Preparation and application method of self-heat-generating and energy-increasing fracturing fluid system suitable for coal bed gas

Abstract

The invention discloses a preparation and application method of a self-heat-generation and energy-increasing fracturing fluid system suitable for coal bed gas. The preparation method comprises the following steps: synthesizing an activator microcapsule; mixing the self-heat-generating and energy-increasing fracturing fluid base fluid and the activator microcapsule according to the mass ratio of 100: (0.8-3) to obtain a self-heat-generating and energy-increasing fracturing fluid system; the self-heat-generating and energy-increasing fracturing fluid system is injected into a stratum, reaction is started when the temperature of the stratum reaches 20 DEG C, heat and gas N2 are generated, the gas phase pressure of a reservoir is increased, and the self-heat-generating and energy-increasing fracturing fluid base fluid is prepared. The self-heat-generation energy-increasing fracturing fluid can be widely applied to preparation and application of the self-heat-generation energy-increasing fracturing fluid of the coal bed gas, the reservoir temperature and the gas phase pressure are remarkably improved, desorption and migration of the coal bed gas are promoted, the gas production rate of a single well is increased, the preparation method is simple and easy to implement, required equipment and process conditions are easy to implement, and the self-heat-generation energy-increasing fracturing fluid is suitable for field application and popularization.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane extraction, specifically to a method for preparing and applying a self-generating thermal fracturing fluid system suitable for coalbed methane. Background Technology

[0002] Coalbed methane (CBM), as a clean energy source, has broad development prospects. However, existing CBM extraction technologies face numerous challenges in practical applications, especially in low-permeability, low-pressure, and low-temperature reservoirs where extraction efficiency is low. Production data from the Qinnan-Xiadian block in the Qinshui Basin shows that although 571 wells have been put into production, the highest daily gas production was only 210,000 cubic meters, which has now dropped to 129,000 cubic meters, with an average daily production of only 282 cubic meters per well. Wells with a production rate below 500 m³ / d account for as much as 43% of the total. The main reasons for this include the low thermal evolution of the coal reservoir, with significantly lower Langmuir volume, Langmuir pressure, reservoir pressure, and temperature compared to other blocks. This results in weak gas displacement capacity, low migration efficiency, and production difficulties during the critical stages of CBM occurrence, desorption, and migration. Furthermore, the predominantly micropore structure, relatively isolated pores, and poor microfracture extension also lead to a narrow two-phase co-permeability zone and low gas migration efficiency.

[0003] Existing technologies, such as low-density proppant, nitrogen foam, and nitrogen co-injection, have failed to effectively increase single-well gas production because they do not fundamentally address the problems of low reservoir pressure, low temperature, and poor pore and fracture development. Therefore, a novel fracturing system is urgently needed that can increase reservoir temperature, increase reservoir gas phase pressure, generate N2, and utilize N2 to fracture and connect micropores, thereby significantly improving CH4 recovery.

[0004] This invention discloses a self-generating thermal fracturing fluid suitable for coalbed methane and its application method. By synthesizing activator microcapsules and preparing the self-generating thermal fracturing fluid base fluid, the shortcomings of existing technologies are overcome. Under the action of an acidic activator, ammonium chloride and sodium nitrite in the self-generating thermal fracturing fluid undergo a thermochemical reaction, generating a large amount of heat and nitrogen gas, significantly increasing reservoir temperature and gas phase pressure, thereby promoting the desorption and migration of coalbed methane and increasing single-well gas production. The activator microcapsules are composed of gel microspheres obtained by cross-linking sodium alginate solution and CaCl2 solution, ensuring uniform distribution of the microcapsules in the formation and a suitable reaction rate, which is beneficial for controlling the heat and gas release process and improving the safety and effectiveness of the operation.

[0005] This invention provides a highly efficient, safe, and environmentally friendly self-heating fracturing fluid and its application method, which solves many shortcomings of existing coalbed methane extraction technologies and has significant technical value and broad application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing and applying a self-heating fracturing fluid system suitable for coalbed methane, in order to solve the technical problem of low extraction efficiency in low-temperature reservoirs in the prior art.

[0007] To achieve the above objectives, the present invention provides a method for preparing a self-generating thermal fracturing fluid system suitable for coalbed methane, comprising the following steps: synthesizing activator microcapsules;

[0008] Preparation of self-heating and energy-enhancing fracturing fluid base fluid;

[0009] The specific preparation method of the synthetic activator microcapsules is as follows:

[0010] The acid is dissolved in 95% ethanol to form solution A, with the ratio of acid to ethanol being 4–8 mg / mL.

[0011] Sodium alginate is completely dissolved and mixed in water to prepare a sodium alginate solution of 15-30 g / L (1.5%-3%) for later use.

[0012] Add solution A to sodium alginate solution, stir well, and stir for 30 minutes to form solution B;

[0013] Add solution B dropwise to a 5-15 g / L (0.5%-1.5%) CaCl2 solution using a syringe, and continue stirring until homogeneous for 30 minutes, then allow to stand for cross-linking.

[0014] The obtained gel microspheres were thoroughly washed with anhydrous ethanol and distilled water, dried at room temperature, and then sieved for later use.

[0015] The specific preparation method of the self-generating thermal energy-enhancing fracturing fluid base is as follows:

[0016] Ammonium chloride, anti-swelling agent, and sodium nitrite are dissolved in water in a certain proportion and mixed evenly to obtain a self-heating fracturing fluid base.

[0017] The beneficial effects of this technical solution are as follows: By synthesizing activator microcapsules and preparing self-generating thermal energy-enhancing fracturing fluid base fluid, this solution effectively improves the efficiency of coalbed methane extraction. Under the action of an acidic activator, ammonium chloride and sodium nitrite undergo a thermochemical reaction in the self-generating thermal energy-enhancing fracturing fluid, generating a large amount of heat and nitrogen, significantly increasing reservoir temperature and gas phase pressure, thereby promoting the desorption and migration of coalbed methane and increasing single-well gas production. The preparation method is simple and easy to implement, and the required equipment and process conditions are easy to achieve, making it suitable for field promotion and application. The chemical raw materials used are relatively safe, and the main products generated are nitrogen and water, resulting in minimal environmental impact. The microcapsule technology controls the reaction rate and release process, improving operational safety. This fracturing fluid system works effectively under low-temperature and low-pressure reservoir conditions, improving fracture extension and pore connectivity through thermal effects and nitrogen generation, thereby increasing gas migration efficiency. In addition to being suitable for coalbed methane extraction, it can also be applied to oil and gas extraction in other low-permeability, low-pressure, and low-temperature reservoirs, demonstrating broad application prospects and market value.

[0018] In some alternative embodiments, the acid is oxalic acid, citric acid, benzoic acid, or acetic acid.

[0019] The beneficial effects of this technical solution are as follows: Under the action of acidic activators (oxalic acid, citric acid, benzoic acid or acetic acid), the self-generating thermal fracturing fluid undergoes a thermochemical reaction between ammonium chloride and sodium nitrite, generating a large amount of heat and nitrogen, which significantly increases the reservoir temperature and gas phase pressure, thereby promoting the desorption and migration of coalbed methane and increasing the gas production of a single well.

[0020] In some alternative embodiments, the syringe has an orifice diameter of 1.6–2 mm.

[0021] The beneficial effects of this technical solution are as follows: using a syringe with a diameter of 1.6 to 2 mm to drop solution B into CaCl2 solution ensures that the microcapsules are of uniform size, which is beneficial for controlling the reaction rate and release process, and further improves the safety of operation.

[0022] In some optional embodiments, the concentration of the CaCl2 solution is 5–15 g / L.

[0023] In some optional embodiments, the self-heating and energy-enhancing fracturing fluid base fluid comprises the following raw material components in parts by weight:

[0024] Ammonium chloride 10-20 parts; anti-swelling agent 0.5-1 part; sodium nitrite 15-30 parts; water 50 parts.

[0025] The beneficial effects of this technical solution are as follows: the base liquid includes 10-20 parts of ammonium chloride, 0.5-1 part of anti-swelling agent, 15-30 parts of sodium nitrite and 50 parts of water, which ensures the optimal conditions for chemical reaction and gas production effect, and is conducive to increasing the reservoir gas phase pressure and temperature, and improving gas migration efficiency.

[0026] In some optional embodiments, the mass ratio of activator microcapsules to base liquid is 100:0.8 to 3.

[0027] The beneficial effects of this technical solution are as follows: the mass ratio of activator microcapsules to base liquid is 100:0.8-3, which ensures the uniform distribution of microcapsules in the formation and a suitable reaction rate, and is conducive to controlling the heat and gas release process.

[0028] Secondly, the present invention provides an application method for a self-generating thermal energy-enhancing fracturing fluid system for coalbed methane, specifically comprising: mixing a self-generating thermal energy-enhancing fracturing fluid base fluid and activator microcapsules at a mass ratio of 100:0.8-3 to obtain a self-generating thermal energy-enhancing fracturing fluid system;

[0029] The self-generating thermal fracturing fluid system is injected into the formation, and it begins to react when the formation temperature reaches 20°C, generating heat and gas N2, which increases the reservoir gas phase pressure.

[0030] The beneficial effects of this technical solution are as follows: This solution obtains a self-generating thermal energy-enhancing fracturing fluid system by mixing the base fluid and activator microcapsules at a mass ratio of 100:0.8-3. This system is then injected into the formation, where it begins to react when the formation temperature reaches 20°C, generating heat and nitrogen gas. This significantly increases the reservoir gas phase pressure, thereby improving coalbed methane production efficiency. The system uses a formula of 15 parts ammonium chloride, 50 parts water, 0.5 parts anti-swelling agent, 25 parts sodium nitrite, and 0.8 parts activator microcapsules, ensuring efficient reaction, facilitating control of heat and gas release, and improving operational safety and effectiveness. The preparation method is simple and easy to implement, and the required equipment and process conditions are readily achievable, making it suitable for field application. The chemical raw materials used are relatively safe, and the main products are nitrogen and water, resulting in minimal environmental impact. This fracturing fluid system works effectively under low-temperature and low-pressure reservoir conditions, improving fracture extension and pore connectivity through thermal effects and nitrogen generation, thereby enhancing gas migration efficiency.

[0031] In some optional embodiments, the self-heating fracturing fluid system is composed of the following raw materials in parts by weight: 15 parts ammonium chloride; 50 parts water; 0.5 parts anti-swelling agent; 25 parts sodium nitrite; and 0.8 parts activator microcapsules.

[0032] The beneficial effects of this technical solution are as follows: the base liquid includes 10-20 parts of ammonium chloride, 0.5-1 part of anti-swelling agent, 15-30 parts of sodium nitrite and 50 parts of water, which ensures the optimal conditions for chemical reaction and gas production effect, and is conducive to increasing the reservoir gas phase pressure and temperature, and improving gas migration efficiency.

[0033] In some optional embodiments, the activator microcapsules comprise gel microspheres obtained by crosslinking sodium alginate solution and CaCl2 solution.

[0034] The beneficial effects of this technical solution are as follows: the activator microcapsules are composed of gel microspheres obtained by cross-linking sodium alginate solution and CaCl2 solution, which ensures the uniform distribution of microcapsules in the formation and a suitable reaction rate.

[0035] In some optional embodiments, the activator microcapsules initiate the reaction when the formation temperature reaches 20°C, and the activator microcapsules are added at temperatures below 40°C. Attached Figure Description

[0036] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a flowchart of a method for preparing a self-heating fracturing fluid system suitable for coalbed methane according to an embodiment of the present invention.

[0039] Figure 2 This diagram illustrates a method for preparing microcapsules of a self-heating fracturing fluid suitable for coalbed methane, according to an embodiment of the present invention.

[0040] Figure 3 This is a diagram illustrating a method for preparing a self-heating fracturing fluid base suitable for coalbed methane, according to an embodiment of the present invention.

[0041] Figure 4 This is a flowchart illustrating the application method of a self-heating fracturing fluid system for coalbed methane according to an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0043] Appendix Figure 1 Appendix Figure 2 and attached Figure 3A method for preparing an autogenous thermal fracturing fluid system suitable for coalbed methane, according to an embodiment of the present invention, is shown, comprising the following steps:

[0044] Synthetic activator microcapsules;

[0045] Preparation of self-heating and energy-enhancing fracturing fluid base fluid;

[0046] The specific preparation method of the synthetic activator microcapsules is as follows:

[0047] The acid is dissolved in 95% ethanol to form solution A, with the ratio of acid to ethanol being 4–8 mg / mL.

[0048] Sodium alginate is completely dissolved and mixed in water to prepare a sodium alginate solution of 15-30 g / L (1.5%-3%) for later use.

[0049] Add solution A to sodium alginate solution, stir well, and stir for 30 minutes to form solution B;

[0050] Add solution B dropwise to a 5-15 g / L (0.5%-1.5%) CaCl2 solution using a syringe, and continue stirring until homogeneous for 30 minutes, then allow to stand for cross-linking.

[0051] The obtained gel microspheres were thoroughly washed with anhydrous ethanol and distilled water, dried at room temperature, and then sieved for later use.

[0052] The specific preparation method of the self-generating thermal energy-enhancing fracturing fluid base is as follows:

[0053] Ammonium chloride, anti-swelling agent, and sodium nitrite are dissolved in water in a certain proportion and mixed evenly to obtain a self-heating fracturing fluid base.

[0054] The preparation process of the synthetic activator microcapsules first involves dissolving an acid in 95% ethanol to improve its solubility and dispersibility, forming solution A, with an acid-to-ethanol ratio of 4–8 mg / mL. Ethanol, as a good solvent, effectively dissolves and disperses organic acids, ensuring uniform mixing with the sodium alginate solution in the subsequent process. Then, sodium alginate is completely dissolved in water to prepare a 15–30 g / L solution for forming the gel matrix. Solution A is added to the sodium alginate solution and stirred for 30 minutes to form a homogeneous solution B. Subsequently, solution B is added dropwise to a 5–15 g / L CaCl2 solution using a syringe for cross-linking, forming gel microspheres. This cross-linking process utilizes the combination of calcium ions from CaCl2 and carboxylic acid groups from sodium alginate, making the microsphere structure more stable. Finally, the gel microspheres are washed, dried, and sieved to obtain the synthetic activator microcapsules. For the preparation of self-heating enhanced fracturing fluid base fluid, ammonium chloride, anti-swelling agent, and sodium nitrite are dissolved in water in a certain proportion to form a base fluid. Through a chemical reaction, heat is spontaneously generated, enhancing the fracturing fluid's performance. Microcapsules prepared using this method can release acid during fracturing, enhancing the acidizing effect, while the self-heating characteristic of the base fluid reduces the need for external heating equipment, improving operational efficiency and safety. This overall method has the advantages of simplified operation, reduced costs, and improved fracturing effect, making it suitable for widespread application in oil and gas extraction.

[0055] The thermochemical reaction of the NH4Cl / NaNO2 autogenous fracturing fluid is a typical acid-catalyzed reaction. The thermochemical reaction occurs under the action of an acidic catalyst, as shown in equation (1). Theoretically, under the conditions of a reactant concentration of 3 mol / L and a molar ratio of 1:1, 1 m 3 A solution of NaNO2 and NH4Cl can release 997.6 MJ of heat and 67.2 mJ of oxygen. 3 N2.

[0056] NH4Cl + NaNO2 → N2↑ + NaCl + 2H2O

[0057] ΔH = -332.85 kJ / mol.

[0058] The specific steps for synthesizing activator microcapsules include: dissolving an acid in 95% ethanol (by volume) to form solution A, with an acid-to-ethanol ratio of 4-8 mg:1 mL; completely dissolving sodium alginate in water to prepare a 15-30 g / L (1.5%-3%) sodium alginate solution for later use; adding the acid to the sodium alginate solution, stirring evenly for 30 min to form solution B; using a syringe to dropwise add solution B into a 5-15 g / L (0.5%-1.5%) 100 g / L (10%) CaCl2 solution, and continuing to stir evenly for 30 min, allowing it to stand for cross-linking, with the syringe having an orifice diameter of 1.6-2 mm; and thoroughly washing the obtained gel microspheres with anhydrous ethanol and distilled water, drying at room temperature, and sieving for later use.

[0059] In the first embodiment, the steps of synthesizing activator microcapsules include: 1. Weighing 100 mg of oxalic acid, dissolving it in 20 mL of 95% ethanol to prepare solutions with concentrations of 0.005 g / L, 0.01 g / L, 0.02 g / L, and 0.025 g / L, and then making up the volume in a 1 mL volumetric flask for later use;

[0060] 2. Prepare 100 mL of 20 g / L sodium alginate solution with ultrapure water at 30℃, and mix well on a shaker or magnetic stirrer for 30 minutes.

[0061] 3. Add oxalic acid dropwise to the sodium alginate solution while stirring, according to different ratios, and stir until homogeneous;

[0062] 4. Use a 2.5 mL syringe to drop the mixed solution from step (3) into a 10 g / L CaCl2 solution and let it stand for cross-linking.

[0063] 5. Wash the obtained gel microspheres with ultrapure water, dry them at room temperature, and then sieve them to obtain activator microcapsules for later use.

[0064] In the second embodiment, the steps for synthesizing activator microcapsules include: 1. Weighing 100 mg of citric acid, dissolving it in 20 mL of 95% ethanol to prepare solutions with concentrations of 0.005 g / L, 0.01 g / L, 0.02 g / L, and 0.025 g / L, and then making up to 1 mL in a volumetric flask for later use.

[0065] 2. Prepare 100 mL of 20 g / L sodium alginate solution with ultrapure water at 30℃, and mix well on a shaker or magnetic stirrer for 30 minutes.

[0066] 3. Add citric acid dropwise to the sodium alginate solution while stirring, according to different ratios, and stir until homogeneous;

[0067] 4. Use a 2.5 mL syringe to drop the mixed solution from step (3) into a 10 g / L CaCl2 solution and let it stand for cross-linking.

[0068] 5. Wash the obtained gel microspheres with ultrapure water, dry them at room temperature, and then sieve them to obtain activator microcapsules for later use.

[0069] In the third embodiment, the steps for synthesizing activator microcapsules include: 1. Weighing 100 mg of benzoic acid, dissolving it in 20 mL of 95% ethanol to prepare solutions with concentrations of 0.005 g / L, 0.01 g / L, 0.02 g / L, and 0.025 g / L, and then making up the volume in a 1 mL volumetric flask for later use;

[0070] 2. Prepare 100 mL of 20 g / L sodium alginate solution with ultrapure water at 30℃, and mix well on a shaker or magnetic stirrer for 30 minutes.

[0071] 3. Add benzoic acid dropwise to the sodium alginate solution while stirring, according to different ratios, and stir until homogeneous;

[0072] 4. Use a 2.5 mL syringe to drop the mixed solution from step (3) into a 10 g / L CaCl2 solution and let it stand for cross-linking.

[0073] 5. Wash the obtained gel microspheres with ultrapure water, dry them at room temperature, and then sieve them to obtain activator microcapsules for later use.

[0074] In the fourth embodiment, the steps for synthesizing activator microcapsules include: 1. Weighing 100 mg of acetic acid, dissolving it in 20 mL of 95% ethanol to prepare solutions with concentrations of 0.005 g / L, 0.01 g / L, 0.02 g / L, and 0.025 g / L, and then making up the volume in a 1 mL volumetric flask for later use;

[0075] 2. Prepare 100 mL of 20 g / L sodium alginate solution with ultrapure water at 30℃, and mix well on a shaker or magnetic stirrer for 30 minutes.

[0076] 3. Add acetic acid dropwise to the sodium alginate solution while stirring, according to different ratios, and stir until homogeneous;

[0077] 4. Use a 2.5 mL syringe to drop the mixed solution from step (3) into a 10 g / L CaCl2 solution and let it stand for cross-linking.

[0078] 5. Wash the obtained gel microspheres with ultrapure water, dry them at room temperature, and then sieve them to obtain activator microcapsules for later use.

[0079] As attached Figure 4 As shown, an application method of a self-generating thermal energy-enhancing fracturing fluid system for coalbed methane includes: mixing the self-generating thermal energy-enhancing fracturing fluid base fluid and activator microcapsules at a mass ratio of 100:0.8-3 to obtain the self-generating thermal energy-enhancing fracturing fluid system;

[0080] The self-generating thermal fracturing fluid system is injected into the formation, and it begins to react when the formation temperature reaches 20°C, generating heat and gas N2, which increases the reservoir gas phase pressure.

[0081] Specifically, the application method of the autogenous heating fracturing fluid system for coalbed methane includes: the autogenous heating fracturing fluid system consists of an autogenous heating fracturing fluid base fluid and activator microcapsules, wherein the base fluid includes ammonium chloride, an anti-swelling agent, and sodium nitrite. After the base fluid is miscible in an aqueous solution, it reacts in the presence of the activator microcapsules, releasing a large amount of heat energy and gas. The mass ratio of NaNO2 to NH4Cl is 1:1-1:2, and the amount of activator microcapsules is 0.8%–3%.

[0082] In the fifth embodiment, a self-generating thermal energy-enhancing fracturing fluid system for coalbed methane is composed of a base fluid and activator microcapsules, wherein the mass ratio of the base fluid to the activator microcapsules is 100:0.8.

[0083] The base liquid comprises the following raw materials:

[0084] 10 kg ammonium chloride, 50 kg water, 0.5 kg anti-swelling agent, 15 kg sodium nitrite;

[0085] The activator microcapsules weigh 0.8 kg.

[0086] The preparation method is as follows:

[0087] According to the above proportions, ammonium chloride, anti-swelling agent, sodium nitrite and water are stirred and mixed evenly to obtain the base liquid.

[0088] In this embodiment, the base fluid and activator microcapsules are injected into the formation simultaneously. The base fluid and activator microcapsules react in the formation (the reaction begins at 20°C, and activator microcapsules need to be added below 40°C) to obtain a self-heating fracturing fluid system for coalbed methane and play a corresponding role.

[0089] In the sixth embodiment, a self-generating thermal fracturing fluid system for coalbed methane is composed of a base fluid and activator microcapsules, wherein the mass ratio of the base fluid to the activator microcapsules is 100:0.8.

[0090] The base liquid comprises the following raw materials:

[0091] 15 kg ammonium chloride, 50 kg water, 0.5 kg anti-swelling agent, 25 kg sodium nitrite;

[0092] The activator microcapsules weigh 0.8 kg.

[0093] The preparation method is as follows:

[0094] According to the above proportions, ammonium chloride, anti-swelling agent, sodium nitrite and water are stirred and mixed evenly to obtain the base liquid.

[0095] In this embodiment, the base fluid and activator microcapsules are injected into the formation simultaneously. The base fluid and activator microcapsules react in the formation (the reaction begins at 20°C, and activator microcapsules need to be added below 40°C) to obtain a self-heating fracturing fluid system for coalbed methane and play a corresponding role.

[0096] In the seventh embodiment, a self-generating thermal energy-enhancing fracturing fluid system for coalbed methane is composed of a base fluid and activator microcapsules, wherein the mass ratio of the base fluid to the activator microcapsules is 100:3.

[0097] The base liquid comprises the following raw materials:

[0098] 20 kg ammonium chloride, 50 kg water, 1 kg anti-swelling agent, 30 kg sodium nitrite;

[0099] The activator microcapsules weigh 3 kg.

[0100] The preparation method is as follows:

[0101] According to the above proportions, ammonium chloride, anti-swelling agent, sodium nitrite and water are stirred and mixed evenly to obtain the base liquid.

[0102] In this embodiment, the base fluid and activator microcapsules are injected into the formation simultaneously. The base fluid and activator microcapsules react in the formation (the reaction begins at 20°C, and activator microcapsules need to be added below 40°C) to obtain a self-heating fracturing fluid system for coalbed methane and play a corresponding role.

[0103] First comparative example, inventive example: In this invention, an experiment was conducted using a ratio of ammonium chloride (20 parts) and sodium nitrite (25 parts); the results showed that, under initial conditions of 20°C, the reaction system raised the temperature to 40°C within 2 hours, releasing 997.6 MJ of heat, while simultaneously generating 67.2 mJ of heat. 3 The nitrogen significantly increased the gas phase pressure of the reservoir, effectively promoting the recovery of coalbed methane.

[0104] Comparative Example: In existing technologies, an experiment is typically conducted using a ratio of ammonium chloride (10 parts) and sodium nitrite (15 parts). Results show that under the same conditions, the reaction system can only raise the temperature to 30°C, with a heat release of 500 MJ and nitrogen gas production of 35 m³ / s. 3 In comparison, the formulation of this invention is significantly superior to the prior art in terms of heat release and nitrogen generation.

[0105] The comparative example of this invention also tested the effects of different ratios of ammonium chloride and sodium nitrite (e.g., 15 parts ammonium chloride and 20 parts sodium nitrite). The results showed that when the ratio of 15 parts ammonium chloride to 20 parts sodium nitrite was reacted at 20°C for 3 hours, and the temperature rose to 35°C, 750 MJ of heat was released and 50 m³ of nitrogen gas was generated.3 This further demonstrates that the optimal ratio of the present invention has significant advantages in terms of thermal effect and gas generation.

[0106] The second comparative example, an inventive example: In this invention, the amount of activator microcapsules used is 2 parts. Experimental results show that the reaction is significantly accelerated within 1 hour after the addition of the activator, the system temperature rapidly rises to 40°C, and remains at a stable high temperature for 4 hours, effectively enhancing the reservoir gas phase pressure.

[0107] Comparative Example: In the prior art, one part of activator microcapsules was used in the experiment. The results showed that the reaction required 3 hours to significantly heat up after the addition of the activator, and the maximum temperature was only 35°C, with a short duration. In contrast, the present invention improves reaction efficiency and temperature stability by increasing the amount of activator.

[0108] Tests were also conducted with different amounts of activator (e.g., 1.5 parts and 2.5 parts). The results for 1.5 parts of activator microcapsules showed that the reaction heated to 38°C within 2 hours of activator addition and remained stable for 3 hours. The results for 2.5 parts of activator microcapsules showed that the reaction heated to 42°C within 45 minutes of activator addition and maintained this high temperature for 5 hours. These experimental data indicate that a dosage of 2 parts of activator microcapsules provides the optimal efficiency and stability.

[0109] Third Comparative Example: Invention Example: In this invention, a 10 g / L CaCl2 solution was used to form microcapsules. Experimental results showed that the formed microcapsules had a stable structure, uniform particle size, and high reactivity, effectively catalyzing thermochemical reactions to generate a large amount of heat and nitrogen gas.

[0110] Comparative Example: In the prior art, an experiment was conducted using a 5 g / L CaCl2 solution. The results showed that the resulting microcapsule structure was unstable, with uneven particle size, low reactivity, and significantly less heat and nitrogen generated than the formulation of this invention. In contrast, this invention improves the quality and reactivity of the microcapsules by optimizing the concentration of the CaCl2 solution.

[0111] The effects of CaCl2 solutions of different concentrations (e.g., 8 g / L and 12 g / L) were also tested. Microcapsules formed with an 8 g / L CaCl2 solution exhibited moderate stability, relatively uniform particle size, and high reactivity, generating 850 MJ of heat and 55 m³ of nitrogen gas. 3 The microcapsule structure formed by a 12 g / L CaCl2 solution is very stable, with very uniform particle size, exhibiting the highest reactivity, generating 1000 MJ of heat and 70 m³ of nitrogen gas. 3 This further validates the superiority of the 10 g / L CaCl2 solution in microcapsule formation.

[0112] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a self-generating thermal fracturing fluid system suitable for coalbed methane, characterized in that, include, Synthetic activator microcapsules; Preparation of self-heating and energy-enhancing fracturing fluid base fluid; The specific preparation method of the synthetic activator microcapsules is as follows: The acid is dissolved in 95% ethanol to form solution A, with the ratio of acid to ethanol being 4–8 mg / mL. Sodium alginate is completely dissolved and mixed in water to prepare a sodium alginate solution of 15-30 g / L (1.5%-3%) for later use. Add solution A to sodium alginate solution, stir well, and stir for 30 minutes to form solution B; Add solution B dropwise to a 5-15 g / L (0.5%-1.5%) CaCl2 solution using a syringe, and continue stirring until homogeneous for 30 minutes, then allow to stand for cross-linking. The obtained gel microspheres were thoroughly washed with anhydrous ethanol and distilled water, dried at room temperature, and then sieved for later use. The specific preparation method of the self-generating thermal energy-enhancing fracturing fluid base is as follows: Ammonium chloride, anti-swelling agent, and sodium nitrite are dissolved in water in a certain proportion and mixed evenly to obtain a self-heating fracturing fluid base.

2. The method for preparing a self-generating thermal fracturing fluid system suitable for coalbed methane according to claim 1, characterized in that, The acid is oxalic acid, citric acid, benzoic acid, or acetic acid.

3. The method for preparing a self-generating thermal fracturing fluid system suitable for coalbed methane according to claim 1, characterized in that, The syringe has a diameter of 1.6–2 mm.

4. The method for preparing a self-heating fracturing fluid system suitable for coalbed methane according to claim 1, characterized in that, The concentration of the CaCl2 solution is 5–15 g / L.

5. The method for preparing a self-generating thermal fracturing fluid system suitable for coalbed methane according to claim 1, characterized in that, The self-generating thermal energy-enhancing fracturing fluid base fluid comprises the following raw material components in parts by weight: Ammonium chloride 10-20 parts; anti-swelling agent 0.5-1 part; sodium nitrite 15-30 parts; water 50 parts.

6. The method for preparing a self-generating thermal fracturing fluid system suitable for coalbed methane according to claim 1, characterized in that, The mass ratio of activator microcapsules to base liquid is 100:0.8-3.

7. A method for applying a self-heating and energy-enhancing fracturing fluid system for coalbed methane, characterized in that, include, The self-generating thermal energy-enhancing fracturing fluid base fluid and activator microcapsules are mixed at a mass ratio of 100:0.8-3 to obtain the self-generating thermal energy-enhancing fracturing fluid system. The self-generating thermal fracturing fluid system is injected into the formation, and it begins to react when the formation temperature reaches 20°C, generating heat and gas N2, which increases the reservoir gas phase pressure.

8. The application method of the self-heating and energy-enhancing fracturing fluid system for coalbed methane according to claim 7, characterized in that, The self-generating thermal energy-enhancing fracturing fluid system is composed of the following raw materials in parts by weight: 15 parts ammonium chloride; 50 parts water; 0.5 parts anti-swelling agent; 25 parts sodium nitrite; 0.8 parts activator microcapsules.

9. The application method of the self-generating thermal energy-enhancing fracturing fluid system for coalbed methane according to claim 7, characterized in that, The activator microcapsules consist of gel microspheres obtained by cross-linking sodium alginate solution and CaCl2 solution.

10. The application method of the self-generating thermal energy-enhancing fracturing fluid system for coalbed methane according to claim 7, characterized in that, The activator microcapsules begin to react when the formation temperature reaches 20°C, and the activator microcapsules are added at temperatures below 40°C.

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