A method for increasing production of coalbed methane reservoir by fracturing and displacement

Abstract

A method for increasing the production of coalbed methane reservoir by fracturing and displacement, comprising the steps of drilling a horizontal fracturing borehole for roof rock formation on one side of an original fracturing borehole toward the roof rock formation; drilling a horizontal fracturing borehole for bottom rock formation toward the bottom rock formation on the other side of the original fracturing borehole; performing hydraulic fracturing operations on the horizontal fracturing borehole for roof rock formation and the horizontal fracturing borehole for bottom rock formation respectively to generate multiple clusters of artificial fractures; injecting CO2 / N2 gas into the artificial fractures in the roof rock formation for pressurization to achieve the first pressurization displacement operation of the coalbed methane reservoir; exploring the reserves of coalbed methane in the bottom rock formation and judging the extraction conditions according to the reserves; if the extraction conditions are suitable, directly using the horizontal fracturing borehole for bottom rock formation to extract the coalbed methane in the bottom rock formation; if the extraction conditions are not suitable, injecting CO2 / N2 gas into the artificial fractures in the bottom rock formation for pressurization to achieve the secondary pressurization displacement operation of the coalbed methane reservoir. This method has a significant effect on increasing the production of coalbed methane.

Description

Technical Field

[0001] The invention belongs to the technical field of efficient coalbed methane exploitation, and in particular relates to a coalbed methane reservoir fracturing displacement production increasing method. Background Art

[0002] my country has abundant reserves of coalbed methane resources, and efficient and high-yield mining operations are of great strategic significance for reducing my country's energy supply security. However, due to the dense formation rock and low permeability of coalbed methane reservoirs, their natural production capacity is far from meeting the needs of industrial development. A series of production-increasing measures, such as fracturing transformation, must be implemented to realize its industrial utilization process.

[0003] At present, hydraulic fracturing technology, as the most commonly used means of increasing the production of coalbed methane reservoirs, has been widely used around the world. It injects high-pressure water into the reservoir to create cracks in the formation rock, thereby increasing the permeability of the coal seam and the production of coalbed methane. However, as the mining time continues to increase, the formation energy gradually decays, and the production of fracturing wells also shows a rapid downward trend. In order to maintain the production capacity of a single well, it is often necessary to carry out secondary or even multiple transformation operations, which undoubtedly increases the cost and technical difficulty of mining.

[0004] In order to solve the technical problems of decreased production capacity and insufficient subsequent production after coalbed methane reservoir fracturing, it is urgent to innovate the existing coalbed methane extraction methods so as to improve the fracturing effect by developing new extraction plans and optimizing fracturing plans, thereby achieving the goal of increasing coalbed methane production and efficiency.

[0005] To sum up, efficient and high-yield exploitation of coalbed methane is an important task currently facing us. It requires the innovation and integration of methods and technologies to achieve increased production and efficiency of coalbed methane, thus injecting new impetus into the sustainable development of my country's energy industry. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for increasing production by fracturing and displacement of coalbed methane reservoirs. The method has a simple operation process, low implementation cost, and significant effect on the displacement and production increase of coalbed methane. It can solve the problem that as the mining of underground coalbed methane progresses, the original gas density gradually decreases and the gas pressure decays, resulting in difficulty in extraction and subsequent decline in production. At the same time, it can provide reliable technical support for efficient and high-yield mining operations of coalbed methane.

[0007] In order to achieve the above object, the present invention provides a method for increasing the production of coalbed methane reservoir by fracturing and displacement, comprising the following steps:

[0008] Step 1: Drilling a horizontal fracturing well in the roof rock formation;

[0009] After selecting the original fracturing borehole with decreased coalbed methane production in the original well field, select a suitable position on the ground on one side of the original fracturing borehole, drill a new horizontal fracturing borehole from the ground to the roof rock formation, that is, the roof rock formation horizontal fracturing borehole, and ensure that the drilling direction of the horizontal well section of the roof rock formation horizontal fracturing borehole is toward the original fracturing borehole;

[0010] Step 2: drilling a horizontal fracturing borehole well in the bottom rock formation;

[0011] Select a suitable location on the ground on the other side of the original fracturing drilling well, drill a new horizontal fracturing drilling well from the ground to the bottom rock formation, that is, the bottom rock formation horizontal fracturing drilling well, and ensure that the drilling direction of the horizontal well section of the bottom rock formation horizontal fracturing drilling well is also towards the original fracturing drilling well;

[0012] Step 3: Perform hydraulic fracturing operations on the top rock layer and the bottom rock layer respectively;

[0013] High-pressure water is continuously pumped into the horizontal fracturing drilling well of the roof rock formation and the horizontal fracturing drilling well of the bottom rock formation through the fracturing equipment on the ground, and the roof rock formation and the bottom rock formation are hydraulically fractured by the high-pressure water, so as to generate multiple clusters of artificial fractures in the length direction of the horizontal well section of the horizontal fracturing drilling well of the roof rock formation and the horizontal fracturing drilling well of the bottom rock formation;

[0014] Step 4: Carry out the first pressure displacement operation;

[0015] After the hydraulic fracturing of the roof stratum is completed, CO2 / N2 gas is injected into the artificial fractures in the roof stratum through the horizontal fracturing drilling well of the roof stratum for pressurization. In this process, the horizontal fracturing drilling well of the roof stratum is used as a pressure hedge well of the original fracturing drilling well. On the one hand, the strong adsorption of coalbed methane is utilized to adsorb the coalbed methane in the roof stratum through the injected CO2 / N2 gas. On the other hand, the environmental pressure of the original coalbed methane reservoir is gradually increased by the continuous injection of CO2 / N2 gas, so as to realize the first pressurized displacement operation of the coalbed methane reservoir and increase the extraction output of the original fracturing drilling well. When the environmental pressure of the coalbed methane reservoir reaches the mining requirement, the extraction operation of coalbed methane continues to be carried out through the original fracturing drilling well.

[0016] Step 5: Determine the mining conditions of the floor rock layer;

[0017] Through the detection equipment on the ground, in conjunction with the horizontal fracturing drilling well of the bottom rock formation, the reserves of coalbed methane in the bottom rock formation are explored, and the extraction conditions are judged according to the reserves; if the extraction conditions are suitable, the horizontal fracturing drilling well of the bottom rock formation is directly used to extract the coalbed methane in the bottom rock formation; if the extraction conditions are not suitable, step six is ​​executed;

[0018] Step 6: Perform secondary pressure displacement operation;

[0019] CO2 / N2 gas is injected into the artificial fractures in the bottom rock formation through the horizontal fracturing drilling well of the bottom rock formation for pressurization. In this process, the horizontal fracturing drilling well of the bottom rock formation is used as a pressure offset well of the original fracturing drilling well. On the one hand, the strong adsorption of coalbed methane is utilized to adsorb the coalbed methane in the bottom rock formation through the injected CO2 / N2 gas. On the other hand, the environmental pressure of the original coalbed methane reservoir is gradually increased by the continuous injection of CO2 / N2 gas, thereby realizing the secondary pressurization displacement operation of the coalbed methane reservoir and further increasing the extraction output of the original fracturing drilling well. When the environmental pressure of the coalbed methane reservoir reaches the mining requirement, the extraction operation of coalbed methane continues to be carried out through the original fracturing drilling well.

[0020] Furthermore, in order to prevent the diffusion of coalbed methane and ensure the subsequent coalbed methane extraction effect, during the fracturing process in step three, the fracture height control technology is used to control the expansion height of the cracks in the roof rock formation to not exceed the thickness of the roof rock formation, and control the expansion height of the cracks in the bottom rock formation to not exceed the thickness of the bottom rock formation, so as to prevent the cracks from extending into the coalbed methane reservoir.

[0021] Furthermore, in order to prevent the cracks in the roof rock formation from connecting with the cracks in the coalbed methane reservoir to form a short-circuit channel, so as to ensure the adsorption effect of coalbed methane and the gas injection and pressurization displacement effect, during the injection of CO2 / N2 gas in step four, the injection pressure of CO2 / N2 gas is controlled to be higher than the pore pressure of the roof rock formation and lower than the extension pressure of the artificial cracks in the roof rock formation.

[0022] Furthermore, in order to prevent the cracks in the roof rock formation from connecting with the cracks in the coalbed methane reservoir to form a short-circuit channel, so as to ensure the adsorption effect of coalbed methane and the gas injection and pressurization displacement effect, during the injection of CO2 / N2 gas in step six, the injection pressure of CO2 / N2 gas is controlled to be higher than the pore pressure of the bottom rock formation and lower than the extension pressure of the artificial cracks in the bottom rock formation.

[0023] Furthermore, in order to ensure the effect of displacement and increased production, in step 2, the distances from the vertical well section of the horizontal fracturing drilling well of the bottom plate rock formation and the vertical well section of the horizontal fracturing drilling well of the top plate rock formation to the original fracturing drilling well are equal, and the horizontal well section of the horizontal fracturing drilling well of the bottom plate rock formation and the horizontal well section of the horizontal fracturing drilling well of the top plate rock formation extend in a direction approaching each other, and at the same time, the distance from the end of the horizontal well section of the horizontal fracturing drilling well of the bottom plate rock formation to the original fracturing drilling well is equal to the distance from the end of the horizontal well section of the horizontal fracturing drilling well of the top plate rock formation to the original fracturing drilling well.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] First, the present invention combines hydraulic fracturing technology with CO2 / N2 displacement technology. The hydraulic fracturing technology can fully improve the permeability of coalbed methane reservoirs, while the CO2 / N2 displacement technology can effectively improve the extraction rate of coalbed methane. Therefore, by effectively combining these two technologies, not only the permeability of coalbed methane coal seams is improved, but also the efficient extraction of coalbed methane is achieved. Specifically, the present invention uses hydraulic fracturing technology to establish fracture channels in different rock formations, fully communicating the pore channels between the coal seam and the top rock formation and the bottom rock formation, so that the coalbed methane that was originally difficult to mine can be released. Then, two groups of "pressure hedging wells" were formed by the horizontal fracturing drilling wells in the roof rock stratum and the horizontal fracturing drilling wells in the bottom rock stratum and the original fracturing drilling wells, and effective seepage channels were formed between the coal seam and the roof rock stratum and the bottom rock stratum. In this way, the CO2 / N2 gas injected into the roof rock stratum and the bottom rock stratum from the horizontal fracturing drilling wells in the roof rock stratum and the horizontal fracturing drilling wells in the bottom rock stratum respectively can smoothly enter the coal seam through the hydraulic fracturing cracks and can be fully diffused in the coal seam, effectively displacing the coalbed methane in the coal seam and realizing the incremental mining of coalbed methane. The horizontal well sections of the horizontal fracturing drilling wells in the roof strata and the horizontal well sections of the horizontal fracturing drilling wells in the floor strata are extended close to the direction of the original fracturing drilling wells, which is conducive to the migration of the displaced coalbed methane in the direction close to the original fracturing drilling wells. At the same time, it is convenient to use the CO2 / N2 gas added to the roof strata and the floor strata to increase the environmental pressure of the coalbed methane reservoir, which is conducive to the continued exploitation of the coalbed methane after displacement using the original fracturing drilling wells.

[0026] Secondly, during the coalbed methane mining process, the underground space will gradually increase as the coalbed methane is extracted. The present invention makes full use of this feature, injects CO2 into these underground spaces, and realizes the geological storage of CO2. At the same time, the complex cracks formed in the rock formation by hydraulic fracturing technology not only increase the storage space of CO2, but also improve the efficiency of storage. In addition, in the process of CO2 entering the coal seam from the horizontal fracturing drilling well of the bottom rock formation, the remaining coalbed methane in the coal seam can be gradually displaced to the original fracturing drilling well of the coal seam, further improving the extraction rate of coalbed methane.

[0027] Furthermore, the application of the present invention not only helps to solve the technical problems of coalbed methane extraction, but also has important significance for promoting the green and sustainable development of the energy industry. With the continuous growth of global energy demand and the increasing awareness of environmental protection, finding efficient and environmentally friendly energy extraction and utilization methods has become an urgent need for the development of the industry. The present invention combines hydraulic fracturing technology with CO2 displacement technology, which not only improves the extraction rate of coalbed methane, but also realizes the geological storage of CO2, reduces greenhouse gas emissions, and provides strong technical support for the green transformation of the energy industry.

[0028] In summary, the present invention has shown significant beneficial effects in the field of coalbed methane mining. It not only improves the extraction rate and production efficiency of coalbed methane, but also achieves the dual goals of environmental protection and benefits through the geological storage of CO2. At the same time, the application of the present invention also provides new ideas and directions for the green and sustainable development of the energy industry. In the future development, the present invention will be widely used and promoted in more fields, making greater contributions to my country's energy industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of a horizontal fracturing drilling well of a roof rock formation in the method of the present invention;

[0030] Figure 2 is a schematic diagram of a horizontal fracturing drilling well of a bottom plate rock formation in the method of the present invention;

[0031] Figure 3 is a schematic diagram of hydraulic fracturing in the method of the present invention;

[0032] Figure 4 Schematic diagram of injecting CO2 / N2 gas into the roof rock layer in the method of the present invention;

[0033] Figure 5 It is a schematic diagram of extraction from a horizontal fracturing borehole well in a bottom rock formation in the method of the present invention;

[0034] Figure 6 It is a schematic diagram of injecting CO2 / N2 gas into the bottom rock layer in the method of the present invention.

[0035] In the figure: 1. artificial fracture, 2. original fracturing borehole, 3. horizontal fracturing borehole in roof rock formation, 4. horizontal fracturing borehole in bottom rock formation, 5. overburden, 6. roof rock formation, 7. coalbed methane reservoir, 8. bottom rock formation, 9. CO2 / N2 gas, 10. coalbed methane, 11. ground. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings.

[0037] The present invention provides a method for increasing the production of coalbed methane reservoir by fracturing displacement. First, on the basis of the original fracturing borehole 2, a horizontal fracturing borehole 3 for drilling the top plate rock layer and a horizontal fracturing borehole 4 for drilling the bottom plate rock layer are drilled in the top plate rock layer 6 and the bottom plate rock layer 8, respectively, to form two groups of "pressure hedging wells" with the original fracturing borehole 2 in the coal seam. Then, hydraulic fracturing operations are performed in the horizontal fracturing borehole 3 for the top plate rock layer and the horizontal fracturing borehole 4 for the bottom plate rock layer, respectively, to form complex large-scale fractures in the top plate rock layer 6 and the bottom plate rock layer 8. Then, two extraction schemes are adopted. Solution 1: Use the horizontal fracturing drilling well 3 of the roof rock formation as a "pressure hedging well" and inject CO2 / N2 gas 9 into the horizontal fracturing drilling well 3 of the roof rock formation. On the one hand, the strong adsorption of coalbed methane 10 (main component CH4) on CO2 / N2 gas 9 can be used to more effectively extract coalbed methane 10. On the other hand, the injected gas can be used to pressurize the coalbed methane reservoir 7, so that the original fracturing drilling well 2 can achieve the purpose of increasing production. Solution 2: Detect the reserves of coalbed methane 10 in the bottom rock formation 8 to determine whether the extraction conditions are suitable. If suitable, directly extract the coalbed methane 10 in the bottom rock formation 8. If not suitable, also drill the horizontal fracturing drilling well 4 of the bottom rock formation as a "pressure hedging well", and inject CO2 / N2 gas 9 into the horizontal fracturing drilling well 4 of the bottom rock formation. Use the injected gas to increase the gas pressure of the original coalbed methane reservoir environment, so that the original fracturing drilling well 2 can achieve the purpose of increasing production.

[0038] Specifically include the following steps:

[0039] Step 1: drilling a horizontal fracturing borehole well 3 in the roof rock formation;

[0040] like Figure 1 As shown, after selecting the original fracturing borehole 2 with decreased coalbed methane 10 production in the original well field, a suitable position is selected on the ground 11 on one side of the original fracturing borehole 2, and a new horizontal fracturing borehole is drilled from the ground 11 to the roof rock layer 6. The horizontal fracturing borehole passes through the overburden 5 and enters the roof rock layer 6, that is, the roof rock layer horizontal fracturing borehole 3, and ensure that the drilling direction of the horizontal well section of the roof rock layer horizontal fracturing borehole 3 is toward the original fracturing borehole 2;

[0041] Step 2: drilling a horizontal fracturing borehole well 4 in the bottom rock formation;

[0042] like Figure 2 As shown, a suitable position is selected on the ground 11 on the other side of the original fracturing borehole 2, and a new horizontal fracturing borehole is drilled from the ground 11 to the bottom rock layer 8. The horizontal fracturing borehole sequentially passes through the overburden 5 and the coalbed methane reservoir 7 to the bottom rock layer 8, that is, the bottom rock layer horizontal fracturing borehole 4, and ensures that the drilling direction of the horizontal well section of the bottom rock layer horizontal fracturing borehole 4 is also toward the original fracturing borehole 2;

[0043] Step 3: Perform hydraulic fracturing operations on the top rock layer 6 and the bottom rock layer 8 respectively;

[0044] like Figure 3 As shown, a high-pressure water flow is continuously pumped into the horizontal fracturing drilling well 3 for the top plate rock formation and the horizontal fracturing drilling well 4 for the bottom plate rock formation through the fracturing equipment on the ground 11, and the top plate rock formation 6 and the bottom plate rock formation 8 are hydraulically fractured by the high-pressure water flow, thereby generating a plurality of multi-cluster artificial fractures 1 in the length direction of the horizontal well section of the horizontal fracturing drilling well 3 for the top plate rock formation and the horizontal fracturing drilling well 4 for the bottom plate rock formation;

[0045] Step 4: Carry out the first pressure displacement operation;

[0046] like Figure 4 As shown, after the hydraulic fracturing of the roof rock formation 6 is completed, CO2 / N2 gas 9 is injected into the artificial fracture 1 in the roof rock formation 6 through the roof rock formation horizontal fracturing borehole 3 for pressurization. In this process, the roof rock formation horizontal fracturing borehole 3 is used as a pressure offset well of the original fracturing borehole 2. On the one hand, the strong adsorption of the coalbed methane 10 is utilized to adsorb the coalbed methane 10 in the roof rock formation 6 through the injected CO2 / N2 gas 9. On the other hand, the environmental pressure of the original coalbed methane reservoir 7 is gradually increased by the continuously injected CO2 / N2 gas 9, so as to realize the first pressurization displacement operation of the coalbed methane reservoir 7 and increase the extraction output of the original fracturing borehole 2. When the environmental pressure of the coalbed methane reservoir 7 reaches the mining requirement, the extraction operation of the coalbed methane 10 is continued through the original fracturing borehole 2.

[0047] Step 5: Determine the mining conditions of the bottom rock layer 8;

[0048] like Figure 5 As shown, the reserves of the coalbed methane 10 in the bottom rock layer 8 are explored by the detection equipment on the ground 11 in cooperation with the horizontal fracturing drilling well 4 of the bottom rock layer, and the extraction conditions are judged according to the reserves; if the extraction conditions are suitable, the coalbed methane 10 in the bottom rock layer 8 is directly extracted by the horizontal fracturing drilling well 4 of the bottom rock layer; if the extraction conditions are not suitable, step six is ​​executed;

[0049] Step 6: Perform secondary pressure displacement operation;

[0050] like Figure 6As shown, CO2 / N2 gas 9 is injected into the artificial fracture 1 in the bottom rock formation 8 through the bottom rock horizontal fracturing drilling well 4 for pressurization. In this process, the bottom rock horizontal fracturing drilling well 4 is used as a pressure offset well for the original fracturing drilling well 2. On the one hand, the strong adsorption of coalbed methane 10 is utilized to adsorb the coalbed methane 10 in the bottom rock formation 8 through the injected CO2 / N2 gas 9. On the other hand, the environmental pressure of the original coalbed methane reservoir 7 is gradually increased by the continuously injected CO2 / N2 gas 9, thereby realizing the secondary pressurization displacement operation of the coalbed methane reservoir 7, and promoting the further increase of the extraction output of the original fracturing drilling well 2. When the environmental pressure of the coalbed methane reservoir 7 reaches the mining requirement, the extraction operation of the coalbed methane 10 continues to be carried out through the original fracturing drilling well 2.

[0051] In order to prevent the diffusion of coalbed methane and ensure the subsequent coalbed methane extraction effect, during the fracturing process in step three, the fracture height control technology is adopted to control the expansion height of the cracks in the roof rock layer 6 not to exceed the thickness of the roof rock layer 6, and control the expansion height of the cracks in the bottom rock layer 8 not to exceed the thickness of the bottom rock layer 8, so as to prevent the cracks from extending into the coalbed methane reservoir 7, and then connecting with the fracture network of the original fracturing drilling well 2 to form a short-circuit channel, thereby causing the diffusion of coalbed methane.

[0052] In order to prevent the cracks in the roof rock formation from connecting with the cracks in the coalbed methane reservoir to form a short-circuit channel, so as to ensure the adsorption effect of coalbed methane and the gas injection and pressurization displacement effect, during the injection of CO2 / N2 gas 9 in step four, the injection pressure of CO2 / N2 gas 9 is controlled to be higher than the pore pressure of the roof rock formation 6 and lower than the extension pressure of the artificial fractures 1 in the roof rock formation 6.

[0053] In order to prevent the cracks in the roof rock formation from connecting with the cracks in the coalbed methane reservoir to form a short-circuit channel, so as to ensure the adsorption effect of coalbed methane and the gas injection and pressurization displacement effect, during the injection of CO2 / N2 gas 9 in step six, the injection pressure of CO2 / N2 gas 9 is controlled to be higher than the pore pressure of the bottom rock formation 8 and lower than the extension pressure of the artificial fractures 1 in the bottom rock formation 8.

[0054] In order to ensure the effect of displacement and increased production, in step 2, the distances from the vertical well section of the bottom rock stratum horizontal fracturing drilling well 4 and the vertical well section of the top rock stratum horizontal fracturing drilling well 3 to the original fracturing drilling well 2 are equal, and the horizontal well section of the bottom rock stratum horizontal fracturing drilling well 4 and the horizontal well section of the top rock stratum horizontal fracturing drilling well 3 extend in a direction approaching each other, and at the same time, the distance from the end of the horizontal well section of the bottom rock stratum horizontal fracturing drilling well 4 to the original fracturing drilling well 2 is equal to the distance from the end of the horizontal well section of the top rock stratum horizontal fracturing drilling well 3 to the original fracturing drilling well 2.

[0055] The present invention combines hydraulic fracturing technology with CO2 / N2 displacement technology. The hydraulic fracturing technology can fully improve the permeability of coalbed methane reservoirs, while the CO2 / N2 displacement technology can effectively improve the extraction rate of coalbed methane. Therefore, by effectively combining these two technologies, not only the permeability of coalbed methane coal seams is improved, but also the efficient extraction of coalbed methane is achieved. Specifically, the present invention uses hydraulic fracturing technology to establish fracture channels in different rock formations, fully communicating the pore channels between the coal seam and the roof rock formation and the bottom rock formation, so that the coalbed methane that was originally difficult to mine can be released. Then, two groups of "pressure hedging wells" were formed by the horizontal fracturing drilling wells in the roof rock stratum and the horizontal fracturing drilling wells in the bottom rock stratum and the original fracturing drilling wells, and effective seepage channels were formed between the coal seam and the roof rock stratum and the bottom rock stratum. In this way, the CO2 / N2 gas injected into the roof rock stratum and the bottom rock stratum from the horizontal fracturing drilling wells in the roof rock stratum and the horizontal fracturing drilling wells in the bottom rock stratum respectively can smoothly enter the coal seam through the hydraulic fracturing cracks and can be fully diffused in the coal seam, effectively displacing the coalbed methane in the coal seam and realizing the incremental mining of coalbed methane. The horizontal well sections of the horizontal fracturing drilling wells in the roof strata and the horizontal well sections of the horizontal fracturing drilling wells in the floor strata are extended close to the direction of the original fracturing drilling wells, which is conducive to the migration of the displaced coalbed methane in the direction close to the original fracturing drilling wells. At the same time, it is convenient to use the CO2 / N2 gas added to the roof strata and the floor strata to increase the environmental pressure of the coalbed methane reservoir, which is conducive to the continued exploitation of the coalbed methane after displacement using the original fracturing drilling wells.

[0056] Secondly, during the coalbed methane mining process, the underground space will gradually increase as the coalbed methane is extracted. The present invention makes full use of this feature, injects CO2 into these underground spaces, and realizes the geological storage of CO2. At the same time, the complex cracks formed in the rock formation by hydraulic fracturing technology not only increase the storage space of CO2, but also improve the efficiency of storage. In addition, in the process of CO2 entering the coal seam from the horizontal fracturing drilling well of the bottom rock formation, the remaining coalbed methane in the coal seam can be gradually displaced to the original fracturing drilling well of the coal seam, further improving the extraction rate of coalbed methane.

[0057] Furthermore, the application of the present invention not only helps to solve the technical problems of coalbed methane extraction, but also has important significance for promoting the green and sustainable development of the energy industry. With the continuous growth of global energy demand and the increasing awareness of environmental protection, finding efficient and environmentally friendly energy extraction and utilization methods has become an urgent need for the development of the industry. The present invention combines hydraulic fracturing technology with CO2 displacement technology, which not only improves the extraction rate of coalbed methane, but also realizes the geological storage of CO2, reduces greenhouse gas emissions, and provides strong technical support for the green transformation of the energy industry.

[0058] In summary, the present invention has shown significant beneficial effects in the field of coalbed methane mining. It not only improves the extraction rate and production efficiency of coalbed methane, but also achieves the dual goals of environmental protection and benefits through the geological storage of CO2. At the same time, the application of the present invention also provides new ideas and directions for the green and sustainable development of the energy industry. In the future development, the present invention will be widely used and promoted in more fields, making greater contributions to my country's energy industry.

Claims

1. A method for increasing the production of coalbed methane reservoir by fracturing and displacement, characterized in that: The steps include: Step 1: drilling a horizontal fracturing borehole well in the roof rock formation (3); After selecting an original fracturing borehole (2) with a decreased production of coalbed methane (10) in the original well field, a suitable position is selected on the ground (11) on one side of the original fracturing borehole (2), and a new horizontal fracturing borehole is drilled from the ground (11) to the roof rock layer (6), namely, the roof rock layer horizontal fracturing borehole (3), and it is ensured that the drilling direction of the horizontal well section of the roof rock layer horizontal fracturing borehole (3) is toward the original fracturing borehole (2); Step 2: drilling a horizontal fracturing borehole well in the bottom rock formation (4); Select a suitable position on the ground (11) on the other side of the original fracturing borehole (2), drill a new horizontal fracturing borehole from the ground (11) to the bottom rock layer (8), namely, the bottom rock layer horizontal fracturing borehole (4), and ensure that the drilling direction of the horizontal well section of the bottom rock layer horizontal fracturing borehole (4) is also toward the original fracturing borehole (2); Step 3: performing hydraulic fracturing operations on the top rock layer (6) and the bottom rock layer (8) respectively; Continuously pumping high-pressure water into the top rock stratum horizontal fracturing drilling well (3) and the bottom rock stratum horizontal fracturing drilling well (4) through the fracturing equipment on the ground (11), and using the high-pressure water flow to perform hydraulic fracturing operations on the top rock stratum (6) and the bottom rock stratum (8), respectively, to generate multiple clusters of artificial fractures (1) in the length direction of the horizontal well section of the top rock stratum horizontal fracturing drilling well (3) and the bottom rock stratum horizontal fracturing drilling well (4); Step 4: Carry out the first pressure displacement operation; After the hydraulic fracturing of the roof stratum (6) is completed, CO2 / N2 gas (9) is injected into the artificial fracture (1) in the roof stratum (6) through the roof stratum horizontal fracturing borehole (3) for pressurization. In this process, the roof stratum horizontal fracturing borehole (3) is used as a pressure offset well for the original fracturing borehole (2). On the one hand, the strong adsorption of coalbed methane (10) is utilized to adsorb the coalbed methane (10) in the roof stratum (6) through the injected CO2 / N2 gas (9). On the other hand, the environmental pressure of the original coalbed methane reservoir (7) is gradually increased by the continuously injected CO2 / N2 gas (9), thereby achieving the first pressurization displacement operation of the coalbed methane reservoir (7) and promoting the increase of the extraction output of the original fracturing borehole (2). When the environmental pressure of the coalbed methane reservoir (7) reaches the mining requirement, the extraction operation of the coalbed methane (10) is continued through the original fracturing borehole (2); Step 5: Determine the mining conditions of the bottom rock layer (8); Through the detection equipment on the ground (11), in cooperation with the horizontal fracturing drilling well (4) of the bottom rock layer, the reserves of the coalbed methane (10) in the bottom rock layer (8) are explored, and the extraction conditions are judged according to the reserves; if the extraction conditions are suitable, the coalbed methane (10) in the bottom rock layer (8) is directly extracted by using the horizontal fracturing drilling well (4) of the bottom rock layer; if the extraction conditions are not suitable, step six is ​​executed; Step 6: Perform secondary pressure displacement operation; CO2 / N2 gas (9) is injected into the artificial fracture (1) in the bottom rock layer (8) through the bottom rock layer horizontal fracturing drilling well (4) for pressurization. In this process, the bottom rock layer horizontal fracturing drilling well (4) is used as a pressure offset well for the original fracturing drilling well (2). On the one hand, the strong adsorption of coalbed methane (10) is utilized to adsorb the coalbed methane (10) in the bottom rock layer (8) through the injected CO2 / N2 gas (9). On the other hand, the environmental pressure of the original coalbed methane reservoir (7) is gradually increased by the continuously injected CO2 / N2 gas (9), thereby realizing a secondary pressurization displacement operation on the coalbed methane reservoir (7) and promoting a further increase in the extraction output of the original fracturing drilling well (2). When the environmental pressure of the coalbed methane reservoir (7) reaches the mining requirement, the extraction operation of the coalbed methane (10) is continued through the original fracturing drilling well (2).

2. A method for increasing production by fracturing and displacement of coalbed methane reservoirs according to claim 1, characterized in that: During the fracturing process in step three, a fracture height control technology is used to control the expansion height of the fractures in the top rock layer (6) to not exceed the thickness of the top rock layer (6), and to control the expansion height of the fractures in the bottom rock layer (8) to not exceed the thickness of the bottom rock layer (8), so as to prevent the fractures from extending into the coalbed methane reservoir (7).

3. A method for increasing production by fracturing and displacement of coalbed methane reservoirs according to claim 1, characterized in that: During the process of injecting the CO2 / N2 gas (9) in step 4, the injection pressure of the CO2 / N2 gas (9) is controlled to be higher than the pore pressure of the roof rock layer (6) and lower than the extension pressure of the artificial fracture (1) in the roof rock layer (6).

4. A method for increasing production by fracturing and displacement of coalbed methane reservoirs according to claim 1, characterized in that: During the process of injecting the CO2 / N2 gas (9) in step six, the injection pressure of the CO2 / N2 gas (9) is controlled to be higher than the pore pressure of the basement rock formation (8) and lower than the extension pressure of the artificial fractures (1) in the basement rock formation (8).

5. A method for increasing production by fracturing and displacement of coalbed methane reservoirs according to claim 1, characterized in that: In step 2, the distances from the vertical well section of the bottom plate rock formation horizontal fracturing drilling well (4) and the vertical well section of the top plate rock formation horizontal fracturing drilling well (3) to the original fracturing drilling well (2) are equal, and the horizontal well section of the bottom plate rock formation horizontal fracturing drilling well (4) and the horizontal well section of the top plate rock formation horizontal fracturing drilling well (3) extend in a direction approaching each other, and at the same time, the distance from the end of the horizontal well section of the bottom plate rock formation horizontal fracturing drilling well (4) to the original fracturing drilling well (2) is equal to the distance from the end of the horizontal well section of the top plate rock formation horizontal fracturing drilling well (3) to the original fracturing drilling well (2).

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