A ground drilling coal reservoir gas pressure water seal type measuring system and method

Abstract

The present application belongs to the technical field of coal mining, and discloses a ground drilling coal reservoir gas pressure water sealing type measuring system and method. The system comprises a monitoring control device arranged on the ground and a gas pressure measuring device arranged in a measuring drill hole. The gas pressure measuring device comprises a drain pipe assembly vertically arranged in the measuring drill hole. The drain pipe assembly comprises an upper drain pipe and a lower drain pipe. The upper drain pipe is coaxially communicated with the lower drain pipe through a sealing device. The lower end of the lower drain pipe is connected with a water pumping device. The device provides a closed measuring space capable of stably measuring gas pressure for gas pressure testing of the coal reservoir in an unmined area through structural design. The measurement of gas pressure is completed by a gas pressure sensor arranged in the closed measuring space. The method cooperatively performs water drainage and measurement. By retaining a certain liquid level in the measuring drill hole, water sealing testing of the gas gathering area is realized.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically relating to a water-sealed measurement system and method for gas pressure in coal reservoirs obtained through surface drilling. Background Technology

[0002] Coal reservoir gas pressure is one of the fundamental parameters of mine gas, and it is of great significance for determining the gas content of coal reservoirs, controlling mine gas outbursts, gas drainage, and preventing coal and gas outbursts. In existing technologies, direct measurement of underground coal reservoir gas pressure mainly involves drilling a cross-layer measuring borehole from the bottom rock roadway of the coal reservoir into the reservoir. After completion, a pressure gauge is inserted into the borehole, and the borehole opening is sealed. Since there is no liquid inside the borehole, the pressure inside gradually balances with the formation pressure, and the pressure gauge can continuously record the pressure change process, ultimately obtaining a value approximating the formation gas pressure. The drawback of this method is that the gas pressure measured underground is greatly affected by mining operations, and the formation / coal reservoir has already undergone water drainage treatment, so the measured gas pressure is not the original gas pressure of the coal reservoir.

[0003] Measuring gas pressure through surface boreholes in unmined areas can yield values ​​close to the original gas pressure. However, since no mines have been built in these areas, the coal reservoirs / formations in the surface boreholes contain water. After drilling, the boreholes are filled with liquid. Under the pressure of the liquid column, the gas in the coal reservoir does not desorb. Furthermore, the water in the boreholes is supplied by the coal reservoirs / formations. Therefore, the following problems arise: If the liquid in the borehole is drained and the pressure gauge is lowered after the gas begins to desorb, the borehole will quickly be filled with water from the coal reservoirs / formations. The gas will stop desorbing under the pressure of the liquid column, making it difficult for the pressure gauge to obtain stable gas pressure data. If the water in the coal reservoirs / formations is drained, the gas will continue to desorb and release over a long period, making it difficult for the pressure gauge to reflect the original gas pressure situation in the formation.

[0004] Therefore, the key and difficult point in measuring gas pressure through ground-based boreholes is how to reduce coal reservoir pressure to promote gas desorption while ensuring that the gas does not diffuse or escape. In other words, how to provide a sealed space for gas accumulation that can measure stable gas pressure is the key technology and difficulty in measuring gas pressure. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a water-sealed measurement system and method for coal reservoir gas pressure in surface boreholes, thereby resolving the technical problem in the prior art of accurately obtaining the original formation gas pressure when measuring gas pressure in surface boreholes in unmined areas.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A ground-drilled coal reservoir gas pressure water-sealed measurement system includes a monitoring and control device installed on the ground and a gas pressure measuring device installed in the measuring borehole. The gas pressure measuring device includes a drainage pipe assembly vertically installed in the measuring borehole. The drainage pipe assembly includes an upper drainage pipe and a lower drainage pipe. The upper drainage pipe is coaxially connected to the lower drainage pipe via a sealing device. A pumping device is connected to the lower end of the lower drainage pipe.

[0008] The sealing device expands outward along the radial direction of the measuring borehole and can fit against the borehole wall.

[0009] A gas pressure sensor is installed below the sealing device; a density sensor is installed outside the lower drain pipe; and a liquid pressure sensor is installed below the suction inlet of the pumping device.

[0010] The monitoring and control device is connected to the pumping device, gas pressure sensor, liquid pressure sensor, density sensor and sealing device via cables.

[0011] The present invention also has the following technical features:

[0012] Specifically, the sealing device includes a sealing device body and an elastic rubber sleeve fitted outside the sealing device body, and a drain outlet is provided on the side wall of the sealing device body where the elastic rubber sleeve is located;

[0013] The enclosure body is provided with an axially penetrating drainage hole and a cable hole, and the two ends of the drainage hole are respectively connected to an upper drainage pipe and a lower drainage pipe.

[0014] The sealing device body is also equipped with a booster pump. The inlet of the booster pump is connected to the sealing liquid suction port opened on the upper surface of the sealing device body, and the outlet of the booster pump is connected to the drain outlet.

[0015] Furthermore, the vertical distance between the density sensor and the upper surface of the pumping device is 10 meters.

[0016] Furthermore, the vertical distance between the liquid pressure sensor and the bottom surface of the pumping device is 0.5 to 1 meter.

[0017] This invention also discloses a method for measuring the gas pressure of coal reservoirs using a water seal method based on surface borehole drilling. This method is implemented using the aforementioned surface borehole coal reservoir gas pressure water seal measurement system and includes the following steps:

[0018] Step 1: Construct a gas pressure measurement borehole, wherein the distance between the bottom of the measurement borehole and the top boundary of the coal reservoir is greater than 20m;

[0019] Step 2: Insert the gas pressure measuring device into the gas pressure measuring borehole, and then connect the gas pressure measuring device and the monitoring and control device.

[0020] Step 3: Control the elastic rubber sleeve of the sealing device to expand radially along the measuring borehole and fit against the borehole wall using the monitoring and control device;

[0021] Step 4: Use a pumping device to drain the coal reservoir. During the drainage process, a sealed measurement space is formed between the liquid level in the gap between the drain pipe and the measuring borehole and the bottom surface of the sealed device body. Continue to drain until the liquid level in the sealed air pressure measurement area drops to between the water inlet of the pumping device and the density sensor, and the distance from the top boundary of the coal reservoir is 10 to 20 meters.

[0022] Step 5: After continuously measuring the gas pressure in the sealed measurement space using a gas pressure sensor, control the elastic rubber sleeve to contract via a monitoring and control device to remove the gas pressure measuring device.

[0023] Furthermore, step 4 specifically includes the following:

[0024] Step 4.1: Determine the dynamic liquid level height in the drain pipe assembly based on the liquid pressure collected by the liquid pressure sensor in the drain pipe.

[0025] Step 4.2: Drain the liquid level at the preset drainage rate to reduce the coal reservoir pressure to the coal reservoir desorption pressure, and the coal reservoir will begin to desorb and produce gas.

[0026] Step 4.3: Based on the relationship model between the liquid level descent rate in the sealed measurement space and the dynamic liquid level in the drain pipe, the liquid level descent rate and height in the sealed measurement space are controlled by controlling the dynamic liquid level descent rate and height in the drain pipe, so that the liquid level in the sealed measurement space is reduced to between the water inlet of the pumping device and the density sensor, and the distance from the top boundary of the coal reservoir is 10-20m.

[0027] Furthermore, the relationship model between the rate of decrease of the liquid level in the sealed measurement space and the height of the dynamic liquid level is as follows:

[0028]

[0029] in,

[0030] v represents the rate at which the liquid level in the sealed measurement space decreases, measured in m / d.

[0031] ρ is the density of the liquid, with units of kg / m³. 3 ;

[0032] H is the height of the dynamic liquid level, in meters (m).

[0033] P is the gas pressure in the confined space, measured in MPa.

[0034] t represents time, expressed in days (d).

[0035] g is the acceleration due to gravity, with a value of 9.8 N / kg.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] (1) The device of the present invention provides a closed measurement space for gas pressure testing of coal reservoirs in unmined areas through structural design. The gas pressure is measured by a gas pressure sensor set in the closed measurement space. The device has a simple structure and is easy to use. It solves the problem that the existing technology cannot accurately measure gas pressure from the ground and obtain the original coal reservoir parameters.

[0038] (2) The device of the present invention can effectively avoid the influence of water from the upper strata of the coal reservoir on the measurement pressure by sealing the measurement point with the help of the sealing device. It only seals the area where the coal reservoir is located, avoiding the replenishment of water into the borehole by other strata, and greatly reducing the difficulty of pumping water.

[0039] (3) The method of the present invention combines drainage and measurement. By maintaining a certain liquid level in the measurement borehole, a water seal is achieved in the gas accumulation area, thereby obtaining the original gas pressure parameters of the unmined area. The gas pressure parameters of the unmined area that are not affected by mining can be measured through the ground borehole, providing parameters for coal reservoir gas extraction, gas disaster prevention and control, and coal and gas outburst risk identification.

[0040] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention;

[0042] Figure 2 This is a cross-sectional view of the enclosed device;

[0043] Figure 3 This is a schematic diagram of the adjustment process for the rate of liquid level descent in the sealed measurement space in Example 2.

[0044] The labels in the diagram represent:

[0045] 1-Drainage pipe assembly, 2-Liquid pressure sensor, 3-Pumping device, 4-Gas pressure sensor, 5-Density sensor;

[0046] 11-Upper drain pipe, 12-Lower drain pipe, 13-Sealing device;

[0047] 131-Sealing device body, 132-Elastic rubber sleeve, 133-Drainage through hole, 134-Cable through hole, 135-Booster, 136-Sealed liquid suction port, 137-Drain port.

[0048] The specific content of the present invention will be further explained in detail below with reference to the accompanying drawings and specific embodiments. Detailed Implementation

[0049] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0050] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "bottom," and "top" are generally defined based on the drawing surface of the corresponding figure, while "inner" and "outer" are defined based on the outline of the corresponding figure.

[0051] Example 1

[0052] Following the above technical solution, such as Figure 1 As shown, this embodiment discloses a monitoring and control device installed on the ground and a gas pressure measuring device installed in a measuring borehole. The gas pressure measuring device is used to collect gas pressure, liquid pressure, and gas-liquid medium information in the measuring borehole and transmit the collected information to the monitoring and control device. The monitoring and control device is used to control the operation of the gas pressure measuring device and to receive the data collected by the gas pressure measuring device.

[0053] The gas pressure measuring device includes a drainage pipe assembly 1 vertically installed in the measuring borehole. The drainage pipe assembly 1 includes an upper drainage pipe 11 and a lower drainage pipe 12. The upper drainage pipe 11 is coaxially connected to the lower drainage pipe 12 via a sealing device 13. The lower end of the lower drainage pipe 12 is connected to a pumping device 3. The pumping device 3 is used to drain water from the measuring borehole. The water pumped out by the pumping device 3 is discharged to the ground through the lower drainage pipe 12, the sealing device, and the upper drainage pipe.

[0054] After the sealing device 13 expands outward along the radial direction of the measuring borehole, it can fit against the borehole wall of the measuring borehole, thereby achieving the sealing and fixing between the sealing device 13 and the borehole wall of the measuring borehole.

[0055] A gas pressure sensor 4 is installed below the sealing device 13; a density sensor 5 is installed outside the drain pipe 12; a liquid pressure sensor 2 is installed below the pumping device 3; the density sensor 5 is used to measure the type of fluid medium above the pumping device 3. When the medium is water, the density sensor 5 transmits a signal to the monitoring and control device. The monitoring and control device has an existing control program that can determine the formation water situation based on the pumping volume and pumping time of the pumping device 3, send a control signal to the pumping device 3, control the pumping device 3 to operate to pump water or adjust the pumping volume, and control the liquid level in the sealed area to drop. When the medium is gas, the sensor transmits a signal to the monitoring and control device, and the monitoring and control device controls the pumping device 3 to reduce the pumping rate or stop pumping.

[0056] The monitoring and control device is connected to the pumping device 3, gas pressure sensor 4, liquid pressure sensor 2, density sensor 5, and sealing device 13 via cables. Gas pressure sensor 4 is used to measure the pressure of gas accumulated in the upper part of the sealed space. Density sensor 5 is used to measure the density of the medium, and the type of medium can be determined by the measured density.

[0057] The sealing device 13 can expand or contract radially along the measuring borehole under the control of the monitoring and control device.

[0058] As a preferred embodiment, the sealing device 13 includes a sealing device body 131 and an elastic rubber cylinder 132 sleeved outside the sealing device body 131. A drain port 137 is provided on the side wall of the sealing device body 131 where the elastic rubber cylinder 132 is located. When liquid enters the elastic rubber cylinder 132 through the drain port 137, the elastic rubber cylinder 132 expands and deforms, thereby realizing the expansion of the sealing device 13 along the radial direction of the measuring borehole.

[0059] The main body 131 of the sealing device is provided with an axially penetrating drainage hole 133 and a cable through hole 134. The two ends of the drainage hole 133 are respectively connected to the upper drainage pipe 11 and the lower drainage pipe 12; a cable is passed through the cable through hole 134.

[0060] The sealing device body 131 is also equipped with a booster pump 135. The inlet of the booster pump 135 is connected to the sealing liquid suction port 136 opened on the upper surface of the sealing device body 131. The outlet of the booster pump 135 is connected to the drain port 137. The booster pump 135 draws in the well fluid above the sealing device body 131 through the sealing liquid suction port, compresses and pressurizes it, and then sends it into the gap between the sealing device body 131 and the elastic rubber cylinder 132 through the drain port 137, causing the elastic rubber cylinder 132 to expand and deform.

[0061] As a preferred embodiment, the vertical distance between the density sensor 5 and the upper surface of the pumping device 3 is 10 meters.

[0062] As a preferred embodiment, the vertical distance between the liquid pressure sensor 2 and the bottom surface of the pumping device 3 is 0.5 to 1 meter.

[0063] The process of using the device of the present invention is as follows:

[0064] For the construction of a gas pressure surface measurement borehole, the distance between the bottom of the borehole and the top boundary of the coal reservoir is greater than or equal to 20m. The gas pressure measuring device is installed at the front end of the pumping pipe and lowered into the borehole, with the lower edge of the sealing device 0-2m away from the top plate of the coal reservoir. Then, the gas pressure measuring device and the surface monitoring and control device are connected. The monitoring and control device controls the elastic rubber sleeve of the sealing device to expand radially along the measuring borehole and fit against the borehole wall, dividing the space on the upper and lower sides of the sealing device. The pumping device is used to drain the measuring borehole. Due to the operation of the sealing device, only water in the coal reservoir is drained. As the water is drained, the gas in the coal reservoir begins to desorb and accumulate on the lower side of the sealing device, which is continuously measured and recorded by the gas pressure sensor.

[0065] Example 2

[0066] This embodiment provides a water-sealed method for measuring the gas pressure in coal reservoirs through surface boreholes. This method is implemented using the water-sealed method for measuring the gas pressure in coal reservoirs through surface boreholes provided in Embodiment 1, and includes the following steps:

[0067] Step 1: Construct a gas pressure measurement borehole, wherein the distance between the bottom of the measurement borehole and the top boundary of the coal reservoir is greater than 20m;

[0068] Step 2: Insert the gas pressure measuring device into the gas pressure measuring borehole, and then connect the gas pressure measuring device and the monitoring and control device.

[0069] Step 3: Control the elastic rubber sleeve of the sealing device to expand radially along the measuring borehole and fit against the borehole wall using the monitoring and control device;

[0070] Step 4: Use a pumping device to drain the coal reservoir. As drainage proceeds, the liquid level in the drain pipe gradually decreases, and the pressure in the coal reservoir also gradually decreases. When the pressure approaches or falls below the desorption pressure of the coal reservoir, the coal reservoir begins to desorb gas. The gas accumulates in the annulus between the drain pipe below the sealing device and the borehole wall, pushing the liquid level in the annulus down. During drainage, a sealed measurement space is formed between the liquid level in the gap between the lower drain pipe and the measuring borehole and the bottom surface of the sealing device body. That is, the liquid level in the annulus achieves a water seal on the gas accumulation area. Continue drainage until the liquid level in the sealed gas pressure measurement area drops to between the inlet of the pumping device and the density sensor, and the distance from the top boundary of the coal reservoir is 10-20m. During the measurement process, the flow rate of the pumping device is adjusted to control the distance between the liquid level and the top boundary of the coal reservoir to be maintained within the range of 10-20m.

[0071] like Figure 3 As shown, in this embodiment, the adjustment of the liquid level descent rate in the sealed measurement space specifically includes the following sub-steps:

[0072] Step 4.1: Determine the dynamic liquid level height in the drain pipe assembly based on the liquid pressure collected by the liquid pressure sensor in the drain pipe.

[0073] Step 4.2: Drain the liquid level at the preset drainage rate to reduce the dynamic liquid level height, so that the coal reservoir pressure drops to the coal reservoir desorption pressure, and the coal reservoir begins to desorb and produce gas until the gas pressure sensor measures the gas pressure, indicating that gas is generated.

[0074] Step 4.3: Based on the established relationship model between the liquid level descent rate and the dynamic liquid level in the sealed measurement space, adjust the liquid level descent rate in the sealed measurement space so that the liquid level in the sealed measurement space is lowered to between the water inlet of the pumping device and the density sensor, and the distance from the top boundary of the coal reservoir is 10-20m.

[0075] The pumping volume control principle is based on the U-tube principle: the pressure measured by the liquid pressure sensor is the pressure at the bottom of the U-tube, denoted as ρgH. From this, the dynamic liquid level height H within the drain pipe assembly can be calculated, where ρgH = ρgh + P, and P is the gas pressure measured by the gas pressure sensor. Therefore, the liquid level height h in the annular space between the lower drain pipe and the orifice wall can be calculated, and its descent speed is:

[0076]

[0077] in,

[0078] v represents the rate at which the liquid level in the sealed measurement space decreases, measured in m / d.

[0079] ρ is the density of the liquid, with units of kg / m³. 3 ;

[0080] H is the height of the dynamic liquid level, in meters (m).

[0081] P is the gas pressure in the confined space, measured in MPa.

[0082] t represents time, expressed in days (d).

[0083] g is the acceleration due to gravity, with a value of 9.8 N / kg.

[0084] When v > 0 m / d, the descent rate of H is gradually reduced by controlling the flow rate. For example, the descent rate of H is adjusted to V = 1.5 m / d, 1 m / d, 0.5 m / d, and 0.2 m / d, until v approaches 0 m / d. When v < 0 m / d, V is adjusted to V = 2.5 m / d, 3 m / d, 3.5 m / d, and 4 m / d, until v approaches 0 m / d, thus achieving a "water seal".

[0085] Make v approach 0 m / d, and then make fine adjustments based on the V value. Use (V±0.01) m / d to adjust the rate of decrease / increase of the H value, and then use the V value to continuously fine adjust to keep h at this height, so as to keep the volume of the closed space stable and achieve "water seal".

[0086] v and V are calculated from the measurement results of the liquid pressure sensor and the gas pressure sensor. The density sensor is used to correct the measurement results to ensure that the part above the density sensor is a gas accumulation space.

[0087] Step 5: After detecting the gas pressure in the sealed measurement space using a gas pressure sensor, control the elastic rubber sleeve to contract via a monitoring and control device to remove the gas pressure measuring device.

[0088] In summary, the device of this invention provides a sealed measurement space for testing the gas pressure of coal reservoirs in unmined areas through its structural design, enabling the measurement of stable gas pressure. The gas pressure is measured by a gas pressure sensor installed in the sealed measurement space. The device has a simple structure and is easy to use, solving the technical problem of difficulty in accurately obtaining the original formation gas pressure when measuring gas pressure in ground boreholes in unmined areas in the prior art.

[0089] In the above description, unless otherwise explicitly specified and limited, terms such as "setup" and "connection" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections or indirect connections, etc. Those skilled in the art can understand the specific meaning of the above terms in this technical solution according to the specific circumstances.

[0090] The specific technical features described in the above embodiments can be combined in any suitable manner without contradiction, as long as they do not violate the spirit of the present invention, and should also be regarded as the content disclosed by the present invention.

Claims

1. A surface borehole coal reservoir gas pressure water seal measurement system, comprising a monitoring and control device installed on the ground, and a gas pressure measuring device installed in the measuring borehole, characterized in that, The gas pressure measuring device includes a drain pipe assembly (1) vertically installed in the measuring borehole. The drain pipe assembly (1) includes an upper drain pipe (11) and a lower drain pipe (12). The upper drain pipe (11) is coaxially connected to the lower drain pipe (12) via a sealing device (13). A pumping device (3) is connected to the lower end of the lower drain pipe (12). The sealing device (13) can fit against the borehole wall after expanding outward along the radial direction of the measuring borehole. A gas pressure sensor (4) is installed below the sealing device (13); a density sensor (5) is installed outside the drain pipe (12); a liquid pressure sensor (2) is installed below the suction port of the pumping device (3); The monitoring and control device is connected to the pumping device (3), gas pressure sensor (4), liquid pressure sensor (2), density sensor (5) and sealing device (13) via cables.

2. The surface borehole coal reservoir gas pressure water seal measurement system as described in claim 1, characterized in that, The sealing device (13) includes a sealing device body (131) and an elastic rubber tube (132) sleeved outside the sealing device body (131). A drain outlet (137) is provided on the side wall of the sealing device body (131) where the elastic rubber tube (132) is located. The enclosure body (131) is provided with an axially penetrating drainage hole (133) and a cable hole (134), and the two ends of the drainage hole (133) are respectively connected to an upper drainage pipe (11) and a lower drainage pipe (12); The sealing device body (131) is also equipped with a booster (135). The inlet of the booster (135) is connected to the sealing liquid suction port (136) opened on the upper surface of the sealing device body (131), and the outlet of the booster (135) is connected to the drain port (137).

3. The surface borehole coal reservoir gas pressure water seal measurement system as described in claim 1, characterized in that, The vertical distance between the density sensor (5) and the upper surface of the pumping device (3) is 10 meters.

4. The surface borehole coal reservoir gas pressure water seal measurement system as described in claim 1, characterized in that, The vertical distance between the liquid pressure sensor (2) and the bottom surface of the pumping device (3) is 0.5 to 1 meter.

5. A method for measuring gas pressure in coal reservoirs using a water seal in surface boreholes, characterized in that, This method is implemented using the ground borehole coal reservoir gas pressure water seal measurement system according to any one of claims 1 to 4, and includes the following steps: Step 1: Construct a gas pressure measurement borehole, wherein the distance between the bottom of the measurement borehole and the top boundary of the coal reservoir is greater than 20m; Step 2: Insert the gas pressure measuring device into the gas pressure measuring borehole, and then connect the gas pressure measuring device and the monitoring and control device. Step 3: Control the elastic rubber sleeve of the sealing device to expand radially along the measuring borehole and fit against the borehole wall using the monitoring and control device; Step 4: Use a pumping device to drain the coal reservoir. During the drainage process, a sealed measurement space is formed between the liquid level in the gap between the drain pipe and the borehole wall and the bottom surface of the sealing device body. Continue to drain until the liquid level in the sealed air pressure measurement area drops to between the water inlet of the pumping device and the density sensor, and the distance from the top boundary of the coal reservoir is 10 to 20 meters. Step 5: After continuously measuring the gas pressure in the sealed measurement space using a gas pressure sensor, control the elastic rubber sleeve to contract via a monitoring and control device to remove the gas pressure measuring device.

6. The water-sealed method for measuring gas pressure in coal reservoirs via surface boreholes as described in claim 5, wherein step 4 specifically includes the following: Step 4.1: Determine the dynamic liquid level height in the drain pipe assembly based on the liquid pressure collected by the liquid pressure sensor in the drain pipe. Step 4.2: Drain the liquid level at the preset drainage rate to reduce the coal reservoir pressure to the coal reservoir desorption pressure, and the coal reservoir will begin to desorb and produce gas. Step 4.3: Based on the established relationship model between the liquid level descent rate and the dynamic liquid level in the sealed measurement space, control the liquid level descent rate in the sealed measurement space so that the liquid level in the sealed measurement space is reduced to between the water inlet of the pumping device and the density sensor, and the distance from the top boundary of the coal reservoir is 10-20m.

7. The method for measuring gas pressure in coal reservoirs by water seal in surface boreholes as described in claim 6, characterized in that, The relationship model between the rate of drop of the liquid level in the sealed measurement space and the height of the dynamic liquid level is as follows: in, v represents the rate at which the liquid level in the sealed measurement space decreases, measured in m / d. ρ is the density of the liquid, with units of kg / m³. 3 ; H is the height of the dynamic liquid level, in meters (m). P is the gas pressure in the confined space, measured in MPa. t represents time, expressed in days (d). g is the acceleration due to gravity, with a value of 9.8 N / kg.

8. The method for measuring gas pressure in coal reservoirs by water seal in surface boreholes as described in claim 6, characterized in that, The preset drainage rate is 3m / d to 20m / d.

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