Gas concentration extraction device and extraction method for mining wells traversing unmined coal seams

Abstract

This invention belongs to the field of coalbed methane extraction technology in mining wells. The purpose is to provide a gas concentration extraction device and method for mining wells traversing unmined coal seams, achieving single-well gas concentration extraction and improving the utilization rate of high-grade resources. The technical solution is as follows: a gas concentration extraction device for mining wells traversing unmined coal seams, wherein a packer is fitted onto the lower part of the tubing, and a guide shoe is fixed to the lower end of the tubing. The packer is located between the lower mined coal seam and the adjacent upper unmined coal seam. A first compressor is connected to the annular gas production channel; a second compressor is connected to the tubing gas production channel. The extraction method involves starting the first and second compressors to perform negative pressure extraction on the annular gas production channel and the tubing gas production channel, respectively. A dynamic control mechanism based on concentration feedback is used to adjust the extraction power of the tubing gas production channel to ensure that the gas concentration output from the annular gas production channel stably meets the requirements of the gathering and transmission network. This invention is used for gas extraction in mining wells.

Description

Technical Field

[0001] This invention relates to a gas concentration extraction device and method for mining wells that traverse unmined coal seams, belonging to the technical field of coalbed methane extraction in mining wells. Background Technology

[0002] Mining wells are typically used to extract gas from underground coal mine working faces in order to reduce underground gas drainage pressure and promote safe production in coal mines.

[0003] In coal mine gas control projects, mining shafts often penetrate multiple coal-bearing strata. Taking the Pingdingshan mining area as an example, the upper coal seam is unmined and has a high gas concentration, while the lower coal seam being mined is affected by mining disturbances and air leakage, resulting in a significant decrease in gas concentration due to the mixing of a large amount of air with the produced gas.

[0004] Currently, conventional coalbed methane extraction technology in mining wells mainly adopts a mixed extraction mode across the entire well section, where gases produced from different coal seams are mixed and extracted to the surface through the same pipeline. This operating method presents significant engineering challenges when faced with concentration differences between seams: the mixing of high-concentration and low-concentration methane within the wellbore results in an overall production concentration that fails to meet the minimum calorific value requirements of long-distance pipelines, forcing high-grade resources to be downgraded or even vented; simultaneously, if the mixed concentration falls within the explosive limit range, it increases the difficulty of safety management for the surface gathering and transportation system.

[0005] Therefore, how to achieve physical isolation and independent transportation of gas sources with different concentrations within a single wellbore, and how to carry out differentiated extraction based on production dynamics, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a gas extraction device and method for mining wells traversing unmined coal seams, thereby achieving gas extraction with varying concentrations in a single well and improving the utilization rate of high-grade resources.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a gas concentration extraction device for mining wells traversing unmined coal seams, comprising an underground isolation assembly, a wellhead sealing assembly, a first compressor, a second compressor, a first concentration detection device, and a second concentration detection device; The downhole isolation assembly includes tubing, a packer, and a guide shoe. The packer is fitted onto the lower part of the tubing near the end. The guide shoe, used to guide the tubing down into the well, is fixed to the lower end of the tubing. The tubing is lowered into the wellbore of the mining well, with its upper end extending out of the wellbore. The packer is located between the lower mined coal seam and the adjacent upper unmined coal seam. The packer, the tubing above the packer, and the wellbore form the annulus gas production channel for the upper unmined coal seam. The wellbore and tubing below the packer form the tubing gas production channel for the lower mined coal seam. The wellhead sealing assembly is installed at the wellhead to seal the annular gas production channel and leave an interface. The first compressor is located on the ground and is connected to the annular gas production channel through an interface on the wellhead sealing assembly. The first concentration detection device is set at the air inlet of the first compressor. The second compressor is located on the ground and is connected to the oil pipeline gas production channel. The second concentration detection device is installed at the air inlet of the second compressor.

[0008] Preferably, the packer is an annular rubber ring with a tapered guide slope at the bottom, and its outer diameter is adapted to the inner diameter of the graded hoop inside the wellbore.

[0009] Preferably, there is a 6-10 mm gap between the packer and the inner wall of the wellbore.

[0010] Preferably, the guide shoe is a hollow round tube with a beveled tip, and its outer diameter is consistent with the outer diameter of the oil pipe coupling.

[0011] Preferably, the first compressor and the annular gas production channel, and the second compressor and the oil pipe gas production channel are both connected by flexible connecting pipes.

[0012] This invention discloses a method for extracting gas concentration from a mining well traversing an unmined coal seam, comprising the following steps: S1. A downhole tubing string is lowered into the mining well. After the packer is fitted onto the lower end of the tubing, a guide shoe is connected and lowered into the mining well until the packer reaches the designated position between the lower mining coal seam and the adjacent upper unmined coal seam. There is a gap between the packer and the wellbore. An annular gas production channel for the upper unmined coal seam is formed between the packer, the tubing above the packer, and the wellbore. A tubing gas production channel for the lower mining coal seam is formed inside the wellbore and tubing below the packer. S2. Install the wellhead sealing assembly to seal the annular gas production channel and leave the interface between the annular gas production channel and the first compressor. S3. Install a ground extraction system, connect the air inlet of the first compressor to the annular gas production channel, connect the air outlet to the gathering and transmission pipeline, and install a first concentration detection device at the air inlet of the first compressor. Connect the air inlet of the second compressor to the oil pipe gas production channel, connect the air outlet to the low-concentration gas utilization pipeline or venting system, and install a second concentration detection device at the air inlet of the second compressor. S4. Start the first compressor and the second compressor to perform negative pressure extraction in the annular gas production channel and the oil pipe gas production channel, respectively. S5. Observe the gas concentration displayed by the first concentration detection device. When the gas concentration is lower than the preset target value, increase the extraction power of the second compressor to increase the extraction force of the oil pipe gas production channel and suppress the intrusion of low-concentration gas into the annular gas production channel. When the gas concentration reaches or exceeds the preset target value, maintain the current operating condition of the second compressor so that the gas concentration produced by the annular gas production channel stably meets the access requirements of the gathering and transmission pipeline network.

[0013] Preferably, in step S5, the preset target value is a pre-set gas concentration value that meets the access requirements of the gathering and transportation pipeline network.

[0014] Compared with the prior art, the present invention has the following beneficial effects.

[0015] 1. In this invention, a packer is used to divide the wellbore into annular gas production channels for the upper unmined coal seam and oil pipe gas production channels for the lower mined coal seam. The high-concentration gas in the upper part and the low-concentration gas in the lower part are extracted to the surface through different channels, avoiding concentration dilution caused by mixed extraction and providing a guarantee for quality utilization.

[0016] 2. In this invention, a dynamic control mechanism based on concentration feedback is adopted. By monitoring the gas concentration produced by the annular gas production channel in real time, the extraction power of the oil pipe gas production channel is adjusted to ensure that the gas concentration output by the annular gas production channel stably meets the grid connection requirements of the gathering and transmission pipeline network, thereby improving the utilization rate of high-quality gas resources.

[0017] 3. This invention enables the differentiated utilization of methane of different concentrations. High-concentration methane is connected to the grid to create economic benefits, while low-concentration methane is used for power generation or safe venting, thus avoiding resource waste and explosion risks.

[0018] 4. The extraction device in this invention has a simple structure, strong on-site adaptability, easy installation and maintenance of ground-based equipment, short construction period, and low cost. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly introduced below.

[0020] Figure 1 This is a schematic diagram of the structure of the present invention.

[0021] Figure 2 This is a schematic diagram of the packer in this invention.

[0022] Figure 3 This is a perspective view of the packer in this invention.

[0023] In the diagram: 1 is the downhole isolation assembly, 101 is the tubing, 102 is the packer, 1021 is the guide ramp, 103 is the guide shoe, 2 is the wellhead sealing assembly, 3 is the first compressor, 301 is the first concentration detection device, 4 is the second compressor, 401 is the second concentration detection device, 5 is the wellbore, 6 is the lower mined coal seam, 7 is the upper unmined coal seam, 8 is the annulus gas production channel, 9 is the tubing gas production channel, 10 is the stage collar, and 11 is the screen pipe. Detailed Implementation

[0024] The technical solutions 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, and not all embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The present invention provides the following embodiments.

[0026] like Figure 1 As shown, the present invention provides a gas concentration extraction device for mining wells traversing unmined coal seams, comprising an underground isolation assembly 1, a wellhead sealing assembly 2, a first compressor 3, and a second compressor 4; The downhole isolation assembly 1 includes tubing 101, packer 102, and guide shoe 103. The packer 102 is fitted on the lower part of the tubing 101 near the end. The guide shoe 103, used to guide the tubing 101 down into the well, is fixed to the lower end of the tubing 101. The tubing 101 is lowered into the wellbore 5 of the mining well, with its upper end extending out of the wellbore 5. The packer 102 is located between the lower mining coal seam 6 and the adjacent upper unmined coal seam 7. The space between the packer 102, the tubing 101 above the packer 102, and the wellbore 5 forms the annulus gas production channel 8 of the upper unmined coal seam 7. The space between the wellbore 5 below the packer 102 and the inside of the tubing 101 forms the tubing gas production channel 9 of the lower mining coal seam 6. The wellhead sealing assembly 2 is installed at the wellhead to seal the annular gas production channel 8 and leave an interface. The first compressor 3 is located on the ground and is connected to the annular gas production channel 8 through the interface on the wellhead sealing assembly 2. The first concentration detection device 301 is installed at the air inlet of the first compressor 3. The second compressor 4 is located on the ground and is connected to the oil pipe gas production channel 9. The second concentration detection device 401 is installed at the air inlet of the second compressor 4.

[0027] like Figure 2 , Figure 3As shown, the packer 102 is an annular rubber ring with a tapered guide slope 1021 at the bottom, and its outer diameter is adapted to the inner diameter of the stage collar 10 inside the wellbore 5. The packer 102 is made of nitrile rubber (NBR) material, but other sealing materials can also be used.

[0028] The packer 102 has a gap of 6-10 mm between itself and the inner wall of the wellbore 5.

[0029] The outer diameter of the packer 102 must be large enough to allow the graded clamp 10 to pass through, and the gap between the packer 102 and the inner wall of the wellbore 5 should be around 7mm.

[0030] Packer 102 does not completely seal the wellbore 5, leaving a gap, which means it only largely prevents the low-concentration gas below from moving upward, and a small amount of low-concentration gas below can still invade upward.

[0031] The guide shoe 103 is a hollow round tube with a beveled tip, and its outer diameter is the same as that of the oil pipe coupling.

[0032] The first compressor 3 is connected to the annular gas production channel 8, and the second compressor 4 is connected to the oil pipe gas production channel 9, all via flexible connecting pipes. These flexible connecting pipes can buffer vibrations and can be made of flexible metal hoses. Both ends of the flexible metal hoses are connected to the corresponding compressor inlet and gas production channel interface via flanges.

[0033] This invention is applicable to mining wells that communicate with underground roadways and have no groundwater. When cementing, a graded hoop 10 is required, and a screen pipe 11 is used for the part that crosses the coal seam. The tubing 101 and packer 102, guided by the guide shoe 103 and the guide ramp 1021 of the packer 102, can smoothly pass through the graded hoop 10 and reach the position in the screen pipe 11 between the lower mined coal seam 6 and the adjacent upper unmined coal seam 7.

[0034] This invention utilizes a packer to divide the wellbore into annular gas production channel 8 for the upper unmined coal seam 7 and oil pipe gas production channel 9 for the lower mined coal seam 6. The high-concentration gas in the upper part and the low-concentration gas in the lower part are extracted to the surface through different channels, avoiding concentration dilution caused by mixed extraction. This achieves the separate utilization of gas of different concentrations. High-concentration gas is connected to the grid to create economic benefits, while low-concentration gas is used for power generation or safe venting, avoiding resource waste and explosion risks.

[0035] The extraction device of this invention has a simple structure, strong on-site adaptability, easy installation and maintenance of ground-based equipment, short construction period, and low cost.

[0036] This invention discloses a method for extracting gas concentration from a mining well traversing an unmined coal seam, comprising the following steps: S1. A downhole tubing string is lowered into the mining well. After the packer 102 is fitted onto the lower end of the tubing 101, it is connected to the guide shoe 103 and lowered into the mining well until the packer 102 reaches the designated position between the lower mining coal seam 6 and the adjacent upper unmined coal seam 7. There is a gap between the packer 102 and the wellbore 5. An annular gas production channel 8 for the upper unmined coal seam 7 is formed between the packer 102, the tubing 101 above the packer 102 and the wellbore 5. A tubing gas production channel 9 for the lower mining coal seam 6 is formed inside the wellbore 5 and the tubing 101 below the packer 102. S2. Install wellhead sealing assembly 2 to seal annular gas production channel 8, leaving an interface between annular gas production channel 8 and first compressor 3; S3. Install a ground extraction system, connect the inlet of the first compressor 3 to the annular gas production channel 8, connect the outlet to the gathering and transmission pipeline, and install a first concentration detection device 301 at the inlet of the first compressor 3. Connect the inlet of the second compressor 4 to the oil pipe gas production channel 9, connect the outlet to the low-concentration gas utilization pipeline or venting system, and install a second concentration detection device 401 at the inlet of the second compressor 4. S4. Start the first compressor 3 and the second compressor 4 to perform negative pressure extraction on the annular gas production channel 8 and the oil pipe gas production channel 9, respectively. S5. Observe the gas concentration displayed by the first concentration detection device 301. When the gas concentration is lower than the preset target value, increase the extraction power of the second compressor 4 and increase the extraction force of the oil pipe gas production channel 9 to suppress the intrusion of low-concentration gas into the annular gas production channel 8. When the gas concentration reaches or exceeds the preset target value, maintain the current operating condition of the second compressor 4 so that the gas concentration produced by the annular gas production channel 8 stably meets the access requirements of the gathering and transmission pipeline network.

[0037] In S5, the preset target value is a pre-set gas concentration value that meets the access requirements of the gathering and transportation pipeline network.

[0038] In this invention, a dynamic control mechanism based on concentration feedback is adopted. By monitoring the gas concentration produced by the annular gas production channel in real time, the extraction power of the oil pipe gas production channel is adjusted to ensure that the gas concentration output by the annular gas production channel stably meets the grid connection requirements of the gathering and transmission pipeline network, thereby improving the utilization rate of high-quality gas resources.

[0039] In this invention, the oil pipe 101 is a 73mm oil pipe, but it can also be replaced by an oil pipe of the same type but different specifications. The displacement of the first compressor 3 and the second compressor 4 can be selected according to the on-site production capacity. The first concentration detection device 301 and the second concentration detection device 401 can be equipped with a display screen to display the measured gas concentration locally, or it can be remotely transmitted to the control room. At the same time, the first compressor 3 and the second compressor 4 can be manually controlled, remotely controlled from the control room, or remotely controlled through a PLC control system.

[0040] This invention has been practically applied in a surface mining shaft in the Pingdingshan mining area. This shaft connects the upper No. 4-2 coal seam (buried at a depth of approximately 800m, with a gas concentration of approximately 92%) and the lower No. 2-1 coal seam (buried at a depth of approximately 1000m, with a measured gas concentration of approximately 50%). If conventional combined mining methods are used, the mixed gas concentration at the wellhead is only about 70%, which cannot meet the ≥90% access standard for the external transmission network. To improve the utilization rate of high-quality gas resources in the upper No. 4-2 coal seam, the device and method described in this invention are used for concentration-specific extraction.

[0041] The gas concentration extraction device for a mining well traversing an unmined coal seam, as per this invention, is installed in the well. The packer 102 is located in the interlayer section between coal seam 4-2 and coal seam 2-1 (at a depth of approximately 900m). The first compressor 3 and the second compressor 4 are two compressors with a rated extraction capacity of 5000 m³ / d. Both the first concentration detection device 301 and the second concentration detection device 401 are equipped with local display instruments for real-time reading by the operator.

[0042] Extraction Method Implementation: Two compressors were started, initially operating at 60% of the industrial frequency load. Operators observed instrument readings: the instantaneous concentration in annular gas production channel 8 was 85%, and the concentration in pipeline gas production channel 9 was 70%. Since the concentration in annular gas production channel 8 was below the 90% pipeline access threshold, operators manually adjusted the inverter setpoint of the second compressor 4, gradually increasing its extraction power. As the speed of the second compressor 4 increased, the extraction negative pressure in pipeline gas production channel 9 increased, enhancing the extraction capacity of gas gushing from the lower goaf and effectively suppressing the interference of low-concentration gas into annular gas production channel 8. After stabilization, the concentration in annular gas production channel 8 rebounded and stabilized at 93%–94%, meeting grid connection requirements; the flow rate in pipeline gas production channel 9 increased, and the concentration dropped to approximately 55%, directly transported to the power plant for blending and utilization.

[0043] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A gas concentration extraction device for mining wells traversing unmined coal seams, characterized in that: It includes a downhole isolation assembly (1), a wellhead sealing assembly (2), a first compressor (3), and a second compressor (4); The downhole isolation assembly (1) includes tubing (101), packer (102) and guide shoe (103). The packer (102) is fitted on the lower part of the tubing (101) near the end. The guide shoe (103) used to guide the tubing (101) down into the well is fixed to the lower end of the tubing (101). The tubing (101) is lowered into the wellbore (5) and the upper end extends out of the wellbore (5). The packer (102) is located between the lower mining coal seam (6) and the adjacent upper unmined coal seam (7). The packer (102), the tubing (101) above the packer (102) and the wellbore (5) form the annulus gas production channel (8) of the upper unmined coal seam (7). The wellbore (5) below the packer (102) and the inside of the tubing (101) form the tubing gas production channel (9) of the lower mining coal seam (6). The wellhead sealing assembly (2) is installed at the wellhead to seal the annular gas production channel (8) and leave an interface. The first compressor (3) is located on the ground and is connected to the annular gas production channel (8) through the interface on the wellhead sealing assembly (2). The first concentration detection device (301) is set at the air inlet of the first compressor (3). The second compressor (4) is located on the ground and is connected to the oil pipe gas production channel (9). The second concentration detection device (401) is set at the air inlet of the second compressor (4).

2. The gas concentration extraction device for a mining well traversing an unmined coal seam according to claim 1, characterized in that: The packer (102) is an annular rubber ring with a tapered guide slope (1021) at the bottom, and its outer diameter is adapted to the inner diameter of the graded hoop (10) inside the wellbore (5).

3. The gas concentration extraction device for a mining well traversing an unmined coal seam according to claim 2, characterized in that: The packer (102) has a gap of 6-10 mm between itself and the inner wall of the wellbore (5).

4. A gas concentration extraction device for a mining well traversing an unmined coal seam according to claim 1 or 2, characterized in that: The guide shoe (103) is a hollow round tube with a beveled tip, and its outer diameter is consistent with the outer diameter of the oil pipe coupling.

5. A gas concentration extraction device for a mining well traversing an unmined coal seam according to claim 1 or 2, characterized in that: The first compressor (3) and the annular gas production channel (8) and the second compressor (4) and the oil pipe gas production channel (9) are connected by flexible connecting pipes.

6. A method for extracting gas concentration from a mining shaft traversing an unmined coal seam, characterized in that... Includes the following steps: S1. A downhole tubing string is lowered into the mining well. After the packer (102) is fitted onto the lower end of the tubing (101), the guide shoe (103) is connected and lowered into the mining well until the packer (102) reaches the designated position between the lower mining coal seam (6) and the adjacent upper unmined coal seam (7). There is a gap between the packer (102) and the wellbore (5). An annular gas production channel (8) for the upper unmined coal seam (7) is formed between the packer (102), the tubing (101) above the packer (102), and the wellbore (5). A tubing gas production channel (9) for the lower mining coal seam (6) is formed inside the wellbore (5) and the tubing (101) below the packer (102). S2. Install the wellhead sealing assembly (2), seal the annular gas production channel (8), and leave the interface between the annular gas production channel (8) and the first compressor (3); S3. Install a ground extraction system, connect the air inlet of the first compressor (3) to the annular gas production channel (8), connect the air outlet to the gathering and transmission pipeline, and set a first concentration detection device (301) at the air inlet of the first compressor (3), connect the air inlet of the second compressor (4) to the oil pipe gas production channel (9), connect the air outlet to the low concentration gas utilization pipeline or venting system, and set a second concentration detection device (401) at the air inlet of the second compressor (4). S4. Start the first compressor (3) and the second compressor (4) to perform negative pressure extraction on the annular gas production channel (8) and the oil pipe gas production channel (9) respectively; S5. Observe the gas concentration displayed by the first concentration detection device (301). When the gas concentration is lower than the preset target value, increase the extraction power of the second compressor (4) and increase the extraction force of the oil pipe gas production channel (9) to suppress the intrusion of low-concentration gas into the annular gas production channel (8). When the gas concentration reaches or exceeds the preset target value, maintain the current operating condition of the second compressor (4) so ​​that the gas concentration produced by the annular gas production channel (8) can stably meet the access requirements of the gathering and transmission pipeline network.

7. The method for extracting gas concentration from a mining well traversing an unmined coal seam according to claim 6, characterized in that: In S5, the preset target value is a pre-set gas concentration value that meets the access requirements of the gathering and transportation pipeline network.

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