Method for changing coal permeability and improving gas desorption by using sodium acetate
By injecting sodium acetate solution and using its crystallization to release heat and reacting with coal minerals, the pore structure and surface properties of coal are changed, and the problems of low permeability and gas desorption rate in the prior art are solved, achieving efficient and environmentally friendly coal seam transformation effect.
Patent Information
- Application Number
- CN202510195350.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-21
- Publication Date
- 2025-04-11
AI Technical Summary
When the prior art improves the gas desorption rate and permeability of low-permeability coal seams, there are problems such as high cost, unstable effect, greater damage to the coal seam structure, and potential harm to the environment.
By injecting sodium acetate solution, using its crystallization to release heat and react with coal minerals, the pore structure and surface properties of coal are changed, thereby improving the permeability of coal and the desorption capacity of gas. The specific steps include determining the target layer, punching and injecting fluid, controlling the injection temperature and pressure, and adjusting the injection pressure in combination with the underground microseismic monitoring system.
It has achieved the improvement of the permeability and gas desorption capacity of the coal seam without destroying the coal seam structure, reducing costs and environmental impact.
Smart Images
Figure CN119801469A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for changing coal permeability, in particular to a method for changing coal permeability and improving gas desorption by using sodium acetate, which is suitable for use in low-permeability coal seams. Background Art
[0002] Traditional gas extraction technology mainly relies on physical methods, such as drilling extraction, hydraulic fracturing, etc. Although these methods can improve gas desorption and flow to a certain extent, they have problems such as high cost, unstable effect, and great damage to coal seam structure.
[0003] In recent years, chemical methods have gradually become a research hotspot, which can improve the gas desorption rate and permeability by injecting chemical reagents to change the physical and chemical properties of coal. However, existing chemical methods mostly use strong acids, strong bases or organic solvents, which not only cause potential harm to coal seams and the environment, but also may affect the subsequent use of coal.
[0004] As a weak alkaline salt, sodium acetate has the advantages of low cost, environmental friendliness, and easy operation. When sodium acetate solution crystallizes in the coal seam, it releases heat, causing the temperature of the surrounding coal to rise. The coal body generates internal stress due to thermal expansion and contraction, thus generating cracks. In addition, sodium acetate can react with minerals in the coal, changing the pore structure and surface properties of the coal, thereby affecting the adsorption and desorption behavior of gas, further improving the permeability of the coal. Summary of the invention
[0005] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for changing coal permeability and improving gas desorption using sodium acetate, which is easy to implement and can improve gas desorption capacity while changing the permeability of coal seams.
[0006] To achieve the above object, the method of using sodium acetate to change coal permeability and improve gas desorption of the present invention comprises the following steps:
[0007] Step 1: Determine the temperature, lithology, permeability, porosity, and ground stress distribution parameters of the formation through seismic exploration and well logging, and identify the target layer suitable for fracturing;
[0008] Step 2: Use a perforating gun to drill small holes in the target rock formation to provide a channel for the sodium acetate solution to enter the rock formation;
[0009] Step 3: injecting sodium acetate solution into the coal seam by a high-pressure pump to ensure that the solution fully penetrates the coal seam;
[0010] Step 4: After the fracturing operation is completed, close the wellhead for three days;
[0011] Step 5: Backflow the waste water to the ground.
[0012] The solution temperature was controlled between 50℃ and 60℃ during injection.
[0013] During the injection process, segmented pulse injection is adopted: the concentration of the solution injected in the front section is between 40% and 45%, which serves as a guide layer, and the concentration of the solution injected in the rear section is between 45% and 55%, which forms a main reaction zone.
[0014] The dynamic adjustment range of injection pressure is 10~20MPa.
[0015] During the injection process, the downhole microseismic monitoring system is used to provide real-time feedback on the fracture development status to adjust the injection pressure in a timely manner.
[0016] Sodium acetate solution crystallizes in the coal seam due to changes in temperature and moisture, releasing a large amount of heat.
[0017] The produced crystals serve as proppant.
[0018] The heat increases the temperature of the coal seam and evaporates the water in the solution. The coal body produces internal stress due to thermal expansion and contraction. The degree of thermal expansion of the coal body in different parts is different, which will form stress concentration. When the stress exceeds the strength of the coal body, cracks will appear in the coal body. The evaporation of water in the solution will also generate steam pressure, further expanding the cracks and intensifying crystallization.
[0019] The heat generated is also used to assist gas desorption. The increase in temperature is conducive to the desorption of gas from the coal surface. The heat released by the crystallization of the sodium acetate solution is transferred to the coal seam, promoting the desorption process of the adsorbed gas in the coal seam. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 The present invention provides a flow chart of the principle of a method for changing coal permeability and improving gas desorption by using sodium acetate.
[0021] Figure 2 The present invention provides a flowchart of the steps of a method for changing coal permeability and improving gas desorption by using sodium acetate. DETAILED DESCRIPTION
[0022] In view of the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for changing coal permeability and improving gas desorption using sodium acetate, which is easy to implement and can improve gas desorption capacity while changing the permeability of coal seams.
[0023] To achieve the above object, the method of using sodium acetate to change coal permeability and improve gas desorption of the present invention comprises the following steps:
[0024] Step 1: Determine the temperature, lithology, permeability, porosity, and ground stress distribution parameters of the formation through seismic exploration and well logging, and identify the target layer suitable for fracturing;
[0025] Step 2: Use a perforating gun to drill small holes in the target rock formation to provide a channel for the sodium acetate solution to enter the rock formation;
[0026] Step 3: injecting sodium acetate solution into the coal seam by a high-pressure pump to ensure that the solution fully penetrates the coal seam;
[0027] Step 4: After the fracturing operation is completed, close the wellhead for three days;
[0028] Step 5: Backflow the waste water to the ground.
[0029] The solution temperature was controlled between 50℃ and 60℃ during injection.
[0030] During the injection process, segmented pulse injection is adopted: the concentration of the solution injected in the front section is between 40% and 45%, which serves as a guide layer, and the concentration of the solution injected in the rear section is between 45% and 55%, which forms a main reaction zone.
[0031] The dynamic adjustment range of injection pressure is 10~20MPa.
[0032] During the injection process, the downhole microseismic monitoring system is used to provide real-time feedback on the fracture development status to adjust the injection pressure in a timely manner.
[0033] Sodium acetate solution forms a transmittance-enhancing effect through the synergy of heat, force and chemical fields: phase change exothermicity, crystallization pressure and surface modification.
[0034] Sodium acetate solution crystallizes in the coal seam due to changes in temperature and moisture, expanding the primary fracture network through crystal growth pressure (up to 10-30MPa), releasing a large amount of heat.
[0035] The resulting crystals serve as proppant.
[0036] The heat increases the temperature of the coal seam and evaporates the water in the solution. The coal body expands and contracts due to the instantaneous release of phase change heat (about 50-80kJ / kg), generating internal stress. The degree of thermal expansion of the coal body in different parts is different, which will form stress concentration. When the stress exceeds the strength of the coal body, cracks will appear in the coal body. The evaporation of water in the solution will also generate steam pressure, further expanding the cracks and intensifying crystallization.
[0037] The heat generated is also used to assist gas desorption. Sodium acetate reacts with oxygen-containing functional groups on the surface of the coal matrix to reduce the methane adsorption potential by 0.5-1.2 eV. At the same time, the surface properties of the coal are changed through thermal effects, reducing the adsorption force between gas molecules and the coal surface, thereby increasing the gas desorption rate.
Claims
1. A method for changing coal permeability and improving gas desorption using sodium acetate, characterized in that: Step 1: Determine the temperature, lithology, permeability, porosity, and ground stress distribution parameters of the formation through seismic exploration and well logging, and identify the target layer suitable for fracturing; Step 2: Use a perforating gun to drill small holes in the target rock formation to provide a channel for the sodium acetate solution to enter the rock formation; Step 3: injecting sodium acetate solution into the coal seam by a high-pressure pump to ensure that the solution fully penetrates the coal seam; Step 4: After the fracturing operation is completed, close the wellhead for three days; Step 5: Backflow the waste water to the ground.
2. A method for changing coal permeability and improving gas desorption using sodium acetate according to claim 1, characterized in that: The solution temperature was controlled between 50℃ and 60℃ during injection.
3. The method of using sodium acetate to change coal permeability and improve gas desorption according to claim 1, characterized in that: During the injection process, segmented pulse injection is adopted: the concentration of the solution injected in the front section is between 40% and 45%, which serves as a guide layer, and the concentration of the solution injected in the rear section is between 45% and 55%, which forms a main reaction zone.
4. The method of using sodium acetate to change coal permeability and improve gas desorption according to claim 1, characterized in that: The dynamic adjustment range of injection pressure is 10~20MPa.
5. The method of using sodium acetate to change coal permeability and improve gas desorption according to claim 1, characterized in that: During the injection process, the downhole microseismic monitoring system is used to provide real-time feedback on the fracture development status to adjust the injection pressure in a timely manner.
6. The method of using sodium acetate to change coal permeability and improve gas desorption according to claim 1, characterized in that: Sodium acetate solution crystallizes in the coal seam due to changes in temperature and moisture, releasing a large amount of heat.
7. A method for changing coal permeability and improving gas desorption using sodium acetate according to claim 6, characterized in that: The resulting crystals serve as proppant.
8. The method of using sodium acetate to change coal permeability and improve gas desorption according to claim 6, characterized in that: The heat increases the temperature of the coal seam and evaporates the water in the solution. The coal body produces internal stress due to thermal expansion and contraction. The degree of thermal expansion of the coal body in different parts is different, which will form stress concentration. When the stress exceeds the strength of the coal body, cracks will appear in the coal body. The evaporation of water in the solution will also generate steam pressure, further expanding the cracks and intensifying crystallization.
9. A method for changing coal permeability and improving gas desorption using sodium acetate according to claim 6, characterized in that: The heat generated is also used to assist gas desorption. The increase in temperature is conducive to the desorption of gas from the coal surface. The heat released by the crystallization of the sodium acetate solution is transferred to the coal seam, promoting the desorption process of the adsorbed gas in the coal seam.