finally, an initiator is added into the first intermediate solution, the second intermediate solution is added dropwise, and a polymerization reaction is performed to obtain the fluid loss additive. The fluid loss additive prepared by using the method has good high-temperature fluid loss resistance, pressure bearing capacity and plugging capacity.

Description

Technical Field

[0001] The invention belongs to the field of petrochemical industry, and particularly relates to a preparation method of a fluid loss reducer and application thereof. Background Art

[0002] In recent years, oil and gas exploration and development depths have gradually expanded from medium and shallow layers to deep and ultra-deep layers. Safe and efficient exploration and development of deep and ultra-deep oil and gas is of great significance. During drilling in deep and ultra-deep formations, drilling fluid can enter the formation through fractures, causing clay minerals in the formation to hydrate and expand, potentially leading to wellbore instability. This places higher demands on the drilling fluid's fluid loss reduction and plugging properties.

[0003] Fluid loss additives are important treatment agents for reducing liquid intrusion into formations. They are primarily classified into two categories: inorganic and organic. Their mechanisms for reducing liquid intrusion primarily include maintaining finely dispersed clay particles to form a dense mud cake, plugging the mud cake and formation pores, and increasing liquid viscosity. CN111778003A discloses an inorganic fluid loss additive that utilizes a silane coupling agent to disperse and bridge smaller hydroxide particles onto the surface of larger, acidified flake graphite to produce an inorganic particle-modified elastic graphite fluid loss additive. This fluid loss additive is resistant to high temperatures and exhibits high elasticity, but its surface exhibits poor water molecule capture and is unable to deform under high temperatures or pressure differentials, making it difficult to effectively plug formation cracks and pore throats.

[0004] CN114437290A discloses a low-viscosity organic phosphonic acid polymer fluid loss additive. Propylene phosphonic acid monomers and acrylamide monomers are polymerized to produce a low-viscosity organic phosphonic acid polymer fluid loss additive. This fluid loss additive features simple synthetic raw materials, low viscosity increase, and good resistance to calcium and magnesium. However, its high-temperature fluid loss reduction performance needs improvement, its pressure bearing capacity is low, and its plugging capacity is limited.

[0005] These fluid loss additives lack the ability to simultaneously provide high-temperature resistance, fluid loss reduction, pressure bearing capacity, and plugging capabilities, making them difficult to meet the requirements for plugging, fluid loss reduction, and other wall reinforcement requirements in high-temperature, high-pressure formations. Therefore, developing a fluid loss additive with excellent high-temperature resistance, fluid loss reduction, pressure bearing capacity, and plugging capabilities is an urgent technical challenge in this field. Summary of the Invention

[0006] The invention provides a preparation method of a fluid loss reducer. The fluid loss reducer obtained by the preparation method has good high-temperature resistance and fluid loss reduction performance, pressure bearing capacity and blocking capacity.

[0007] The present invention also provides a fluid loss reducer, which has good high-temperature resistance, fluid loss reduction performance, pressure bearing capacity and plugging capacity.

[0008] The present invention also provides a water-based drilling fluid, which contains the above-mentioned fluid loss reducer.

[0009] In a first aspect, the present invention provides a method for preparing a fluid loss additive, comprising:

[0010] 1) under acidic conditions, dropwise adding a silane coupling agent containing a double bond into a graphite dispersion to carry out a grafting reaction to obtain silane coupling agent-modified graphite, then adding a crosslinking agent to the silane coupling agent-modified graphite, and adjusting the pH to neutral to obtain a first intermediate solution;

[0011] 2) mixing acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing a cyclic group and a large side chain, and adjusting the pH to neutral to form a second intermediate solution;

[0012] 3) After adding an initiator to the first intermediate solution, the second intermediate solution is added dropwise to carry out a polymerization reaction to obtain the fluid loss additive.

[0013] The preparation method as described above, wherein the silane coupling agent containing a double bond comprises at least one of γ-methacryloxypropyltrimethoxysilane, vinyltri(methoxyethoxy)silane, and vinyltriethoxysilane; and / or,

[0014] The sulfonic acid monomer includes at least one of 2-acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-1-hydroxy-1-propanesulfonic acid sodium salt, and sodium allylsulfonate; and / or,

[0015] The cationic monomer includes at least one of diallyldimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and diallylamine; and / or,

[0016] The monomer containing a cyclic group and a large side chain includes at least one of vinyl pyrrolidone, allyl polyoxyethylene ether, and methyl allyl polyoxyethylene ether; and / or,

[0017] The initiator includes potassium persulfate.

[0018] The preparation method as described above, wherein the graphite dispersion is prepared by a method comprising the following steps:

[0019] Graphite is dispersed in water, the pH is adjusted to 3-3.5, and ultrasonic dispersion treatment is performed to obtain the graphite dispersion liquid.

[0020] In the preparation method as described above, in the grafting reaction, the mass ratio of the silane coupling agent containing a double bond to the graphite in the graphite dispersion is (1-2):(8-20).

[0021] As described above, in the preparation method, the mass ratio of the cross-linking agent in the first intermediate solution to the acrylamide, sulfonic acid monomer, cationic monomer and monomer containing cyclic group and large side chain in the second intermediate solution is (0.1-0.5): (30-31).

[0022] The preparation method as described above, wherein, in the polymerization reaction, the mass ratio of the initiator, acrylamide, sulfonic acid monomer, cationic monomer and monomer containing a cyclic group and a large side chain is (0.1-0.3): (14-20): (3-6): (2-8): (2-10).

[0023] In the preparation method as described above, the grafting reaction is carried out at a temperature of 40-60° C. and for a time of 4-6 hours.

[0024] The preparation method as described above, wherein, in the polymerization reaction, the temperature is 50-70° C. and the time is 4-8 hours.

[0025] In a second aspect, the present invention provides a fluid loss additive, which is prepared by the preparation method described in the first aspect.

[0026] In a third aspect, the present invention provides a water-based drilling fluid, wherein the water-based drilling fluid includes the fluid loss reducer described in the second aspect.

[0027] The present invention first adds a silane coupling agent containing a double bond dropwise into a graphite dispersion for grafting reaction to obtain silane coupling agent modified graphite, then adds a cross-linking agent, acrylamide, a sulfonic acid monomer, a cationic monomer, and a monomer containing a cyclic group and a large side chain. Under the action of an initiator, acrylamide, a sulfonic acid monomer, a cationic monomer, and a monomer containing a cyclic group and a large side chain are introduced into the surface and pores of the silane coupling agent modified graphite through a polymerization reaction to form a fluid loss reducer with a macromolecular network structure. The fluid loss reducer prepared by the preparation method has strong high-temperature fluid loss resistance, pressure bearing capacity, and sealing capacity. The fluid loss reducer deforms under high-temperature and high-pressure conditions, can adapt to the heterogeneity of the formation, match the different crack shapes of the formation, and effectively inhibit the intrusion of filtrate into the formation. The water-based drilling fluid containing the above-mentioned fluid loss reducer has good rheological properties and high-temperature and high-pressure fluid loss resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a photo of the filter cake formed by the high-temperature and high-pressure (200°C, 3.5MPa) filtration loss test of the water-based drilling fluid in Comparative Example 4 of the present invention after aging at 220°C for 16 hours;

[0029] Figure 2 For the present invention Figure 2This is a photo of the filter cake formed by conducting a high-temperature and high-pressure (200°C, 3.5 MPa) filtration loss test on the water-based drilling fluid in Example 10 after aging at 220°C for 16 hours. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] The present invention provides a method for preparing a fluid loss additive, comprising:

[0032] 1) under acidic conditions, dropwise adding a silane coupling agent containing a double bond into a graphite dispersion to carry out a grafting reaction to obtain silane coupling agent-modified graphite, then adding a crosslinking agent to the silane coupling agent-modified graphite, and adjusting the pH to neutral to obtain a first intermediate solution;

[0033] 2) mixing acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing a cyclic group and a large side chain, and adjusting the pH to neutral to form a second intermediate solution;

[0034] 3) After adding an initiator to the first intermediate solution, the second intermediate solution is added dropwise to carry out a polymerization reaction to obtain a fluid loss reducer.

[0035] Specifically, the preparation method of the fluid loss reducer of the present invention comprises: 1) under acidic conditions, dropwise adding a silane coupling agent containing a double bond into a graphite dispersion, wherein the silane coupling agent containing a double bond undergoes dehydration condensation with activated hydroxyl groups on the surface of graphite in the graphite dispersion to perform a grafting reaction to obtain silane coupling agent-modified graphite, then adding a crosslinking agent to the silane coupling agent-modified graphite, and adjusting the pH to neutral to obtain a first intermediate solution;

[0036] 2) mixing acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing a cyclic group and a large side chain, and adjusting the pH to neutral to form a second intermediate solution containing multiple polymerizable monomers;

[0037] 3) After adding an initiator to the first intermediate solution, the second intermediate solution is added dropwise to carry out a polymerization reaction. In the polymerization reaction, acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing a cyclic group and a large side chain are combined with double bonds in the silane coupling agent-modified graphite under the action of the initiator. At the same time, acrylamide, sulfonic acid monomer, cationic monomer, monomer containing a cyclic group and a large side chain, and a cross-linking agent are polymerized on the surface and pores of the silane coupling agent-modified graphite, so that the polymer is interspersed in the pores of the graphite to obtain a fluid loss reducer.

[0038] In some embodiments, in step 1), a grafting reaction is carried out under acidic and stirring conditions to obtain silane coupling agent-modified graphite, and then a crosslinking agent is added to the silane coupling agent-modified graphite, and ultrasonic treatment is performed for 30 minutes. The mixture can be stirred at room temperature for 2 hours, and the pH is adjusted to neutral with a 30% NaOH aqueous solution to obtain a first intermediate solution.

[0039] In some embodiments, in step 2), the second intermediate solution further comprises water. The acrylamide, sulfonic acid monomer, cationic monomer, monomer containing a cyclic group and a large side chain, and water can be stirred to uniformly mix the acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing a cyclic group and a large side chain. The pH is then adjusted to neutral using a 30% NaOH aqueous solution to obtain a second intermediate solution.

[0040] In some embodiments, in step 3), an initiator can be added to the first intermediate solution under stirring conditions, and then the second intermediate solution can be added dropwise to the first intermediate solution using a dropping funnel to perform a polymerization reaction, and then dried and pulverized to obtain a fluid loss reducer.

[0041] Through grafting and polymerization reactions, acrylamide, sulfonic acid monomers, cationic monomers, and monomers containing cyclic groups and large side chains are grafted onto the surface and pores of silane coupling agent-modified graphite, forming a fluid loss additive with a macromolecular network structure. The fluid loss additive produced by this method exhibits excellent high-temperature resistance, pressure bearing capacity, and plugging capabilities. The preparation method is simple to operate and suitable for widespread application.

[0042] In the present invention, the silane coupling agent containing a double bond includes at least one of γ-methacryloxypropyltrimethoxysilane, vinyltri(methoxyethoxy)silane, and vinyltriethoxysilane. The silane coupling agent containing a double bond reacts with graphite in a graphite dispersion through a coupling reaction, thereby introducing double bonds on the surface of the graphite and promoting subsequent polymerization reactions, thereby obtaining a fluid loss reducer with good high-temperature resistance and pressure bearing capacity.

[0043] Furthermore, the cross-linking agent includes N,N-methylenebisacrylamide, which contains two double bonds. The cross-linking agent penetrates into the pores of the modified graphite so that subsequent polymers can be cross-linked in the graphite pores. During the polymerization reaction, the cross-linking agent connects small molecule chains to form a macromolecular network structure, allowing the polymer to be interspersed inside the graphite pores, thereby giving the fluid loss reducer excellent high-temperature resistance, pressure bearing capacity and plugging ability.

[0044] Furthermore, the sulfonic acid monomer includes at least one of 2-acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-1-hydroxy-1-propanesulfonic acid sodium salt, and sodium allyl sulfonate, which contains a sulfonic acid group and can give the fluid loss reducer excellent high temperature and salt resistance and fluid loss reduction properties by strong hydration and inhibition of polymer hydrolysis.

[0045] Furthermore, the cationic monomer includes at least one of diallyldimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and diallylamine, and the molecule thereof contains a cationic quaternary ammonium group, which can improve the solubility and dispersibility of the fluid loss agent in water.

[0046] Furthermore, the monomer containing a cyclic group and a large side chain includes at least one of vinyl pyrrolidone, allyl polyoxyethylene ether, and methyl allyl polyoxyethylene ether, and the monomer containing a cyclic group and a large side chain contains a cyclic group and a large side chain, which inhibits the curling of the molecular chain under high temperature and high salt conditions through steric hindrance, so that the fluid loss reducer has better temperature and salt resistance and fluid loss reduction performance.

[0047] Furthermore, the initiator includes potassium persulfate, which can effectively promote the polymerization reaction and achieve better polymerization effect.

[0048] According to the technical solution of the present invention, the graphite dispersion is prepared by a method comprising the following steps:

[0049] Graphite is dispersed in water and the pH is adjusted to 3-3.5. The acidic environment can change the charge distribution on the graphite surface and improve the dispersibility of graphite in water. Ultrasonic dispersion treatment is then performed, and the cavitation effect of ultrasound is used to reduce the surface energy of graphite with high energy and high vibration, so that the graphite is evenly dispersed in water to obtain a graphite dispersion.

[0050] Furthermore, glacial acetic acid is used to adjust the pH to 3-3.5, and the ultrasonic dispersion treatment time is 10-20 minutes, so that the graphite is more evenly dispersed in the water.

[0051] In the present invention, in the grafting reaction, the mass ratio of the silane coupling agent containing double bonds to the graphite in the graphite dispersion is (1-2):(8-20), an appropriate amount of the silane coupling agent containing double bonds is introduced onto the surface of the graphite particles, and in the subsequent polymerization reaction, more acrylamide, sulfonic acid monomers, cationic monomers and monomers containing cyclic groups and large side chains are grafted onto the particle surfaces and pores of the graphite modified by the silane coupling agent, thereby obtaining a fluid loss reducer with good high-temperature resistance, good pressure bearing capacity and strong plugging capacity.

[0052] In some embodiments, the mass ratio of the cross-linking agent in the first intermediate solution to the acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing a cyclic group and a large side chain in the second intermediate solution is (0.1-0.5): (30-31). By regulating the amount of silane coupling agent-modified graphite, the viscosity-increasing performance of the fluid loss agent in the aqueous phase is adjusted, thereby making the fluid loss agent have better high-temperature resistance and fluid loss reduction properties and plugging ability.

[0053] In some embodiments, during the polymerization reaction, the mass ratio of the initiator, acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing a cyclic group and a large side chain is (0.1-0.3):(14-20):(3-6):(2-8):(2-10), so that the polymerization reaction proceeds smoothly and efficiently, thereby obtaining a fluid loss reducer with good high-temperature resistance and pressure-bearing capacity.

[0054] According to the technical solution of the present invention, during the grafting reaction, the temperature is 40-60° C. and the time is 4-6 hours, so that the silane coupling agent and graphite can fully undergo the grafting reaction.

[0055] In the present invention, during the polymerization reaction, the temperature is 50-70° C. and the time is 4-8 hours, which can effectively improve the polymerization reaction efficiency, thereby obtaining a fluid loss reducer with good high-temperature resistance, good pressure bearing capacity and strong plugging capacity.

[0056] In a second aspect, the present invention provides a fluid loss reducer prepared by the preparation method of the first aspect. The fluid loss reducer has good high temperature resistance, pressure bearing capacity and plugging ability.

[0057] In a third aspect, the present invention provides a water-based drilling fluid, which includes the fluid loss reducer of the second aspect. The water-based drilling fluid has good rheological properties and resistance to high temperature and high pressure fluid loss.

[0058] The present invention is described in detail below through specific embodiments:

[0059] Example 1

[0060] The fluid loss reducer of this embodiment is prepared by a method comprising the following steps:

[0061] (1) Measure 100 mL of water, adjust the pH to 3.5 with glacial acetic acid, add 20 g of graphite, perform ultrasonic treatment, stir for 15 min to obtain a graphite dispersion, and heat the graphite dispersion to 50°C;

[0062] (2) adding 1 g of KH570 dropwise to the graphite dispersion under stirring, carrying out a grafting reaction at 50° C. for 6 h to obtain silane coupling agent-modified graphite, then adding 0.1 g of N,N-methylenebisacrylamide to the silane coupling agent-modified graphite, ultrasonically treating for 30 min, cooling to 25° C., stirring and mixing for 2 h, and adjusting the pH value to 7 with a 30% NaOH aqueous solution to obtain a first intermediate solution;

[0063] (3) Weighing 18 g of acrylamide, 4.5 g of 2-acrylamido-2-methylpropanesulfonic acid, 6 g of diallyldimethylammonium chloride, and 2 g of vinyl pyrrolidone, and adding them to 20 g of water, the pH value was adjusted to 7 with a 30% aqueous solution of NaOH to obtain a second intermediate solution;

[0064] (4) The first intermediate solution was heated to 60° C. under stirring conditions, condensation water was opened, 0.3 g of potassium persulfate was added to the first intermediate solution, and then the second intermediate solution was added dropwise to the first intermediate solution using a dropping funnel to carry out polymerization reaction for 4 hours, and then dried and crushed to obtain a filtration reducer.

[0065] Example 2

[0066] The preparation method of the fluid loss additive in this embodiment is basically the same as that in Example 1, except that the amount of KH570 in step 2) is adjusted to 0.5 g.

[0067] Example 3

[0068] The preparation method of the fluid loss additive in this embodiment is basically the same as that in Example 1, except that the amount of N,N-methylenebisacrylamide in step 2) is adjusted to 0.3 g.

[0069] Example 4

[0070] The preparation method of the fluid loss additive in this embodiment is basically the same as that in Example 1, except that: in step 2), 0.1 g of N,N-methylenebisacrylamide is added to 80 g of silane coupling agent-modified graphite.

[0071] Example 5

[0072] The preparation method of the fluid loss additive in this embodiment is basically the same as that in Example 1, except that: in step 2), 0.1 g of N,N-methylenebisacrylamide is added to 50 g of silane coupling agent-modified graphite.

[0073] Example 6

[0074] The preparation method of the fluid loss reducer in this embodiment is basically the same as that in Example 1, except that in step 3), the amount of 2-acrylamido-2-methylpropanesulfonic acid is adjusted to 9 g, and the amount of diallyldimethylammonium chloride is adjusted to 3 g.

[0075] Example 7

[0076] The preparation method of the fluid loss additive in this embodiment is basically the same as that in Example 1, except that: in step 4), the temperature of the polymerization reaction is adjusted to 50°C.

[0077] Example 8

[0078] The preparation method of the fluid loss reducer in this embodiment is basically the same as that in Example 1, except that: in step 4), the amount of ammonium persulfate is adjusted to 0.2 g.

[0079] Example 9

[0080] The preparation method of the fluid loss additive in this embodiment is basically the same as that in Example 1, except that: in step 4), the polymerization reaction time is adjusted to 8 hours.

[0081] Comparative Example 1

[0082] (1) Prepare 100 mL of a mixed solution of water and ethanol, wherein the volume ratio of water to ethanol is 3:1, adjust the pH of the mixed solution to 3.5 with glacial acetic acid, add 10 g of graphite, perform ultrasonic treatment, and stir for 15 minutes to obtain a graphite dispersion, and heat the graphite dispersion to 50°C;

[0083] (2) Dissolve 1 g of KH570 in 10 mL of ethanol, add the graphite dispersion dropwise using a dropping funnel under stirring, and react at 50 °C for 6 h. Then, dry and crush the mixture to obtain a fluid loss reducer.

[0084] Comparative Example 2

[0085] (1) 18 g of acrylamide, 4.5 g of 2-acrylamido-2-methylpropanesulfonic acid, 6 g of diallyldimethylammonium chloride, and 2 g of vinylpyrrolidone were weighed and added to 20 g of water to obtain a mixed solution 1, and the pH value thereof was adjusted to 7 with a 30% aqueous solution of NaOH;

[0086] (2) Add 0.3 g of potassium persulfate to 100 mL of deionized water to obtain a mixed solution 2. Use a dropping funnel to add the mixed solution 1 dropwise to the mixed solution 2, react for 4 h, and then dry and crush to obtain a filtrate reducer.

[0087] Comparative Example 3

[0088] Untreated graphite was used as a fluid loss reducer.

[0089] Comparative Example 4

[0090] Polyacrylamide polymer (DSP-1, Deshunyuan) was used as a fluid loss reducer.

[0091] Application Examples 1-9 and Application Comparative Examples 1-5

[0092] 16 g of bentonite and 0.56 g of anhydrous sodium carbonate were added to 400 mL of water and stirred at 1500 rpm for 20 minutes. Clay adhering to the container walls was scraped off, and the mixture was sealed and cured at room temperature for 24 hours to obtain a base slurry (as Comparative Application Example 5). 2 wt % of the fluid loss additives prepared in Examples 1-9 and Comparative Examples 1-4 were added to the 400 mL base slurry and stirred at 1500 rpm for 20 minutes. Any slurry adhering to the container walls was scraped off to obtain a water-based drilling fluid.

[0093] Application Example 10

[0094] The preparation method of the water-based drilling fluid in this application example is different from the preparation method of the water-based drilling fluid in Example 1 in that the amount of the fluid loss agent is adjusted to 0.5 wt %.

[0095] The water-based drilling fluids prepared in Examples 1-10 and Comparative Examples 1-5 were placed in a roller aging furnace at an aging temperature of 220°C for 16 hours. The rheological and high-temperature and high-pressure fluid loss properties of the water-based drilling fluids before and after aging were evaluated with reference to GBT 16783.2, including apparent viscosity (AV), plastic viscosity (PV), dynamic shear force (YP), and high-temperature and high-pressure fluid loss (FL). HTHP ), where the high temperature and high pressure fluid loss test conditions are 200℃ and 3.5MPa. The test results are shown in Figure 1 and Table 1.

[0096] Depend on Figure 1 It can be seen that the filter cake formed by the water-based drilling fluid using polyacrylamide polymer as a fluid loss reducer under high temperature and high pressure conditions in Comparative Example 4 is thick and loose, and cannot play an effective plugging role. Figure 2 It can be seen that the filter cake formed by the water-based drilling fluid added with 0.5 wt% of fluid loss agent in Application Example 10 under high temperature and high pressure conditions is thin and dense, indicating that the addition of the fluid loss agent effectively prevents a portion of the mud from entering the formation, thereby preventing the expansion of cracks and the loss of water in the drilling fluid.

[0097] Table 1

[0098]

[0099] As can be seen from Table 1, the water-based drilling fluids prepared using Examples 1-9 have good high-temperature resistance, fluid loss reduction performance, pressure bearing capacity and plugging ability.

[0100] Compared to Application Example 2, Application Example 1 increased the amount of KH570 in the fluid loss additive, resulting in an increase in the amount of polymer grafted onto the graphite particle surface. The high-temperature, high-pressure fluid loss of the aged water-based drilling fluid decreased from 52.6 mL to 43.2 mL, demonstrating improved high-temperature fluid loss control. This is due to the dehydration condensation between KH570 and the activated hydroxyl groups on the graphite surface. Further, in the subsequent polymerization reaction, the polymer monomers can bond with the double bonds in KH570, grafting the polymer onto the graphite particle surface and within its pores, thereby imparting excellent ultra-high-temperature fluid loss control to the fluid loss additive.

[0101] Compared with Application Example 3, Application Example 1 uses an appropriate amount of N,N-methylenebisacrylamide, which is beneficial to enhancing the cross-linking effect between polymers and further improving the high-temperature resistance and fluid loss reduction performance of the fluid loss control agent.

[0102] Compared with Application Example 4 and Application Example 5, the amount of silane coupling agent-modified graphite added in Application Example 1 is increased, which reduces the proportion of polymer in the fluid loss reducer. The water-based drilling fluid in Application Example 1 has better rheological properties and resistance to high temperature and high pressure fluid loss.

[0103] Compared with Application Example 1, in Application Example 6, the amounts of 2-acrylamido-2-methylpropanesulfonic acid and diallyldimethylammonium chloride were adjusted, and the high-temperature and high-pressure filtration loss of the water-based drilling fluid changed less.

[0104] Compared to Application Example 1, Application Comparative Example 1 uses only KH570-modified graphite as a fluid loss additive. The high-temperature, high-pressure fluid loss of the water-based drilling fluid increases from 43.2 mL to 158 mL. This is because the modified graphite has no water trapping effect and no deformation ability, making it difficult to match the different fracture shapes of the formation to form a dense seal. Compared to Application Example 1, Application Comparative Example 2 does not add silane coupling agent to modify the graphite as a fluid loss additive. The high-temperature, high-pressure fluid loss of the water-based drilling fluid increases from 43.2 mL to 124 mL, and the viscosity increase is more serious. Compared to Application Example 1, Application Comparative Example 3 uses untreated graphite as a fluid loss additive. Its high-temperature fluid loss resistance is far worse than that of Application Example 1.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a fluid loss additive, characterized in that: include: Under acidic conditions, a silane coupling agent containing a double bond is added dropwise to a graphite dispersion to carry out a grafting reaction to obtain silane coupling agent-modified graphite, and then a cross-linking agent is added to the silane coupling agent-modified graphite, and the pH is adjusted to neutral to obtain a first intermediate solution; After mixing acrylamide, sulfonic acid monomer, cationic monomer, and monomer containing cyclic group and large side chain, the pH is adjusted to neutral to form a second intermediate solution; After adding an initiator to the first intermediate solution, the second intermediate solution is added dropwise to carry out a polymerization reaction to obtain the fluid loss reducer; The monomer containing a cyclic group and a large side chain includes at least one of vinyl pyrrolidone, allyl polyoxyethylene ether, and methyl allyl polyoxyethylene ether.

2. The preparation method according to claim 1, characterized in that The silane coupling agent containing a double bond includes at least one of γ-methacryloxypropyltrimethoxysilane, vinyl tris(methoxyethoxy)silane, and vinyl triethoxysilane; and / or, The sulfonic acid monomer includes at least one of 2-acrylamide-2-methylpropanesulfonic acid, 3-allyloxy-1-hydroxy-1-propanesulfonic acid sodium salt, and sodium allylsulfonate; and / or, The cationic monomer includes at least one of diallyldimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and diallylamine; and / or, The initiator includes potassium persulfate.

3. The preparation method according to claim 1 or 2, characterized in that The graphite dispersion is prepared by a method comprising the following steps: Graphite is dispersed in water, the pH is adjusted to 3-3.5, and ultrasonic dispersion treatment is performed to obtain the graphite dispersion liquid.

4. The preparation method according to claim 1, characterized in that In the grafting reaction, the mass ratio of the silane coupling agent containing a double bond to the graphite in the graphite dispersion is (1-2):(8-20).

5. The preparation method according to claim 1, characterized in that The mass ratio of the cross-linking agent in the first intermediate solution to the acrylamide, sulfonic acid monomer, cationic monomer and monomer containing cyclic group and large side chain in the second intermediate solution is (0.1-0.5): (30-31).

6. The preparation method according to claim 1, characterized in that In the polymerization reaction, the mass ratio of the initiator, acrylamide, sulfonic acid monomer, cationic monomer and monomer containing cyclic group and large side chain is (0.1-0.3): (14-20): (3-6): (2-8): (2-10).

7. The preparation method according to claim 1, characterized in that During the grafting reaction, the temperature is 40-60° C. and the time is 4-6 hours.

8. The preparation method according to claim 1, characterized in that During the polymerization reaction, the temperature is 50-70° C. and the time is 4-8 hours.

9. A fluid loss additive, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

10. A water-based drilling fluid, characterized in that: Including the fluid loss reducer according to claim 9.

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