Deep coal bed gas well cementing slurry and preparation method thereof

Abstract

The application discloses a deep coal bed gas well cementing slurry and a preparation method thereof. The deep coal bed gas well cementing slurry is prepared from 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 silicon dioxide solution, 0.5-1.8 parts of calcium sulfate whisker, 0.2-0.6 parts of composite coating fiber, 1.2-1.8 parts of fluid loss reducer, 0.5-1.8 parts of retarder, 0.3-0.5 parts of drag reducer, 0.2-0.5 parts of defoaming agent and 38-42 parts of water. The composite coating fiber is a hydrophilic epoxy resin modified polyethylene fiber. The cementing slurry can improve the cementing and sealing quality of coal bed well cementing and has good filter loss.

Description

TECHNICAL FIELD

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

[0002] Coalbed methane as a new unconventional natural gas resource, has realized the breakthrough in the depth of 1800m, which provides new impetus for supporting the national energy structure strategy of "stabilizing oil and increasing gas". At present, the exploration and development of coalbed methane is in the strategic transformation from "shallow" to "deep", which provides important resource support for guaranteeing national energy security.

[0003] The deep coalbed methane reservoir has the characteristics of complex geological structure and high temperature gradient. Since the coal reservoir belongs to a fractured reservoir, a large number of mine dissection examples have proved that the near-wellbore coal reservoir is seriously affected by the invasion of well cementing slurry. The well cementing slurry invades into the reservoir along the coal rock fissure of the well wall, and forms a "plate-shaped" cementation filter cake in the fracture. For the gas well in the tectonic soft coal, the well cementing cement stone thickens in the long axis direction of the ellipse and expands the wellbore, which leads to the difficulty of subsequent perforation. In view of the above problems of the invasion of the well cementing slurry in the coal reservoir, a series of technical measures have been proposed, including the development of high-efficiency viscosity-reducing and flushing fluid, the development of high-early-strength and toughness cement slurry system, the optimization of slurry column structure design and the development of supporting technical measures, aiming to improve the well cementing quality and ensure the long-term and efficient exploitation of coalbed methane wells. In addition, the low mechanical strength of coal rock, the distribution characteristics and lithological characteristics of the reservoir, including the thickness of the coal seam, the burial depth, the strong ground stress sensitivity and other factors lead to the limited construction displacement, the low displacement efficiency, the strong contamination of the drilling mud to the cement slurry and other problems, which cause a lot of safety hazards in well cementing construction. In addition, the coal rock matrix is mainly organic matter, and the surface presents strong lipophilicity and hydrophobicity. The interface bonding capacity with the conventional cement slurry (hydrophilic) is very poor, which leads to the insufficient cementation strength of the well cementing interface, and easily causes the wellbore instability, gas channeling and annular pressure and other problems. For the well cementing of deep coalbed methane horizontal wells, the traditional well cementing slurry system is difficult to meet the demand, and the cementation strength of the well cementing interface decreases with the increase of temperature in the presence of part of the mud cake. With the increase of temperature, the thickness of the clay particle water film in the mud cake becomes thinner, the force between the clay particles decreases, the holes in the mud cake become more and more large, and the overall permeability of the mud cake increases, which finally leads to the poor cementation quality of the well cementing interface.

[0004] At the same time, the coalbed methane horizontal section well cementing has a long operation time in the well cementing operation, and the environment of the stratum passed by the cement slurry is complex and harsh. In order to ensure that the cement slurry is injected and replaced in place, it is necessary to ensure that the cement slurry has sufficient pumping time and good suspension stability. With the gradual transition of coalbed methane development from shallow to deep, the quality problem of coalbed methane well cementing is more and more obvious. In order to further develop the cement slurry system under the complex well cementing conditions of coalbed methane, its comprehensive performance has gradually become an urgent problem to be reconciled.

[0005] Patent CN119683914A discloses a cement suitable for cementing coalbed methane wells and its preparation method. The cement comprises, by weight percentage: 55-75 wt% G-grade cement, 15-20 wt% active mineral materials, 3-5 wt% composite reinforcing materials, 5-15 wt% weight-reducing agent, 1-3 wt% fluid loss control agent, and 1-2 wt% dispersant. The invented cement slurry for coalbed methane well cementing exhibits excellent workability at low temperatures, rapid strength development, good anti-channeling properties, and good toughness. It utilizes a large amount of solid waste as raw material, increasing solid waste disposal capacity and possessing green environmental protection and low cost characteristics. However, it lacks sufficient sealing effect on micro-fractures in coal seams, resulting in significant leakage that can negatively impact later development, and its operating temperature is not suitable for deep coalbed methane well cementing.

[0006] Patent CN110054440A discloses a low-temperature, early-strength, low-density cement slurry system for coalbed methane cementing. This cement slurry system is achieved by mixing oil well cement with slag powder, fly ash, and cenospheres in a certain proportion, and adding a certain amount of cement slurry admixtures such as water loss reducers, early-strength agents, expanding agents, dispersants, and retarders. This improves the strength, rheological properties, 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 extraction in coalbed methane extraction. However, it does not consider issues such as formation filtration, plugging, and the bonding strength of the cementing interface.

[0007] Therefore, it is crucial to improve the cementing quality of deep coalbed methane horizontal wells by effectively enhancing the hydrophilicity of the coal and rock surfaces and improving the bonding between the cementing interfaces. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a deep coalbed methane cement slurry and its preparation method. The cement slurry can improve the cementing and sealing quality of coalbed methane wells and has good filtration loss and settling stability.

[0009] A deep coalbed methane cement slurry is composed of the following raw materials in parts by weight: 100 parts of Grade G 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 water loss reducing agent, 0.5-1.8 parts of retarder, 0.3-0.5 parts of drag reducing agent, 0.2-0.5 parts of defoamer, and 38-42 parts of water; wherein the composite coating fiber is a hydrophilic epoxy resin modified polyethylene fiber.

[0010] Preferably, the composite coated fiber is prepared by the following method:

[0011] (1) Mix epoxy resin, acetylacetone, triethylamine and deionized water, stir and react at 80-90℃ for 2-4h, then add adipic acid, and continue to react for 6-12h while maintaining the temperature to obtain hydrophilic resin.

[0012] (2) Add polyethylene fiber to the hydrophilic resin, stir until uniformly dispersed, then add curing agent and defoaming agent, continue stirring for 10-20 min, filter, dry, and obtain pre-modified polyethylene fiber;

[0013] (3) Add the pre-modified polyethylene fiber to the dispersant solution, shake and adsorb at 25-30℃ for 30-40 min, filter and dry.

[0014] Preferably, in step (1), the weight ratio of epoxy resin, acetylacetone, and triethylamine is (70-90):(12.5-25.5):(0.5-3); the weight ratio of deionized water and adipic acid is (150-200):(2-5); and the total weight of epoxy resin, acetylacetone, and triethylamine accounts for 30-45% of the weight of deionized water.

[0015] Preferably, in step (2), the weight ratio of hydrophilic resin, polyethylene fiber, curing agent and defoaming agent is 100:(15-25):(10-15):(0.1-0.3).

[0016] Preferably, in step (3), the weight ratio of the pre-modified polyethylene fiber to the dispersant solution is (5-10):(50-100).

[0017] Preferably, the drying conditions are drying at 60-65℃ for 40-48 hours; the drying conditions are drying at 90-95℃ until constant weight.

[0018] Preferably, the curing agent is a water-soluble epoxy curing agent, the defoaming aid is a mixture of organosiloxane defoamers, organopolyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8, and the concentration of the dispersant solution is 25-30 wt%; the average length of the polyethylene fiber is 1-2 mm, and the density is 0.97-0.98 g / cm³. 3 .

[0019] Preferably, the water loss reducing agent is an AMPS-type water loss reducing agent;

[0020] The retarder is an AMPS-type retarder;

[0021] The drag-reducing agent is a ketaldehyde condensate;

[0022] The defoamer is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8.

[0023] Preferably, the concentration of the nano-silica solution is 30-35 wt%, and the particle size of the nano-silica is 10-20 nm;

[0024] The density of the calcium sulfate whiskers is 2.68-2.73 g / cm³. 3 The average diameter is 1-4 μm and the average length is 50-200 μm.

[0025] The preparation method of the deep coalbed methane cement slurry is as follows: drag reducer, defoamer, and waterborne epoxy resin are added to water and stirred at 500 r / min for 10-20 seconds. Then, composite coating fiber is added and stirred at a stirring rate of 2500-3000 r / min for 10-20 seconds. Next, nano silica solution, calcium sulfate whiskers, retarder, fluid loss reducer, and Grade G oil well cement are added sequentially. Then, the mixture is stirred at 12000 r / min for 35 seconds to obtain the deep coalbed methane cement slurry.

[0026] The AMPS described in this invention is 2-acrylamido-2-methylpropanesulfonic acid.

[0027] Advantages of this invention:

[0028] (1) The composite coating fibers contained in the raw materials of this invention form a tough fibrous network in the leakage area of ​​coalbed methane wells, which successfully seals solid particles in the cement slurry system and prevents cementing leakage. In addition, under the action of interfacial forces, the composite coating fibers form a rich area on the cement sheath-coal-rock contact surface, thereby improving the hydrophilicity of the coal-rock surface and forming a dense filter cake to enhance the impermeability of the cement stone in the later stage, which is beneficial to improving the cementing quality; when compounded with other raw materials, it can effectively improve the interface state between cement slurry, filter cake and well wall, and further achieve the purpose of improving the bonding quality of the cementing interface.

[0029] (2) In the cement slurry of the present invention, nano-silica is used as a reinforcing agent to improve the early compressive strength of cement stone and generate a certain amount of lattice micro-expansion to prevent the generation of micro-annular gaps and improve the interfacial bonding strength; calcium sulfate whiskers are used as a toughening agent to be evenly distributed between cement particles. When the cement stone formed is subjected to external force, it absorbs a certain amount of stress and generates a small elastic deformation, which improves the brittleness of cement stone and reduces the elastic modulus of cement stone. This significantly shortens the cementing construction waiting time, reduces construction risks, and reduces construction costs in the later stage of coal seam fracturing. Through water epoxy resin material, toughening agent, filler composite coating fiber, and auxiliary material of a certain amount of fine active filler material nano-silica and whiskers, the filling is assisted to form a denser filter cake and reduce water loss.

[0030] (3) The raw materials are widely available and abundant, the cost is low, the preparation conditions are mature, the use is convenient, and the application prospects are good. Detailed Implementation

[0031] In this invention, the waterborne epoxy resin used is waterborne epoxy resin BH-653;

[0032] AMPS-type water loss reducing agent uses multi-component copolymer G310 from Weihui Chemical Co., Ltd.

[0033] The AMPS-type retarder used is the vinyl acrylamide polymer HX-36L from Chengdu Omec Petroleum Technology Co., Ltd.

[0034] The organosiloxane defoamer used is defoamer DF-900;

[0035] Organic polyether defoamers use polyether defoamer GPE;

[0036] The organosilicone ether defoamer used is defoamer FAG470;

[0037] The dispersant used is AKN-2290;

[0038] The water-soluble epoxy curing agent used is water-based epoxy curing agent BH-532;

[0039] The drag-reducing agent is a ketaldehyde condensate, USZ.

[0040] Example 1

[0041] A deep coalbed methane cement 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 whiskers, 0.3 parts of composite coating fiber, 1.2 parts of water loss reducing agent, 1 part of retarder, 0.3 parts of drag reducing agent, 0.2 parts of defoamer, and 42 parts of water;

[0042] The concentration of the nano-silica solution is 30 wt%, and the particle size of the nano-silica is 10-20 nm.

[0043] The density of the calcium sulfate whiskers is 2.68 g / cm³. 3 The average diameter is 1-4 μm and the average length is 50-100 μm.

[0044] The defoamer is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8;

[0045] The composite coated fiber is a hydrophilic epoxy resin modified polyethylene fiber, and the preparation method is as follows:

[0046] (1) Epoxy resin, acetylacetone, triethylamine and deionized water are mixed and stirred at 80°C and 200 rpm for 2 hours. Then adipic acid is added and the reaction is continued at the same temperature for 6 hours to obtain a hydrophilic resin. The weight ratio of epoxy resin, acetylacetone and triethylamine is 70:18.5:1.5, the weight ratio of deionized water and adipic acid is 150:4, and the total weight of epoxy resin, acetylacetone and triethylamine accounts for 45% of the weight of deionized water.

[0047] (2) Take 100 parts of the hydrophilic resin, add 20 parts of polyethylene fiber, stir for 20 minutes to disperse evenly, then add 12 parts of water-soluble epoxy curing agent and 0.1 parts of defoaming agent, 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 / cm³. 3 The average length is 1 mm; the defoaming agent is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8;

[0048] (3) Add 10 parts of the pre-modified polyethylene fiber to 100 parts of 25wt% dispersant solution, shake and adsorb at 30°C for 30 min, filter, and dry at 90°C to constant weight.

[0049] The preparation method of the deep coalbed methane cement slurry is as follows: Add drag reducer, defoamer, and waterborne epoxy resin to water, stir at 500 r / min for 10 seconds, then add composite coating fiber at a stirring rate of 2500 r / min and stir for 10 seconds, then add nano silica solution, calcium sulfate whiskers, retarder, fluid loss reducer and G-grade oil well cement in sequence, and then stir at 12000 r / min for 35 seconds.

[0050] Example 2

[0051] A deep coalbed methane cement 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 water loss reducing agent, 1 part of retarder, 0.3 parts of drag reducing agent, 0.2 parts of defoamer, and 42 parts of water;

[0052] Everything else is the same as in Example 1.

[0053] Example 3

[0054] A deep coalbed methane cement 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 whiskers, 0.4 parts of composite coating fiber, 1.8 parts of water loss reducing agent, 1 part of retarder, 0.3 parts of drag reducing agent, 0.2 parts of defoamer, and 42 parts of water;

[0055] Everything else is the same as in Example 1.

[0056] Example 4

[0057] A deep coalbed methane cement 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 reducer, 0.5 parts of retarder, 0.5 parts of drag reducer, 0.5 parts of defoamer, and 38 parts of water;

[0058] The concentration of the nano-silica solution is 35 wt%, and the particle size of the nano-silica is 10-20 nm.

[0059] The density of the calcium sulfate whiskers is 2.73 g / cm³. 3 The average diameter is 1-2 μm and the average length is 100-200 μm.

[0060] The defoamer is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8;

[0061] The composite coated fiber is a hydrophilic epoxy resin modified polyethylene fiber, and the preparation method is as follows:

[0062] (1) Epoxy resin, acetylacetone, triethylamine and deionized water are mixed and stirred at 90°C and 200 rpm for 4 hours. Then adipic acid is added and the reaction is continued for 12 hours while maintaining the temperature to obtain a hydrophilic resin. The weight ratio of epoxy resin, acetylacetone and triethylamine is 90:12.5:0.5, the weight ratio of deionized water and adipic acid is 200:2, and the total weight of epoxy resin, acetylacetone and triethylamine accounts for 30% of the weight of deionized water.

[0063] (2) Take 100 parts of the hydrophilic resin, add 15 parts of polyethylene fiber, stir for 20 minutes to disperse evenly, then add 10 parts of water-soluble epoxy curing agent and 0.1 parts of defoaming agent, 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 / cm³. 3The average length is 2 mm; the defoaming agent is a mixture of organosiloxane defoamer, organic polyether defoamer, and organosilicone ether defoamer in a mass ratio of 1:3:1.8;

[0064] (3) Add 5 parts of the pre-modified polyethylene fiber to 50 parts of 30wt% dispersant solution, shake and adsorb at 25°C for 40 min, filter, and dry at 95°C to constant weight.

[0065] The preparation method of the deep coalbed methane cement slurry is as follows: Add drag reducer, defoamer, and waterborne epoxy resin to water, stir at 500 r / min for 20 seconds, then add composite coating fiber at 3000 r / min and stir for 20 seconds, then add nano silica solution, calcium sulfate whiskers, retarder, fluid loss reducer and G-grade oil well cement in sequence, and then stir at 12000 r / min for 35 seconds.

[0066] Example 5

[0067] A deep coalbed methane cement slurry is composed of the following raw materials in parts by weight: 100 parts of Grade G oil well cement, 10 parts of water-based epoxy resin, 2 parts of nano silica solution, 1 part of calcium sulfate whiskers, 0.6 parts of composite coating fiber, 1.2 parts of water loss reducing agent, 1.8 parts of retarder, 0.3 parts of drag reducing agent, 0.2 parts of defoamer, and 40 parts of water;

[0068] The density of the nano-silica solution is 1.11 g / cm³. 3 The particle size of the nano-silica is 10-20 nm;

[0069] 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.

[0070] The defoamer is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8;

[0071] The composite coated fiber is a hydrophilic epoxy resin modified polyethylene fiber, and the preparation method is as follows:

[0072] (1) Epoxy resin, acetylacetone, triethylamine and deionized water are mixed and stirred at 85°C and 200 rpm for 3 hours. Then adipic acid is added and the reaction is continued for 10 hours while maintaining the temperature to obtain a hydrophilic resin. The weight ratio of epoxy resin, acetylacetone and triethylamine is 80:25.5:3, the weight ratio of deionized water and adipic acid is 180:2, and the total weight of epoxy resin, acetylacetone and triethylamine accounts for 40% of the weight of deionized water.

[0073] (2) Take 100 parts of the hydrophilic resin, add 25 parts of polyethylene fiber, stir for 20 minutes to disperse evenly, then add 15 parts of water-soluble epoxy curing agent and 0.3 parts of defoaming agent, 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 / cm³. 3 The average length is 1 mm; the defoaming agent is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8;

[0074] (3) Add 8 parts of the pre-modified polyethylene fiber to 100 parts of 28wt% dispersant solution, shake and adsorb at 30°C for 30 min, filter, and dry at 90°C to constant weight.

[0075] The preparation method of the deep coalbed methane cement slurry is the same as that in Example 1.

[0076] Comparative Example 1

[0077] It does not contain water-based epoxy resin, and is otherwise the same as in Example 1.

[0078] Comparative Example 2

[0079] It does not contain nano-silica solution or calcium sulfate whiskers, but is otherwise the same as in Example 1.

[0080] Comparative Example 3

[0081] It does not contain composite coated fibers, but is otherwise the same as in Example 1.

[0082] Comparative Example 4

[0083] The polyethylene fibers are unmodified, meaning they have a density of 0.97 g / cm³. 3 Polyethylene fibers with an average length of 1 mm were used instead of composite coated fibers, and everything else was the same as in Example 1.

[0084] Performance testing

[0085] I. Cement Grout Performance Testing

[0086] After the cement slurry was thoroughly mixed, the mixture was poured into an atmospheric pressure thickener and cured at 90℃ for 30 min. After curing, its water loss performance at 60℃ and 6.9 MPa was tested using a high temperature and high pressure water loss instrument. The experimental results are shown in Table 1.

[0087] Table 1. Test results of cement grout performance

[0088]

[0089] As shown in Table 1, compared with Comparative Example 1, the water loss of the slurry in Example 1 was reduced within 30 minutes, indicating that the water-based epoxy resin improved the water loss performance of the cement slurry. The cement slurry systems prepared in Examples 1-3 had a water loss of less than 40 mL and low SPN values ​​(anti-channeling coefficient), demonstrating excellent anti-channeling ability, and the thickening time generally met the construction requirements. Compared with Example 1, the various engineering properties of the cement slurry systems in Comparative Examples 1-4 showed varying degrees of deterioration.

[0090] II. Mechanical Property Testing

[0091] The prepared cement slurry was used to prepare test samples according to SY / T 6466-2016 "Test Method for Performance of Cement Stone in Oil Wells". After curing in a 60℃ water bath for 1 day, 2 days and 14 days, the mechanical properties were measured. The results are shown in Table 2.

[0092] Table 2 Results of Mechanical Property Tests

[0093]

[0094] As shown in Table 2, the cement slurry prepared by this invention can rapidly hydrate in a short period of time, and the strength of the cement stone develops rapidly, which is beneficial to shortening the cementing waiting time in oil and gas wells. Furthermore, it exhibits high strength, with a 14-day compressive strength exceeding 36 MPa. In addition, the elastic modulus indicates that the cement slurry of this invention effectively improves the toughness of the cement stone, resulting in cement stone with excellent toughness. This meets the performance requirements of cement slurry in cementing engineering and effectively solves the problem of low strength and insufficient toughness of cement stone under long-term medium-temperature conditions, which is beneficial for later-stage fracturing operations in deep coalbed methane horizontal sections. Comparative Examples 1-4 show that the water-based epoxy resin material, nano-silica and whisker materials, and composite coating fibers in the cement slurry system all have varying degrees of influence on the various properties of the cement stone.

[0095] III. Test of bonding strength at the casing-cement stone-coal seam interface

[0096] Cement slurry was poured into a cylindrical mold and the whole thing was placed in a 60℃ water bath for 1 day, 2 days and 14 days. The maximum shear force per unit area of ​​the cement block-cylindrical mold contact surface was measured, which is the bonding strength of the sleeve-cement stone interface, i.e. the first interface bonding strength.

[0097] To more realistically simulate underground conditions, a coal core of equal diameter was prepared. The preparation steps for the coal core are as follows: the coal and rock on site were ground into coal powder, and 150 g was weighed; then 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) were weighed and mixed evenly; then the mixture of epoxy resin and curing agent was poured into a container containing coal powder, stirred thoroughly, and then poured into a cylindrical mold of equal diameter. After being placed in a 90℃ oven for 48 hours, it was taken out for use.

[0098] Pour an appropriate amount of deep coalbed methane cement slurry into the mold. Place the prepared coal core into the cement slurry after constant-speed stirring for 30 seconds. After removing it, place it vertically into the center of the mold containing the cement slurry from top to bottom to simulate the bottom-up injection process of cement slurry during construction. Then, seal the entire cement strength specimen mold from top to bottom and place it under normal pressure and 60℃ for curing for 1 day, 2 days and 14 days. After curing, use a compressive strength testing machine to measure the maximum shear force at the coal block-cement ring interface, that is, the strength of the second interface cementing surface; the results are shown in Table 3.

[0099] Table 3. Test results of interfacial bonding strength of cement stone

[0100]

[0101] As can be seen from Table 3, the cement slurry system prepared in the embodiments of the present invention can significantly improve the bonding strength of the casing-cement stone-coal seam interface in the short term. Comparative Examples 1, 3, and 4 show that the cement slurry system with added water-based epoxy resin and composite coating fiber can ensure that the casing-cement stone-coal seam interface has a certain bonding strength in the short term, especially for the bonding strength of the two interfaces of coal and rock strata. Moreover, the bonding strength of the interface develops stably after long-term curing, effectively meeting the cementing performance requirements of the horizontal section of deep coalbed methane and ensuring the safety of subsequent horizontal section mining.

Claims

1. A cement slurry for cementing deep coalbed methane wells, characterized in that: It is composed of the following raw materials in parts by weight: 100 parts of Grade G 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 water loss reducing agent, 0.5-1.8 parts of retarder, 0.3-0.5 parts of drag reducing agent, 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; The composite coated fiber is prepared by the following method: (1) Mix epoxy resin, acetylacetone, triethylamine and deionized water, stir and react at 80-90℃ for 2-4h, then add adipic acid, and continue to react for 6-12h while maintaining the temperature to obtain hydrophilic resin. (2) Add polyethylene fiber to the hydrophilic resin, stir until uniformly dispersed, then add curing agent and defoaming agent, continue stirring for 10-20 min, filter, dry, and obtain pre-modified polyethylene fiber; (3) Add the pre-modified polyethylene fiber to the dispersant solution, shake and adsorb at 25-30℃ for 30-40 min, filter and dry.

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

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

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

5. The deep coalbed methane cement slurry according to claim 4, characterized in that: The drying conditions are: drying at 60-65℃ for 40-48 hours; drying at 90-95℃ until constant weight.

6. The deep coalbed methane cement slurry according to claim 1, characterized in that: The curing agent is a water-soluble epoxy curing agent; the defoaming aid is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.8; the concentration of the dispersant solution is 25-30 wt%; the average length of the polyethylene fiber is 1-2 mm, and the density is 0.97-0.98 g / cm³. 3 .

7. The deep coalbed methane cement slurry according to claim 1, characterized in that: The water loss reducing agent is an AMPS-type water loss reducing agent; The retarder is an AMPS-type retarder; The drag-reducing agent is a ketaldehyde condensate; The defoamer is a mixture of organosiloxane defoamers, organic polyether defoamers, and organosilicone ether defoamers in a mass ratio of 1:3:1.

8.

8. The deep coalbed methane cement slurry according to claim 1, characterized in that: 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 / cm³. 3 The average diameter is 1-4 μm and the average length is 50-200 μm.

9. The method for preparing the deep coalbed methane cement slurry according to claim 1, characterized in that: The preparation method is as follows: drag reducer, defoamer, and waterborne epoxy resin are added to water and stirred at 500 r / min for 10-20 seconds. Then, composite coating fiber is added and stirred at a stirring rate of 2500-3000 r / min for 10-20 seconds. Next, nano silica solution, calcium sulfate whiskers, retarder, fluid loss reducer, and Grade G oil well cement are added sequentially. Then, the mixture is stirred at 12000 r / min for 35 seconds to obtain the deep coalbed methane cement slurry.

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