A dynamic reversible cross-linking agent for temperature-resistant and salt-resistant solid-free water-based drilling fluid, and a preparation method and application thereof

Abstract

This invention provides a dynamic reversible crosslinking shearing agent for temperature- and salt-resistant, solids-free water-based drilling fluids, its preparation method, and its application, belonging to the field of oilfield drilling technology. The shearing agent of this invention is prepared from the following raw materials: 2-acrylamido-2-methylpropanesulfonic acid, 2-methacryloyloxyethyl phosphocholine, diacetone acrylamide, adipate dihydrazide, N,N-dimethylacrylamide, lauryl methacrylate, bis[2-(methacryloyloxy)ethyl] phosphate, initiator, deionized water, Span 80, and OP-10. The shearing agent of this invention exhibits excellent structural stability under high temperature and high salt conditions, while also possessing low-shear shearing capacity; the polymer network contains reversible acylhydrazone bonds, endowing the system with excellent shear recovery and structural reconstruction capabilities.

Description

Technical Field

[0001] This invention relates to a dynamic reversible crosslinking and shearing agent for temperature- and salt-resistant solid-free water-based drilling fluid, its preparation method and application, belonging to the field of oilfield drilling technology. Background Technology

[0002] Deep and ultra-deep reservoirs contain abundant oil and natural gas resources. These formations are typically characterized by high bottom-hole temperatures, high salinity, and widespread distribution of salt-gypsum layers, which places higher demands on the temperature resistance and salt tolerance of drilling fluid systems.

[0003] Solids-free water-based drilling fluids, due to the absence of solid particles such as bentonite, offer advantages such as system cleanliness, good reservoir protection, excellent lubrication, and improved mechanical drilling speed, making them promising for deep and complex formation drilling. However, solids-free drilling fluid systems lack the structural support provided by solid particles; their rheological properties rely entirely on polymeric treatment agents to construct a spatial network structure. Among these, cutting agents play a decisive role in maintaining system stability, improving low-shear shear stress, and enhancing cuttings suspension capacity.

[0004] Existing water-based drilling fluid skimmers are mostly linear or micro-crosslinked polymer systems, which exhibit poor stability under high-temperature and high-salt conditions. At high temperatures, the polymer backbone is prone to thermal degradation or breakage; under high salinity conditions, Na... + K + and Ca 2+ Plasma significantly compresses the electrical bilayer of polymer molecular chains, weakening the repulsive forces between chains and causing the chain segments to change from an extended state to a coiled and collapsed state, making it difficult to form an effective three-dimensional network structure. Meanwhile, traditional shearing agents mainly rely on a single covalent structure or weak physical association to maintain system stability. Once subjected to strong shear or high-temperature aging, the network structure is irreversibly destroyed, lacking effective self-recovery capabilities, leading to a significant decrease in the low-shear shear force and static shear force of the drilling fluid.

[0005] The aforementioned problems are particularly pronounced in solids-free drilling fluid systems. Once the cutting agent fails, the system will quickly lose its spatial structural support, resulting in a decrease in drilling fluid viscosity and a weakening of its cuttings-carrying capacity. This makes it difficult to effectively suspend and transport drill cuttings, thereby affecting wellbore cleanliness and wellbore stability. In severe cases, it may even induce safety risks such as well kicks and blowouts.

[0006] Chinese patent document CN 115572347 A discloses a high-temperature and high-salt resistant thickening and shearing agent for water-based drilling fluids, its preparation method, and its application. This invention is prepared by emulsion polymerization of acrylamide monomers, temperature- and salt-resistant monomers, cationic monomers, ethyl methacrylate-2-(2-ureido-4[1H]-6-methylpyrimidinone)-methacrylate (UPyMA), and a chemical crosslinking agent, triallyl. While this invention can improve rheological properties under high-temperature and high-salt conditions, it has shortcomings in balancing high shear fluidity and low shear structural recovery.

[0007] Therefore, developing a shearing agent with excellent structural stability and shear recovery capability under high temperature and high salinity conditions is of great significance for ensuring the safe and efficient application of solid-free water-based drilling fluid systems in deep and ultra-deep formations. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a dynamic reversible crosslinking shearing agent for temperature- and salt-resistant, solid-free water-based drilling fluids, its preparation method, and its applications. The shearing agent of this invention exhibits excellent structural stability under high-temperature and high-salt conditions, while also possessing low-shear shearing capability. The polymer network of the shearing agent contains reversible acylhydrazone bonds, which can undergo reversible destructive processes under high shear, thereby preventing excessive thickening of the system in the high-shear region. When shearing stops or weakens, acylhydrazone bonds can be re-formed, and the network structure is re-established, thus endowing the system with excellent shear recovery and structural reconstruction capabilities.

[0009] The technical solution of the present invention is as follows:

[0010] A dynamic reversible crosslinking and shearing agent for temperature- and salt-resistant, solid-free water-based drilling fluid is prepared from the following raw materials in parts by weight: 12-18 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6-8 parts of 2-methacryloyloxyethyl phosphocholine, 3-5 parts of diacetone acrylamide, 3-5 parts of adipic acid dihydrazide, 6-8 parts of N,N-dimethylacrylamide, 0.5-1.5 parts of lauryl methacrylate, 0.2-0.3 parts of bis[2-(methacryloyloxy)ethyl] phosphate, 3-4 parts of initiator, 80-120 parts of deionized water, 5-15 parts of Span 80, and 0.5-2 parts of OP-10.

[0011] According to a preferred embodiment of the present invention, a dynamic reversible crosslinking and shearing agent for temperature- and salt-resistant solids-free water-based drilling fluid is prepared from the following raw materials in parts by weight: 12-18 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6-8 parts of 2-methacryloyloxyethyl phosphocholine, 3-5 parts of diacetone acrylamide, 3-5 parts of adipic acid dihydrazide, 6-8 parts of N,N-dimethylacrylamide, 0.5-1.5 parts of lauryl methacrylate, 0.2-0.3 parts of bis[2-(methacryloyloxy)ethyl] phosphate, 3-4 parts of initiator, 100 parts of deionized water, 10 parts of Span 80, and 1 part of OP-10.

[0012] According to a preferred embodiment of the present invention, the initiator is an aqueous solution of ammonium persulfate with a mass concentration of 5-15 wt% and an aqueous solution of sodium bisulfite with a mass concentration of 5-15 wt%; the mass ratio of the aqueous solution of ammonium persulfate to the aqueous solution of sodium bisulfite is 2-3:1-2, preferably 2:1-2.

[0013] The preparation method of the above-mentioned temperature- and salt-resistant solid-free water-based drilling fluid dynamic reversible crosslinking shearing agent includes the following steps:

[0014] (1) Span 80, OP-10 and lauryl methacrylate were added to deionized water and emulsified by shearing to obtain a micelle emulsion;

[0015] (2) Disperse 2-acrylamido-2-methylpropanesulfonic acid thoroughly in deionized water and adjust the pH to 7-8; add 2-methacryloyloxyethyl phosphate choline, diacetone acrylamide, N,N-dimethylacrylamide, and bis[2-(methacryloyloxy)ethyl] phosphate in sequence and mix thoroughly to obtain a monomer solution;

[0016] (3) Add the micelle emulsion to the monomer solution, mix thoroughly, and adjust the pH value to neutral; add the initiator to carry out free radical polymerization reaction; add adipic dihydrazide, adjust the pH to 5, and after aging reaction, filter, wash, dry and pulverize to obtain a temperature-resistant and salt-resistant solid-phase water-based drilling fluid dynamic reversible crosslinking and cutting agent.

[0017] According to a preferred embodiment of the present invention, the mass ratio of deionized water in step (1) to deionized water in step (2) is 5-10:90-95.

[0018] According to a preferred embodiment of the present invention, in step (2), the pH is adjusted using an aqueous sodium hydroxide solution with a mass concentration of 25-30%.

[0019] According to a preferred embodiment of the present invention, in step (3), the dropwise addition is carried out under stirring conditions; the pH is adjusted to neutral using an aqueous acetic acid solution with a mass concentration of 25-30%; the free radical polymerization reaction temperature is 35-50℃, the reaction time is 2-6h, and the reaction is carried out under the protection of a protective gas and under stirring conditions; the protective gas is nitrogen or argon.

[0020] According to a preferred embodiment of the present invention, in step (3), the pH is adjusted to 5 using an aqueous acetic acid solution with a mass concentration of 25-30%; the aging reaction temperature is 40-45°C; the aging reaction time is 1-3 hours; and the aging reaction is carried out under the protection of a protective gas and under stirring conditions; the protective gas is nitrogen or argon.

[0021] The above-mentioned dynamic reversible crosslinking and shearing agent for temperature- and salt-resistant solid-free water-based drilling fluids is applied in solid-free water-based drilling fluids.

[0022] The technical features and beneficial effects of this invention are as follows:

[0023] 1. This invention utilizes 2-acrylamido-2-methylpropanesulfonic acid and 2-methacryloyloxyethyl phosphoric acid to synergistically construct a salt-tolerant system. 2-acrylamido-2-methylpropanesulfonic acid provides a strong hydration sulfonic acid group, enabling the maintenance of a stable hydration layer under high salinity conditions; 2-methacryloyloxyethyl phosphoric acid introduces a phosphoric acid structure, further enhancing the polymer's hydrophilicity and interfacial stability. The synergistic effect of these two components effectively inhibits polymer chain shrinkage under high-salt conditions, maintaining a large hydrodynamic volume and spatially expanded structure, thus providing a foundation for the formation of network structures in solid-free drilling fluid systems.

[0024] 2. This invention uses bis[2-(methacryloyloxy)ethyl]phosphate as a phosphorus-containing bifunctional polymerizable crosslinking agent, which participates in the copolymerization reaction during free radical polymerization to form a stable three-dimensional covalent crosslinked network. This crosslinking agent not only provides permanent crosslinking points but also introduces phosphate ester structures into the network nodes, giving the crosslinking nodes strong polarity and aqueous compatibility. This permanent covalent network is not easily destroyed under high temperature and continuous shear conditions, which can significantly improve the structural stability of the shearing agent and prevent network collapse in the solids-free drilling fluid system after thermal aging. Its high-temperature resistance and structural retention capabilities ensure that the system retains its basic spatial support framework after thermal rolling aging.

[0025] 3. This invention introduces diacetone acrylamide and diacylhydrazine compounds to construct a carbonyl-hydrazine dynamic covalent bond. Diacetone acrylamide provides the ketone group reaction site, while the diacylhydrazine compound provides the hydrazine group reaction site. The two form a reversible hydrazone bond within the polymer network. Therefore, this dynamic covalent bond can undergo reversible destructive and exchange under high shear, transforming the local network from a compact state to a relatively loose state, thus preventing excessive viscosity in the high-shear region. When shearing stops or weakens, the two can re-form the hydrazone bond, the network is re-established, and low-shear shear stress and static suspension capacity are restored, thus endowing the system with excellent shear recovery and structural reconstruction capabilities. In practical field applications, this directly addresses key requirements in drilling fluid applications: avoiding excessive thickening during surface mixing and circulation; and rapidly restoring the structure and suspending rock cuttings under conditions of pump shutdown, low flow rate, or low annular shear.

[0026] 4. This invention incorporates a small amount of lauryl methacrylate containing hydrophobic associating units and polar groups, along with a phosphorus-containing crosslinked network and dynamic covalent bonds, to synergistically construct a reversible physical association shearing system. Each unit works synergistically to enable the drilling fluid to form a spatial support structure under low shear conditions and improve its ability to suspend cuttings. It also possesses high-temperature and high-salt stability, low-shear shearing ability, and excellent shear recovery ability. Attached Figure Description

[0027] Figure 1 The infrared spectrum of the cutting agent prepared in Example 3. Detailed Implementation

[0028] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0029] Unless otherwise specified, the reagents, materials and equipment used in the examples are commercially available; the experimental methods described below are conventional methods unless otherwise specified.

[0030] Example 1

[0031] A temperature- and salt-resistant, solid-free, water-based drilling fluid dynamic reversible crosslinking and shearing agent A1 is prepared from the following raw materials in parts by weight:

[0032] 15 parts of 2-acrylamido-2-methylpropanesulfonic acid, 7 parts of 2-methacryloyloxyethyl phosphocholine, 4 parts of diacetone acrylamide, 4 parts of adipic acid dihydrazide, 7 parts of N,N-dimethylacrylamide, 1 part of lauryl methacrylate, 0.25 parts of bis[2-(methacryloyloxy)ethyl] phosphate, 3 parts of initiator (2 parts of 10wt% ammonium persulfate aqueous solution and 1 part of 10wt% sodium bisulfite aqueous solution), 100 parts of deionized water, 10 parts of Span 80, and 1 part of OP-10.

[0033] The preparation method of the above-mentioned temperature- and salt-resistant solids-free water-based drilling fluid dynamic reversible crosslinking shearing agent A1 includes the following steps:

[0034] (1) After mixing lauryl methacrylate with Span 80 and OP-10, add it to 5 parts of deionized water and place it on a mixer to stir for 20 minutes to emulsify, so that lauryl methacrylate is fully dispersed to obtain a micelle emulsion;

[0035] (2) Add 2-acrylamido-2-methylpropanesulfonic acid to 95 parts of deionized water, stir to dissolve, adjust the pH to 7.0-8.0 with 30% sodium hydroxide aqueous solution, then add 2-methacryloyloxyethyl phosphate choline, diacetone acrylamide, N,N-dimethylacrylamide and bis[2-(methacryloyloxy)ethyl] phosphate in sequence, stir until uniformly dispersed to obtain monomer solution.

[0036] (3) Under stirring conditions, the micelle emulsion was added dropwise to the monomer solution using a dropping funnel. After thorough stirring, the pH of the solution was adjusted to neutral 7 using a 30% acetic acid aqueous solution to obtain a mixed reaction solution. The mixed reaction solution was transferred to a three-necked flask, and nitrogen gas was purged for 30 min to remove oxygen. The temperature was then raised to 40°C, and an initiator was added to carry out redox-initiated polymerization stirring reaction for 4 hours. Subsequently, adipic acid dihydrazide was added, and the pH was adjusted to 5 using a 30% acetic acid aqueous solution. The reaction was carried out at 40°C under nitrogen atmosphere with stirring for 2 hours to obtain a viscous crude polymer. The crude polymer was filtered, and the filtrate was washed twice with acetone. It was then vacuum dried at 70°C for 24 hours and pulverized to obtain a temperature- and salt-resistant, solid-free, water-based drilling fluid dynamic reversible crosslinking and shearing agent A1.

[0037] Example 2

[0038] A temperature- and salt-resistant, solid-free, water-based drilling fluid dynamic reversible crosslinking and shearing agent A2 is prepared from the following raw materials in parts by weight:

[0039] 12 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6 parts of 2-methacryloyloxyethyl phosphocholine, 3 parts of diacetone acrylamide, 3 parts of adipic acid dihydrazide, 6 parts of N,N-dimethylacrylamide, 0.5 parts of lauryl methacrylate, 0.2 parts of bis[2-(methacryloyloxy)ethyl] phosphate, 3 parts of initiator (2 parts of 10wt% ammonium persulfate aqueous solution and 1 part of 10wt% sodium bisulfite aqueous solution), 100 parts of deionized water, 10 parts of Span 80, and 1 part of OP-10.

[0040] The preparation method of the above-mentioned temperature- and salt-resistant solid-free water-based drilling fluid dynamic reversible crosslinking shearing agent A2 is the same as in Example 1.

[0041] Example 3

[0042] A temperature- and salt-resistant, solid-free, water-based drilling fluid dynamic reversible crosslinking and shearing agent A3 is prepared from the following raw materials in parts by weight:

[0043] 18 parts of 2-acrylamido-2-methylpropanesulfonic acid, 8 parts of 2-methacryloyloxyethyl phosphocholine, 5 parts of diacetone acrylamide, 5 parts of adipic acid dihydrazide, 8 parts of N,N-dimethylacrylamide, 1.5 parts of lauryl methacrylate, 0.3 parts of bis[2-(methacryloyloxy)ethyl] phosphate, 4 parts of initiator (2 parts of 10wt% ammonium persulfate aqueous solution and 2 parts of 10wt% sodium bisulfite aqueous solution), 100 parts of deionized water, 10 parts of Span 80, and 1 part of OP-10.

[0044] The preparation method of the above-mentioned temperature- and salt-resistant solid-free water-based drilling fluid dynamic reversible crosslinking shearing agent A3 is the same as in Example 1.

[0045] The infrared spectrum prepared in this embodiment is as follows: Figure 1 As shown, the obtained cutting agent has a cutting depth of 3200–3300 cm. -1 A broad absorption peak appears nearby, which can be attributed to the stretching vibration of NH in the amide, acylhydrazide, and hydrazinohydrazone structures; 2921 cm⁻¹ -1 The nearby absorption peaks correspond to the stretching vibrations of CH in the polymer backbone and the long-chain alkyl group of lauryl methacrylate, indicating that a hydrophobic long-chain structure has been introduced into the polymer system. (1620 cm⁻¹) -1 The presence of a characteristic C=N absorption peak nearby indicates that the carbonyl group in diacetone acrylamide reacts with adipic acid dihydrazide to form a hydrazone / acylhydrazone type dynamic covalent bond. (1180 cm⁻¹) -1 The nearby absorption peak can be attributed to the S=O stretching vibration of the sulfonic acid group in 2-acrylamido-2-methylpropanesulfonic acid, and may overlap with the P=O absorption in the phosphorus-containing structure; 1110 cm⁻¹ -1The nearby absorption peaks correspond to the COC and POC structures, indicating that ester-containing and phosphorus-containing functional structures such as 2-methacryloyloxyethyl phosphocholine and bis[2-(methacryloyloxy)ethyl] phosphate have been successfully introduced. (950 cm⁻¹) -1 The nearby absorption peaks can be attributed to the CN in the quaternary ammonium salt structure. + Vibration, 630 cm -1 The nearby absorption peaks are related to the CS or sulfonate-related vibrations in 2-acrylamido-2-methylpropanesulfonic acid. In summary, the infrared spectrum shows characteristic absorption peaks for sulfonic acid groups, phosphorus-containing groups, amide / hydrazone structures, hydrazone / hydrazone dynamic bonds, and long-chain alkyl groups. This indicates that functional structures such as 2-acrylamido-2-methylpropanesulfonic acid, 2-methacryloyloxyethyl phosphorocholine, diacetone acrylamide, adipic acid dihydrazide, N,N-dimethylacrylamide, lauryl methacrylate, and phosphorus-containing crosslinking monomers have been successfully introduced into the polymer. The resulting product exhibits multiple structural features, including hydrophobic association, phosphorus-containing crosslinking, and dynamic reversible crosslinking, consistent with the molecular design of the multi-crosslinked slicing agent of this invention.

[0046] Comparative Example 1

[0047] A cutting agent DA1 is as described in Example 3, except that lauryl methacrylate is not added; the composition of other raw materials is the same as in Example 3.

[0048] The preparation method of the above-mentioned cutting agent is the same as described in Example 3, except that the cutting agent DA1 is obtained.

[0049] Comparative Example 2

[0050] A cutting agent DA2 is as described in Example 3, except that 2-methacryloyloxyethyl phosphocholine is not added; the composition of other raw materials is the same as in Example 3.

[0051] The preparation method of the above-mentioned cutting agent is the same as described in Example 3, except that the cutting agent DA2 is obtained.

[0052] Comparative Example 3

[0053] A cutting agent DA3 is as described in Example 3, except that diacetone acrylamide is not added; the composition of other raw materials is the same as in Example 3.

[0054] The preparation method of the above-mentioned cutting agent is the same as described in Example 3, except that the cutting agent DA3 is obtained.

[0055] Comparative Example 4

[0056] A cutting agent DA4 is as described in Example 3, except that lauryl methacrylate is replaced with an equal amount of methacrylate; the composition of other raw materials is the same as in Example 3.

[0057] The preparation method of the above-mentioned cutting agent is the same as that described in Example 3, except that the cutting agent DA4 is obtained.

[0058] Comparative Example 5

[0059] A cutting agent DA5 is used as described in Example 3, except that N,N-dimethylacrylamide is replaced with an equal amount of acrylamide. The composition of other raw materials is the same as in Example 3.

[0060] The preparation method of the above-mentioned cutting agent is the same as that described in Example 3, except that the cutting agent DA5 is obtained.

[0061] Comparative Example 6

[0062] A cutting agent DA6 is as described in Example 3, except that 2-acrylamido-2-methylpropanesulfonic acid is not added; the composition of other raw materials is the same as in Example 3.

[0063] The preparation method of the above-mentioned cutting agent is as described in Example 3, except that: in step (2), 2-acrylamido-2-methylpropanesulfonic acid is not added, and the pH adjustment step is omitted accordingly. Other steps and conditions are the same as in Example 1. The cutting agent DA6 is obtained.

[0064] Comparative Example 7

[0065] A cutting agent DA7 is as described in Example 3, except that adipic acid dihydrazide is not added; the composition of other raw materials is the same as in Example 3.

[0066] The preparation method of the above-mentioned cutting agent is as described in Example 3, except that: in step (3), adipic acid dihydrazide is not added, and the step of "adjusting the pH to 5 and stirring at 40°C for 2 hours under nitrogen atmosphere" is omitted accordingly. Other steps and conditions are the same as in Example 3. The cutting agent DA7 is obtained.

[0067] Comparative Example 8

[0068] A cutting agent DA8 is as described in Example 3, except that bis[2-(methacryloyloxy)ethyl] phosphate is not added; the composition of other raw materials is the same as in Example 3.

[0069] The preparation method of the above-mentioned cutting agent is the same as that described in Example 3, except that the cutting agent DA8 is obtained.

[0070] Test case

[0071] The performance of the slitting agents prepared in the examples and comparative examples was tested.

[0072] The test slurry preparation process is as follows:

[0073] (1) Using a variable frequency high-speed mixer, disperse 3g of soda ash and 40g of sodium clay in 1000mL of water under stirring conditions, stir at 10000rpm for 30min, and then place at room temperature for 48h to obtain fresh water-based slurry.

[0074] (2) At 11000 rpm, a shearing agent of 2% of the water in the base slurry was added to the base slurry. After stirring for 20 min, NaCl (concentration of 15 wt% in the test slurry) was added and stirred for another 20 min to obtain the first set of test slurries. At the same time, a control group test slurry (base slurry + NaCl) without the addition of shearing agent was set up.

[0075] (3) Add a shearing agent at 2% of the water content in the base slurry at 11000 rpm and stir for 20 min to obtain the slurry; then add barite to increase the weight so that the drilling fluid density reaches 2.0 g / cm³. 3 The second set of test slurries was obtained. At the same time, a control group test slurry (base slurry + barite) without the addition of a cutting agent was set up.

[0076] The drilling fluid test slurry prepared using cutting agents A1-A3 in (2) is named F1-F3, and the drilling fluid test slurry prepared using cutting agents DA1-DA8 is named DF1-DF8; the drilling fluid test slurry prepared using cutting agents A1-A3 in (3) is named G1-G3, and the drilling fluid test slurry prepared using cutting agents DA1-DA8 is named DG1-DG8.

[0077] 1. Drilling fluid performance testing

[0078] Take 400 mL of the above drilling fluid test slurries F1-F3, DF1-DF8, and control group test slurry respectively. After stirring at 5000 rpm for 20 min, pour them into an aging tank, place them in a roller furnace, and roll them at 200℃ for 16 hours. After cooling to room temperature, stir at 5000 rpm for another 20 min. Then, according to GB / T16783.1-2025, determine the apparent viscosity (AV, mPa.s), dynamic shear force (YP, Pa), Φ3 reading of a six-speed viscometer at 3 revolutions, initial shear force, and final shear force of the above drilling fluids. The test temperature is room temperature, and the apparent viscosity is 1022 s. -1 The reading Φ3 at 3 revolutions was obtained through testing and calculation at high shear rates, and was found to be 5.11 s. -1 The results were measured at low shear rates and are shown in Table 1.

[0079] Table 1 Drilling Fluid Performance Tests

[0080]

[0081] The data above show that after adding the shear-enhancing agent of this invention, the drilling fluid system maintains a low and suitable apparent viscosity under high shear conditions. This indicates that the internal network structure of the system can undergo temporary disintegration under high shear, thus maintaining good fluidity and meeting the pumping and flow requirements during circulation. Compared with the base slurry and most comparative examples, the drilling fluid system with the shear-enhancing agent of this invention has a higher Φ3 value, indicating that the shear-enhancing agent can effectively enhance the structural strength of the drilling fluid under low shear conditions, improve the system's suspension capacity for cuttings and weighting materials, and improve the anti-settling stability of the drilling fluid. Simultaneously, the initial and final shear values ​​of the drilling fluid with the shear-enhancing agent of this invention are both at a high level, indicating that the shear-enhancing agent can enable the drilling fluid to quickly form and maintain a certain strength of the spatial network structure under static or low shear conditions, thereby increasing the system's shear strength and enhancing its cuttings carrying and suspension performance. The results are consistent with the variation of dynamic shear force YP, that is, the drilling fluid system after adding the shear-enhancing agent of the present invention has a higher dynamic shear force, indicating that its structural support capacity is stronger and its low-shear rheological properties are better.

[0082] In summary, the cutting agent of this invention can effectively improve the rheological properties of drilling fluid under conditions of 200 ℃ and 15 wt% NaCl, enabling the drilling fluid to maintain good fluidity under high shear conditions and exhibit strong structural recovery ability, suspending and cuttings carrying capacity and anti-settling performance under low shear conditions, demonstrating excellent high temperature and high salt adaptability.

[0083] Because DA1, the shear strength and thixotropy of DF1 are weakened due to the lack of hydrophobic associative structures introduced by the shearing agent DA1, the shear strength and thixotropy of DF1 are weakened. DA2, lacking phosphorus-containing monomers and phosphorus-containing sites in its polymer chains, cannot form a stable cross-linked structure with phosphorus-containing cross-linking agents, resulting in decreased structural stability and insufficient polymer network structure retention in the test slurry DF2. DA3, lacking dynamic covalent bond building units, caused the test slurry DF3 to show a certain increase in viscosity, but its dynamic shear strength remained low, indicating that the strength of the spatial network structure formed by the system is limited, and its reconstruction and recovery ability after structural damage is poor. In addition, DA5 and DA6, prepared by changing the original formulation, also failed to show ideal rheological regulation effects, indicating that the synergistic effect of key functional monomers is crucial to the system performance. DA7, the shearing agent, is difficult to form a dynamic reversible cross-linked structure. Although it still has some rheological regulation ability, its structural recovery ability (initial and final shear strength) and shear strength maintenance ability (dynamic shear strength) are both low. The lack of permanent crosslinking sites in the cutting agent DA8 resulted in a decrease in the overall structural support capacity of the obtained test slurry DF8, indicating that the permanent crosslinking structure also makes a significant contribution to enhancing the stability and structural retention of the polymer network. In summary, the raw material composition and preparation method disclosed in this invention can effectively construct a multi-network structure possessing hydrophobic association, permanent crosslinking, and dynamic reversible crosslinking characteristics, thereby enabling the obtained cutting agent to exhibit superior high-temperature and high-salt adaptability, rheological regulation ability, and suspension and chip-carrying performance.

[0084] 2. Drilling fluid weighting capacity test

[0085] 400 mL of the above drilling fluid test slurries G1-G3, DG1-DG8, and control group test slurry were taken respectively. After stirring at 5000 rpm for 20 min, they were placed in an aging tank and put into a roller furnace. After constant temperature rolling at 200℃ for 16 hours, they were taken out and cooled to room temperature, and then stirred at 5000 rpm for 20 min. Then, the apparent viscosity (AV, mPa.s), dynamic shear force (YP, Pa), reading Φ3 of a six-speed viscometer at 3 revolutions, initial shear force, and final shear force of the above drilling fluid were determined according to GB / T16783.1-2025. The test temperature was room temperature, and the apparent viscosity was 1022 s. -1 The reading Φ3 at 3 revolutions was obtained through testing and calculation at high shear rates, and was found to be 5.11 s. -1 The results were measured at low shear rates and are shown in Table 2.

[0086] Table 2 Performance Tests of Drilling Fluid After Weighting

[0087]

[0088] Based on the AV and YP data in Table 2, the plastic viscosity PV and dynamic-plastic ratio YP / PV of each test slurry were further calculated. The results show that the dynamic-plastic ratio of G1 to G3 is significantly higher than that of DG1 to DG8, with G3 having the highest dynamic-plastic ratio. This indicates that it can maintain a high dynamic shear force despite a lower plastic viscosity, and has superior low-shear cuttings carrying and suspension capabilities. In contrast, the dynamic-plastic ratio of the comparative sample is lower, indicating that its structural support is weaker. In particular, the lack of 2-acrylamido-2-methylpropanesulfonic acid, 2-methacryloyloxyethylphosphocholine, diacetone acrylamide / ADH (adipic acid dihydrazide), or long-chain hydrophobic association structures significantly reduces the shear capacity of the drilling fluid under high temperature and high salinity conditions.

[0089] This shear enhancer can strengthen the low-shear structure of drilling fluid under high-density conditions, enabling the system to form and maintain an effective spatial network structure under low-shear or static conditions, thereby improving the suspension capacity of cuttings and barite. In contrast, the Φ3 and initial and final shear values ​​of each comparative example decreased to varying degrees, indicating that the synergistic effect between the hydrophobic associative structure, dynamic cross-linking structure, permanent cross-linking structure, and salt-resistant functional monomers is the key to maintaining the low-shear rheological properties and anti-settling stability of high-density drilling fluids.

[0090] 3. Drilling fluid settling stability test

[0091] The settling stability of the drilling fluid system was quantitatively evaluated using the static settling factor. 400 mL of the above-mentioned drilling fluid test slurries G1-G3, DG1-DG8, and the control group test slurry were taken respectively, stirred at 5000 rpm for 20 min, and then placed into an aging tank. After vertical static aging at 200 ℃ for 16 h, 24 h, 36 h, 48 h, 60 h, and 72 h, the density ρ at the top of the drilling fluid column was measured. t and the density ρ at the bottom b The static sedimentation factor of the drilling fluid system was calculated, and the experimental results are shown in Table 3.

[0092] The calculation method for the static settlement factor is shown in Equation (1-1).

[0093] (1-1)

[0094] In the formula, SF is the static settlement factor, which is dimensionless.

[0095] ρ t —Drilling fluid top density, g·cm³ -3 ;

[0096] ρ b —Drilling fluid bottom density, g·cm³ -3 .

[0097] Table 3 Drilling fluid settling stability test (static settling factor)

[0098]

[0099] As can be seen from the table, the sedimentation factor of the drilling fluid system after 48 hours of vertical static aging is less than 0.53, indicating that the drilling fluid system of the present invention has good high-temperature sedimentation stability at 200 ℃.

[0100] In summary, the dual-crosslinked cutting agent for high-temperature, high-salt, solid-free water-based drilling fluid of this invention, through permanent crosslinking, dynamic covalent bonds, and hydrophobic association, enables drilling fluid to flow normally under high shear without clogging the drill bit's waterholes, and efficiently cuts suspended cuttings under low shear. This effectively resolves the contradiction between drilling fluid flowability and cuttings carrying capacity in practical engineering, improving the actual application effect of drilling fluid. Furthermore, controlling the raw material composition and proportion within the range of this invention is necessary to obtain a cutting agent with excellent performance.

[0101] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. In addition, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be considered as the content disclosed by the present invention.

Claims

1. A dynamic reversible crosslinking and shearing agent for temperature- and salt-resistant, solid-free water-based drilling fluids, characterized in that, The raw materials are prepared in the following proportions by weight: 12-18 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6-8 parts of 2-methacryloyloxyethyl phosphocholine, 3-5 parts of diacetone acrylamide, 3-5 parts of adipic acid dihydrazide, 6-8 parts of N,N-dimethylacrylamide, 0.5-1.5 parts of lauryl methacrylate, 0.2-0.3 parts of bis[2-(methacryloyloxy)ethyl] phosphate, 3-4 parts of initiator, 80-120 parts of deionized water, 5-15 parts of Span 80, and 0.5-2 parts of OP-10.

2. The temperature- and salt-resistant, solid-free, water-based drilling fluid dynamic reversible crosslinking and shearing agent according to claim 1, characterized in that, A dynamic reversible crosslinking and shearing agent for temperature- and salt-resistant solids-free water-based drilling fluid is prepared from the following raw materials in parts by weight: 12-18 parts of 2-acrylamido-2-methylpropanesulfonic acid, 6-8 parts of 2-methacryloyloxyethyl phosphocholine, 3-5 parts of diacetone acrylamide, 3-5 parts of adipic acid dihydrazide, 6-8 parts of N,N-dimethylacrylamide, 0.5-1.5 parts of lauryl methacrylate, 0.2-0.3 parts of bis[2-(methacryloyloxy)ethyl] phosphate, 3-4 parts of initiator, 100 parts of deionized water, 10 parts of Span 80, and 1 part of OP-10.

3. The temperature- and salt-resistant, solid-free, water-based drilling fluid dynamic reversible crosslinking and shearing agent according to claim 1, characterized in that, The initiator is an aqueous solution of ammonium persulfate with a mass concentration of 5-15 wt% and an aqueous solution of sodium bisulfite with a mass concentration of 5-15 wt%; the mass ratio of the aqueous solution of ammonium persulfate to the aqueous solution of sodium bisulfite is 2-3:1-2.

4. The preparation method of the temperature- and salt-resistant, solid-free water-based drilling fluid dynamic reversible crosslinking and shearing agent as described in any one of claims 1-3, characterized in that, Including the following steps: (1) Span 80, OP-10 and lauryl methacrylate were added to deionized water and emulsified by shearing to obtain a micelle emulsion; (2) Disperse 2-acrylamido-2-methylpropanesulfonic acid thoroughly in deionized water and adjust the pH to 7-8; add 2-methacryloyloxyethyl phosphate choline, diacetone acrylamide, N,N-dimethylacrylamide, and bis[2-(methacryloyloxy)ethyl] phosphate in sequence and mix thoroughly to obtain a monomer solution; (3) Add the micelle emulsion dropwise to the monomer solution, mix thoroughly, and adjust the pH to neutral; An initiator was added to carry out a free radical polymerization reaction; adipate dihydrazide was added to adjust the pH to 5, and after aging reaction, the mixture was filtered, washed, dried, and pulverized to obtain a temperature- and salt-resistant, solid-free, water-based drilling fluid dynamic reversible crosslinking and shearing agent.

5. The preparation method of the temperature- and salt-resistant, solid-free water-based drilling fluid dynamic reversible crosslinking and shearing agent according to claim 4, characterized in that, The mass ratio of deionized water in step (1) to deionized water in step (2) is 5-10:90-95.

6. The preparation method of the temperature- and salt-resistant, solid-free water-based drilling fluid dynamic reversible crosslinking and shearing agent according to claim 4, characterized in that, In step (2), the pH is adjusted using a sodium hydroxide aqueous solution with a mass concentration of 25-30%.

7. The preparation method of the temperature- and salt-resistant, solid-free water-based drilling fluid dynamic reversible crosslinking and shearing agent according to claim 4, characterized in that, In step (3), the dropwise addition is carried out under stirring conditions; the pH is adjusted to neutral using an aqueous acetic acid solution with a mass concentration of 25-30%; the free radical polymerization reaction temperature is 35-50℃, the reaction time is 2-6h, and the reaction is carried out under the protection of a protective gas and under stirring conditions; the protective gas is nitrogen or argon.

8. The preparation method of the temperature- and salt-resistant, solid-free water-based drilling fluid dynamic reversible crosslinking and shearing agent according to claim 4, characterized in that, In step (3), the pH is adjusted to 5 using an aqueous acetic acid solution with a mass concentration of 25-30%; the aging reaction temperature is 40-45℃, the aging reaction time is 1-3 hours, and the aging reaction is carried out under the protection of a protective gas and stirring conditions; the protective gas is nitrogen or argon.

9. The application of the dynamic reversible crosslinking and shearing agent for temperature- and salt-resistant solid-free water-based drilling fluid as described in any one of claims 1-3 in solid-free water-based drilling fluid.

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