Cementing slurry for improving cementing strength of coal-rock interface, and preparation method and application thereof

Abstract

The application relates to the technical field of cementing materials, and discloses a cementing slurry for improving the cementing strength of an interface coal rock, a preparation method and application of the cementing slurry, which is composed of 50-150 parts of oil well cement, 5-50 parts of epoxy resin, 0.2-2 parts of a slow-release curing agent, 0.05-0.2 parts of a defoaming agent, 1.75-11 parts of an auxiliary agent and 40-80 parts of water in terms of mass fraction; the slow-release curing agent is prepared by substitution reaction and complexation reaction of imidazole organic matter, propylene carbonate and a transition metal chloride; the cementing slurry has good rheological performance, adjustable density, excellent compressive strength and low Young's modulus after cement curing, and can improve the cementing strength of the coal rock and the cement ring; the slow-release curing agent can be gradually released along with the cement hydration reaction, the crosslinking rate of the epoxy resin can be accurately controlled, the problem of abnormal thickening of the epoxy resin cementing slurry can be solved, a high-strength-low-elastic-modulus-strong-cementing resin cement composite material meeting the requirements of coal rock gas cementing can be formed, the safety of cementing construction can be ensured, and the long-term performance stability of the resin cement ring can be ensured.

Description

Technical Field

[0001] This invention relates to the field of cementing materials technology, and more specifically, to cementing slurry for improving the bonding strength of coal and rock interfaces, its preparation method, and its application. Background Technology

[0002] The main components of coal and rock are organic matter, with organic polymers primarily composed of condensed aromatic rings. Therefore, the surface of coal and rock has poor hydrophilicity and smooth cleavage surfaces, resulting in low bonding strength between the coal / rock and cement sheath. The quality rate of the cementing interface is only about 34.81%, severely impacting the subsequent development of coal gas resources. Furthermore, horizontal wells and large-volume fracturing are currently recognized as effective drilling and cementing technologies for increasing coal gas production. However, the poor bonding between the coal / rock and cement sheath easily leads to micro-gaps, which can easily cause fracturing fluid to further disrupt the interface bonding during fracturing. Therefore, to ensure a high quality rate of cementing interface bonding and guarantee the long-term stable operation of coal gas wells, higher requirements are placed on the performance of the cementing cement sheath.

[0003] Current resin-cement slurry systems are mainly used in high-temperature, high-pressure conventional oil and gas wells. They improve cement sheath performance through resin modification, nanomaterial reinforcement, and fiber toughening. However, research on the unique weakly cemented formations and low-temperature, low-pressure environments of coal-rock gas cementing is lacking, and existing systems cannot meet the core requirement of improving the interfacial bonding strength between coal and cement sheaths. Therefore, developing a cementing slurry system suitable for coal-rock gas well cementing that can significantly improve the interfacial bonding strength between coal and cement sheaths has significant theoretical and practical application value. Summary of the Invention

[0004] In view of this, the present invention provides a cementing slurry for improving the bonding strength between coal and rock, its preparation method, and its application. This cementing slurry exhibits good rheological properties, adjustable density, and an API water loss of less than 50 ml. Furthermore, after cement curing, it possesses excellent compressive strength and a low Young's modulus, thereby improving the bonding strength between coal and rock and the cement sheath. The curing agent in this system is a slow-release curing agent, which is gradually released during the cement hydration reaction. This allows for precise control of the epoxy resin crosslinking rate, solving the problem of abnormal thickening of the epoxy resin cement slurry. The result is a high-strength, low-modulus, and strong-bonding resin-cement composite material that meets the requirements of coal-rock gas cementing, ensuring safe cementing operations and long-term performance stability of the resin cement sheath.

[0005] The technical solution of this invention is as follows:

[0006] In a first aspect, the present invention provides a cementing slurry for improving the bonding strength of coal and rock at the interface, the cementing slurry being composed of 50-150 parts by weight of oil well cement, 5-50 parts by weight of epoxy resin, 0.2-2 parts by weight of slow-release curing agent, 0.05-0.2 parts by weight of defoamer, 1.75-11 parts by weight of auxiliary agent and 40-80 parts by weight of water;

[0007] The slow-release curing agent is prepared by imidazole organic compounds, propylene carbonate, and transition metal chlorides through substitution and complexation reactions.

[0008] The molar ratio of the imidazole organic compound to the propylene carbonate and the transition metal chloride is 1:(1-8):(0.05-1).

[0009] Furthermore, the imidazole organic compounds include at least one of 2-phenylimidazole, 4-phenylimidazole, and 2-methylimidazole and their derivatives.

[0010] Furthermore, the transition metal chloride includes at least one of cobalt chloride, nickel chloride, ferric chloride, and copper chloride.

[0011] Furthermore, the preparation method of the slow-release curing agent includes the following steps:

[0012] Imidazole organic compounds are preheated with propylene carbonate at 55-75°C and reacted at 125-145°C until the solid phase of the imidazole organic compounds is completely dissolved to generate N-substituted hydroxymethyl imidazole derivatives; a transition metal chloride solution is added to the N-substituted hydroxymethyl imidazole derivatives and the mixture is stirred for 4-5 hours to obtain the slow-release curing agent; the concentration of the transition metal chloride solution is 0.5-30%.

[0013] Furthermore, the adjuvant consists of 0.5-2 parts by weight of an early-strength agent, 0.5-4 parts by weight of a water-loss reducing agent, 0.2-1 parts by weight of a dispersant, 0.05-2 parts by weight of a retarder, and 0.5-2 parts by weight of an expanding agent.

[0014] Furthermore, the early strength agent is a nano-based composite reinforcing material with nano-CSH as the core; the water loss reducing agent is a copolymer of 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid; the dispersant includes at least one of polycarboxylate and sulfonated acetone formaldehyde condensate; the retarder is a polymer of hydroxycarboxylic acid and its salts; and the expanding agent is a mixture of alum stone, gypsum, high-alumina clinker or aluminate cement clinker as raw materials.

[0015] Furthermore, the epoxy resin is a bisphenol A type epoxy resin emulsion; the defoamer includes at least one of organosilicon defoamers, mineral oil defoamers, polyether defoamers, and polyether-modified organosilicon defoamers.

[0016] Furthermore, the chemical structure of the bisphenol A type epoxy resin emulsion is as follows:

[0017] .

[0018] Secondly, based on the same inventive concept, this invention provides a method for preparing cementing slurry for improving the interfacial bonding strength of coal and rock as described in any of the first aspects, comprising the following steps:

[0019] The oil well cement and additives are mixed evenly to obtain a solid mixture; epoxy resin, defoamer, slow-release curing agent and water are stirred at 3500-4500 rpm for 10-20 seconds to obtain a liquid mixture; the solid mixture is added to the liquid mixture at 3500-4000 rpm and stirred continuously for 40-60 seconds, then the speed is reduced to 0 rpm to eliminate air bubbles, and the cementing slurry is obtained.

[0020] Thirdly, based on the same inventive concept, this invention provides the application of the cementing slurry for improving the interfacial bonding strength of coal and rock as described in any of the first aspects, or the cementing slurry for improving the interfacial bonding strength of coal and rock prepared by the preparation method described in any of the second aspects, in cementing coal and rock gas wells.

[0021] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0022] 1. The slow-release curing agent of the present invention is prepared by substitution reaction and complexation reaction. It is liquid at room temperature and has excellent compatibility and dispersibility with epoxy resin. The curing agent can gradually release its activity with the cement hydration reaction, precisely control the crosslinking rate of epoxy resin, avoid abnormal thickening phenomena such as step formation and core encapsulation in cement slurry, and ensure the safety of cementing construction.

[0023] 2. The cement slurry system forms a dual-curing system with good rheological properties, stable settling, and low free liquid content, meeting the rheological and stability requirements of cementing construction in coal and rock gas wells.

[0024] 3. After cement hardens, its early strength develops rapidly. The compressive strength can reach 7.9MPa in 4 hours, 16.1MPa in 6 hours, 34.23MPa in 12 hours, 40.2MPa in 24 hours, and 48.02MPa in 48 hours. The strength development is continuous and stable, which can provide reliable mechanical support for the well shaft.

[0025] 4. Significantly improves the interfacial bonding strength between coal and rock and cement sheath. The interfacial bonding strength can reach 2.22 MPa and 3.1 MPa at 24 hours; and 2.68 MPa and 3.19 MPa at 48 hours. This is a significant improvement over the interfacial bonding strength of conventional cement slurry, effectively solving the core problem of poor interfacial bonding in coal gas well cementing.

[0026] 5. The slow-release curing agent is chemically stable and non-toxic, and can be stored for a long time. The cement slurry system is suitable for the weak cementing, low temperature and low pressure cementing environment of coal and rock gas wells. It can cover operation scenarios such as cementing and formation sealing of coal and rock gas wells. It is highly practical and can ensure the long-term stable service of coal and rock gas wells. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The above is a hydrogen NMR spectrum of the slow-release curing agent according to an embodiment of the present invention;

[0029] Figure 2 The cement slurry thickening curve is shown in the embodiment of the present invention.

[0030] Figure 3 This is the cement slurry thickening curve of Comparative Example 1 of the present invention;

[0031] Figure 4 This is the cement slurry thickening curve of Comparative Example 2 of the present invention;

[0032] Figure 5 This is the cement slurry thickening curve of Comparative Example 3 of the present invention;

[0033] Figure 6 This is the cement slurry thickening curve of Comparative Example 4 of the present invention;

[0034] Figure 7 This is a comparison of the early compressive strength of the embodiments and comparative examples of the present invention;

[0035] Figure 8 This is a comparison of the interfacial bonding strength between the embodiments and comparative examples of the present invention;

[0036] Figure 9 This is a comparison of the coal-rock interface bonding strength between the embodiments of the present invention and the comparative examples;

[0037] Figure 10The present invention provides a comparison of the bonding strength at the interface between different rocks in the embodiments and comparative examples.

[0038] Figure 11 The results show the triaxial Young's modulus comparison between the embodiments and comparative examples of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0041] To address the technical problems existing in the prior art, according to one aspect of the embodiments of this disclosure, a cementing slurry for improving the bonding strength of coal and rock at the interface is provided. The cementing slurry is composed of 50-150 parts by weight of oil well cement, 5-50 parts by weight of epoxy resin, 0.2-2 parts by weight of slow-release curing agent, 0.05-0.2 parts by weight of defoamer, 1.75-11 parts by weight of auxiliary agent and 40-80 parts by weight of water.

[0042] The slow-release curing agent is prepared by imidazole organic compounds, propylene carbonate (PC), and transition metal chlorides through substitution and complexation reactions;

[0043] The molar ratio of imidazole organic compounds to propylene carbonate and transition metal chlorides is 1:(1-8):(0.05-1).

[0044] It should be noted that the synthetic route of the slow-release curing agent includes: using PC to replace the active hydrogen atom on the pyridine nitrogen atom at position ① of the imidazole five-membered ring to generate an N-substituted hydroxymethyl imidazole derivative; then using a transition metal chloride to complex the pyrrole N atom at position ③. The complexation product still has the curing effect on the resin, but only reduces the catalytic activity of the N-substituted hydroxymethyl imidazole derivative, thus producing a slow-release curing agent.

[0045] Specifically, the reaction equations for the substitution reaction are shown in (a) and (b):

[0046] ;

[0047] The above substitution reactions include: ① Acylation addition (nucleophilic ring-opening reaction): Under the catalysis of the nitrogen atom at the N-3 position of the basic imidazole ring, the nitrogen atom at the N-1 position of the imidazole ring acts as a nucleophilic site, attacking the carbonyl carbon of the cyclic anhydride, and undergoing a nucleophilic addition-ring-opening reaction. After the cyclic anhydride ring opens, a carboxylic acid ester intermediate is generated; ② Decarboxylation reaction (CO2 release): The carboxyl group (-COOH) in the intermediate breaks the C-C bond through the six-membered ring transition state, releasing CO2 gas, and finally generating an N-substituted hydroxymethyl imidazole derivative.

[0048] The purpose of the above substitution reaction is to transform solid imidazole organic curing agents into liquid N-substituted hydroxymethyl imidazole derivatives, thereby improving the dispersibility of the curing agent in resin cement slurry systems. In the reactants of the above substitution reaction, R is a stable organic substituent (such as methyl, phenyl, ethyl, etc.) of the imidazole curing agent. The above N-substituted hydroxymethyl imidazole derivatives have hydroxyl groups, are easily soluble in water, and can be uniformly dispersed in water. The above N-substituted hydroxymethyl imidazole derivatives are two isomers, where (a) the methyl group is farther from the imidazole ring and has less steric hindrance, and (b) the methyl group is closer to the imidazole ring and has greater steric hindrance. This leads to certain differences in the properties of the two reaction products, mainly manifested in the following aspects:

[0049] Molecules with greater steric hindrance have weaker hydrogen bonding with polar solvents and lower solubility; the product of reaction (a) has higher solubility in polar solvents. Molecules with greater steric hindrance have looser intermolecular packing and lower melting / boiling points; the product of reaction (a) has a higher melting / boiling point. The magnitude of steric hindrance affects the direction of reagent attack; the methyl group of the product of reaction (a) has less steric hindrance, making it easier for epoxy resin to access and resulting in higher curing efficiency than the product of reaction (b). The nitrogen atom of the imidazole ring is a common metal coordination site; the steric hindrance of the methyl group hinders the coordination of metal ions with nitrogen and reduces the stability of the complex. Obviously, the product of reaction (a) also has better coordination properties.

[0050] The reaction equations for the complexation reactions described above are shown in (c) and (d):

[0051] .

[0052] The complexation reaction described above is a chemical process that is essentially a coordination reaction. M n+ As the central metal ion, it provides an empty orbital; the N-substituted hydroxymethyl imidazole derivatives form a coordinate bond by donating lone pairs of electrons through the N-3 atom on the imidazole ring.

[0053] The purpose of the above complexation reaction is to block the active sites of the curing agent, regulate the curing rate of the curing agent and epoxy resin, and ensure the thickening performance of the resin-cement slurry dual curing system; the complex formed is an aggregate of metal ions and multiple ligands, and the aggregate formed is the slow-release curing agent.

[0054] The product of reaction (a) has low steric hindrance and excellent coordination. The molecules of the resulting complex (c) can be packed tightly and regularly. The resulting aggregates are large in size and have strong intermolecular forces. They are not easily dispersed by solvents and have low solubility. The product of reaction (b) has high steric hindrance and poor coordination. The molecules of the resulting complex (d) cannot be packed tightly. The aggregates have a loose structure, small size, are more easily dispersed by solvents, and have high solubility.

[0055] When the aforementioned slow-release curing agent is added to the resin cement slurry, complex (d) first decoordinates and activates the curing agent, causing the resin to begin curing. As the cement hydration reaction releases heat, complex (c) decoordinates and activates the curing agent, accelerating the resin curing efficiency and synergistically curing the cement slurry. The sequential action of the two complexes can ensure the thickening performance of the cement slurry, prevent abnormal thickening phenomena such as step formation and core encapsulation during the thickening process, and shorten the cement slurry thickening over-thickening time.

[0056] It is worth noting that the aforementioned slow-release curing agent is chemically stable, non-toxic, and can be stored for a long time.

[0057] In some examples, imidazole organic compounds include at least one of 2-phenylimidazole, 4-phenylimidazole, and 2-methylimidazole and their derivatives.

[0058] In some examples, the transition metal chloride includes at least one of cobalt chloride, nickel chloride, ferric chloride, and copper chloride.

[0059] Specifically, the preparation method of the slow-release curing agent includes the following steps:

[0060] Imidazole organic compounds are preheated with propylene carbonate at 55-75℃ and reacted at 125-145℃ until the solid phase of the imidazole organic compounds is completely dissolved to generate N-substituted hydroxymethyl imidazole derivatives. A transition metal chloride solution is added to the N-substituted hydroxymethyl imidazole derivatives and the mixture is stirred for 4-5 hours to obtain a slow-release curing agent. The concentration of the transition metal chloride solution is 0.5-30%.

[0061] It should be noted that the concentration of the transition metal chloride solution is 0.5-30%.

[0062] In some examples, the adjuvant consists of 0.5-2 parts by weight of an early-strength agent, 0.5-4 parts by weight of a water-loss reducing agent, 0.2-1 parts by weight of a dispersant, 0.05-2 parts by weight of a retarder, and 0.5-2 parts by weight of an expansion agent.

[0063] For example, the early strength agent, by weight, includes but is not limited to 0.5 parts, 1 part, 1.2 parts, 1.7 parts, or 2 parts; the water loss reducing agent, by weight, includes but is not limited to 0.5 parts, 1 part, 1.2 parts, 1.7 parts, or 2 parts; the dispersant, by weight, includes but is not limited to 0.2 parts, 0.5 parts, 0.7 parts, or 1 part; the retarder, by weight, includes but is not limited to 0.05 parts, 0.2 parts, 1 part, 1.5 parts, or 2 parts; and the expanding agent, by weight, includes but is not limited to 0.3 parts, 0.5 parts, 0.7 parts, 1 part, 1.5 parts, or 2 parts.

[0064] Specifically, the early strength agent is a nano-based composite reinforcing material with nano-CSH as the core; the water loss reducing agent is a copolymer of 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid; the dispersant includes at least one of polycarboxylate and sulfonated acetone formaldehyde condensate; the retarder is a polymer of hydroxycarboxylic acid and its salts; and the expansion agent is made by grinding and mixing alum stone, gypsum (anhydrous or dihydrate), high alumina clinker or aluminate cement clinker as the main raw materials.

[0065] In some examples, the defoamer includes at least one of silicone defoamers, mineral oil defoamers, polyether defoamers, and polyether-modified silicone defoamers.

[0066] In some examples, the well cement is API Grade G well cement.

[0067] In some examples, the epoxy resin is a bisphenol A type epoxy resin emulsion.

[0068] Specifically, the chemical structure of the bisphenol A type epoxy resin emulsion is as follows:

[0069] .

[0070] According to another aspect of the embodiments of this application, a method for preparing cementing slurry to improve the bonding strength of coal and rock at the interface is also provided, specifically including: mixing oil well cement and additives evenly to obtain a solid mixture; stirring epoxy resin, defoamer, slow-release curing agent and water at 3500-4500 rpm for 10-20s to obtain a liquid mixture; adding the solid mixture to the liquid mixture at 3500-4000 rpm, continuing to stir for 40-60s, slowly reducing the speed to 0 rpm to eliminate air bubbles, and obtaining cementing slurry.

[0071] It should be noted that the above preparation method, in accordance with the GB / T19139-2012 standard, produces cement slurry, which is then degassed to obtain cementing slurry.

[0072] According to another aspect of the embodiments of this application, the application of cementing slurry for improving the bonding strength of coal and rock interface as described in any one of the first aspects or cementing slurry for improving the bonding strength of coal and rock interface prepared by any one of the second aspects in cementing coal and rock gas wells is also provided.

[0073] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0074] Example 1

[0075] This embodiment 1 provides a method for preparing cementing slurry to improve the bonding strength of coal and rock at the interface, including the following steps:

[0076] S1. Synthesis and preparation of slow-release curing agent: 2-phenylimidazolium and propylene carbonate (PC) were prepared in a molar ratio of 1:3. The molecular weight of 2-phenylimidazolium was 144.17 g / mol, and the molecular weight of PC was 102.089 g / mol. 2-phenylimidazolium was used as the solute and PC was used as the solvent.

[0077] Weigh 21.24 g of PC and add it to a 100 mL three-necked flask. Using a temperature sensor and a spherical condenser-based stirring device, fix the three-necked flask in an oil bath and stir and heat the sample to 65 °C.

[0078] Weigh 10g of 2-phenylimidazole and add it to a three-necked flask while stirring. Heat to 135℃, stop stirring, and react until the 2-phenylimidazole solid phase is completely dissolved and the product is a reddish-brown viscous fluid. Stop heating and cool to room temperature.

[0079] 10 mL of a 10% FeCl3・6H2O solution was slowly added dropwise while stirring for 4-5 hours to obtain a brown, viscous, liquid slow-release curing agent.

[0080] S2. Preparation of cementing slurry system for improving the bonding strength between coal and rock and cement sheath: The cementing system in this embodiment consists of 100 parts by weight of G-grade oil well cement, 0.75 parts of early strength agent, 0.5 parts of fluid loss reducing agent, 0.1 parts of dispersant, 0.2 parts of retarder, 0.5 parts of expansion agent, 10 parts of epoxy resin, 0.15 parts of defoamer, 0.3 parts of slow-release curing agent and 36 parts of water;

[0081] Specifically, weigh out 1000 g of G-grade oil well cement, 7.5 g of early strength agent, 5 g of fluid loss reducer, 1 g of dispersant, 2 g of retarder, 5 g of expansion agent, 100 g of epoxy resin, 0.15 g of defoamer, 3 g of curing agent, and 360 g of water.

[0082] The solid phase component is obtained by uniformly mixing oil well cement, early strength agent, fluid loss reducer, dispersant, retarder, and expansion agent; the liquid phase component is obtained by uniformly mixing epoxy resin, defoamer, slow-release curing agent, and water using a cement mixer at 4000 rpm for 15 seconds.

[0083] The solid phase component is added to the liquid phase component at 4000 rpm within 15 seconds, and the mixture is stirred continuously for 50 seconds. During the stirring process, the cement ash adhering to the inner wall of the slurry cup is scraped into the slurry cup using a stirring rod. After 50 seconds, the speed of the cement mixer is slowly reduced, and the stirring rod is used to eliminate air bubbles in the cement slurry to obtain cementing slurry.

[0084] In this embodiment, the G-grade oil well cement is a commercially available product conforming to the GB / T 10238-2015 standard; the early strength agent is used to improve the early strength of the cement stone, and it is a nano-based composite material with nano-CSH as the core; the water loss reducer is used to reduce the water loss of the cement slurry, and it is a copolymer of 2-acrylamide-2-methylpropanesulfonic acid and acrylic acid; the dispersant is used to adjust the rheological properties of the cement slurry, and it is an ether-type polycarboxylate superplasticizer, the chemical name of which is sodium salt of polyethylene glycol monomethyl ether acrylate-acrylic acid copolymer; the retarder is used to adjust the thickening time of the cement slurry, and it is polyhydroxy acrylic acid; the expansion agent is used to improve the strength and low permeability of the cement stone, and it is composed of alum stone, gypsum, high-alumina clinker or aluminate cement clinker as raw materials through grinding and mixing; the resin is bisphenol A type epoxy resin; the defoamer is a mineral oil defoamer, the main components of which are mineral oil, wax and hydrophobic silica, and it is prepared by mixing mineral oil and hydrophobic particles at high temperature and then adding an emulsifier.

[0085] Comparative Example 1

[0086] This comparative example uses a cement slurry tailings system commonly used in the coal and gas fields of the Changqing Ordos Basin. It is basically the same as Example 1, except that no slow-release curing agent and resin were added, in order to verify the impact of not adding slow-release curing agent and resin on the performance of cement products.

[0087] Comparative Example 2

[0088] This comparative example is basically the same as Example 1, except that no transition metal chloride was added to the slow-release curing agent.

[0089] Comparative Example 3

[0090] This comparative example is basically the same as Example 1, except that propylene carbonate and transition metal chlorides were not added to the slow-release curing agent, and only imidazole organic compounds were used as curing agents.

[0091] Comparative Example 4

[0092] This comparative example is basically the same as Example 1, except that no slow-release curing agent was added.

[0093] To better understand the present invention, the following tests were performed on the embodiments and comparative examples.

[0094] Test methods and standards: Cement slurry was prepared according to the specifications in GB / T 19139-2012, "Test Methods for Oil Well Cement," and its engineering properties under normal temperature conditions were determined. Cement stone was cured at 65℃ / 25MPa, and its early-stage (4h, 6h, 8h, 12h, 24h, 48h) compressive strength was tested. The thickening properties of the cement slurry were tested at 65℃ / 30MPa / 30min.

[0095] Test Example 1

[0096] This test example demonstrates 1H NMR spectroscopy analysis of the slow-release curing agent before and after modification. Please refer to [reference needed]. Figure 1 ,Depend on Figure 1 It can be seen that the curve of 2-phenylimidazole has no characteristic absorption peak in the range of 0-5 ppm; PC has obvious methyl and -OH characteristic absorption peaks in the range of 0-5 ppm; the curve of the finally obtained slow-release curing agent also shows obvious methyl and -OH characteristic absorption peaks in the range of 0-5 ppm, indicating that the slow-release curing agent was successfully prepared.

[0097] Test Example 2

[0098] This test case is a performance test of cement grout engineering. The test results are as follows: Figure 2-6 As shown in Table 1:

[0099]

[0100] Depend on Figure 2 (Cement slurry thickening curve of the example) Figure 3 (Thickening curve of cement slurry in Comparative Example 1) Figure 4 (Thickening curve of cement slurry in Comparative Example 2) Figure 5 (Thickening curve of cement slurry in Comparative Example 3) Figure 6(Comparative Example 4 cement slurry thickening curve) and the data in Table 1 show that the resin cement slurry system has good workability. Adding resin together with the slow-release curing agent has no effect on the thickening time of the cement slurry, and adding resin can improve the stability of the slurry. After removing the excessive metal chloride, the activity of the curing agent is improved, which leads to a gradual increase in the consistency of the cement slurry during the thickening experiment. When imidazole organic matter is used directly as a curing agent, the resin crosslinking rate is significantly increased, the thickening time is significantly shortened, and obvious abnormal thickening phenomenon occurs. After removing the slow-release curing agent, the consistency of the cement slurry increases significantly after the heating and pressurization are completed, indicating that adding resin alone will not affect the thickening time of the cement slurry, but it will lead to abnormal cement slurry consistency.

[0101] It should be noted that the cement slurry thickening test conditions were 65 ℃ / 30 MPa, and the heating and pressurization time was 30 min.

[0102] Test Example 3

[0103] This test case demonstrates the early mechanical properties of cement paste. The test results are as follows: Figure 7 As shown in Table 2:

[0104]

[0105] Depend on Figure 7 (Comparison of early compressive strength between the examples and the comparative examples) and Table 2 show that, under the same amount of admixture, the higher the activity of the curing agent, the higher the strength of the resin cement paste, and both are higher than those of the comparative example 1, indicating that the resin cement paste system has excellent early strength.

[0106] It should be noted that the compressive strength of the cement slurry under curing conditions is 65 ℃ / 25 MPa, and the heating and pressurization time is 60 min.

[0107] Test Example 4

[0108] This test example demonstrates the bonding performance between cement stone and coal / rock. The test results are as follows: Figure 8-9 As shown in Table 3:

[0109]

[0110] Depend on Figure 8 (Comparison of interfacial bonding strength between the examples and the comparative examples) Figure 9 (Comparison of bonding strength between coal and rock interface in the examples and comparative examples) and Table 3 show that the bonding strength between the resin cement slurry system of the examples and the coal and rock interface and the casing interface is significantly better than that between the conventional coal and rock gas cement slurry system of Comparative Example 1 and the coal and rock interface and the casing interface.

[0111] Test Example 5

[0112] This test example demonstrates the bonding performance of cement stone with different core samples. The test results are as follows: Figure 10 As shown in Table 4:

[0113]

[0114] Depend on Figure 10 (Comparison of bonding strength between the two interfaces of different rocks in the examples and Table 4) It can be seen that the bonding strength between the resin cement slurry system of the examples and coal and rock is comparable to that between the conventional coal gas cement slurry system of the comparative example and sandstone. However, sandstone is a type of rock core that is conducive to cement bonding. Therefore, the cement bonding strength between the examples and coal and rock is significantly superior to that between the conventional coal gas cementing slurry system of Comparative Example 1 and coal and rock.

[0115] It should be noted that no bonding strength test was conducted on the examples, comparative examples 2, 3, and 4 with sandstone, because sandstone is a strongly cemented rock and coal is a weakly cemented rock. The experimental results show that the bonding strength of the examples with added resin with coal is comparable to that of comparative example 1 without added resin, which demonstrates the advantage of the resin cement slurry system of this invention in improving bonding strength compared to conventional systems.

[0116] Test Example 6

[0117] This test case is for the triaxial Young's modulus of cement stone. The test results are as follows: Figure 11 As shown in Table 5:

[0118]

[0119] Depend on Figure 11 (Triaxial Young's modulus of cement stone) and Table 5 show that the triaxial Young's modulus of the embodiments is significantly lower than that of Comparative Example 1, and the Young's modulus of the other Comparative Examples 2-4 is also relatively lower than that of Comparative Example 1. Adding resin will reduce the triaxial Young's modulus of cement stone, and adding a slow-release curing agent can further reduce the Young's modulus of cement stone.

[0120] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0121] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A cement slurry for improving the cementing strength of coal and rock interfaces, characterized in that, The cementing slurry is composed of 50-150 parts of oil well cement, 5-50 parts of epoxy resin, 0.2-2 parts of slow-release curing agent, 0.05-0.2 parts of defoaming agent, 1.75-11 parts of auxiliary agent and 40-80 parts of water in terms of mass fraction; The preparation method of the slow-release curing agent comprises the following steps: The imidazole organic matter is preheated with propylene carbonate at 55-75 DEG C, and reacted at 125-145 DEG C until the imidazole organic matter is completely dissolved in solid phase to generate N-substituted hydroxymethyl imidazole derivative; a transition metal chloride solution is added to the N-substituted hydroxymethyl imidazole derivative, and stirred for 4-5 h to obtain the slow-release curing agent; the concentration of the transition metal chloride solution is 0.5-30%; The imidazole organic matter comprises at least one of 2-phenylimidazole, 4-phenylimidazole and 2-methyl imidazole and derivatives thereof; The transition metal chloride comprises at least one of cobalt chloride, nickel chloride, ferric chloride and copper chloride; The molar ratio of the imidazole organic matter to the propylene carbonate and the transition metal chloride is 1: (1-8): (0.05-1).

2. The cement slurry of claim 1, wherein, The auxiliary agent is composed of 0.5-2 parts of early strength agent, 0.5-4 parts of fluid loss agent, 0.2-1 part of dispersing agent, 0.05-2 parts of retarder and 0.5-2 parts of expansive agent in terms of mass fraction.

3. The cement slurry of claim 2, wherein, The early strength agent is nano-based composite reinforcing material with nano C-S-H as core; the fluid loss agent is 2-acrylamide-2-methylpropane sulfonic acid and acrylic acid copolymer; the dispersing agent comprises at least one of polycarboxylate and sulfonated acetone formaldehyde condensate; the retarder is hydroxyl carboxylic acid and salt polymer thereof; and the expansive agent is made of alum stone, gypsum, high-alum clinker or aluminate cement clinker as raw material.

4. The cement slurry of claim 1, wherein, The epoxy resin is bisphenol A type epoxy resin emulsion; and the defoaming agent comprises at least one of silicone defoaming agent, mineral oil defoaming agent, polyether defoaming agent and polyether modified silicone defoaming agent.

5. The cement slurry of claim 4, wherein, The chemical structure of the bisphenol A type epoxy resin emulsion is as follows: 。 6. A method for preparing the cementing slurry for improving the cementation strength of the coal rock at the interface according to any one of claims 1-5, characterized in that, The preparation method comprises the following steps: The oil well cement and auxiliary agent are mixed uniformly to obtain a solid mixture; the epoxy resin, defoaming agent, slow-release curing agent and water are stirred at 3500-4500 rpm for 10-20 s to obtain a liquid mixture; the solid mixture is added to the liquid mixture at 3500-4000 rpm, and stirring is continued for 40-60 s, and the speed is reduced to 0 rpm to eliminate bubbles, thereby obtaining the cementing slurry.

7. Application of the cementing slurry for improving the cementing strength of interface coal rock in well cementing of coal rock gas well according to any one of claims 1-5.

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