Coalbed gas and sand gas co-production production pipe column and co-production method

Abstract

The present application relates to unconventional oil and gas coalbed methane gas exploration and development field, especially to a coalbed methane and sandstone gas production pipe column and a method for producing the same, the present application comprises an outer casing, an inner casing, a tubing, a first distribution system, a second distribution system and a packer, wherein the outer casing and the inner casing form a first annulus, the inner casing and the tubing form a second annulus, the first distribution system, the second distribution system and the packer are located in the first annulus, the packer can separate the coalbed methane and the sandstone gas, the first distribution system and the second distribution system can selectively connect the two gas reservoirs, so that the two gas reservoirs can realize auxiliary gas lift liquid discharge without external gas source, thereby reducing the cost and operation difficulty.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane exploration and development technology in unconventional oil and gas, and particularly to a production tubing and method for co-producing coalbed methane and sandstone gas. Background Technology

[0002] In the process of coalbed methane development, the production of tight sandstone gas in tight sandstone gas layers is often accompanied by the production of tight sandstone gas. Tight sandstone gas is mainly free gas, and its extraction relies on the reservoir's own energy to seep into the wellbore. However, the extraction of coalbed methane relies on external forces to drain the water in the reservoir, reducing the coalbed methane layer pressure to below the desorption pressure of the coalbed methane layer. Only then will the gas slowly desorb and be produced, and then diffuse and seep into the wellbore. Therefore, controlling the coalbed methane layer pressure by controlling the dynamic liquid level and casing pressure is a common method in coalbed methane extraction.

[0003] Therefore, for gas wells where both coalbed methane and tight sandstone gas layers coexist, it is difficult to effectively control the dynamic fluid level height using a conventional single tubing structure, thus making it impossible to accurately control the coalbed methane layer pressure. Moreover, when the tight sandstone gas production is large, it will directly affect the depressurization process of the coalbed methane layer, making it difficult for the coalbed methane to desorb and causing difficulties in coalbed methane extraction. Therefore, the common practice is to drill and extract coalbed methane and sandstone gas separately. This method results in a large footprint for the extraction equipment and high cost.

[0004] To this end, patent application CN2018113986322 proposes a production string and extraction method for co-production of coalbed methane and sandstone gas in a well. The co-production string for coalbed methane and sandstone gas in a well includes: casing, an outer coiled tubing and an inner coiled tubing disposed within the casing. The lower end of the outer coiled tubing is connected to a release valve via a connector, and the lower end of the release valve is sequentially connected to a safety valve, a sliding sleeve device, a packer, and a screen blocker. A first annular space is formed between the casing and the outer coiled tubing. The packer is located within the first annular space to isolate and separate the sandstone gas layer and the coalbed methane layer in the wellbore. The opening pressure of the safety valve is lower than the opening pressure of the sliding sleeve device but higher than the maximum bottom hole pressure during gas lift and drainage. The corresponding extraction method is as follows: First, coalbed methane and sandstone gas are run into the well using the same production tubing. In the initial stage of production, coalbed methane and sandstone gas are extracted and discharged separately using gas lift. In the middle stage of production, coalbed methane and sandstone gas are extracted separately in the same well, and liquid is discharged using gas lift. In the later stage of production, sandstone gas and coalbed methane are co-extracted. This invention can achieve separate extraction, gas lift discharge, and co-extraction of coalbed methane and sandstone gas in the same wellbore, while also reducing costs.

[0005] However, the aforementioned production tubing and mining methods require the use of an air compressor to inject gas into the second annular space from the outside when gas-lifting liquid from the coalbed methane layer, and to ensure that the bottom hole pressure is lower than the opening pressure of the safety valve. When liquid accumulates in the first annular space, gas also needs to be injected into the second annular space, and the bottom hole pressure needs to be higher than the opening pressure of the safety valve, in order to lift the accumulated liquid to the surface. This operation is cumbersome and reduces mining efficiency. Summary of the Invention

[0006] One of the objectives of this invention is to provide a production tubing for the co-production of coalbed methane and sandstone gas, which can utilize sandstone gas to achieve gas lift and liquid drainage of the coalbed methane layer, and utilize coalbed methane to achieve gas lift and liquid drainage of the sandstone gas layer, thereby reducing operational difficulty and improving mining efficiency.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] A production string for co-extraction of coalbed methane and sandstone gas includes a vertical well and a horizontal well. The horizontal well is configured in two sections, extending into the sandstone gas layer and the coalbed methane layer respectively, and both are connected to the vertical well. The vertical well includes:

[0009] An outer casing, an inner casing, and a tubing are arranged sequentially from the outside to the inside. The annular space between the outer casing and the inner casing is a first annulus, and a sandstone gas outlet is provided at the top of the first annulus. The annular space between the inner casing and the tubing is a second annulus, and the top of the second annulus is closed. The tubing extends out of the outer casing and has a coalbed methane outlet.

[0010] A first distribution system, a second distribution system, and a packer are installed in the first annulus. The first distribution system, the second distribution system, and the packer divide the first annulus into four sections from top to bottom: annulus section one, annulus section two, annulus section three, and annulus section four. Annulus section four is connected to the coalbed methane layer, and annulus section two is connected to the sandstone methane layer. The first distribution system is configured to selectively distribute gas from the sandstone methane layer to either annulus section one or annulus section two. The second distribution system is configured to distribute liquid from the sandstone methane layer to annulus section two.

[0011] Optionally, the first distribution system includes a pressurizing device and a one-way valve. The one-way valve is configured as two sets, namely one-way valve A and one-way valve B. The outlet of one-way valve A is connected to a section of the annulus, and the outlet of one-way valve B is connected to the inner sleeve. One-way valve A and one-way valve B can be opened selectively. The pressurizing device is configured to provide the one-way valve with pressure-adjustable gas to realize the opening and closing of the one-way valve.

[0012] Optionally, the first distribution system further includes a housing, which cooperates with the pressurizing device to form a closed distribution space. Both the one-way valve A and the one-way valve B are disposed inside the housing. The pressurizing device has multiple outlets, which are more than the number of one-way valves A. A portion of the outlets of the pressurizing device is connected to the inlet of the one-way valve A, and another portion supplies gas into the housing. The outlet of the one-way valve A is disposed through the top of the housing, and the outlet of the one-way valve B is disposed through the inner shell wall of the housing and connected to the inner sleeve.

[0013] Optionally, the free state of the one-way valve A is the open state, and the free state of the one-way valve B is the closed state.

[0014] Optionally, the second distribution system includes a pressurizing device and a one-way valve, wherein the inlet of the one-way valve is connected to the outlet of the pressurizing device, and the outlet of the one-way valve is connected to the inner sleeve.

[0015] Optionally, the free state of the one-way valve is the closed state.

[0016] Optionally, the second distribution system further includes a mounting sleeve, which is fixedly sleeved on the inner sleeve, and a plurality of the one-way valves are radially disposed through the mounting sleeve.

[0017] Optionally, the booster device includes a housing, an impeller, and a drive unit. The housing is a hollow ring and is fixedly sleeved on the inner sleeve with the same outer diameter as the inner diameter of the outer sleeve. An inlet and an outlet are provided on opposite sides of the housing. The impeller is coaxially rotatably disposed inside the housing, and the drive unit is configured to drive the impeller to rotate.

[0018] Optionally, the driving components are a stator and a rotor, with the stator fixed to the inner shell wall of the housing and the rotor fixed to the inner side of the central hole of the impeller.

[0019] Another objective of this invention is to provide a method for the simultaneous extraction of coalbed methane and sandstone gas, achieved using the aforementioned coalbed methane and sandstone gas co-extraction production tubing, specifically including the following steps:

[0020] The coalbed methane and sandstone gas co-production tubing is lowered into the well for fracturing operations.

[0021] In the initial stage of production, the first distribution system distributes sandstone gas to the second annulus;

[0022] After the coalbed methane forms a pressure drop funnel, the first distribution system distributes the sandstone gas to the annulus section.

[0023] When liquid accumulates in the sandstone gas layer, the second distribution system distributes the accumulated liquid to the second annulus.

[0024] The beneficial effects of this invention are as follows: The production tubing and method for co-extracting coalbed methane and sandstone gas proposed in this invention involve setting an inner casing and tubing inside an outer casing, thereby forming a first annulus and a second annulus. The first annulus is connected to the sandstone gas layer, and the second annulus is connected to the coalbed methane. Coalbed methane and sandstone gas can be discharged to the surface from the tubing and the first annulus, respectively. Furthermore, a first distribution system and a second distribution system are set in the first annulus, which can selectively connect the first and second annulus. When the coalbed methane is not desorbed, sandstone gas can enter the second annulus through the first distribution system to achieve gas lift and liquid drainage of the coalbed methane layer. When liquid accumulates in the sandstone gas layer, the accumulated liquid can enter the second annulus through the second distribution system to achieve gas lift and liquid drainage of the sandstone gas layer. This achieves mutual auxiliary extraction of coalbed methane and sandstone gas without the need for an external gas source, and the operation is simple and low-cost. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the production tubing for co-extraction of coalbed methane and sandstone gas proposed in this embodiment of the invention;

[0026] Figure 2 This is a cross-sectional view of the first allocation system proposed in this embodiment of the invention;

[0027] Figure 3 This is a cross-sectional view of the one-way valve proposed in the embodiments of the present invention;

[0028] Figure 4 This is a schematic diagram of the pressurization device proposed in the embodiments of the present invention;

[0029] Figure 5 This is a schematic diagram of the coalbed methane drainage path proposed in the embodiments of the present invention;

[0030] Figure 6 This is a schematic diagram of the multi-channel mining direction proposed in the embodiments of the present invention;

[0031] Figure 7 This is a schematic diagram of the drainage direction of the sandstone gas layer proposed in the embodiments of the present invention.

[0032] In the diagram: 1. Outer casing; 11. Sandstone gas outlet; 2. Inner casing; 3. Oil pipe; 31. Coalbed methane outlet; 4. Pressurization device; 41. Shell; 42. Impeller; 43. Drive unit; 5. Check valve; 51. Valve body; 52. Sealing ball; 53. Elastic element; 6. Cover; 7. Mounting sleeve; 8. Packer; I. ​​Sandstone gas layer; II. Coalbed methane layer. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0034] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0035] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0036] In the description of this embodiment, the terms "upper," "lower," "left," and "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0037] To address the coexistence of coalbed methane and sandstone gas resources, this embodiment proposes a production string for the co-production of coalbed methane and sandstone gas. It employs a "vertical well + horizontal well" structure, utilizing a three-section well depth configuration. In the first and second sections, outer and inner casings are respectively installed and cemented. The third section, a horizontal well, is drilled within both the sandstone gas and coalbed methane layers. After drilling, fracturing operations are performed to create artificial fracture channels. Both layers share a vertical well and are extracted simultaneously. During extraction, depending on different extraction conditions, the sandstone gas layer can selectively connect with the coalbed methane layer, mutually assisting in achieving gas lift and fluid removal.

[0038] refer to Figure 1-4As shown, the coalbed methane and sandstone gas co-production production string proposed in this embodiment includes a vertical well and a horizontal well. The horizontal well is configured in two sections, extending into sandstone gas layer I and coalbed methane layer II respectively, and both are connected to the vertical well. The vertical well includes an outer casing 1, an inner casing 2, tubing 3, a packer 8, a first distribution system, and a second distribution system. The tubing 3 and the inner casing 2 are coaxially arranged from the inside to the outside within the outer casing 1. The annular space between the outer casing 1 and the inner casing 2 is the first annulus, and a sandstone gas outlet 11 is provided at the top of the first annulus. The annular space between the inner casing 2 and the tubing 3 is the second annulus, and the top of the second annulus is closed. The tubing 3... A coalbed methane outlet 31 is provided at the top of the outer casing 1. A first distribution system, a second distribution system, and a packer 8 are provided in the first annulus and sleeved on the inner casing 2, dividing the first annulus into annulus section 1, annulus section 2, annulus section 3, and annulus section 4 arranged sequentially from top to bottom. The fourth annulus section is connected to the coalbed methane layer II, the second annulus section is connected to the sandstone gas layer, and the lower end of the inner casing 2 passes through the packer 8 and is connected to the coalbed methane layer II. The first distribution system is configured to selectively distribute the gas produced by the sandstone gas layer to the second annulus section 2 and the second annulus. The second distribution system is configured to distribute the liquid from the sandstone gas layer to the second annulus.

[0039] In this embodiment, the production string for co-extraction of coalbed methane and sandstone gas uses packers 8 to separate the two gas reservoirs and extracts them by taking into account the different characteristics of coalbed methane and sandstone gas production at each stage. In the initial stage of production, sandstone gas overflows from sandstone gas layer I into the first annulus. Due to the high bottom-hole pressure in the early stages of coalbed methane extraction, the coalbed methane cannot be desorbed. The first distribution system distributes the sandstone gas to the second annulus and performs gas lift to drain the fluid in coalbed methane layer II. The fluid flows from tubing 3 to the surface and is then separated into gas and water by a surface gas-liquid separator. In the middle stage of production, a pressure drop funnel forms in coalbed methane layer II, allowing coalbed methane to be desorbed and produced. The first distribution system distributes sandstone gas to the first annulus section, from which the sandstone gas is discharged, while the coalbed methane is produced from tubing 3. During production, if liquid accumulates in the first annulus where sandstone gas layer I is located, the second distribution system distributes the accumulated liquid to the second annulus. The accumulated liquid is then gas lift out along with the coalbed methane, preventing gas lock and ensuring normal sandstone gas extraction.

[0040] refer to Figure 2-4 As shown, the first distribution system includes a pressurizing device 4 and a check valve 5. The check valve 5 is configured in two groups, namely check valve A and check valve B. The outlet of check valve A is connected to a section of the annulus, and the outlet of check valve B is connected to the inner sleeve 2. Check valve A and check valve B can be opened selectively. The pressurizing device 4 is located below the check valve 5 and is configured to provide pressure-adjustable fluid to check valve A and check valve B to realize the opening and closing of the check valve.

[0041] The one-way valve 5 includes a valve body 51, a sealing ball 52, and an elastic element 53. The sealing ball 52 and the elastic element 53 are located inside the valve cavity of the valve body 51. One end of the elastic element 53 is connected to the sealing ball 52, and the other end is connected to the valve body 51. The sealing ball 52 is used to block the inlet or outlet. Specifically, the sealing ball 52 of one-way valve A is used to block the outlet. The free state of one-way valve A is the open state, and its closing pressure is greater than the bottom hole pressure of the sandstone gas formation. That is, under normal circumstances, the sealing ball 52 is far from the outlet, and the gas from the sandstone gas formation can be distributed to a section of the annulus through one-way valve A and discharged from the sandstone gas outlet 11. The sealing ball 52 of one-way valve B is used to block the inlet. The free state of one-way valve B is the closed state, and its opening pressure is also greater than the bottom hole pressure of the sandstone gas formation. That is, under normal circumstances, the sealing ball 52 is against the inlet, making the first and second annulus independent of each other. When the pressurization device provides gas pressure reaching the opening and closing pressure of the check valve, the sealing ball 52 of check valve A moves towards the outlet to block the outlet, and check valve A is closed. Meanwhile, the sealing ball 52 of check valve B moves away from the inlet, and check valve B is opened. Gas from the sandstone gas layer is then distributed to the second annulus through check valve B, thus switching the gas path in the sandstone gas layer. In this embodiment, the elastic element 53 is a helical spring.

[0042] Specifically, the inlet or outlet that can be sealed by the sealing ball 52 is set to a frustum shape, with its radius gradually increasing from the outside of the valve body 51 to the inside of the valve body 51, which can further improve the sealing performance of the sealing ball 52.

[0043] The booster device 4 includes a housing 41, an impeller 42, and a drive unit 43. The housing 41 is hollow and annular, with an outlet on its upper surface and an inlet on its lower surface. The central hole of the housing 41 is the same as the outer diameter of the inner sleeve 2, allowing it to be fixed to the inner sleeve 2. The outer diameter of the housing 41 is the same as the inner diameter of the outer sleeve 1, ensuring that the gas produced from the sandstone gas layer can only flow through the inlet and outlet of the booster device 4. The impeller 42 is coaxially rotatably disposed inside the housing 41. The drive unit 43 is configured to drive the impeller 42 to rotate. When the impeller 42 rotates, the blades on the impeller 42 can push the gas from the inlet direction to the outlet direction, increasing the gas pressure at the outlet, thereby achieving the purpose of opening or closing the one-way valve 5.

[0044] For example, the driving component 43 consists of a stator and a rotor, wherein the stator is fixed to the inner shell wall of the housing 41, and the rotor is fixed to the inner side of the shaft hole of the impeller 42. After being energized, the rotor drives the impeller 42 to rotate at high speed under the action of electromagnetic force. In order to reduce the friction when the impeller 42 rotates, a bearing is also provided between the impeller 42 and the inner shell wall of the housing 41, and the bearing and the stator are distributed along the axial direction of the inner sleeve 2.

[0045] Furthermore, to prevent sand and gravel from entering the booster device 4, the size of the inlet of the booster device 4 is determined according to the actual geological conditions of the mining area, and multiple inlets are generally provided, evenly distributed on the upper surface of the casing 41 to improve air intake efficiency. Multiple outlets are also provided to supply gas to check valves A and B respectively. The outlets and inlets are evenly distributed on the upper and lower surfaces of the casing 41 to increase the gas flow velocity.

[0046] Multiple check valves can be installed in each group A and each group B to increase the gas flow rate. To ensure that the gas in sandstone gas layer I can flow only through one-way valves A or B without being limited by the number of outlets of the pressurizing device 4, a cover 6 is connected to the top surface of the housing 41 of the pressurizing device 4. The cover 6 and the pressurizing device 4 cooperate to form a closed distribution space. The cover 6 is configured as a double layer, with the inner layer fixedly sleeved on the inner sleeve 2. Multiple one-way valves A are vertically arranged at intervals inside the cover 6. Their inlets are connected to the outlets of the pressurizing device 4, and their outlets are set through the top surface of the cover 6, so that the gas can enter the second annulus through the one-way valves A. The number of one-way valves A is less than the number of outlets of the pressurizing device 4, so that gas can flow into the cover 6. One-way valves B are horizontally arranged inside the cover 6, so that the gas can enter the one-way valves B from inside the cover 6. The outlet of one-way valve B penetrates the inner shell wall of the cover 6 and is connected to the inner sleeve 2, so that the gas can enter the inner sleeve 2, i.e., the second annulus, through the one-way valves B.

[0047] It is understandable that the housing 6 can serve as the valve body of the one-way valve B, that is, a through hole is directly opened on the inner shell wall of the housing 6, and the two ends of the through hole are respectively used as the inlet and outlet. The elastic element 53 and the sealing ball 52 are placed in the through hole to form the one-way valve B.

[0048] In this embodiment, in order to reduce the assembly difficulty, the cover 6 and the pressurizing device 4 are integrally formed, and the outer diameter of the cover 6 is the same as the outer diameter of the pressurizing device 4 and the inner diameter of the outer sleeve 1.

[0049] The second distribution system also includes a pressurizing device 4 and a check valve 5. Unlike the first distribution system, only one set of check valves 5 is provided, capable of connecting the third annulus section and the third annulus. The pressurizing device 4 is configured to provide pressurized liquid to the check valve 5 to achieve its opening and closing. Simultaneously, the pressurizing device 4 also functions to connect the second annulus section and the third annulus section. The check valve 5 is located below the pressurizing device 4, and its outlet is connected to the inner sleeve 2. Specifically, the structure of the check valve 5 here is the same as that of check valve B. Its inner sealing ball 52 is used to block the inlet, and its free state is closed. When the liquid pressure increases, the sealing ball 52 moves away from the inlet, the check valve 5 is opened, and the third annulus section connects to the second annulus. It can be understood that at this time, the inlet of the pressurizing device 4 faces upwards, and the outlet faces downwards.

[0050] The second distribution system also includes an annular mounting sleeve 7, which can be fixedly sleeved on the inner sleeve 2 to simultaneously fix multiple check valves 5. Similar to check valve B, check valve 5 can also use the mounting sleeve 7 as the valve body 51, that is, a through hole is opened in the radial direction of the mounting sleeve 7, and a sealing ball and spring are set in the through hole to form check valve 5.

[0051] refer to Figure 5-7 As shown, this embodiment also proposes a method for the co-extraction of coalbed methane and sandstone gas, which is achieved using the aforementioned co-extraction production tubing. The fluid paths differ at different extraction stages (the fluids include gas and liquid from coalbed methane layer II and sandstone gas layer), and specifically includes the following steps:

[0052] The production tubing for both coalbed methane and sandstone gas is run into the well, and fracturing operations are carried out. Specifically, during construction, a three-section well structure is adopted. In the first and second sections, outer casing 1 and inner casing 2 are run and cemented, respectively. The third section is a horizontal well drilled in sandstone gas layer I and coalbed methane layer II. After drilling is completed, fracturing operations are carried out. Fracturing can be carried out using "smooth casing injection fracturing" and "bridge plug isolation segmentation" methods, and fracturing is achieved through continuous perforation.

[0053] In the initial production phase, the sandstone gas layer primarily produces gas, while coalbed methane layer II primarily produces liquid. When the booster device 4 in the first distribution system is activated, the sandstone gas is pressurized by the booster device 4. The increased gas pressure closes one-way valve A and opens one-way valve B. The sandstone gas flows from the annulus section II through one-way valve B into the inner casing 2, and then from the inner casing 2 into the tubing 3, performing gas lift to drain the fluid from coalbed methane layer II. The fluid flows from the tubing 3 to the surface, where it is separated into gas and water by a surface gas-liquid separator. Throughout this process, the one-way valve 5 in the second distribution system remains closed. By adjusting the rotational speed of the impeller 42 in the booster device 4, the drainage rate of coalbed methane layer II can be adjusted, thereby achieving control of the wellbore fluid surface and realizing precise drainage of coalbed methane layer II.

[0054] After the coalbed methane layer II forms a pressure drop funnel, the sandstone gas layer mainly produces gas, while the coalbed methane layer II desorbs and also produces gas. The pressurization device 4 of the first distribution system is shut down, the one-way valve A is opened, the sandstone gas enters the annulus section I from the second annulus section and is discharged from the sandstone gas outlet 11, while the coalbed methane enters the tubing 3 through the inner casing 2 and is discharged from the coalbed methane outlet 31, which means that the same well is produced through multiple channels.

[0055] When liquid accumulates in sandstone gas layer I, the booster device 4 in the second distribution system is turned on to increase the hydraulic pressure near the one-way valve 5 in the second distribution system. The one-way valve 5 opens, and the liquid in sandstone gas layer I enters the inner casing 2 through the one-way valve 5. The coalbed methane lifts the liquid from sandstone gas layer I. The fluid flows from the oil pipe 3 to the ground and then passes through the ground gas-liquid separator to separate the gas and water.

[0056] The above-mentioned method for co-extraction of coalbed methane and sandstone gas enables the mutual auxiliary extraction of coalbed methane and sandstone gas without the need for external gas sources. It is simple to operate and has low cost.

[0057] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A production tubing string for co-producing coalbed methane and sandstone gas, comprising a vertical well and a horizontal well, wherein the horizontal well is configured in two sections, extending into the sandstone gas layer (Ⅰ) and the coalbed methane layer (Ⅱ) respectively, and both sections are connected to the vertical well, characterized in that, The vertical well includes: An outer casing (1), an inner casing (2), and a tubing (3) are arranged sequentially from the outside to the inside. The annular space between the outer casing (1) and the inner casing (2) is a first annulus. A sandstone gas outlet (11) is provided at the top of the first annulus. The annular space between the inner casing (2) and the tubing (3) is a second annulus. The top of the second annulus is closed. The tubing (3) passes through the outer casing (1) and has a coalbed methane outlet (31). A first distribution system, a second distribution system, and a packer (8) are installed in the first annulus. The first distribution system, the second distribution system, and the packer (8) divide the first annulus into annulus section one, annulus section two, annulus section three, and annulus section four from top to bottom. The fourth annulus section is connected to the coalbed methane layer (II), and the second annulus section is connected to the sandstone gas layer. The first distribution system is configured to selectively distribute the gas from the sandstone gas layer to the first annulus section or the second annulus. The second distribution system is configured to distribute the liquid from the sandstone gas layer to the second annulus.

2. The production tubing for co-extraction of coalbed methane and sandstone gas according to claim 1, characterized in that, The first distribution system includes a pressurizing device (4) and a one-way valve (5). The one-way valve (5) is configured as two groups, namely one-way valve A and one-way valve B. The outlet of one-way valve A is connected to a section of the annulus, and the outlet of one-way valve B is connected to the inner sleeve (2). One-way valve A and one-way valve B can be opened selectively. The pressurizing device (4) is configured to provide the one-way valve (5) with adjustable pressure gas to realize the opening and closing of the one-way valve (5).

3. The production tubing for co-extraction of coalbed methane and sandstone gas according to claim 2, characterized in that, The first distribution system also includes a housing (6), which, together with the pressurizing device (4), forms a closed distribution space. Both the one-way valve A and the one-way valve B are located inside the housing (6). The pressurizing device (4) has multiple outlets, more than the number of one-way valves A. A portion of the outlets is connected to the inlet of the one-way valve A, and the other portion supplies gas into the housing (6). The outlet of the one-way valve A is located through the top of the housing (6), and the outlet of the one-way valve B is located through the inner shell wall of the housing (6) and connected to the inner sleeve (2).

4. The production tubing for co-extraction of coalbed methane and sandstone gas according to claim 2, characterized in that, The free state of one-way valve A is open, and the free state of one-way valve B is closed.

5. The production tubing for co-extraction of coalbed methane and sandstone gas according to claim 1, characterized in that, The second distribution system includes a booster device (4) and a one-way valve (5). The inlet of the one-way valve (5) is connected to the outlet of the booster device (4), and the outlet of the one-way valve (5) is connected to the inner sleeve (2).

6. The production tubing for co-extraction of coalbed methane and sandstone gas according to claim 5, characterized in that, The free state of the one-way valve (5) is the closed state.

7. The production tubing for co-extraction of coalbed methane and sandstone gas according to claim 5, characterized in that, The second distribution system also includes an installation sleeve (7), which is fixedly sleeved on the inner sleeve (2), and a plurality of one-way valves (5) are radially disposed on the installation sleeve (7).

8. The production tubing for co-production of coalbed methane and sandstone gas according to claim 2 or 5, characterized in that, The booster device (4) includes a housing (41), an impeller (42), and a drive unit (43). The housing (41) is a hollow ring. The housing (41) is fixedly sleeved on the inner sleeve (2) and its outer diameter is the same as the inner diameter of the outer sleeve (1). An inlet and an outlet are provided on opposite sides of the housing (41). The impeller (42) is coaxially rotatably disposed inside the housing (41). The drive unit (43) is configured to drive the impeller (42) to rotate.

9. The production tubing for co-extraction of coalbed methane and sandstone gas according to claim 8, characterized in that, The drive unit (43) consists of a stator and a rotor. The stator is fixed to the inner shell wall of the housing (41), and the rotor is fixed to the inner side of the central hole of the impeller (42).

10. A method for co-extracting coalbed methane and sandstone gas, characterized in that, The co-production production tubing for coalbed methane and sandstone gas as described in any one of claims 1-9 is achieved by the following steps: The coalbed methane and sandstone gas co-production tubing is lowered into the well for fracturing operations. In the initial stage of production, the first distribution system distributes sandstone gas to the second annulus; After the coalbed methane forms a pressure drop funnel, the first distribution system distributes the sandstone gas to the annulus section. When liquid accumulates in the sandstone gas layer (Ⅰ), the second distribution system distributes the accumulated liquid to the second annulus.

Images