Water-swellable rubber particles, composite cement paste system containing same and preparation method of water-swellable rubber particles

Abstract

The invention relates to a water-swellable rubber particle, a composite cement paste system containing the same and a preparation method, and the water-swellable rubber particle is prepared from the following raw materials in parts by weight: 90-110 parts of matrix rubber; 30-80 parts of a water absorption component; 4-6 parts of a water absorption auxiliary agent; 0.5-2 parts of a vulcanizing agent; 15 to 23 parts of an accelerant; 45 to 60 parts of a reinforcing agent; the water absorption component comprises sodium polyacrylate and / or polyacrylamide; the water absorption auxiliary agent comprises polyethylene glycol. The water-absorbing swelling rubber particles are added into the composite cement paste system provided by the invention, and the expanded rubber particles can greatly reduce the elasticity modulus of the system and improve the capacity of a cement sheath for absorbing the displacement load of a stratum, so that the risk of deformation of a shale oil and gas casing is reduced, and the overall benefit of shale oil and gas development is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and natural gas extraction, and in particular to water-swelling rubber particles, a composite cement slurry system containing the same, and a preparation method thereof. Background Art

[0002] Currently, casing deformation is a prominent issue during hydraulic fracturing in my country's shale oil and gas production, increasing the cost and difficulty of fracturing operations. Field operations require the use of undersized fracturing tools or discarded fracturing stages, resulting in low well production and the inability to operate some wells. This severely restricts the growth of shale oil and gas production in my country. Despite field operators using casing with larger steel grades and thicker walls, the deformation problem remains unresolved.

[0003] For years, researchers have analyzed the mechanisms and causes of casing deformation during shale oil and gas fracturing, drawing on data from the researchers. These findings reveal that shale gas and shale oil reservoirs are characterized by extensive bedding, fractures, and faults. During the fracturing process, the fracturing fluid enters these developed fractures through various pathways, primarily through fractures, bedding planes, and cracks at the interface between the cement sheath and the formation. This increases the formation pressure within these fractures, reduces the friction coefficient at these fracture surfaces, and triggers slippage within the fractures, leading to deformation of the reservoir casing. Analysis of field data reveals that the amount of shear displacement caused by formation movement is related to the size of the fractures. Therefore, conventional "hard-core" approaches, such as increasing casing steel grade and wall thickness, are ineffective in combating deformation caused by formation slip. A different approach is needed, such as the use of flexible solutions that can absorb formation slip deformation, thus absorbing formation displacement through a "soft-hard" approach.

[0004] At present, reducing the elastic modulus of the cement slurry system to absorb stratum displacement is an important measure to prevent casing deformation. For example, CN115286306A discloses a cement slurry for suppressing casing deformation and its preparation method. The spherical borosilicate hollow material added to the cement slurry can be broken and provide space for stratum slip, thereby avoiding casing deformation. CN104774601A discloses a gypsum microsphere and a low elastic modulus expansive cement system suitable for medium and low temperature cementing. The gypsum microspheres added to the cement system can reduce the elastic modulus of the cement slurry system, but the reduction value of the elastic modulus is limited (the lowest can only reach 7.5GPa), which cannot achieve the purpose of fully absorbing the load capacity of stratum displacement.

[0005] Therefore, how to reduce the elastic modulus of the cement slurry system, effectively prevent the risk of shale oil and gas casing deformation, and improve the overall efficiency of shale oil and gas development is a technical problem that needs to be solved in this field. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the purpose of the present invention is to provide water-swelling rubber particles, a composite cement slurry system containing the same, and a preparation method. Compared with the existing technology, the composite cement slurry system provided by the present invention adds water-swelling rubber particles. The expanded rubber particles will significantly reduce the elastic modulus of the system and increase the ability of the cement sheath to absorb formation displacement loads, thereby reducing the risk of shale oil and gas casing deformation and improving the overall benefits of shale oil and gas development.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides water-swelling rubber particles. The raw materials for preparing the water-swelling rubber particles include the following components in parts by weight:

[0009]

[0010]

[0011] The water-absorbing component includes sodium polyacrylate and / or polyacrylamide;

[0012] The water absorption aid includes polyethylene glycol.

[0013] The present invention achieves excellent water-swelling properties by controlling the composition of the water-swelling rubber particles. When added to a composite cement slurry system, the expanded rubber particles significantly reduce the elastic modulus of the entire system, increasing the cement sheath's ability to absorb formation displacement loads and helping to reduce the risk of casing deformation. The water-absorbing component and the water-absorbing additive work synergistically, imparting excellent water-swelling properties to the rubber particles while further enhancing water absorption, ultimately achieving excellent water-swelling results.

[0014] In the present invention, the polyethylene glycol can be polyethylene glycol of a molecular weight commonly used in the art, such as PEG-6000, PEG-4000, PEG-3350, etc. In the present invention, the water absorption and expansion effect can be further ensured by controlling the mass fraction of the water absorption auxiliary agent. When the amount of water absorption auxiliary agent added is too small, the water absorption performance is poor. When the amount of water absorption auxiliary agent added is too large, it is easy to cause excessive precipitation of water absorption components, affecting the overall expansion effect.

[0015] The base rubber is 90-110 parts, for example, it can be 90 parts, 92 parts, 94 parts, 96 parts, 98 parts, 100 parts, 102 parts, 104 parts, 106 parts, 108 parts or 110 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the water-absorbing component is 30-80 parts, for example, it can be 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts or 80 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the water-absorbing auxiliary agent is 4-6 parts, for example, it can be 4 parts, 5 parts or 6 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. The values ​​listed above are also applicable; the vulcanizing agent is 0.5-2 parts, for example, it can be 0.5 parts, 1 part, 1.5 parts or 2 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the accelerator is 15-23 parts, for example, it can be 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, 21 parts, 22 parts or 23 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the reinforcing agent is 45-60 parts, for example, it can be 45 parts, 46 parts, 48 ​​parts, 50 parts, 52 parts, 54 parts, 56 parts, 58 parts or 60 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] Preferably, the base rubber comprises nitrile rubber and / or hydrogenated nitrile rubber.

[0017] In the present invention, the selection of the base rubber is generally determined according to the temperature conditions of the reservoir, and the selected base rubber is generally suitable for reservoir temperature conditions of 90-180°C.

[0018] Preferably, the particle size of the sodium polyacrylate is 75-85 μm, for example, 75 μm, 78 μm, 80 μm, 82 μm, 84 μm or 85 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] Preferably, the particle size of the polyacrylamide is 50-70 μm, for example, 50 μm, 52 μm, 55 μm, 58 μm, 60 μm, 62 μm, 65 μm, 68 μm or 70 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, when the water-absorbing component is sodium polyacrylate, the amount of sodium polyacrylate is 30-40 parts by weight, for example, 30 parts, 32 parts, 34 parts, 36 parts, 38 parts or 40 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, when the water-absorbing component is polyacrylamide, the polyacrylamide is 70-80 parts by weight, for example, 70 parts, 72 parts, 74 parts, 76 parts, 78 parts or 80 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] Preferably, the vulcanizing agent comprises sulfur and / or dicumyl peroxide.

[0023] In the present invention, by preferably controlling the vulcanizing agent to include sulfur and / or dicumyl peroxide, the rubber can be acted upon to transform the linear macromolecules in the rubber into a three-dimensional network structure, thereby making the rubber have higher elasticity and temperature resistance.

[0024] Preferably, when the vulcanizing agent is sulfur, the sulfur is 0.5-1.5 parts by weight, for example, 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts or 1.5 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, when the vulcanizing agent is dicumyl peroxide, the amount of dicumyl peroxide is 0.5-2 parts by weight, for example, 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the accelerator includes any one of N-cyclohexyl-2-benzothiazolesulfenamide, zinc oxide or sodium hydroxide, or a combination of at least two thereof.

[0027] Preferably, when the accelerator comprises a combination of N-cyclohexyl-2-benzothiazole sulfenamide and zinc oxide, the weight portion of N-cyclohexyl-2-benzothiazole sulfenamide is 2-3 parts, for example, 2 parts, 2.5 parts or 3 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. The weight portion of zinc oxide is 15-20 parts, for example, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, when the accelerator includes a combination of N-cyclohexyl-2-benzothiazole sulfenamide, zinc oxide and sodium hydroxide, the weight portion of N-cyclohexyl-2-benzothiazole sulfenamide is 2-3 parts, for example, 2 parts, 2.5 parts or 3 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the weight portion of zinc oxide is 5-6 parts, for example, 5 parts, 5.5 parts or 6 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the weight portion of sodium hydroxide is 8-10 parts, for example, 8 parts, 8.5 parts, 9 parts, 9.5 parts or 10 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the reinforcing agent includes any one of carbon black, white carbon black or calcium sulfate whiskers, or a combination of at least two of them.

[0030] In the present invention, white carbon black and carbon black can improve the mechanical properties of the water-swellable rubber particles, significantly enhancing their mechanical properties after the addition of a reinforcing agent. The calcium sulfate whiskers can be, for example, modified calcium sulfate whiskers commonly used in the art, such as calcium sulfate whiskers modified with coupling agent 11-100, calcium sulfate whiskers modified with silane coupling agents KH550 or KH570, or calcium sulfate whiskers modified with aluminate coupling agent HYA1. These whiskers can provide pathways for water molecules, achieving the dual effects of improving mechanical properties and water absorption.

[0031] Preferably, when the reinforcing agent includes a combination of carbon black and white carbon black, the carbon black is 20-25 parts by weight, for example, 20 parts, 21 parts, 22 parts, 23 parts, 24 parts or 25 parts, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable. The white carbon black is 25-30 parts, for example, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts or 30 parts, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, when the reinforcing agent includes a combination of carbon black, white carbon black and calcium sulfate whiskers, the carbon black is 15-20 parts by weight, for example, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts or 20 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable; the white carbon black is 25-30 parts, for example, 25 parts, 26 parts, 27 parts, 28 parts, 29 parts or 30 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable; the calcium sulfate whisker is 8-10 parts, for example, 8 parts, 8.5 parts, 9 parts, 9.5 parts or 10 parts, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0033] It should be noted that when the base rubber is either nitrile rubber or hydrogenated nitrile rubber, different reinforcing agents can be selected due to the different strength and water absorption properties of the rubber itself. Specifically, when the base rubber is nitrile rubber, a combination of carbon black, silica, and calcium sulfate whiskers is generally used as the reinforcing agent, while when the base rubber is hydrogenated nitrile rubber, a combination of carbon black and silica is generally used as the reinforcing agent.

[0034] Preferably, the raw materials for preparing the water-swellable rubber particles further include a compatibilizer.

[0035] Preferably, the preparation raw materials include 8-10 parts of the compatibilizer in parts by weight, for example, 8 parts, 8.5 parts, 9 parts, 9.5 parts or 10 parts, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the compatibilizer comprises a polyurethane prepolymer.

[0037] In the present invention, the compatibilizer preferably includes a polyurethane prepolymer, which can improve the dispersibility of reinforcing agents such as silica in the rubber particles and enhance the reinforcing effect of silica. However, this can also affect the water absorption rate of the water-swelling rubber particles. This is because the polyurethane prepolymer can hydrogen bond with water molecules, increasing the water absorption expansion rate to a certain extent. The polyurethane prepolymer is commonly used in the art and is commercially available.

[0038] In the present invention, the method for preparing water-swellable rubber particles using the above-mentioned raw materials comprises the following steps:

[0039] A closed rubber mixer is used to carry out step-by-step mixing at a speed of 15-20 r / min and a pressure of 10-20 MPa: first, the base rubber, water-absorbing components, water-absorbing aids, and reinforcing agents are mixed at a temperature of 50-70°C, and a compatibilizer is optionally added, and the mixture is mixed for 35-45 minutes until uniform dispersion; then, a vulcanizing agent and an accelerator are added, the vulcanization temperature is controlled at 130-150°C, the mixture is reacted for 35-45 minutes, and then extrusion and granulation are carried out to obtain water-swelling rubber particles.

[0040] In a second aspect, the present invention provides a composite cement slurry system, wherein the raw materials for preparing the composite cement slurry system include the following components in parts by weight:

[0041] 80-115 parts of base cement;

[0042] 2-10 parts of water-swelling rubber particles;

[0043] 0.5-2 parts of crack arrest material

[0044] 1.2-1.5 parts of fluid loss additive

[0045] Dispersant 0.15-0.25 parts;

[0046] The water-swelling rubber particles are the water-swelling rubber particles according to any one of claims 1 to 5.

[0047] In the present invention, the composite cement slurry system comprises a core system consisting of base cement, water-swellable rubber particles, a crack-arresting material, a fluid loss additive, and a dispersant. The water-swellable rubber particles incorporated into the composite cement slurry system absorb water and swell, creating cracks between the particles and the cement, thereby reducing the elastic modulus of the system and increasing the cement sheath's ability to absorb formation displacement loads. It should be noted that cracks caused by the expansion of the water-swelling rubber particles can affect the strength and integrity of the cement system. The addition of the crack-arresting material in the present invention reduces the impact of the water-swelling rubber particles on the overall performance of the cement, ensuring that the cement's performance meets construction requirements.

[0048] The matrix cement is 80-115 parts, for example, it can be 80 parts, 85 parts, 90 parts, 95 parts, 100 parts, 105 parts, 110 parts or 115 parts, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the water-swelling rubber particles are 2-10 parts, for example, it can be 2 parts, 4 parts, 6 parts, 8 parts or 10 parts, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable; the crack-stopping material is 0.5-2 parts, for example, it can be 0.5 parts, 0.6 parts, 0.8 parts, 1 part, 1.2 parts, 1.4 parts, The amount of the fluid loss additive is 1.2-1.5 parts, for example, 1.2 parts, 1.3 parts, 1.4 parts or 1.5 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the amount of the dispersant is 0.15-0.25 parts, for example, 0.15 parts, 0.18 parts, 0.20 parts, 0.22 parts, 0.24 parts or 0.25 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] Preferably, the matrix cement includes any one of tricalcium silicate, dicalcium silicate, tetracalcium aluminoferrite or tricalcium aluminate, or a combination of at least two thereof.

[0050] Preferably, the matrix cement includes 50-60 parts of tricalcium silicate, for example, 50 parts, 52 parts, 54 parts, 56 parts, 58 parts or 60 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; 10-25 parts of dicalcium silicate, for example, 10 parts, 12 parts, 14 parts, 15 parts, 16 parts, 18 parts, 20 parts, 22 parts, 24 parts or 25 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; 10-15 parts of tetracalcium aluminoferrite, for example, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable. 10-15 parts of tricalcium aluminate, for example, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts or 15 parts, but not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0051] Preferably, the particle size of the water-swellable rubber particles is 0.15-0.18 mm, for example, 0.15 mm, 0.16 mm, 0.17 mm or 0.18 mm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, the crack-stopping material comprises polyethylene fibers and / or polyvinyl alcohol fibers.

[0053] Preferably, the mass percentage of polyvinyl alcohol fiber in the crack-arresting material is ≤50%, for example, it can be 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10% or 5%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] In the present invention, the preferred control crack arrest material includes polyethylene fiber and / or polyvinyl alcohol fiber, wherein polyvinyl alcohol fiber (PVA) is a hydrophilic fiber. As the cement hydration continues, the chemical bonding strength between the polyvinyl alcohol fiber and the matrix interface continues to increase, thereby improving the overall elastic modulus of the cement; polyethylene fiber (PE) is a hydrophobic fiber. Its bonding with the matrix is ​​relatively less affected by cement hydration. In terms of the ability to control crack width, polyvinyl alcohol fiber is superior to polyethylene fiber. In terms of improving the overall strength of cement, polyethylene fiber is superior to polyvinyl alcohol fiber. Therefore, the present invention can further control the elastic modulus, crack width, strength, etc. by preferably controlling the content of polyvinyl alcohol fiber in the crack arrest material, thereby achieving good comprehensive performance.

[0055] Preferably, the fluid loss additive comprises polyvinylpyrrolidone.

[0056] Preferably, the dispersant comprises sodium hexametaphosphate.

[0057] In a third aspect, the present invention provides a method for preparing the composite cement slurry system according to the second aspect of the present invention, characterized in that the preparation method comprises the following steps:

[0058] (1) mixing raw materials according to the formula to obtain a mixed material;

[0059] (2) diluting and stirring the mixture obtained in step (1) to obtain cement slurry.

[0060] The preparation method provided by the present invention can fully promote the uniform dispersion of various components of the composite cement slurry system, avoid the agglomeration of water-swelling rubber particles and crack-arresting materials, and achieve consistency of overall performance.

[0061] Preferably, the dilution and stirring treatment in step (2) includes adding water and stirring in sequence.

[0062] Preferably, the dilution and stirring treatment is performed 3-5 times, for example, 3 times, 4 times or 5 times.

[0063] Preferably, the cement slurry obtained in step (2) is injected into the wellbore annulus within 1.5-2 hours, for example, it can be 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0064] In the present invention, by optimally controlling the injection time of cement slurry, it is possible to avoid the swelling of rubber particles in the cement slurry after absorbing water due to excessive injection time, affecting the fluidity of the cement slurry during the pumping stage, increasing the cementing construction pump pressure, and increasing the wellbore safety risk.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (1) The water-swelling rubber particles provided by the present invention are added to the composite cement slurry system. After absorbing water and swelling, they can reduce the elastic modulus of the system, increase the ability of the cement sheath to absorb formation displacement loads, and help reduce the risk of casing deformation.

[0067] (2) The composite cement slurry system provided by the present invention is composed of a core system consisting of base cement, water-absorbing and swelling rubber particles, crack-stopping materials, fluid loss reducers and dispersants. Under optimal conditions, the time from the water-absorbing and swelling rubber particles to initial expansion after contact with water is 135-140 minutes, the time from contact with water to completion of water absorption is 160-165 minutes, and the expansion rate after completion of water absorption is 91.82-123.57%. Under optimal conditions, the compressive strength of the composite cement slurry system provided by the present invention reaches 21.4-23.6 MPa, the elastic modulus reaches below 4.3 GPa, the crack width reaches below 82 μm, and the casing diameter reduction reaches below 7.1 mm.

[0068] (3) The present invention addresses the problem of casing deformation caused by the activation of unconventional oil and gas casing cracks. Water-absorbing and swelling rubber particles are added to the composite cement slurry system. During the waiting stage of the cement slurry, the water-absorbing and swelling rubber particles can fully absorb water and expand, thereby forming a large number of tiny spaces inside the cement stone, significantly reducing the elastic modulus of the cement stone, and achieving a large-scale absorption of sliding displacement when hydraulic fracturing-induced fracture activation occurs, avoiding deformation of the oil layer casing, ensuring the smooth construction of horizontal well fracturing, and increasing the single-well production of shale oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a microscopic morphology of the composite cement slurry system obtained in Application Example 1 of the present invention after curing for 7 days;

[0070] Figure 2 This is a microscopic morphology of the composite cement slurry system obtained in Application Example 4 of the present invention after curing for 7 days;

[0071] Figure 3 This is a microscopic morphology of the composite cement slurry system obtained in Comparative Example 3 of the present invention after curing for 7 days;

[0072] Figure 4 This is a microscopic morphology of the composite cement slurry system obtained in Comparative Example 4 of the present invention after curing for 7 days. DETAILED DESCRIPTION

[0073] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0074] The materials used in the present invention are as follows:

[0075] Nitrile butadiene rubber, Lanhua 3305, was purchased from Lanzhou Petrochemical Company.

[0076] Hydrogenated nitrile rubber, Therban 1707, was purchased from Alantai Rubber (Nantong) Chemical Industry Co., Ltd.

[0077] Sodium polyacrylate, particle size 75 μm-85 μm, Acusol 445N, was purchased from The Dow Chemical Company, USA.

[0078] Polyacrylamide, particle size 50 μm-70 μm, VC312CT (cationic type), was purchased from Shanghai Woshan Chemical Co., Ltd.

[0079] Polyethylene glycol, PEG-6000, was purchased from The Dow Chemical Company, USA.

[0080] Sulfur, HS-7020, was purchased from Jiangxi Hengxingyuan Chemical Co., Ltd.

[0081] Dicumyl peroxide, industrial grade DCP, was purchased from Shandong Yingshi Chemical Co., Ltd.

[0082] N-cyclohexyl-2-benzothiazolesulfenamide, rubber accelerator CZ (CBS), was purchased from Tesco Chemical (Hubei) Co., Ltd.

[0083] Zinc oxide, industrial-grade zinc oxide, was purchased from Jinan Century Tongda Chemical Co., Ltd.

[0084] Sodium hydroxide, HYGAIN, was purchased from Qingdao Haiwan Group.

[0085] Carbon black, N220, was purchased from Jiangxi Black Cat Carbon Black Co., Ltd.

[0086] Silica, type GH-7, was purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0087] Calcium sulfate whiskers, modified with coupling agent 11-100 (γ-aminopropyltriethoxysilane), with an aspect ratio of 20-50, brand ONODA-GPF, were purchased from Shanghai Chengfeng Whiskers Co., Ltd.

[0088] Polyurethane prepolymer, T2080, was purchased from Liming Chemical Research and Design Institute Co., Ltd.

[0089] Tricalcium silicate, ZD3170, was purchased from Hubei Jusheng Technology Co., Ltd.

[0090] Dicalcium silicate, TB41462, was purchased from Hubei Tuobang Chemical Co., Ltd.

[0091] Tetracalcium aluminoferrite, Jiahua G grade, was purchased from Jiahua Special Cement Co., Ltd.

[0092] Tricalcium aluminate, ZD3355, was purchased from Hubei Xinhongli Chemical Co., Ltd.

[0093] Polyethylene fiber, Ruiyuan, purchased from Qilu Petrochemical.

[0094] Polyvinyl alcohol fiber, (VICK), purchased from Shenzhen Vitner New Materials Co., Ltd.

[0095] Polyvinylpyrrolidone, PVP K15, was purchased from Shanghai Qifuqing Material Technology Co., Ltd.

[0096] Sodium hexametaphosphate was purchased from Kandis Chemical (Hubei) Co., Ltd.

[0097] Examples 1-4

[0098] Examples 1-4 provide water-swelling rubber particles, respectively. The raw materials for preparing the water-swelling rubber particles are shown in Table 1 in parts by weight.

[0099] Table 1

[0100]

[0101] The method for preparing water-swellable rubber particles using the above-mentioned raw materials comprises the following steps:

[0102] A closed rubber mixer is used to carry out step-by-step mixing at a speed of 18 r / min and a pressure of 15 MPa: first, the base rubber, water-absorbing component, water-absorbing aid, and reinforcing agent are mixed at a temperature of 60°C, and a compatibilizer is optionally added, and mixed for 40 minutes until uniformly dispersed; then, the vulcanizing agent and accelerator are added, the vulcanization temperature is controlled at 140°C, the reaction is carried out for 40 minutes, and then extrusion and granulation are carried out to obtain water-absorbing and swelling rubber particles.

[0103] Example 5

[0104] This embodiment provides water-swelling rubber particles. The raw materials for preparing the water-swelling rubber particles differ from those in Example 1 only in that calcium sulfate whiskers are not added, the total mass fraction of the reinforcing agent is kept unchanged, and the fractions of carbon black and white carbon black are adjusted in equal proportions.

[0105] Example 6

[0106] This embodiment provides water-swelling rubber particles. The raw materials for preparing the water-swelling rubber particles differ from those in Example 1 only in that no compatibilizer is added.

[0107] Comparative Example 1

[0108] This comparative example provides a rubber particle. The raw materials for preparing the rubber particle differ from those in Example 1 only in that no water-absorbing component is added.

[0109] Comparative Example 2

[0110] This comparative example provides a rubber particle. The raw materials for preparing the rubber particle differ from those in Example 1 only in that no water-absorbing auxiliary agent is added.

[0111] The time from the start of expansion to the completion of water absorption of the water-swellable rubber particles provided in the above examples and comparative examples is shown in Table 2. The water-swellable rubber particles fully absorb water and swell within 2-4 hours. The expansion rate after the completion of water absorption is measured by volume measurement, as shown in Table 2.

[0112] Table 2

[0113]

[0114]

[0115] It should be noted that, given the characteristics of cementing operations in shale oil and gas reservoirs, it is necessary to ensure that the cement slurry does not expand during the pumping process to prevent the cement slurry from losing fluidity and avoid the risk of pressure buildup and pumping difficulties. At the same time, the cement slurry needs to expand from the time it reaches the target location to before the cement slurry solidifies, in order to achieve the performance requirement of reducing the elastic modulus. Generally, the elastic modulus of ordinary cement is greater than 10GPa, the temperature of shale oil and gas reservoirs is 90-180°C, the cementing pumping operation time is 1.5-2h, and the cement slurry loses fluidity after reaching the initial setting time of 3-4h. Therefore, the water-absorbing and swelling rubber particles need not expand within 2h and fully absorb water and expand within 2-4h.

[0116] From the data in Table 2 we can see that:

[0117] (1) Under optimal conditions, the time from contact with water to initial expansion of the water-swelling rubber particles provided in Examples 1-4 is 135-140 min, the time from contact with water to completion of water absorption is 160-165 min, and the expansion rate after completion of water absorption is 91.82-123.57%, which meets the above-mentioned process requirements.

[0118] (2) From the comparison between Example 1 and Example 5, it can be seen that when the present invention uses nitrile rubber as the base rubber, the expansion rate can be further increased by preferably adding calcium sulfate whiskers.

[0119] (3) From the comparison between Example 1 and Example 6, it can be seen that by preferably adding a compatibilizer to the rubber particles provided by the present invention, although the water absorption completion time is increased, the water absorption expansion rate of the rubber particles can be further improved.

[0120] (4) From the comparison between Example 1 and Comparative Examples 1-2, it can be seen that the present invention can give the rubber particles good water absorption and expansion properties by controlling the addition of water-absorbing components and water-absorbing aids through the synergistic effect of the two.

[0121] Application Examples 1-4

[0122] The present application examples 1-4 respectively provide a composite cement slurry system, wherein the composite cement slurry system respectively uses the water-swelling rubber particles (particle size of 0.15-0.18 mm) provided in Examples 1-4. The raw materials for preparing the composite cement slurry system are calculated in parts by weight, as shown in Table 3.

[0123] Table 3

[0124]

[0125] Using the above-mentioned raw materials, the preparation method of the composite cement slurry system includes the following steps:

[0126] (1) mixing raw materials according to the formula to obtain a mixed material;

[0127] (2) The mixture obtained in step (1) is diluted and stirred for 5 times, wherein each dilution and stirring treatment includes sequentially adding water and stirring to obtain cement slurry, and the cement slurry is injected into the wellbore annulus within 2 hours.

[0128] Taking Application Example 1 as an example, the microscopic morphology of the composite cement slurry system after curing for 7 days is as follows: Figure 1 Taking Application Example 4 as an example, the microscopic morphology of the composite cement slurry system after curing for 7 days is shown as follows: Figure 2 shown.

[0129] Application Examples 5-6

[0130] Application Examples 5-6 provide a composite cement slurry system respectively. The difference between the composite cement slurry system and Application Example 1 is that the water-swelling rubber particles are replaced by the water-swelling rubber particles provided in Examples 6-5 respectively.

[0131] Application Examples 7-8

[0132] Application Examples 7-8 provide a composite cement slurry system respectively. The difference between the composite cement slurry system and Application Example 1 is that the total proportion of the crack-stopping material remains unchanged, and the proportion of polyvinyl alcohol fiber is 75% and 100% respectively.

[0133] Application Comparative Example 1-2

[0134] Comparative Examples 1-2 of this application respectively provide a composite cement slurry system, and the difference between the composite cement slurry system and Application Example 1 is that the water-swelling rubber particles are replaced by the water-swelling rubber particles provided in Comparative Examples 1-2 respectively.

[0135] Application Comparative Example 3

[0136] This comparative example provides a composite cement slurry system. The composite cement slurry system differs from Application Example 1 only in that water-swelling rubber particles are not added.

[0137] The micromorphology of the composite cement slurry system obtained in this comparative example after curing for 7 days is as follows Figure 3 shown.

[0138] from Figure 1 and Figure 3 It can be seen from the comparison that after adding water-absorbing and expanding rubber particles, micro cracks appear in the cement, which will cause the overall strength to decrease.

[0139] Comparative Application Example 4

[0140] This comparative example provides a composite cement slurry system, which differs from Application Example 1 only in that no crack arresting material is added.

[0141] The micromorphology of the composite cement slurry system obtained in this comparative example after curing for 7 days is as follows Figure 4 shown.

[0142] from Figure 2 and Figure 4 From the comparison, it can be seen that the crack width around the rubber particles is 50-70 μm after the crack-stopping material is added, while the crack width around the rubber particles is 110-130 μm when the crack-stopping material is not added. It can be seen that the present invention can effectively reduce the crack width by adding the crack-stopping material.

[0143] After seven days of curing, the composite cement slurry systems provided in the aforementioned application examples and comparative examples were tested for compressive strength and elastic modulus at 150°C using an RTR-1000 triaxial rock mechanics testing system. The width of cracks induced by rubber particles in the cement was measured using a scanning electron microscope. Furthermore, the cement systems provided in the aforementioned application examples and comparative examples were used for cementing, with displacement controlled at 6.3-9.6 mm. The internal casing deformation was measured using an unconventional oil and gas wellbore simulation test (UGT) system to determine the casing reduction. These results are shown in Table 4.

[0144] Table 4

[0145]

[0146] From Table 4 we can see that:

[0147] (1) The data from Application Examples 1-4 show that, under optimal conditions, the composite cement slurry system provided by the present invention exhibits high compressive strength, low elastic modulus, and small crack width. The compressive strength reaches 21.4-23.6 MPa, the elastic modulus is below 4.3 GPa, the crack width is below 82 μm, and the casing diameter reduction is below 7.1 mm. It should be noted that a high expansion rate of the water-swellable rubber particles can reduce the elastic modulus and the risk of casing deformation, but the strength of the cement will also decrease. Generally, a cement strength of 21.2 MPa or above meets construction requirements.

[0148] (2) From the comparison between Application Example 1 and Application Examples 5-6, it can be seen that the present invention can further reduce the elastic modulus of cement and the diameter reduction of the casing by preferably adding calcium sulfate whiskers or a compatibilizer to the rubber particles.

[0149] (3) From the comparison between Application Example 1 and Application Examples 7-8, it can be seen that the present invention can avoid the elastic modulus of the cement system from being too high while ensuring a small crack width and high compressive strength by preferentially controlling the proportion of polyvinyl alcohol fibers in the crack-stopping material, thereby reducing the elastic modulus.

[0150] (4) From the comparison between Application Example 1 and Application Comparative Example 3, it can be seen that the present invention can reduce the elastic modulus of the composite cement slurry system by adding water-absorbing and swelling rubber particles to the composite cement slurry system. From the comparison between Application Example 1 and Application Comparative Examples 1-2, it can be seen that controlling the addition of water-absorbing components or water-absorbing aids to the rubber particles can further reduce the elastic modulus of cement and the diameter reduction of the casing.

[0151] (5) By comparing Application Example 1 and Comparative Example 4, it can be seen that the composite cement slurry system provided by the present invention can significantly reduce the crack width by adding crack-stopping materials.

[0152] In summary, the composite cement slurry system provided by the present invention incorporates water-swelling rubber particles. The expanded rubber particles significantly reduce the elastic modulus of the system, increasing the cement sheath's ability to absorb formation displacement loads, thereby reducing the risk of shale oil and gas casing deformation and improving the overall benefits of shale oil and gas development.

[0153] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A water-swellable rubber particle, characterized in that: The raw materials for preparing the water-swellable rubber particles include the following components in parts by weight: The water-absorbing component includes sodium polyacrylate and / or polyacrylamide; The water absorption aid includes polyethylene glycol.

2. The water-swellable rubber particles according to claim 1, characterized in that The base rubber includes nitrile rubber and / or hydrogenated nitrile rubber; Preferably, the particle size of the sodium polyacrylate is 75-85 μm; Preferably, the particle size of the polyacrylamide is 50-70 μm.

3. The water-swellable rubber particles according to claim 1 or 2, characterized in that: The vulcanizing agent includes sulfur and / or dicumyl peroxide; Preferably, the accelerator includes any one of N-cyclohexyl-2-benzothiazolesulfenamide, zinc oxide or sodium hydroxide, or a combination of at least two thereof.

4. The water-swellable rubber particles according to any one of claims 1 to 3, characterized in that: The reinforcing agent includes any one of carbon black, white carbon black or calcium sulfate whiskers or a combination of at least two thereof; Preferably, when the reinforcing agent comprises a combination of carbon black and white carbon black, the carbon black is 20-25 parts by weight and the white carbon black is 25-30 parts by weight; Preferably, when the reinforcing agent comprises a combination of carbon black, white carbon black and calcium sulfate whiskers, the carbon black is 15-20 parts, the white carbon black is 25-30 parts, and the calcium sulfate whiskers is 8-10 parts in parts by weight.

5. The water-swellable rubber particles according to any one of claims 1 to 4, characterized in that: The raw materials for preparing the water-swelling rubber particles also include a compatibilizer; Preferably, the raw materials for preparation include 8-10 parts of a compatibilizer in parts by weight; Preferably, the compatibilizer comprises a polyurethane prepolymer.

6. A composite cement slurry system, characterized in that: The raw materials for preparing the composite cement slurry system include the following components in parts by weight: The water-swelling rubber particles are the water-swelling rubber particles according to any one of claims 1 to 5.

7. The composite cement slurry system according to claim 6, characterized in that: The matrix cement comprises any one of tricalcium silicate, dicalcium silicate, tetracalcium aluminoferrite or tricalcium aluminate, or a combination of at least two thereof; Preferably, in parts by weight, the matrix cement comprises 50-60 parts of tricalcium silicate, 10-25 parts of dicalcium silicate, 10-15 parts of tetracalcium aluminoferrite, and 10-15 parts of tricalcium aluminate.

8. The composite cement slurry system according to claim 6 or 7, characterized in that: The particle size of the water-swellable rubber particles is 0.15-0.18 mm; Preferably, the crack arresting material comprises polyethylene fibers and / or polyvinyl alcohol fibers; Preferably, the mass percentage of polyvinyl alcohol fiber in the crack-stopping material is ≤50%; Preferably, the fluid loss additive comprises polyvinyl pyrrolidone; Preferably, the dispersant comprises sodium hexametaphosphate.

9. A method for preparing the composite cement slurry system according to any one of claims 6 to 8, characterized in that: The preparation method comprises the following steps: (1) mixing raw materials according to the formula to obtain a mixed material; (2) diluting and stirring the mixture obtained in step (1) to obtain cement slurry.

10. The preparation method according to claim 9, characterized in that The dilution and stirring treatment in step (2) includes adding water and stirring in sequence; Preferably, the dilution and stirring treatment is performed 3-5 times; Preferably, the cement slurry obtained in step (2) is injected into the wellbore annulus within 1.5-2 hours.

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