Gas-containing oil-rich coal seam destructive distillation and methane yield increasing method and system capable of injecting air to generate heat

Abstract

The invention relates to a gas-containing oil-rich coal seam destructive distillation and methane production increasing method and system capable of injecting air to generate heat automatically. The system comprises a vertical injection well and a horizontal recovery well which are arranged in an oil-rich coal seam, a fracture network formed by conducting staged fracturing on the coal seam, and a gas-containing gas-rich coal seam destructive distillation and methane production increasing method and system capable of achieving gas-injection gas-rich coal seam destructive distillation and methane production increasing through ignition of the coal seam at each vertical well branch of the vertical injection well, air is continuously injected, and the air and the oil-rich coal seam react and combust to form a combustion working face; a plurality of vertical well branches are arranged at the bottom of the vertical injection well, and a high-temperature-resistant temporary sealing agent is arranged in the horizontal recovery well; when air and the oil-rich coal seam are reacted and combusted, a reduction-dry distillation area, a heating-desorption area and a CO2 replacement desorption area are formed in the coal seam from near to far through matrix heat transfer and convective heat transfer. On the basis that coal seam combustion self-generated heat is used for destructive distillation, desorption and migration output of methane in a far-end coal seam are promoted through heat radiation, and the problems that in-situ destructive distillation of the oil-rich coal is large in external energy consumption, and methane in the coal is difficult to output are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of in-situ conversion and mining of energy minerals, and in particular relates to a method for dry distillation and methane production increase of gas-rich and oil-bearing coal seams by injecting air for self-heat generation. Background Art

[0002] The main energy status of coal in my country will not change in the short term. For example, the oil-rich coal widely distributed in western my country can be used to extract tar and coal gas through pyrolysis. Faced with the problems of large oil and gas demand, many supply constraints, and large demand gap in China, the rich potential oil and gas resources in oil-rich coal play an important role in improving the domestic oil and gas security capabilities. In-situ retorting of oil-rich coal is a revolutionary technology that injects heat into the coal seam to reach the pyrolysis temperature and extracts pyrolysis oil and gas in situ. However, the in-situ retorting of oil-rich coal requires a large amount of external heat, and the huge energy consumption reduces the economic efficiency of the in-situ retorting technology. In addition, coalbed methane (methane) is generally adsorbed in oil-rich coal seams, and there are widespread problems in the region that lead to poor coalbed methane drainage and low production due to geological engineering factors, resulting in serious insufficient returns on initial capital investment. Therefore, how to solve the dual problems of high energy consumption of in-situ retorting of oil-rich coal and low methane drainage in oil-rich coal seams is crucial to achieving green and low-carbon development of oil-rich coal. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a method for dry distillation and methane production increase in gas-rich and oil-rich coal seams by injecting air to generate self-heat. The method can promote the desorption and migration of methane in remote coal seams through thermal radiation on the basis of dry distillation based on the self-heat generated by coal seam combustion, thereby solving the problems of large external energy consumption for in-situ dry distillation of oil-rich coal and difficulty in producing methane in coal.

[0004] In order to achieve the above object, the technical solution of the present invention is: a method for dry distillation and methane production increase of gas-rich coal seams by injecting air to generate heat automatically, the method comprising the following steps:

[0005] Step S1, respectively setting a vertical injection well and a horizontal recovery well in the oil-rich coal seam, setting a plurality of vertical well branches at the bottom of the vertical injection well, and setting a high-temperature resistant temporary sealing agent in the horizontal recovery well;

[0006] Step S2, performing staged fracturing on the oil-rich coal seam to form a fracture network;

[0007] Step S3, ignite the coal seam in each vertical well branch of the vertical injection well, and continuously inject air, the injected air reacts with the oil-rich coal seam to burn, forming a combustion working face, the combustion releases high-temperature gas, the high-temperature gas flows in the coal seam through the fracture network, and forms a reduction-drying zone, a heating-desorption zone, a CO 2 -desorption zone from near to far from the combustion working face in the coal seam through matrix heat transfer and convection heat transfer. 2 displacement desorption zone;

[0008] Step S4, when the combustion work surface advances toward the recovery well, the high temperature resistant temporary sealing agent fails to seal, and the high temperature resistant temporary sealing agent is injected through the pipeline injection method to form a new seal at the new boundary position of the horizontal hole section, ensuring that the sealing position moves backward dynamically with the advancement of the combustion work;

[0009] Step S5: The coal seam in the reduction-drying zone is pyrolyzed to produce tar and coal gas. The produced tar is driven by the high-temperature gas and migrated to the horizontal recovery well through the fracture network; the heating-desorption zone heats the coal seam by convection of high-temperature coal gas and combustion gas, so that the methane in the coal pores is mainly physically desorbed; CO 2 Replacement desorption zone to achieve cooling of CO 2 CH 4 Competitive adsorption to achieve partial CH 4 Physical desorption.

[0010] In the above-mentioned method for dry distillation and methane production increase of gas-rich coal seams with air injection and self-heating, the vertical injection well is arranged on the downward side of the oil-rich coal seam; the horizontal recovery well is arranged on the upward side of the oil-rich coal seam, and its horizontal section is located at the bottom of the oil-rich coal seam, and the end extends downward to branch out from the vertical well.

[0011] In the above-mentioned method for gas-rich coal seam dry distillation and methane production enhancement by injecting air for self-heating, when a high-temperature resistant temporary sealing agent is set in the horizontal recovery well in step S1, the setting position of the high-temperature resistant temporary sealing agent is close to the boundary between the reduction-drying zone and the heating-desorption zone.

[0012] In the above-mentioned method for dry distillation and methane production enhancement of gas-rich coal seams by injecting air for self-heat generation, when injecting air in step S3, the pressure of the injected air is adjusted by a surface pressure control device.

[0013] In the above-mentioned method for dry distillation and methane production increase of gas-rich coal seams by injecting air for self-heating, when the air reacts and burns with the oil-rich coal seams in step S3, the high-temperature gas released by the combustion includes CO 2 gas, CO gas and H 2 O gas.

[0014] The present invention also discloses a gas-containing oil-rich coal seam dry distillation and methane production enhancement system for realizing the above-mentioned method by injecting air for self-heating, comprising a vertical injection well and a horizontal recovery well arranged in the oil-rich coal seam, a fracture network formed by staged fracturing of the oil-rich coal seam, and a combustion working face formed by igniting the coal seam in each vertical well branch of the vertical injection well and continuously injecting air, and the injected air reacts and burns with the oil-rich coal seam; a plurality of vertical well branches are arranged at the bottom of the vertical injection well, and a high-temperature resistant temporary sealing agent is arranged in the horizontal recovery well; when the injected air reacts and burns with the oil-rich coal seam, a reduction-drying zone, a heating-desorption zone, a CO 2 -desorption zone, a heat transfer zone, and a heat transfer zone are formed in the coal seam from near to far from the combustion working face through matrix heat transfer and convection heat transfer.2 Replacement desorption zone.

[0015] In the above-mentioned air-injected self-heating gas-rich coal seam distillation and methane production enhancement system, the vertical injection well is arranged on the downward side of the oil-rich coal seam; the horizontal recovery well is arranged on the upward side of the oil-rich coal seam, and its horizontal section is located at the bottom of the oil-rich coal seam, and the end extends downward to the vertical well branch.

[0016] In the above-mentioned gas-rich coal seam dry distillation and methane production enhancement system with air injection and self-heating, the high-temperature resistant temporary sealing agent is arranged near the boundary between the reduction-dry distillation zone and the heating-desorption zone.

[0017] Technical effects and advantages of the present invention:

[0018] 1. The method for dry distillation and methane production increase of gas-rich coal seams by injecting air for self-heating provided by the present invention comprises a plurality of vertical well branches arranged at the bottom of the vertical injection well, which can ensure the formation of a wider combustion working surface; the coal seams are ignited in each vertical well branch of the vertical injection well, and air is continuously injected, the injected air reacts and burns with the oil-rich coal seams to form a combustion working surface, the combustion releases high-temperature gas, the high-temperature gas flows in the coal seams through the fracture network, and forms a reduction-dry distillation zone, a heating-desorption zone, a CO 2 -desorption zone from near to far from the combustion working surface in the coal seams through matrix heat transfer and convection heat transfer. 2 Replacement desorption zone; the way to control hot gas convection is: a high-temperature resistant temporary sealing agent is set in the horizontal hole of the horizontal recovery well, which is dynamically moved backward with the advancement of the combustion working face, and is set near the boundary between the reduction-retorting zone and the heating-desorption zone, so as to promote the high-temperature gas to flow in the coal seam through the fracture network, thereby expanding the action range of the reduction-retorting zone and the heating-desorption zone; the coal seam in the reduction-retorting zone is pyrolyzed to produce tar and coal gas, and the produced tar is driven by the high-temperature gas and migrated to the horizontal recovery well 2 through the fracture network; the heating-desorption zone heats the coal seam by convection of high-temperature coal gas and combustion gas, so that the methane in the coal pores is mainly physically desorbed; CO 2 Replacement desorption zone to achieve cooling of CO 2 CH 4 Competitive adsorption to achieve partial CH 4 Physical desorption: Based on the self-heated distillation of coal seams, it can promote the desorption and migration of methane in remote coal seams through thermal radiation, solving the problem of high external energy consumption for in-situ distillation of oil-rich coal and difficulty in producing methane in coal, which is crucial to achieving green and low-carbon development of oil-rich coal.

[0019] 2. The gas-rich coal seam dry distillation and methane production enhancement system with air injection and self-heating provided by the present invention is easy to implement. It can promote the desorption and migration of methane in remote coal seams through thermal radiation on the basis of dry distillation based on the self-heating of coal seam combustion, thus solving the problems of large external energy consumption for in-situ dry distillation of oil-rich coal and difficulty in producing methane in coal, which is crucial to achieving green and low-carbon development of oil-rich coal. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flowchart of the method for dry distillation and methane production increase of gas-rich coal seam by injecting air to generate heat automatically according to the present invention;

[0021] Figure 2 It is a three-dimensional schematic diagram of the gas-rich coal seam dry distillation and methane production enhancement system with air injection and autothermal generation according to the present invention;

[0022] Figure 3 It is a cross-sectional schematic diagram of the gas-rich coal seam dry distillation and methane production enhancement system with air injection and self-heating according to the present invention.

[0023] Reference numerals

[0024] 1—injection well; 2—recovery well; 3—vertical well branch;

[0025] 4—combustion working surface; 5—reduction-pyrolysis zone; 6—heating-desorption zone;

[0026] 7—CO2 displacement desorption zone; 8—crack network; 9—high temperature resistant temporary sealing agent. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the embodiments given in the accompanying drawings.

[0028] Example 1

[0029] See also Figure 1 to Figure 3 As shown, a method for dry distillation and methane production increase of gas-rich coal seams by injecting air to generate heat automatically comprises the following steps:

[0030] Step S1, a vertical injection well 1 and a horizontal recovery well 2 are respectively set in the oil-rich coal seam, and a plurality of vertical well branches 3 are set at the bottom of the vertical injection well 1 to ensure the formation of a wider combustion working surface 4, and a high-temperature resistant temporary sealing agent 9 is set in the horizontal recovery well 2;

[0031] Step S2, performing staged fracturing on the oil-rich coal seam to form a fracture network 8 to enhance air permeability;

[0032] Step S3, ignite the coal seam in each vertical well branch 3 of the vertical injection well 1, and continuously inject air, the injected air reacts with the oil-rich coal seam to burn, forming a combustion working face 4, the combustion releases high-temperature gas, the high-temperature gas flows in the coal seam through the fracture network 8, and forms a reduction-drying zone 5, a heating-desorption zone 6, and a CO 2-desorption zone 7 from near to far in the coal seam through matrix heat transfer and convection heat transfer. 2 displacement desorption zone 7;

[0033] Step S4, when the combustion working face 4 advances toward the recovery well, the high temperature resistant temporary sealing agent 9 naturally expands due to combustion, gasification and other conditions, making the plugging of the high temperature resistant temporary sealing agent 9 ineffective. At this time, the high temperature resistant temporary sealing agent 9 is injected through the pipeline injection method to form a new plugging at the new boundary position of the horizontal hole section, ensuring that the plugging position moves backward dynamically with the advancement of the combustion work;

[0034] Step S5: The coal seam in the reduction-drying zone 5 is pyrolyzed to produce tar and coal gas. The produced tar is driven by the high-temperature gas and migrated to the horizontal recovery well 2 through the fracture network 8; the heating-desorption zone 6 heats the coal seam by convection of high-temperature coal gas and combustion gas, so that the methane in the coal pores is mainly physically desorbed; CO 2 Replacement desorption zone 7 to achieve cooling of CO 2 CH 4 Competitive adsorption to achieve partial CH 4 Physical desorption.

[0035] In this embodiment, the vertical injection well 1 is set on the downward side of the oil-rich coal seam; the horizontal recovery well 2 is set on the upward side of the oil-rich coal seam, and its horizontal section is located at the bottom of the oil-rich coal seam, and the end extends downward to the vertical well branch 3.

[0036] In this embodiment, when the high-temperature resistant temporary sealing agent 9 is set in the horizontal recovery well 2 in step S1, the setting position of the high-temperature resistant temporary sealing agent 9 is close to the boundary between the reduction-retorting zone 5 and the heating-desorption zone 6 to ensure that the high-temperature gas flows in the coal seam through the fracture network 8, thereby improving the heat exchange efficiency between the coal seam and the high-temperature gas, thereby expanding the scope of action of the reduction-retorting zone 5 and the heating-desorption zone 6.

[0037] In this embodiment, when injecting air in step S3, the pressure of the injected air is adjusted by a ground pressure control device.

[0038] In specific implementation, the degree to which the surface pressure control device adjusts the pressure of the injected air is determined according to the gas flow and composition of the recovery well.

[0039] In this embodiment, when the air reacts and burns with the oil-rich coal seam in step S3, the high-temperature gas released by the combustion includes CO 2 gas, CO gas and H 2 O gas.

[0040] Example 2

[0041] See also Figure 2 and Figure 3 As shown, the gas-rich coal seam dry distillation and methane production enhancement system with air injection self-heating in this embodiment comprises a vertical injection well 1 and a horizontal recovery well 2 arranged in the oil-rich coal seam, a fracture network 8 formed by staged fracturing of the oil-rich coal seam, and a combustion working face 4 formed by igniting the coal seam in each vertical well branch 3 of the vertical injection well 1 and continuously injecting air, and the injected air reacts and burns with the oil-rich coal seam; a plurality of vertical well branches 3 are arranged at the bottom of the vertical injection well 1 to ensure the formation of a wider combustion working face 4; a high-temperature resistant temporary sealing agent 9 is arranged in the horizontal recovery well 2; when the injected air reacts and burns with the oil-rich coal seam, a reduction-drying zone 5, a heating-desorption zone 6, a CO 2-desorption zone 7 and a CO 2-desorption zone 8 are formed in the coal seam from near to far from the combustion working face 4 through matrix heat transfer and convection heat transfer. 2 Displacement desorption zone 7.

[0042] In this embodiment, the vertical injection well 1 is set on the downward side of the oil-rich coal seam; the horizontal recovery well 2 is set on the upward side of the oil-rich coal seam, and its horizontal section is located at the bottom of the oil-rich coal seam, and the end extends downward to the vertical well branch 3.

[0043] In this embodiment, the high-temperature resistant temporary sealing agent 9 is arranged near the boundary between the reduction-retorting zone 5 and the heating-desorption zone 6 to ensure that the high-temperature gas flows in the coal seam through the fracture network 8, thereby improving the heat exchange efficiency between the coal seam and the high-temperature gas, thereby expanding the scope of action of the reduction-retorting zone 5 and the heating-desorption zone 6.

[0044] In summary, the present invention can promote the desorption and migration of methane in remote coal seams through thermal radiation on the basis of dry distillation of coal seam combustion self-heat, thereby solving the problem of high external energy consumption for in-situ dry distillation of oil-rich coal and difficulty in producing methane in coal.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for dry distillation and methane production increase of gas-rich coal seams by injecting air for autothermal heat generation, characterized in that: The method comprises the following steps: Step S1, respectively setting a vertical injection well (1) and a horizontal recovery well (2) in the oil-rich coal seam, setting a plurality of vertical well branches (3) at the bottom of the vertical injection well (1), and setting a high-temperature resistant temporary sealing agent (9) in the horizontal recovery well (2); Step S2, performing staged fracturing on the oil-rich coal seam to form a fracture network (8); Step S3, igniting the coal seam in each vertical well branch (3) of the vertical injection well (1), and continuously injecting air, the injected air reacts with the oil-rich coal seam and burns to form a combustion working surface (4), the combustion releases high-temperature gas, the high-temperature gas flows in the coal seam through the fracture network (8), and forms a reduction-drying zone (5), a heating-desorption zone (6), and a CO2 replacement desorption zone (7) in the coal seam from near to far from the combustion working surface (4) through matrix heat transfer and convection heat transfer; Step S4, when the combustion working face (4) advances toward the recovery well, the high temperature resistant temporary sealing agent (9) fails to seal, and at this time, the high temperature resistant temporary sealing agent (9) is injected through the pipeline injection method to form a new seal at the new boundary position of the horizontal hole section, ensuring that the sealing position moves backward dynamically as the combustion work advances; In step S5, the coal seam in the reduction-pyrolysis zone (5) is pyrolyzed to produce tar and coal gas. The produced tar is driven by the high-temperature gas and transported to the horizontal recovery well (2) through the fracture network (8); the heating-desorption zone (6) heats the coal seam by convection of high-temperature coal gas and combustion gas, so that the methane in the coal pores is mainly physically desorbed; the CO2 displacement desorption zone (7) realizes the competitive adsorption of the cooled CO2 with the CH4 in the coal pores, so as to realize the physical desorption of part of the CH4.

2. The method for dry distillation and methane production increase of gas-rich coal seams by injecting air for autothermal generation according to claim 1, characterized in that: The vertical injection well (1) is arranged on the downward side of the oil-rich coal seam; the horizontal recovery well (2) is arranged on the upward side of the oil-rich coal seam, and its horizontal section is located at the bottom of the oil-rich coal seam, and the end extends downwardly toward the vertical well branch (3).

3. The method for dry distillation and methane production increase of gas-rich coal seams by injecting air for autothermal generation according to claim 1, characterized in that: When the high temperature resistant temporary sealing agent (9) is arranged in the horizontal recovery well (2) in step S1, the high temperature resistant temporary sealing agent (9) is arranged close to the boundary between the reduction-retorting zone (5) and the heating-desorption zone (6).

4. The method for dry distillation and methane production increase of gas-rich coal seams by injecting air for autothermal generation according to claim 1, characterized in that: When injecting air in step S3, the pressure of the injected air is adjusted by a ground pressure control device.

5. The method for dry distillation and methane production increase of gas-rich coal seams by injecting air for autothermal generation according to claim 1, characterized in that: When the air reacts and burns with the oil-rich coal seam in step S3, the high-temperature gases released by the combustion include CO2 gas, CO gas and H2O gas.

6. A system for dry distillation and methane production enhancement of gas-rich coal seams by injecting air for self-heating according to the method of claim 1, characterized in that: The invention comprises a vertical injection well (1) and a horizontal recovery well (2) arranged in an oil-rich coal seam, a fracture network (8) formed by staged fracturing of the oil-rich coal seam, and a combustion working face (4) formed by igniting the coal seam at each vertical well branch (3) of the vertical injection well (1) and continuously injecting air, wherein the injected air reacts and burns with the oil-rich coal seam; a plurality of vertical well branches (3) are arranged at the bottom of the vertical injection well (1), and a high-temperature resistant temporary sealing agent (9) is arranged in the horizontal recovery well (2); when the injected air reacts and burns with the oil-rich coal seam, a reduction-drying zone (5), a heating-desorption zone (6), and a CO2 replacement desorption zone (7) are formed in the coal seam from near to far from the combustion working face (4) through matrix heat transfer and convection heat transfer.

7. The system for dry distillation and methane production enhancement of gas-rich coal seams with air injection and autothermal generation according to claim 6 is characterized in that: The vertical injection well (1) is arranged on the downward side of the oil-rich coal seam; the horizontal recovery well (2) is arranged on the upward side of the oil-rich coal seam, and its horizontal section is located at the bottom of the oil-rich coal seam, and the end extends downwardly toward the vertical well branch (3).

8. The system for dry distillation and methane production enhancement of gas-rich coal seams with air injection and autothermal generation according to claim 6 is characterized by: The high temperature resistant temporary sealing agent (9) is arranged near the boundary between the reduction-drying zone (5) and the heating-desorption zone (6).

Images