A sealing effect detection device and quantitative evaluation method for extraction boreholes

Abstract

The present invention discloses a sealing effect detection device and a quantitative evaluation method for a drainage borehole, which relates to the field of gas extraction detection technology. The quantitative evaluation method increases the pressure in the pipeline to a set value at the initial stage of extraction and then closes it. It determines whether there is air leakage in the hole by monitoring the change value of the air pressure in the hole, monitors the air flow outside the hole by a leak detection fan and a wind speed sensor, and determines whether the leakage type is crack leakage in the borehole or crack leakage outside the borehole. The extraction borehole is divided into zones, and the extraction probe detects the gas volume fraction and flow difference at different positions to accurately identify the location of the leakage. In the middle stage of extraction, by obtaining the leakage ratio of the extraction borehole during the extraction cycle, that is, taking the ratio of the average growth rate of the leakage volume in the extraction borehole to the gas extraction scalar attenuation fitting curve as an evaluation index, the borehole with leakage and repair value is identified, and the comprehensive quantitative evaluation of the repair value of the extraction borehole is achieved under the time effect, thereby establishing a complete new method system for accurate evaluation of the sealing effect.

Description

Technical Field

[0001] The present invention relates to the technical field of gas extraction detection, and in particular to a sealing effect detection device and a quantitative evaluation method for a gas extraction borehole. Background Art

[0002] Gas disasters are one of the most difficult problems in coal mine safety production, and their prevention and control have always been the focus of mine safety research. With the increase in the depth of deep coal mining, the importance of gas extraction technology and its safety management has become increasingly prominent. In the technology of gas accident prevention and control, coal seam gas extraction is one of the main technical measures, and has been widely used in mines at home and abroad. Gas extraction is mainly completed by drilling and sealing holes. Sealing holes is an important part of gas extraction. One of the main criteria for measuring the effect of gas extraction is the sealing effect of the borehole. However, due to geological conditions and coal quality, the sealing quality of the extraction borehole is sometimes not ideal, and the extraction borehole leaks, which affects the effect of coal seam gas extraction, and may affect the normal safety production of coal mines.

[0003] At present, traditional gas sealing effect evaluation methods mostly rely on qualitative or quantitative evaluation at a certain moment in the drilling and extraction process, and lack comprehensive quantitative evaluation methods for drilling and extraction under the time effect.

[0004] For example, the Chinese invention patent No. 201510440987.3 proposes a gas extraction borehole sealing detection device, including a cylindrical cavity, one end of the cylindrical cavity is open, a central hole is opened in the middle of the other end, a circle of air inlets is opened around the central hole, the extraction pipe passes through the central hole and is inserted into the borehole on the coal wall, and the hole is sealed with a sealing material, a circle of air bags are installed at the central hole, and after inflation, the airbags are tightly combined with the extraction pipe; the open end of the cylindrical cavity is fixed on the coal wall and welded with a circle of air bag grooves, and the air bags are placed in the air bag grooves, and the air bags are tightly combined with the coal wall after inflation; a circle of slide rails is arranged along the circumference of the cylindrical cavity, one end of the telescopic rod is mounted on the slide rail through a sliding device, and the other end is provided with a wind speed and wind direction sensor; the air bag is connected to the air bag pump. The programmable controller is connected with the wind speed and wind direction sensor, the telescopic rod and the sliding device through a connecting line, so that the sealing detection of different boreholes can be realized. However, the detection device can only detect the location and amount of air leakage in the borehole at a certain moment during the drilling and extraction process, and cannot achieve a comprehensive quantitative evaluation under the time effect. At the same time, after determining the location and amount of air leakage in the borehole, it is also impossible to further quantitatively evaluate the value of the borehole repair. Therefore, the scientificity and effectiveness of the gas accident prevention and control strategy are greatly limited. Summary of the invention

[0005] In order to solve the technical problems mentioned in the background technology, the present invention provides a sealing effect detection device for a drainage borehole, comprising:

[0006] a drainage main extending into a drainage borehole into the coal seam;

[0007] The extraction borehole is provided with a sealing grouting unit near the hole mouth;

[0008] The first end of the extraction main pipe passing through the sealing grouting unit and extending into the extraction borehole is in a blocked state;

[0009] A plurality of sieve holes are evenly arranged at the first end of the extraction main pipe;

[0010] A gas inlet for inputting high-pressure gas is provided on the second end of the extraction main pipe located outside the extraction borehole;

[0011] A first control valve is arranged at the air inlet;

[0012] The second end of the extraction main pipe is connected to the first flow guide pipe through a first tee on a section of the pipeline close to the extraction borehole;

[0013] The first flow guide pipe is connected to a second control valve;

[0014] A section of the pipeline near the air inlet at the second end of the extraction main pipe is connected to the second flow guide pipe through a second tee;

[0015] The second flow guide pipe is connected to a third control valve;

[0016] The first flow guide pipe and the second flow guide pipe are both connected to the extraction main pipe;

[0017] A extraction probe tube is installed inside the extraction main pipe;

[0018] One end of the extraction probe tube located in the extraction borehole extends to the sieve hole area, and a plurality of sampling holes are arranged at the end;

[0019] One end of the extraction probe pipe located outside the extraction borehole crosses the first flow guide pipe opening and extends to the second flow guide pipe opening;

[0020] A pressure gauge and a flow meter are provided at the outlet of the second flow guide pipe on the extraction main pipe;

[0021] The extraction main pipe is located between the first flow guide pipe and the second flow guide pipe and is provided with a detachable plug for plugging the extraction main pipe;

[0022] The second flow guide pipe is provided with an air extraction port;

[0023] The air extraction port is connected to an air extraction cylinder;

[0024] The vacuum cylinder is connected to the gas sample bag via a hose;

[0025] The gas sample bag is externally connected to a light interference type gas detector.

[0026] Furthermore, a leakage detection fan is arranged at the second end of the extraction main pipe near one side of the extraction borehole; and a wind speed sensor is connected to the leakage detection fan.

[0027] Based on the above-mentioned sealing effect detection device for the extraction borehole, the present invention also provides a quantitative evaluation method for the sealing effect of the extraction borehole, comprising the following steps:

[0028] S100: Divide the detection period into two stages: the initial stage of extraction and the middle stage of extraction;

[0029] S200: At the initial stage of extraction, perform positive pressure air tightness test on the extraction borehole, remove the plug, open the first control valve, close the second control valve and the third control valve, introduce a certain amount of high-pressure gas into the extraction main pipe through the air inlet until the pressure in the extraction main pipe reaches the set value, and close the first control valve;

[0030] S300: After the air pressure in the extraction main pipe is stable, judging whether the extraction borehole is leaking by the pressure drop value of the pressure gauge;

[0031] If there is no air leakage, it will enter the middle stage of extraction;

[0032] If there is air leakage, determine the type of borehole fracture, obtain sample gas at different detection points in the extraction borehole through the extraction probe, compare the gas volume fraction difference and flow difference at different detection points, identify the main location of the air leakage, and drill the main location of the air leakage for repair. After the repair, repeat the above steps to ensure that there is no air leakage, and then enter the middle stage of extraction;

[0033] S400: In the middle of extraction, the extraction negative pressure is kept constant, and sample gas at different detection points in the extraction borehole is obtained through the extraction probe, and the gas volume fraction difference and flow rate difference at different detection points are compared to determine whether there is air leakage and identify the main location of the air leakage;

[0034] S500: After confirming the existence of air leakage and identifying the main location of the air leakage, continuously track and measure the total amount of borehole leakage and the total pure amount of gas during the detection period, and determine the development of the extraction borehole cracks by calculating the borehole leakage ratio to determine whether the extraction borehole needs to be repaired.

[0035] Furthermore, in step S100, the detection period is divided into two stages: the initial stage of extraction and the middle stage of extraction, including:

[0036] S101: The 1-3 days before sampling in the overall detection cycle are defined as the initial sampling period, and the subsequent period is defined as the middle sampling period.

[0037] Furthermore, judging whether the extraction borehole is leaking air by the pressure drop value of the pressure gauge in step S300 includes:

[0038] S301: If the pressure value drops by more than 1 / 3 of the original pressure value, the pressure value drops too much, indicating that there is obvious air leakage in the borehole.

[0039] Furthermore, determining the type of drilling fracture in step S300 includes:

[0040] S302: Monitor the air flow rate through the leak detection fan and the wind speed sensor to determine whether the air leakage type is crack leakage inside the borehole or crack leakage outside the borehole.

[0041] Furthermore, in step S300, the sample gas at different detection points in the extraction borehole is obtained through the extraction probe, and the gas volume fraction difference and flow difference at different detection points are compared to identify the main location of the air leakage, including:

[0042] S303: Evenly divide the extraction borehole into n detection areas and arrange n+1 detection points;

[0043] S304: Install the plug and open the second control valve, extend the extraction probe into the extraction main pipe, and place it at different detection points for repeated detection. The gas collected at each detection point per unit time enters the second flow guide pipe through the extraction probe, and the gas flow rate of each detection point is obtained through the flow meter. Then, the unit volume of gas is filled into the optical interference gas detector through the extraction bag to detect the gas volume fraction.

[0044] S305: Identify the detection area where the air leakage is located by comparing the gas volume fraction difference and flow rate difference at different detection points.

[0045] Furthermore, in step S500, after determining that there is air leakage and identifying the main location of the air leakage, the total amount of borehole air leakage and the total pure amount of gas per unit time in the detection cycle are continuously tracked and measured, and the development of the extraction borehole fissure is determined by calculating the borehole air leakage ratio, and whether the extraction borehole needs to be repaired is determined, including the following steps:

[0046] S501: Obtain the total pure amount of gas extracted from the borehole per unit time during the detection cycle, including:

[0047] S5011: Install the plug and open the second control valve, extend the extraction probe into the extraction main pipe, and place it at different detection points for repeated detection. The gas collected at each detection point per unit time enters the second guide pipe through the extraction probe;

[0048] S5012: Fill a unit volume of gas into the optical interference gas detector through the vacuum bag to detect the gas volume fraction, calculate the gas volume at each detection point and summarize it to obtain the gas volume Q per unit time of the extraction borehole. e ;

[0049] S502: Obtaining the total amount of air leakage in the extraction borehole per unit time during the detection cycle, including:

[0050] S5021: Calculate the air leakage per unit time at each detection point using the following formula:

[0051]

[0052] S5022: Calculate the total amount of air leakage in the extraction borehole:

[0053]

[0054] Where: q (i-1)-i The air leakage of each measuring unit of the drilling hole, in m 3 / min;

[0055] C1~C n is the volume fraction of gas extracted from each measuring unit in the borehole, in %;

[0056] Q e The pure amount of gas extracted from the borehole, in m 3 / min;

[0057] S503: Calculate the air leakage ratio of the extraction borehole, including:

[0058] S5031: Perform linear fitting on the gas scalar change value within the detection period to obtain a gas scalar attenuation function, and obtain an average attenuation rate of the gas scalar attenuation fitting curve; wherein the gas scalar attenuation function is:

[0059] f(t)=Q en =Q e ×e -βt ;

[0060] S5032: Linearly fit the change value of the borehole air leakage in the detection period to obtain a linear function of the borehole air leakage rate, and calculate the change rate of the gas leakage rate; wherein the linear function of the borehole air leakage rate is:

[0061] y = at + b;

[0062] S5033: Obtain the absolute value ratio of the gas leakage volume change rate to the average gas pure volume attenuation rate as the evaluation basis for drilling repair. The specific ratio is as follows:

[0063]

[0064] Where: q Leakage ratio; t—extraction time, days; a—borehole leakage coefficient; β—borehole gas attenuation coefficient;

[0065] Furthermore, the absolute value ratio of the gas leakage rate change to the average attenuation rate of the pure gas is obtained as the evaluation basis for drilling repair, including: if δ q The air leakage ratio is less than 1, which means that even if the drainage borehole is repaired, it is difficult to significantly improve the drilling capacity; if δ q When the air leakage ratio is greater than or equal to 1, it means that the development of borehole cracks has seriously affected the borehole extraction efficiency, and timely repair can improve the borehole extraction efficiency.

[0066] Compared with the prior art, the sealing effect detection device for extraction boreholes designed in the present invention can realize the sealing detection of different boreholes, determine the type and location of air leakage, and then calculate the effective method to test the sealing effect, thereby providing a basis for further improving the gas extraction effect and extraction efficiency, and is practical, safe, accurate and efficient.

[0067] The quantitative evaluation method for sealing effect of the extraction borehole designed by the present invention divides the extraction cycle into the initial extraction period and the middle extraction period. In the initial extraction period, the pressure in the pipeline is increased to a set value and then sealed. By monitoring the change value of the air pressure in the hole, it is judged whether there is air leakage in the hole. The air flow outside the hole is monitored by a leak detection fan and a wind speed sensor to judge whether the leakage type is crack leakage in the hole or crack leakage outside the hole. By dividing the extraction borehole into zones and using the extraction probe to detect the gas volume fraction and flow difference at different positions, the main position of the air leakage can be accurately identified. It provides an accurate basis for the repair of the borehole in the initial extraction period. In the middle extraction period, by obtaining the air leakage ratio of the extraction borehole in the extraction period, that is, the ratio of the average growth rate of the air leakage in the extraction borehole to the gas extraction scalar attenuation fitting curve is used as an evaluation index, the borehole with air leakage and repair value is identified, and the repair value of the extraction borehole is comprehensively and quantitatively evaluated under the time effect, thereby establishing a complete new method system for accurate evaluation of the sealing effect and achieving accurate evaluation of the sealing effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 It is a schematic diagram of the overall structure of the sealing effect detection device of the extraction borehole of the present invention;

[0069] Figure 2 It is a schematic diagram of the physical model of the borehole fracture channel;

[0070] Figure 3 A schematic diagram of the arrangement of the extraction drilling points in an embodiment of the present invention;

[0071] Figure 4 is a borehole leakage ratio test diagram in an embodiment of the present invention, wherein Figure 4(a) is a borehole leakage ratio test diagram No. 1, Figure 4(b) is a borehole leakage ratio test diagram No. 2, 4(c) is a borehole leakage ratio test diagram No. 3, and 4(d) is a borehole leakage ratio test diagram No. 4.

[0072] in:

[0073] 1-extraction drilling hole, 2-extraction main pipe, 3-sealing grouting unit, 4-sieve hole, 5-air inlet, 6-first control valve, 7-first three-way, 8-first guide pipe, 9-second control valve, 10-second three-way, 11-second guide pipe, 12-third control valve, 13-extraction main pipe, 14-extraction probe, 15-sampling hole, 16-pressure gauge, 17-flow meter, 18-detachable plug, 19-extraction port, 20-extraction cylinder, 21-gas sample bag, 22-optical interference gas detector, 23-leak detection fan, 24-wind speed sensor. DETAILED DESCRIPTION

[0074] In order to facilitate those skilled in the art to understand the technical solution of the present invention, further description will be given below with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention.

[0075] In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may be implemented without these specific details. In addition, in the following description, descriptions of known structures and techniques are omitted to avoid unnecessary confusion of concepts of the present invention.

[0076] It should be known that the sealing effect refers to the ability of the sealing section of the borehole to effectively resist the tendency of external air to flow into the borehole from the inside of the borehole, the cracks in the surrounding rock, etc., to ensure the sealing and stability of the target coal seam to be extracted. The sealing effect is closely related to factors such as geological structure, sealing technology, and sealing materials. When the loose circle is depressurized, cracks are connected, and the sealing material is damaged, the borehole is prone to air leakage to varying degrees during the extraction process, resulting in a loose seal of the borehole, which in turn affects the gas extraction effect. Figure 2 As shown in the figure, there are two main forms of borehole air leakage, namely, the air leakage channel in the borehole and the channel through the surrounding rock cracks. The air leakage channel in the borehole exists in the area between the extraction main pipe and the borehole wall, including leakage of the seal body itself and leakage of the gap between the seal body and the borehole wall. During the sealing process, if the sealing material ratio is not good or the grouting pressure is insufficient, it may cause the outside to pass through the air leakage channel in the borehole and enter the extraction pipeline. The surrounding rock through cracks exist in the coal seam fissure body outside the borehole wall, which means that during the drilling process of the extraction borehole, the redistribution of the borehole stress will inevitably lead to the existence of more cracks around the borehole wall. During the drilling and extraction process, the surrounding rock cracks around the borehole will gradually develop. When the developed cracks are interconnected, they provide channels for air intake.

[0077] The present invention first designs a sealing effect detection device for a drainage borehole, including a drainage main pipe 2 extending into a drainage borehole 1 of a coal seam, the drainage borehole 1 having a sealing grouting unit 3 near the hole mouth, the drainage main pipe 2 passes through the sealing grouting unit 3 and extends to the first end of the drainage borehole 1 in a blocked state, and a plurality of sieve holes 4 are evenly arranged at the first end of the drainage main pipe 2 for collecting the mixed gas in the drainage borehole 1. An air inlet 5 for inputting high-pressure gas is provided on the second end of the extraction main pipe 2 located outside the extraction borehole 1. A first control valve 6 for controlling the opening and closing of the air inlet is provided at the air inlet 5. The second end of the extraction main pipe 2 is connected to a first guide pipe 8 through a first tee 7 on a section of the pipeline close to the extraction borehole 1. The first guide pipe 8 is connected to a second control valve 9. The second end of the extraction main pipe 2 is connected to a second guide pipe 11 through a second tee 10 on a section of the pipeline close to the air inlet 5. The second guide pipe 11 is connected to a third control valve 12. Both the first guide pipe 8 and the second guide pipe 11 are connected to the extraction main pipe 13. In this embodiment, an extraction probe tube 14 is inserted into the extraction main pipe 2. One end of the extraction probe tube 14 located in the extraction borehole 1 extends to the sieve hole 4 area, and a plurality of sampling holes 15 are arranged at the end thereof. One end of the extraction probe tube 14 located outside the extraction borehole 1 crosses the pipe opening of the first guide pipe 8 and extends to the pipe opening of the second guide pipe 11. A pressure gauge 16 and a flow meter 17 are arranged at the pipe opening of the second guide pipe 11 of the extraction main pipe 2. A detachable plug 18 for blocking the extraction main pipe 2 is arranged on the pipeline between the first guide pipe 8 and the second guide pipe 11 of the extraction main pipe 2. An exhaust port 19 is arranged on the second guide pipe 11. An exhaust cylinder 20 is connected to the exhaust port 19. The exhaust cylinder 20 is connected to a gas sample bag 21 through a hose. The gas sample bag 21 is externally connected to an optical interference gas detector 22.

[0078] In addition, the present invention provides a leakage detection fan 23 at the second end of the extraction main pipe 2 close to the extraction borehole 1 , and the leakage detection fan 23 is connected to a wind speed sensor 24 .

[0079] The sealing effect detection device for extraction boreholes designed in the present invention can realize the sealing detection of different boreholes, determine the leakage type and leakage position, and then calculate the sealing effect that can be effectively tested, providing a basis for further improving the gas extraction effect and extraction efficiency, and is practical, safe, accurate and efficient.

[0080] Based on the above-mentioned sealing effect detection device for the extraction borehole, the present invention proposes a quantitative evaluation method for the sealing effect of the extraction borehole, comprising the following steps:

[0081] S100: Divide the detection period into two stages: the initial stage of extraction and the middle stage of extraction;

[0082] During specific implementation, the first 1-3 days of the drilling extraction process can be defined as the initial extraction stage, and the subsequent period as the middle extraction stage based on gas extraction parameters and experience.

[0083] S200: At the initial stage of extraction, perform positive pressure air tightness test on the extraction borehole, remove the plug, open the first control valve 6, close the second control valve 9 and the third control valve 12, introduce a certain amount of high-pressure gas into the extraction main pipe 2 through the air inlet 5 until the pressure in the extraction main pipe 2 reaches the set pressure value, and close the first control valve 6;

[0084] S300: After the air pressure in the extraction main pipe 2 is stabilized, judging whether the extraction borehole 1 is leaking by the pressure drop value of the pressure gauge 16;

[0085] In specific implementation, if the pressure value drops by more than 1 / 3 of the original pressure value, the pressure value drops too much, indicating that there is obvious air leakage in the extraction borehole 1. Taking the pressurized gas as 0.15Mpa as an example, if the pressure drop does not exceed 0.05Mpa, the extraction capacity of the extraction borehole 1 will decrease, but it can still maintain a good extraction capacity. When the pressure drop exceeds 0.05Mpa, the extraction capacity of the extraction borehole 1 will drop rapidly. Therefore, for the initial detection of the extraction borehole, the pressure drop exceeds 0.05Mpa and needs to be repaired immediately.

[0086] If there is no air leakage, enter the middle stage of extraction directly.

[0087] If there is air leakage, determine the type of drilling cracks.

[0088] In specific implementation, the air flow is monitored by the leak detection fan 23 and the wind speed sensor 24 to determine whether the air leakage type is crack leakage inside the borehole or crack leakage outside the borehole. Since the leak detection fan 23 is set close to the wall of the extraction borehole, if the wind speed sensor reading is high, it indicates that a large amount of air is gushing out from the inside of the borehole to the borehole mouth, and the cracks in the hole are the main leakage channel. Otherwise, it means that there are other crack channels in the borehole.

[0089] After determining the type of borehole fracture, determine the main air leakage location in the borehole, obtain sample gas at different detection points in the extraction borehole through the extraction probe, compare the gas volume fraction difference and flow rate difference at different detection points, and identify the main air leakage location.

[0090] The specific implementation includes the following steps:

[0091] S303: Evenly divide the extraction borehole 1 into n detection areas and arrange n+1 detection points;

[0092] During the specific implementation, considering the multiple factors that cause air leakage, such as casing joints and the depth of the loose circle in the tunnel, the common air leakage locations should be allocated to independent measurement units when arranging the measuring points to ensure that the data accurately reflects the situation of a single air leakage point and determines the specific location of the air leakage. The measuring point arrangement is shown in Figure 4.

[0093] S304: Install the removable plug 18 and open the second control valve 9, extend the extraction probe 14 into the extraction main pipe 2, and place it in different detection points for repeated detection in turn. The gas collected per unit time at each detection point enters the second flow guide pipe 11 through the extraction probe 14, and the gas flow rate of each detection point is obtained through the flow meter 17. Then, the unit volume of gas is filled into the optical interference gas detector 22 through the gas sample bag 21 to detect the gas volume fraction;

[0094] S305: Identify the detection area where the air leakage is located by comparing the gas volume fraction difference and flow rate difference at different detection points. If there is a significant change in the gas volume fraction difference and flow rate difference at a certain detection point, it indicates that there is obvious air leakage in the detection area where the detection point is located, that is, drill holes to repair the main location of the air leakage, repeat the above steps after repair to ensure that there is no air leakage, and then enter the mid-term extraction. In specific implementation, for boreholes with obvious air leakage, the in-situ borehole method can be used for repair. After the repair, the extraction time of the borehole is re-measured until the borehole inspection is qualified at the initial stage of extraction, and then enter the mid-term extraction.

[0095] S400: In the middle of extraction, the extraction negative pressure is kept constant, and the sample gas at different detection points in the extraction borehole is obtained through the extraction probe 14, and the gas volume fraction difference and flow rate difference at different detection points are compared to determine whether there is air leakage and identify the main location of the air leakage;

[0096] S500: After confirming the existence of air leakage and identifying the main location of the air leakage, continuously track and measure the total amount of borehole leakage and the total pure amount of gas during the detection period, and determine the development of the extraction borehole cracks by calculating the borehole leakage ratio to determine whether the extraction borehole needs to be repaired.

[0097] The specific implementation includes the following steps:

[0098] S501: Obtain the total pure amount of gas extracted from the borehole per unit time during the detection cycle, including:

[0099] S5011: Install the removable plug 18 and open the second control valve 9, extend the extraction probe 14 into the extraction main pipe 2, and place it in different detection points for repeated detection. The gas collected per unit time at each detection point enters the second guide pipe through the extraction probe;

[0100] S5012: Fill a unit volume of gas into the optical interference gas detector through the gas sample bag 21 to detect the gas volume fraction, calculate the gas volume at each detection point and summarize it to obtain the gas volume Q per unit time of the extraction borehole. e ;

[0101] S502: Obtain the total amount of air leakage in the borehole extracted per unit time during the detection cycle. It should be known that when there is an air leakage point in the borehole, the parameters of the front and rear measuring points in the measurement unit where the air leakage point is located will change. The gas concentration at the measuring point near the orifice position of the air leakage point is small and the flow rate is high. However, the pure amount of gas in different detection areas inside the borehole can be regarded as equal everywhere in a short time. Based on the above principle, the calculation formula for the air leakage of the borehole is obtained, and the specific implementation is as follows:

[0102] S5021: Calculate the air leakage per unit time at each detection point using the following formula:

[0103]

[0104] S5022: Calculate the total amount of air leakage in the extraction borehole:

[0105]

[0106] Where: q (i-1)-i The air leakage of each measuring unit of the drilling hole, in m 3 / min;

[0107] C1~C n is the volume fraction of gas extracted from each measuring unit in the borehole, in %;

[0108] Q e The pure amount of gas extracted from the borehole, in m 3 / min;

[0109] S503: Calculate the air leakage ratio of the extraction borehole. During the extraction process of the borehole, under the condition of constant extraction negative pressure, the air leakage of the borehole increases steadily, approximately linearly. The pure gas quantity fluctuates. The pure gas quantity attenuation fitting curve is used to calculate and analyze the average attenuation rate of the pure gas quantity fitting curve during the monitoring period. The absolute value ratio of the gas leakage volume change rate to the average attenuation rate of the pure gas quantity is used as the evaluation basis for borehole repair. Including:

[0110] S5031: Perform linear fitting on the gas scalar change value within the detection period to obtain a gas scalar attenuation function, and obtain an average attenuation rate of the gas scalar attenuation fitting curve; wherein the gas scalar attenuation function is:

[0111] f(t)=Q en =Q e ×e -βt ;

[0112] S5032: Linearly fit the change value of the borehole air leakage in the detection period to obtain a linear function of the borehole air leakage rate, and calculate the change rate of the gas leakage rate; wherein the linear function of the borehole air leakage rate is:

[0113] y = at + b;

[0114] S5033: Obtain the absolute value ratio of the gas leakage volume change rate to the average gas pure volume attenuation rate as the evaluation basis for drilling repair. The specific ratio is as follows:

[0115]

[0116] Where: q Leakage ratio; t—extraction time, days; a—borehole leakage coefficient; β—borehole gas attenuation coefficient.

[0117] In specific implementation, if δ q The air leakage ratio is less than 1, which means that even if the drainage borehole is repaired, it is difficult to significantly improve the drilling capacity; if δ q When the air leakage ratio is greater than or equal to 1, it means that the development of borehole cracks has seriously affected the borehole extraction efficiency, and timely repair can improve the borehole extraction efficiency.

[0118] Table 1 is a classification table of borehole sealing effects. When the pressure of the drilling rig air pipe is 0.15Mpa, the sealing effect detection device of the above-mentioned extraction borehole is used to detect leaks, and different treatment measures are taken respectively.

[0119] Table 1 Drilling and sealing effect classification

[0120]

[0121] In the following, taking a coal seam working face as an example, a qualitative and quantitative evaluation of the borehole sealing quality is carried out based on the on-site drilling tracking detection data, the borehole leakage point is determined, and the in-situ along-the-hole method is used for repair. After the borehole repair, the extraction parameters are tracked and measured, and the borehole repair efficiency is compared, verified and analyzed.

[0122] 1) Drilling and measuring point arrangement

[0123] The borehole diameter is 94mm, with 9 holes in each group every 5m, and the length of the hole is 15m. After the drilling construction is completed, the "two blocking and two injection" sealing method is used to seal the hole. The sealing bag is at the junction of coal and rock in the lower part of the coal seam. After the drilling and sealing, network extraction is carried out.

[0124] like Figure 3 As shown, according to the arrangement principle of borehole measuring points and the actual sealing situation of the borehole, six measuring points are arranged in the test borehole, namely, measuring point 1-inner end of the borehole flexible zone, measuring point 2-outer end of the borehole flexible zone, measuring point 3-inner end of the sealing grouting section, and measuring point 4-outer end of the sealing grouting section.

[0125] 2) Evaluation of drilling and sealing effect

[0126] The four extraction boreholes in the coal seam were tracked and monitored: in the early stage of extraction, the extraction boreholes were tested for air tightness under positive pressure, and the failed boreholes were repaired in situ; in the stable extraction stage, the borehole air leakage volume and gas purity were continuously tracked and measured within 45 days, the borehole air leakage ratio was calculated, and finally the quality grade of the borehole sealing effect was determined. The test results are shown in Table 2.

[0127] Table 2 Drilling extraction quality classification

[0128]

[0129] As shown in Table 2, the initial air leakage of boreholes 1-3 was qualified, and the initial air leakage of borehole 4 was unqualified. The speed of the leakage detection fan was 569rpm, and it was determined to be an internal leakage. After repair by plugging the orifice and continued observation, the average air leakage dropped sharply from 8.12L / min to 0.48L / min.

[0130] The growth rate of air leakage at different measuring points of the borehole was tested by using a fixed-point leak detection device. As shown in Figure 4(a), the gas pure amount decrease rate of borehole No. 1 is faster, and the growth rate of air leakage is slower, indicating that borehole No. 1 has always maintained efficient extraction, and the air leakage ratio is only 0.063, which is a high-quality borehole.

[0131] As shown in Figure 4(b), the gas pure quantity of borehole No. 2 decreases slowly and the pure quantity is generally low, and the growth rate of air leakage is not high, indicating that the low pure quantity of gas in this borehole is not related to air leakage, and even if it is repaired, it cannot effectively improve the extraction efficiency of the borehole;

[0132] As shown in Figure 4(c), the gas volume of borehole No. 3 decreases slowly, but the air leakage increases rapidly, with a leakage ratio as high as 2.199, indicating that the borehole has repair value, and the gas extraction efficiency of the borehole is greatly improved after repair.

[0133] As shown in Figure 4(d), borehole 4 had obvious gas leakage at the beginning of extraction. After the borehole was repaired and the pressure difference inside and outside the borehole was tested again, the trend of the change of gas extraction quantity and leakage rate was similar to that of borehole 1 at the same extraction time. The leakage rate was relatively small, only 0.139. The initial repair effect was obvious, and the repaired borehole always maintained an efficient extraction effect.

[0134] In summary, the quantitative evaluation method for the sealing effect of the extraction borehole designed by the present invention divides the extraction cycle into the initial extraction period and the middle extraction period. In the initial extraction period, the pressure in the pipeline is increased to the set value and then closed. By monitoring the change value of the air pressure in the hole, it is judged whether there is air leakage in the hole. The air flow outside the hole is monitored by the leak detection fan and the wind speed sensor to judge whether the leakage type is crack leakage in the borehole or crack leakage outside the borehole. By dividing the extraction borehole into zones and using the extraction probe to detect the gas volume fraction and flow difference at different positions, the main position of the air leakage can be accurately identified. Provide an accurate basis for the repair of the borehole in the initial extraction period. In the middle extraction period, by obtaining the air leakage ratio of the extraction borehole in the extraction period, that is, the ratio of the average growth rate of the air leakage in the extraction borehole to the gas extraction scalar attenuation fitting curve is used as an evaluation index, the borehole with air leakage and repair value is identified, and the comprehensive quantitative evaluation of the repair value of the extraction borehole is achieved under the time effect, thereby establishing a complete new method system for accurate evaluation of the sealing effect, and achieving accurate evaluation of the sealing effect.

[0135] The above embodiments are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for quantitatively evaluating the sealing effect of a drainage borehole, using a sealing effect detection device for a drainage borehole, the sealing effect detection device for a drainage borehole comprising: a drainage main extending into a drainage borehole into the coal seam; The extraction borehole is provided with a sealing grouting unit near the hole mouth; The first end of the extraction main pipe passing through the sealing grouting unit and extending into the extraction borehole is in a blocked state; A plurality of sieve holes are evenly arranged at the first end of the extraction main pipe; A gas inlet for inputting high-pressure gas is provided on the second end of the extraction main pipe located outside the extraction borehole; A first control valve is arranged at the air inlet; The second end of the extraction main pipe is connected to the first flow guide pipe through a first tee on a section of the pipeline close to the extraction borehole; The first flow guide pipe is connected to a second control valve; A section of the pipeline near the air inlet at the second end of the extraction main pipe is connected to the second flow guide pipe through a second tee; The second flow guide pipe is connected to a third control valve; The first flow guide pipe and the second flow guide pipe are both connected to the extraction main pipe; A extraction probe tube is installed inside the extraction main pipe; One end of the extraction probe tube located in the extraction borehole extends to the sieve hole area, and a plurality of sampling holes are arranged at the end; One end of the extraction probe pipe located outside the extraction borehole crosses the first flow guide pipe opening and extends to the second flow guide pipe opening; A pressure gauge and a flow meter are provided at the outlet of the second flow guide pipe on the extraction main pipe; The extraction main pipe is located between the first flow guide pipe and the second flow guide pipe and is provided with a detachable plug for plugging the extraction main pipe; The second flow guide pipe is provided with an air extraction port; The air extraction port is connected to an air extraction cylinder; The vacuum cylinder is connected to the gas sample bag via a hose; The gas sample bag is externally connected to a light interference type gas detector, which is characterized by comprising the following steps: S100: Divide the detection period into two stages: the initial stage of extraction and the middle stage of extraction; S200: At the initial stage of extraction, perform positive pressure air tightness test on the extraction borehole, remove the plug, open the first control valve, close the second control valve and the third control valve, introduce a certain amount of high-pressure gas into the extraction main pipe through the air inlet until the pressure in the extraction main pipe reaches the set value, and close the first control valve; S300: After the air pressure in the extraction main pipe is stable, judging whether the extraction borehole is leaking by the pressure drop value of the pressure gauge; If there is no air leakage, it will enter the middle stage of extraction; If there is air leakage, determine the type of borehole fracture, obtain sample gas at different detection points in the extraction borehole through the extraction probe, compare the gas volume fraction difference and flow difference at different detection points, identify the main location of the air leakage, and drill the main location of the air leakage for repair. After the repair, repeat the above steps to ensure that there is no air leakage, and then enter the middle stage of extraction; S400: In the middle of extraction, the extraction negative pressure is kept constant, and sample gas at different detection points in the extraction borehole is obtained through the extraction probe, and the gas volume fraction difference and flow rate difference at different detection points are compared to determine whether there is air leakage and identify the main location of the air leakage; S500: After determining that there is air leakage and identifying the main location of the air leakage, continuously track and measure the total amount of air leakage and the total pure amount of gas in the borehole during the detection period, calculate the borehole air leakage ratio, determine the development of the extraction borehole fissure, classify the borehole sealing effect level, and determine whether the extraction borehole needs to be repaired; In the step S500, after determining that there is air leakage and identifying the main location of the air leakage, the total amount of borehole air leakage and the total pure amount of gas per unit time in the detection cycle are continuously tracked and measured, and the development of the extraction borehole fissure is determined by calculating the borehole air leakage ratio, and whether the extraction borehole needs to be repaired, including the following steps: S501: Obtain the total pure amount of gas extracted from the borehole per unit time during the detection cycle, including: S5011: Install the plug and open the second control valve, extend the extraction probe into the extraction main pipe, and place it at different detection points for repeated detection. The gas collected at each detection point per unit time enters the second guide pipe through the extraction probe; S5012: Fill a unit volume of gas into the optical interference gas detector through the vacuum bag to detect the gas volume fraction, calculate the gas volume at each detection point and summarize it to obtain the gas volume Q per unit time of the extraction borehole. e ; S502: Obtaining the total amount of air leakage in the extraction borehole per unit time during the detection cycle, including: S5021: Calculate the air leakage per unit time at each detection point using the following formula: S5022: Calculate the total amount of air leakage in the extraction borehole: Where: q (i-1)-i The air leakage of each measuring unit of the drilling hole, in m 3 / min; C1~C n is the volume fraction of gas extracted from each measuring unit in the borehole, in %; Q e The pure amount of gas extracted from the borehole, in m 3 / min; S503: Calculate the air leakage ratio of the extraction borehole, including: S5031: Perform linear fitting on the gas scalar change value within the detection period to obtain a gas scalar attenuation function, and obtain an average attenuation rate of the gas scalar attenuation fitting curve; wherein the gas scalar attenuation function is: f(t)=Q en =Q e ×e -αt ; S5032: Linearly fit the change value of the borehole air leakage in the detection period to obtain a linear function of the borehole air leakage rate, and calculate the change rate of the gas leakage rate; wherein the linear function of the borehole air leakage rate is: y = at + b; S5033: Obtain the absolute value ratio of the gas leakage volume change rate to the average gas pure volume attenuation rate as the evaluation basis for drilling repair. The specific ratio is as follows: Where: q Leakage ratio; t—extraction time, days; a—borehole leakage coefficient; β—borehole gas attenuation coefficient; The absolute value ratio of the gas leakage rate change to the average gas pure amount attenuation rate is obtained as the evaluation basis for drilling repair, including: if δ q The air leakage ratio is less than 1, which means that even if the drainage borehole is repaired, it is difficult to significantly improve the drilling capacity; if δ q When the air leakage ratio is greater than or equal to 1, it means that the development of borehole cracks has seriously affected the borehole extraction efficiency, and timely repair can improve the borehole extraction efficiency.

2. The method for quantitatively evaluating the sealing effect of a drainage borehole according to claim 1, characterized in that: A leak detection fan is arranged on one side of the second end of the extraction main pipe close to the extraction borehole; and a wind speed sensor is connected to the leak detection fan.

3. The method for quantitatively evaluating the sealing effect of a drainage borehole according to claim 2, characterized in that: In step S100, the detection period is divided into two stages: the initial extraction stage and the middle extraction stage, including: S101: The 1-3 days before sampling in the overall detection cycle are defined as the initial sampling period, and the subsequent period is defined as the middle sampling period.

4. The method for quantitatively evaluating the sealing effect of a drainage borehole according to claim 3, characterized in that: In step S300, judging whether the extraction borehole is leaking air by the pressure drop value of the pressure gauge includes: S301: If the pressure value drops by more than 1 / 3 of the original pressure value, the pressure value drops too much, indicating that there is obvious air leakage in the borehole.

5. The method for quantitatively evaluating the sealing effect of a drainage borehole according to claim 4, characterized in that: The determination of the drilling fracture type in step S300 includes: S302: Monitor the air flow rate through the leak detection fan and the wind speed sensor to determine whether the air leakage type is crack leakage inside the borehole or crack leakage outside the borehole.

6. The method for quantitatively evaluating the sealing effect of a drainage borehole according to claim 5, characterized in that: In step S300, the sample gas at different detection points in the extraction borehole is obtained through the extraction probe, and the gas volume fraction difference and flow difference at different detection points are compared to identify the main location of the air leakage, including: S303: Evenly divide the extraction borehole into n detection areas and arrange n+1 detection points; S304: Install the plug and open the second control valve, extend the extraction probe into the extraction main pipe, and place it at different detection points for repeated detection. The gas collected at each detection point per unit time enters the second flow guide pipe through the extraction probe, and the gas flow rate of each detection point is obtained through the flow meter. Then, the unit volume of gas is filled into the optical interference gas detector through the extraction bag to detect the gas volume fraction. S305: Identify the detection area where the air leakage is located by comparing the gas volume fraction difference and flow rate difference at different detection points.

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