Downward drilling coal seam gas pressure active measuring device and testing method

Abstract

The application discloses a kind of downward drilling coal seam gas pressure active determination device, including in the roadway floor construction downward pressure measuring borehole, downward pressure measuring borehole enters determination coal seam and penetrates determination coal seam into coal seam floor, several sections of pressure measuring tube are placed in the downward pressure measuring borehole and are connected in turn, the topmost section of pressure measuring tube extends roadway floor, and is connected with the bottom port of four-way connecting pipe, the left and right ports of four-way connecting pipe are connected with water injection valve, drainage valve respectively, the upper port of four-way connecting pipe is additionally connected with pressure measuring air chamber pipe, and pressure measuring air chamber pipe is connected with precision pressure gauge.The application discloses a kind of downward drilling coal seam gas pressure active determination device simultaneously disclosed testing method.The application can realize downward drilling coal seam gas pressure accurate determination by manually controlling or automatically controlling active water injection to downward pressure measuring borehole, and greatly reduces test error.Simplify test procedure, and operation is more relaxed;Shorten test cycle, improve test efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct determination of coal seam gas pressure in a mine, in particular to a device and method for active determination of coal seam gas pressure in a downward drilling hole. BACKGROUND

[0002] Coal seam gas pressure is an important basic parameter of coal seam gas, which can be used for coal and gas outburst risk prediction, gas extraction standard evaluation, gas resource storage evaluation and other site work, and has important basic significance for ensuring coal mine safety production. The industry standard AQ / T1047-2007 "Direct determination method of coal seam gas pressure in a mine" gives a correction method for water-containing drilling holes, but is limited to upward pressure measuring drilling holes. How the pressure generated by the water section in the downward drilling hole affects the pressure measurement is not mentioned. In fact, the process of gas pressure balance in the downward drilling hole is also a process of mechanical balance of coal seam gas pressure, water column gravity in the pressure measuring system and gas pressure (gauge pressure) accumulated on the water column. The test standard specification does not explain this, so the site test process also omits the important link of water pressure correction for downward drilling holes. The reason is that during the recovery process of gas pressure in the downward drilling hole, the liquid seepage from the hole wall or the residual liquid from drilling will deposit in the pressure measuring pipeline. Since there is no direct means to extract the liquid from the downward drilling hole, the liquid volume cannot be accurately obtained, so the actual influence of liquid pressure on coal seam gas pressure cannot be further calculated.

[0003] At present, during the process of continuously observing gas pressure after sealing the downward pressure measuring drilling hole, the coal and rock hole wall will continuously seep water into the hole. In order to exclude the influence of water column on the measured value, the pressure wind system is generally used to blow air to drain water in the hole before sealing the hole. The residual water in the hole is discharged by relying on the pressure wind flow. This operation process is complex and not easy to control. Moreover, the effect of pressure wind blowing and draining residual water and debris in the hole is poor due to the influence of large inclination and large hole depth drilling hole shape, and the measured value accuracy cannot be achieved. As can be seen from the above, the downward pressure measuring technology cannot directly measure the volume of the water section in the hole, which causes the technical shortcoming and deficiency that the water pressure cannot be accurately removed in the downward drilling hole pressure measuring process. The actual measured gauge pressure is smaller than the real coal seam gas pressure, and the error increases with the length of the water column. The gas pressure obtained in this process cannot effectively guide the prevention and control of mine gas disasters. SUMMARY

[0004] The present application aims at the problems of large pressure error and long test time in the downward pressure measurement borehole, especially the water-containing borehole, and aims to overcome the technical shortcomings of the previous downward pressure measurement borehole, such as the complex liquid drainage step in the borehole before sealing, the interference of residual liquid in the borehole after sealing, and the long gas pressure recovery time caused by the large free space of the pressure measurement pipeline, and considers the influence of the water column on the gas pressure recovery process, and provides a downward borehole coal seam gas pressure active measurement device and test method.

[0005] The above-mentioned purpose of the present application is realized by the following technical scheme:

[0006] The downward borehole coal seam gas pressure active measurement device comprises a downward pressure measurement borehole constructed on a roadway floor, the downward pressure measurement borehole enters a measured coal seam and penetrates the measured coal seam to enter a coal seam floor, a plurality of sections of pressure measurement pipes are placed in the downward pressure measurement borehole in sequence, a plurality of through holes are formed on the bottom end of the last section of pressure measurement pipe to form a pressure measurement flower pipe, the top end of the first section of pressure measurement pipe extends out of the roadway floor and is connected with the bottom port of a four-way connecting pipe, the left and right ports of the four-way connecting pipe are connected with a water injection valve and a drainage valve respectively, the upper port of the four-way connecting pipe is additionally connected with a pressure measurement air chamber pipe, the water injection valve is sequentially connected with a first high-pressure rubber pipe, a high-pressure stop valve and a downhole water supply pipeline, the drainage valve is connected with a micro water pump through a second high-pressure rubber pipe, and the pressure measurement air chamber pipe is connected with a precision pressure gauge.

[0007] The downward borehole coal seam gas pressure active measurement device comprises a downward pressure measurement borehole constructed on a roadway floor, the downward pressure measurement borehole enters a measured coal seam and penetrates the measured coal seam to enter a coal seam floor, a plurality of sections of pressure measurement pipes are placed in the downward pressure measurement borehole in sequence, a plurality of through holes are formed on the bottom end of the last section of pressure measurement pipe to form a pressure measurement flower pipe, the top end of the first section of pressure measurement pipe extends out of the roadway floor and is connected with the bottom port of a four-way connecting pipe, the left and right ports of the four-way connecting pipe are connected with a water injection valve and a drainage valve respectively, the upper port of the four-way connecting pipe is additionally connected with a pressure measurement air chamber pipe, the water injection valve is sequentially connected with a first high-pressure rubber pipe, a high-pressure stop valve and a downhole water supply pipeline, the drainage valve is connected with a micro water pump through a second high-pressure rubber pipe, and the pressure measurement air chamber pipe is connected with a precision pressure gauge.

[0008] Further, a sealing capsule is arranged outside the pressure measurement pipe at the junction of the rock section of the downward pressure measurement borehole and the measured coal seam.

[0009] Further, the pressure measuring tube is made of a hollow circular tube, the length of the hollow circular tube is 2m, and the inner diameter is 12.7mm.

[0010] Further, the length from the bottom end of the pressure measuring tube to the bottom of the downward pressure measuring borehole is 0.5m, and the length of the top end of the pressure measuring tube above the roadway floor is 0.5m.

[0011] The application also provides a testing method of the downward borehole coal seam gas pressure active measuring device, which is realized by using the above downward borehole coal seam gas pressure active measuring device and includes the following steps.

[0012] A. Constructing a downward pressure measuring borehole at a suitable position of the roadway floor, and recording the borehole inclination angle θ1, the borehole length, the coal section length, the coal seam inclination angle and the coal seam thickness;

[0013] B. Taking n pressure measuring tubes and one of them to make a pressure measuring tube;

[0014] C. Connecting the made pressure measuring tube and the remaining pressure measuring tubes one by one, binding 1-2 groups of hole sealing capsules on the pressure measuring tube connected with the pressure measuring tube, and sending the pressure measuring tube into the downward pressure measuring borehole, and placing the pressure measuring tube in the borehole orifice to the borehole bottom of the downward pressure measuring borehole;

[0015] D. Injecting water or air into the hole sealing capsule to make it expand around the downward pressure measuring borehole wall to support the pressure measuring tube and isolate the coal section and rock section in the downward pressure measuring borehole; injecting the prepared slurry into the downward pressure measuring borehole, stopping the grouting when the slurry fills the downward pressure measuring borehole, ensuring that the slurry is in the position of the hole sealing capsule to the borehole orifice of the downward pressure measuring borehole, and forming a sealing section;

[0016] E. After the slurry solidifies for 24h, connecting the water injection valve, the water drainage valve and the pressure measuring chamber tube through the four-way connecting pipe at the top end of the pressure measuring tube, sequentially connecting the first high-pressure rubber pipe, the high-pressure stop valve and the underground water supply pipeline to the water injection valve; connecting the micro water pump to the other end of the water drainage valve; and installing the precision pressure gauge to the other end of the pressure measuring chamber tube;

[0017] F. Manually controlling the active water injection into the downward pressure measuring borehole, and filling the water from the water injection valve to the bottom of the downward pressure measuring borehole, and ending the active water injection process;

[0018] The water volume of the active water injection forms a water column in the n pressure measuring tubes, and the water pressure P1 is generated due to the gravity; the water pressure P1 refers to the pressure generated by the water section length L actually directly acting on the coal body surface, L refers to the length from the bottom end of the water injection valve and the water drainage valve to the bottom end of the pressure measuring tube, that is, the total length of the n pressure measuring tubes, and the length of each pressure measuring tube is 2m, so L=2n;

[0019] G.When the gauge pressure P2 of the precision pressure gauge is less than 0.015 MPa within 3 days, the pressure is considered stable, and the coal seam gas pressure P is calculated according to the numerical law, with the unit of MPa;

[0020] 1) When P2> 0, the coal seam gas pressure P is measured by calculating formula (1) and formula (2):

[0021] P = P1 + P2 (1)

[0022] P = 2p.g.n.sinθ1 + P2 (2)

[0023] In formula (1) and formula (2):

[0024] P—Measured coal seam gas pressure, Pa; P1—Water pressure actually acting on the water section of the coal body surface of the pressure measuring pipe, Pa; P2—Precision pressure reading, Pa; n—Number of sections of the pressure measuring pipe, 2 m per section; θ1—Drilling inclination, °; p—Density of water in the pressure measuring pipe, taking 1.0 g / cm 3 ; g—Gravitational acceleration, m / s 2 ;

[0025] 2) When P2 = 0, open the drain valve and start the micro water pump to slowly drain the water in the pressure measuring pipe, thereby reducing the actual water pressure acting on the coal body surface in the pressure measuring pipe by shortening the water section length. A small amount of water is extracted by manually controlling the micro water pump at one time, with the volume V being cm 3 ; the water volume V extracted each time is the water volume of the water section with a length of l in the pressure measuring pipe, which is calculated according to formula (3). After each drainage is completed, the drain valve and the micro water pump are closed, and the reading of the precision pressure gauge is observed;

[0026] V = π.r 2 ·l (3)

[0027] In formula (3), r is the radius of the pressure measuring pipe, with the unit of cm;

[0028] a. If the precision pressure gauge shows a reading within 10 h, continue to observe, and record the gauge pressure P2 when the pressure is stable. According to the water pressure P1 in the pressure measuring pipe, the water extraction volume V, and the gauge pressure P2 data, the true measured coal seam gas pressure P is calculated according to formula (4):

[0029]

[0030] b.If the precision pressure gauge still has no reading within 10h, reopen the drain valve, start the micro water pump to slowly drain the water in the pressure pipe, always keep the water volume V extracted each time, after the drainage is completed, close the drain valve and the micro water pump in turn, repeat the water release and observation of the precision pressure gauge reading, when the precision pressure gauge shows the reading within 10h of drainage, the drainage work is completed, and the drainage times N are recorded; the total drainage water volume is calculated according to the N times of drainage, and the real measured coal seam gas pressure P is calculated according to formula (5):

[0031]

[0032] In formula (4) and formula (5): P-measured coal seam gas pressure, Pa; P1-actual water pressure of the water section of the pressure pipe acting on the coal body surface, Pa; P2-precision pressure reading, Pa; n-number of sections of the pressure pipe, 2m per section; θ1-drilling inclination, °; ρ-density of water in the pressure pipe, 1.0g / cm 3 ; g-acceleration of gravity, m / s 2 ; V-water volume of length l in the pressure pipe automatically extracted by the micro water pump at one time, cm 3 ; N-drainage times of the micro water pump; r-radius of the pressure pipe, cm.

[0033] Further, the active water injection process of the step F is: opening the high-pressure stop valve, connecting the first high-pressure rubber pipe and the downhole water supply pipeline, and simultaneously opening the drain valve to connect the pressure pipe with the external environment; opening the water injection valve to inject water into the pressure pipe, and closely observing the water discharge state of the drain valve, when the connected micro water pump has water discharged, the active water injection process is completed, and the water injection valve and the drain valve are closed in turn, and the water from the water injection valve to the bottom of the pressure drilling hole is full of water.

[0034] The application also provides another testing method of the downhole drilling coal seam gas pressure active measurement device, which is realized by using the downhole drilling coal seam gas pressure active measurement device, and comprises the following steps.

[0035] A. Constructing a downhole pressure drilling hole at a suitable position of the roadway floor 3, and recording the drilling inclination θ1, the drilling length, the coal section length, the coal seam inclination and the coal seam thickness;

[0036] B.taking n sections of pressure pipes and taking one section to make a pressure flower pipe;

[0037] C.connecting the made pressure flower pipe and all the remaining pressure pipes section by section, binding 1-2 groups of sealing capsules on the section of the pressure pipe connected with the pressure flower pipe, and sending the pressure pipe into the downhole pressure drilling hole together with the pressure pipe, and the pressure pipe is placed from the orifice to the bottom of the downhole pressure drilling hole;

[0038] D. Water or air is injected into the sealing capsule to make it swell and embrace the sidewall of the downward pressure borehole for supporting the pressure pipe and isolating the coal section and rock section in the borehole; the prepared slurry is injected into the downward pressure borehole, and the injection is stopped when the slurry fills the downward pressure borehole, so that the slurry is formed in the sealing capsule and the position of the downward pressure borehole to the borehole mouth;

[0039] E. After the slurry is solidified for 24 hours, the water injection electromagnetic valve, the water drainage electromagnetic valve and the pressure chamber pipe are connected to the top end of the pressure pipe through the four-way connecting pipe; the water injection electromagnetic valve is sequentially connected to the first high-pressure rubber pipe, the electromagnetic stop valve and the downhole water supply pipeline; the other end of the water drainage electromagnetic valve is sequentially connected to the flowmeter and the micro water pump; the other end of the pressure chamber pipe is installed with the pressure sensor; the electromagnetic stop valve, the water injection electromagnetic valve, the pressure sensor, the water drainage electromagnetic valve, the flowmeter and the micro water pump are electrically connected with the PLC programmable controller;

[0040] F. The active water injection into the downward pressure borehole is automatically controlled: the electromagnetic stop valve is automatically opened by the PLC programmable controller to connect the first high-pressure rubber pipe and the downhole water supply pipeline; at the same time, the water drainage electromagnetic valve is opened to connect the pressure pipe and the external environment; the water injection electromagnetic valve is opened to inject water into the pressure pipe, and the water drainage state of the water drainage electromagnetic valve is closely observed; when the flowmeter shows the flow, the water injection electromagnetic valve and the water drainage electromagnetic valve are automatically closed in turn, at this time, the downward pressure borehole is filled with water from the water injection electromagnetic valve to the bottom of the downward pressure borehole, and the active water injection process is completed;

[0041] The water in the pressure pipe forms a water column, and the water pressure P1 is generated due to the gravity; the water pressure P1 refers to the pressure generated by the length L of the water section directly acting on the surface of the coal body, L refers to the length from the bottom end of the water injection electromagnetic valve and the water drainage electromagnetic valve to the bottom end of the pressure pipe, that is, the total length of n sections of the pressure pipe, and the length of each section of the pressure pipe is 2m, so L=2n;

[0042] G. When the pressure sensor shows P2 less than 0.015 MPa within 3 days, it is considered that the pressure is stable, and the coal seam gas pressure P is calculated according to the numerical law, with the unit of MPa;

[0043] 1) When P2>0, the coal seam gas pressure P is calculated by formula (1) and formula (2):

[0044] P=P1+P2 (1)

[0045] P=2p·g·n·sinθ1+P2 (2)

[0046] In formula (1) and formula (2):

[0047] P—Measured coal seam gas pressure, Pa; P1—Water pressure of the piezometer acting on the surface water section of the coal seam, Pa; P2—Precision pressure gauge reading, Pa; n—Number of sections of the piezometer, 2m per section; θ1—Borehole inclination angle, °; ρ—Density of water in the piezometer, taken as 1.0g / cm³. 3 g—acceleration due to gravity, m / s² 2 ;

[0048] 2) When P2 = 0, the drain solenoid valve automatically opens, and the micro water pump starts to slowly pump water from the pressure measuring tube. By shortening the water section length, the actual water pressure acting on the coal surface in the pressure measuring tube is reduced. Using a PLC programmable controller, the micro water pump is programmed to pump a small amount of water at a time, with a volume of V (in cm³). 3 The water volume V extracted each time is the water volume of the water section with a length of l in the pressure measuring tube. It is calculated according to formula (3). After each extraction, the drain solenoid valve and the micro water pump are closed, and the reading of the pressure sensor is monitored.

[0049] V = π·r 2 ·l (3)

[0050] In equation (3), r is the radius of the pressure measuring tube, in cm;

[0051] a. If the pressure sensor displays a reading within 10 hours, continue monitoring until the reading stabilizes and record it as gauge pressure P2; based on the water pressure P1 in the pressure measuring tube, the extracted water volume V, and the gauge pressure P2, calculate the actual measured coal seam gas pressure P according to formula (4):

[0052]

[0053] b. If the pressure sensor still has no reading within 10 hours, automatically open the drain solenoid valve and restart the micro pump to slowly drain the water from the pressure measuring tube. The amount of water automatically drained each time is always V. After the drainage is completed, close the drain solenoid valve and the micro pump in sequence. Repeat the draining and observation of the pressure sensor reading. When the pressure sensor displays a reading within 10 hours of drainage, the drainage work is completed. Record the number of drainages N times. Calculate the total drainage volume based on the N drainage processes. Calculate the actual measured coal seam gas pressure P according to formula (5):

[0054]

[0055] In equations (4) and (5): P—measured coal seam gas pressure, Pa; P1—actual water pressure acting on the surface water section of the coal body in the pressure measuring pipeline, Pa; P2—pressure sensor reading, Pa; n—number of sections of the pressure measuring pipe, 2m per section; θ1—drill hole inclination angle, °; ρ—density of water in the pressure measuring pipe, taken as 1.0g / cm³. 3 g—acceleration due to gravity, m / s² 2; V - the water volume of the length of l in the pressure measuring pipe is automatically extracted by the micro water pump once, cm 3 ; N - the number of times of pumping by the micro water pump, r - the radius of the pressure measuring pipe, cm.

[0056] Further, the surface of the pressure measuring pipe in step B is bundled with fine mesh window screen to prevent coal dust from entering the pressure measuring pipe through the small holes.

[0057] The working principle of the present application is as follows: the present application actively injects water downward into the pressure measuring borehole through manual control or automatic control, mixes with the residual water in the borehole, uses the water pressure generated by the self-weight of water to simulate and create free gas pressure, thereby inhibiting the desorption and release of coal seam gas and shortening the desorption time of coal seam gas; at the same time, the incompressibility of water is used to reduce the free space of the pressure measuring pipe by the amount of injected water, thereby accelerating the pressure recovery speed of the pressure measuring gas chamber and reducing the pressure measuring observation time; under the premise of active water injection, the volume of the reserved water in the pipeline is accurately obtained, and the dynamic balance relationship among the coal seam gas pressure, water column pressure and gas pressure of the downward borehole is used to accurately calculate the real coal seam gas pressure.

[0058] Compared with the prior art, the present application has the following beneficial effects:

[0059] (1) The present application can realize accurate measurement of the coal seam gas pressure of the downward borehole and greatly reduce the test error. The balance relationship among the water pressure, gauge pressure and coal seam gas pressure is used to actively inject a certain amount of water into the pressure measuring pipe, accurately measure the coal seam gas pressure, completely eliminate the water pressure error omitted in the traditional downward borehole pressure measuring technology, and accurately obtain the real coal seam gas pressure of the downward borehole.

[0060] (2) The test process is simplified, and the operation is more relaxed. The residual water in the borehole does not need to be discharged before sealing the hole in the measurement process, but the key parameters such as water column pressure are actively controlled through active water volume, which not only omits the water discharge link, but also improves the process operation ability.

[0061] (3) The test cycle is shortened, and the test efficiency is improved. The active water injection can occupy a certain free space inside the pressure measuring pipeline, reduce the free volume of the pressure measuring gas chamber, and be beneficial to the rapid recovery and stability of the gas in a smaller space, thereby shortening the pressure recovery time. In addition, the water pressure generated by the water section can inhibit the desorption of coal seam gas, shorten the desorption and release process of the coal seam adsorbed gas to the outside, and promote the rapid and stable balance of the coal seam gas pressure, water pressure and gauge pressure in the pressure measuring gas chamber. BRIEF DESCRIPTION OF DRAWINGS

[0062] Figure 1 is the structure diagram of the active measurement device for the coal seam gas pressure of the downward borehole in the first embodiment provided by the present application.

[0063] Figure 2It is the structure schematic view of the downward drilling coal seam gas pressure active measuring device in the second embodiment provided by the present application.

[0064] Figure 3 It is the connection relation view of the PLC programmable controller of the downward drilling coal seam gas pressure active measuring device in the second embodiment.

[0065] In the figure: 1-measuring coal seam; 2-downward pressure measuring drilling hole; 3-roadway floor; 4-pressure measuring pipe; 41-pressure measuring flower pipe; 5-four-way connecting pipe; 6-hole sealing capsule; 7-blocking section; 8-water injection valve; 9-drainage valve; 10-precision pressure gauge; 111-first high-pressure rubber pipe; 112-second high-pressure rubber pipe; 12-underground water supply pipeline; 13-high-pressure stop valve; 14-pressure measuring air chamber pipe; 15-micro water pump; 16-electromagnetic stop valve; 17-water injection electromagnetic valve; 18-drainage electromagnetic valve; 100-water; 20-flow meter; 30-PLC programmable controller; 40-pressure sensor. DETAILED DESCRIPTION

[0066] The detailed content of the present application and the specific implementation mode thereof will be further explained in combination with the drawings and specific embodiments.

[0067] Embodiment one

[0068] Reference Figure 1 The downward drilling coal seam gas pressure active measuring device comprises a downward pressure measuring drilling hole 2 constructed in a roadway floor 3, the downward pressure measuring drilling hole 2 enters a measuring coal seam 1 and penetrates the measuring coal seam 1 to enter a coal seam floor, a plurality of sections of pressure measuring pipes 4 are placed in the downward pressure measuring drilling hole 2 in sequence, a plurality of through holes are formed on the bottommost section of pressure measuring pipes 4 to form pressure measuring flower pipes 41, one through hole is arranged on the circumferential surface of the bottommost section of pressure measuring pipes 4 every 5-10 cm, the through holes are arranged to provide a channel for gas migration, which is beneficial to the rapid entry of gas in the downward pressure measuring drilling hole 2 into the pressure measuring pipes 4, so as to measure the coal seam gas pressure, the topmost section of pressure measuring pipes 4 extends out of the roadway floor 3 and is connected with the bottom port of a four-way connecting pipe 5, the left and right ports of the four-way connecting pipe 5 are respectively connected with a water injection valve 8 and a drainage valve 9, the four-way connecting pipe 5 is additionally connected with a pressure measuring air chamber pipe 14, the water injection valve 8 is sequentially connected with a first high-pressure rubber pipe 111, a high-pressure stop valve 13 and an underground water supply pipeline 12, the drainage valve 9 is connected with a micro water pump 15 through a second high-pressure rubber pipe 112, and the pressure measuring air chamber pipe 14 is connected with a precision pressure gauge 10.

[0069] A hole sealing capsule 6 is arranged outside the pressure measuring pipe 4 at the junction of the rock section of the downward pressure measuring drilling hole 2 and the measuring coal seam 1.

[0070] The pressure measuring pipe 4 is made of a hollow circular pipe, the length of the hollow circular pipe is 2 m, and the inner diameter is 12.7 mm.

[0071] The length from the bottom end of the pressure measuring flower tube 41 to the hole bottom of the downward pressure measuring borehole 2 is 0.5 m, and the top end of the pressure measuring tube 4 is 0.5 m higher than the roadway floor 3.

[0072] Example Two

[0073] Reference Figures 2-3 The downward borehole coal seam gas pressure active measuring device includes a downward pressure measuring borehole 2 constructed on the roadway floor 3, the downward pressure measuring borehole 2 enters the measuring coal seam 1 and penetrates the measuring coal seam 1 to enter the coal seam floor, a plurality of sections of pressure measuring tubes 4 are placed in the downward pressure measuring borehole 2, a plurality of through holes are formed on the bottom end of the pressure measuring tube 4 to form a pressure measuring flower tube 41, a through hole is arranged on the circumferential surface of the bottom end of the pressure measuring tube 4 every 5-10 cm, the through hole provides a channel for gas migration, which is conducive to the rapid entry of gas in the downward pressure measuring borehole 2 into the pressure measuring tube 4, so as to measure the coal seam gas pressure, the top end of the pressure measuring tube 4 extends out of the roadway floor 3 and is connected with a water injection electromagnetic valve 17 and a drainage electromagnetic valve 18 through a four-way connecting pipe 5, the four-way connecting pipe 5 is further connected with a pressure measuring gas chamber pipe 14, the water injection electromagnetic valve 17 is sequentially connected with a first high-pressure rubber pipe 111, an electromagnetic stop valve 16, and a downhole water supply pipe 12, the drainage electromagnetic valve 18 is connected with a micro water pump 15 through a second high-pressure rubber pipe 112, a flow meter 20 is arranged on the second high-pressure rubber pipe 112, the pressure measuring gas chamber pipe 14 is connected with a pressure sensor 40, and the water injection electromagnetic valve 17, the drainage electromagnetic valve 18, the electromagnetic stop valve 16, the micro water pump 15, the flow meter 20, and the pressure sensor 40 are electrically connected with a PLC programmable controller 30.

[0074] A sealing capsule 6 is arranged outside the pressure measuring tube 4 at the junction of the rock section of the downward pressure measuring borehole 2 and the measuring coal seam 1.

[0075] The pressure measuring tube 4 is made of a hollow circular tube with a length of 2 m and an inner diameter of 12.7 mm.

[0076] The length from the bottom end of the pressure measuring flower tube 41 to the hole bottom of the downward pressure measuring borehole 2 is 0.5 m, and the top end of the pressure measuring tube 4 is 0.5 m higher than the roadway floor 3.

[0077] Example Three

[0078] The test method of the downward borehole coal seam gas pressure active measuring device is realized by using the downward borehole coal seam gas pressure active measuring device in Example One, and includes the following steps:

[0079] A. A downward pressure measuring borehole 2 is constructed on the roadway floor 3 at a suitable position, and the diameter of the downward pressure measuring borehole 2 is preferably 100-150 mm. the downward pressure borehole 2, the downward pressure borehole 2 enters the coal seam 1 and penetrates the coal seam to the coal floor 0.5m, records the borehole inclination θ1, the borehole length, the coal section length, the coal seam inclination, and the coal seam thickness;

[0080] B. Take n sections of the pressure pipe 4 and take one section to make the pressure flower pipe 41 (the length of the pressure pipe 4 is 2m, and the inner diameter is 12.7mm), and bind fine and dense microporous window screen on the surface of the pressure flower pipe 41 to prevent coal dust from entering the pressure flower pipe 41 through the small holes;

[0081] C. Connect the made pressure flower pipe 41 and all the remaining pressure pipes 4 section by section, bind 1-2 groups of hole sealing capsules 6 on the pressure pipe 4 connected with the pressure flower pipe 41, and send them into the downward pressure borehole 2 together with the pressure pipe 4, the pressure pipe 4 is placed from the orifice to the bottom of the downward pressure borehole 2; the length from the bottom end of the pressure flower pipe 41 to the bottom of the downward pressure borehole 2 is 0.5m; the top end of the pressure pipe 4 is 0.5m higher than the roadway floor 3;

[0082] D. Inject water or air into the hole sealing capsule 6 to make it expand around the wall of the downward pressure borehole 2, which is used to support the pressure pipe 4 and isolate the coal section and rock section in the borehole; use the mature grouting hole sealing technology and slurry to inject the prepared slurry into the downward pressure borehole 2, stop grouting when the slurry fills the downward pressure borehole 2, ensure that there is slurry from the position of the hole sealing capsule 6 to the orifice of the downward pressure borehole 2, and form a sealing section 7;

[0083] E. After the slurry solidifies for 24h, connect the water injection valve 8, the water drainage valve 9, and the pressure chamber pipe 14 through the four-way connecting pipe 5 at the top end of the pressure pipe 4; sequentially connect the first high-pressure rubber pipe 111, the high-pressure stop valve 13, and the underground water supply pipeline 12 to the water injection valve 8; connect the micro water pump 15 to the other end of the water drainage valve 9; the length of the pressure chamber pipe 14 is 0.5m; install the precision pressure gauge 10 with a precision not less than 1.0 level at the other end of the pressure chamber pipe 14;

[0084] F. Manually control the active water injection into the downward pressure borehole 2, and fill the water 100 from the water injection valve 8 to the bottom of the downward pressure borehole 2, and the active water injection process is ended, which is specifically as follows:

[0085] Open the high-pressure stop valve 13 to connect the first high-pressure rubber pipe 111 and the underground water supply pipeline 12; at the same time, open the water drainage valve 9 to connect the pressure pipe 4 with the external environment; open the water injection valve 8 to inject water into the pressure pipe 4, and closely observe the water discharge state of the water drainage valve 9; when the connected micro water pump 15 discharges water, the active water injection process is ended, and the water injection valve 8 and the water drainage valve 9 are closed in turn, at this time, the pressure pipe 4 is filled with water 100 from the water injection valve 8 to the bottom;

[0086] The water quantity of active water injection forms a water column in the pressure pipe 4, and the water pressure P1 is generated by its own gravity; the water pressure P1 refers to the pressure generated by the water section length L actually acting on the surface of the coal body, L refers to the length from the bottom end of the water injection valve 8 and the water drainage valve 9 to the bottom end of the pressure pipe 41, that is, the total length of n sections of the pressure pipe 4, and the length of each section of the pressure pipe 4 is 2m, so L=2n;

[0087] G. When the gauge pressure P2 of the precision pressure gauge 10 is less than 0.015MPa within 3 days, it is considered that the pressure is stable, and the coal seam gas pressure P is calculated according to the numerical law, with the unit of MPa;

[0088] 1) When P2>0, it indicates that the coal seam gas breaks through the water column pressure, and the measured coal seam gas pressure P>P1, at this time, the measured coal seam gas pressure P in the downward pressure measuring borehole 2, the water pressure P1 of the pressure pipe 4 actually acting on the surface of the coal body, and the gauge pressure P2 reach balance, and the real measured coal seam gas pressure P is calculated by formula (1) and formula (2):

[0089] P=P1+P2 (1)

[0090] According to the length L, the water pressure P1 of the pressure pipe 4 actually acting on the surface of the coal body is obtained, and thus the coal seam gas pressure P is obtained:

[0091] P=2p·g·n·sinθ1+P2 (2)

[0092] In formula (1) and formula (2):

[0093] P-the measured coal seam gas pressure, Pa; P1-the water pressure of the pressure pipe 4 actually acting on the surface of the coal body, Pa; P2-the precision pressure value, Pa; n-the number of sections of the pressure pipe 4, each section is 2m; θ1-the drilling angle, °; p-the density of water in the pressure pipe 4, the value is 1.0g / cm 3 ; g-acceleration of gravity, m / s 2 ;

[0094] 2) When P2=0, it indicates that the coal seam gas is small and does not break through the water pressure P1 in the pressure pipe 4, and the measured coal seam gas pressure P 3 ; each time the water quantity V is the water quantity of the water section length l (l is in cm, and l generally takes the value of 100-500cm) in the pressure pipe 4, and according to formula (3), the water drainage valve 9 and the micro water pump 15 are closed after each time of pumping and drainage is finished, and the reading of the precision pressure gauge 10 is observed;

[0095] V=π·r2 • I (3)

[0096] In formula (3), r is the radius of the pressure pipe 4, in cm;

[0097] a. If the precision pressure gauge 10 shows a reading within 10h, continue to observe, and record the gauge pressure P2 after the pressure is stable; according to the water pressure PI in the pressure pipe 4, the water volume V, and the gauge pressure P2 data, calculate the real measured coal seam gas pressure P according to formula (4):

[0098]

[0099] b. If the precision pressure gauge 10 still has no reading within 10h, reopen the drain valve 9, start the micro water pump 15 to slowly drain the water 100 in the pressure pipe 4, always keep the water volume V each time, close the drain valve 9 and the micro water pump 15 in turn after the drainage is completed, repeat the water release and observe the precision pressure gauge 10 reading according to step b, when the precision pressure gauge 10 shows a reading within 10h of drainage, the drainage work is completed, and the drainage times N are recorded; according to the total drainage volume calculated in N times of drainage, calculate the real measured coal seam gas pressure P according to formula (5):

[0100]

[0101] In formula (4) and formula (5), P is the measured coal seam gas pressure, Pa; PI is the water pressure of the water section actually acting on the coal body surface of the pressure pipe 4, Pa; P2 is the precision pressure reading, Pa; n is the number of sections of the pressure pipe 4, 2m per section; θ1 is the drilling inclination, °; ρ is the density of water in the pressure pipe 4, taking 1.0g / cm 3 ; g is the acceleration of gravity, m / s 2 ; V is the water volume of the micro water pump automatically extracted from the pressure pipe 4 at a time, cm 3 ; N is the number of times of drainage of the micro water pump; r is the radius of the pressure pipe 4, cm.

[0102] Example Four

[0103] The test method of the downward drilling coal seam gas pressure active measuring device is realized by using the downward drilling coal seam gas pressure active measuring device in Example Two, including the following steps:

[0104] A. Construct a downward pressure drilling hole 2 with a diameter of 2.5-3.5cm at a suitable position of the roadway floor 3, the downward pressure drilling hole 2 enters the measured coal seam 1 and penetrates the coal seam into the coal seam floor by 0.5m, record the drilling inclination θ1, the drilling length, the coal section length, the coal seam inclination, and the coal seam thickness;

[0105] ​B. Take n pressure tube 4 and take one of them to make pressure tube 41 (the length of pressure tube 4 is 2m, and the inner diameter is 12.7mm), and bind fine and dense microporous window screen on the surface of pressure tube 41 to prevent coal dust from entering pressure tube 41 through the small holes;

[0106] C. Connect the prepared pressure tube 41 and all the remaining pressure tubes 4 one by one, bind 1-2 groups of sealing capsules 6 on the pressure tube 4 connected with the pressure tube 41, and send them into the downward pressure borehole 2 together with the pressure tube 4. The pressure tube 4 is placed from the orifice to the bottom of the downward pressure borehole 2. The length from the bottom end of the pressure tube 41 to the bottom of the downward pressure borehole 2 is 0.5m. The top end of the pressure tube 4 is 0.5m higher than the floor 3 of the roadway;

[0107] D. Inject water or air into the sealing capsule 6 to make it swell around the wall of the downward pressure borehole 2 to support the pressure tube 4 and isolate the coal section from the rock section in the borehole. Inject the prepared slurry into the downward pressure borehole 2. Stop injecting the slurry when the slurry fills the downward pressure borehole 2 to ensure that the position of the sealing capsule 6 in the downward pressure borehole 2 to the orifice is filled with slurry, forming a sealing section 7;

[0108] E. After the slurry solidifies for 24h, connect the water injection electromagnetic valve 17, the water drainage electromagnetic valve 18, and the pressure chamber tube 14 to the top end of the pressure tube 4 through the four-way connection tube 5. The water injection electromagnetic valve 17 is sequentially connected with the first high-pressure rubber tube 111, the electromagnetic shut-off valve 16, and the downhole water supply pipeline 12. The other end of the water drainage electromagnetic valve 18 is sequentially connected with the flowmeter 20 and the micro water pump 15. The other end of the pressure chamber tube 14 is installed with the pressure sensor 40. The electromagnetic shut-off valve 16, the water injection electromagnetic valve 17, the pressure sensor 40, the water drainage electromagnetic valve 18, the flowmeter 20, and the micro water pump 15 are electrically connected with the PLC programmable controller 30 to realize automatic control of each link;

[0109] F. Automatically control the active water injection into the downward pressure borehole 2: automatically open the electromagnetic shut-off valve 16 through the PLC programmable controller 30 to connect the first high-pressure rubber tube 111 and the downhole water supply pipeline 12. At the same time, open the water drainage electromagnetic valve 18 to connect the pressure tube 4 with the external environment. Open the water injection electromagnetic valve 17 to inject water into the pressure tube 4, and closely observe the water discharge state of the water drainage electromagnetic valve 18. When the flowmeter 20 shows the flow, automatically close the water injection electromagnetic valve 17 and the water drainage electromagnetic valve 18 in turn. At this time, the water from the water injection electromagnetic valve 17 to the bottom of the downward pressure borehole 2 is full of water 100, and the active water injection process is completed;

[0110] The water quantity of active water injection forms a water column in the pressure pipe 4, and water pressure P1 is generated due to its own gravity; the water pressure P1 refers to the pressure generated by the water section length L actually acting on the surface of the coal body, L refers to the length from the bottom end of the water injection electromagnetic valve 17 and the drainage electromagnetic valve 18 to the bottom end of the pressure measuring pipe 41, that is, the total length of n sections of the pressure measuring pipe 4, and the length of each section of the pressure measuring pipe 4 is 2 m, so L = 2n;

[0111] G. When the pressure sensor 40 shows P2 less than 0.015 MPa within 3 days, it is considered that the pressure is stable, and the coal seam gas pressure P is calculated according to the numerical law, with the unit of MPa;

[0112] 1) When P2 > 0, it indicates that the coal seam gas breaks through the water column pressure, the coal seam gas pressure P measured is greater than P1, and the part of the free gas higher than the water column pressure enters the pressure measuring chamber pipe 14 to accumulate, and the gas pressure generated, that is, the gauge pressure P2 of the pressure sensor 40, at this time, the coal seam gas pressure P measured in the downward pressure measuring borehole 2, the water pressure P1 of the pressure measuring pipe 4 actually acting on the water section of the coal body surface, and the gauge pressure P2 reach balance, and the real coal seam gas pressure P is calculated by formula (1) and formula (2):

[0113] P = P1 + P2 (1)

[0114] The water pressure P1 of the pressure measuring pipe 4 actually acting on the water section of the coal body surface is obtained according to the length L, so as to obtain the coal seam gas pressure P:

[0115] P = 2p.g.n.sinθ1 + P2 (2)

[0116] In formula (1) and formula (2):

[0117] P—measured coal seam gas pressure, Pa; P1—water pressure of the pressure measuring pipe 4 actually acting on the water section of the coal body surface, Pa; P2—precision pressure display number, Pa; n—number of sections of the pressure measuring pipe 4, each section is 2 m; θ1—drilling angle, °; p—density of water in the pressure measuring pipe 4, the value is 1.0 g / cm 3 ; g—acceleration of gravity, m / s 2 ;

[0118] 2) When P2 = 0, it indicates that the coal seam gas is small and does not break through the water pressure P1 in the pressure measuring pipe 4, and the measured coal seam gas pressure P < P1, at this time, the drainage electromagnetic valve 18 is automatically opened, the micro water pump 15 is started to slowly drain the water 100 in the pressure measuring pipe 4, the water section length is shortened to reduce the water pressure actually acting on the coal body surface in the pressure measuring pipe 4, and the PLC programmable controller 30 is used to control the micro water pump 15 to extract a small amount of water at one time, with the volume V of cm 3Each time, the water volume V is the water volume in the pressure measuring tube 4 with a water section length of l (l is in cm, and l is generally taken as 100-500 cm). It is calculated according to formula (3). After each pumping is completed, the drainage solenoid valve 18 and the micro water pump 15 are closed, and the reading of the pressure sensor 40 is observed.

[0119] V = π·r 2 ·l (3)

[0120] In equation (3), r is the radius of the pressure measuring tube 4, in cm;

[0121] a. After each pumping operation, close the drain solenoid valve 18 and the micro pump 15, monitor the pressure sensor 40, and record the reading of the pressure sensor 40 within 10 hours. Continue monitoring until the reading stabilizes and record it as the gauge pressure P2. Based on the water pressure P1 in the pressure measuring tube 4, the pumped water volume V, and the gauge pressure P2, calculate the actual measured coal seam gas pressure P according to formula (4):

[0122]

[0123] b. If the pressure sensor 40 still has no reading within 10 hours, the drain solenoid valve 18 will be opened automatically, and the micro pump 15 will be restarted to slowly pump out 100% of the water from the pressure measuring pipe 4. The amount of water automatically pumped each time will always be V. After the pumping is completed, the drain solenoid valve 18 and the micro pump 15 will be closed in sequence. Following step b, the water will be drained and the reading of the pressure sensor 40 will be observed again. When the pressure sensor 40 displays a reading within 10 hours of pumping, the pumping work will be completed. The number of pumping times N will be recorded. The total amount of water pumped will be calculated based on the N pumping processes. The actual measured coal seam gas pressure P will be calculated according to formula (5):

[0124]

[0125] In equations (4) and (5): P—measured coal seam gas pressure, Pa; P1—actual water pressure of the pressure measuring tube 4 acting on the water section of the coal surface, Pa; P2—reading of pressure sensor 40, Pa; n—number of sections of pressure measuring tube 4, each section is 2m; θ1—drill hole inclination angle, °; ρ—density of water in pressure measuring tube 4, taken as 1.0g / cm³. 3 g—acceleration due to gravity, m / s² 2 V—A miniature water pump automatically extracts water (cm) from a pressure measuring tube 4 of length l. 3 N—Number of pumping cycles of the micro pump; r—Radius of the pressure measuring tube 4, in cm.

[0126] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A testing method for a downward drilling coal seam gas pressure active measuring device, which is realized by using the downward drilling coal seam gas pressure active measuring device, the downward drilling coal seam gas pressure active measuring device comprises a downward pressure measuring drill hole constructed on a roadway floor, the downward pressure measuring drill hole enters a measured coal seam and penetrates the measured coal seam to enter a coal seam floor, a plurality of pressure measuring tubes connected in sequence are placed in the downward pressure measuring drill hole, a plurality of through holes are formed on a bottommost pressure measuring tube to form a pressure measuring flower tube, a topmost pressure measuring tube extends out of the roadway floor and is connected with a bottom port of a four-way connecting pipe, left and right ports of the four-way connecting pipe are respectively connected with a water injection valve and a water drainage valve, an upper port of the four-way connecting pipe is additionally connected with a pressure measuring air chamber pipe, the water injection valve is sequentially connected with a first high-pressure rubber pipe, a high-pressure stop valve and an underground water supply pipeline, the water drainage valve is connected with a micro water pump through a second high-pressure rubber pipe, and the pressure measuring air chamber pipe is connected with a precision pressure gauge; characterized in that The method comprises the following steps: A. Construction of the lower to the roadway floor in a suitable position to measure pressure drilling, record the drilling angle , drilling length, coal length, coal seam inclination, coal seam thickness; B. Take n The section of the pressure measuring tube is taken and one section is made into a pressure measuring flower tube. C. The prepared pressure measuring flower tube and all the remaining pressure measuring tubes are connected in sections, 1-2 groups of hole sealing capsules are bound on the pressure measuring tube connected with the pressure measuring flower tube, and the pressure measuring tube is sent into the downward pressure measuring drill hole together with the pressure measuring flower tube, and the pressure measuring tube is placed at an orifice to a bottom of the downward pressure measuring drill hole; D. Water or air is injected into the hole sealing capsules to make the hole sealing capsules expand and embrace walls of the downward pressure measuring drill hole, so as to support the pressure measuring tube and isolate a coal section and a rock section in the downward pressure measuring drill hole; slurry is injected into the downward pressure measuring drill hole, and the slurry injection is stopped after the slurry fills the downward pressure measuring drill hole, so that the downward pressure measuring drill hole position where the hole sealing capsules are located to the orifice is filled with the slurry, and a sealing section is formed; E. After the slurry is solidified for 24 hours, the water injection valve, the water drainage valve and the pressure measuring air chamber pipe are connected with the top end of the pressure measuring tube through the four-way connecting pipe, the water injection valve is sequentially connected with the first high-pressure rubber pipe, the high-pressure stop valve and the underground water supply pipeline, the other end of the water drainage valve is sequentially connected with the micro water pump, and the other end of the pressure measuring air chamber pipe is installed with the precision pressure gauge; F. The active water injection process in the step F is that the high-pressure stop valve is opened, the first high-pressure rubber pipe and the underground water supply pipeline are connected, the water drainage valve is opened at the same time, the pressure measuring tube is connected with the external environment, the water injection valve is opened to inject water into the pressure measuring tube, the water drainage state is closely observed, the active water injection process is ended when the micro water pump connected with the water drainage valve has water drained, and the water injection valve and the water drainage valve are sequentially closed, and the downward pressure measuring drill hole is filled with water from the water injection valve to the bottom of the downward pressure measuring drill hole. The water quantity of active water injection is in n The water column is formed in the section piezometer, and the water pressure is generated by its own gravity The water pressure The length of water section actually directly acting on the surface of coal body L The pressure generated, L The length from the bottom of the water injection valve and the water discharge valve to the bottom of the section piezometer, that is, n The total length of the section piezometer, and the length of each section piezometer is 2m, In the formula (1) and the formula (2), ; G.When the gauge pressure of the precision pressure gauge is less than 0.015 MPa within 3 days, the pressure is considered stable, and the coal seam gas pressure is calculated according to the numerical law Within 3 days, less than 0.015 MPa, considered stable pressure, according to the numerical law to calculate the coal seam gas pressure P , unit: MPa; 1) when > 0, determine the gas pressure of the coal seam P by formula (1) and formula (2): ； ； θ P - gas pressure in coal seam, Pa; P 1 - water pressure in the section of the coal body surface, Pa; P 2 - precise pressure indication, Pa; n - number of sections of the measuring tube, 2 m per section; θ 1 - inclination of the borehole, °; - density of water in the measuring tube, taken as 1.0 g / cm 3 ; g - acceleration of gravity, m / s 2 ; 2) When P 2=0, open the drain valve, start the micro-pump to slowly drain the water in the pressure pipe, reduce the actual water pressure in the pressure pipe by shortening the water length, and control the micro-pump manually to extract a small amount of water at a time, with a volume of V , unit: cm 3 , and the water volume extracted each time is V , which is the water volume in the pressure pipe with a water length of l . According to formula (3), close the drain valve and micro-pump after each extraction and drainage, and observe the reading of the precision pressure gauge. ； In formula (3), r R is the radius of the pressure tube in cm. a. If the reading of the precision pressure gauge is shown within 10 h, continue to observe, and record the gauge pressure after the pressure is stable P 2; According to the water pressure in the pressure pipe P 1, the amount of water drawn V and the gauge pressure P 2 data, calculate the true measured coal seam gas pressure according to formula (4) P : ； b.If the precision pressure gauge still has no reading within 10 h, reopen the drain valve, start the micro water pump to slowly drain the water in the pressure pipe, always keep the water volume extracted each time V , close the drain valve and the micro water pump in turn after the drainage is completed, repeat the water release and observation of the precision pressure gauge reading, when the precision pressure gauge shows a reading within 10 h of water drainage, the drainage work is completed, and the number of drainage times is recorded N ; according to N times of drainage process, calculate the total drainage water volume, and calculate the real measured coal seam gas pressure according to formula (5) P : ； in formula (4) and formula (5): P — Coal seam gas pressure, Pa; P 1— Actual water pressure of the pressure measuring tube acting on the water section of the coal body surface, Pa; P 2— Precision pressure display number, Pa; n — Number of sections of the pressure measuring tube, 2 m per section; The active water injection process in the step F is that the high-pressure stop valve is opened, the first high-pressure rubber pipe and the underground water supply pipeline are connected, the water drainage valve is opened at the same time, the pressure measuring tube is connected with the external environment, the water injection valve is opened to inject water into the pressure measuring tube, the water drainage state is closely observed, the active water injection process is ended when the micro water pump connected with the water drainage valve has water drained, and the water injection valve and the water drainage valve are sequentially closed, and the downward pressure measuring drill hole is filled with water from the water injection valve to the bottom of the downward pressure measuring drill hole. 1— Drilling inclination, °; — Density of water in the pressure measuring tube, 1.0 g / cm 3 ; g — Acceleration of gravity, m / s 2 ; V — Length of water volume automatically extracted by the micro water pump at one time, cm l ; 3 ; N — Number of times of extraction and discharge by the micro water pump; r — Radius of the pressure measuring tube, cm.

2. The testing method of the downward drilling coal seam gas pressure active measuring device according to claim 1, characterized in that, ​ 3. A testing method of a downward drilling coal seam gas pressure active measuring device, which is realized by using the downward drilling coal seam gas pressure active measuring device, the downward drilling coal seam gas pressure active measuring device comprises a downward pressure measuring drilling hole constructed in a roadway floor, the downward pressure measuring drilling hole enters a measured coal seam and penetrates the measured coal seam to enter a coal seam floor, a plurality of pressure measuring tubes connected in sequence are placed in the downward pressure measuring drilling hole, a plurality of through holes are formed on a bottommost pressure measuring tube to form a pressure measuring flower tube, a topmost pressure measuring tube extends out of the roadway floor and is connected with a bottom port of a four-way connecting pipe, left and right ports of the four-way connecting pipe are connected with a water injection electromagnetic valve and a water drainage electromagnetic valve respectively, an upper port of the four-way connecting pipe is additionally connected with a pressure measuring air chamber pipe, the water injection electromagnetic valve is sequentially connected with a first high-pressure rubber pipe, an electromagnetic stop valve and a downhole water supply pipeline, the water drainage electromagnetic valve is connected with a micro water pump through a second high-pressure rubber pipe, a flow meter is arranged on the second high-pressure rubber pipe, the pressure measuring air chamber pipe is connected with a pressure sensor, and the water injection electromagnetic valve, the water drainage electromagnetic valve, the electromagnetic stop valve, the micro water pump, the flow meter and the pressure sensor are electrically connected with a PLC programmable controller. characterized in that The method comprises the following steps: A. Construction of the lower to the roadway floor in a suitable position to measure pressure borehole, record the borehole inclination θ 1. Drilling length, coal length, coal seam inclination, coal seam thickness; B. Take n section pressure measuring tube and make a pressure measuring flower tube from one of the sections; C. The pressure measuring flower tube and the remaining pressure measuring tubes are connected in sections, 1-2 groups of hole sealing capsules are bound on the pressure measuring tube connected with the pressure measuring flower tube, and the pressure measuring tubes are sent into the downward pressure measuring drilling hole together, and the pressure measuring tubes are placed in the hole mouth to the hole bottom of the downward pressure measuring drilling hole. D. Water or air is injected into the hole sealing capsules to make the hole sealing capsules expand and embrace the hole wall of the downward pressure measuring drilling hole, the pressure measuring tubes are supported, and the coal section and the rock section in the drilling hole are isolated, slurry is injected into the downward pressure measuring drilling hole, the slurry injection is stopped after the slurry fills the downward pressure measuring drilling hole, the position of the hole sealing capsule to the hole mouth of the downward pressure measuring drilling hole is ensured to have the slurry, and a sealing section is formed. E. After the slurry is solidified for 24 hours, the water injection electromagnetic valve, the water drainage electromagnetic valve and the pressure measuring air chamber pipe are connected with the top end of the pressure measuring tube through the four-way connecting pipe, the water injection electromagnetic valve is sequentially connected with the first high-pressure rubber pipe, the electromagnetic stop valve and the downhole water supply pipeline, the other end of the water drainage electromagnetic valve is sequentially connected with the flow meter and the micro water pump, the other end of the pressure measuring air chamber pipe is installed with the pressure sensor, and the electromagnetic stop valve, the water injection electromagnetic valve, the pressure sensor, the water drainage electromagnetic valve, the flow meter and the micro water pump are electrically connected with the PLC programmable controller. F. The downward pressure measuring drilling hole is automatically controlled to be actively injected with water: the electromagnetic stop valve is automatically opened through the PLC programmable controller, the first high-pressure rubber pipe and the downhole water supply pipeline are connected, the water drainage electromagnetic valve is opened at the same time, the pressure measuring tube is connected with the external environment, the water injection electromagnetic valve is opened to inject water into the pressure measuring tube, the water drainage state of the water drainage electromagnetic valve is closely observed, the water injection electromagnetic valve and the water drainage electromagnetic valve are automatically closed in sequence when the flow meter displays the flow, at this time, the downward pressure measuring drilling hole is filled with water from the water injection electromagnetic valve to the hole bottom, and the active water injection process is completed. The water volume of active water injection forms a water column in the pressure pipe, and water pressure is generated due to its own gravity P 1; water pressure P 1 refers to the length of the water section actually acting directly on the surface of the coal body L The generated pressure, L refers to the length from the bottom end of the water injection electromagnetic valve and the drainage electromagnetic valve to the bottom end of the pressure measuring pipe, that is, n The total length of the section pressure pipe, the length of each section pressure pipe is 2m, L=2n ; G.When the pressure sensor shows P 2Less than 0.015 MPa in 3 days, considered as stable pressure, calculate the coal seam gas pressure according to the numerical law P , unit: MPa; 1) when P 2 > 0, measure the gas pressure of the coal seam P Calculate by formula (1) and formula (2): ； ； In formula (1) and formula (2): P - gas pressure in coal seam, Pa; P 1 - water pressure in the section of the coal body surface, Pa; P 2 - precise pressure reading, Pa; n - number of sections of the measuring tube, 2 m per section; θ 1 - inclination of the borehole, °; - density of water in the measuring tube, taken as 1.0 g / cm 3 ; g - acceleration of gravity, m / s 2 ; 2) When P 2=0, the drain electromagnetic valve is automatically opened, the micro water pump is started to slowly pump out the water in the pressure measuring pipe, the actual water pressure acting on the coal surface in the pressure measuring pipe is reduced by shortening the water length, and the PLC programmable controller is used to control the micro water pump to pump out a small amount of water at a time. The water volume is monitored through the flow meter, and the water volume pumped out each time is V , which is cm 3 . The water volume in the pressure measuring pipe with a water length of l is calculated according to formula (3). After each pumping and discharging is completed, the drain electromagnetic valve and the micro water pump are closed, and the reading of the monitoring pressure sensor is monitored. ； In formula (3), r R is the radius of the pressure tube in cm. a. If the pressure sensor shows readings within 10 h, continue monitoring, and record the gauge pressure after the readings are stable P 2; According to the water pressure in the pressure pipe P 1, the amount of water drawn V and gauge pressure P 2 data, calculate the true measured coal seam gas pressure according to formula (4) P : ； b.If the pressure sensor still has no reading within 10h, open the drain electromagnetic valve automatically, restart the micro water pump to slowly pump out the water in the pressure pipe, and the automatic water extraction volume is always V After the pumping is completed, close the drain electromagnetic valve and the micro water pump in turn; repeat the water release and observe the pressure sensor reading, and when the pressure sensor shows a reading within 10h of pumping, the pumping work is completed, and the pumping frequency is recorded N times; according to N times of pumping process, calculate the total pumped water volume, and calculate the real measured coal seam gas pressure according to formula (5) P : ； In formula (4) and formula (5): P — Coal seam gas pressure, Pa; P 1— Actual water pressure of the pressure measuring tube acting on the water section of the coal body surface, Pa; P 2— Pressure sensor reading, Pa; n — Number of sections of the pressure measuring tube, 2 m per section; θ 1— Drilling inclination, °; — Density of water in the pressure measuring tube, 1.0 g / cm 3 ; g — Acceleration of gravity, m / s 2 ; V — Length of water volume automatically extracted by the micro water pump at one time, cm l ; 3 ; N — Number of times of extraction and discharge by the micro water pump; r — Radius of the pressure measuring tube, cm.

4. The testing method of the apparatus for active determination of gas pressure in a coal seam in a downward drill hole according to claim 1 or 3, characterized in that, The surface of the pressure measuring flower tube in step B is bound with fine and dense mesh window screens to prevent coal dust from entering the pressure measuring flower tube through the small holes.

5. The testing method of the apparatus for active determination of gas pressure in a coal seam in a downward drill hole according to claim 1 or 3, characterized in that, Hole sealing capsules are arranged outside the pressure measuring tube at the junction of the rock section of the downward pressure measuring drilling hole and the measured coal seam.

6. The testing method of the apparatus for active determination of gas pressure in a coal seam in a downward drill hole according to claim 1 or 3, characterized in that, The pressure measuring pipe is made of a hollow circular pipe, the length of the hollow circular pipe is 2 m, and the inner diameter is 12.7 mm.

7. The testing method of the apparatus for active determination of gas pressure in a coal seam in a downward drill hole according to claim 1 or 3, characterized in that, The length from the bottom end of the pressure measuring pipe to the bottom of the downward pressure measuring borehole is 0.5 m, and the top end of the pressure measuring pipe is 0.5 m higher than the length of the roadway floor.

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