Method for fracturing deep coal bed gas reservoir by using industrial greenhouse gas

Abstract

The invention relates to a method for fracturing a deep coal bed gas reservoir by using industrial greenhouse gas, which comprises the following steps: collecting the treated industrial greenhouse gas, and liquefying at low temperature to obtain liquid carbon dioxide; for a deep coal bed gas reservoir, a vertical well is drilled firstly, then a plurality of horizontal wells are drilled with the bottom of the vertical well as the starting point, and the horizontal wells are evenly distributed in a radial mode with the circle center of the bottom of the vertical well as the center; the horizontal well is evenly divided into a plurality of perforation sections in the length direction of the horizontal well, the lengths of all the horizontal wells and the number and length of the perforation sections are the same, and the perforation sequence is gradual retreating type perforation from the tail end to the starting end; the method comprises the following steps: sequentially perforating one perforation section of each horizontal well in a clockwise or anticlockwise direction, then sequentially fracturing the perforated perforation sections of each horizontal well in the same sequence, and using liquid carbon dioxide during fracturing; and according to the sequence from the tail end to the starting end of the horizontal well, perforation and fracturing are conducted on the perforation sections of all the horizontal wells in sequence according to the operation.

Description

Technical Field

[0001] The invention belongs to the technical field of coalbed methane reservoir fracturing, and in particular relates to a method for fracturing deep coalbed methane reservoirs using industrial greenhouse gases. Background Art

[0002] At present, the development of deep coalbed methane resources mainly adopts the method of hydraulic fracturing reservoirs. Large-scale hydraulic fracturing can transform the geological microstructure of deep coalbed methane reservoirs and promote the release of coalbed methane. Large-scale hydraulic fracturing requires a lot of water, and the main distribution areas of my country's coal mining areas are mostly arid and water-scarce areas. The lack of water resources restricts hydraulic fracturing transformation.

[0003] On the other hand, most of my country's coal mining areas are also heavy industrial clusters, which facilitates the use of coal and gas resources at close range and at low cost. Heavy industry is the main source of industrial greenhouse gases. At present, a large amount of waste gas, after treatment, contains less sulfur and nitrogen, but a higher carbon dioxide content. These tail gases are discharged into the atmosphere, which will aggravate the greenhouse phenomenon. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for fracturing a deep coalbed methane reservoir using industrial greenhouse gas, comprising the following steps: S1: Collect the processed industrial greenhouse gas and perform low-temperature liquefaction to obtain liquid carbon dioxide; S2: For deep coalbed methane reservoirs, first drill a vertical well, then take the bottom of the vertical well as the starting point and drill several horizontal wells, so that the beginning of the horizontal well is connected to the bottom of the vertical well, and the several horizontal wells are evenly distributed in a radial shape with the center of the bottom of the vertical well as the center; S3: The horizontal well is evenly divided into several perforation sections along the length direction of the horizontal well. The length, number and length of the perforation sections of all horizontal wells are the same, and the perforation sequence is a gradual perforation from the end to the beginning; S4: perforating a perforation section of each horizontal well in a clockwise or counterclockwise direction, and then fracturing the perforated sections of each horizontal well in the same order, using the liquid carbon dioxide obtained in step S1 during fracturing; In order from the end to the beginning of the horizontal well, the perforation sections of all the horizontal wells are perforated and fractured in sequence according to the operation of step S4.

[0005] Optionally, in step S2, several horizontal wells have the same length, forming a circle with the center of the vertical well as the center and the length of the horizontal well as the radius. The ends of the several horizontal wells are evenly distributed along the circumference of the circle. The horizontal wells are located in the deep coalbed methane reservoir, forming an open umbrella shape, which can be fractured in multiple directions around the deep reservoir, greatly improving the fracturing effect, which is conducive to increasing the coalbed methane production later; at the same time, liquid carbon dioxide is used for fracturing in multiple horizontal wells, and deep geological injection of carbon dioxide is also completed at the same time.

[0006] Optionally, in step S3, the perforation mode in the horizontal well is defined, and the horizontal well is divided into several sections along the length direction of the horizontal well, and perforation and fracturing are performed in sections, and the sections are named as the first perforation section, the second perforation section, etc., from the end to the beginning of the horizontal well, until the nth perforation section, where n is the number of perforation sections; Specifically, the progressive perforation is to first perforate the first perforation section, then perform fracturing, then perforate the second perforation section, and then perform fracturing in the second perforation section, so that perforation and fracturing are performed section by section from the end to the beginning of the horizontal well until the perforation section closest to the beginning is reached.

[0007] Optionally, step S4 is specifically: (1) lowering the perforating gun along the vertical well to the bottom of the vertical well, and perforating the first perforating section of each horizontal well in turn in a clockwise or counterclockwise direction; (2) Using liquid carbon dioxide, starting from the first perforated horizontal well, the first perforated section of each horizontal well is sequentially fractured in the same direction as step (1). After a horizontal well is fractured with carbon dioxide, it is supplemented with fracturing fluid without draining the fluid. Then, the perforated section that has been fractured is plugged with a soluble bridge plug; (3) Repeating the operation of step (1) to sequentially perforate the second perforation section of each horizontal well; then repeating the operation of step (2) to sequentially perform liquid carbon dioxide fracturing and fracturing fluid fracturing on the second perforation section of each horizontal well without draining the fluid, and then setting the seal; Repeat step (3) until all perforation sections of all horizontal wells are fractured and then drained uniformly.

[0008] Further optionally, in step (2), for the same perforation section, carbon dioxide is first used for primary fracturing to initially expand the fissures, cracks, and rock channels, and then conventional fracturing fluid is used for secondary fracturing. The fracturing fluid is superior to carbon dioxide gas in physical size and can form physical support expansion in the fissures with proppants (coarse sand and fine sand), which is conducive to forming a richer fracture network.

[0009] The present invention provides a novel perforating device, comprising a conventional vertical perforating rod, a horizontal perforating rod and a perforating gun, wherein the perforating gun is installed on the horizontal perforating rod, a rotatable liquid blocking part is provided at the bottom of the vertical perforating rod, and the horizontal perforating rod is connected below the liquid blocking part and can perform perforation on different horizontal wells with the rotation position of the liquid blocking part; The liquid-blocking part includes a driving motor, a support and several liquid-blocking branches on the support. The liquid-blocking branch is a retractable rod and a hemispherical liquid-blocking plate is provided at the front end. When the liquid-blocking part descends along the vertical well, the liquid-blocking branch is retracted to an upright position. After the liquid-blocking part descends to the bottom of the vertical well, the liquid-blocking branch is released to point to each horizontal well. At this time, the liquid-blocking plate corresponds to the starting end of the horizontal well.

[0010] Optionally, the support is annular and sleeved on the outer side of the bottom of the vertical perforating rod, and a plurality of liquid blocking branches are evenly arranged along the circumference of the support, the number of liquid blocking branches is one less than the number of horizontal wells, each liquid blocking branch can point to a corresponding horizontal well, and there is a horizontal well that is not blocked by the liquid blocking plate and can be fractured; one end of the liquid blocking branch is hinged to the support, and the other end is fixedly connected to the liquid blocking plate; One end of the horizontal perforating rod is connected to the bottom of the support, and the other end is connected to the perforating gun.

[0011] Optionally, the two sections at the bottom of the vertical perforating rod are hollow, and a driving motor is provided inside the upper section. The rotating shaft of the driving motor is connected to the inner wall of the lower section through a connecting rod, and can drive the lower section and the support to rotate.

[0012] Optionally, the interior of the liquid blocking plate is hollow, and when the liquid blocking branch is unfolded, the opening of the liquid blocking plate faces away from the vertical perforating rod, the opening is a vertical circle, and the circle passes through the center of the liquid blocking plate, and the vertex of the side surface of the liquid blocking plate protruding toward the vertical perforating rod is connected to the corresponding liquid blocking branch through a spring.

[0013] Since the temperature of deep coalbed methane reservoirs is high, liquid carbon dioxide is affected by underground temperature. In order to avoid premature gasification, the present invention proposes a cooling sleeve, which is sleeved on the outside of the carbon dioxide fracturing pipe. The cross section of the cooling sleeve is annular. The interior of the cooling sleeve is used to accommodate cooling water to cool the carbon dioxide fracturing pipe and keep the interior of the carbon dioxide fracturing pipe in liquid state. A support frame is provided on the top of the cooling jacket to support the overall shape of the cooling jacket; a liquid inlet pipe and a liquid discharge pipe are provided on the top of the cooling jacket, and the liquid inlet pipe and the liquid discharge pipe are connected to the chiller on the ground to provide circulating cooling water for the cooling jacket; at least two steel cables are connected to the support frame, which are respectively connected to two winches on the ground for lowering and lifting the cooling jacket; the bottom of the cooling jacket is connected to the outlet end of the carbon dioxide fracturing pipe.

[0014] Optionally, a plurality of support rings are provided along the length direction of the cooling jacket, and the support rings are arranged on the outer surface of the cooling jacket. A plurality of telescopic mechanisms are provided on the support rings, and the telescopic mechanisms include an electromagnetic controller and a telescopic rod, which can control the extension of the telescopic rod so that the end of the telescopic rod is against the inner wall of the vertical well, so as to support the cooling jacket filled with cooling water. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the fracturing effect of the vertical well and the horizontal well of the present invention; Figure 2 is a schematic diagram of the structure of the perforating device; Figure 3 A schematic diagram of the placement of the drive motor in the vertical perforating rod; Figure 4 It is a schematic diagram of the structure of the cooling jacket.

[0016] In the attached drawings, 1-vertical well, 2-horizontal well, 3-vertical perforating rod, 4-horizontal perforating rod, 5-perforating gun, 6-driving motor, 7-support, 8-liquid blocking branch, 9-liquid blocking plate, 10-spring, 11-cooling sleeve, 12-support frame, 13-steel cable, 14-support ring, 15-telescopic rod, 16-rotating shaft. DETAILED DESCRIPTION

[0017] This embodiment provides a method for fracturing deep coalbed methane reservoirs using industrial greenhouse gases, such as Figure 1 As shown, the following steps are included: S1: Collect the processed industrial greenhouse gas and perform low-temperature liquefaction to obtain liquid carbon dioxide; S2: For deep coalbed methane reservoirs, first drill a vertical well 1, then take the bottom of the vertical well 1 as the starting point, drill several horizontal wells 2, so that the starting end of the horizontal well 2 is connected to the bottom of the vertical well 1, and the several horizontal wells 2 are evenly distributed in a radial shape with the bottom center of the vertical well 1 as the center; S3: The horizontal well is evenly divided into several perforation sections along the length direction of the horizontal well. The length, number and length of the perforation sections of all horizontal wells are the same, and the perforation sequence is a gradual perforation from the end to the beginning; S4: perforating a perforation section of each horizontal well in a clockwise or counterclockwise direction, and then fracturing the perforated sections of each horizontal well in the same order, using the liquid carbon dioxide obtained in step S1 during fracturing; In order from the end to the beginning of the horizontal well, the perforation sections of all the horizontal wells are perforated and fractured in sequence according to the operation of step S4.

[0018] Optionally, in step S1, the source of industrial greenhouse gas is industrial production equipment or workshops, such as thermal power plants, coal chemical plants, oil processing plants, etc. The industrial tail gas or waste gas discharged from the industrial production equipment or workshops is subjected to conventional dust removal, desulfurization, and denitrification treatments. If necessary, other chemical treatments may be added to minimize the content of corrosive gases in the treated industrial greenhouse gas to avoid corrosion of liquefaction equipment and fracturing equipment.

[0019] The nitrogen dioxide content in the treated industrial greenhouse gas is 60-90 vol%. The nitrogen dioxide in the industrial greenhouse gas is liquefied by conventional methods, such as low-temperature liquefaction and pressurized low-temperature liquefaction. The gas that cannot be liquefied is mainly nitrogen, which can be discharged to the external environment.

[0020] Optionally, in step S2, conventional exploration and detection of the above-ground and underground geological conditions of the coal mining area are carried out in advance, and then combined with existing historical geological data, the geological environment and conditions of the deep coalbed methane reservoir and the strata above it are comprehensively analyzed to determine the appropriate drilling location, formulate an appropriate drilling strategy, and drill a vertical well 1 and several horizontal wells.

[0021] Optionally, several horizontal wells have the same length, forming a circle with the center of the vertical well 1 as the center and the length of the horizontal well as the radius. The ends of the several horizontal wells are evenly distributed along the circumference of the circle. The horizontal wells are located in the deep coalbed methane reservoir, forming an open umbrella shape, which can be fractured in multiple directions around the deep reservoir, greatly improving the fracturing effect, which is conducive to increasing the coalbed methane production later; at the same time, liquid carbon dioxide is used for fracturing in multiple horizontal wells, and deep geological injection of carbon dioxide is also completed at the same time.

[0022] Optionally, in step S3, the perforation mode in the horizontal well is defined, and the horizontal well is divided into several sections along the length direction of the horizontal well, and perforation and fracturing are performed in sections, and the sections are named as the first perforation section, the second perforation section, etc., from the end to the beginning of the horizontal well, until the nth perforation section, where n is the number of perforation sections; Specifically, the progressive perforation is to first perforate the first perforation section, then perform fracturing, then perforate the second perforation section, and then perform fracturing in the second perforation section, so that perforation and fracturing are performed section by section from the end to the beginning of the horizontal well until the perforation section closest to the beginning is reached.

[0023] Optionally, step S4 is specifically: (1) lowering the perforating gun 5 along the vertical well 1 to the bottom of the vertical well 1, and perforating the first perforating section of each horizontal well in turn in a clockwise or counterclockwise direction; (2) Using liquid carbon dioxide, starting from the first perforated horizontal well, the first perforated section of each horizontal well is sequentially fractured in the same direction as step (1). After a horizontal well is fractured with carbon dioxide, it is supplemented with fracturing fluid without draining the fluid. Then, the perforated section that has been fractured is plugged with a soluble bridge plug; (3) Repeating the operation of step (1) to sequentially perforate the second perforation section of each horizontal well; then repeating the operation of step (2) to sequentially perform liquid carbon dioxide fracturing and fracturing fluid fracturing on the second perforation section of each horizontal well without draining the fluid, and then setting the seal; Repeat step (3) until all perforation sections of all horizontal wells are fractured and then drained uniformly.

[0024] The present invention collects the treated industrial greenhouse gas to prevent it from being directly discharged into the atmosphere, and then liquefies it. According to the properties of carbon dioxide, a conventional low-temperature and high-pressure liquefaction method can be used. Below the critical temperature of carbon dioxide, pressurization and / or lowering of temperature can obtain liquefied carbon dioxide. Liquid carbon dioxide with a certain pressure can be used to fractur the perforated section of the horizontal well through a pipeline. The present invention not only utilizes industrial carbon dioxide, injects carbon dioxide into the deep coalbed methane reservoir, and completes deep geological storage, but also uses high-pressure carbon dioxide fluid as a fracturing medium to fractur the horizontal well section that has been perforated. Once the high-pressure carbon dioxide fluid is released into the horizontal well, the temperature in the deep coalbed methane reservoir is higher than the ground, higher than the critical temperature of carbon dioxide, and the liquid carbon dioxide will quickly gasify and quickly overflow from the perforation channel left after perforation to the coal seam outside the horizontal well. Compared with the traditional fracturing fluid containing coarse sand and fine sand, the size range of the formation gaps that carbon dioxide gas can enter is wider, that is, carbon dioxide gas can enter large cracks, small cracks, and even fine cracks, and perform more comprehensive fracturing and expansion of the reservoir. Carbon dioxide and methane form a competitive adsorption relationship, which promotes the desorption of methane from the reservoir and the adsorption of carbon dioxide, making the carbon dioxide storage effect better.

[0025] In step (2), after the perforation of the first perforation section of all horizontal wells is completed, the first perforation sections of the horizontal wells adjacent to the first perforation section of any horizontal well are all perforated, that is, the reservoir between the first perforation sections of two adjacent horizontal wells has been perforated from both sides, and both sides have perforation channels. Carbon dioxide fracturing in the first perforation section of a horizontal well is equivalent to carbon dioxide fracturing from one side (for example, the left side) of the corresponding reservoir, and the fractures in the reservoir extend from the left side to the right side. Carbon dioxide fracturing in the first perforation section of the adjacent horizontal well is equivalent to carbon dioxide fracturing from the other side (for example, the right side) of the corresponding reservoir, and the fractures in the reservoir extend from the right side to the left side. In this way, the reservoir can withstand two fracturings from both sides, and the fractures on both sides extend into the reservoir. After meeting, they can influence and promote each other to continue to expand, forming a more complex and multi-dimensional fracture network, which is conducive to the deep storage of carbon dioxide and deep fracturing of reservoirs, and promotes coalbed methane production.

[0026] Further optionally, in step (2), for the same perforation section, carbon dioxide is first used for primary fracturing to initially expand the fissures, cracks, and rock channels, and then conventional fracturing fluid is used for secondary fracturing. The fracturing fluid is superior to carbon dioxide gas in physical size and can form physical support expansion in the fissures with proppants (coarse sand and fine sand), which is conducive to forming a richer fracture network.

[0027] Due to the basic role of the primary fracturing, the amount of fracturing fluid and pressure of the secondary fracturing can be reduced, and the amount of coarse sand and fine sand can also be reduced, saving the amount of proppant and water as well as energy consumption. The process conditions of the primary fracturing and the secondary fracturing are adjusted according to the actual storage conditions.

[0028] Since the present invention needs to perform perforation, primary fracturing, and secondary fracturing on each perforation section of each horizontal well in sequence, carbon dioxide will be gasified during fracturing. In addition to most of the carbon dioxide overflowing from the pores formed by the perforation, a small amount of carbon dioxide returns to the bottom of the vertical well 1 along the horizontal well and diffuses to other horizontal wells, reducing the fracturing effect of carbon dioxide. In addition, after the fracturing fluid in the perforation section of the horizontal well is fracturing, no fluid is discharged, and it is necessary to minimize the impact of the fracturing fluid on other horizontal wells, that is, part of the fracturing fluid flows to other horizontal wells, affecting the fracturing effect.

[0029] In order to solve the above problems, the present invention provides a new type of perforating device, such as Figure 2-Figure 3 As shown, it includes a conventional vertical perforating rod 3, a horizontal perforating rod 4 and a perforating gun 5. The perforating gun 5 is installed on the horizontal perforating rod 4. A rotatable liquid blocking part is provided at the bottom of the vertical perforating rod 3. The horizontal perforating rod 4 is connected to the bottom of the liquid blocking part and can rotate with the liquid blocking part to perform perforation on different horizontal wells. The liquid-blocking part includes a driving motor 6, a support 7 and a plurality of liquid-blocking branches 8 on the support 7. The liquid-blocking branch 8 is a retractable rod and a hemispherical liquid-blocking plate 9 is provided at the front end. When the liquid-blocking part descends along the vertical well 1, the liquid-blocking branch 8 is retracted to an upright position. After the liquid-blocking part descends to the bottom of the vertical well 1, the liquid-blocking branch 8 is released and points to each horizontal well. The liquid-blocking plate 9 covers the starting end of the corresponding horizontal well.

[0030] Optionally, the support 7 is annular and sleeved on the outer side of the bottom of the vertical perforating rod 3. A plurality of liquid blocking branches 8 are evenly arranged along the circumference of the support 7. The number of liquid blocking branches 8 is one less than the number of horizontal wells. Each liquid blocking branch 8 can point to a corresponding horizontal well, and there is a horizontal well that is not blocked by the liquid blocking plate 9 and can be fractured. One end of the liquid blocking branch 8 is hinged to the support 7, and the other end is fixedly connected to the liquid blocking plate 9. One end of the horizontal perforating rod 4 is connected to the bottom of the support 7 , and the other end is connected to the perforating gun 5 .

[0031] Optionally, the two sections at the bottom of the vertical perforating rod 3 are hollow, and a driving motor 6 is provided inside the upper section. The rotating shaft 16 of the driving motor 6 is connected to the inner wall of the lower section through a connecting rod, and can drive the lower section and the support 7 to rotate.

[0032] Optionally, the liquid blocking branch 8 is in a mechanically controlled form, for example, the liquid blocking branch 8 is connected to a hollow lower section at the bottom of the vertical perforating rod 3 through a telescopic rod 15, and a telescopic control device is installed inside the section, and the telescopic control device corresponds to the liquid blocking branch 8 one by one.

[0033] Optionally, the liquid-blocking branch 8 is in an electromagnetically controlled form, for example, one or more electromagnetic devices are installed in a hollow lower section at the bottom of the vertical perforating rod 3, and the electromagnetic devices are connected to and control the liquid-blocking branch 8. One electromagnetic device can control multiple liquid-blocking branches 8, or one electromagnetic device can control one liquid-blocking branch 8.

[0034] The telescopic control device and the electromagnetic device are both connected to the inner wall of the lower section and can rotate with the section.

[0035] Optionally, the interior of the liquid blocking plate 9 is hollow. When the liquid blocking branch 8 is unfolded, the opening of the liquid blocking plate 9 faces away from the vertical perforating rod 3. The opening is a vertical circle that passes through the center of the liquid blocking plate 9. The vertex of the side of the liquid blocking plate 9 that protrudes toward the vertical perforating rod 3 is connected to the corresponding liquid blocking branch 8 through the spring 10.

[0036] When in use, the vertical perforating rod 3 is on the central axis of the vertical well 1, and the liquid blocking part, the horizontal perforating rod 4, and the perforating gun 5 are lowered along the vertical well 1 together with the vertical perforating rod 3. During the descent process, the liquid blocking branch 8 is in a retracted state. Since the openings of each liquid blocking plate 9 are facing upwards, surrounding the vertical perforating rod 3, the openings of each liquid blocking plate 9 are clustered together, and there are different degrees of inclination. In order to cooperate with the liquid blocking plate 9, each liquid blocking branch 8 is in an upright state as a whole, and there are also different degrees of inclination. Since the vertex of the liquid blocking plate 9 is connected to the corresponding liquid blocking branch 8 through the spring 10, the liquid blocking plate 9 is allowed to have a certain swing amplitude.

[0037] The inner diameter of the bottom of the vertical well 1 is larger than the inner diameter of other parts of the vertical well 1. When the liquid blocking part reaches the bottom of the vertical well 1, each liquid blocking branch 8 remains in the retracted state, and the support 7 is rotated by the driving motor 6 so that the perforating gun 5 faces the horizontal well to be perforated first. The vertical perforating rod 3, the horizontal perforating rod 4 and the perforating gun 5 are all conventional structures and usage methods. The horizontal perforating rod 4 sends the perforating gun 5 into the first perforating section of the horizontal well for perforation, and then the support 7 rotates, and the perforating gun 5 completes the perforation of the first perforating section of each horizontal well in turn, and then the perforating gun 5 is retracted to the bottom of the liquid blocking part.

[0038] When the carbon dioxide fracturing pipe is extended into a horizontal well and is ready to be fractured with carbon dioxide, all the liquid blocking branches 8 are unfolded, and the opening of the liquid blocking plate 9 covers the beginning of the corresponding horizontal well. When the output carbon dioxide is gasified, a small part of the carbon dioxide returns to the bottom of the vertical well 1 along the horizontal well, and there is also a strong air flow impact, and the carbon dioxide airflow expands to the surroundings at the bottom of the vertical well 1, pressing each liquid blocking plate 9 to buckle to the corresponding horizontal well, preventing the carbon dioxide airflow from entering each horizontal well. After carbon dioxide fracturing, most of the carbon dioxide is discharged from the perforation section, and the air pressure at the bottom of the vertical well 1 is gradually reduced, the spring 10 is reset, and the liquid blocking plate 9 is separated from the beginning of the horizontal well (without affecting the rotation of the liquid blocking plate 9 driven by the support 7).

[0039] When the fracturing fluid perforates the horizontal well, the carbon dioxide fracturing pipe is retracted to the bottom of the vertical well 1, and the fracturing fluid fracturing pipe is extended into a horizontal well for fracturing. Similarly, the strong impact of the fracturing fluid will also cause part of the fracturing fluid to return to the bottom of the vertical well 1 and expand around, forcing each fluid blocking plate 9 to buckle to the corresponding horizontal well, preventing the fracturing fluid from entering each horizontal well. After fracturing, a soluble bridge plug is used to seal and no fluid is discharged. The spring 10 is reset, and the fluid blocking plate 9 is separated from the beginning of the horizontal well.

[0040] After all the horizontal wells are perforated, the liquid blocking branch 8 is retracted and leaves the vertical well 1 along with the vertical perforating rod 3 .

[0041] Since the temperature of deep coalbed methane reservoirs is relatively high, liquid carbon dioxide is affected by underground temperature. To avoid premature gasification, the present invention proposes a cooling sleeve 11, such as Figure 4As shown, the cooling sleeve 11 is sleeved on the outside of the carbon dioxide fracturing pipe, and the cross section of the cooling sleeve 11 is circular. The interior of the cooling sleeve 11 is used to contain cooling water to cool the carbon dioxide fracturing pipe and keep the interior of the carbon dioxide fracturing pipe in liquid state; A support frame 12 is provided on the top of the cooling jacket 11 for supporting the overall shape of the cooling jacket 11; a liquid inlet pipe and a liquid discharge pipe are provided on the top of the cooling jacket 11, and the liquid inlet pipe and the liquid discharge pipe are connected to a chiller on the ground to provide circulating cooling water for the cooling jacket 11; at least two steel cables 13 are connected to the support frame 12, which are respectively connected to two winches on the ground for lowering and lifting the cooling jacket 11; the bottom of the cooling jacket 11 is connected to the outlet end of the carbon dioxide fracturing pipe.

[0042] Optionally, a plurality of support rings 14 are provided along the length direction of the cooling jacket 11. The support rings 14 are provided on the outer side surface of the cooling jacket 11. A plurality of telescopic mechanisms are provided on the support rings 14. The telescopic mechanisms include an electromagnetic controller and a telescopic rod 15. The telescopic rod 15 can be controlled to extend so that the end of the telescopic rod 15 is against the inner wall of the vertical well 1, so as to support the cooling jacket 11 filled with cooling water.

[0043] When in use, the cooling jacket 11 does not need to cover the entire carbon dioxide fracturing pipe. Through actual measurement, the specific situation of the geological temperature increasing with the depth is obtained, and a certain depth underground is determined as the starting point for cooling (i.e., the top position of the cooling jacket 11). The cooling jacket 11 is lowered along the vertical well 1 together with the carbon dioxide fracturing pipe. When it reaches the above starting point, the winch stops lowering, and the support frame 12 at the top of the cooling jacket 11 stays at the above starting point. The steel cable 13 pulls the cooling jacket 11; the other parts of the cooling jacket 11 continue to descend and unfold with the carbon dioxide fracturing pipe. At the same time, a small amount of water is filled into the cooling jacket 11, so that the weight at the bottom of the cooling jacket 11 increases, forming a downward force, and the cooling jacket 11 can be smoothly unfolded.

[0044] Several support rings 14 are evenly distributed along the length from the starting point to the bottom of the vertical well 1, so as to assist in supporting the cooling jacket 11 filled with water. When the cooling jacket 11 is deployed to a support ring 14, the telescopic rod 15 of the support ring 14 is ejected outwards and abuts against the inner wall of the vertical well 1, so as to assist in supporting the cooling jacket 11.

[0045] When the CO2 fracturing pipe extends to the bottom of the vertical well 1, the front section of the cooling sleeve 11 is fully deployed, and the rear section is not deployed. When the CO2 fracturing pipe continues to extend into the horizontal well, the rear section of the cooling sleeve 11 continues to be gradually deployed. In the above manner, the cooling sleeve 11 is wrapped around the outer side of the CO2 fracturing pipe that needs to be cooled.

[0046] The carbon dioxide fracturing pipe and the fracturing fluid fracturing pipe are respectively arranged on both sides of the vertical perforating rod 3 , and the three do not interfere with each other. The cooling sleeve 11 and the telescopic rod 15 do not contact the vertical perforating rod 3 either.

Claims

1. A method for fracturing deep coalbed methane reservoirs using industrial greenhouse gases, characterized in that: The following steps are involved: S1: Collect the processed industrial greenhouse gas and perform low-temperature liquefaction to obtain liquid carbon dioxide; S2: For deep coalbed methane reservoirs, first drill a vertical well, then take the bottom of the vertical well as the starting point and drill several horizontal wells, so that the beginning of the horizontal well is connected to the bottom of the vertical well, and the several horizontal wells are evenly distributed in a radial shape with the center of the bottom of the vertical well as the center; S3: The horizontal well is evenly divided into several perforation sections along the length direction of the horizontal well. The length, number and length of the perforation sections of all horizontal wells are the same, and the perforation sequence is a gradual perforation from the end to the beginning; S4: perforating a perforation section of each horizontal well in a clockwise or counterclockwise direction, and then fracturing the perforated sections of each horizontal well in the same order, using the liquid carbon dioxide obtained in step S1 during fracturing; In order from the end to the beginning of the horizontal well, the perforation sections of all the horizontal wells are perforated and fractured in sequence according to the operation of step S4.

2. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gases according to claim 1, characterized in that: In step S2, the lengths of the plurality of horizontal wells are the same, and a circle is formed with the center of the vertical well as the center and the length of the horizontal well as the radius, and the ends of the plurality of horizontal wells are evenly distributed along the circumference of the circle.

3. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gases according to claim 1, characterized in that: In step S3, the perforation mode in the horizontal well is defined, and the horizontal well is divided into several sections along the length direction of the horizontal well, and perforation and fracturing are performed in sections. From the end to the beginning of the horizontal well, they are named the first perforation section, the second perforation section, and the nth perforation section, where n is the number of perforation sections. Specifically, the progressive perforation is to first perforate the first perforation section, then perform fracturing, then perforate the second perforation section, and then perform fracturing in the second perforation section, so that perforation and fracturing are performed section by section from the end to the beginning of the horizontal well until the perforation section closest to the beginning is reached.

4. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gas according to claim 1, characterized in that: Step S4 is specifically as follows: (1) lowering the perforating gun along the vertical well to the bottom of the vertical well, and perforating the first perforating section of each horizontal well in turn in a clockwise or counterclockwise direction; (2) Using liquid carbon dioxide, starting from the first perforated horizontal well, the first perforated section of each horizontal well is sequentially fractured in the same direction as step (1). After a horizontal well is fractured with carbon dioxide, it is supplemented with fracturing fluid without draining the fluid. Then, the perforated section that has been fractured is plugged with a soluble bridge plug; (3) Repeating the operation of step (1) to sequentially perforate the second perforation section of each horizontal well; then repeating the operation of step (2) to sequentially perform liquid carbon dioxide fracturing and fracturing fluid fracturing on the second perforation section of each horizontal well without draining the fluid, and then setting the seal; Repeat step (3) until all perforation sections of all horizontal wells are fractured and then drained uniformly.

5. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gas according to claim 4, characterized in that: In step (2), for the same perforation section, carbon dioxide is first used for primary fracturing to initially expand the fissures, cracks, and rock channels, and then conventional fracturing fluid is used for secondary fracturing.

6. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gas according to claim 4, characterized in that: In step S4, a perforating device is used for perforating, including a vertical perforating rod, a horizontal perforating rod and a perforating gun. The perforating gun is installed on the horizontal perforating rod. A rotatable liquid blocking part is provided at the bottom of the vertical perforating rod. The horizontal perforating rod is connected to the bottom of the liquid blocking part and can rotate with the liquid blocking part to perform perforation on different horizontal wells. The liquid-blocking part includes a driving motor, a support and several liquid-blocking branches on the support. The liquid-blocking branch is a retractable rod and a hemispherical liquid-blocking plate is provided at the front end. When the liquid-blocking part descends along the vertical well, the liquid-blocking branch is retracted to an upright position. After the liquid-blocking part descends to the bottom of the vertical well, the liquid-blocking branch is released to point to each horizontal well. At this time, the liquid-blocking plate corresponds to the starting end of the horizontal well.

7. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gas according to claim 6, characterized in that: The support is annular and sleeved on the outer side of the bottom of the vertical perforating rod. A plurality of liquid blocking branches are evenly arranged along the circumference of the support. The number of liquid blocking branches is one less than the number of horizontal wells. Each liquid blocking branch can point to a corresponding horizontal well. One end of the liquid blocking branch is hinged to the support, and the other end is fixedly connected to the liquid blocking plate. One end of the horizontal perforating rod is connected to the bottom of the support, and the other end is connected to the perforating gun.

8. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gas according to claim 7, characterized in that: The two sections at the bottom of the vertical perforating rod are hollow, a driving motor is arranged inside the upper section, and the rotating shaft of the driving motor is connected to the inner wall of the lower section through a connecting rod, so as to drive the lower section and the support to rotate.

9. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gas according to claim 4, characterized in that: In step S4, a cooling sleeve is used for fracturing. The cooling sleeve is sleeved on the outside of the carbon dioxide fracturing pipe. The cross section of the cooling sleeve is annular. The interior of the cooling sleeve is used to contain cooling water to cool the carbon dioxide fracturing pipe and keep the interior of the carbon dioxide fracturing pipe in liquid state. A support frame is provided on the top of the cooling jacket to support the overall shape of the cooling jacket; a liquid inlet pipe and a liquid discharge pipe are provided on the top of the cooling jacket, and the liquid inlet pipe and the liquid discharge pipe are connected to the chiller on the ground to provide circulating cooling water for the cooling jacket; at least two steel cables are connected to the support frame, which are respectively connected to two winches on the ground for lowering and lifting the cooling jacket; the bottom of the cooling jacket is connected to the outlet end of the carbon dioxide fracturing pipe.

10. The method for fracturing deep coalbed methane reservoirs using industrial greenhouse gas according to claim 9, characterized in that: Several support rings are provided along the length direction of the cooling jacket. The support rings are arranged on the outer side of the cooling jacket. Several telescopic mechanisms are provided on the support rings. The telescopic mechanisms include an electromagnetic controller and a telescopic rod, which can control the extension of the telescopic rod so that the end of the telescopic rod rests against the inner wall of the vertical well, thereby supporting the cooling jacket filled with cooling water.

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