A method for measuring coal seam gas pressure

Abstract

The present invention discloses a method for measuring gas pressure in a coal seam, which comprises the following steps: drilling a hole at a location where the gas pressure of the coal seam is predetermined to be measured, installing a hollow tube in the hole, and extending one end of the tube away from a pressure measuring chamber out of the hole; a pressure measuring device for measuring the pressure in the hole and a flow measuring device for measuring the flow rate at the hole are provided at one end of the tube located outside the orifice; an adjusting device for adjusting the size of the orifice opening is also provided at the tube, and the size of the orifice opening is adjusted by the adjusting device to obtain three or more groups of different values ​​of the pressure in the hole and the flow rate at the hole, and the original gas pressure value in the coal seam can be accurately obtained by performing a joint solution on the measured data.

Description

Technical Field

[0001] The invention relates to the field of coal mine safety, and in particular to a method for measuring coal seam gas pressure. Background Art

[0002] Coal seam gas pressure is the main driving force of coal and gas outbursts, and is also a parameter indicator of coal seam gas fluidity and gas storage status. The size of coal seam gas pressure has a direct impact on the difficulty of gas extraction. Accurately measuring coal seam gas pressure before coal mining can assess the danger of coal seam outbursts, and then formulate effective control measures to reduce the occurrence of gas outburst accidents. Coal seam gas pressure is closely related to geological conditions such as coal seam burial depth and geological structure. By determining coal seam gas pressure, the geological conditions of the coal seam can be analyzed, providing an important basis for subsequent coal mining plans.

[0003] In the related technology, when the coal seam is not affected by mining and is in the original gas storage state, the equilibrium gas pressure in the coal seam is the original gas pressure of the coal seam. When the coal seam is affected by mining and a part of the gas gushes out, the pressure of the remaining gas in the coal seam is the residual gas pressure of the coal seam. At present, the common method for measuring coal seam gas pressure is the direct pressure measurement method. The direct pressure measurement method is to drill a hole from the rock layer tunnel or coal seam tunnel to the predetermined location for measuring gas pressure, and then lead a pipe and a pressure measuring device from the borehole, and then seal and plug the borehole. The blocked part of the borehole is the pressure measuring chamber, and a pressure gauge or a pressure measuring device is connected to the lead-out pipe to measure the gas pressure in the coal seam.

[0004] Regarding the above-mentioned related technologies, when using the direct pressure measurement method to measure the coal seam gas pressure, most of the time, horizontal drilling is carried out into the coal seam. Since the coal seam itself is relatively soft and has many cracks, the coal seam gas pressure will leak. On the one hand, when the borehole is sealed, the gas in the coal seam gradually flows into the borehole and leaks. On the other hand, a part of the gas will leak through the cracks in the coal seam, resulting in inaccurate measured coal seam gas pressure and deviation from the actual coal seam gas pressure. Summary of the invention

[0005] In order to accurately measure the gas pressure of a coal seam, the present application provides a method for measuring the gas pressure of a coal seam.

[0006] The present application provides a method for measuring coal seam gas pressure, which adopts the following technical solution:

[0007] A method for measuring coal seam gas pressure comprises the following steps:

[0008] S1, drilling a hole at a location where the gas pressure of the coal seam is to be measured, the hole comprising a strip-shaped cavity and a pressure measuring chamber, the pressure measuring chamber being located at one end away from the hole opening, a hollow tube tube matching the inner diameter of the strip-shaped cavity being installed in the hole, and one end of the tube tube away from the pressure measuring chamber extending out of the hole;

[0009] S2, a pressure measuring device for measuring the pressure in the hole and a flow measuring device for measuring the flow rate at the orifice are provided at one end of the trustee located outside the orifice, and an adjusting device for adjusting the size of the orifice opening is also provided at the trustee;

[0010] S3, when the coal seam is not affected by mining and is in the original gas storage state, the original gas pressure in the coal seam is set to P0, and the coal seam gas pressure in the pressure measuring chamber is set to P x , the gas flow from the coal seam to the pressure measuring chamber obeys Darcy's law, its flow rate is set to Q1, the flow permeability coefficient is set to k1, and the wind resistance of the entire coal seam flowing to the pressure measuring chamber is R1; the flow rate leaking from the pressure measuring chamber to the coal seam cracks into the tunnel space is set to Q2, and the wind resistance is set to R2; the gas flow permeability coefficient is set to k2;

[0011] The regulating device controls the orifice flow rate Q3 at a relatively small value. The wind resistance between the pressure measuring chamber and the orifice is set to R4, and the wind resistance at the orifice is set to R3. Then R3>>R4, so the pressure in the pressure measuring chamber is approximately the same as that at the orifice, which is the displayed value of the pressure measuring device. The development of coal seam fissures will not change in a short time, so k1 and k2 will not change in a short time.

[0012] According to the law of conservation of mass, the calculation equation ① can be obtained in the equilibrium state: Q1=Q2+Q3;

[0013] According to Darcy's law: ΔP = kQ,

[0014] Where P x and Q3 will change with the change of R3, while P0, k1 and k2 can be considered stable during the measurement;

[0015] The first state: the orifice is completely blocked. At this time, there is no flow at the orifice, Q 30 =0, at this time the gas pressure in the pressure measuring chamber is the value displayed by the pressure measuring device P x0 According to the above equation ①, the calculation equation ② can be obtained:

[0016] P x0 It is the coal seam gas pressure value in the pressure measuring chamber when the orifice is completely blocked;

[0017] S4, the second state: the cross-sectional opening area at the orifice is adjusted for the first time by the regulating device; the flow rate Q at the orifice is measured 31At this time, the pressure in the pressure measuring chamber is the value displayed by the pressure measuring device P x1 , and then we get the calculation equation ③:

[0018] S5, the third state: the cross-sectional opening area at the orifice is adjusted for the second time by the regulating device, so that the cross-sectional opening area at the orifice is different from that in the second state, and the flow rate Q at the orifice is measured again 32 At this time, the pressure in the pressure measuring chamber is the value displayed by the pressure measuring device P x2 , and then we get the calculation equation ④:

[0019]

[0020] S6, P in the above equations ②, ③, and ④ x0 , P x1 , P x2 , Q 31 , Q 32 is a known measured value, P0, k1 and k2 are unknown quantities, and P0 can be calculated jointly to obtain the accurate original gas pressure of the coal seam.

[0021] Optionally, the drilling hole for measuring coal seam gas pressure is selected in a coal seam or a dense and complete rock area, avoiding aquifers.

[0022] Optionally, the regulating device adopts a ball valve.

[0023] Optionally, the pressure measuring device is a pressure gauge.

[0024] Optionally, the flow measuring device adopts a flow meter.

[0025] In summary, the present application includes at least one of the following beneficial technical effects:

[0026] 1. When the borehole cannot be completely sealed or cannot be sealed, some gas leaks through the cracks in the coal seam. The measurement method of the present invention measures the orifice pressure value when the orifice is completely blocked according to Darcy's law, and the orifice pressure and flow values ​​under two different orifice cross-sectional opening areas when the orifice is not completely blocked. After measuring several sets of data and performing calculations, the original gas pressure value in the coal seam can be accurately obtained;

[0027] 2. When drilling a hole to measure coal seam gas pressure, select an area with dense and complete rock, avoid aquifers, and reduce the impact of liquid on the borehole, which is beneficial to improving the accuracy of coal seam gas pressure measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of an embodiment of the present application.

[0029] Explanation of the reference numerals: 1. coal seam; 2. borehole; 21. orifice; 22. strip cavity; 23. trustee; 3. pressure measuring chamber; 4. pressure measuring device; 5. flow measuring device; 6. regulating device. DETAILED DESCRIPTION

[0030] The present application is further described in detail below in conjunction with all the accompanying drawings.

[0031] The embodiment of the present application discloses a method for measuring coal seam gas pressure.

[0032] Example

[0033] Reference Figure 1 , a method for measuring coal seam gas pressure, comprising the following steps:

[0034] S1, drilling a borehole 2 at a predetermined location for measuring gas pressure in the coal seam 1, selecting a dense and complete rock area for drilling the borehole 2 to measure gas pressure in the coal seam 1, avoiding aquifers, and reducing the impact of liquid on the borehole 2; the borehole 2 includes a strip-shaped cavity 22 and a pressure measuring chamber 3, the pressure measuring chamber 3 is located at one end away from the orifice 21 of the borehole 2, a hollow tube 23 matching the inner diameter of the strip-shaped cavity 22 is installed in the borehole 2, and one end of the tube 23 away from the pressure measuring chamber 3 extends out of the borehole 2;

[0035] S2, the orifice 21 of the borehole 2 is connected to the pressure measuring chamber 3, and the end of the trustee 23 located outside the orifice 21 is provided with a pressure measuring device 4 for measuring the pressure in the hole and a flow measuring device 5 for measuring the flow of the orifice 21. The flow measuring device 5 adopts a flow meter, and the pressure measuring device 4 adopts a pressure gauge; the trustee 23 is also provided with an adjusting device 6 for adjusting the opening size of the orifice 21, and the adjusting device 6 adopts a ball valve;

[0036] S3, when coal seam 1 is not affected by mining and is in the original gas storage state, the original gas pressure in coal seam 1 is set to P0, and the gas pressure of coal seam 1 in pressure measuring chamber 3 is set to P x , the gas flow from coal seam 1 to pressure measuring chamber 3 obeys Darcy's law, its flow rate is set to Q1, the flow permeability coefficient is set to k1, and the wind resistance of the entire coal seam 1 flowing to the pressure measuring chamber 3 is R1; the flow rate leaking from the cracks of coal seam 1 to the tunnel space through the pressure measuring chamber 3 is set to Q2, and the wind resistance is set to R2; the gas flow permeability coefficient is set to k2;

[0037] The regulating device 6 controls the flow rate Q3 of the orifice 21 to a relatively small value. The wind resistance between the pressure measuring chamber 3 and the orifice 21 is set to R4, and the wind resistance at the orifice 21 is set to R3. Then R3>>R4, so the pressure in the pressure measuring chamber 3 is approximately the same as that at the orifice 21, which is the displayed value of the pressure measuring device 4. The development of the cracks in the coal seam 1 will not change in a short time, so k1 and k2 will not change in a short time.

[0038] According to the law of conservation of mass, the calculation equation ① can be obtained in the equilibrium state: Q1=Q2+Q3;

[0039] According to Darcy's law: ΔP = kQ,

[0040] Where P x and Q3 will change with the change of R3, while P0, k1 and k2 can be considered stable during the measurement;

[0041] The first state: the orifice 21 is completely blocked. At this time, there is no flow at the orifice 21, Q 30 =0, at this time the gas pressure in the pressure measuring chamber 3 is the value displayed by the pressure measuring device 4 P x0 According to the above equation ①, the calculation equation ② can be obtained:

[0042] P x0 It is the gas pressure value of coal seam 1 in pressure measuring chamber 3 when orifice 21 is completely blocked;

[0043] S4, second state: the cross-sectional opening area at the orifice 21 is adjusted for the first time by the adjusting device 6; the flow rate Q at the orifice 21 is measured 31 At this time, the pressure in the pressure measuring chamber 3 is the value displayed by the pressure measuring device 4, P x1 , and then we get the calculation equation ③:

[0044] S5, third state: the cross-sectional opening area at the orifice 21 is adjusted for the second time by the adjusting device 6, so that the cross-sectional opening area at the orifice 21 is different from that in the second state, and the flow rate Q at the orifice 21 is measured again 32 At this time, the pressure in the pressure measuring chamber 3 is the value displayed by the pressure measuring device 4, P x2 , and then we get the calculation equation ④:

[0045] S6, P in the above equations ②, ③, and ④ x0 , P x1 , P x2 , Q 31 , Q 32 is a known measured value, P0, k1 and k2 are unknown quantities, and P0 can be calculated jointly to obtain the accurate original gas pressure of coal seam 1.

[0046] The implementation principle of a coal seam gas pressure measurement method in an embodiment of the present application is as follows: when the borehole 2 cannot be completely sealed or cannot be sealed, some gas leaks through the cracks in the coal seam 1. The pressure value of the orifice 21 when the orifice 21 is completely blocked is measured according to Darcy's law, as well as the pressure and flow values ​​of the orifice 21 under two different cross-sectional opening areas of the orifice 21 when the orifice 21 is not completely blocked. By measuring several sets of data and then solving them, the original gas pressure value in the coal seam 1 can be accurately obtained.

[0047] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for measuring coal seam gas pressure, characterized in that: The following steps are involved: S1, drilling a borehole (2) at a predetermined location in a coal seam (1) for measuring gas pressure, the borehole (2) comprising a strip-shaped cavity (22) and a pressure measuring chamber (3), the pressure measuring chamber (3) being located at an end away from the orifice (21) of the borehole (2), a hollow trustee (23) matching the inner diameter of the strip-shaped cavity (22) being installed in the borehole (2), and an end of the trustee (23) away from the pressure measuring chamber (3) extending out of the borehole (2); S2, a pressure measuring device (4) for measuring the pressure in the hole and a flow measuring device (5) for measuring the gas flow rate of the orifice (21) are provided at one end of the trustee (23) located outside the orifice (21), and an adjusting device (6) for adjusting the opening size of the orifice (21) is also provided at the trustee (23); S3, when the coal seam (1) is not affected by mining and is in the original gas storage state, the original gas pressure in the coal seam (1) is set to P0, and the gas pressure of the coal seam (1) in the pressure measuring chamber (3) is set to P x , the gas flow from the coal seam (1) to the pressure measuring chamber (3) obeys Darcy's law, its flow rate is set to Q1, the flow permeability coefficient is set to k1, and the wind resistance of the entire coal seam (1) flowing to the pressure measuring chamber (3) is R1; the flow rate leaking from the cracks of the coal seam (1) through the pressure measuring chamber (3) to the tunnel space is set to Q2, and the wind resistance is set to R2; the gas flow permeability coefficient is set to k2; The regulating device (6) controls the orifice flow rate Q3 at a relatively small value, the wind resistance between the pressure measuring chamber (3) and the orifice (21) is set to R4, and the wind resistance at the orifice (21) is set to R3, then R3>>R4, so the pressure in the pressure measuring chamber (3) is approximately the same as that at the orifice (21), which is the displayed value of the pressure measuring device (4). The development of the cracks in the coal seam (1) will not change in the short term, so k1 and k2 will not change in the short term; According to the law of conservation of mass, in equilibrium, the calculation equation ① can be obtained: Q1 = Q2 + Q3; according to Darcy's law: ΔP = kQ, Where P x and Q3 will change with the change of R3, while P0, k1 and k2 can be considered stable during the measurement; The first state: the orifice (21) is completely blocked. At this time, there is no flow at the orifice (21), Q 30 = 0, at which point the gas pressure in the pressure measuring chamber (3) is the value displayed by the pressure measuring device (4) P x0 According to the above equation ①, the calculation equation ② can be obtained: P x0 is the coal seam gas pressure value of the pressure measuring chamber (3) when the orifice (21) is completely blocked; S4, second state: the cross-sectional opening area at the orifice (21) is adjusted for the first time by the adjusting device (6); the flow rate Q at the orifice (21) is measured. 31 At this time, the pressure in the pressure measuring chamber (3) is the value displayed by the pressure measuring device (4) P x1 , and then we get the calculation equation ③: S5, third state: the cross-sectional opening area at the orifice (21) is adjusted for the second time by the adjusting device (6), so that the cross-sectional opening area at the orifice (21) is different from that in the second state, and the flow rate Q at the orifice (21) is measured again. 32 At this time, the pressure in the pressure measuring chamber (3) is the value displayed by the pressure measuring device (4) P x2 , and then we get the calculation equation ④: S6, P in the above equations ②, ③, and ④ x0 , P x1 , P x2 , Q 31 , Q 32 is a known measured value, P0, k1 and k2 are unknown quantities, and P0 can be calculated jointly to obtain the accurate original gas pressure of the coal seam (1).

2. A method for measuring coal bed gas pressure according to claim 1, characterized in that: The location for drilling a hole (2) to measure the gas pressure of the coal seam (1) is selected from a coal seam or a dense and complete rock area, avoiding aquifers.

3. A method for measuring coal bed gas pressure according to claim 1, characterized in that: The regulating device (6) adopts a ball valve.

4. A method for measuring coal bed gas pressure according to claim 1, characterized in that: The pressure measuring device (4) is a pressure gauge.

5. A method for measuring coal bed gas pressure according to claim 1, characterized in that: The flow measurement device (5) is a flow meter.

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