Filtrate reducer, water-based drilling fluid and application of filtrate reducer in underground high-temperature environment drilling engineering

Abstract

The invention provides a filtrate reducer, a water-based drilling fluid and application of the filtrate reducer in underground high-temperature environment drilling engineering. The filtrate reducer comprises carboxymethyl cellulose and a water-soluble polymer containing an epoxy group, and in-situ self-crosslinking of carboxymethyl cellulose in a high-temperature environment of a low-earth deep well is induced by utilizing a ring-opening coupling reaction of carboxyl and the epoxy group in the high-temperature environment, so that the filtrate reduction performance of the filtrate reducer at the high temperature is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a filtration reducer, an aqueous drilling fluid, and the application of the filtration reducer in a drilling engineering under a high-temperature environment underground, belonging to the technical field of oilfield chemistry. Background Art

[0002] With the rapid increase in the demand for oil and gas energy and the increasing depletion of shallow oil and gas resources, the exploration and development of deep oil and gas are important ways for the sustainable development of China's oil industry and energy security. However, as the exploration and development move deeper, the formation temperature is getting higher and higher. In the drilling engineering under a high-temperature environment underground, high temperature has the most serious damage to the performance of the drilling fluid. The loss of the drilling fluid performance is likely to cause complex situations such as wellbore instability and stuck pipe, seriously affecting the safety, economy, and efficiency of the drilling engineering. At the same time, the chemical treatment agents in the drilling fluid exposed to the soil, surface water, and groundwater will cause serious pollution to the surrounding environment. With the increasing awareness of environmental protection and the increasingly strict environmental protection regulations and measures in various countries around the world, green and environmentally friendly drilling fluid treatment agents and systems have become the future trend. Therefore, developing a drilling fluid system that can meet the requirements of drilling engineering under high-temperature and high-pressure complex conditions and meet the environmental protection requirements is a common technical problem and important challenge faced at home and abroad, and has important significance and application value for the exploration and development of deep oil and gas resources.

[0003] Filtration reducers are the core treating agents for drilling fluids. Research and development of an environmentally friendly and high-temperature-resistant filtration reducer system is the key to maintaining and controlling the filtration properties of drilling fluids under high temperature and high pressure conditions, and is also a key technology determining the success or failure of drilling in high-temperature underground environments. Filtration reducers mainly include synthetic polymer-based filtration reducers and bio-based natural polymer-based filtration reducers. Due to the wide range of raw material sources, low price, easy biodegradability, and environmental friendliness, the development and utilization of natural polymers have become an important research direction in filtration reduction technology. Among many natural polymer materials, cellulose and its derivatives, which are inexpensive and the most abundant in source, have been widely used to prepare drilling fluid treating agents such as filtration reducers. In particular, carboxymethyl cellulose (CMC) and the like have become one of the most widely used filtration reducers [Carbohydrate Polymers, 2021, 259, 117740; Polymer Reviews, 2022, 62, 585 - 625; ACS Applied Materials Interfaces 2015, 7, 8, 5006–5016]. However, the main chain of cellulose molecules is connected by ether bonds. Under high temperature and shear action, the main chain of cellulose molecules is prone to thermal oxidative degradation or hydrolysis, resulting in the breakage of the main chain of cellulose molecules, thereby losing the ability to control filtration. In addition, the main chain of cellulose molecules is not rigid enough, and its molecular chain is prone to curl and deform under high temperature, reducing the high-temperature dispersion and coalescence ability of clay particles, and losing the control of the filtration properties and rheological properties of drilling fluids [Carbohydrate Polymers, 2021, 259, 117740; Polymer Reviews, 2022, 62, 585 - 625].

[0004] In the prior art, in order to improve the fluid loss reduction performance of cellulose fluid loss reducers in underground high temperature environments, researchers at home and abroad have carried out a lot of research on the physical and chemical modification of cellulose polymer chains, mainly using the esterification, etherification, sulfonation, cross-linking, grafting copolymerization and other reactions of hydroxyl groups on glucose units in cellulose molecular chains [Journal of Applied Polymer Science 2012, 124, 2340-2347; Carbohydrate Polymers, 2021, 259, 117740; Carbohydrate Polymers 2020, 229, 115465; RSC Adv., 2020, 10, 43204-43212; Polymer Reviews, 2022, 62, 585-625; International Journal of Molecular Sciences 2021, 22, 352; Carbohydrate Polymers 2009, 78, 95–99].

[0005] However, the above modification methods still have limited room for improving the temperature resistance of cellulose fluid loss agents, and the temperature resistance of the modified cellulose fluid loss agents is generally lower than 150°C. In addition, modification methods such as graft copolymerization also have problems such as complex processes, introduction of non-degradable and environmentally unfriendly polymer segments, and huge impact on the rheological properties of drilling fluids, which is not conducive to drilling construction. Moreover, most of the conventional modification methods are currently only applicable to the modification of cellulose containing a large number of hydroxyl groups in the main chain, while there are few studies on the modification methods of the most commonly used fluid loss agents such as carboxymethyl cellulose containing a large number of carboxyl groups on the polymer chain. Therefore, the research and development of environmentally friendly fluid loss agents with excellent high-temperature fluid loss reduction performance is an important issue that needs to be urgently solved in the fields of oilfield chemistry and drilling engineering. Summary of the invention

[0006] The main purpose of the present invention is to provide a fluid loss reducer, a water-based drilling fluid and the application of the fluid loss reducer in underground high-temperature environment drilling projects, so as to solve the problems of insufficient temperature resistance, environmental unfriendliness, high cost and complicated operation in the existing cellulose fluid loss agents during temperature resistance modification.

[0007] In order to achieve the above object, according to one aspect of the present invention, there is provided a fluid loss reducer, which comprises carboxymethyl cellulose and a water-soluble polymer containing an epoxy group, wherein the water-soluble polymer containing an epoxy group is selected from one or more of a compound of a structure shown in Formula I1, a compound of a structure shown in Formula I2, or a compound of a structure shown in Formula I3;

[0008]

[0009] In Formula I1, Formula I2, and Formula I3, x:y are each independently 1:20 to 5, and n are each independently 3 to 20; the number-average molecular weight of the water-soluble polymer containing an epoxy group is 5000 to 50000.

[0010] First of all, carboxymethyl cellulose is not only easily obtainable and environmentally friendly, but more importantly, its polymer chain contains a large number of carboxyl groups. Therefore, without any chemical modification, by simply blending it with the above water-soluble polymer containing an epoxy group of the present invention, the ring-opening coupling reaction can occur between carboxymethyl cellulose (containing carboxyl groups) and the water-soluble polymer (containing epoxy groups) under the subsequent high-temperature and water-containing environment in the underground, inducing in-situ self-crosslinking of carboxymethyl cellulose in the high-temperature environment underground, reducing the influence of high-temperature hydrolysis and chain scission of the cellulose main chain while increasing the rigidity of the cellulose polymer main chain, thereby significantly improving the high-temperature resistance of the fluid loss reducer on the basis of lower cost, simpler operation, and more environmentally friendly, enabling it to maintain excellent fluid loss reduction performance even in high-temperature operation environments. The above ring-opening coupling reaction is shown in the following formula:

[0011]

[0012] Secondly, it should be further noted that different from the traditional pre-crosslinking method, the self-crosslinking reaction of the above fluid loss reducer of the present invention occurs in the subsequent high-temperature environment underground. Before crosslinking, it is the viscosity of carboxymethyl cellulose itself, and after crosslinking, it can maintain the viscosity of carboxymethyl cellulose at the bottom of the well at high temperature, and also avoid the influence of the fluid loss reducer on the rheological properties of the drilling fluid.

[0013] In a preferred embodiment, the weight ratio of the water-soluble polymer containing an epoxy group to carboxymethyl cellulose is 1:10 to 1:5, for example, it can be 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10.

[0014] In an alternative embodiment, the water-soluble polymer containing an epoxy group represented by Formula I1 can be prepared by free radical copolymerization of a functional monomer glycidyl methacrylate containing an epoxy group and a hydrophilic monomer poly(ethylene glycol) methyl ether acrylate. The synthesis route is shown as follows:

[0015]

[0016] Specifically, the free radical copolymerization of glycidyl methacrylate and poly(ethylene glycol) methyl ether acrylate is to dissolve glycidyl methacrylate and poly(ethylene glycol) methyl ether acrylate in a solvent (such as N,N-dimethylformamide) according to the stoichiometric ratio, add an initiator (such as azobisisobutyronitrile) for polymerization, and then precipitate in ice ether and vacuum dry to obtain the above water-soluble polymer containing an epoxy group.

[0017] During the preparation process, it is preferred that the number-average molecular weight of polyethylene glycol in the hydrophilic monomer methoxypolyethylene glycol acrylate is 130-1100, that is, the number of -CH2CH2O- units is 3-20. Further preferably, the methoxypolyethylene glycol acrylate with a number-average molecular weight of polyethylene glycol of 440 is used, that is, the number of -CH2CH2O- units is 10. It is preferred that the molar ratio of glycidyl methacrylate to methoxypolyethylene glycol acrylate is 1:20-5, and further preferably 1:11-9. It is preferred that the polymerization temperature is 60-80 °C and the polymerization time is 12-24 h.

[0018] In another alternative embodiment, the water-soluble polymer containing an epoxy group represented by Formula I2 can be prepared by free radical copolymerization of a functional monomer glycidyl methacrylate containing an epoxy group and a hydrophilic monomer methoxypolyethylene glycol methacrylate. The synthesis route is as follows:

[0019]

[0020] Specifically, glycidyl methacrylate and methoxypolyethylene glycol methacrylate are dissolved in a solvent (such as N,N-dimethylformamide) according to the stoichiometric ratio, an initiator (such as azobisisobutyronitrile) is added for polymerization, and then the above-mentioned water-soluble polymer containing an epoxy group is obtained after precipitation in ice ether and vacuum drying.

[0021] During the preparation process, it is preferred that the number-average molecular weight of polyethylene glycol in the hydrophilic monomer methoxypolyethylene glycol methacrylate is 130-1100, that is, the number of -CH2CH2O- units is 3-20. Further preferably, the methoxypolyethylene glycol acrylate with a number-average molecular weight of polyethylene glycol of 440 is used, that is, the number of -CH2CH2O- units is 10. It is preferred that the molar ratio of glycidyl methacrylate to methoxypolyethylene glycol methacrylate is 1:20-5, and more preferably 1:11-9. It is preferred that the polymerization temperature is 50-80 °C and the polymerization time is 8-24 h.

[0022] In another alternative embodiment, the water-soluble polymer containing an epoxy group represented by Formula I3 can be prepared by free radical copolymerization of a functional monomer glycidyl methacrylate containing an epoxy group and a hydrophilic monomer methacryloylethyl sulfobetaine. The synthesis route is as follows:

[0023]

[0024] Specifically, the radical copolymerization of glycidyl methacrylate and methacryloylethyl sulfobetaine is carried out by dissolving glycidyl methacrylate and methacryloylethyl sulfobetaine in a solvent (such as a mixed solution of water and N,N-dimethylformamide, with a volume ratio of 5 to 20:1) according to the stoichiometric ratio, adding an initiator (such as ammonium persulfate and / or potassium persulfate) for polymerization, and then dialyzing in water and freeze-drying to obtain the above-mentioned water-soluble polymer containing epoxy groups.

[0025] During the preparation process, the molar ratio of glycidyl methacrylate to methacryloylethyl sulfobetaine is preferably 1:20 to 5, more preferably 1:11 to 9; the polymerization temperature is preferably 40 to 80 °C, and the polymerization time is 16 to 48 h.

[0026] Furthermore, it should be noted that the above-mentioned water-soluble polymer containing epoxy groups in the present invention can be obtained by copolymerizing commercially available glycidyl methacrylate and hydrophilic monomers. The polymerization reaction is simple and easy to perform, and the epoxy group content is easy to control, which is suitable for large-scale industrial production and has better industrial application prospects.

[0027] The present invention does not make special limitations on carboxymethyl cellulose. The carboxymethyl cellulose used in the present invention is the well-known, commercially available and widely used carboxymethyl cellulose. Considering the performance optimization of the filtration reducer such as solubility, thickening property, stability, acid resistance and salt resistance, carboxymethyl cellulose with a carboxymethyl substitution degree of 0.5 to 2.0 and a glucose unit polymerization degree of 200 to 1000 is preferably used.

[0028] To achieve the above object, according to another aspect of the present invention, an aqueous drilling fluid is provided, which includes the aforementioned filtration reducer, and in the aqueous drilling fluid, the weight content of the filtration reducer is 1 to 6 wt%. Due to the above reasons, the aqueous drilling fluid of the present invention has excellent high-temperature resistance performance.

[0029] To achieve the above object, according to another aspect of the present invention, an application of the aforementioned filtration reducer in the drilling engineering of high-temperature underground environment is provided, and the temperature of the high-temperature environment is 150 to 220 °C. Due to the above reasons, the filtration reducer has excellent filtration reduction performance in the high-temperature underground environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Shows the 1 HNMR nuclear magnetic spectrum of the water-soluble polymer prepared in Example 1 of the present invention.

[0031] Figure 2 Shows the FTIR spectrum of the water-soluble polymer prepared in Example 1 of the present invention.

[0032] Figure 3 The HNMR nuclear magnetic spectrum of the water-soluble polymer prepared in Example 9 of the present invention is shown. 1 HNMR nuclear magnetic spectrum.

[0033] Figure 4 The FTIR spectrum of the water-soluble polymer prepared in Example 9 of the present invention is shown.

[0034] Figure 5 The filter cake photo after aging at 160 °C for 16 h in Example 16 of the present invention is shown.

[0035] Figure 6 The filter cake photo after aging at 160 °C for 16 h in Example 23 of the present invention is shown. Detailed implementation manners

[0036] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the implementable scope of the present invention.

[0037] Preparation examples of water-soluble polymers containing epoxy groups

[0038] Example 1

[0039] Glycidyl methacrylate (1.42 g, 10 mmol), polyethylene glycol methyl ether acrylate with 3 ethylene glycol units (10.9 g, 50 mmol), and AIBN (0.24 g, 1.5 mmol) were added to a 100 mL reaction flask. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the system was purged with nitrogen three times by evacuation to thoroughly remove the oxygen in the system. Then, the polymerization reaction was carried out at 80 °C for 12 h, and the solution was slowly dropped into a large amount of ice ether for precipitation. After centrifugation, the supernatant was discarded, and the white precipitate was dried in a vacuum oven for 24 h to obtain a water-soluble polymer containing epoxy groups.

[0040] For the prepared water-soluble polymer containing epoxy groups, 1 HNMR characterization was carried out, and the nuclear magnetic spectrum is shown in the appendix Figure 1 The characteristic peaks of hydrogen in the methylene and methine groups in the polymer main chain, the characteristic peaks of hydrogen in the methylene and methine groups adjacent to the epoxy group, and the characteristic peaks of hydrogen in the methylene group in the polyethylene glycol unit can all be observed in Figure 1 , confirming that the water-soluble polymer containing epoxy groups was successfully prepared, and the number-average molecular weight is about 12,000.

[0041] For the prepared water-soluble polymer containing epoxy groups, FTIR characterization was carried out, and the spectrum is shown in the appendix Figure 2As shown. The characteristic peaks of methylene and methylene in the polymer main chain, the characteristic peak of epoxy bond, and the characteristic peak of carbon-oxygen bond in the polyethylene glycol unit are in Figure 2 All can be observed, confirming that the water-soluble polymer containing epoxy groups is successfully prepared.

[0042] Example 2

[0043] In a 100 mL reaction flask, glycidyl methacrylate (0.284 g, 2 mmol), polyethylene glycol methyl ether acrylate with 3 ethylene glycol units (8.72 g, 40 mmol), and AIBN (0.164 g, 1 mmol) were added. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the oxygen in the system was thoroughly removed by three vacuum-evacuation and nitrogen-filling operations. Then, the polymerization reaction was carried out at 60 °C for 24 h. After that, the solution was slowly dropped into a large amount of ice-cold diethyl ether for precipitation. After centrifugation, the supernatant was discarded. The white precipitate was placed in a vacuum oven and dried for 24 h to obtain a water-soluble polymer containing epoxy groups, with a number-average molecular weight of approximately 25,000.

[0044] Example 3

[0045] In a 150 mL reaction flask, glycidyl methacrylate (0.284 g, 2 mmol), polyethylene glycol methyl ether acrylate with 10 ethylene glycol units (10.52 g, 20 mmol), and AIBN (0.328 g, 2 mmol) were added. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the oxygen in the system was thoroughly removed by three vacuum-evacuation and nitrogen-filling operations. Then, the polymerization reaction was carried out at 60 °C for 24 h. After that, the solution was slowly dropped into a large amount of ice-cold diethyl ether for precipitation. After centrifugation, the supernatant was discarded. The white precipitate was placed in a vacuum oven and dried for 24 h to obtain a water-soluble polymer containing epoxy groups, with a number-average molecular weight of approximately 45,000.

[0046] Example 4

[0047] In a 150 mL reaction flask, glycidyl methacrylate (0.284 g, 2 mmol), polyethylene glycol methyl ether acrylate with 20 ethylene glycol units (11.86 g, 10 mmol), and AIBN (0.328 g, 2 mmol) were added. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the oxygen in the system was thoroughly removed by three vacuum-evacuation and nitrogen-filling operations. Then, the polymerization reaction was carried out at 80 °C for 12 h. After that, the solution was slowly dropped into a large amount of ice-cold diethyl ether for precipitation. After centrifugation, the supernatant was discarded. The white precipitate was placed in a vacuum oven and dried for 24 h to obtain a water-soluble polymer containing epoxy groups, with a number-average molecular weight of approximately 35,000.

[0048] Example 5

[0049] In a 100 mL reaction flask, glycidyl methacrylate (1.42 g, 10 mmol), polyethylene glycol methyl ether methacrylate with 3 ethylene glycol units (11.6 g, 50 mmol), and AIBN (0.24 g, 1.5 mmol) were added. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the oxygen in the system was thoroughly removed through three vacuum-nitrogen filling operations. Then, the polymerization reaction was carried out at 80 °C for 8 h. After that, the solution was slowly dropped into a large amount of ice ether for precipitation. After centrifugation, the supernatant was discarded. The white precipitate was placed in a vacuum oven and dried for 24 h to obtain a water-soluble polymer containing epoxy groups, with a number-average molecular weight of approximately 8000.

[0050] Example 6

[0051] In a 100 mL reaction flask, glycidyl methacrylate (0.284 g, 2 mmol), polyethylene glycol methyl ether methacrylate with 3 ethylene glycol units (9.28 g, 40 mmol), and AIBN (0.164 g, 1 mmol) were added. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the oxygen in the system was thoroughly removed through three vacuum-nitrogen filling operations. Then, the polymerization reaction was carried out at 70 °C for 18 h. After that, the solution was slowly dropped into a large amount of ice ether for precipitation. After centrifugation, the supernatant was discarded. The white precipitate was placed in a vacuum oven and dried for 24 h to obtain a water-soluble polymer containing epoxy groups, with a number-average molecular weight of approximately 15000.

[0052] Example 7

[0053] In a 150 mL reaction flask, glycidyl methacrylate (0.284 g, 2 mmol), polyethylene glycol methyl ether methacrylate with 10 ethylene glycol units (10.8 g, 20 mmol), and AIBN (0.328 g, 2 mmol) were added. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the oxygen in the system was thoroughly removed through three vacuum-nitrogen filling operations. Then, the polymerization reaction was carried out at 50 °C for 24 h. After that, the solution was slowly dropped into a large amount of ice ether for precipitation. After centrifugation, the supernatant was discarded. The white precipitate was placed in a vacuum oven and dried for 24 h to obtain a water-soluble polymer containing epoxy groups, with a number-average molecular weight of approximately 32000.

[0054] Example 8

[0055] In a 150 mL reaction flask, glycidyl methacrylate (0.284 g, 2 mmol), polyethylene glycol methyl ether methacrylate with 20 ethylene glycol units (12 g, 10 mmol), and AIBN (0.328 g, 2 mmol) were added. Subsequently, 80 mL of N,N-dimethylformamide was added. After complete dissolution, the system was evacuated and filled with nitrogen three times to thoroughly remove the oxygen in the system. Then, the polymerization reaction was carried out at 80 °C for 12 h. After that, the solution was slowly dropped into a large amount of ice-cold diethyl ether for precipitation. After centrifugation, the supernatant was discarded. The white precipitate was placed in a vacuum oven and dried for 24 h to obtain a water-soluble polymer containing epoxy groups, with a number-average molecular weight of approximately 50,000.

[0056] Example 9

[0057] Glycidyl methacrylate (0.284 g, 2 mmol) and 5 mL of N,N-dimethylformamide were stirred and dissolved in a 50 mL reaction flask. Subsequently, methacryloylethyl sulfobetaine (2.79 g, 10 mmol) dissolved in 25 mL of water was added. After mixing and stirring evenly, ammonium persulfate (0.23 g, 1 mmol) was added. After complete dissolution and nitrogen purging to remove oxygen, the polymerization reaction was carried out at 40 °C for 48 h. Then, the solution was transferred to a dialysis bag and dialyzed with deionized water for 48 h to remove unreacted monomers and impurities such as N,N-dimethylformamide. After freeze-drying, a water-soluble polymer containing epoxy groups was obtained, with a number-average molecular weight of approximately 5,000.

[0058] For the prepared water-soluble polymer containing epoxy groups, 1 HNMR characterization was carried out, and the NMR spectrum is shown in the appendix Figure 3 . The characteristic peaks of hydrogen in the methylene and methine groups in the polymer main chain, the characteristic peaks of hydrogen in the methylene and methine groups adjacent to the epoxy group, the characteristic peaks of hydrogen in the methyl and methylene groups adjacent to the nitrogen atom, and the characteristic peaks of hydrogen in the methylene group adjacent to the sulfonate group can all be observed in Figure 3 , confirming that the water-soluble polymer containing epoxy groups was successfully prepared.

[0059] For the prepared water-soluble polymer containing epoxy groups, FTIR characterization was carried out, and the spectrum is shown in the appendix Figure 4 . The characteristic peaks of methine and methylene in the polymer main chain, the characteristic peaks of the epoxy bond, the characteristic peaks of the methyl and methylene adjacent to the nitrogen atom and the carbon-nitrogen bond, and the characteristic peaks of the carbon-sulfur bond in the sulfonate group can all be observed in Figure 4 , confirming that the water-soluble polymer containing epoxy groups was successfully prepared.

[0060] Example 10

[0061] Glycidyl methacrylate (0.284 g, 2 mmol) and 5 mL of N,N-dimethylformamide were stirred and dissolved in a 100 mL reaction flask. Subsequently, methacryloylethyl sulfobetaine (5.6 g, 20 mmol) dissolved in 50 mL of water was added. After mixing and stirring evenly, ammonium persulfate (0.35 g, 1.5 mmol) was added. After being fully dissolved and purged with nitrogen to remove oxygen, the mixture was placed at 60 °C for a polymerization reaction for 32 h. Then, the solution was transferred to a dialysis bag and dialyzed with deionized water for 48 h to remove unreacted monomers and impurities such as N,N-dimethylformamide. After freeze-drying, a water-soluble polymer containing epoxy groups was obtained, and the number-average molecular weight was about 14,000.

[0062] Example 11

[0063] Glycidyl methacrylate (0.142 g, 1 mmol) and 2 mL of N,N-dimethylformamide were stirred and dissolved in a 50 mL reaction flask. Subsequently, methacryloylethyl sulfobetaine (5.6 g, 20 mmol) dissolved in 40 mL of water was added. After mixing and stirring evenly, ammonium persulfate (0.46 g, 2 mmol) was added. After being fully dissolved and purged with nitrogen to remove oxygen, the mixture was placed at 80 °C for a polymerization reaction for 16 h. Then, the solution was transferred to a dialysis bag and dialyzed with deionized water for 48 h to remove unreacted monomers and impurities such as N,N-dimethylformamide. After freeze-drying, a water-soluble polymer containing epoxy groups was obtained, and the number-average molecular weight was about 21,000.

[0064] Example 12

[0065] Glycidyl methacrylate (0.284 g, 2 mmol) and 5 mL of N,N-dimethylformamide were stirred and dissolved in a 50 mL reaction flask. Subsequently, methacryloylethyl sulfobetaine (4.2 g, 15 mmol) dissolved in 30 mL of water was added. After mixing and stirring evenly, ammonium persulfate (0.23 g, 1 mmol) was added. After being fully dissolved and purged with nitrogen to remove oxygen, the mixture was placed at 50 °C for a polymerization reaction for 32 h. Then, the solution was transferred to a dialysis bag and dialyzed with deionized water for 48 h to remove unreacted monomers and impurities such as N,N-dimethylformamide. After freeze-drying, a water-soluble polymer containing epoxy groups was obtained, and the number-average molecular weight was about 18,000.

[0066] Example 13

[0067] The water-soluble polymer containing epoxy groups prepared in Example 1 was blended with carboxymethyl cellulose (carboxymethyl substitution degree of 0.5 and degree of polymerization of glucose units of 200) in a high-speed crusher, and the blending weight ratio was 1:10 to prepare a fluid loss reducer.

[0068] According to Q / SY17111-2019 "Classification and Detection Methods for the Biological Toxicity of Oilfield Chemical Agents and Drilling Fluids" for the biological toxicity test of this filtration reducer, the results show that the water-soluble polymer containing epoxy groups prepared in this example and the filtration reducer formed by blending with carboxymethyl cellulose are non-toxic and free of heavy metals, and are safe, environmentally friendly.

[0069] Example 14

[0070] The water-soluble polymer containing epoxy groups prepared in Example 5 was blended with carboxymethyl cellulose (carboxymethyl substitution degree of 0.8 and glucose unit polymerization degree of 500) using a high-speed grinder, and the blending weight ratio was 1:5 to prepare a filtration reducer.

[0071] According to Q / SY17111-2019 "Classification and Detection Methods for the Biological Toxicity of Oilfield Chemical Agents and Drilling Fluids" for the biological toxicity test of this filtration reducer, the results show that the water-soluble polymer containing epoxy groups prepared in this example and the filtration reducer formed by blending with carboxymethyl cellulose are non-toxic and free of heavy metals, and are safe, environmentally friendly.

[0072] Example 15

[0073] The water-soluble polymer containing epoxy groups prepared in Example 10 was blended with carboxymethyl cellulose (carboxymethyl substitution degree of 2.0 and glucose unit polymerization degree of 1000) using a high-speed grinder, and the blending weight ratio was 1:8 to prepare a filtration reducer.

[0074] According to Q / SY17111-2019 "Classification and Detection Methods for the Biological Toxicity of Oilfield Chemical Agents and Drilling Fluids" for the biological toxicity test of this filtration reducer, the results show that the water-soluble polymer containing epoxy groups prepared in this example and the filtration reducer formed by blending with carboxymethyl cellulose are non-toxic and free of heavy metals, and are safe, environmentally friendly.

[0075] Examples 16 - 26

[0076] The water-soluble polymers containing epoxy groups prepared in Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 were respectively blended with carboxymethyl cellulose (carboxymethyl substitution degree of 0.5 and glucose unit polymerization degree of 500) using a high-speed grinder to prepare filtration reducers with different compositions, and the formulations are shown in Table 1.

[0077] Preparation of fresh water base mud with a mass concentration of 2%: Add 400 mL of water to a high-speed stirring cup. Under stirring conditions, add 16 g of bentonite and 1.2 g of sodium carbonate to the water, and stir at high speed for 20 minutes until uniform. Seal and place for curing for 24 h. Subsequently, take a certain amount of fresh water base mud and add 2 wt% of carboxymethyl cellulose or 2 wt% of filtration loss reducer. After stirring and dissolving evenly, divide it into two equal volumes. One part is cured at room temperature (25 °C) for 24 h, and the other part is aged at 160 °C for 16 h. Then, evaluate the apparent viscosity and filtration loss reduction performance (FL API ) of the filtration loss reducer according to GB / T 16783.1-2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids". The test results are shown in Table 1:

[0078] Table 1

[0079]

[0080] As can be seen from Table 1, in Example 16, carboxymethyl cellulose was added as a filtration loss reducer to the fresh water base mud. After high-temperature aging, the viscosity of the base mud decreased significantly, from 42.3 mPa·s to 8.2 mPa·s, indicating that the carboxymethyl cellulose filtration loss reducer underwent obvious high-temperature hydrolysis during the high-temperature aging process. This also led to a significant increase in its API filtration loss, from 11.2 mL to 34.8 mL, indicating that the high-temperature filtration loss reduction performance of this filtration loss reducer is poor. Attached Figure 5 is the filter cake formed after high-temperature aging of Example 16. From Figure 5 it can be seen that the filter cake is thick and porous, confirming that high temperature leads to a decrease in the filtration loss reduction performance of this filtration loss reducer.

[0081] As can be seen from Table 1, in Examples 17-32, the performances before and after aging of carboxymethyl cellulose filtration loss reducers mixed with different contents of water-soluble polymers containing epoxy groups are provided. In the fresh water base mud, carboxymethyl cellulose filtration loss reducers containing water-soluble polymers with epoxy groups of Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12 were mixed. After aging at 160 °C for 16 h, the decrease in viscosity caused by the thermal degradation of carboxymethyl cellulose was significantly reduced, indicating that its high-temperature stability was significantly improved. Moreover, compared with before aging, the increase in API filtration loss was very small, indicating that the filtration loss reducers used in Examples 17-26 have good high-temperature filtration loss reduction effects. In addition, representatively, attached Figure 6 is the filter cake formed after high-temperature aging of Example 23. From Figure 6 it can be seen that the filter cake is very thin and dense, further indicating that good high-temperature filtration loss reduction effects can be obtained by using the filtration loss reducer of Example 23.

[0082] Example 33

[0083] The water-soluble polymer containing epoxy groups prepared in Example 7 was blended with carboxymethyl cellulose using a high-speed grinder, and the blending weight ratio was 1:10 to obtain a filtration reducer.

[0084] The preparation process of the fresh water-based mud with a mass concentration of 4% is as follows: Add 400 mL of water to a high-speed stirring cup, add 16 g of bentonite and 1.2 g of sodium carbonate to the water under stirring conditions, stir at high speed for 20 minutes until uniform, and seal and place for curing for 24 h. Subsequently, a certain amount of the fresh water-based mud was taken and 4% of the above filtration reducer was added. After stirring and dissolving evenly, it was divided into two equal-volume portions. One portion was cured at room temperature (25 °C) for 24 h, and the other portion was aged at 150 °C for 16 h. Then, the filtration reduction performance (FL API ) of the filtration reducer was evaluated according to GB / T 16783.1-2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids". The results show that the API filtration loss before aging was 9.8 mL, and after aging at 150 °C for 16 h, the API filtration loss was 12.7 mL. The increase in the API filtration loss compared with that before aging was very small, indicating that the used filtration reducer has good high-temperature filtration reduction effect.

[0085] Example 34

[0086] The water-soluble polymer containing epoxy groups prepared in Example 9 was blended with carboxymethyl cellulose using a high-speed grinder, and the blending weight ratio was 1:10 to obtain a filtration reducer.

[0087] The preparation process of the fresh water-based mud with a mass concentration of 2% is as follows: Add 400 mL of water to a high-speed stirring cup, add 16 g of bentonite and 1.2 g of sodium carbonate to the water under stirring conditions, stir at high speed for 20 minutes until uniform, and seal and place for curing for 24 h. Subsequently, a certain amount of the fresh water-based mud was taken and 2 wt% of the above filtration reducer was added. After stirring and dissolving evenly, it was divided into two equal-volume portions. One portion was cured at room temperature (25 °C) for 24 h, and the other portion was aged at 180 °C for 16 h. Then, the filtration reduction performance (FL API ) of the filtration reducer was evaluated according to GB / T 16783.1-2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids". The results show that the API filtration loss before aging was 13.4 mL, and after aging at 180 °C for 16 h, the API filtration loss was 18.6 mL. The increase in the API filtration loss compared with that before aging was still very small, indicating that the used filtration reducer has good high-temperature filtration reduction effect.

[0088] Example 35

[0089] The water-soluble polymer containing epoxy groups prepared in Example 5 was blended with carboxymethyl cellulose using a high-speed grinder, and the blending weight ratio was 1:8 to obtain a fluid loss reducer.

[0090] The preparation process of the fresh water-based mud with a mass concentration of 2% is as follows: Add 400 mL of water to a high-speed stirring cup, add 16 g of bentonite and 1.2 g of sodium carbonate to the water under stirring conditions, stir at high speed for 20 minutes until uniform, and seal and place for curing for 24 h. Subsequently, take a certain amount of the fresh water-based mud and add 6 wt% of the above fluid loss reducer, stir and dissolve evenly, and divide it into two equal volumes. One portion is cured at room temperature (25 °C) for 24 h, and the other portion is aged at 200 °C for 16 h. Then, evaluate the fluid loss reduction performance (FL API ) of the fluid loss reducer according to GB / T 16783.1-2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids". The results show that the API fluid loss before aging is 10.2 mL, and after aging at 200 °C for 16 h, the API fluid loss is 17.6 mL. The increase in the API fluid loss compared with that before aging is still very small, indicating that the fluid loss reducer used has good high-temperature fluid loss reduction effect.

[0091] Example 36

[0092] The water-soluble polymer containing epoxy groups prepared in Example 12 was blended with carboxymethyl cellulose using a high-speed grinder, and the blending weight ratio was 1:6 to obtain a fluid loss reducer.

[0093] The preparation process of the fresh water-based mud with a mass concentration of 2% is as follows: Add 400 mL of water to a high-speed stirring cup, add 16 g of bentonite and 1.2 g of sodium carbonate to the water under stirring conditions, stir at high speed for 20 minutes until uniform, and seal and place for curing for 24 h. Subsequently, take a certain amount of the fresh water-based mud and add 6 wt% of the above fluid loss reducer, stir and dissolve evenly, and divide it into two equal volumes. One portion is cured at room temperature (25 °C) for 24 h, and the other portion is aged at 220 °C for 16 h. Then, evaluate the fluid loss reduction performance (FL API ) of the fluid loss reducer according to GB / T 16783.1-2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids". The results show that the API fluid loss before aging is 12.1 mL, and after aging at 220 °C for 16 h, the API fluid loss is 16.9 mL. The increase in the API fluid loss compared with that before aging is still very small, indicating that the fluid loss reducer used has good high-temperature fluid loss reduction effect.

Claims

1. A fluid loss reducer, characterized in that, It includes carboxymethyl cellulose and a water-soluble polymer containing an epoxy group, and the water-soluble polymer containing an epoxy group is selected from one or more of the compounds with the structure shown in Formula I1, the compounds with the structure shown in Formula I2, or the compounds with the structure shown in Formula I3; In Formula I1, Formula I2 and Formula I3, x:y are each independently 1:20 to 5, and n are each independently 3 to 20; the number-average molecular weight of the water-soluble polymer containing an epoxy group is 5000 to 50000.

2. The fluid loss reducer according to claim 1, wherein The weight ratio of the water-soluble polymer containing an epoxy group to the carboxymethyl cellulose is 1:10 to 5.

3. The fluid loss reducer according to claim 1, wherein The compound with the structure shown in Formula I1 is obtained by free radical copolymerization of glycidyl methacrylate and methoxypolyethylene glycol acrylate in a molar ratio of 1:20 to 5.

4. The fluid loss reducer according to claim 3, wherein The polymerization temperature of glycidyl methacrylate and methoxypolyethylene glycol acrylate is 60 to 80 °C, and the polymerization time is 12 to 24 h.

5. The fluid loss reducer according to claim 1, wherein The compound with the structure shown in Formula I2 is obtained by free radical copolymerization of glycidyl methacrylate and methoxypolyethylene glycol methacrylate in a molar ratio of 1:20 to 5.

6. The fluid loss reducer according to claim 5, wherein The polymerization temperature of glycidyl methacrylate and methoxypolyethylene glycol methacrylate is 50 to 80 °C, and the polymerization time is 8 to 24 h.

7. The fluid loss reducer according to claim 1, characterized in that, The compound with the structure shown in Formula I3 is obtained by free radical copolymerization of glycidyl methacrylate and methacryloylethyl sulfobetaine in a molar ratio of 1:20 to 5.

8. The fluid loss reducer according to claim 7, wherein The polymerization temperature of glycidyl methacrylate and methacryloylethyl sulfobetaine is 40 to 80 °C, and the polymerization time is 16 to 48 h.

9. A water-based drilling fluid, characterized in that, It includes the fluid loss reducer according to any one of claims 1 to 8, and in the drilling fluid, the weight content of the fluid loss reducer is 1 to 6 wt%.

10. Application of the fluid loss reducer according to any one of claims 1 to 8 in a drilling engineering in a high-temperature environment underground, and the temperature of the high-temperature environment is 150 to 220 °C.

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