Deep coal bed gas well cementation cement paste and preparation method thereof

Abstract

The invention discloses deep coal bed gas well cementation cement paste and a preparation method thereof, and the deep coal bed gas well cementation cement paste is prepared from the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 5-15 parts of water-borne epoxy resin, 1.5-3 parts of a nano silicon dioxide solution, 0.5-1.8 parts of calcium sulfate whiskers, 0.2-0.6 part of composite coating fibers, 1.2-1.8 parts of a fluid loss agent and 0.5-1.8 parts of a retarder. 0.3 to 0.5 part of a drag reducer, 0.2 to 0.5 part of a defoaming agent and 38 to 42 parts of water; wherein the composite coating fiber is hydrophilic epoxy resin modified polyethylene fiber. The cement paste can improve the well cementation cementing packing quality of a coal seam, and has good filtration property.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas wells, and in particular to a deep coalbed methane cementing slurry and a preparation method thereof. Background Art

[0002] Coalbed methane, a new unconventional natural gas resource, has achieved breakthroughs in extraction at depths exceeding 1,800 meters, injecting new momentum into China's energy strategy of "stabilizing oil production and increasing natural gas production." Currently, coalbed methane exploration and development is undergoing a strategic shift from shallow to deep exploration, providing crucial resource support for national energy security.

[0003] Deep coalbed methane (CBM) reservoirs are characterized by complex geological structures and high temperature gradients. Because coalbed methane (CBM) reservoirs are fractured, numerous mine dissections have confirmed that near-wellbore coal reservoirs are severely impacted by cementing slurry invasion. Cementing slurry intrudes into the reservoir along the wellbore's coal rock fractures, forming a "plate-like" cementing filter cake within the fractures. For gas wells located in tectonic soft coal, the cement stone expands along the wellbore diameter and thickens along the major axis of the ellipse, making subsequent perforation difficult. To address this issue of cementing slurry invasion in these coal reservoirs, a series of technical measures have been proposed, including the development of efficient viscosity-reducing flushing fluids, the development of high-early-strength and high-toughness cement slurry systems, the optimization of slurry column design, and the development of supporting technical measures. These measures aim to improve cementing quality and ensure the long-term, efficient production of CBM wells. Furthermore, the low mechanical strength of coal rock, reservoir distribution characteristics, and lithologic features, including coal seam thickness, burial depth, and high sensitivity to in-situ stresses, limit cementing capacity, resulting in low displacement efficiency and high contamination of the drilling mud by the cement slurry. These factors pose numerous safety risks during cementing operations. Furthermore, the coal rock matrix is ​​primarily composed of organic matter, and its surface exhibits strong oleophilic and hydrophobic properties, resulting in extremely poor interfacial bonding with conventional (hydrophilic) cement slurries. This results in insufficient bonding strength at the cementing interface, which can easily lead to problems such as wellbore instability, gas channeling, and annular pressure. For deep CBM horizontal well cementing, conventional cement slurry systems are unable to meet the requirements, and the bonding strength at the cementing interface decreases with increasing temperature in the presence of some mud cake. In the presence of mud cake, as temperature increases, the thickness of the water film bound to the clay particles in the mud cake decreases, and the interaction between the clay particles decreases, resulting in more and larger pores in the mud cake, an increase in the overall permeability of the mud cake, and ultimately a deterioration in the bonding quality of the cementing interface.

[0004] Furthermore, horizontal CBM cementing operations require long operation times, and the formation environment in which the cement slurry passes is complex and harsh. To ensure effective cement slurry injection, sufficient pumping time and good suspension stability are essential. As CBM development gradually shifts from shallow to deep formations, CBM cementing quality issues are becoming increasingly prominent. To further research cement slurry systems under complex CBM cementing conditions, their comprehensive performance is becoming an increasingly pressing issue.

[0005] Patent CN119683914A discloses a cement suitable for coalbed methane (CBM) cementing and its preparation method. The cement comprises, by weight percentage, 55-75% G-grade cement, 15-20% active mineral material, 3-5% composite reinforcement, 5-15% lightening agent, 1-3% fluid loss additive, and 1-2% dispersant. The invented CBM cement slurry exhibits excellent workability in low-temperature environments, with rapid strength development, excellent channeling resistance, and toughness. The cement is prepared using a large amount of solid waste as raw material, increasing solid waste disposal capacity and achieving environmentally friendly, low-cost characteristics. However, it lacks sufficient sealing effect on micro-fractures in coal seams, resulting in high leakage that could affect subsequent development. Furthermore, the operating temperature is not suitable for deep CBM cementing.

[0006] Patent CN110054440A discloses a low-temperature, early-strength, low-density cement slurry system for coalbed methane cementing. This cement slurry system is prepared by mixing oil well cement with slag powder, fly ash, and buoyant beads in a certain proportion, and adding a certain amount of cement slurry admixtures such as fluid loss reducer, early strength agent, expansion agent, dispersant, and retarder. This improves the strength, rheology, and density of the cement slurry system to a certain extent, and can meet the requirements of low temperature, early strength, and low density in cementing construction and mining during coalbed methane extraction. However, it does not consider issues such as formation filtration, plugging, and cementing interface bonding strength.

[0007] Therefore, it is very critical to improve the cementing quality of deep coalbed methane horizontal wells by effectively improving the hydrophilicity of the coal rock surface and enhancing the bonding of the cementing interface. Summary of the Invention

[0008] In view of the defects of the prior art, the present invention provides a deep coalbed methane cementing slurry and a preparation method thereof, wherein the cement slurry can improve the cementing and sealing quality of coalbed cementing and has good filtration loss and sedimentation stability.

[0009] A deep coalbed methane cementing slurry is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 5-15 parts of water-based epoxy resin, 1.5-3 parts of nano-silica solution, 0.5-1.8 parts of calcium sulfate whiskers, 0.2-0.6 parts of composite coating fiber, 1.2-1.8 parts of fluid loss additive, 0.5-1.8 parts of retarder, 0.3-0.5 parts of drag reducer, 0.2-0.5 parts of defoamer, and 38-42 parts of water; wherein the composite coating fiber is polyethylene fiber modified with hydrophilic epoxy resin.

[0010] Preferably, the composite coated fiber is prepared by the following method: (1) Epoxy resin, acetylacetone, triethylamine, and deionized water were mixed and stirred at 80-90°C for 2-4 hours, and then adipic acid was added and the temperature was maintained to continue the reaction for 6-12 hours to obtain a hydrophilic resin; (2) adding polyethylene fiber to the hydrophilic resin, stirring until uniformly dispersed, then adding a curing agent and a defoaming agent, continuing stirring for 10-20 minutes, filtering, and drying to obtain pre-modified polyethylene fiber; (3) Add the pre-modified polyethylene fiber to the dispersant solution, oscillate and adsorb at 25-30°C for 30-40 minutes, filter and dry.

[0011] Preferably, in step (1), the weight ratio of the epoxy resin, acetylacetone, and triethylamine is (70-90): (12.5-25.5): (0.5-3); the weight ratio of the deionized water and adipic acid is (150-200): (2-5); and the total weight of the epoxy resin, acetylacetone, and triethylamine accounts for 30-45% of the weight of the deionized water.

[0012] Preferably, in step (2), the weight ratio of the hydrophilic resin, the polyethylene fiber, the curing agent, and the defoaming agent is 100: (15-25): (10-15): (0.1-0.3).

[0013] Preferably, in step (3), the weight ratio of the pre-modified polyethylene fiber to the dispersant solution is (5-10): (50-100).

[0014] Preferably, the drying condition is drying at 60-65° C. for 40-48 hours; the drying condition is drying at 90-95° C. to constant weight.

[0015] Preferably, the curing agent is a water-soluble epoxy curing agent, the defoaming agent is a mixture of an organic silicone defoamer, an organic polyether defoamer, and an organic silicone ether defoamer in a mass ratio of 1:3:1.8, the concentration of the dispersant solution is 25-30wt%; the average length of the polyethylene fiber is 1-2mm and the density is 0.97-0.98g / cm 3 .

[0016] Preferably, the fluid loss additive is an AMPS type fluid loss additive; The retarder is an AMPS retarder; The drag reducer is a ketone-aldehyde condensation polymer; The defoaming agent is a mixture of an organic silicone defoaming agent, an organic polyether defoaming agent, and an organic silicone ether defoaming agent in a mass ratio of 1:3:1.8.

[0017] Preferably, the concentration of the nano-silica solution is 30-35 wt %, and the particle size of the nano-silica is 10-20 nm; The density of the calcium sulfate whiskers is 2.68-2.73 g / cm 3 , with an average diameter of 1-4 μm and an average length of 50-200 μm.

[0018] The preparation method of the deep coalbed methane cementing slurry comprises the following steps: adding a drag reducer, a defoamer, and a water-based epoxy resin to water, stirring at 500 r / min for 10-20 seconds, then adding a composite coated fiber at a stirring rate of 2500-3000 r / min and stirring for 10-20 seconds, then sequentially adding a nano-silica solution, calcium sulfate whiskers, a retarder, a fluid loss additive, and a G-grade oil well cement, and then stirring at 12000 r / min for 35 seconds to obtain the deep coalbed methane cementing slurry.

[0019] The AMPS described in the present invention is 2-acrylamido-2-methylpropanesulfonic acid.

[0020] Advantages of the present invention: (1) The composite coating fibers contained in the raw materials of the present invention successfully isolate the solid particles in the cement slurry system by forming a tough fibrous network in the leakage zone of the coalbed methane well, thereby preventing cementing leakage. In addition, under the action of interfacial forces, the composite coating fibers form an enriched area on the contact surface between the cement sheath and the coal rock, thereby improving the hydrophilicity of the coal rock surface while forming a dense filter cake to enhance the permeability of the cement stone in the later stage, which is beneficial to improving the cementing quality. When combined with other raw materials, it can effectively improve the interface between the cement slurry, the filter cake and the well wall, further achieving the purpose of improving the bonding quality of the cementing interface. (2) The cement slurry of the present invention uses nano-silica as a reinforcing agent to improve the early compressive strength of the cement stone, and produces a certain amount of lattice micro-expansion, thereby preventing the generation of micro-annular gaps and improving the interface bonding strength; calcium sulfate whiskers are used as toughening agents and are evenly distributed between cement particles. When the formed cement stone is subjected to external force, it absorbs a certain amount of stress and produces a small elastic deformation, thereby improving the brittleness of the cement stone and reducing the elastic modulus of the cement stone. This significantly shortens the waiting time for cementing construction in order to prevent the layer from being channeled during the later fracturing of the coal seam, thereby reducing construction risks and construction costs; water epoxy resin materials, toughening agents, filling composite coating fibers, and auxiliary materials such as a certain amount of fine active filling materials nano-silica and whiskers are used to assist in filling and form a denser filter cake to reduce water loss; (3) The raw materials are widely available and abundant, the cost is low, the preparation conditions are mature, the use is convenient, and the prospects for promotion and application are good. DETAILED DESCRIPTION

[0021] In the present invention, the waterborne epoxy resin used is waterborne epoxy resin BH-653; AMPS fluid loss additive uses multi-polymer G310 from Weihui Chemical Co., Ltd. AMPS retarder uses vinyl acrylamide polymer HX-36L produced by Chengdu OMEC Petroleum Technology Co., Ltd. The organosiloxane defoamer uses defoamer DF-900; The organic polyether defoamer uses polyether defoamer GPE; The organosilicon ether defoamer uses defoamer FAG470; The dispersant used is dispersant AKN-2290; The water-soluble epoxy curing agent uses water-based epoxy curing agent BH-532; The drag reducer is ketone-aldehyde condensate USZ.

[0022] Example 1 A deep coalbed methane cementing slurry is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 10 parts of water-based epoxy resin, 2 parts of nano-silica solution, 1 part of calcium sulfate whisker, 0.3 parts of composite coating fiber, 1.2 parts of fluid loss additive, 1 part of retarder, 0.3 parts of drag reducer, 0.2 parts of defoamer, and 42 parts of water; Wherein, the concentration of the nano-silica solution is 30wt%, wherein the particle size of the nano-silica is 10-20nm; The density of the calcium sulfate whiskers is 2.68 g / cm 3 , average diameter is 1-4μm, average length is 50-100μm; The defoaming agent is a mixture of an organosiloxane defoaming agent, an organic polyether defoaming agent, and an organosilicon ether defoaming agent in a mass ratio of 1:3:1.8; The composite coating fiber is a hydrophilic epoxy resin modified polyethylene fiber, and the preparation method is as follows: (1) Epoxy resin, acetylacetone, triethylamine, and deionized water were mixed, stirred and reacted at 80°C and 200 rpm for 2 h, and then adipic acid was added and the temperature was maintained and the reaction was continued for 6 h to obtain a hydrophilic resin; wherein the weight ratio of epoxy resin, acetylacetone, and triethylamine was 70:18.5:1.5, the weight ratio of deionized water and adipic acid was 150:4, and the total weight of the epoxy resin, acetylacetone, and triethylamine accounted for 45% of the weight of deionized water; (2) Take 100 parts of the hydrophilic resin, add 20 parts of polyethylene fiber thereto, stir for 20 minutes, disperse evenly, then add 12 parts of water-soluble epoxy curing agent and 0.1 parts of defoaming agent thereto, continue stirring for 10 minutes, filter, and dry at 60°C for 48 hours to obtain pre-modified polyethylene fiber; wherein the density of the polyethylene fiber is 0.97 g / cm 3 , the average length is 1 mm; the defoaming agent is a mixture of an organic silicone defoamer, an organic polyether defoamer, and an organic silicone ether defoamer in a mass ratio of 1:3:1.8; (3) Add 10 parts of the pre-modified polyethylene fibers to 100 parts of a 25 wt% dispersant solution, shake and adsorb at 30°C for 30 minutes, filter, and dry at 90°C to constant weight.

[0023] The preparation method of the deep coalbed methane cementing slurry comprises the following steps: adding a drag reducer, a defoamer, and a water-based epoxy resin to water, stirring at 500 r / min for 10 seconds, then adding a composite coated fiber at a stirring rate of 2500 r / min and stirring for 10 seconds, then sequentially adding a nano-silica solution, calcium sulfate whiskers, a retarder, a fluid loss additive, and G-grade oil well cement, and then stirring at 12000 r / min for 35 seconds.

[0024] Example 2 A deep coalbed methane cementing slurry is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 15 parts of water-based epoxy resin, 2.5 parts of nano-silica solution, 0.5 parts of calcium sulfate whiskers, 0.5 parts of composite coating fiber, 1.2 parts of fluid loss additive, 1 part of retarder, 0.3 parts of drag reducer, 0.2 parts of defoamer, and 42 parts of water; The rest is the same as Example 1.

[0025] Example 3 A deep coalbed methane cementing slurry is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 10 parts of water-based epoxy resin, 3 parts of nano-silica solution, 1 part of calcium sulfate whisker, 0.4 parts of composite coating fiber, 1.8 parts of fluid loss additive, 1 part of retarder, 0.3 parts of drag reducer, 0.2 parts of defoamer, and 42 parts of water; The rest is the same as Example 1.

[0026] Example 4 A deep coalbed methane cementing slurry is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 5 parts of water-based epoxy resin, 1.5 parts of nano-silica solution, 1.8 parts of calcium sulfate whiskers, 0.2 parts of composite coating fiber, 1.6 parts of fluid loss additive, 0.5 parts of retarder, 0.5 parts of drag reducer, 0.5 parts of defoamer, and 38 parts of water; Wherein, the concentration of the nano-silica solution is 35wt%, wherein the particle size of the nano-silica is 10-20nm; The density of the calcium sulfate whiskers is 2.73 g / cm 3 , average diameter is 1-2μm, average length is 100-200μm; The defoaming agent is a mixture of an organosiloxane defoaming agent, an organic polyether defoaming agent, and an organosilicon ether defoaming agent in a mass ratio of 1:3:1.8; The composite coating fiber is a hydrophilic epoxy resin modified polyethylene fiber, and the preparation method is as follows: (1) Epoxy resin, acetylacetone, triethylamine, and deionized water were mixed, stirred and reacted at 90°C and 200 rpm for 4 hours, and then adipic acid was added and the temperature was maintained and the reaction was continued for 12 hours to obtain a hydrophilic resin; wherein the weight ratio of epoxy resin, acetylacetone, and triethylamine was 90:12.5:0.5, the weight ratio of deionized water and adipic acid was 200:2, and the total weight of the epoxy resin, acetylacetone, and triethylamine accounted for 30% of the weight of deionized water; (2) Take 100 parts of the hydrophilic resin, add 15 parts of polyethylene fiber thereto, stir for 20 minutes, disperse evenly, then add 10 parts of water-soluble epoxy curing agent and 0.1 parts of defoaming agent thereto, continue stirring for 20 minutes, filter, and dry at 65°C for 40 hours to obtain pre-modified polyethylene fiber; wherein the density of the polyethylene fiber is 0.98 g / cm 3 , the average length is 2 mm; the defoaming agent is a mixture of an organic silicone defoamer, an organic polyether defoamer, and an organic silicone ether defoamer in a mass ratio of 1:3:1.8; (3) Add 5 parts of the pre-modified polyethylene fiber to 50 parts of a 30 wt% dispersant solution, shake and adsorb at 25°C for 40 minutes, filter, and dry at 95°C to constant weight.

[0027] The preparation method of the deep coalbed methane cementing slurry comprises the following steps: adding a drag reducer, a defoamer, and a water-based epoxy resin to water, stirring at 500 r / min for 20 seconds, then adding a composite coated fiber at a stirring rate of 3000 r / min and stirring for 20 seconds, then sequentially adding a nano-silica solution, calcium sulfate whiskers, a retarder, a fluid loss additive, and G-grade oil well cement, and then stirring at 12000 r / min for 35 seconds.

[0028] Example 5 A deep coalbed methane cementing slurry is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 10 parts of water-based epoxy resin, 2 parts of nano-silica solution, 1 part of calcium sulfate whisker, 0.6 parts of composite coating fiber, 1.2 parts of fluid loss additive, 1.8 parts of retarder, 0.3 parts of drag reducer, 0.2 parts of defoamer, and 40 parts of water; The density of the nano-silica solution is 1.11 g / cm 3 , wherein the particle size of nano-silicon dioxide is 10-20nm; The calcium sulfate whiskers have a concentration of 32 wt%, an average diameter of 1-4 μm, and an average length of 50-100 μm; The defoaming agent is a mixture of an organosiloxane defoaming agent, an organic polyether defoaming agent, and an organosilicon ether defoaming agent in a mass ratio of 1:3:1.8; The composite coating fiber is a hydrophilic epoxy resin modified polyethylene fiber, and the preparation method is as follows: (1) Epoxy resin, acetylacetone, triethylamine, and deionized water were mixed, stirred and reacted at 85°C and 200 rpm for 3 hours, and then adipic acid was added and the temperature was maintained and the reaction was continued for 10 hours to obtain a hydrophilic resin; wherein the weight ratio of epoxy resin, acetylacetone, and triethylamine was 80:25.5:3, the weight ratio of deionized water and adipic acid was 180:2, and the total weight of the epoxy resin, acetylacetone, and triethylamine accounted for 40% of the weight of deionized water; (2) Take 100 parts of the hydrophilic resin, add 25 parts of polyethylene fiber thereto, stir for 20 minutes, disperse evenly, then add 15 parts of water-soluble epoxy curing agent and 0.3 parts of defoaming agent thereto, continue stirring for 10 minutes, filter, and dry at 60°C for 48 hours to obtain pre-modified polyethylene fiber; wherein the density of the polyethylene fiber is 0.97 g / cm 3 , the average length is 1 mm; the defoaming agent is a mixture of an organic silicone defoamer, an organic polyether defoamer, and an organic silicone ether defoamer in a mass ratio of 1:3:1.8; (3) 8 parts of the pre-modified polyethylene fibers were added to 100 parts of a 28 wt% dispersant solution, and adsorbed by shaking at 30°C for 30 minutes. After filtering, the solution was dried at 90°C to a constant weight.

[0029] The preparation method of the deep coalbed methane cementing slurry is the same as that in Example 1.

[0030] Comparative Example 1 The other steps are the same as those in Example 1 except that the water-based epoxy resin is not contained.

[0031] Comparative Example 2 The same as example 1 except that the solution without nano-silica and calcium sulfate whisker.

[0032] Comparative example 3 The same as example 1 except that the composite coated fiber is not used.

[0033] Comparative example 4 The polyethylene fiber is not modified, i.e. polyethylene fiber with a density of 0.97 g / cm 3 The same as example 1 except that the composite coated fiber is replaced by polyethylene fiber with a density of 0.97 g / cm

[0034] Performance test I. Cement slurry performance test After the cement slurry is fully stirred, the mixed slurry is poured into a normal pressure thickener, and cured at a temperature of 90°C for 30 min. After curing, the water loss performance of the slurry at 60°C and 6.9 MPa is tested using a high temperature and high pressure water loss instrument. The experimental results are shown in Table 1. Table 1 Cement slurry performance test results As shown in Table 1, compared with comparative example 1, the 30 min water loss of the slurry of example 1 is reduced, indicating that the waterborne epoxy resin improves the water loss performance of the cement slurry. The water loss of the cement slurry system prepared in examples 1-3 is less than 40 mL, and the SPN value (anti-channeling coefficient) is low, which has excellent anti-channeling ability, and the thickening time can well meet the construction requirements. Compared with example 1, the engineering performance of the cement slurry system of comparative examples 1-4 has deteriorated to varying degrees.

[0035] II. Mechanical property test The prepared cement slurry is prepared according to SY / T 6466-2016 "Oil well cement stone performance test method" to prepare test samples, and the mechanical properties are measured after curing in a 60°C water bath for 1d, 2d and 14d. The results are shown in Table 2. Table 2 Mechanical property test results As shown in Table 2, the cement slurry prepared by the application can be rapidly hydrated in a short period, and the cement stone strength develops rapidly, which is beneficial to shorten the cementing waiting-on-time of oil and gas wells, and the strength is relatively high, and the 14d compressive strength can reach more than 36MPa. In addition, as shown by the elastic modulus, the cement slurry effectively improves the toughness of the cement stone for well cementing, and the prepared cement stone has excellent toughness, that is, it can meet the performance requirements of the cement slurry for well cementing, and can effectively solve the problems of low strength and insufficient toughness of the cement stone in the long-term medium-temperature environment, which is beneficial to the fracturing construction in the late stage of the cementing of the deep coalbed methane horizontal section. As shown in Comparative Examples 1-4, the water-based epoxy resin material, nano-silicon dioxide and whisker material, and composite coating fiber in the cement slurry system have different degrees of influence on the performance of the cement stone.

[0036] III. Test of casing-cement stone-coal bed interface cementing strength The cement slurry is filled in a cylindrical mold, and the whole is placed in a 60℃ water bath box for curing for 1d, 2d and 14d, and the maximum shear force of the cement block-cylindrical mold contact surface per unit area, that is, the casing-cement stone interface cementing strength, that is, the first interface cementing surface strength, is measured; In order to more truly simulate the downhole conditions, an isotropic coal rock core is prepared, and the preparation steps of the coal rock core are as follows: 150 g of coal powder is obtained by grinding the field coal rock; 69 g of epoxy resin and 23 g of the aforementioned water-soluble epoxy curing agent (epoxy resin: water-soluble epoxy curing agent = 3:1) are weighed and uniformly mixed; the uniformly mixed mixture of the epoxy resin and the curing agent is poured into a container containing the coal powder, and after being uniformly stirred, it is poured into an isotropic cylindrical mold, and after being placed in a 90℃ oven for 48h, it is taken out for standby; An appropriate amount of deep coalbed methane well cementing cement slurry is poured into the mold, the coal rock core prepared above is placed in the cement slurry after constant speed stirring for 30s, and then it is vertically placed from top to bottom in the center of the mold filled with the cement slurry, to simulate the upward injection process of the cement slurry in the construction process, and then the cementing strength test piece mold is sealed as a whole, and is placed in a constant pressure and 60℃ environment for curing for 1d, 2d and 14d, and then taken out, and the maximum shear force of the coal rock block-cement ring interface, that is, the second interface cementing surface strength, is measured by using a compressive strength testing machine; the results are shown in Table 3. Table 3 Test results of cemented cement stone interface cementing strength As can be seen from Table 3, the cement slurry system prepared by the embodiment of the application can significantly improve the short-term cementing strength of the casing-cement stone-coal seam interface. As can be seen from Comparative Examples 1, 3 and 4, the cement slurry system shows that the cement slurry added with the water-based epoxy resin and the composite coating fiber can ensure that the casing-cement stone-coal seam interface has a certain interface cementing strength in the short term, especially for the coal seam section, the interface cementing strength is obviously improved, and the interface cementing strength develops stably after long-term maintenance, effectively meeting the performance requirements of the deep coal seam gas horizontal section cementing, and ensuring the safety of the later horizontal section mining.

Claims

1. A deep coalbed methane cementing slurry, characterized by: The invention is composed of the following raw materials in parts by weight: 100 parts of G-grade oil well cement, 5-15 parts of water-based epoxy resin, 1.5-3 parts of nano-silica solution, 0.5-1.8 parts of calcium sulfate whiskers, 0.2-0.6 parts of composite coating fiber, 1.2-1.8 parts of fluid loss additive, 0.5-1.8 parts of retarder, 0.3-0.5 parts of drag reducer, 0.2-0.5 parts of defoamer, and 38-42 parts of water; wherein the composite coating fiber is polyethylene fiber modified by hydrophilic epoxy resin.

2. The deep coalbed methane cementing slurry according to claim 1, characterized in that: The composite coated fiber is prepared by the following method: (1) Epoxy resin, acetylacetone, triethylamine, and deionized water were mixed and stirred at 80-90°C for 2-4 hours, and then adipic acid was added and the temperature was maintained to continue the reaction for 6-12 hours to obtain a hydrophilic resin; (2) adding polyethylene fiber to the hydrophilic resin, stirring until uniformly dispersed, then adding a curing agent and a defoaming agent, continuing stirring for 10-20 minutes, filtering, and drying to obtain pre-modified polyethylene fiber; (3) Add the pre-modified polyethylene fiber to the dispersant solution, oscillate and adsorb at 25-30°C for 30-40 minutes, filter and dry.

3. The deep coalbed methane cementing slurry according to claim 2, characterized in that: In step (1), the weight ratio of the epoxy resin, acetylacetone, and triethylamine is (70-90): (12.5-25.5): (0.5-3); the weight ratio of the deionized water and adipic acid is (150-200): (2-5); and the total weight of the epoxy resin, acetylacetone, and triethylamine accounts for 30-45% of the weight of the deionized water.

4. The deep coalbed methane cementing slurry according to claim 3, characterized in that: In step (2), the weight ratio of the hydrophilic resin, the polyethylene fiber, the curing agent, and the defoaming agent is 100: (15-25): (10-15): (0.1-0.3).

5. The deep coalbed methane cementing slurry according to claim 4, characterized in that: In step (3), the weight ratio of the pre-modified polyethylene fiber to the dispersant solution is (5-10): (50-100).

6. The deep coalbed methane cementing slurry according to claim 5, characterized in that: The drying conditions are as follows: drying at 60-65° C. for 40-48 hours; and drying at 90-95° C. until constant weight.

7. The deep coalbed methane cementing slurry according to claim 2, characterized in that: The curing agent is a water-soluble epoxy curing agent, the defoaming agent is a mixture of an organosiloxane defoamer, an organic polyether defoamer, and an organosilicone ether defoamer in a mass ratio of 1:3:1.8, the concentration of the dispersant solution is 25-30wt%; the average length of the polyethylene fiber is 1-2mm and the density is 0.97-0.98g / cm 3 .

8. The deep coalbed methane cementing slurry according to claim 1, characterized in that: The fluid loss additive is an AMPS type fluid loss additive; The retarder is an AMPS retarder; The drag reducer is a ketone-aldehyde condensation polymer; The defoaming agent is a mixture of an organic silicone defoaming agent, an organic polyether defoaming agent, and an organic silicone ether defoaming agent in a mass ratio of 1:3:1.

8.

9. The deep coalbed methane cementing slurry according to claim 1, characterized in that: The concentration of the nano-silica solution is 30-35wt%, and the particle size of the nano-silica is 10-20nm; The density of the calcium sulfate whiskers is 2.68-2.73 g / cm 3 , with an average diameter of 1-4 μm and an average length of 50-200 μm.

10. The method for preparing the deep coalbed methane cementing slurry according to claim 1, characterized in that: The preparation method is as follows: adding a drag reducer, a defoamer, and a water-based epoxy resin to water, stirring at 500 r / min for 10-20 seconds, then adding a composite coated fiber at a stirring rate of 2500-3000 r / min and stirring for 10-20 seconds, then sequentially adding a nano-silica solution, calcium sulfate whiskers, a retarder, a fluid loss additive, and G-grade oil well cement, and then stirring at 12000 r / min for 35 seconds to obtain the deep coalbed methane cementing slurry.

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