Fluid loss additives, methods of making and using the same

Abstract

This invention relates to the field of oilfield filtration loss control agents, and discloses a filtration loss control agent, its preparation method, and its application. The method includes the following steps: (1) mixing a sulfonic acid-containing monomer, a heterocyclic monomer, a nonionic monomer, and water in an inert gas, and then mixing the resulting mixture with an initiator to carry out a first polymerization reaction; (2) mixing the material after the first polymerization reaction in step (1) with a modified nanomonomer in an inert gas to carry out a second polymerization reaction. The modified nanomonomer contains carbon-carbon double bonds and nanomaterials. The filtration loss control agent has excellent high temperature and salt resistance, and stronger interaction with clay particles, thereby enhancing the ability of the filtration loss control agent to control the filtration loss of drilling fluid, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of oilfield filtration loss control agents, specifically to a filtration loss control agent, its preparation method, and its application. Background Technology

[0002] In recent years, China's dependence on imported oil and natural gas has continued to rise, seriously threatening energy security. Therefore, the efficient development of ultra-deep oil and gas resources is crucial for enhancing oil and gas security and is an important measure to ensure energy security. Oil and gas exploration and development are inseparable from drilling engineering, and drilling fluid is the lifeblood of drilling, playing roles such as carrying cuttings, lubricating the drill bit, and stabilizing the wellbore. Drilling fluid plays a key role in ensuring safe, high-quality, and efficient drilling. However, ultra-deep geological conditions are complex, and drilling fluids face numerous severe challenges under the "four extremes" of ultra-high temperature, ultra-high salinity, ultra-high pressure, and ultra-high stress. Whether drilling fluids can maintain their original performance under such harsh conditions determines the success or failure of drilling. Therefore, ultra-high temperature and high salinity resistant drilling fluid technology is an indispensable guarantee for deep / ultra-deep oil and gas drilling.

[0003] As one of the key materials in drilling fluid, filtration loss reducers can form a dense, thin mud cake on the wellbore. On the one hand, this can prevent drilling fluid from invading the formation and causing problems such as wellbore instability and reservoir damage. On the other hand, it can prevent mud cake from getting stuck and jammed, which is crucial for safe and rapid drilling.

[0004] Currently, filtration loss reducing agents are mainly divided into two categories: natural polymers and synthetic polymers. However, the temperature in ultra-deep formations is generally higher than 200℃, and polymer molecules are prone to shrinkage and breakage, resulting in a significant decrease in their filtration loss reducing performance. This can easily lead to complex downhole conditions and even drilling failure. The lack of filtration loss reducing agents resistant to ultra-high temperature and ultra-high salinity severely restricts the safe and efficient exploration and development of deep / ultra-deep oil and gas.

[0005] Therefore, there is an urgent need to invent a polymer filtration reducer that is resistant to ultra-high temperature and high salt, to promote the development of ultra-deep well drilling fluid technology and help to efficiently develop ultra-deep oil and gas. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of insufficient resistance to high temperature, high salt, and high pressure in existing filtration loss control agents, and to provide a filtration loss control agent, its preparation method, and its application. This method involves a distribution polymerization reaction of monomers containing sulfonic acid groups, monomers containing heterocyclic structures, nonionic monomers, and modified nanomonomers to prepare the filtration loss control agent. The filtration loss control agent possesses excellent resistance to high temperature and salt, and exhibits stronger interaction with clay particles, thereby enhancing its ability to control the filtration loss of drilling fluids, and has broad application prospects.

[0007] To achieve the above objectives, the present invention provides a method for preparing a filtration agent, the method comprising the following steps:

[0008] (1) In an inactive gas, a sulfonic acid-containing monomer, a heterocyclic monomer, a nonionic monomer and water are mixed, and then the resulting mixture is mixed with an initiator and subjected to a first polymerization reaction at 35-45°C.

[0009] (2) In an inactive gas, the material after the first polymerization reaction in step (1) is mixed with the modified nanomonomer and carried out a second polymerization reaction at 35-45°C.

[0010] The modified nanomonomer is silane coupling agent-modified nano-calcium carbonate with carbon-carbon double bonds.

[0011] Preferably, the sulfonic acid-containing monomer is selected from one or more of sodium allyl sulfonate, sodium methpropylene sulfonate, and sodium 2-acrylamide-2-methylpropanesulfonate.

[0012] Preferably, the heterocyclic monomer is selected from one or more of N-vinylpyrrolidone, N-vinylpiperidone, and N-vinylcaprolactam.

[0013] Preferably, the nonionic monomer is selected from one or more of N-methyl-2-acrylamide, N,N-dimethylacrylamide, methacrylamide, and N-(hydroxymethyl)acrylamide.

[0014] Preferably, the modified nanomonomer is selected from one or more of vinylmethyldiethoxysilane-modified nano-calcium carbonate, vinylmethyldiemethoxysilane-modified nano-calcium carbonate, and vinyltriethoxysilane-modified nano-calcium carbonate.

[0015] Preferably, in step (2), the modified nanomonomer is added by dropwise addition.

[0016] Preferably, the initiator is azobisisopropylimidazoline hydrochloride.

[0017] Preferably, the weight ratio of the sulfonic acid-containing monomer, the heterocyclic monomer, the nonionic monomer, and the modified nanomonomer is 2-3:2-3:5-7:1.

[0018] Preferably, the total weight ratio of the sulfonic acid-containing monomer, the heterocyclic monomer, and the nonionic monomer to the weight of water is 1-2:5.

[0019] Preferably, the first polymerization reaction and the second polymerization reaction are at the same temperature;

[0020] Preferably, the first polymerization reaction takes 1-2 hours, and the second polymerization reaction takes 2-3 hours.

[0021] A second aspect of the present invention provides a filtration loss reducer prepared by the above method.

[0022] A third aspect of the present invention provides the application of the aforementioned filtration loss reducing agent in the preparation of water-based drilling fluid filtration loss reducing agents.

[0023] The method described in this invention enhances the salt resistance of the filtration loss reducer by introducing sulfonic acid groups into the filtration loss reducer using a sulfonic acid-containing monomer. Furthermore, it enhances the temperature resistance of the filtration loss reducer by using a monomer containing a heterocyclic structure. The introduction of sulfonic acid groups and heterocyclic structures ensures the stability of the molecular structure of the filtration loss reducer under high temperature and high salt conditions. Additionally, in the method described in this invention, modified nanomonomers containing carbon-carbon double bonds and nano-calcium carbonate are added for preparation. The carbon-carbon double bonds on the modified nanomonomers participate in the polymerization reaction, grafting the modified nanomonomers into the polymer molecular structure, thereby further enhancing the temperature resistance of the filtration loss reducer. Moreover, the grafted modified nanomonomers are less prone to detachment, further improving the adsorption capacity of the filtration loss reducer. Furthermore, the modified nanomonomers used in the method described in this invention contain nano-calcium carbonate. This nano-calcium carbonate enhances the thermal and chemical stability of the polymer molecules and strengthens their adsorption effect on clay particles. This allows the filtration loss reducer, when added to drilling fluid, to maintain a good filtration loss reduction effect even in high-concentration brine and high-temperature environments, thereby improving its ability to control drilling fluid filtration loss. This further enhances the performance of the prepared filtration loss reducer. Detailed Implementation

[0024] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] The method for preparing the filtration loss reducing agent according to the present invention includes the following steps:

[0027] (1) In an inactive gas, a sulfonic acid-containing monomer, a heterocyclic monomer, a nonionic monomer and water are mixed, and then the resulting mixture is mixed with an initiator and subjected to a first polymerization reaction at 35-45°C.

[0028] (2) In an inactive gas, the material after the first polymerization reaction in step (1) is mixed with the modified nanomonomer and carried out a second polymerization reaction at 35-45°C.

[0029] In the method described in this invention, sulfonic acid-containing monomers, heterocyclic monomers, and nonionic monomers are first polymerized to form polymer segments. Sulfonic acid groups are then grafted onto these polymer segments, resulting in a more superior salt resistance effect for the prepared filtration loss reducer. Further, heterocyclic monomers are used to introduce large-molecule heterocyclic structures into the polymer, enhancing the salt and high-temperature resistance of the prepared filtration loss reducer. More importantly, this invention employs a two-stage polymerization process, using modified nanomonomers as raw materials in the second polymerization reaction. The modified nanomonomers are covalently bonded after copolymerization, making them less prone to detachment compared to common methods like encapsulation or physical mixing in existing technologies. The added modified nanomonomers further enhance the stability of the polymer molecules, improving temperature and salt resistance. Furthermore, the nano-calcium carbonate in the modified nanomonomers further enhances the temperature resistance of the prepared filtration loss reducer, strengthens the polymer's adsorption capacity, and increases the interaction between the polymer and clay particles, thereby strengthening its ability to control drilling fluid filtration loss.

[0030] In a preferred embodiment, the sulfonic acid-containing monomer is selected from one or more of sodium allyl sulfonate, sodium methpropylene sulfonate, and sodium 2-acrylamide-2-methylpropanesulfonate.

[0031] In a preferred embodiment, the heterocyclic monomer is selected from one or more of N-vinylpyrrolidone, N-vinylpiperidone, and N-vinylcaprolactam.

[0032] In a preferred embodiment, the nonionic monomer is selected from one or more of N-methyl-2-acrylamide, N,N-dimethylacrylamide, methacrylamide, and N-(hydroxymethyl)acrylamide.

[0033] In the method described in this invention, the initiator is azobisisopropylimidazoline hydrochloride.

[0034] In some specific embodiments, in step (1), the initiator is added dropwise to the mixture using a constant pressure funnel.

[0035] In a specific embodiment, the initiator is provided by an initiator solution. Specifically, the initiator is dissolved in water to obtain an initiator solution, which is then added dropwise to the mixture. Specifically, the concentration of the initiator in the initiator solution is 0.008-0.015 g / mL.

[0036] In a specific embodiment, the total weight ratio of the sulfonic acid-containing monomer, the heterocyclic monomer, the nonionic monomer, and the modified nanomonomer to the weight of the initiator is 500-2000:1.

[0037] In the method described in this invention, by adding the modified nanomonomer for copolymerization, the salt and high temperature resistance of the filtration loss reducer can be further improved, and the adsorption capacity of the polymer can be further enhanced, thereby improving the ability of the prepared filtration loss reducer to control the filtration loss of drilling fluid.

[0038] In the method described in this invention, the modified nanomonomer is silane coupling agent-modified nano-calcium carbonate with carbon-carbon double bonds. The carbon-carbon double bonds participate in the polymerization reaction, grafting the modified nanomonomer onto the polymer chain through polymerization. The nano-calcium carbonate not only enhances the temperature resistance of the filtration loss reducer but also enhances its adsorption capacity, resulting in stronger interactions between the filtration loss reducer and clay particles. This strengthens its ability to control the filtration loss of drilling fluid, ensuring that the prepared filtration loss reducer, when added to drilling fluid, still exhibits excellent filtration loss reduction effects under high-concentration brine and high-temperature environments.

[0039] In a preferred embodiment, in order to further improve the temperature and salt resistance of the filtration loss reducer, the modified nanomonomer is selected from one or more of vinylmethyldiethoxysilane modified nano-calcium carbonate, vinylmethyldiemethoxysilane modified nano-calcium carbonate, and vinyltriethoxysilane modified nano-calcium carbonate.

[0040] In a preferred embodiment, the method for preparing the modified nanomonomer includes the following steps:

[0041] (1) Mix nano-calcium carbonate with water at a weight ratio of 1:4-6, and then adjust the pH of the mixture to 8.5-9.5 using an alkaline solution;

[0042] (2) The material obtained in step (1) is mixed with a silane coupling agent containing double bonds and subjected to a hydrothermal reaction;

[0043] The hydrothermal reaction temperature is 60-75℃, and the hydrothermal reaction time is 5.5-7h; the double-bonded silane coupling agent is selected from one or more of vinylmethyldiethoxysilane, vinylmethyldimethoxysilane, and vinyltriethoxysilane.

[0044] In a preferred embodiment, in the preparation method of the modified nanomonomer, the ratio of the double-bonded silane coupling agent to nano-calcium carbonate is 1:4.8-5.5.

[0045] In a specific embodiment, in step (2), in order to promote a more uniform dispersion of the modified nanomonomers added in the reaction, the modified nanomonomers are mixed with the material after the first polymerization reaction in step (1) by dropwise addition. In a specific embodiment, the modified nanomonomers are added dropwise to the material after the first polymerization reaction using a dropping funnel.

[0046] In a preferred embodiment, in order to further improve the performance of the prepared filtration loss reducer, the weight ratio of the sulfonic acid-containing monomer, the heterocyclic monomer, the nonionic monomer and the modified nanomonomer is 2-3:2-3:5-7:1.

[0047] In a preferred embodiment, to control the degree of reaction in the first polymerization reaction and facilitate better participation of the subsequently added modified nanomonomers in the polymerization reaction, the weight ratio of the total weight of the sulfonic acid-containing monomer, the heterocyclic monomer, and the nonionic monomer to the weight of water is limited to 1-2:5, preferably 5-7:20. Specifically, the weight ratio of the total weight of the sulfonic acid-containing monomer, the heterocyclic monomer, and the nonionic monomer to the weight of water can be 1:5, 1.5:5, or 2:5.

[0048] In specific embodiments, the temperatures of the first and second polymerization reactions are extremely important. When the polymerization temperature is lower than the temperature specified in this invention, neither the first nor the second polymerization reaction will occur. When the polymerization temperature exceeds the temperature specified in this invention, the reaction will be violent, and the filtration loss reducing agent described in this invention will not be successfully prepared. Specifically, in this invention, the temperature of the first polymerization reaction is 35-45℃, preferably 38-42℃; the temperature of the second polymerization reaction is 35-45℃, preferably 38-42℃. Specifically, the temperature of the first polymerization reaction can be 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, or 45℃; the temperature of the second polymerization reaction can be 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, or 45℃.

[0049] In a preferred embodiment, the temperature of the first polymerization reaction is the same as the temperature of the second polymerization reaction.

[0050] In a preferred embodiment, to further control the degree of reaction in the first polymerization reaction and to facilitate better participation of the modified nanomonomers in the second polymerization reaction, the time for the first polymerization reaction is limited to 1-2 hours, preferably 1.5 hours. Specifically, the time for the first polymerization reaction can be 1 hour, 1.5 hours, or 2 hours. In a specific embodiment, the time for the first polymerization reaction includes the dropping time of the initiator solution.

[0051] In a preferred embodiment, the second polymerization reaction takes 2-3 hours, preferably 2.5 hours. Specifically, the second polymerization reaction can take 2 hours, 2.5 hours, or 3 hours. Specifically, since the added time of the modified nanomonomer is relatively short, the time of the second polymerization reaction includes the added time of the modified nanomonomer.

[0052] In the method described in this invention, the inactive gas refers to a gas that does not participate in the reaction during the reaction process. In a specific embodiment, the inactive gas is selected from at least one of nitrogen and an inert gas (such as argon).

[0053] In a specific implementation, step (2) further includes: mixing the obtained reaction product with ethanol, then filtering, drying the obtained insoluble matter to obtain a white solid, and the pulverized white powder is the nanocomposite polymer filtration loss reducer.

[0054] The present invention further provides a filtration loss reducing agent prepared by the above method. In the method described in the present invention, by adopting a stepwise polymerization method and using modified nanomonomers for copolymerization, the modified nanomonomers are tightly bound to the polymer chain segments through covalent bonds, thereby further improving the temperature and salt resistance properties of the prepared filtration loss reducing agent, making the performance of the prepared filtration loss reducing agent more superior.

[0055] This invention also provides an application of the aforementioned filtration loss reducer in the preparation of filtration loss reducers for water-based drilling fluids. The filtration loss reducer prepared using the method described in this invention exhibits excellent high-temperature and salt resistance properties, and the interaction between the filtration loss reducer and clay particles is stronger, thereby enhancing the filtration loss control capability of the filtration loss reducer on drilling fluids, enabling its better application in water-based drilling fluids.

[0056] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0057] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0058] Preparation Example 1

[0059] Vinylmethyldiethoxysilane-modified nano-calcium carbonate was prepared using the following method:

[0060] 10g of nano-calcium carbonate was dispersed in 50g of water to form a suspension. The pH was adjusted to 9.0 with sodium hydroxide. The suspension was added to a reaction vessel, which was then heated to 70℃. 2g of vinylmethyldiethoxysilane was added under stirring at 300r / min for hydrothermal reaction. After 6h of reaction, the product was filtered, the solid was washed with anhydrous ethanol, and dried to obtain vinylmethyldiethoxysilane-modified nano-calcium carbonate.

[0061] Preparation Example 2

[0062] Vinylmethyldimethoxysilane-modified nano-calcium carbonate was prepared using the following method:

[0063] 10g of nano-calcium carbonate was dispersed in 50g of water to form a suspension. The pH was adjusted to 9.0 with sodium hydroxide. The suspension was added to a reaction vessel, which was then heated to 70℃. 2g of vinylmethyldimethoxysilane was added under stirring at 300r / min for hydrothermal reaction. After 6h of reaction, the product was filtered, the solid was washed with anhydrous ethanol, and dried to obtain vinylmethyldimethoxysilane-modified nano-calcium carbonate.

[0064] Preparation Example 3

[0065] Vinyltriethoxysilane-modified nano-calcium carbonate was prepared using the following method:

[0066] 10g of nano-calcium carbonate was dispersed in 50g of water to form a suspension. The pH was adjusted to 9.0 with sodium hydroxide. The suspension was added to a reaction vessel, which was then heated to 70°C. 2g of vinyltriethoxysilane was added under stirring at 300r / min for hydrothermal reaction. After 6h of reaction, the product was filtered, the solid was washed with anhydrous ethanol, and dried to obtain vinyltriethoxysilane-modified nano-calcium carbonate.

[0067] Example 1

[0068] (1) Dissolve 8g of sodium allyl sulfonate, 8g of N-vinylpyrrolidone, and 20g of N-methyl-2-acrylamide in 130g of water to obtain a mixed solution; then, under stirring, add the obtained mixed solution to a reaction flask, continuously purge nitrogen gas, and set the stirrer speed to 300r / min.

[0069] (2) Heat the reaction system of step (1) to 35°C, then dissolve 0.02g of azobisisopropylimidazoline hydrochloride in 2mL of water to obtain azobisisopropylimidazoline hydrochloride solution. After nitrogen gas is introduced for 30min, add azobisisopropylimidazoline hydrochloride solution dropwise to the reaction system. The dropwise addition rate is controlled at one drop every 3s. The addition is completed within 3min to carry out the first polymerization reaction. The reaction time is 2h.

[0070] (3) After the reaction in step (2) is completed, 4g of vinylmethyldiethoxysilane modified nano-calcium carbonate is dispersed in 4g of water to obtain a dispersion. Then, the dispersion is loaded into a constant pressure dropping funnel and slowly added to the reaction flask. The dropping rate is controlled at one drop every 2 seconds. After the dropping is completed, the second polymerization reaction is continued for 2.5 hours and the reaction temperature is 35°C. After the reaction is completed, it is naturally cooled to room temperature to obtain a transparent viscous gel.

[0071] (4) The transparent viscous gel is mixed with anhydrous ethanol, then filtered, and the resulting insoluble substance is dried to obtain a white solid. The white powder after pulverization is the filtrate loss reducer.

[0072] Example 2

[0073] (1) Dissolve 10g sodium methacrylate, 10g N-vinylpiperidone, and 25g N,N-dimethylacrylamide in 160g water to obtain a mixed solution; then add the obtained mixed solution to the reaction flask while stirring, continuously purge with nitrogen gas, and set the stirrer speed to 300r / min.

[0074] (2) Heat the reaction system of step (1) to 40°C, then dissolve 0.04 g of azobisisopropylimidazoline hydrochloride in 4 mL of water to obtain azobisisopropylimidazoline hydrochloride solution. After nitrogen gas is introduced for 30 min, azobisisopropylimidazoline hydrochloride solution is added dropwise to the reaction system at a rate of one drop every 2 seconds. The addition is completed within 3 min to carry out the first polymerization reaction. The reaction time is 1.5 h.

[0075] (3) After the reaction in step (2) is completed, 5g of vinylmethyldimethoxysilane modified nano-calcium carbonate is dispersed in 5g of water to obtain a dispersion. Then, the dispersion is loaded into a constant pressure dropping funnel and slowly added to the reaction flask. The dropping rate is controlled at one drop every 2 seconds. After the dropping is completed, the second polymerization reaction is continued for 2.5 hours and the reaction temperature is 40°C. After the reaction is completed, it is naturally cooled to room temperature to obtain a transparent viscous gel.

[0076] (4) The transparent viscous gel is mixed with anhydrous ethanol, then filtered, and the resulting insoluble substance is dried to obtain a white solid. The white powder after pulverization is the filtrate loss reducer.

[0077] Example 3

[0078] (1) Dissolve 12g of sodium 2-acrylamide-2-methylpropanesulfonate, 12g of N-vinylcaprolactam and 30g of methacrylamide in 190g of water to obtain a mixed solution; then add the obtained mixed solution to the reaction flask while stirring, continuously purge nitrogen gas, and set the stirrer speed to 300r / min.

[0079] (2) Heat the reaction system of step (1) to 40°C, then dissolve 0.12g of azobisisopropylimidazoline hydrochloride in 12mL of water to obtain azobisisopropylimidazoline hydrochloride solution. After nitrogen gas is introduced for 30min, add azobisisopropylimidazoline hydrochloride solution dropwise to the reaction system. The dropwise addition rate is controlled at one drop every 0.5s. The addition is completed within 3min to carry out the first polymerization reaction. The reaction time is 1.5h.

[0080] (3) After the reaction in step (2) is completed, 6g of vinyltriethoxysilane modified nano-calcium carbonate is dispersed in 6g of water to obtain a dispersion. Then, the dispersion is loaded into a constant pressure dropping funnel and slowly added to the reaction flask. The dropping rate is controlled at one drop every 2 seconds. After the dropping is completed, the second polymerization reaction is continued for 3 hours and the reaction temperature is 40°C. After the reaction is completed, it is naturally cooled to room temperature to obtain a transparent viscous gel.

[0081] (4) The transparent viscous gel is mixed with anhydrous ethanol, then filtered, and the resulting insoluble substance is dried to obtain a white solid. The white powder after pulverization is the filtrate loss reducer.

[0082] Example 4

[0083] (1) Dissolve 12g of sodium 2-acrylamide-2-methylpropanesulfonate, 12g of N-vinylcaprolactam, 15g of methacrylamide and 15g of N-(hydroxymethyl)acrylamide in 190g of water to obtain a mixed solution; then add the obtained mixed solution to the reaction flask under stirring, continuously purge nitrogen gas, and set the stirrer speed to 300r / min.

[0084] (2) Heat the reaction system of step (1) to 45°C, then dissolve 0.09 g of azobisisopropylimidazoline hydrochloride in 9 mL of water to obtain azobisisopropylimidazoline hydrochloride solution. After nitrogen gas is introduced for 30 min, azobisisopropylimidazoline hydrochloride solution is added dropwise to the reaction system at a rate of one drop per 1 second. The addition is completed within 3 min to carry out the first polymerization reaction. The reaction time is 1.5 h.

[0085] (3) After the reaction in step (2) is completed, 6g of vinylmethyldiethoxysilane modified nano-calcium carbonate is dispersed in 6g of water to obtain a dispersion. Then, the dispersion is loaded into a constant pressure dropping funnel and slowly added to the reaction flask. The dropping rate is controlled at one drop every 2 seconds. After the dropping is completed, the second polymerization reaction is continued for 2 hours and the reaction temperature is 40°C. After the reaction is completed, it is naturally cooled to room temperature to obtain a transparent viscous gel.

[0086] (4) The transparent viscous gel is mixed with anhydrous ethanol, then filtered, and the resulting insoluble substance is dried to obtain a white solid. The white powder after pulverization is the filtrate loss reducer.

[0087] Comparative Example 1

[0088] The preparation was carried out according to the method of Example 3, except that no modified nanomonomers were added during the preparation, that is, step (3) was not performed. The specific steps are as follows:

[0089] (1) Dissolve 12g of sodium 2-acrylamide-2-methylpropanesulfonate, 12g of N-vinylcaprolactam and 30g of methacrylamide in 190g of water to obtain a mixed solution; then add the obtained mixed solution to the reaction flask while stirring, continuously purge nitrogen gas, and set the stirrer speed to 300r / min.

[0090] (2) The reaction system from step (1) was heated to 40°C. Then, 0.12 g of azobisisopropylimidazoline hydrochloride was dissolved in 12 mL of water to obtain an azobisisopropylimidazoline hydrochloride solution. After nitrogen gas was introduced for 30 min, the azobisisopropylimidazoline hydrochloride solution was added dropwise to the reaction system at a rate of one drop every 0.5 s, and the addition was completed within 3 min to carry out the first polymerization reaction. The reaction time was 4.5 h. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a transparent viscous gel. The transparent viscous gel was mixed with anhydrous ethanol, then filtered, and the resulting filter residue was dried to obtain a white solid.

[0091] Comparative Example 2

[0092] The preparation was carried out according to the method of Example 3, except that the temperature of the first polymerization reaction and the second polymerization reaction was 55°C.

[0093] Comparative Example 3

[0094] The preparation was carried out according to the method of Example 3, except that the temperature of the first polymerization reaction and the second polymerization reaction was 30°C.

[0095] The reaction failed because the reaction temperature was too low, resulting in the inability to obtain the reaction product.

[0096] Comparative Example 4

[0097] The preparation was carried out according to the method of Example 3, except that N-vinylcaprolactam was not added during the preparation process.

[0098] Test case

[0099] The filtration loss reducers prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance testing, and the specific methods are as follows:

[0100] Preparation of freshwater-based slurry: Add 16g of bentonite and 2.4g of anhydrous sodium carbonate to 400mL of water, stir at high speed for 20min, and cure at room temperature for 24h to obtain freshwater-based slurry;

[0101] Preparation of brine-based slurry: Add saturated NaCl to freshwater slurry, stir at high speed for 20 minutes, and cure at room temperature for 24 hours to obtain saturated brine-based slurry;

[0102] Preparation of test slurry: Add 4g of the sample to be tested to fresh water or saturated salt water-based slurry and stir at high speed for 20 minutes to obtain the corresponding test slurry;

[0103] Aging: Add the prepared mud to the aging tank and heat-roll it at different temperatures for 16 hours;

[0104] The rheological parameters, API filtration loss, and HTHP filtration loss of the drilling fluid were tested in accordance with the national standard GB / T 16783.1-2014 Petroleum and Natural Gas Industry Drilling Fluid Field Testing Part 1: Water-based Drilling Fluids. The test results are shown in Table 1.

[0105] Table 1

[0106]

[0107]

[0108] As shown in Table 1, after adding the filtration loss reducer prepared in Examples 1-4 of this invention, when the aging temperature increased from 160℃ to 220℃, the apparent viscosity, plastic viscosity, dynamic shear force, and API filtration loss of the saturated brine drilling fluid remained almost unchanged, while the HTHP filtration loss showed a slight increase. In other words, the filtration loss reducer prepared in Examples 1-4 did not change its rheological properties or filtration loss under saturated brine and different aging temperatures; even when the aging temperature reached 220℃, it still exhibited a good filtration loss reduction effect. However, after adding the filtration loss reducer prepared in Comparative Example 1, the apparent viscosity, plastic viscosity, and dynamic shear force of the saturated brine drilling fluid before aging were similar, and the effect on controlling the filtration loss of the drilling fluid was also more significant. However, after aging at 160℃, 180℃, 200℃, and 220℃ for 16 hours respectively, the apparent viscosity and plastic viscosity of the saturated brine drilling fluid decreased significantly, and the API and HTHP filtration losses decreased even more drastically. When the aging temperature increased to 220℃, the filtration loss reducer prepared in Comparative Example 1 almost lost its ability to control the filtration loss of the drilling fluid. The filtration loss reducer prepared in Comparative Example 2 had no filtration loss reduction effect on brine drilling fluid. This is because the reaction temperature in the preparation process of Comparative Example 2 was too high, and the same monomer dosage could not produce a high-performance filtration loss reducer under these conditions. The filtration loss reducer prepared in Comparative Example 4 exhibits excellent filtration loss reduction effects at room temperature. However, with increasing aging temperature, the filtration loss reduction effect decreases significantly or even completely fails. This is because the preparation method of Comparative Example 4 does not include heterocyclic monomers. Although the addition of modified nanomaterials enhances its adsorption performance, resulting in excellent filtration loss reduction effects on drilling fluids in saturated brine at room temperature, the lack of heterocyclic structures prevents improvement in the temperature resistance of the filtration loss reducer. Therefore, in the method described in this invention, all four polymeric monomers are indispensable. The filtration loss reducer prepared by the method described in this invention has the advantages of chemical stability and good temperature and salt resistance. After preparation using modified nanomonomers, the modified nanomonomers are covalently bonded to the polymer molecular chain, giving the polymer even better salt resistance and high temperature resistance.

[0109] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a filtration loss reducing agent, characterized in that, The method includes the following steps: (1) In an inactive gas, a sulfonic acid-containing monomer, a heterocyclic monomer, a nonionic monomer and water are mixed, and then the resulting mixture is mixed with an initiator and subjected to a first polymerization reaction at 35-45°C. (2) In an inactive gas, the material after the first polymerization reaction in step (1) is mixed with the modified nanomonomer and carried out a second polymerization reaction at 35-45°C. The modified nanomonomer is silane coupling agent-modified nano-calcium carbonate with carbon-carbon double bonds; The sulfonic acid-containing monomer is selected from one or more of sodium allyl sulfonate, sodium methpropylene sulfonate, and sodium 2-acrylamido-2-methylpropanesulfonate; the heterocyclic monomer is selected from one or more of N-vinylpyrrolidone, N-vinylpiperidone, and N-vinylcaprolactam; and the nonionic monomer is selected from one or more of N-methyl-2-acrylamide, N,N-dimethylacrylamide, methacrylamide, and N-(hydroxymethyl)acrylamide. The weight ratio of the sulfonic acid-containing monomer, the heterocyclic monomer, the nonionic monomer, and the modified nanomonomer is 2-3:2-3:5-7:

1. The modified nanomonomer is selected from one or more of vinylmethyldiethoxysilane modified nano-calcium carbonate, vinylmethyldimethoxysilane modified nano-calcium carbonate, and vinyltriethoxysilane modified nano-calcium carbonate. In the preparation method of the modified nanomonomer, the ratio of the silane coupling agent with carbon-carbon double bonds to the nano-calcium carbonate is 1:4.8-5.

5.

2. The method of claim 1, wherein, The modified nanomonomers are added by dropwise addition.

3. The method of claim 1, wherein, The initiator is azobisisopropylimidazoline hydrochloride.

4. The method of claim 1, wherein, The total weight ratio of the sulfonic acid-containing monomer, the heterocyclic monomer, and the nonionic monomer to the weight of water is 1-2:

5.

5. The method of claim 1, wherein, The first polymerization reaction and the second polymerization reaction are carried out at the same temperature.

6. The method of claim 1, wherein, The first polymerization reaction takes 1-2 hours, and the second polymerization reaction takes 2-3 hours.

7. The filtration loss reducer prepared by any one of claims 1-6.

8. The application of the filtration loss reducer according to claim 7 in the preparation of water-based drilling fluid filtration loss reducers.

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