Water-swelling rubber for oil casing, its preparation method and application

Abstract

The present application belongs to the technical field of water-swelling rubber for oil casing, and particularly relates to a water-swelling rubber for oil casing, a preparation method and application thereof. The water-swelling rubber for oil casing is prepared by using butyronitrile rubber with a medium acrylonitrile content, introducing salt-resistant water-absorbing resin to improve the water-absorbing capacity of the rubber in a salt water medium, and introducing a coupling agent to improve the dispersion of the water-absorbing resin in the rubber, so as to realize the incremental filling of the water-absorbing resin and shorten the water contact time of the inner layer of the rubber. The rubber obtained by the method solves the problem of slow water absorption and swelling of the existing rubber, and enables the water-swelling rubber to be effectively applied in oil casing.

Description

Technical Field

[0001] This invention belongs to the technical field of water-swellable rubber for oil casing, specifically relating to a water-swellable rubber for oil casing, its preparation method, and its application. Background Technology

[0002] Water-swellable self-expanding rubber (WSR) is a new type of special rubber that can continuously absorb water and expand in volume within a certain time and at a certain rate in the presence of an aqueous medium. Therefore, it possesses both the high elasticity of rubber and the unique water-absorbing and swelling characteristics. The mechanism involves polar rubber being physically blended or grafted with strongly hydrophilic components or groups. Upon contact with water, water molecules form a strong affinity with the hydrophilic groups through diffusion, capillary action, and surface adsorption, encapsulating the water molecules within the rubber and achieving a significant expansion in volume and mass. When the stress resisting deformation and the osmotic pressure difference reach equilibrium, the water-absorbing rubber maintains a relatively stable elastic pressure-bearing, buffering, and leak-stopping effect.

[0003] Oil well casing is mainly used to support the wellbore during and after drilling to ensure the drilling process and the normal operation of the entire well after completion. Oil well casing is the lifeline for maintaining well operation; damage to the casing itself for any reason can lead to reduced production or even abandonment of the entire well. Due to varying geological conditions, the downhole stress state is complex, with tensile, compressive, bending, and torsional stresses acting on the casing, which places high demands on the quality of the casing itself. In practice, the casing is prone to deformation due to the complex stress, directly affecting the quality and efficiency of operations. To address this, some manufacturers have proposed various countermeasures, including increasing the casing steel grade and thickness to improve its mechanical strength, but these have limited effectiveness in preventing casing deformation. The patent disclosed by Xiang Degui et al. (2018) employs an innovative technical concept: while the outer diameter of the casing changes, the inner diameter remains constant, allowing the wellbore to remain intact for a period of time. The casing is covered with water-swellable rubber. Its working principle is as follows: the water-swellable rubber is covered on the outer wall of the casing. After reaching the well site, the water-swellable rubber absorbs water and expands, and the rubber layer becomes several times thicker. Because rubber has a certain degree of flexibility and viscoelasticity, it has a high elastic deformation capacity. When subjected to various impact forces from the formation, the rubber undergoes elastic deformation within a certain range, absorbing and dispersing part of the impact force. The rubber can also concentrate the impact force to a local area, where it undergoes elastic deformation, thereby gradually releasing the energy. In addition, the molecules inside the rubber will undergo relative motion due to shearing, thereby consuming some of the impact force energy. All of these processes can slow down the transmission of impact force and play a buffering and shock absorption role.

[0004] However, the current use of water-swellable rubber to prevent deformation in sleeves still has certain drawbacks. The reason is that water-swellable rubber, as a macromolecular network structure, has strong intermolecular attraction and exhibits a certain tensile strength. Therefore, the process of water absorption is actually a process of water absorption and expansion versus overcoming molecular attraction. As a result, the expansion effect, especially the initial expansion rate, is extremely slow. Specifically, water-swellable rubber generally comes in mechanically blended and chemically grafted types, and its expansion ratio can be divided into high expansion ratio (above 3.5 times), medium expansion ratio (2 to 3.5 times), and low expansion ratio (0.5 to 2 times). Meanwhile, the water absorption effect of rubber is greatly affected by temperature, medium, and surface area exposed to water. Especially in brine, due to the strong bonds between salt ions and water molecules, the hydrophilic groups of the large molecules exhibit weaker covalent bonds during water absorption. Combined with the structural characteristics of casing products, this significantly reduces the rubber's surface area exposed to water. The expansion of the rubber sleeve becomes a one-sided, restricted expansion, resulting in a substantial decrease in the rubber's water absorption rate and saturation absorption rate. Ultimately, in practical applications, the casing rubber, once lowered to the well site, cannot fully expand within a certain time due to its slow water absorption rate, thus weakening its cushioning and shock-absorbing function. Therefore, to effectively prevent casing deformation, it is essential to increase the expansion rate of the water-swellable rubber after it has been lowered to the well site.

[0005] Regarding improving water absorption speed, patent CN101139448A designed a method to improve the water absorption speed of water-swellable rubber using fibers. While adding short fibers can increase the water absorption speed of water-swellable rubber, it did not consider the specific application requirements of the product. Firstly, the combined sleeve adds a layer of water-absorbing rubber to the outer wall of the sleeve. This rubber has a certain thickness, and only the outermost surface is in contact with water. Therefore, the water absorption speed improvement effect of this method is not significant when applied to the sleeve. Secondly, although the water-absorbing rubber designed in this method has increased tensile strength through fibers, in sleeve applications, the higher tensile strength actually becomes a resistance to the rapid water absorption and expansion of the rubber, further affecting its actual performance within the sleeve. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a water-swellable rubber for oil casing, its preparation method, and its application. This invention solves the problem of slow water absorption and expansion of existing rubbers, enabling the effective application of water-swellable rubber in oil casing.

[0007] The technical solution provided by this invention is as follows:

[0008] A method for preparing a water-swellable rubber for oil casing, characterized by comprising the following steps:

[0009] 1) Obtain the raw materials, including the following components in parts by weight: 100 parts of nitrile rubber, 60-80 parts of reinforcing agent, 0-5 parts of antioxidant, 3-10 parts of plasticizer, 1.2-3 parts of crosslinking agent, 2-6 parts of crosslinking aid, 80-120 parts of salt-resistant water-absorbing resin, 1-3 parts of coupling agent, and 8-30 parts of foaming agent;

[0010] 2) Mix nitrile rubber, reinforcing agent, and plasticizer in the above proportions, and knead at a temperature range of 80~120℃ for 5.5-6 minutes;

[0011] 3) Add antioxidant, salt-resistant water-absorbing resin, coupling agent, foaming agent, and crosslinking agent according to the above proportions, mix and then knead at 75~85℃ for 4-5 minutes;

[0012] 4) Finally, add the crosslinking agent according to the above ratio, mix and then knead at a temperature of 70~90℃ for 3-4 minutes, then discharge the material to obtain the rubber that expands rapidly when exposed to water for oil casing.

[0013] In the above technical solution:

[0014] Using nitrile butadiene rubber with a medium acrylonitrile content can improve compatibility with plasticizers, facilitate the dispersion of water-absorbing resins, and thus improve the water absorption effect of rubber.

[0015] Introducing salt-resistant water-absorbing resin can passivate the sensitivity of rubber to the properties of the water medium and improve the water absorption capacity of rubber in salt water medium;

[0016] Introducing coupling agents can promote the compatibility of salt-resistant water-absorbing resin particles with the rubber matrix, prevent particle aggregation and agglomeration, promote the uniform dispersion of water-absorbing resin and reinforcing agent in the rubber body, and further ensure the effective utilization of water-absorbing resin and the increase of rubber swelling rate when exposed to water.

[0017] The foamed structure can shorten the water contact time of the inner layer of rubber.

[0018] By combining the above methods, the water absorption and expansion rate of the water-absorbing rubber is increased, thus giving the water-swellable rubber a significant advantage in the application of oil casing.

[0019] In addition, the addition of plasticizers improves the flowability of rubber; crosslinking agents improve the mechanical properties of rubber.

[0020] Specifically, nitrile rubber is nitrile rubber with a bound acrylonitrile content of 25-30%, which can be selected from existing technologies, such as JSR N240S from Japan and FRN501 from the United States.

[0021] Specifically, the reinforcing agent is a mixture of rapid extrusion black and fumed silica in a weight ratio of (15-20):(45-60). The rapid extrusion black can be selected from existing technologies, such as ExxonMobil's Vulcan. ® The product grade XC-72 is Jiangxi Black Cat Carbon Black Co., Ltd.'s Black Cat brand N550 carbon black. Fumed silica can be obtained from existing technologies, such as Kruss's Printex. ® 160V product of brand name; Shanghai Cabot Chemical Co., Ltd., Cabot, CAB-O-SILLM150.

[0022] Specifically, the antioxidant is a mixture of 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline in a weight ratio of (0-2):(0-3). The 2,2,4-trimethyl-1,2-dihydroquinoline polymer can be selected from existing technologies, for example, Corning's Corning... ® PC-1000 product.

[0023] Specifically, the plasticizers are dioctyl sebate, di(undecyl) phthalate, or ethylene glycol monolaurate.

[0024] Specifically, the crosslinking agent is sulfur powder, which can be selected from existing technologies, such as AkzoNobel's Sulphur Powder product.

[0025] Specifically, the crosslinking aid is a mixture of tetraethylthiuram disulfide and 2-thiol-phenylprophiazole in a weight ratio of (0.5-1.5):(1.5-4.5).

[0026] Specifically, the salt-resistant superabsorbent polymer (SAP) is sodium polyacrylate superabsorbent polymer (SAP), acrylamide superabsorbent polymer (SAP), or a mixture of both in a weight ratio of (60-90):(20-30). The SAP can be selected from existing technologies, such as BASF SE's Lupasol WF brand SAP and Sumitomo Seika Chemicals Co., Ltd.'s Aqua Keep AM brand SAP.

[0027] Specifically, the coupling agent is at least one of vinyltriethoxysilane, vinyltri(β-methoxyethoxy)silane, or γ-methacryloxypropyltrimethoxysilane.

[0028] Specifically, the foaming agent is one or a mixture of azodicarbonamide or hydrazine p-toluenesulfonate.

[0029] Preferably, the reinforcing agent is a mixture of rapid-extrusion furnace black and fumed silica in a weight ratio of 1:3. This ratio is chosen to achieve a certain strength while simultaneously improving the processing properties of the rubber.

[0030] Preferably, the antioxidant is a mixture of 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline in a weight ratio of 1:1.5. This ratio is used to achieve a greater synergistic effect and further improve resistance to flexural cracking.

[0031] Preferably, the crosslinking aid is a mixture of tetraethylthiuram disulfide and 2-thiol-phenylprophiazole in a weight ratio of 1:3. This ratio is used because the combined use of primary and secondary crosslinking aids achieves a suitable vulcanization rate.

[0032] Preferably, the salt-resistant water-absorbing resin is either alone or a mixture of the two in a 3:1 weight ratio. The reason for using a mixture of the two is that their compatibility in rubber can be improved.

[0033] Furthermore, step 5) involves packaging and rolling the water-swellable rubber compound obtained in step 4) into 1.5-2mm thin sheets on a two-roll mill at below 100°C, adjusting the roller gap to produce sheet-like water-swellable rubber for oil casing. The rubber obtained in the above steps can then be vulcanized at (160-180)°C for (12-18) minutes.

[0034] Based on the above technical solution, the sheet material can be directly used in the process of manufacturing oil casing.

[0035] The present invention also provides a rubber for oil casing that expands rapidly upon contact with water.

[0036] This invention also provides the application of water-swellable rubber for oil casing, used in the manufacture of oil casing.

[0037] Specifically, it is used to adhere to the surface of steel oil casing as an absorbent rubber layer.

[0038] The water-swellable rubber provided by this invention can be directly fixed to the outer wall of the oil casing by an adhesive during molding, and the oil casing can be assembled in one step. The process is simple, can be mass-produced, and will not change the existing downhole operation process of oil casing. This ensures the promotion and application of the new oil casing downhole, improves the feasibility and safety of the application of the expandable rubber, and ultimately achieves the self-protection of the oil casing.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] The water-swellable rubber provided by this invention significantly improves the expansion rate of rubber used in oil casing. By using nitrile butadiene rubber with a medium propylene content, salt-resistant water-absorbing resin particles, and passivating the rubber's sensitivity to the properties of the water medium, the expansion rate in salt water is greatly enhanced. The effective use of a foaming agent increases the number of pores in the rubber's network structure, improves the rubber's water permeability, increases the water contact area of ​​thick products under unidirectional water contact, and shortens the water contact time of the rubber strip's matrix in contact with the oil casing, significantly improving the overall water absorption and expansion rate of the rubber. The introduction of coupling agents and plasticizers promotes the uniform dispersion of salt-resistant water-absorbing resin and reinforcing agents in the rubber body, further ensuring the effective utilization of the water-absorbing resin and the increased water-swelling rate of the rubber. This rubber has a simple preparation process, is easy to mold, and can optimize the damage mode of oil casing during operation, thereby improving the service life of the oil casing.

[0041] Specific effects of the invention:

[0042] The water-swellable rubber provided by this invention, when mixed and vulcanized according to the above-described preparation process, and tested according to corresponding standards, yields representative test data including: tensile strength ≥ 4 MPa, hardness ≥ 70 Shore A, tear strength ≥ 20 kN / m, and after immersion in high-temperature water at 100°C for 4 hours, the volume expansion rate of a 20mm×20mm×2mm sample is ≥ 3 times, with a saturated expansion time < 1 day. After immersion in high-temperature salt water at 100°C for 4 hours, the weight expansion ratio of a rubber tube with a diameter of 20cm × height of 30cm × thickness of 5cm is ≥ 1 time. The invention incorporates salt-resistant, water-absorbing resin particles, making it more adaptable to the expansion environment of downhole cement slurry. The use of coupling agents promotes the compatibility between the salt-resistant, water-absorbing resin particles and the rubber matrix, preventing particle aggregation and further maximizing the effectiveness of hydrophilic groups. The optimized foaming agent naturally forms a large number of void structures inside the rubber, providing conditions for rapid water contact in parts of the rubber body away from the surface cement slurry. The water-swellable rubber preparation process in this invention is simple. By coating the outside of the base pipe, it expands rapidly in the cement slurry environment. Its excellent high elasticity reduces the impact of fault slippage on the shear deformation of the oil casing. The expanding rubber converts and consumes the extreme non-uniform external extrusion load energy that may be generated during multi-stage fracturing, making it superior to a buffer spring. Attached Figure Description

[0043] Figure 1 These are comparative diagrams of the conventional physical properties of the embodiments and comparative examples of the present invention, wherein, from left to right, they correspond to Embodiments 1, 2, and 3 and Comparative Examples 1, 2, and 3, respectively.

[0044] Figure 2 This is a comparison chart of the water absorption and expansion performance of the embodiments and comparative examples of the present invention, wherein, from left to right, they correspond to Embodiments 1, 2, and 3 and Comparative Examples 1, 2, and 3, respectively. Detailed Implementation

[0045] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0046] Example 1

[0047] This embodiment provides a water-swellable rubber with the following formulation: 100 parts nitrile rubber JSRN240S, 20 parts carbon black N550, 60 parts silica CABOT, 2 parts antioxidant RD, 3 parts antioxidant AW, 2 parts sulfur, 1.5 parts accelerator M, 0.5 parts TETD, 4 parts DOS, 100 parts SAP, 2 parts KH-570, and 10 parts Aceto AD.

[0048] After completing the compounding process as described above, the rubber was left to stand for 16 hours and then vulcanized on a flat vulcanizing agent under vulcanization conditions of 170℃ for 15 minutes. The rubber sample was then removed and left to stand at room temperature for 24 hours. The tensile strength was 5.4 MPa, the elongation at break was 430%, the tear strength was 31 kN / m, and the hardness was 78 Shore A. After immersion in hot water at 100℃ for 4 hours, the volume expansion rate of a 20 mm × 20 mm × 2 mm sample was 300%, the equilibrium saturation expansion time was 23 hours, and the equilibrium saturation expansion rate was 610%.

[0049] Oil immersion tests were conducted on 20cm×20cm×2cm films to complete free expansion. The oil sample used was oil-based drilling fluid for shale gas wells. The immersion temperature was room temperature, the pressure was 0MPa, and the time was 48h. A wide-mouth bottle was used. The immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 1, in the static oil-based mud used, had a free state of room temperature and high temperature weight expansion ratio of 0.07 times.

[0050] A water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. Distilled water was used as the water sample, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 1 showed a shape-restricted weight expansion ratio of 2.2 times in the static distilled water.

[0051] A salt water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. The water sample used was a 2% KCl solution, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 1 showed a shape-restricted weight expansion ratio of 1.3 times in the static 2% KCl solution.

[0052] A cement slurry immersion test was conducted on a 20cm×20cm×2cm film to complete the free expansion. The medium used was cement slurry for cementing with added slow-release agent. The immersion temperature was 100℃, the pressure was 100MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-frequency stirring high-temperature furnace. The water-swellable rubber provided in Example 1, in the dynamic cement slurry used, had a weight expansion ratio of 1.1 times in the free state.

[0053] Example 2

[0054] This embodiment provides a water-swellable rubber with the following formulation: 100 parts nitrile rubber JSRN240S, 15 parts carbon black N550, 45 parts silica CABOT, 1 part RD protection, 1.5 parts AW protection, 3 parts sulfur, 1.5 parts M accelerator, 0.5 parts TETD, 6 parts DOS, 120 parts SAP, 2 parts A-151, and 15 parts Aceto AD.

[0055] After completing the compounding process as described above, the rubber was left to stand for 16 hours and then vulcanized on a flat vulcanizing agent at 170℃ for 15 minutes. The rubber sample was then removed and left to stand at room temperature for 24 hours. The tensile strength was 5.1 MPa, the elongation at break was 550%, the tear strength was 35 kN / m, and the hardness was 74 Shore A. After immersion in hot water at 100℃ for 4 hours, the volume expansion rate of a 20 mm × 20 mm × 2 mm sample was 320%, the equilibrium saturation expansion time was 22 hours, and the equilibrium saturation expansion rate was 650%.

[0056] Oil immersion tests were conducted on 20cm×20cm×2cm films to complete free expansion. The oil sample used was oil-based drilling fluid for shale gas wells. The immersion temperature was room temperature, the pressure was 0MPa, and the time was 48h. A wide-mouth bottle was used, and the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 2, in the static oil-based mud used, had a free state of room temperature and high temperature weight expansion ratio of 0.08 times.

[0057] A water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. Distilled water was used as the water sample, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 2, in the static distilled water used, had a shape-restricted weight expansion ratio of 2.1 times.

[0058] A salt water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. The water sample used was a 2% KCl solution, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 2, in the static 2% KCl solution used, had a shape-restricted weight expansion ratio of 1.5 times.

[0059] A cement slurry immersion test was conducted on a 20cm×20cm×2cm film to complete the free expansion. The medium used was cement slurry for cementing with added slow-release agent. The immersion temperature was 100℃, the pressure was 100MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-frequency stirring high-temperature furnace. The water-swellable rubber provided in Example 2, in the dynamic cement slurry used, had a weight expansion ratio of 1.1 times in the free state.

[0060] Example 3

[0061] This embodiment provides a water-swellable rubber with the following formulation: 100 parts nitrile rubber JSRN240S, 15 parts carbon black N550, 45 parts silica CABOT, 1 part RD protection, 1.5 parts AW protection, 1.3 parts sulfur, 3 parts M accelerator, 1 part TETD, 6 parts DOS, 120 parts SAP, 2 parts A-172, and 12 parts Aceto AD.

[0062] The compound was prepared according to the above mixing method. After standing for 16 hours, it was vulcanized on a flat vulcanizing agent under vulcanization conditions of 170℃×15min. The rubber sample was then removed and left to stand at room temperature for 24 hours. Its tensile strength was 4.2MPa, elongation at break was 530%, tear strength was 28kN / m, hardness was 72ShoreA, and after immersion in hot water at 100℃ for 4 hours, the volume expansion rate of a 20mm×20mm×2mm sample was 360%, the equilibrium saturation expansion time was 18 hours, and the equilibrium saturation expansion rate was 665%.

[0063] Oil immersion tests were conducted on 20cm×20cm×2cm films to complete free expansion. The oil sample used was oil-based drilling fluid for shale gas wells. The immersion temperature was room temperature, the pressure was 0MPa, and the time was 48h. A wide-mouth bottle was used, and the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 3, in the static oil-based mud used, had a free state of room temperature and high temperature weight expansion ratio of 0.07 times.

[0064] A water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. Distilled water was used as the water sample, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 3 showed a shape-restricted weight expansion ratio of 2.2 times in the static distilled water.

[0065] A salt water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. The water sample used was a 2% KCl solution, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 3 showed a shape-restricted weight expansion ratio of 1.6 times in the static 2% KCl solution.

[0066] A cement slurry immersion test was conducted on a 20cm×20cm×2cm film to complete the free expansion. The medium used was cement slurry for cementing with added slow-release agent. The immersion temperature was 100℃, the pressure was 100MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-frequency stirring high-temperature furnace. The water-swellable rubber provided in Example 3, in the dynamic cement slurry used, had a weight expansion ratio of 1.2 times in the free state.

[0067] Comparative Example 1

[0068] This comparative example provides a water-swellable rubber with the following formulation: 100 parts nitrile rubber JSRN230S, 20 parts carbon black N550, 60 parts silica CABOT, 2 parts RD protection, 3 parts AW protection, 2 parts sulfur, 1.5 parts M accelerator, 0.5 parts TETD, 4 parts DOS, 100 parts SAP, 2 parts KH-570, and 10 parts Aceto AD.

[0069] After completing the compounding process as described above, the rubber was left to stand for 16 hours and then vulcanized on a flat vulcanizing agent under vulcanization conditions of 170℃ for 15 minutes. The rubber sample was then removed and left to stand at room temperature for 24 hours. The tensile strength was 8.7 MPa, the elongation at break was 230%, the tear strength was 35 kN / m, and the hardness was 80 Shore A. After immersion in hot water at 100℃ for 4 hours, the volume expansion rate of a 20 mm × 20 mm × 2 mm sample was 228%, the equilibrium saturation expansion time was 36 hours, and the equilibrium saturation expansion rate was 350%.

[0070] Oil immersion tests were conducted on 20cm×20cm×2cm films to complete free expansion. The oil sample used was oil-based drilling fluid for shale gas wells. The immersion temperature was room temperature, the pressure was 0MPa, and the time was 48h. A wide-mouth bottle was used, and the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 1, in the static oil-based mud used, had a free state of room temperature and high temperature weight expansion ratio of 0.11 times.

[0071] A water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. Distilled water was used as the water sample, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 1 showed a shape-restricted weight expansion ratio of 0.9 times in the static distilled water.

[0072] A salt water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter × 30cm in height × 5cm in thickness to complete the shape-restricted expansion. The water sample used was a 2% KCl solution, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 1 showed a shape-restricted weight expansion ratio of 0.5 times in the static 2% KCl solution.

[0073] A cement slurry immersion test was conducted on a 20cm×20cm×2cm film to complete the free expansion. The medium used was cement slurry for cementing with added slow-release agent. The immersion temperature was 100℃, the pressure was 100MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-frequency stirring high-temperature furnace. The water-swellable rubber provided in Example 1, in the dynamic cement slurry used, had a weight expansion ratio of 0.6 times in the free state.

[0074] A comparison with the examples shows that changes in the acrylonitrile content in nitrile rubber can significantly affect the expansion rate and expansion percentage of the expanded rubber.

[0075] Comparative Example 2

[0076] This comparative example provides a water-swellable rubber with the following formulation: 100 parts nitrile rubber JSRN240S, 15 parts carbon black N550, 45 parts silica CABOT, 1 part RD inhibitor, 1.5 parts AW inhibitor, 3 parts sulfur, 1.5 parts M accelerator, 0.5 parts TETD, 6 parts DOS, 20 parts SAP, 2 parts A-151, and 15 parts Aceto AD.

[0077] After completing the compounding process as described above, the rubber was left to stand for 16 hours and then vulcanized on a flat vulcanizing agent at 170℃ for 15 minutes. The rubber sample was then removed and left to stand at room temperature for 24 hours. The tensile strength was 7.8 MPa, the elongation at break was 680%, the tear strength was 20 kN / m, and the hardness was 58 Shore A. After immersion in hot water at 100℃ for 4 hours, the volume expansion rate of a 20 mm × 20 mm × 2 mm sample was 100%, the equilibrium saturation expansion time was 49 hours, and the equilibrium saturation expansion rate was 320%.

[0078] Oil immersion tests were conducted on 20cm×20cm×2cm films to complete free expansion. The oil sample used was oil-based drilling fluid for shale gas wells. The immersion temperature was room temperature, the pressure was 0MPa, and the time was 48h. A wide-mouth bottle was used, and the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 2, in the static oil-based mud used, had a free state of room temperature and high temperature weight expansion ratio of 0.06 times.

[0079] A water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. Distilled water was used as the water sample, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 2, in the static distilled water used, had a shape-restricted weight expansion ratio of 0.8 times.

[0080] A salt water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter × 30cm in height × 5cm in thickness to complete the shape-restricted expansion. The water sample used was a 2% KCl solution, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 2, in the static 2% KCl solution, showed a shape-restricted weight expansion ratio of 0.4 times.

[0081] A cement slurry immersion test was conducted on a 20cm×20cm×2cm film to complete the free expansion. The medium used was cement slurry for cementing with added slow-release agent. The immersion temperature was 100℃, the pressure was 100MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-frequency stirring high-temperature furnace. The water-swellable rubber provided in Example 2, in the dynamic cement slurry used, had a weight expansion ratio of 0.4 times in the free state.

[0082] A comparison with the examples shows that reducing the amount of salt-resistant water-absorbing resin significantly affects the time it takes for the expanded rubber to reach water absorption equilibrium saturation and the expansion rate.

[0083] Comparative Example 3

[0084] This comparative example provides a water-swellable rubber with the following formulation: 100 parts nitrile rubber JSRN240S, 15 parts carbon black N550, 45 parts silica CABOT, 1 part RD protection, 1.5 parts AW protection, 1.3 parts sulfur, 3 parts M accelerator, 1 part TETD, 6 parts DOS, 120 parts SAP, and 12 parts Aceto AD.

[0085] After completing the compounding process as described above, the rubber was left to stand for 16 hours and then vulcanized on a flat vulcanizing agent at 170℃ for 15 minutes. The rubber sample was then removed and left to stand at room temperature for 24 hours. The tensile strength was 4.0 MPa, the elongation at break was 450%, the tear strength was 24 kN / m, the hardness was 69 Shore A, and after immersion in hot water at 100℃ for 4 hours, the volume expansion rate of a 20 mm × 20 mm × 2 mm sample was 260%. The equilibrium saturation expansion time was 20 hours, and the equilibrium saturation expansion rate was 430%.

[0086] Oil immersion tests were conducted on 20cm×20cm×2cm films to complete free expansion. The oil sample used was oil-based drilling fluid for shale gas wells. The immersion temperature was room temperature, the pressure was 0MPa, and the time was 48h. A wide-mouth bottle was used, and the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 3, in the static oil-based mud used, had a free state of room temperature and high temperature weight expansion ratio of 0.07 times.

[0087] A water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. Distilled water was used as the water sample, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 3 showed a shape-restricted weight expansion ratio of 1.7 times in the static distilled water.

[0088] A salt water immersion test was conducted on a rubber tube with dimensions of 20cm in diameter, 30cm in height, and 5cm in thickness to complete the shape-restricted expansion. The water sample used was a 2% KCl solution, the immersion temperature was 100℃, the pressure was 1MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-temperature furnace. The water-swellable rubber provided in Example 3 showed a shape-restricted weight expansion ratio of 0.9 times in the static 2% KCl solution.

[0089] A cement slurry immersion test was conducted on a 20cm×20cm×2cm film to complete the free expansion. The medium used was cement slurry for cementing with added slow-release agent. The immersion temperature was 100℃, the pressure was 100MPa, and the time was 4h. The high-temperature test equipment was a pressurized high-frequency stirring high-temperature furnace. The water-swellable rubber provided in Example 3, in the dynamic cement slurry used, had a weight expansion ratio of 0.5 times in the free state.

[0090] A comparison with the examples shows that when the amount of coupling agent added is 0 parts, the strength of the expanded rubber is reduced, reflecting that the salt-resistant water-absorbing resin is not evenly dispersed, which leads to a significant reduction in the water absorption rate.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a water-swellable rubber for oil casing, characterized in that, Includes the following steps: 1) Obtain the raw materials, including the following components in parts by weight: 100 parts of nitrile rubber, 60-80 parts of reinforcing agent, 0-5 parts of antioxidant, 3-10 parts of plasticizer, 1.2-3 parts of crosslinking agent, 2-6 parts of crosslinking aid, 80-120 parts of salt-resistant water-absorbing resin, 1-3 parts of coupling agent, and 8-30 parts of foaming agent; 2) Mix nitrile rubber, reinforcing agent, and plasticizer in the above proportions, and knead at a temperature range of 80~120℃ for 5.5-6 minutes; 3) Add antioxidant, salt-resistant water-absorbing resin, coupling agent, foaming agent, and crosslinking agent according to the above proportions, mix and then knead at 75~85℃ for 4-5 minutes; 4) Finally, add the crosslinking agent according to the above ratio, mix and then knead at 70~90℃ for 3-4 minutes, then discharge the material to obtain the rubber for oil casing that expands rapidly when exposed to water. 5) The water-swellable rubber compound for oil casing obtained in step 4) is packaged and rolled in 1.5-2mm thin strips on a two-roll mill at a temperature below 100℃. The roll gap is adjusted to produce sheet-like water-swellable rubber for oil casing. Nitrile rubber is nitrile rubber with a bound acrylonitrile content of 25-30%; The reinforcing agent is a mixture of fast-pressed furnace black and fumed silica in a weight ratio of 1:

3. The antioxidant is a mixture of 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline in a weight ratio of (0-2):(0-3); The plasticizers are dioctyl sebacate, di(undecyl) phthalate, or ethylene glycol monolaurate; The crosslinking agent is sulfur powder; The crosslinking aid is a mixture of tetraethylthiuram disulfide and 2-thiol-phenylprophiazole in a weight ratio of (0.5-1.5):(1.5-4.5); The salt-resistant superabsorbent resin is a mixture of sodium polyacrylate superabsorbent resin and acrylamide superabsorbent resin in a weight ratio of 3:

1. The coupling agent is γ-methacryloyloxypropyltrimethoxysilane; The foaming agent is azodicarbonamide.

2. The method for preparing water-swellable rubber for oil casing according to claim 1, characterized in that: The nitrile rubber is selected from JSR N240S or FRN501; The fast-pressed carbon black is selected from Jiangxi Black Cat N550; the fumed silica is selected from Cabot CAB-O-SIL LM150.

3. A type of rubber for oil casing that rapidly expands upon contact with water, prepared by the method according to any one of claims 1 to 2, characterized in that: Tensile strength ≥4MPa, hardness ≥70ShoreA, tear strength ≥20kN / m, after soaking in high-temperature water at 100℃ for 4 hours, the volume expansion rate of a 20mm×20mm×2mm sample is ≥3 times, and the saturation expansion time is <1 day; after soaking in high-temperature salt water at 100℃ for 4 hours, the weight expansion multiple of a rubber tube with a diameter of 20cm×height of 30cm×thickness is ≥1 time.

4. The application of the water-swellable rubber for oil casing according to claim 3, characterized in that: Used to adhere to the surface of steel oil casing as an absorbent rubber layer.

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