Fracturing, gasification and carbon sequestration integrated method for thin mutual coal seam

Abstract

The invention discloses a thin mutual coal seam fracturing, gasification and carbon sequestration integrated method. The method comprises the steps of geological exploration and coal seam refined evaluation; a middle horizontal well is drilled downwards from the ground; top and bottom horizontal wells are planned and drilled in the uppermost and lower sandstone stratums of the thin mutual coal seam; a plurality of top and bottom fishbone wells are drilled obliquely downwards and upwards in the top and bottom horizontal wells; oxygen-enriched water vapor is injected into the middle horizontal well through a continuous oil pipe, the oxygen-enriched water vapor is squeezed into the reservoir under the action of high pressure, and fracturing operation is conducted; initiating an underground gasification process of the coal seam, and synchronously performing extraction operation of the coal seam gas; supercritical CO2 fracturing operation is conducted on the top horizontal well and the bottom horizontal well; injecting water-based fracturing fluid into the top horizontal well and the bottom horizontal well; gasified materials generated by coal seam combustion gasification and desorbed methane gas are extracted through the middle horizontal well, and supercritical carbon dioxide injected before is sealed for a long time. According to the method, the limitation of a traditional hydraulic fracturing technology can be solved, and the transformation effect of the reservoir can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal and unconventional natural gas development, and in particular relates to an integrated method for fracturing, gasification and carbon sequestration of thin interbedded coal seams. Background Art

[0002] As a clean energy, the development of thin interbedded coalbed methane plays an important role in alleviating the national energy tension and ensuring energy security. Especially in the process of my country's energy structure transformation, its large-scale development is particularly important. However, the development of thin interbedded coalbed methane faces multiple difficulties. First, the thickness of thin interbedded coal seams is extremely uneven, and coal seams and sandstone formations frequently alternate, resulting in the need to frequently adjust the mining strategy during the mining process, which not only increases the difficulty and cost of mining, but also means that the controlled reserves of a single well are limited, requiring more well locations and denser well network arrangements, further pushing up the mining cost. Secondly, due to the undeveloped micro-cracks in the coal seams and the generally low permeability, it is difficult for coalbed methane to flow naturally to the production wells, which requires effective production-increasing measures to increase the permeability of the coal seams during the mining process to increase the production of coalbed methane. In addition, the gas pressure of thin interbedded coal seams is usually low, which means that the natural driving energy of coalbed methane is insufficient and it is difficult to maintain a long-term stable gas production. Therefore, specific technical means are needed to supplement energy and maintain or improve the mining efficiency of coalbed methane. The geological structure of thin interbedded coal seams is often complex, with various geological phenomena such as faults and folds, which will have a significant impact on the migration and enrichment of coalbed methane. Therefore, the impact of geological structure needs to be fully considered during the mining process, and the well location and mining plan need to be scientifically and rationally designed. In addition, more efficient production-increasing measures need to be explored, such as supercritical CO2 fracturing and methane in-situ explosion fracturing. In order to overcome these technical difficulties, innovative mining technologies and methods need to be adopted to achieve clean utilization of coalbed methane and carbon sequestration operations while improving mining efficiency and safety. Summary of the invention

[0003] In view of some problems existing in the prior art, the present invention provides an integrated method for fracturing, gasification and carbon sequestration of thin interbedded coal seams. The method has the advantages of high efficiency, environmental protection and sustainability, and can provide a new technical path for the development of coalbed methane in thin interbedded coal seams. It can not only solve the limitations of traditional hydraulic fracturing technology, but also improve the transformation effect of the reservoir, significantly improve the effect and efficiency of coal seam mining, and has important application prospects and promotion value.

[0004] In order to achieve the above object, the present invention provides an integrated method for fracturing, gasification and carbon sequestration of thin interbedded coal seams, comprising the following steps:

[0005] Step 1: Geological exploration and detailed assessment of coal seams;

[0006] S11: Conduct ground geological surveys on the development block, observe coal seam outcrop rock samples, and record coal seam characteristics. The surface of the development block is mudstone strata, and the part below the mudstone strata is a thin interbedded coal structure with alternating coal seams and sandstone strata;

[0007] S12: Detect the distribution of underground coal seams, determine the thickness and distribution range of coal seams, as well as the interlayer relationship between coal seams and mudstone strata, and the interlayer relationship between coal seams and sandstone strata. At the same time, obtain the key parameters of coal seams, fully understand the geological structure of coal seams, and analyze the impact of the geological structure of coal seams on the migration and enrichment of coalbed methane;

[0008] S13: Determine the gas content, pressure data and gas composition in the coal seam through logging, sampling and analysis techniques;

[0009] S14: Comprehensively evaluate the coal seams based on geological exploration results, logging data, gas content and pressure data, determine the development potential of the coal seams, and scientifically and rationally determine the location of subsequent intermediate horizontal well drilling. At the same time, formulate an integrated plan for subsequent drilling, fracturing, gasification and carbon storage;

[0010] Step 2: drilling of intermediate horizontal wells;

[0011] S21: Based on the geological exploration data of the coal seam, the thickness, inclination and permeability of the coal seam are comprehensively analyzed, and based on the distribution range of the mudstone stratum, sandstone stratum and coal seam, the coal seam with good reservoir properties in the middle position is selected as the drilling position of the intermediate horizontal well;

[0012] S22: Based on the selected drilling layer, the 3D geological model is used to plan the drilling path to ensure that the drilling trajectory can pass through the target coal seam and that the layer encountered by the intermediate horizontal well has good reservoir properties;

[0013] S23: Use coalbed methane drilling equipment and process technology to drill an intermediate horizontal well from the ground downward;

[0014] Step 3: Drilling of top horizontal well and bottom horizontal well;

[0015] In the uppermost sandstone formation of the thin interbedded coal seam, plan and drill the top horizontal well, while ensuring that the axis of the top horizontal well is parallel to the axis of the middle horizontal well, and the top horizontal well is located 1 / 5 to 1 / 4 below the interior of the upper sandstone formation;

[0016] In the sandstone formation at the bottom of the thin interbedded coal seam, plan and drill the bottom horizontal well, and at the same time, ensure that the axis of the bottom horizontal well is parallel to the axis of the middle horizontal well, and the bottom horizontal well is located at the upper 1 / 5 to 1 / 4 position of the lower sandstone formation;

[0017] Step 4: Fishbone well drilling;

[0018] In the top horizontal well, use a directional sidetracking tool to drill the first top fishbone well obliquely downward in a clockwise direction of 45 to 60 degrees; repeat the above process multiple times, drill the remaining top fishbone wells in the top horizontal well in turn, and ensure that the spacing between adjacent top fishbone wells is between 20 and 30 meters; in the bottom horizontal well, use a directional sidetracking tool to drill the first bottom fishbone well obliquely upward in a clockwise direction of 45 to 60 degrees; repeat the above process multiple times, drill the remaining bottom fishbone wells in the bottom horizontal well in turn, and ensure that the spacing between adjacent bottom fishbone wells is between 20 and 30 meters;

[0019] A three-dimensional well pattern is formed in the thin interbedded coal seam structure by using the middle horizontal well, the top horizontal well, the bottom horizontal well, the top herringbone well and the bottom herringbone well;

[0020] Step 5: fracturing of the intermediate horizontal well;

[0021] S51: lower the fracturing tool to a predetermined position in the intermediate horizontal well through the coiled tubing, install the surface equipment and connect it to the fracturing tool, and ensure the stable transmission of feedback signals and control signals during the fracturing process;

[0022] S52: Pure water is converted into water vapor through a heating device on the ground, and a certain proportion of oxygen is mixed in to form oxygen-rich water vapor;

[0023] S53: Use a surface pump group to inject oxygen-rich water vapor into the intermediate horizontal well through a coiled tubing, squeeze the oxygen-rich water vapor into the reservoir under high pressure, and perform fracturing operations. During the fracturing process, the high temperature and high pressure of the oxygen-rich water vapor is used to generate thermal stress in the reservoir rock, promote the formation and expansion of cracks, and form a complex large-scale artificial fracture network;

[0024] S54: Continuously pumping in oxygen-rich water vapor allows the fractures to expand not only in the coal seam where the intermediate horizontal well is located, but also to extend upward and downward into the adjacent coal seams, thereby increasing the connectivity of the artificial fractures;

[0025] Step 6: Underground coal seam gasification and coal seam methane extraction;

[0026] S61: During the fracturing process of the intermediate horizontal well, when the oxygen-rich steam input reaches 300-400m 3 When the oxygen-rich water vapor injection operation is stopped, an ignition rod is then dropped to the bottom of the middle horizontal well through a special dropping device, and the coal seam is ignited by the ignition rod, thus initiating the underground gasification process of the coal seam.

[0027] S62: After the coal seam is ignited, oxygen-rich steam is continuously injected into the intermediate horizontal well to maintain the continuous coal seam gasification process. At the same time, the high temperature and high pressure of the oxygen-rich steam is used to promote the further expansion of the cracks, and the gas and heat generated by the coal seam gasification are simultaneously used to promote the formation and expansion of the cracks;

[0028] While the gasification operation of the middle horizontal well is in progress, the coalbed methane extraction operation is carried out synchronously by using the top horizontal well and the bottom horizontal well. At the same time, the pressure in the coal seam is reduced by the extraction process, further promoting the in-depth gasification reaction of the middle horizontal well;

[0029] S63: When the gasification process of the middle horizontal well is completed, the gasification agent injection system of the middle horizontal well is closed, and the well is shut in to allow the downhole combustion process to proceed fully. Through the combustion process, a combustion void zone is formed around the artificial seam network in the middle horizontal well; at the same time, the extraction operation of the top horizontal well and the bottom horizontal well is continued, and the extraction process is continued until the set extraction time ends;

[0030] Step 7: Supercritical CO2 fracturing and replacement;

[0031] After the extraction operation is completed, supercritical CO2 fracturing operations are immediately carried out on the top horizontal well and the bottom horizontal well. During the supercritical CO2 fracturing process, the injection flow rate of supercritical carbon dioxide is precisely controlled to induce further expansion of the internal cracks of the coal seam, forming a more complex and more connected three-dimensional crack network. At the same time, the strong adsorption capacity of supercritical carbon dioxide is used to replace the adsorbed methane in the coal seam with a free state. At the same time, the high diffusivity and low surface tension of supercritical carbon dioxide are used to allow supercritical carbon dioxide to penetrate into the micropores of the coal seam, further increasing the content of free methane in the coal seam.

[0032] Step 8: Hydraulic fracturing and CO2 storage;

[0033] After the injection of a predetermined amount of supercritical carbon dioxide is completed, water-based fracturing fluid is injected into the top horizontal well and the bottom horizontal well at a set flow rate. The injected water-based fracturing fluid is used to gradually expand the cracks inside the coal seam, forming a complex fracture network; at the same time, the water-based fracturing fluid is used to squeeze the supercritical carbon dioxide into the deep part of the reservoir to further displace the methane gas in the coal seam;

[0034] During the injection of water-based fracturing fluid, the high molecular polymer and cross-linking agent in the water-based fracturing fluid gradually form a high-strength and high-toughness plugging layer in the cracks. The formed plugging layer effectively supports the cracks to prevent the cracks from closing after pressure relief. At the same time, the formed plugging layer effectively prevents supercritical carbon dioxide from escaping from the cracks and returning to the wellbore.

[0035] Step 9: Gasification and coal-bed methane extraction;

[0036] S91: The gasification products and desorbed methane gas generated by coal seam combustion and gasification are extracted through the intermediate horizontal well, and separated and processed by the gas separation device after being extracted to the ground; during the extraction process, the parameters of the gas returned from the intermediate horizontal well are monitored in real time through the sensor installed in the extraction well, and the intermediate horizontal well is closed when no significant combustible gas is returned from the intermediate horizontal well for a long time and the gas concentration is stably maintained within the set low concentration range;

[0037] S92: Keep the top horizontal well and the bottom horizontal well closed at the same time, and store the supercritical carbon dioxide injected previously for a long time to achieve the carbon emission reduction target.

[0038] As a preferred embodiment, in step one, geological radar and seismic exploration techniques are used to detect the distribution of underground coal seams.

[0039] Furthermore, in order to ensure the scientific and rational nature of subsequent fracturing, gasification and carbon storage plans, in step 2 S23, after the intermediate horizontal well drilling operation is completed, the drilling effect is evaluated through logging technology. The evaluation content includes the accuracy of the drilling trajectory and the penetration of the coal seam. Based on the evaluation results, the subsequent fracturing, gasification and carbon storage plans are adjusted and optimized.

[0040] Furthermore, in order to ensure the quality of the horizontal well and the subsequent fracturing effect, during the drilling process in step three, the drilling trajectory and formation changes are monitored in real time to ensure the accuracy of the position of the horizontal well and the smoothness of the trajectory. At the same time, the top horizontal well and the bottom horizontal well share a vertical well.

[0041] Furthermore, in order to ensure the quality of the fishbone well and to effectively increase the control range of the top horizontal well and the bottom horizontal well through the fishbone well, in step four, during the drilling process of the top fishbone well, the inclination and azimuth of the top fishbone well are monitored in real time to ensure that the top fishbone well extends according to the predetermined trajectory, and at the same time, ensure that the top fishbone well passes through at least one group of adjacent coal seams and sandstone formations after penetrating the formation encountered by the connected top horizontal well; during the drilling process of the bottom fishbone well, the inclination and azimuth of the bottom fishbone well are monitored in real time to ensure that the bottom fishbone well extends according to the predetermined trajectory, and at the same time, ensure that the bottom fishbone well passes through at least one group of adjacent coal seams and sandstone formations after penetrating the formation encountered by the connected bottom horizontal well.

[0042] As a preferred embodiment, in step 4, the multiple bottom fishbone wells and the multiple top fishbone wells are symmetrically distributed, and the spacing between two adjacent bottom fishbone wells and two adjacent top fishbone wells is the same. At the same time, the lengths of the bottom fishbone wells and the top fishbone wells are the same.

[0043] Furthermore, in order to ensure the fracturing effect and efficiency, in step 5 S52, the volume fraction of oxygen mixed in the water vapor is 40% to 60%; in step 5 S53, during the fracturing process, the flow rate of the oxygen-enriched water vapor is adjusted to 3.0 to 4.5 m / s. 3 / min.

[0044] Furthermore, in order to ensure the extraction effect and extraction efficiency, in step six S63, the extraction time is set to be no less than 5 to 7 hours.

[0045] Furthermore, in order to ensure the fracturing effect and efficiency, in step 7, the injection flow rate of supercritical carbon dioxide is 2-3m 3 / min.

[0046] Furthermore, in order to ensure the effect and efficiency of water-based fracturing, in step eight, the injection flow rate of the water-based fracturing fluid is 8 to 10 m 3 / min.

[0047] The present invention proposes an innovative integrated method for the development of thin interbedded coal seams and carbon emission reduction, which effectively integrates fracturing, gasification and carbon sequestration technologies, and realizes efficient development of resources and environmentally friendly protection. Specifically, firstly, through the early geological exploration and coal seam detailed evaluation process, the location of the intermediate horizontal well can be reasonably planned, and at the same time, a scientific and reasonable integrated plan for subsequent drilling, fracturing, gasification and carbon sequestration can be formulated; secondly, the location of the top and bottom horizontal wells is reasonably planned, and effective coverage of deep thin interbedded coal seams is achieved, thereby providing great convenience for subsequent gasification, fracturing and other operations, which not only reduces the engineering workload and cost, but also improves the overall efficiency of mining operations; thirdly, by setting a plurality of top fishbone wells obliquely below the top horizontal well, and at the same time, setting a plurality of bottom fishbone wells obliquely above the bottom horizontal well, the control range of the top horizontal well over the thin interbedded coal seam below can be effectively increased, and at the same time, the control range of the bottom horizontal well over the thin interbedded coal seam above can be increased. The control range of the inter-coal layer can be further improved by using the middle horizontal well, the top horizontal well, the bottom horizontal well, the top fishbone well and the bottom fishbone well to form a three-dimensional well network in the thin inter-coal layer structure; secondly, the use of oxygen-rich water vapor as the fracturing medium not only reduces the dependence on water resources, but also makes full use of the high temperature and high pressure of oxygen-rich water vapor to generate thermal stress in the reservoir rock, promote the formation and expansion of cracks, and form a complex large-scale artificial fracture network; thirdly, the gasification process of the middle horizontal well is combined with the synchronous extraction of the top and bottom horizontal wells to form an efficient gasification-extraction cycle, which significantly improves the gasification efficiency and extraction efficiency; thirdly, the use of supercritical CO2 fracturing operations further expands the fracture network inside the coal seam, significantly improving the fluidity of coalbed methane. At the same time, through the displacement effect of supercritical CO2, the adsorbed methane in the coal seam can be effectively converted into a free state, thereby significantly improving the production and quality of coalbed methane; furthermore, through the injection of water-based fracturing fluid, not only can the internal cracks of the coal seam be further expanded, but supercritical carbon dioxide can also be squeezed into the deep reservoir to further displace the methane gas in the coal seam. At the same time, the high molecular polymers and cross-linking agents in the water-based fracturing fluid can gradually form a high-strength and high-toughness plugging layer in the cracks. In this way, the plugging layer can be used to effectively support the cracks to prevent the cracks from closing after unloading, and the plugging layer can also be used to effectively prevent supercritical carbon dioxide from escaping from the cracks. Finally, the use of intermediate horizontal wells to extract gasification and methane gas can achieve more complete exploitation of thin interbedded coal seams.

[0048] The present invention combines oxygen-enriched steam fracturing, supercritical CO2 fracturing and traditional hydraulic fracturing technology. By combining the high temperature and high pressure of oxygen-enriched steam with the supporting effect of coal gangue particles, a complex and stable fracture network can be formed, which significantly improves the permeability of the reservoir and can produce additional gas production. The combined technology of hydraulic fracturing and supercritical CO2 storage further enhances the sealing of the formation, thereby ensuring the carbon storage effect. As a result, the present invention significantly improves the opening degree and gasification efficiency of the fractures, realizes the in-situ fluidized mining of coal resources, and reduces the generation of solid waste and the degree of damage to the surface.

[0049] In summary, the integrated method of fracturing, gasification and carbon sequestration of thin interbedded coal seams proposed in the present invention has the remarkable characteristics of high efficiency, environmental protection and sustainability, and provides a new technical path for the development of coalbed methane in thin interbedded coal seams. This method not only solves the limitations of traditional hydraulic fracturing technology, but also effectively improves the transformation effect of the reservoir and significantly improves the mining effect and efficiency of the coal seams. Therefore, it has important application prospects and promotion value. This technology is expected to become one of the important technical means for coalbed methane development in the future. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of horizontal well layout in thin interbedded coal seams in the present invention;

[0051] Figure 2 It is a schematic diagram of the drilling and distribution of fishbone wells in the present invention;

[0052] Figure 3 This is a schematic diagram of fracturing and seaming of an intermediate horizontal well in the present invention;

[0053] Figure 4 It is a schematic diagram of coalbed gasification and coalbed methane extraction in the intermediate horizontal well of the present invention;

[0054] Figure 5 It is a schematic diagram of fishbone well fracturing in the present invention.

[0055] In the figure: 1. Mudstone formation, 2. Sandstone formation, 3. Coal seam, 4. Intermediate horizontal well, 5. Top horizontal well, 6. Bottom horizontal well, 7. Top fishbone well, 8. Bottom fishbone well, 9. Oxygen-enriched water vapor, 10. Artificial fracture network, 11. Coalbed methane, 12. Combustion zone, 13. Supercritical carbon dioxide, 14. Three-dimensional fracture network. DETAILED DESCRIPTION

[0056] The present invention will be further described below.

[0057] like Figures 1 to 5As shown, the present invention provides an integrated method for fracturing, gasification and carbon sequestration of thin interbedded coal seams, which comprehensively applies geological exploration, horizontal well drilling, fracturing, underground gasification and supercritical CO2 sequestration and other technical means, uses oxygen-enriched water vapor, supercritical CO2 and water-based fracturing fluid as working fluids, uses part of the underground coal seams as fuel, and improves the desorption efficiency of coalbed methane through the high-temperature products and heating effect generated by the gasification of the intermediate coal seams, thereby achieving the production increase transformation of the thin interbedded coal seams, and finally achieving the efficient development of coalbed methane and carbon sequestration, which specifically includes the following steps:

[0058] Step 1: Geological exploration and detailed assessment of coal seams 3;

[0059] S11: Before developing the thin interbedded coal seams, firstly, a ground geological survey is conducted on the development block, the outcrop rock samples of the coal seam 3 are observed, and the characteristics of the coal seam 3 are recorded, specifically the occurrence, color, gloss, fracture and other characteristics of the coal seam 3. Among them, the surface of the development block is the mudstone stratum 1, and the part below the mudstone stratum 1 is the thin interbedded coal seam structure of the coal seam 3 and the sandstone stratum 2 alternating.

[0060] S12: Detect the distribution of underground coal seams 3, determine the thickness and distribution range of coal seams 3, as well as the interlayer relationship between coal seams 3 and mudstone strata 1, and the interlayer relationship between coal seams 3 and sandstone strata 2. At the same time, obtain key parameters of coal seams 3, such as the thickness and number of layers of coal seams 3, fully understand the geological structure of coal seams 3, such as faults and folds, and analyze the influence of the geological structure of coal seams 3 on the migration and enrichment of coalbed methane 11;

[0061] As a preferred embodiment, geological radar, seismic exploration and other technical means are used to detect the distribution of the underground coal seam 3.

[0062] S13: Determine the gas content, pressure data and gas composition in the coal seam 3 by means of logging, sampling and analysis techniques;

[0063] S14: Comprehensively evaluate coal seam 3 based on geological exploration results, logging data, gas content and pressure data, determine the development potential and feasibility of coal seam 3, and scientifically and rationally determine the location of subsequent drilling of intermediate horizontal well 4. At the same time, formulate an integrated plan for subsequent drilling, fracturing, gasification and carbon storage, providing a reliable basis for the design of subsequent drilling, fracturing, gasification and carbon storage plans;

[0064] Step 2: drilling of intermediate horizontal well 4;

[0065] S21: Figure 1As shown, according to the geological exploration data of the coal seam 3, the thickness, inclination, permeability and other factors of the coal seam 3 are comprehensively analyzed, and according to the distribution range of the mudstone formation 1, the sandstone formation 2 and the coal seam 3, the coal seam 3 with good reservoir properties in the middle position is selected as the drilling layer of the intermediate horizontal well 4; this layer should have good reservoir properties, which is conducive to subsequent fracturing and gasification operations;

[0066] S22: Based on the selected drilling layer, the three-dimensional geological model is used to plan the drilling path to ensure that the drilling trajectory can pass through the target coal seam 3 and that the layer encountered by the intermediate horizontal well 4 has good reservoir properties;

[0067] S23: using CBM 11 drilling equipment and process technology, drilling an intermediate horizontal well 4 from the ground downward;

[0068] As a preferred option, after the drilling operation of the intermediate horizontal well 4 is completed, the drilling effect is evaluated by means of logging technology, etc. The evaluation content includes the accuracy of the drilling trajectory and the penetration of the coal seam, and the subsequent fracturing, gasification and carbon storage plans are adjusted and optimized based on the evaluation results.

[0069] Step 3: Drilling the top horizontal well 5 and the bottom horizontal well 6;

[0070] After the drilling of the middle horizontal well 4 is completed, the top horizontal well 5 is planned and drilled in the sandstone formation 2 at the uppermost part of the thin interbedded coal seam. At the same time, it is ensured that the axis of the top horizontal well 5 is parallel to the axis of the middle horizontal well 4, and the top horizontal well 5 is located at a position 1 / 5 to 1 / 4 below the interior of the upper sandstone formation 2, so as to facilitate subsequent fracturing operations;

[0071] In the sandstone formation 2 at the bottom of the thin interbedded coal seam, a bottom horizontal well 6 is planned and drilled. At the same time, it is ensured that the axis of the bottom horizontal well 6 is parallel to the axis of the middle horizontal well 4, and the bottom horizontal well 6 is located at the upper 1 / 5 to 1 / 4 position of the lower sandstone formation 2, so as to facilitate subsequent fracturing operations;

[0072] As a preferred embodiment, during the drilling process, the drilling trajectory and formation changes are monitored in real time to ensure that the position of the horizontal well is accurate and the trajectory is smooth. At the same time, the top horizontal well 5 and the bottom horizontal well 6 share a vertical well.

[0073] Step 4: Fishbone well drilling;

[0074] like Figure 2As shown, in the top horizontal well 5, a directional side drilling tool is used to drill the first top fishbone well 7 obliquely downward in a clockwise direction of 45 to 60 degrees; the above process is repeated many times to drill the remaining top fishbone wells 7 in the top horizontal well 5 in turn, and it is ensured that the spacing between adjacent top fishbone wells 7 is between 20 and 30 meters, so as to effectively reduce the stress interference between the fishbone wells in the subsequent fracturing process; as a preferred embodiment, during the drilling process of the top fishbone well 7, the inclination and azimuth of the top fishbone well 7 are monitored in real time to ensure that the top fishbone well 7 extends according to a predetermined trajectory, and at the same time, it is ensured that the top fishbone well 7 passes through at least one group of adjacent coal seams 3 and sandstone formations 2 after passing through the formation encountered by the connected top horizontal well 5, so that the control range of the top horizontal well 5 can be effectively increased.

[0075] In the bottom horizontal well 6, a directional side drilling tool is used to drill the first bottom fishbone well 8 obliquely upward in a clockwise direction of 45 to 60 degrees; the above process is repeated multiple times to drill the remaining bottom fishbone wells 8 in the bottom horizontal well 6 in turn, and it is ensured that the spacing between adjacent bottom fishbone wells 8 is between 20 and 30 meters, so as to effectively reduce the stress interference between the fishbone wells during the subsequent fracturing process; as a preferred embodiment, during the drilling process of the bottom fishbone well 8, the inclination and azimuth of the bottom fishbone well 8 are monitored in real time to ensure that the bottom fishbone well 8 extends according to a predetermined trajectory. At the same time, it is ensured that the bottom fishbone well 8 passes through at least one group of adjacent coal seams 3 and sandstone formations 2 after passing through the formation encountered by the connected bottom horizontal well 6, so that the control range of the bottom horizontal well 6 can be effectively increased.

[0076] As a further preference, the multiple bottom fishbone wells 8 and the multiple top fishbone wells 7 are symmetrically distributed, and the spacing between two adjacent bottom fishbone wells 8 and two adjacent top fishbone wells 7 is the same. At the same time, the lengths of the bottom fishbone wells 8 and the top fishbone wells 7 are the same.

[0077] A three-dimensional well pattern is formed in the thin interbedded coal seam structure by using the middle horizontal well 4, the top horizontal well 5, the bottom horizontal well 6, the top fishbone well 7 and the bottom fishbone well 8;

[0078] Step 5: fracturing the intermediate horizontal well 4;

[0079] Since the control range of the three-dimensional well network composed of horizontal wells and herringbone wells is limited, in order to increase the influence range of the three-dimensional well network, reservoir transformation is continued on the basis of the existing well network. The specific process is as follows:

[0080] S51: lowering the fracturing tool to a predetermined position in the intermediate horizontal well 4 through the coiled tubing, installing the surface equipment and connecting it to the fracturing tool, and ensuring stable transmission of feedback signals and control signals during the fracturing process;

[0081] S52: converting pure water into water vapor through a heating device on the ground, and mixing a certain proportion of oxygen into it to form oxygen-enriched water vapor 9; as a preferred embodiment, the volume fraction of oxygen mixed into the water vapor is 40% to 60%;

[0082] S53: Using a surface pump group, oxygen-rich water vapor 9 is injected into the intermediate horizontal well 4 through a coiled tubing, and the oxygen-rich water vapor 9 is squeezed into the reservoir under high pressure to perform a fracturing operation, such as Figure 3 As shown, during the fracturing process, the high temperature and high pressure of oxygen-rich water vapor 9 is used to generate thermal stress in the reservoir rock, promoting the formation and expansion of cracks, and forming a complex large-scale artificial fracture network 10;

[0083] As a preferred method, during the fracturing process, the flow rate of the oxygen-enriched steam 9 is adjusted to 3.0-4.5 m 3 / min.

[0084] S54: Continuously pumping in oxygen-rich water vapor 9, so that the fractures can not only expand in the coal seam 3 where the intermediate horizontal well 4 is located, but also extend upward and downward to the adjacent coal seams 3, thereby increasing the connectivity range of the artificial fractures 10;

[0085] Step 6: underground gasification of coal seam 3 and extraction of coal seam methane 11;

[0086] S61: During the fracturing process of the intermediate horizontal well 4, when the input of oxygen-rich steam 9 reaches 300-400m 3 When the oxygen-enriched water vapor 9 is injected, the injection operation is stopped; then an ignition rod is dropped into the bottom of the middle horizontal well 4 by a special dropping device, and the coal seam 3 is ignited by the ignition rod, thereby initiating the underground gasification process of the coal seam 3;

[0087] S62: Figure 4 As shown, after the coal seam 3 is ignited, oxygen-rich steam 9 is continuously injected into the intermediate horizontal well 4 to maintain the continuous gasification process of the coal seam 3. At the same time, the high temperature and high pressure of the oxygen-rich steam 9 is used to promote the further expansion of the cracks, and the gas and heat generated by the gasification of the coal seam 9 are simultaneously used to promote the formation and expansion of the cracks;

[0088] While the gasification operation of the middle horizontal well 4 is in progress, the coalbed methane 11 is extracted by the top horizontal well 5 and the bottom horizontal well 6 simultaneously. At the same time, the pressure in the coal seam 3 is reduced by the extraction process, further promoting the in-depth gasification reaction of the middle horizontal well 4, thus forming a virtuous cycle.

[0089] S63: When the gasification process of the middle horizontal well 4 is completed, the gasification agent injection system of the middle horizontal well 4 is closed, and the well is shut down to allow the downhole combustion process to proceed fully. Through the combustion process, a combustion zone 12 is formed around the artificial seam network 10 in the middle horizontal well 4; at the same time, the extraction operation of the top horizontal well 5 and the bottom horizontal well 6 is continued, and this extraction process is continued until the set extraction time ends. As a preferred embodiment, the extraction time is set to be not less than 5 to 7 hours.

[0090] Step 7: Supercritical CO2 fracturing and replacement;

[0091] like Figure 5 As shown, after the extraction operation is completed, the top horizontal well 5 and the bottom horizontal well 6 are immediately subjected to supercritical CO2 fracturing. During the supercritical CO2 fracturing process, the injection flow rate of supercritical carbon dioxide 13 is precisely controlled to induce further expansion of the internal cracks of the coal seam 3, forming a more complex and more connected three-dimensional fracture network 14. As a preferred embodiment, the injection flow rate of supercritical carbon dioxide 13 is 2 to 3 m 3 / min.

[0092] At the same time, the supercritical carbon dioxide 13 is used to replace the adsorbed methane in the coal seam 3 with a free state by using its strong adsorption capacity. At the same time, the supercritical carbon dioxide 13 is used to penetrate into the micropores of the coal seam 3 by using its high diffusivity and low surface tension, thereby further increasing the content of free methane in the coal seam 3.

[0093] Step 8: Hydraulic fracturing and CO2 storage;

[0094] After the injection of the predetermined amount of supercritical carbon dioxide 13 is completed, a water-based fracturing fluid is injected into the top horizontal well 5 and the bottom horizontal well 6 at a set flow rate. As a preferred embodiment, the injection flow rate of the water-based fracturing fluid is 8 to 10 m 3 / min, using the injected water-based fracturing fluid to gradually expand the internal cracks of the coal seam 3 to form a complex fracture network; at the same time, using the water-based fracturing fluid to squeeze supercritical carbon dioxide 13 into the deep part of the reservoir to further displace the methane gas in the coal seam 3;

[0095] During the injection of water-based fracturing fluid, the high molecular weight polymer and cross-linking agent in the water-based fracturing fluid gradually form a high-strength and high-toughness plugging layer in the cracks. The formed plugging layer effectively supports the cracks to prevent the cracks from closing after pressure relief. At the same time, the formed plugging layer effectively prevents supercritical carbon dioxide 13 from escaping from the cracks and returning to the wellbore.

[0096] Step nine: extraction of gasified products and coal-bed methane 11;

[0097] S91: The gases generated during the gasification process are mainly carbon monoxide, hydrogen and other gasification products. The gasification products generated by the combustion and gasification of the coal seam 3 and the desorbed methane gas are extracted through the intermediate horizontal well 4, and separated and processed by the gas separation device after being extracted to the ground; during the extraction process, the parameters of the gas returned from the intermediate horizontal well 4 are monitored in real time through the sensors installed in the extraction well, such as gas flow rate, gas composition and other parameters. When the intermediate horizontal well 4 has no significant combustible gas returned for a long time and the gas concentration is stably maintained within the set low concentration range, the intermediate horizontal well 4 is closed;

[0098] S92: Keep the top horizontal well 5 and the bottom horizontal well 6 in a closed state at the same time, and store the previously injected supercritical carbon dioxide 13 for a long time to achieve the carbon emission reduction target.

[0099] The present invention proposes an innovative integrated method for the development of thin interbedded coal seams and carbon emission reduction, which effectively integrates fracturing, gasification and carbon sequestration technologies, and realizes efficient development of resources and environmentally friendly protection. Specifically, firstly, through the early geological exploration and coal seam detailed evaluation process, the location of the intermediate horizontal well can be reasonably planned, and at the same time, a scientific and reasonable integrated plan for subsequent drilling, fracturing, gasification and carbon sequestration can be formulated; secondly, the location of the top and bottom horizontal wells is reasonably planned, and effective coverage of deep thin interbedded coal seams is achieved, thereby providing great convenience for subsequent gasification, fracturing and other operations, which not only reduces the engineering workload and cost, but also improves the overall efficiency of mining operations; thirdly, by setting a plurality of top fishbone wells obliquely below the top horizontal well, and at the same time, setting a plurality of bottom fishbone wells obliquely above the bottom horizontal well, the control range of the top horizontal well over the thin interbedded coal seam below can be effectively increased, and at the same time, the control range of the bottom horizontal well over the thin interbedded coal seam above can be increased. The control range of the inter-coal layer can be further improved by using the middle horizontal well, the top horizontal well, the bottom horizontal well, the top fishbone well and the bottom fishbone well to form a three-dimensional well network in the thin inter-coal layer structure; secondly, the use of oxygen-rich water vapor as the fracturing medium not only reduces the dependence on water resources, but also makes full use of the high temperature and high pressure of oxygen-rich water vapor to generate thermal stress in the reservoir rock, promote the formation and expansion of cracks, and form a complex large-scale artificial fracture network; thirdly, the gasification process of the middle horizontal well is combined with the synchronous extraction of the top and bottom horizontal wells to form an efficient gasification-extraction cycle, which significantly improves the gasification efficiency and extraction efficiency; thirdly, the use of supercritical CO2 fracturing operations further expands the fracture network inside the coal seam, significantly improving the fluidity of coalbed methane. At the same time, through the displacement effect of supercritical CO2, the adsorbed methane in the coal seam can be effectively converted into a free state, thereby significantly improving the production and quality of coalbed methane; furthermore, through the injection of water-based fracturing fluid, not only can the internal cracks of the coal seam be further expanded, but supercritical carbon dioxide can also be squeezed into the deep reservoir to further displace the methane gas in the coal seam. At the same time, the high molecular polymers and cross-linking agents in the water-based fracturing fluid can gradually form a high-strength and high-toughness plugging layer in the cracks. In this way, the plugging layer can be used to effectively support the cracks to prevent the cracks from closing after unloading, and the plugging layer can also be used to effectively prevent supercritical carbon dioxide from escaping from the cracks. Finally, the use of intermediate horizontal wells to extract gasification and methane gas can achieve more complete exploitation of thin interbedded coal seams.

[0100] The present invention combines oxygen-enriched steam fracturing, supercritical CO2 fracturing and traditional hydraulic fracturing technology. By combining the high temperature and high pressure of oxygen-enriched steam with the supporting effect of coal gangue particles, a complex and stable fracture network can be formed, which significantly improves the permeability of the reservoir and can produce additional gas production. The combined technology of hydraulic fracturing and supercritical CO2 storage further enhances the sealing of the formation, thereby ensuring the carbon storage effect. As a result, the present invention significantly improves the opening degree and gasification efficiency of the fractures, realizes the in-situ fluidized mining of coal resources, and reduces the generation of solid waste and the degree of damage to the surface.

[0101] In summary, the integrated method of fracturing, gasification and carbon sequestration of thin interbedded coal seams proposed in the present invention has the remarkable characteristics of high efficiency, environmental protection and sustainability, and provides a new technical path for the development of coalbed methane in thin interbedded coal seams. This method not only solves the limitations of traditional hydraulic fracturing technology, but also effectively improves the transformation effect of the reservoir and significantly improves the mining effect and efficiency of the coal seams. Therefore, it has important application prospects and promotion value. This technology is expected to become one of the important technical means for coalbed methane development in the future.

Claims

1. A method for integrating fracturing, gasification and carbon sequestration of thin interbedded coal seams, characterized in that: The following steps are involved: Step 1: Geological exploration and coal seam (3) detailed assessment; S11: Conduct ground geological survey on the development block, observe outcrop rock samples of the coal seam (3), and record the characteristics of the coal seam (3), wherein the surface of the development block is a mudstone stratum (1), and the part below the mudstone stratum (1) is a thin interbedded structure of alternating coal seams (3) and sandstone strata (2); S12: Detect the distribution of the underground coal seam (3), determine the thickness and distribution range of the coal seam (3), and the interlayer relationship between the coal seam (3) and the mudstone stratum (1), and the interlayer relationship between the coal seam (3) and the sandstone stratum (2), and at the same time, obtain the key parameters of the coal seam (3), fully understand the geological structure of the coal seam (3), and analyze the influence of the geological structure of the coal seam (3) on the migration and enrichment law of the coalbed methane (11); S13: Determine the gas content, pressure data and gas composition in the coal seam (3) by means of logging, sampling and analysis techniques; S14: Comprehensively evaluate the coal seam (3) based on geological exploration results, logging data, gas content and pressure data, determine the development potential of the coal seam (3), and scientifically and rationally determine the location of subsequent intermediate horizontal wells (4) for drilling. At the same time, formulate an integrated plan for subsequent drilling, fracturing, gasification and carbon storage; Step 2: drilling of the intermediate horizontal well (4); S21: Based on the geological exploration data of the coal seam (3), the thickness, inclination and permeability of the coal seam (3) are comprehensively analyzed, and based on the distribution range of the mudstone stratum (1), the sandstone stratum (2) and the coal seam (3), a coal seam (3) with good reservoir properties in the middle position is selected as the drilling layer of the middle horizontal well (4); S22: Based on the selected drilling layer, the three-dimensional geological model is used to plan the drilling path to ensure that the drilling trajectory can pass through the target coal seam (3) and that the layer encountered by the intermediate horizontal well (4) has good reservoir properties; S23: using coalbed methane (11) drilling equipment and process technology, drilling an intermediate horizontal well (4) from the ground downward; Step 3: Drilling the top horizontal well (5) and the bottom horizontal well (6); In the uppermost sandstone formation (2) of the thin interbedded coal seam, a top horizontal well (5) is planned and drilled, and at the same time, the axis of the top horizontal well (5) is ensured to be parallel to the axis of the middle horizontal well (4), and the top horizontal well (5) is located at a position 1 / 5 to 1 / 4 below the interior of the upper sandstone formation (2); In the sandstone formation (2) at the bottom of the thin interbedded coal seam, a bottom horizontal well (6) is planned and drilled, and at the same time, the axis of the bottom horizontal well (6) is ensured to be parallel to the axis of the middle horizontal well (4), and the bottom horizontal well (6) is located at a position 1 / 5 to 1 / 4 above the interior of the lower sandstone formation (2); Step 4: Fishbone well drilling; In the top horizontal well (5), a directional sidetracking tool is used to drill a first top fishbone well (7) obliquely downward in a clockwise direction of 45 to 60 degrees; the above process is repeated multiple times to drill the remaining top fishbone wells (7) in the top horizontal well (5) in turn, and ensure that the spacing between adjacent top fishbone wells (7) is between 20 and 30 meters; in the bottom horizontal well (6), a directional sidetracking tool is used to drill a first bottom fishbone well (8) obliquely upward in a clockwise direction of 45 to 60 degrees; the above process is repeated multiple times to drill the remaining bottom fishbone wells (8) in the bottom horizontal well (6) in turn, and ensure that the spacing between adjacent bottom fishbone wells (8) is between 20 and 30 meters; A three-dimensional well pattern is formed in the thin interbedded coal seam structure by using the middle horizontal well (4), the top horizontal well (5), the bottom horizontal well (6), the top herringbone well (7) and the bottom herringbone well (8); Step 5: fracturing the intermediate horizontal well (4); S51: lowering the fracturing tool to a predetermined position in the intermediate horizontal well (4) through the coiled tubing, installing the surface equipment and connecting it to the fracturing tool, and ensuring stable transmission of feedback signals and control signals during the fracturing process; S52: converting pure water into water vapor through a heating device on the ground, and mixing a certain proportion of oxygen into it to form oxygen-enriched water vapor (9); S53: using a surface pump group to inject oxygen-rich water vapor (9) into the intermediate horizontal well (4) through a coiled tubing, and squeezing the oxygen-rich water vapor (9) into the reservoir under high pressure to perform a fracturing operation. During the fracturing process, the high temperature and high pressure of the oxygen-rich water vapor (9) is used to generate thermal stress in the reservoir rock, thereby promoting the formation and expansion of cracks and forming a complex large-scale artificial fracture network (10); S54: Continuously pumping in oxygen-rich water vapor (9) allows the fracture to not only expand in the coal seam (3) where the intermediate horizontal well (4) is located, but also extend upward and downward into adjacent coal seams (3), thereby increasing the connectivity range of the artificial fracture (10); Step 6: Underground gasification of coal seam (3) and extraction of coal seam methane (11); S61: During the fracturing process of the intermediate horizontal well (4), when the input of oxygen-rich steam (9) reaches 300-400m 3 When the injection of oxygen-enriched water vapor (9) is stopped, an ignition rod is dropped into the bottom of the intermediate horizontal well (4) by a special dropping device, and the coal seam (3) is ignited by the ignition rod, thereby initiating an underground gasification process of the coal seam (3); S62: After the coal seam (3) is ignited, oxygen-enriched steam (9) is continuously injected into the intermediate horizontal well (4) to maintain the continuous gasification process of the coal seam (3). At the same time, the high temperature and high pressure of the oxygen-enriched steam (9) is used to promote further expansion of the cracks, and the gas and heat generated by the gasification of the coal seam (9) are simultaneously used to promote the formation and expansion of the cracks; While the gasification operation of the middle horizontal well (4) is being carried out, the top horizontal well (5) and the bottom horizontal well (6) are used to synchronously carry out the extraction operation of the coalbed methane (11). At the same time, the extraction process is used to reduce the pressure in the coal seam (3), further promoting the in-depth progress of the gasification reaction of the middle horizontal well (4); S63: When the gasification process of the middle horizontal well (4) is completed, the gasification agent injection system of the middle horizontal well (4) is closed, and the well is shut down to allow the downhole combustion process to proceed fully. Through the combustion process, a combustion void zone (12) is formed around the artificial seam network (10) in the middle horizontal well (4); at the same time, the extraction operation of the top horizontal well (5) and the bottom horizontal well (6) is continued, and the extraction process is continued until the set extraction time ends; Step 7: Supercritical CO2 fracturing and replacement; After the extraction operation is completed, the top horizontal well (5) and the bottom horizontal well (6) are immediately subjected to supercritical CO2 fracturing. During the supercritical CO2 fracturing process, the injection flow rate of the supercritical carbon dioxide (13) is precisely controlled to induce further expansion of the internal cracks of the coal seam (3), thereby forming a more complex three-dimensional crack network (14) with a larger connectivity range. Simultaneously, the adsorbed methane in the coal seam (3) is replaced with a free state by utilizing the powerful adsorption capacity of the supercritical carbon dioxide (13). At the same time, the supercritical carbon dioxide (13) is used to penetrate into the micropores of the coal seam (3) due to its high diffusivity and low surface tension, thereby further increasing the content of free methane in the coal seam (3); Step 8: Hydraulic fracturing and CO2 storage; After the injection of a predetermined amount of supercritical carbon dioxide (13) is completed, a water-based fracturing fluid is injected into the top horizontal well (5) and the bottom horizontal well (6) at a set flow rate, and the injected water-based fracturing fluid is used to gradually expand the internal cracks of the coal seam (3) to form a complex fracture network; at the same time, the water-based fracturing fluid is used to squeeze the supercritical carbon dioxide (13) into the deep part of the reservoir to further displace the methane gas in the coal seam (3); During the injection of the water-based fracturing fluid, the high molecular weight polymer and the cross-linking agent in the water-based fracturing fluid gradually form a high-strength and high-toughness plugging layer in the cracks. The formed plugging layer is used to effectively support the cracks to prevent the cracks from closing after pressure relief. At the same time, the formed plugging layer effectively prevents supercritical carbon dioxide (13) from escaping from the cracks and returning to the wellbore. Step 9: Extraction of gasified products and coal-bed methane (11); S91: The gasification products and desorbed methane gas generated by the combustion and gasification of the coal seam (3) are extracted through the intermediate horizontal well (4), and separated and processed by a gas separation device after being extracted to the ground; during the extraction process, the parameters of the gas returned from the intermediate horizontal well (4) are monitored in real time through sensors installed in the extraction well, and the intermediate horizontal well (4) is closed when no significant combustible gas is returned from the intermediate horizontal well (4) for a long time and the gas concentration is stably maintained within a set low concentration range; S92: The top horizontal well (5) and the bottom horizontal well (6) are kept closed at the same time, and the supercritical carbon dioxide (13) injected previously is sealed for a long term to achieve the carbon emission reduction target.

2. The method for integrated fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 1, characterized in that: In step one, geological radar and seismic exploration techniques are used to detect the distribution of underground coal seams (3).

3. A method for integrating fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 1 or 2, characterized in that: In step 2 S23, after the drilling operation of the intermediate horizontal well (4) is completed, the drilling effect is evaluated by logging technology. The evaluation content includes the accuracy of the drilling trajectory and the penetration of the coal seam (3). Based on the evaluation results, the subsequent fracturing, gasification and carbon storage plans are adjusted and optimized.

4. The method for integrated fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 3, characterized in that: During the drilling process in step three, the drilling trajectory and formation changes are monitored in real time to ensure that the horizontal well is accurately positioned and has a smooth trajectory. At the same time, the top horizontal well (5) and the bottom horizontal well (6) share a vertical well.

5. The method for integrated fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 4, characterized in that: In step 4, during the drilling process of the top fishbone well (7), the inclination and azimuth of the top fishbone well (7) are monitored in real time to ensure that the top fishbone well (7) extends along a predetermined trajectory, and at the same time, ensure that the top fishbone well (7) passes through at least one group of adjacent coal seams (3) and sandstone formations (2) after penetrating the formation encountered by the connected top horizontal well (5); during the drilling process of the bottom fishbone well (8), the inclination and azimuth of the bottom fishbone well (8) are monitored in real time to ensure that the bottom fishbone well (8) extends along a predetermined trajectory, and at the same time, ensure that the bottom fishbone well (8) passes through at least one group of adjacent coal seams (3) and sandstone formations (2) after penetrating the formation encountered by the connected bottom horizontal well (6).

6. The method for integrated fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 5, characterized in that: In step 4, the plurality of bottom fishbone wells (8) and the plurality of top fishbone wells (7) are symmetrically distributed, and the spacing between two adjacent bottom fishbone wells (8) and two adjacent top fishbone wells (7) is the same, and at the same time, the lengths of the bottom fishbone wells (8) and the top fishbone wells (7) are the same.

7. The method for integrating fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 6, characterized in that: In step 5 S52, the volume fraction of oxygen mixed in the water vapor is 40% to 60%; in step 5 S53, during the fracturing process, the flow rate of the oxygen-enriched water vapor (9) is adjusted to 3.0 to 4.5 m 3 / min.

8. The method for integrated fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 7, characterized in that: In step six S63, the extraction time is set to be no less than 5 to 7 hours.

9. The method for integrating fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 8, characterized in that: In step 7, the injection rate of supercritical carbon dioxide (13) is 2-3 m 3 / min.

10. The method for integrated fracturing, gasification and carbon sequestration of thin interbedded coal seams according to claim 9, characterized in that: In step eight, the injection flow rate of the water-based fracturing fluid is 8 to 10 m 3 / min.

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