A deep coal rock gas medium-low pressure gathering and transportation system and design method

Abstract

This invention belongs to the field of deep coalbed methane technology, specifically relating to a low-pressure gathering and transportation system and design method for deep coalbed methane. In this system, multiple well sites within a well site group transport medium-pressure coalbed methane to a central well site via a medium-pressure gas production trunk line, and multiple well sites within the same group transport low-pressure coalbed methane to the same central well site via a low-pressure gas production trunk line. The central well site then supplies coalbed methane to a purification plant via a gathering pipeline, where the purification plant performs dust removal treatment. This invention provides a low-pressure gathering and transportation system for deep coalbed methane. By using a medium-pressure gas production trunk line to transport medium-pressure coalbed methane from both new and old wells, and a low-pressure gas production trunk line to transport low-pressure coalbed methane from both new and old wells, this system avoids the problem of pressure mismatch between new and old wells, thus improving production capacity. Simultaneously, the purification plant removes coal dust from the coalbed methane, eliminating the need for filter separators and offering advantages such as improved gas extraction efficiency and reduced costs.

Description

Technical Field

[0001] This invention belongs to the field of deep coal and rock gas technology, specifically relating to a low-pressure gathering and transportation system and design method for deep coal and rock gas. Background Technology

[0002] Deep coal and rock gas is mainly formed into "artificial gas reservoirs" through large-scale hydraulic fracturing. After fracturing, free gas from the flowback holes is rapidly produced under high pressure through these artificial fractures. Relying on the formation's own energy and the gas's ability to carry liquid, fracturing fluid and a small amount of mobile water are carried out, achieving self-flowing production. This gas production then reduces reservoir pressure, promoting the desorption of adsorbed gas. Initially, free gas production accounts for a high proportion, contributing mainly to the first 1-2 years. Later, low-pressure adsorbed gas desorption achieves long-term relatively stable production. The gas-water variation pattern also exhibits a "five-stage" characteristic:

[0003] Phase 1 (≤2 days): Liquid is produced but no gas is produced, with a daily liquid production of 35–150 m³. 3 / d;

[0004] Phase 2 (7-26 days): The amount of refluxed fluid increases rapidly, reaching a maximum of 577-1134 m³. 3 / d; Free gas begins to be produced, ignitable and combustible;

[0005] Phase 3 (7-65 days): Daily liquid production rapidly decreases to 43-222 m³. 3 / d, daily gas production (mainly free gas) rose rapidly (8.4×10 4 ~15.5×10 4 m 3 / d), the casing pressure rises to 3.9~8.5MPa, and production is carried out using a bare casing-oil casing annulus;

[0006] Phase 4 (>240 days), daily fluid production slowly decreases to 10m³. 3 The following production levels remain stable or decline slowly, with free gas and desorbed gas produced together, mainly using oil-jacketed annulus production.

[0007] Phase 5, low-production phase, with daily water and gas production maintained at low levels, employing pressurized air lift / artificial lift.

[0008] Deep coal gas formations are characterized by complex geological conditions, including deep burial, high ground stress, and strong plasticity. Deep coal gas wells are characterized by high initial pressure and rapid pressure decay, leading to: ① Constrained production capacity release from new wells, affecting the overall production capacity of the block; ② Surface processes must adapt to both the high pressure and large water volume in the early stages and the low pressure and small gas volume in the later stages, considering both the initial use of formation pressure for self-flowing production and the later use of surface supporting facilities such as jet pumps; ③ The presence of coal dust in the produced gas from deep coal gas formations necessitates frequent filter element replacements in the gas gathering station's filter separators, making it unsuitable for surface processes; ④ Large pressure fluctuations in deep coal gas formations, coupled with the presence of coal dust in the produced gas, limit the selection of compressors.

[0009] In view of this, the present invention is hereby proposed. Summary of the Invention

[0010] To address the problem of limited production capacity release from new deep coal and shale gas wells, and the resulting pressure mismatch between new and old wells when connecting to existing pipelines, leading to reduced production capacity, this invention provides a medium-low pressure gathering and transportation system for deep coal and shale gas.

[0011] This invention includes the following technical solutions:

[0012] The first aspect of the present invention provides a medium-low pressure gathering and transportation system for deep coal and rock gas, including a well site group, a central well site and a purification plant. Multiple well sites in a well site group transport medium-pressure coal and rock gas to a central well site through a medium-pressure gas production trunk line, and multiple well sites in a well site group transport low-pressure coal and rock gas to a central well site through a low-pressure gas production trunk line.

[0013] The central well site supplies coal gas to the purification plant through a gas gathering pipeline, and the purification plant performs dust removal treatment on the coal gas.

[0014] Furthermore, each well site group has multiple well sites connected to the medium-pressure gas production trunk line and the low-pressure gas production trunk line via gas production pipelines.

[0015] Furthermore, the gas production pipeline includes a first transport section, a second transport section, and a third transport section. A well site is connected to the input end of the first transport section. The output end of the first transport section is connected to the input ends of the second transport section and the third transport section, respectively. The output end of the second transport section is connected to the medium-pressure gas production trunk line, and the output end of the third transport section is connected to the low-pressure gas production trunk line. Valves are installed on both the second and third transport sections.

[0016] Furthermore, the well site is equipped with a gas production tree, a metering separation skid, a circulating water tank skid, a power pump skid, a booster pump module, and a water collection pipeline. The gas production tree is used to collect coal and rock gas from the well site. The first outlet and the second outlet of the gas production tree are respectively connected to the air inlet and water inlet of the metering separation skid. The air outlet of the metering separation skid is connected to the input end of the first conveying section. The water outlet of the metering separation skid is connected to the water inlet of the circulating water tank skid. The water outlet of the circulating water tank skid is respectively connected to the water inlet of the booster pump module and the water inlet of the power pump skid. The water outlet of the booster pump module is connected to the input end of the water collection pipeline. The water outlet of the power pump skid is connected to the gas production tree.

[0017] Furthermore, the metering separation skid includes a wellhead control valve, a rotating metering device, a single-well metering device, and a separator module. The first outlet of the gas production tree is connected to the inlet of the wellhead control valve; the outlet of the wellhead control valve is connected to the air inlet of the rotating metering device, and the air outlet of the rotating metering device is connected to the air inlet of the separator module; the second outlet of the gas production tree is connected to the water inlet of the single-well metering device, and the water outlet of the single-well metering device is connected to the water inlet of the separator module; the air outlet of the separator module is connected to the input end of the gas production pipeline, and the water outlet of the separator module is connected to the water inlet of the circulating water tank skid.

[0018] Furthermore, the central well site is equipped with a first pigging valve skid, a second pigging valve skid, a first emergency shut-off valve, a second emergency shut-off valve, a medium and low pressure gas gathering and separation skid, a pig launching tube skid, and a sewage discharge pool;

[0019] The outlet of the medium-pressure gas production line is connected to the inlet of the first pigging valve skid, the outlet of the first pigging valve skid is connected to the inlet of the first emergency shut-off valve, and the outlet of the first emergency shut-off valve is connected to the inlet of the medium-low pressure gas collection and separation skid.

[0020] The outlet of the low-pressure gas collection trunk line is connected to the inlet of the second pigging valve skid, the outlet of the second pigging valve skid is connected to the inlet of the second emergency shut-off valve, and the outlet of the second emergency shut-off valve is connected to the inlet of the medium-low pressure gas collection and separation skid.

[0021] The outlet end of the medium-low pressure gas collection and separation skid is connected to the sewage tank, the outlet end of the medium-low pressure gas collection and separation skid is connected to the inlet end of the ball launcher skid, and the outlet end of the ball launcher skid is connected to the gas collection pipe.

[0022] Furthermore, the central well site is also equipped with a compressor skid. The gas outlet of the medium- and low-pressure gas gathering and separation skid includes a medium-pressure coal and rock gas outlet and a low-pressure coal and rock gas outlet. The medium-pressure coal and rock gas outlet is connected to the inlet of the launch tube skid, the low-pressure coal and rock gas outlet is connected to the inlet of the compressor skid, and the outlet of the compressor skid is connected to the inlet of the launch tube skid.

[0023] Furthermore, the purification plant also performs separation, pressurization, decarbonization, and dehydration treatment on the coal gas.

[0024] A second aspect of the present invention provides a design method for a low-pressure gathering and transportation system for deep coal and rock gas, used to arrange the gathering and transportation system described above, the method comprising the following steps:

[0025] Based on the pressure gradient of the medium and low pressure gathering and transmission system obtained from the dynamic simulation model of the large pipeline network and the medium and low pressure gathering and transmission system, the gas gathering and transmission volume of different regions is adjusted according to the pressure gradient.

[0026] The number of well sites in each well site group is determined based on the gas gathering and transmission volume in different regions.

[0027] Dynamic calculations are performed on each well site group to obtain the changes in pressure and production, increased production revenue, and production energy consumption of each well site, thereby determining the optimal layout location of the central well site.

[0028] It also includes the following steps:

[0029] The outlet pressure of the central well site and the outlet pressure of the well site are obtained based on the inlet pressure of the purification plant.

[0030] Equipment selection is based on the outlet pressure of the central well site and the outlet pressure of the well site.

[0031] By adopting the above technical solution, the present invention has the following advantages:

[0032] 1. This invention transports medium-pressure coal and rock gas from new and old wells through a medium-pressure gas production trunk line, and transports low-pressure coal and rock gas from new and old wells through a low-pressure gas production trunk line, thus avoiding the problem of mismatch between pipeline pressures between new and old wells and improving production capacity.

[0033] 2. The gathering and transportation system of the present invention can adapt to the entire mining cycle of deep coal and rock gas, and can flexibly switch between the self-flowing and jet pump stages with high efficiency.

[0034] 3. The metering separation skid of the present invention performs gas-liquid separation on the collected coal gas, avoiding the accumulation of liquid in the pipeline during the transportation of coal gas, which would form slug flow and affect the safe and stable operation of the pipeline and equipment.

[0035] 4. The equipment used in this invention adopts a skid-mounted design, which greatly increases the reusability of the equipment and reduces costs.

[0036] 5. The present invention uses a rotating metering device, which can rotate the metering of coal and rock gas produced from multiple wells in a well site, and has the advantages of improving gathering and transportation efficiency and saving energy and reducing consumption.

[0037] 6. The gathering and transportation system of the present invention removes coal powder from coal rock gas through a purification plant, avoiding the use of filter separators, which has the advantages of improving gas extraction efficiency and reducing costs.

[0038] 7. The gathering and transportation system of the present invention transports coal and rock gas to the central well site through the gathering and transportation trunk lines (medium-pressure gas production trunk line and low-pressure gas production trunk line), which can adapt to large gas volumes and also take into account small gas volumes, and can also avoid the impact of excessive coal powder accumulation on transportation.

[0039] 8. The design method of the present invention can design the location of the central well site, which has the advantage of reducing costs.

[0040] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of a low-pressure gathering and transportation system for deep coal and rock gas in an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of the connection structure between a well site group and a central well site in an embodiment of the present invention. Figure 1 ;

[0044] Figure 3 This is a schematic diagram of the connection structure between a well site group and a central well site in an embodiment of the present invention. Figure 2 ;

[0045] Figure 4 This is a schematic diagram of the equipment installed at the well site in an embodiment of the present invention. Figure 1 ;

[0046] Figure 5 This is a schematic diagram of the equipment installed at the central well site in an embodiment of the present invention;

[0047] Figure 6This is a schematic diagram of the equipment installed at the well site in an embodiment of the present invention. Figure 2 ;

[0048] In the diagram, 10-Well site group, 20-Central well site, 21-First pigging valve skid, 22-Second pigging valve skid, 23-First emergency shut-off valve, 24-Second emergency shut-off valve, 25-Medium and low-pressure gas gathering and separation skid, 26-Pile launcher skid, 27-Sewage tank, 28-Compressor skid, 30-Medium-pressure gas production trunk line, 40-Low-pressure gas production trunk line, 50-Gas production pipeline, 51-First conveying section, 52-Second conveying section, 53-Third conveying section, 60-Valve, 71-Gas tree, 72-Metering separation skid, 721-Wellhead control valve, 722-Rotation metering device, 723-Single well metering device, 724-Separator module, 73-Circulating water tank skid, 74-Power pump skid, 75-Boost pump module, 76-Water collection pipeline, 80-Gas collection pipeline, 90-Purification plant. Detailed Implementation

[0049] The following description provides many different embodiments or examples for implementing various features of the invention. The elements and arrangements described in the specific examples below are only for concise expression of the invention and are merely examples, not intended to limit the invention.

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] This embodiment provides a low-pressure gathering and transportation system for deep coal and rock gas, such as Figure 1 As shown, it includes well site group 10, central well site 20, purification plant 90 and downstream users. Multiple well sites in a well site group 10 transport medium-pressure coal and rock gas to a central well site 20 through medium-pressure gas production trunk line 30, and multiple well sites in a well site group 10 transport low-pressure coal and rock gas to a central well site 20 through low-pressure gas production trunk line 40.

[0052] The central well site 20 delivers coal gas to the purification plant 90 through the gas collection pipeline 80. After the purification plant 90 performs dust removal treatment on the coal gas, it delivers the coal gas to the downstream user through the pipeline.

[0053] It should be noted that the specific pressure values ​​of medium-pressure coal rock gas and low-pressure coal rock gas are not limited by this invention. Any system that meets the requirement that the pressure of the medium-pressure coal rock gas transported by the medium-pressure gas production trunk line 30 is higher than the pressure of the low-pressure coal rock gas transported by the low-pressure gas production trunk line 40 should be within the protection scope of this invention.

[0054] Preferably, the pressure of the medium-pressure coal gas is 2.5 MPa to 3.0 MPa; and the pressure of the low-pressure coal gas is 0.5 MPa to 1.0 MPa.

[0055] like Figure 1 , Figure 2 As shown in the figure, there are three central well sites 20 and three well site groups 10. One central well site 20 and one well site group 10 are connected only by one medium-pressure gas production trunk line 30 and one low-pressure gas production trunk line 40. In the structure shown, since multiple well site groups 10 are located in the same direction as the central well site 20, the transportation of medium-pressure coal rock gas and low-pressure coal rock gas can be achieved through one medium-pressure gas production trunk line 30 and one low-pressure gas production trunk line 40.

[0056] like Figure 3 As shown in the figure, multiple well sites in a well site group 10 are located in different directions of the central well site 20. Therefore, multiple well sites located above the central well site 20 are connected to the central well site 20 through a medium-pressure gas production trunk line 30 and a low-pressure gas production trunk line 40. Multiple well sites located below the central well site 20 are connected to the central well site 20 through a medium-pressure gas production trunk line 30 and a low-pressure gas production trunk line 40.

[0057] It should be noted that the number of medium-pressure gas production trunk lines 30 and low-pressure gas production trunk lines 40 mentioned above is only an illustrative example and does not represent a limitation on the present invention; in actual use, the number of medium-pressure gas production trunk lines 30 and low-pressure gas production trunk lines 40 is determined according to the positional relationship between well site group 10 and central well site 20.

[0058] In some embodiments, such as Figure 2 As shown, multiple well sites in each well site group 10 are connected to the medium-pressure gas production line 30 and the low-pressure gas production line 40 respectively via gas production pipelines 50. Each gas production pipeline 50 has a pre-installed methanol injection port, which can be selected according to requirements.

[0059] In some embodiments, such as Figure 2As shown, the gas production pipeline 50 includes a first conveying section 51, a second conveying section 52, and a third conveying section 53. A well site is connected to the input end of the first conveying section 51. The output end of the first conveying section 51 is connected to the input ends of the second conveying section 52 and the third conveying section 53, respectively. The output end of the second conveying section 52 is connected to the medium-pressure gas production trunk line 30, and the output end of the third conveying section 53 is connected to the low-pressure gas production trunk line 40. Valves 60 are installed on both the second conveying section 52 and the third conveying section 53.

[0060] In some embodiments, such as Figure 4 As shown, the well site is equipped with a gas production tree 71, a metering separation skid 72, a circulating water tank skid 73, a power pump skid 74, a booster pump module 75, and a water collection pipeline 76. The gas production tree 71 is used to collect coal and rock gas from the well site. A well site includes multiple wells, and all the wells collect gas through the gas production tree 71. The first outlet and the second outlet of the gas production tree 71 are respectively connected to the air inlet and water inlet of the metering separation skid 72. The air outlet of the metering separation skid 72 is connected to the input end of the first conveying section 51. The water outlet of the metering separation skid 72 is connected to the water inlet of the circulating water tank skid 73. The water outlet of the circulating water tank skid 73 is respectively connected to the water inlet of the booster pump module 75 and the water inlet of the power pump skid 74. The water outlet of the booster pump module 75 is connected to the input end of the water collection pipeline 76. The water outlet of the power pump skid 74 is connected to the gas production tree 71.

[0061] In some embodiments, such as Figure 4 As shown, the metering separation skid 72 includes a wellhead control valve 721, a rotating metering device 722, a single-well metering device 723, and a separator module 724. The first outlet of the gas production tree 71 is connected to the inlet of the wellhead control valve 721; the outlet of the wellhead control valve 721 is connected to the air inlet of the rotating metering device 722, and the air outlet of the rotating metering device 722 is connected to the air inlet of the separator module 724; the second outlet of the gas production tree 71 is connected to the water inlet of the single-well metering device 723, and the water outlet of the single-well metering device 723 is connected to the water inlet of the separator module 724; the air outlet of the separator module 724 is connected to the input of the gas production pipeline 50, and the water outlet of the separator module 724 is connected to the water inlet of the circulating water tank skid 73. The rotating metering device enables metering of gas production from different wells, reducing equipment usage and lowering costs.

[0062] The gas separation module is a gas-liquid separator.

[0063] In some embodiments, such as Figure 5As shown, the central well site 20 is equipped with a first pigging valve skid 21, a second pigging valve skid 22, a first emergency shut-off valve 23, a second emergency shut-off valve 24, a medium and low pressure gas gathering and separation skid 25, a pig launching tube skid 26, and a sewage discharge tank 27.

[0064] The outlet of the medium-pressure gas collection trunk line 30 is connected to the inlet of the first pigging valve skid 21, the outlet of the first pigging valve skid 21 is connected to the inlet of the first emergency shut-off valve 23, and the outlet of the first emergency shut-off valve 23 is connected to the inlet of the medium-low pressure gas collection and separation skid 25.

[0065] The outlet of the low-pressure gas collection trunk line 40 is connected to the inlet of the second pigging valve skid 22, the outlet of the second pigging valve skid 22 is connected to the inlet of the second emergency shut-off valve 24, and the outlet of the second emergency shut-off valve 24 is connected to the inlet of the medium and low pressure gas collection and separation skid 25.

[0066] The water outlet of the medium-low pressure gas collection and separation skid 25 is connected to the sewage tank 27, the air outlet of the medium-low pressure gas collection and separation skid 25 is connected to the air inlet of the ball launcher skid 26, and the air outlet of the ball launcher skid 26 is connected to the gas collection pipe 80.

[0067] In some embodiments, such as Figure 5 As shown, the central well site 20 is also equipped with a compressor skid 28. The gas outlet of the medium and low pressure gas gathering and separation skid 25 includes a medium pressure coal and rock gas outlet and a low pressure coal and rock gas outlet. The medium pressure coal and rock gas outlet is connected to the gas inlet of the launch tube skid 26, the low pressure coal and rock gas outlet is connected to the gas inlet of the compressor skid 28, and the gas outlet of the compressor skid 28 is connected to the gas inlet of the launch tube skid 26.

[0068] In some embodiments, the purification plant 90 further separates, pressurizes, decarbonizes, and dehydrates the coal gas before exporting it.

[0069] The gas extraction process of the gathering and transportation system of the present invention is as follows:

[0070] The self-flowing stage (well site venting and testing stage): Because the gas-liquid content in the well is high at this time, it can produce gas naturally under formation pressure; at this time, the well site is equipped with a gas production tree 71, a desander, an emergency shut-off valve 60, a choke manifold, a single-well metering device 723, a production separator, and a water tank and water pump for gas production; specifically, such as Figure 6 As shown, the gas and water produced by the gas production tree 71 are both extracted from the first outlet of the gas production tree 71. The extracted gas and water pass through the emergency shut-off valve 60 (regulation) and enter the production separator after passing through the single well. The separated extracted gas passes through the gas production pipe to be transported to the central well site 20, and the separated water enters the water collection pipeline 76 through the water pump (including pressure reducing bypass) and is transported to the central well site 20.

[0071] Jet pump stage (well site production stage): Since there is no formation pressure for self-flowing production at this time, water needs to be injected for production; therefore, each well site group 10 is equipped with a gas production tree 71, a metering and separation skid 72, a circulating water tank skid 73, a power pump skid 74, a lift pump module 75, and a water collection pipeline 76. The produced gas is extracted from the first outlet of the gas production tree 71, and the produced water is extracted from the second outlet of the gas production tree 71. The produced gas enters the gas-water separator after passing through the rotating metering device 722, and the produced water enters the gas-water separator after passing through the single-well metering device 723. The separated coal and rock gas is transported to the central well site 20 through the gas production pipeline 50, and the separated water enters the circulating water tank skid 73. The water then enters the water collection pipeline 76 through the lift pump module 75 (including pressure reduction bypass) and is transported to the central well site 20. It then returns to the gas production tree 71 through the power pump skid and is injected into the bottom of the well through the gas production tree 71.

[0072] The gas extraction process rationally utilizes wellhead back pressure and elevation difference to extract water, and has developed a combined gravity pipeline transportation and booster pump transportation process system, which greatly reduces energy consumption.

[0073] This embodiment also provides a design method for a low-pressure gathering and transportation system for deep coal and rock gas, used to arrange the gathering and transportation system as described above. The method includes the following steps:

[0074] The pressure gradient of the medium-low pressure gathering and transportation system is obtained from the dynamic simulation model of the large pipeline network and the medium-low pressure gathering and transportation system. The gas gathering and transportation volume in different areas is adjusted according to the pressure gradient. The pipeline network of the large pipeline network and the medium-low pressure gathering and transportation system is obtained by determining the number and connection relationship of the pressure-producing gas trunk line, the low-pressure gas producing trunk line 40, the central well site 20 and the well site group 10.

[0075] The number of well sites in each well site group (10) is determined based on the gas gathering and transmission volume in different regions.

[0076] Dynamic calculations are performed on each well site group 10 to obtain the pressure and production changes, increased production revenue, and production energy consumption of each well site, thereby determining the optimal location of the central well site 20. Since each well site group 10 has multiple well sites, and multiple well sites need to supply coal and rock gas to a central well site 20, it is necessary to determine the location of the central well site 20 to reduce costs.

[0077] It also includes the following steps: obtaining the outlet pressure of the central well site 20 and the well site outlet pressure based on the inlet pressure of the purification plant 90; and selecting equipment based on the outlet pressure of the central well site 20 and the well site outlet pressure.

[0078] Specifically, using the Pipes IM software, based on the determined inlet pressure of the purification plant (90) and the gas volume of each central well site (20), the outlet pressure of each central well site (20) is obtained, and then the inlet pressure of each central well site (20) is obtained. Based on the determined inlet pressure of each central well site (20) and the gas volume of each well site, the outlet pressure of each well site is obtained.

[0079] The design of the low- and medium-pressure gas gathering and separation skid 25, compressor skid 28, and valve 60 ball skid of the central well site 20 is based on the obtained outlet pressure of the well site; simultaneously, the design of the metering and separation skid 72 of the gas-liquid mixing suction skid is based on the obtained outlet pressure of the well site. Specifically: to reduce equipment costs, the inlet pressure of the purification plant 90 is 2MPa. The gathering and transportation system is constructed using Pipesim software. Based on the gathering and transportation system, the inlet pressure of the purification plant 90 (2MPa), and other control parameters, the outlet pressure of the central well site 20 is obtained as 2.5MPa. The outlet pressure of the well site includes low-pressure outlet pressure and medium-pressure outlet pressure. The low-pressure outlet pressure is 0.4MPa to 1MPa, and the medium-pressure outlet pressure is 2.5MPa to 3MPa.

[0080] Based on the outlet pressure of 2MPa at the central well site 20, the gas flow rate of the medium-low pressure gas separator is set to 100×10⁻⁶. 4 m 3 / d, water volume is 10m 3 / d, operating pressure is 2.5MPa; compressor skid 28 is selected as 15×10 4 m 3 / d screw compressor or 25×10⁴m 3 The screw compressor has the following design parameters: inlet pressure 0.4 MPa, discharge pressure 2.5 MPa; the inlet pressure of the launching tube skid 26 is 2.0–3.8 MPa, and the air volume is 100 × 10⁴ m³ / s. 3 / d.

[0081] Based on the low-pressure outlet pressure of 0.4MPa~1MPa and the medium-pressure outlet pressure of 2.5MPa~3MPa at the well site, the gas volume of the metering separation skid is set to 10×10 4 Nm 3 / d, water volume is 100-300m³ 3 / d, operating pressure is 2.5MPa; or gas volume is 17×10 4 Nm 3 / d, water volume is 150~450m³ 3 / d, operating pressure is 2.5MPa; or gas volume is 25×10 4 Nm 3 / d, water volume is 200-600m³ 3 / d, operating pressure is 2.5MPa.

[0082] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0083] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of multiple components or the interaction between multiple components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0084] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A deep coal rock gas medium-low pressure gathering and transportation system, characterized in that, It includes a well site group (10), a central well site (20) and a purification plant (90). Multiple well sites of a well site group (10) transport medium-pressure coal gas to a central well site (20) through a medium-pressure gas production trunk line (30), and multiple well sites of a well site group (10) transport low-pressure coal gas to a central well site (20) through a low-pressure gas production trunk line (40). The central well site (20) transports coal gas to the purification plant (90) through the gas collection pipeline (80), and the purification plant (90) performs dust removal treatment on the coal gas.

2. The low-pressure collection and transmission system for deep coal rock gas according to claim 1, characterized in that, Each well site group (10) has multiple well sites connected to the medium-pressure gas production trunk line (30) and the low-pressure gas production trunk line (40) respectively via gas production pipelines (50).

3. The low-pressure collection and transmission system for deep coalbed gas according to claim 2, characterized in that, The gas production pipeline (50) includes a first transport section (51), a second transport section (52), and a third transport section (53). A well site is connected to the input end of the first transport section (51). The output end of the first transport section (51) is connected to the input end of the second transport section (52) and the input end of the third transport section (53), respectively. The output end of the second transport section (52) is connected to the medium-pressure gas production trunk line (30), and the output end of the third transport section (53) is connected to the low-pressure gas production trunk line (40). Valves (60) are provided on both the second transport section (52) and the third transport section (53).

4. The system according to any one of claims 2-3, wherein, The well site is equipped with a gas extraction tree (71), a metering separation skid (72), a circulating water tank skid (73), a power pump skid (74), a booster pump module (75), and a water collection pipeline (76). The gas extraction tree (71) is used to extract coal and rock gas from the well site. The first outlet and the second outlet of the gas extraction tree (71) are respectively connected to the air inlet and water inlet of the metering separation skid (72). The air outlet of the metering separation skid (72) is connected to the input end of the gas extraction pipeline (50). The water outlet of the metering separation skid (72) is connected to the water inlet of the circulating water tank skid (73). The water outlet of the circulating water tank skid (73) is respectively connected to the water inlet of the booster pump module (75) and the water inlet of the power pump skid (74). The water outlet of the booster pump module (75) is connected to the input end of the water collection pipeline (76). The water outlet of the power pump skid (74) is connected to the gas extraction tree (71).

5. The system according to claim 4, wherein, The metering separation skid (72) includes a wellhead control valve (721), a rotating metering device (722), a single-well metering device (723), and a separator module (724). The first outlet of the gas production tree (71) is connected to the inlet of the wellhead control valve (721); the outlet of the wellhead control valve (721) is connected to the air inlet of the rotating metering device (722), and the air outlet of the rotating metering device (722) is connected to the air inlet of the separator module (724); the second outlet of the gas production tree (71) is connected to the water inlet of the single-well metering device (723), and the water outlet of the single-well metering device (723) is connected to the water inlet of the separator module (724); the air outlet of the separator module (724) is connected to the input end of the gas production pipeline (50), and the water outlet of the separator module (724) is connected to the water inlet of the circulating water tank skid (73).

6. The system according to any one of claims 2-3, wherein, The central well site (20) is equipped with a first pigging valve skid (21), a second pigging valve skid (22), a first emergency shut-off valve (23), a second emergency shut-off valve (24), a medium and low pressure gas collection and separation skid (25), a ball launcher skid (26), and a sewage tank (27); The outlet of the medium-pressure gas collection trunk line (30) is connected to the inlet of the first pigging valve skid (21), the outlet of the first pigging valve skid (21) is connected to the inlet of the first emergency shut-off valve (23), and the outlet of the first emergency shut-off valve (23) is connected to the inlet of the medium-low pressure gas collection and separation skid (25). The outlet of the low-pressure gas collection trunk line (40) is connected to the inlet of the second pigging valve skid (22), the outlet of the second pigging valve skid (22) is connected to the inlet of the second emergency shut-off valve (24), and the outlet of the second emergency shut-off valve (24) is connected to the inlet of the medium and low pressure gas collection and separation skid (25). The outlet end of the medium-low pressure gas collection and separation skid (25) is connected to the sewage tank (27), the outlet end of the medium-low pressure gas collection and separation skid (25) is connected to the inlet end of the ball launcher skid (26), and the outlet end of the ball launcher skid (26) is connected to the gas collection pipe (80).

7. The system according to claim 6, wherein, The central well site (20) is also equipped with a compressor skid (28). The gas outlet of the medium and low pressure gas collection and separation skid (25) includes a medium pressure coal and rock gas outlet and a low pressure coal and rock gas outlet. The medium pressure coal and rock gas outlet is connected to the gas inlet of the launch tube skid (26). The low pressure coal and rock gas outlet is connected to the gas inlet of the compressor skid (28). The gas outlet of the compressor skid (28) is connected to the gas inlet of the launch tube skid (26).

8. The system according to claim 6, wherein, The purification plant (90) also performs separation, pressurization, decarbonization and dehydration treatment on coal gas.

9. A design method of a low-pressure gathering and transportation system for deep coal rock gas, characterized in that, For arranging the collection and transportation system as described in any one of claims 1-8, the method comprises the following steps: Based on the pressure gradient of the medium and low pressure gathering and transmission system obtained from the dynamic simulation model of the large pipeline network and the medium and low pressure gathering and transmission system, the gas gathering and transmission volume of different regions is adjusted according to the pressure gradient. The number of well sites in each well site group (10) is determined based on the gas gathering and transmission volume in different regions; Dynamic calculations were performed on each well site group (10) to obtain the pressure and production changes, increased production revenue, and production energy consumption of each well site, and to determine the optimal layout location of the central well site (20).

10. The method of claim 9, wherein the low-pressure collection and transportation system for deep coal rock gas is designed to have a pressure of 5 to 10 MPa. It also includes the following steps: The outlet pressure of the central well site and the outlet pressure of the well site are obtained based on the inlet pressure of the purification plant. Equipment selection is based on the outlet pressure of the central well site and the outlet pressure of the well site.

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