A process for releasing and discharging coal-bed gas in-situ after hydraulic fracturing of a coal-bed gas well

Abstract

The application discloses an in-situ coal bed gas well hydraulic fracturing post-bleeding process and belongs to the technical field of coal bed gas development. The in-situ coal bed gas well hydraulic fracturing post-bleeding process is divided into four stages, i.e., a test bleeding stage, a constant-speed bleeding stage, a bleeding speed slow increase stage and a bleeding speed rapid decrease stage. After the same fracturing fluid volume as the wellbore volume is discharged at a bleeding speed of 0.2-0.3 m 3 / h in the test bleeding stage, the bleeding speed is increased step by step; in the constant-speed bleeding stage, a reasonable bleeding speed is determined according to the ORP and turbidity value of the bleeding output liquid, and the fracturing wellhead pressure is gradually decreased in the constant-speed bleeding process; in the bleeding speed slow increase stage, the bleeding speed is slowly increased, and the ORP value of the bleeding output liquid is ensured to be higher than-180 mV and the turbidity value is ensured to be lower than 9.5 NTU; in the bleeding speed rapid decrease stage, the opening degree of the needle valve is gradually increased, and the fracturing wellhead pressure is continuously decreased until the wellhead is completely opened. The process can significantly reduce the proppant return amount in the bleeding process and maintain a relatively high flow conductivity of the coal reservoir fracturing fracture.

Description

Technical Field

[0001] This invention relates to an in-situ coalbed methane well hydraulic fracturing post-blowing process, particularly a hydraulic fracturing process applicable to vertical, directional, and segmented horizontal wells in low-permeability coal reservoirs under high geostress conditions. By optimizing the hydraulic fracturing post-blowing regime, it avoids the retention of large amounts of fine coal powder around the wellbore and the backflow of large amounts of proppant, thus maintaining the artificial fractures around the wellbore of the in-situ coalbed methane well with continuous high conductivity. This invention belongs to the field of coalbed methane development technology. Background Technology

[0002] Large-scale development of coalbed methane can reduce greenhouse gas emissions in coal mine production and generate significant economic, environmental, safety and social benefits.

[0003] In coalbed methane development areas where the coal morphology is generally high, the coal reservoir permeability is poor. Therefore, most in-situ coalbed methane wells require hydraulic fracturing to improve the permeability of the coal reservoir around the wellbore, ensuring good gas production during the well's drainage process. After the in-situ coalbed methane well fracturing operation, on-site personnel need to gradually reduce the wellhead pressure by performing blowout operations, followed by subsequent drilling plugging, well washing, and pump installation. For a long time, due to unreasonable control of the blowout rate after hydraulic fracturing in in-situ coalbed methane wells, a large amount of fine coal dust around the wellbore cannot be discharged when the blowout rate is too low, or a large amount of proppant is backflowed when the blowout rate is too high. As a result, coal dust blockage or severe closure of the fracturing fractures around the wellbore occurs, significantly reducing the conductivity of the fractures around the wellbore, which is detrimental to high and long-term stable production of in-situ coalbed methane wells. In order to comprehensively promote the surface development of coalbed methane, it is necessary to solve the problems of unclear venting stage after hydraulic fracturing of in-situ coalbed methane wells, unreasonable venting speed, and lack of basis for adjusting venting speed. This is to avoid damage to the conductivity of the fracturing fractures around the wellbore caused by venting operations, and thus ensure the high production and long-term stable production of in-situ coalbed methane wells. Summary of the Invention

[0004] Technical Problem: The purpose of this invention is to overcome the problems existing in the prior art and provide an in-situ coalbed methane well hydraulic fracturing and subsequent venting process to solve the problem that the conductivity of the fracturing fractures around the wellbore in in-situ coalbed methane wells under high geostress background is easily damaged, resulting in low gas production and short stable production time.

[0005] Technical Solution: To achieve the above objectives, the in-situ coalbed methane well hydraulic fracturing and subsequent blowout process of the present invention includes a trial blowout stage, a constant-rate blowout stage, a slow increase in blowout rate stage, and a rapid decrease in blowout rate stage; a. During the trial release phase, the on-site release personnel will open the needle valve on the fracturing wellhead 12 hours after the hydraulic fracturing operation has stopped, and control the initial release rate to 0.2–0.3 m / s by adjusting the opening of the needle valve. 3 After the cumulative volume of the vented fluid reaches the volume of the in-situ coalbed methane wellbore, the venting rate is increased in stages until the ORP value of the vented fluid drops to -120 to -100 mV and the turbidity value of the vented fluid is below 6 NTU. This determines the maximum venting rate for the trial venting stage. The trial venting stage lasts for 1 to 2 days. During the trial venting stage, the on-site venting personnel adjust the opening of the needle valve on the fracturing wellhead, providing a basis for determining the venting rate parameters for the subsequent constant-rate venting stage. During the trial venting stage, the on-site venting personnel collect one sample of the vented fluid every 0.5 hours and test the ORP value, turbidity value, and pH value of the sample within 3 minutes after sampling. The ORP value and turbidity value of the vented fluid are used as the basis for gradually increasing the venting rate. b. During the constant-rate venting phase, the on-site venting personnel maintain the venting rate at this stage by frequently adjusting the opening of the needle valve on the fracturing wellhead to the same rate as the later stage of the test venting phase. They also continuously sample the venting produced fluid and monitor the on-site water quality until the pressure at the fracturing wellhead drops to 50% of the initial pressure at the fracturing wellhead during the test venting phase. c. During the slow increase phase of the venting rate, the on-site venting personnel gradually increased the opening of the needle valve on the fracturing wellhead to slowly increase the venting rate, and ensured that the ORP value of the venting produced fluid was higher than -180 mV and the turbidity value of the venting produced fluid was lower than 9.5 NTU. d. During the rapid decrease in the venting rate, the on-site venting personnel further increased the opening of the needle valve on the fracturing wellhead, causing the pressure at the fracturing wellhead to continue to decrease. The venting rate decreased rapidly under the low pressure difference formed by the coal reservoir pressure and the wellbore fluid pressure. After the pressure at the fracturing wellhead dropped to 0, the needle valve on the fracturing wellhead was removed first, and then the fracturing wellhead was fully opened, thus ending the overflow operation.

[0006] In step a, the trial venting stage begins 12 hours after the pump is shut down during the hydraulic fracturing operation of the coal reservoir in the in-situ coalbed methane well. It ends when the venting rate is increased stepwise until the ORP value of the venting produced fluid drops to -120 to -100 mV and the turbidity value of the venting produced fluid is below 6 NTU. The maximum venting rate of the trial venting stage is determined based on this and the stage ends.

[0007] In step b, the constant-rate blowout phase begins when the ORP value of the blowout produced fluid decreases to -120 to -100 mV and the turbidity value of the blowout produced fluid is below 6 NTU. Based on this, the maximum blowout rate of the test blowout phase is determined, and it ends when the pressure at the fracturing wellhead decreases to 50% of the initial pressure at the fracturing wellhead during the test blowout phase. The constant-rate blowout phase lasts for 2 to 3 days. During the constant-rate blowout phase, the on-site blowout personnel frequently adjust the opening of the needle valve at the fracturing wellhead to maintain a stable blowout rate and a continuous decrease in the fracturing wellhead pressure. During the constant-rate blowout phase, the on-site blowout personnel collect one sample of the blowout produced fluid every 0.5 hours, and test the ORP value, turbidity value, and pH value of the collected blowout produced fluid sample within 3 minutes after sampling, ensuring that the ORP value of the blowout produced fluid is above -180 mV and the turbidity value is below 9.5 NTU. When the ORP value of the effluent is below -180 mV, or the turbidity value of the effluent is above 9.5 NTU, adjust and reduce the effluent speed.

[0008] In step c, the slow increase phase of the venting rate begins after the pressure at the fracturing wellhead drops to 50% of the initial pressure at the fracturing wellhead during the trial venting phase, and ends when the venting rate slowly increases to its maximum value. The duration of the slow increase phase of the venting rate is affected by the scale of fracturing, the original permeability of the coal reservoir, and the effect of fracturing stimulation.

[0009] The duration of the slow increase in the venting rate is affected by the scale of fracturing, the original permeability of the coal reservoir, and the effect of fracturing stimulation. When the fracturing scale is large, the original permeability of the coal reservoir is low, and the fracturing effect is poor, the slow increase in the venting rate lasts for 3 to 4 days. When the fracturing scale is small, the original permeability of the coal reservoir is high, and the fracturing effect is good, the slow increase in the venting rate lasts for 2 to 3 days. During the slow increase phase of the venting rate, on-site personnel frequently adjusted the opening of the needle valve at the fracturing wellhead to gradually increase the venting rate while continuously reducing the pressure at the fracturing wellhead. During this slow venting rate increase phase, on-site personnel collected one sample of the vented fluid every 0.5 hours. Within 3 minutes of sampling, they tested the ORP value, turbidity value, and pH value of the vented fluid, ensuring that the ORP value was above -180 mV and the turbidity value was below 9.5 NTU.

[0010] When the ORP value of the venting product is below -180 mV, or the turbidity value of the venting product is above 9.5 NTU, the venting speed needs to be stabilized in time to ensure that the ORP value of the venting product is above the lower limit of the ORP value of the venting product, the lower limit of the ORP value of the venting product (12) is -200 mV, and the upper limit of the turbidity value of the venting product is below 10 NTU of the upper limit of the turbidity value of the venting product; after the ORP value of the venting product is above -180 mV and the turbidity value of the venting product is below 9.5 NTU, the venting speed is slowly increased to the maximum value.

[0011] In step d, the rapid decline phase of the venting rate begins when the venting rate slowly increases to its maximum value and ends with the completion of the overflow operation. The duration of the rapid decline phase is affected by the scale of fracturing, the original permeability of the coal reservoir, and the fracturing effect. When the scale of fracturing is large, the original permeability of the coal reservoir is low, and the fracturing effect is poor, the rapid decline phase of the venting rate lasts longer, usually 2-3 days; when the scale of fracturing is small, the original permeability of the coal reservoir is high, and the fracturing effect is good, the rapid decline phase of the venting rate lasts shorter, usually 1-2 days. During the rapid decline phase of the venting rate, the on-site venting personnel gradually increase the opening of the needle valve at the fracturing wellhead, causing the overflow rate and the pressure at the fracturing wellhead to continuously decrease to 0, while the ORP and pH values ​​of the vented fluid continuously increase, and the turbidity value of the vented fluid rapidly decreases. During the rapid decline of the ejection rate, the on-site ejection personnel collected one sample of the ejection product every 0.5 hours, and tested and recorded the ORP value, turbidity value, and pH value of the collected ejection product sample within 3 minutes after sampling.

[0012] Beneficial Effects: By adopting the above technical solution, this invention overcomes the problems of fine coal powder not being able to be discharged or large amounts of proppant being returned after hydraulic fracturing of in-situ coalbed methane wells, and the easy damage to the conductivity of the fracturing fractures around the wellbore, which are often caused by the traditional venting method. First, based on the changes in venting velocity during the venting process, the venting process is divided into four stages, and control principles are formulated for each stage. Second, during the entire venting process, on-site venting personnel collect one sample of the venting produced fluid every 0.5 hours, and conduct water quality tests on the venting produced fluid samples, using the ORP value and pH value of the venting produced fluid as the basis for adjusting the venting velocity. Third, data such as venting velocity, fracturing wellhead pressure, and water quality parameters of the venting produced fluid are recorded throughout the entire venting process, and the venting control measures for in-situ coalbed methane wells in the area are further optimized based on data analysis. This technology is particularly suitable for hydraulically fracturing vertical wells, directional wells, and staged fracturing horizontal wells in low-permeability coal reservoirs under high geostress conditions. By optimizing the post-fracturing blowout regime, it avoids the retention of large amounts of fine coal powder around the wellbore and the excessive backflow of proppant, thus maintaining the continuity of artificial fractures around the wellbore in in-situ coalbed methane wells. It has broad applicability in this technical field. Its main advantages compared to existing technologies include: ①Based on the overflow velocity, fracturing wellhead pressure, and water quality characteristics of the venting fluid during the venting process, the venting stages should be reasonably divided, and the venting control principles and measures should be determined in stages.

[0013] ② Continuously test the quality of the effluent produced by the venting, and use it as the basis for adjusting the venting speed accordingly. The venting system is adjusted in a timely and reasonable manner throughout the entire process.

[0014] ③ The venting process is simple, easy to operate on-site, has low operating costs, and offers good economic, environmental and social benefits. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the in-situ coalbed methane well hydraulic fracturing and subsequent blowout process of the present invention.

[0016] In the figure: 1-Trial release stage; 2-Constant rate release stage; 3-Slow increase in release rate stage; 4-Rapid decrease in release rate stage; 5-Release time axis; 6-Release and water quality parameter change axis; 7-Release rate; 8-Fracturing wellhead pressure; 9-ORP value of release produced fluid; 10-Turbidity value of release produced fluid; 11-pH value; 12-Lower limit of ORP value of release produced fluid; 13-Upper limit of turbidity of release produced fluid. Detailed Implementation

[0017] The present invention will be further described below with reference to an embodiment in the accompanying drawings: like Figure 1 As shown, the present invention provides an in-situ coalbed methane well hydraulic fracturing and subsequent blowout process, comprising four stages: a trial blowout stage 1, a constant-rate blowout stage 2, a slow increase in blowout rate stage 3, and a rapid decrease in blowout rate stage 4. a. During the initial test run phase 1, 12 hours after the hydraulic fracturing operation and pump shutdown, the on-site personnel opened the needle valve at the wellhead and controlled the initial release velocity (7) to be 0.2–0.3 m / s by adjusting the valve opening. 3After the cumulative volume of the vented fluid reaches the volume of the in-situ coalbed methane wellbore, the venting rate 7 is increased in stages until the ORP value 9 of the vented fluid drops to -120 to -100 mV and the turbidity value 10 of the vented fluid is below 6 NTU. The maximum venting rate 7 for the first trial venting stage is determined based on this. The first trial venting stage begins 12 hours after the pump is shut down during hydraulic fracturing of the coal reservoir in the in-situ coalbed methane well. It ends when the venting rate 7 is increased in stages until the ORP value 9 of the vented fluid drops to -120 to -100 mV and the turbidity value 10 of the vented fluid is below 6 NTU. The duration of the first trial venting stage is relatively short, typically 1 to 2 days. During the first trial venting stage, the on-site venting personnel adjust the opening of the needle valve at the fracturing wellhead, providing a basis for determining the venting rate 7 parameters for the subsequent constant-rate venting stage 2. During the trial release phase 1, on-site release personnel collected one sample of the release product every 0.5 hours. Within 3 minutes after sampling, the ORP value (9), turbidity value (10), and pH value (11) of the released product were tested. The ORP value (9) and turbidity value (10) of the released product were used as the basis for the stepwise increase of the release rate (7).

[0018] b. Constant-rate blowout stage 2: On-site blowout personnel maintain the blowout rate 7 at a rate consistent with the later stage of test blowout stage 1 by frequently adjusting the opening of the needle valve on the fracturing wellhead. Continuous sampling of the blowout produced fluid and on-site water quality monitoring are conducted until the fracturing wellhead pressure 8 drops to 50% of the initial fracturing wellhead pressure 8 of test blowout stage 1. The constant-rate blowout stage 2 begins when the ORP value 9 of the blowout produced fluid drops to -120 to -100 mV and the turbidity value 10 of the blowout produced fluid is below 6 NTU, thus determining the start of the maximum blowout rate 7 of test blowout stage 1, and ends when the fracturing wellhead pressure 8 drops to 50% of the initial fracturing wellhead pressure 8 of test blowout stage 1. The constant-rate blowout stage 2 lasts for a relatively long time, typically 2–3 days. On-site blowout personnel maintain a stable blowout rate 7 and a continuously decreasing fracturing wellhead pressure 8 by frequently adjusting the opening of the needle valve on the fracturing wellhead during the constant-rate blowout stage 2. During the constant-rate venting phase 2, on-site venting personnel collect one sample of the venting product every 0.5 hours. Within 3 minutes of sampling, the ORP value (9), turbidity value (10), and pH value (11) of the venting product are tested, ensuring that the ORP value (9) is higher than -180 mV and the turbidity value (10) is lower than 9.5 NTU. If the ORP value (9) is lower than -180 mV or the turbidity value (10) is higher than 9.5 NTU, the venting rate is adjusted and reduced.

[0019] c. In the slow increase phase 3 of the venting rate, the on-site venting personnel gradually increase the opening of the needle valve at the fracturing wellhead, thus slowly increasing the venting rate 7, ensuring that the ORP value 9 of the vented fluid is higher than -180 mV and the turbidity value 10 of the vented fluid is lower than 9.5 NTU. This slow increase phase 3 begins after the fracturing wellhead pressure 8 drops to 50% of the initial fracturing wellhead pressure 8 in the trial venting phase 1, and ends when the venting rate 7 slowly increases to its maximum value. The duration of the slow increase phase 3 is affected by the fracturing scale, the original permeability of the coal reservoir, and the fracturing effect. When the fracturing scale is large, the original permeability of the coal reservoir is low, and the fracturing effect is poor, the slow increase phase 3 lasts longer, typically 3–4 days; when the fracturing scale is small, the original permeability of the coal reservoir is high, and the fracturing effect is good, the slow increase phase 3 lasts shorter, typically 2–3 days. During the slow increase phase 3 of the venting process, the on-site venting personnel frequently adjusted the opening of the needle valve at the fracturing wellhead to gradually increase the venting rate 7 and continuously decrease the fracturing wellhead pressure 8. During this phase, the on-site venting personnel collected one sample of the vented fluid every 0.5 hours. Within 3 minutes of sampling, they tested the ORP value 9, turbidity value 10, and pH value 11 of the vented fluid, ensuring that the ORP value 9 was above -180 mV and the turbidity value 10 was below 9.5 NTU. When the ORP value 9 of the effluent is below -180 mV, or the turbidity value 10 of the effluent is above 9.5 NTU, the effluent velocity 7 must be stabilized promptly to ensure that the ORP value 9 of the effluent is above the lower limit 12 of the effluent ORP value (which is -200 mV), and that the upper limit 13 of the effluent turbidity value is below the upper limit 10 NTU of the effluent turbidity value. Once the ORP value 9 of the effluent is above -180 mV and the turbidity value 10 of the effluent is below 9.5 NTU, the effluent velocity 7 can be slowly increased to its maximum value.

[0020] d. Rapid Decrease in Bleeding Rate Phase 4: On-site personnel further increase the opening of the needle valve at the fracturing wellhead, causing the wellhead pressure 8 to continuously decrease. The bleeding rate 7 decreases rapidly under the low pressure differential between the coal reservoir pressure and the wellbore fluid pressure. Once the wellhead pressure 8 reaches zero, the needle valve is removed, and the wellhead is fully opened, ending the overflow operation. Phase 4 of the rapid decrease in bleeding rate begins when the bleeding rate 7 slowly increases to its maximum value and ends when the overflow operation is completed. The duration of Phase 4 is affected by the fracturing scale, the original permeability of the coal reservoir, and the fracturing effect. When the fracturing scale is large, the original permeability of the coal reservoir is low, and the fracturing effect is poor, Phase 4 of the rapid decrease in bleeding rate lasts longer, typically 2–3 days. When the fracturing scale is small, the original permeability of the coal reservoir is high, and the fracturing effect is good, Phase 4 of the rapid decrease in bleeding rate lasts shorter, typically 1–2 days. During the rapid decrease in venting rate (phase 4), the on-site venting personnel gradually increased the opening of the needle valve at the fracturing wellhead, causing the overflow velocity (7) and fracturing wellhead pressure (8) to continuously decrease to 0. Simultaneously, the ORP value (9) and pH value (11) of the vented fluid continuously increased, while the turbidity value (10) of the vented fluid rapidly decreased. During this rapid decrease in venting rate (phase 4), the on-site venting personnel collected one sample of the vented fluid every 0.5 hours, and tested and recorded the ORP value (9), turbidity value (10), and pH value (11) of the collected sample within 3 minutes of sampling.

Claims

1. A post-hydraulic fracturing and blowout release process for in-situ coalbed methane wells, characterized in that: It includes four stages: trial release stage (1), constant speed release stage (2), slow increase in release speed stage (3), and rapid decrease in release speed stage (4); a. In the aforementioned trial release stage (1), the on-site release personnel, 12 hours after the hydraulic fracturing operation of the in-situ coalbed methane well in the coal reservoir was stopped, opened the needle valve on the fracturing wellhead and controlled the initial release rate (7) to be 0.2–0.3 m by adjusting the opening degree of the needle valve. 3 / h, after the cumulative volume of the vented fluid reaches the volume of the in-situ coalbed methane wellbore, the venting rate is increased stepwise (7) until the ORP value (9) of the vented fluid drops to -120 to -100 mV and the turbidity value (10) of the vented fluid is below 6 NTU, and the maximum venting rate (7) of the test venting stage (1) is determined accordingly; the test venting stage (1) lasts for 1 to 2 days; the on-site venting personnel adjust the opening of the needle valve on the fracturing wellhead through the test venting stage (1) to provide a basis for determining the venting rate (7) parameters of the subsequent constant rate venting stage (2); during the test venting stage (1), the on-site venting personnel collect one sample of the vented fluid every 0.5 hours, and after sampling, 3 Within min, samples of the effluent ORP value (9), turbidity value (10), and pH value (11) were collected. The effluent ORP value (9) and turbidity value (10) were then used as the basis for the stepwise increase of the effluent rate (7). b. In the constant-rate venting stage (2), the on-site venting personnel adjust the opening of the needle valve on the fracturing wellhead at a high frequency to maintain the venting speed (7) of the constant-rate venting stage (2), in order to continue the venting speed (7) in the later stage of the test venting stage (1), and continuously sample the venting produced fluid and monitor the on-site water quality until the fracturing wellhead pressure (8) drops to 50% of the initial fracturing wellhead pressure (8) of the test venting stage (1); c. During the slow increase phase of the venting speed (3), the on-site venting personnel gradually increased the opening of the needle valve on the fracturing wellhead to slowly increase the venting speed (7), and ensured that the ORP value (9) of the venting produced fluid was higher than -180 mV and the turbidity value (10) of the venting produced fluid was lower than 9.5 NTU. d. During the rapid decrease of the venting speed (4), the on-site venting personnel further increased the opening of the needle valve on the fracturing wellhead, causing the fracturing wellhead pressure (8) to continue to decrease. The venting speed (7) decreased rapidly under the low pressure difference formed by the coal reservoir pressure and the well fluid pressure. After the fracturing wellhead pressure (8) dropped to 0, the needle valve on the fracturing wellhead was removed first, and then the fracturing wellhead was fully opened, and the overflow operation was completed.

2. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 1, characterized in that: In step a, the trial venting stage (1) begins 12 hours after the pump is shut down during the hydraulic fracturing operation of the coal reservoir in the in-situ coalbed methane well. The venting speed (7) is increased stepwise until the ORP value (9) of the venting produced liquid decreases to -120 to -100 mV and the turbidity value (10) of the venting produced liquid is less than 6 NTU. Based on this, the maximum venting speed (7) of the trial venting stage (1) is determined and then the process ends.

3. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 1, characterized in that: In step b, the constant-rate venting stage (2) begins when the ORP value (9) of the venting produced fluid decreases to -120 to -100 mV and the turbidity value (10) of the venting produced fluid is less than 6 NTU. Based on this, the maximum venting rate (7) of the test venting stage (1) is determined to end when the pressure (8) at the fracturing wellhead decreases to 50% of the initial pressure (8) at the fracturing wellhead in the test venting stage (1). The duration of the constant-rate venting stage (2) is 2 to 3 days. During the constant-rate venting stage (2), the on-site venting personnel frequently adjust the opening of the needle valve on the fracturing wellhead to maintain a stable venting rate (7) and make the pressure (8) at the fracturing wellhead continuously decrease. During the constant-rate venting stage (2), the on-site venting staff collected one sample of the venting output liquid every 0.5 hours. Within 3 minutes after sampling, the ORP value (9), turbidity value (10), and pH value (11) of the venting output liquid were tested. The ORP value (9) of the venting output liquid was ensured to be higher than -180 mV and the turbidity value (10) of the venting output liquid was lower than 9.5 NTU.

4. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 3, characterized in that: When the ORP value (9) of the effluent is below -180 mV, or the turbidity value (10) of the effluent is above 9.5 NTU, adjust and reduce the effluent speed (7).

5. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 1, characterized in that: In step c, the slow increase phase (3) of the release rate begins after the pressure (8) at the fracturing wellhead drops to 50% of the initial pressure (8) at the fracturing wellhead in the trial release phase (1) and ends when the release rate (7) slowly increases to the maximum value. The duration of the slow increase phase (3) of the release rate (7) is affected by the scale of fracturing, the original permeability of the coal reservoir, and the effect of fracturing.

6. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 5, characterized in that: The duration of the slow increase phase (3) of the venting rate (7) is affected by the scale of fracturing, the original permeability of the coal reservoir, and the effect of fracturing stimulation. When the fracturing scale is large, the original permeability of the coal reservoir is low, and the fracturing effect is poor, the slow increase in the venting rate (3) lasts for 3 to 4 days. When the fracturing scale is small, the original permeability of the coal reservoir is high, and the fracturing effect is good, the slow increase in the venting rate (3) lasts for 2 to 3 days. During the slow increase phase (3) of the venting speed, the on-site venting staff frequently adjusted the opening of the needle valve on the fracturing wellhead to slowly increase the venting speed (7) and continuously decrease the fracturing wellhead pressure (8). During the slow increase phase (3) of the venting speed (7), the on-site venting staff collected one sample of the venting produced fluid every 0.5 hours and tested the ORP value (9), turbidity value (10), and pH value (11) of the venting produced fluid within 3 minutes after sampling. The ORP value (9) of the venting produced fluid was higher than -180 mV and the turbidity value (10) of the venting produced fluid was lower than 9.5 NTU.

7. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 6, characterized in that: When the ORP value (9) of the effluent is below -180 mV, or the turbidity value (10) of the effluent is above 9.5 NTU, the effluent velocity (7) needs to be stabilized in time to ensure that the ORP value (9) of the effluent is above the lower limit (12) of the ORP value of the effluent, which is -200 mV, and that the upper limit (13) of the turbidity value of the effluent is below 10 NTU; after the ORP value (9) of the effluent is above -180 mV and the turbidity value (10) of the effluent is below 9.5 NTU, the effluent velocity (7) is slowly increased to the maximum value.

8. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 1, characterized in that: In step d, the rapid decrease in the venting speed (4) lasts from the venting speed (7) slowly increasing to its maximum value until the overflow construction ends. The duration of the rapid decrease in the venting speed (4) is affected by the scale of fracturing, the original permeability of the coal reservoir, and the effect of fracturing.

9. The in-situ coalbed methane well hydraulic fracturing and subsequent blowout process as described in claim 8, characterized in that: The duration of the rapid decrease in the venting rate (4) is affected by the scale of fracturing, the original permeability of the coal reservoir, and the effect of fracturing stimulation. When the fracturing scale is large, the original permeability of the coal reservoir is low, and the fracturing effect is poor, the rapid decline in the venting rate (4) lasts for 2 to 3 days. When the fracturing scale is small, the original permeability of the coal reservoir is high, and the fracturing effect is good, the rapid decrease in the venting rate (4) lasts for 1 to 2 days. During the rapid decrease of the venting speed (4), the on-site venting staff gradually increased the opening of the needle valve on the fracturing wellhead, causing the overflow speed (7) and the fracturing wellhead pressure (8) to continuously decrease to 0. The ORP value (9) and pH value (11) of the venting produced fluid continued to increase, and the turbidity value (10) of the venting produced fluid decreased rapidly. During the rapid decrease of the venting speed (4), the on-site venting staff collected one sample of the venting produced fluid every 0.5 hours, and tested and recorded the ORP value (9), turbidity value (10), and pH value (11) of the collected venting produced fluid within 3 minutes after sampling.

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