A method for predicting the original coal seam gas pressure

Abstract

The present invention provides a method for predicting the original coal seam gas pressure, comprising: (1) opening a central extraction hole A on the coal wall, sealing the hole, measuring the original coal seam gas pressure a, the gas pressure change rate A j , (2) Eight surrounding extraction holes B are set around the central extraction hole A i , the surrounding extraction hole B i The hole is sealed and the coal seam gas pressure C is measured. j , control coal seam gas pressure B j (B j =a+C j );(3) Drill the surrounding extraction hole B i The porosity of the circular coal pillar obtained by measuring the porosity P j , (4) The obtained data is the change rate of the hole wall gas pressure A j , coal seam gas pressure B j , coal pillar porosity P j , establish the formula relationship, and know the change rate of the hole wall gas pressure A j , coal pillar porosity P j Obtain coal seam gas pressure B j . The problem that the original coal seam gas pressure cannot be predicted and the pressure of the nitrogen gas source is too high or too low is solved.

Description

Technical Field

[0001] The present invention relates to a method for predicting the original coal seam gas pressure. Specifically, the porosity of the coal seam and the rate of change of the pore wall gas pressure are used as variables. The formula obtained by the experiment is applied to obtain an estimated value of the coal seam gas pressure. Based on the obtained estimated value, isobaric nitrogen is filled into the borehole to achieve rapid equilibrium of the gas pressure. Background Art

[0002] Predicting coal seam gas pressure is very important in studying and evaluating gas reserves, gas outburst, gas flow, gas extraction and gas outburst. At present, some achievements have been made in the study of active gas replenishment pressure measurement. When the gas pressure of coal seams is directly measured by drilling method, a certain amount of gas is released during the hole forming process. If the gas supply in the coal seams around the hole is relied on after the hole is sealed, it often takes a long time. Active gas replenishment can shorten this period of time, especially for low permeability coal seams. However, if the active gas replenishment pressure is too high or too low, pressure attenuation or pressure recovery will occur. Therefore, the closer the gas replenishment pressure is to the original gas pressure of the coal seam, the more conducive it is to rapid pressure measurement. However, the problem of how to predict coal seam gas pressure has not yet been solved. The predecessors estimated the pressure value of the measuring point in advance based on the pressure measurement data of the previous pressure measurement location or the pressure measurement data of the same area and depth, and selected the gas source pressure close to the original gas pressure of the coal seam as much as possible for gas replenishment operation. However, in actual operation, the work efficiency is often reduced because of the need to blindly adjust the pressure value. Summary of the invention

[0003] The purpose of the present invention is to provide a method for predicting the original coal seam gas pressure, so as to solve the problem that the original coal seam gas pressure cannot be predicted and the pressure of the nitrogen gas source is too high or too low.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] Under the action of different coal seam gas pressures, the gas seepage rate in the borehole is different. Based on this principle, this experiment conducts the following experiments to establish the relationship between the gas pressure change rate, coal seam permeability and coal seam gas pressure.

[0006] Specifically, a method for predicting the original coal seam gas pressure includes the following steps:

[0007] (1) A central drainage hole A is opened on the coal wall, and the central drainage hole A is sealed. An electronic pressure gauge is first connected to the central drainage hole A. After the pressure indication is stable, the borehole gas pressure a is measured for the first time. Then, the change law of the gas pressure in the borehole with time is continuously recorded, and the gas pressure change rate A is calculated. j , where j = 1, 2, 3, 4, ...;

[0008] (2) Arrange eight drainage holes B around the central drainage hole A i , where i = I, II, III, IV… Seal the surrounding drainage holes B i , and connect a gas bottle with an electronic pressure gauge into the surrounding drainage hole B i . Control the coal seam gas pressure C filled into the surrounding drainage hole B by adjusting the rotary valve i , where j = 1, 2, 3, 4… Thus, control the coal seam gas pressure B j (B j = a + C j ); j )

[0009] (3) Label the circular coal pillar obtained when drilling the surrounding drainage hole B i and take it back to the laboratory for porosity measurement to obtain the porosity P j , where j = 1, 2, 3, 4…;

[0010] (4) For the obtained data, the gas pressure change rate A of the hole wall j , the coal seam gas pressure B j , and the coal pillar porosity P j , where j = 1, 2, 3, 4…, establish a formula relationship according to the on-site test data. Given the gas pressure change rate A of the hole wall j and the coal pillar porosity P j , obtain the coal seam gas pressure B j .

[0011] Specifically: The central drainage hole A and the surrounding drainage holes B i both have a hole diameter of 94 mm and a hole depth of 20 m, and are arranged perpendicular to the working face

[0012] The sealing method is capsule sealing

[0013] The surrounding drainage holes B i are arranged in a circular pattern

[0014] The distance between the central drainage hole A and the surrounding drainage holes B i is 1.5 m. That is, with the central drainage hole A as the center and a radius of 1 m, determine the position of the surrounding drainage holes B i ;

[0015] The central drainage hole A and the surrounding drainage holes B i are drilled using a drilling rig

[0016] When using the above technical method for active air supplement pressure measurement, it is no longer necessary to pre-estimate the pressure value of the measurement point based on the pressure measurement data of the previous pressure measurement location or the pressure measurement data of the same depth in the same area. Only the gas pressure change rate A of the borehole wall needs to be obtained. j , the porosity P of the coal pillar j Calculate the coal seam gas pressure B j , and fill nitrogen with a pressure of B j into the borehole to achieve the purpose of filling the nitrogen pressure closest to the original coal seam pressure, so that the gas pressure quickly reaches equilibrium. Description of the drawings

[0017] Figure 1 Schematic diagram of the central drainage hole drilled for the present invention;

[0018] Figure 2 Schematic diagram of the peripheral drainage holes of the present invention. Detailed implementation manners

[0019] The following takes a coal seam that is easy to drain as an example, and the present invention will be described in detail with reference to the accompanying drawings.

[0020] (1) Preparation before construction

[0021] 1) One drilling rig, 25 m of drill pipes, 3 alloy drill bits;

[0022] 2) One 20 m tape measure and one angle measuring instrument;

[0023] Several capsules for hole sealing and one high-pressure water pump;

[0024] One electronic pressure gauge for measuring gas pressure.

[0025] Construction steps:

[0026] Select a working face in a relatively straight and debris-free roadway as the on-site test location, and transport the construction equipment and hole-sealing materials to the vicinity of the test location.

[0027] As Figure 1 shown, find a position on the working face 1 to first arrange a central drainage hole A2. After arranging a pressure measurement pipe 4 in the central drainage hole, immediately inject high-pressure water into the hole-sealing capsule 3 for hole sealing. Then, connect an electronic pressure gauge 5 to the outer end of the pressure measurement pipe. After the reading of the electronic pressure gauge is stable, the original coal seam gas pressure a can be known.

[0028] Drill the first peripheral drainage hole B I 8 at a distance of 1.5 m from the central drainage hole A2, and quickly in the peripheral drainage hole B IAfter arranging the gas pipeline 9 inside, immediately inject high-pressure water into the sealing capsule 7 for hole sealing. An electronic pressure gauge 10 for checking the gas pressure at the outlet of the gas bottle is connected to the gas pipeline. The outer end of the gas pipeline is connected to the gas bottle 11, and then open the gas bottle valve 14 to pump gas into the surrounding drainage hole B I with a gas pressure of 0.4 MPa

[0029] Label and collect the coal pillar obtained when drilling the first surrounding drainage hole B I and take it back to the laboratory to measure its porosity

[0030] Through the above operations, a set of data on the gas pressure change rate A 1 , coal seam gas pressure B 1 , and porosity P 1 can be obtained

[0031] Drain the high-pressure water in the sealing capsule 7 to prepare for the next set of experiments

[0032] Next, as Figure 2 shown, arrange the second surrounding drainage hole B I at a distance of 21.5 m from the central drainage hole A and at a position 45° clockwise from the straight line AB II 12. Quickly arrange the gas pipeline 9 inside the surrounding drainage hole B II and immediately inject high-pressure water into the sealing capsule 7 for hole sealing. An electronic pressure gauge 10 for checking the gas pressure at the outlet of the gas bottle is connected to the gas pipeline. The outer end of the gas pipeline is connected to the gas bottle 11, and then open the gas bottle valve 14 to pump gas into the surrounding drainage hole B II with a gas pressure of 0.6 MPa. Different coal seam gas pressure change rates A 2 will be obtained at different coal seam gas pressures

[0033] Label and collect the coal pillar obtained when drilling the second surrounding drainage hole B II and take it back to the laboratory to measure its porosity

[0034] Through the above operations, a set of data on the gas pressure change rate A 2 , coal seam gas pressure B 2 , and porosity P 2 can be obtained

[0035] Drain the high-pressure water in the sealing capsule 7 to prepare for the next set of experiments

[0036] Next, drill the third surrounding drainage hole B II at a distance of 21.5 m from the central drainage hole A and at a position 45° clockwise from the straight line AB III 13. Quickly arrange the gas pipeline 9 inside the surrounding drainage hole B IIIAfter arranging the gas pipeline 9 inside and immediately injecting high-pressure water into the sealing capsule 7 for hole sealing, an electronic pressure gauge 10 for checking the gas pressure at the outlet of the gas bottle is connected to the gas pipeline. The outer end of the gas pipeline is connected to the gas bottle 11, and then the gas bottle valve 14 is opened to pump gas into the surrounding drainage hole B III with gas at a pressure of 0.8 MPa. Different coal seam gas pressure change rates A will be obtained under different coal seam gas pressures 3 .

[0037] Label and collect the coal pillar obtained when drilling the third surrounding drainage hole B III and take it back to the laboratory to measure its porosity.

[0038] Through the above operations, a set of gas pressure change rates A 3 , coal seam gas pressures B 3 , and porosities P 3 of data can be obtained.

[0039] Drain the high-pressure water in the sealing capsule 7 to prepare for the next set of experiments.

[0040] Repeat the above steps until the data recording of the eighth group of surrounding drainage holes is completed. Use numerical analysis software to process these eight groups of data and solve the formula among the three. Thus, the original gas pressure of the coal body can be calculated and predicted based on the internal gas pressure change rate after borehole sealing and the coal body porosity parameter.

[0041] The method of the present invention is simple and easy to understand. According to the relationship between the coal seam gas pressure, the change rate of borehole gas pressure, and the porosity, the original coal seam gas pressure is accurately predicted. Based on the predicted gas pressure, the active pressure measurement and gas injection pressure are determined, greatly shortening the gap between the theoretical value and the actual value of gas injection during the active pressure measurement process and shortening the gas pressure balance time.

Claims

1. A method for predicting the gas pressure of the original coal seam, characterized in that, it includes the following steps: (1)A central drainage hole A is drilled in the coal wall, and the central drainage hole A is sealed. First, an electronic pressure gauge is connected into the central drainage hole A. After the pressure gauge reading stabilizes, the gas pressure a in the borehole is measured for the first time. Subsequently, the change law of the gas pressure in the borehole with time is continuously recorded, and the gas pressure change rate A is calculated. j , where j = 1, 2, 3, 4...; (2) Arrange eight surrounding gas drainage holes B around the central gas drainage hole A i , where i = I, II, III, IV… Seal the surrounding gas drainage holes B i . Connect a gas cylinder with an electronic pressure gauge into the surrounding gas drainage hole B i , and control the coal seam gas pressure C i filled into the surrounding gas drainage hole B by adjusting the rotary valve j , where j = 1, 2, 3, 4…, thus controlling the coal seam gas pressure B j (B j = a + C j ); (3) Label the circular coal pillar obtained when drilling the surrounding drainage holes B i and bring it back to the laboratory for porosity measurement to obtain the porosity P j , where j = 1, 2, 3, 4…; (4) The obtained change rate A of the gas pressure in the data hole wall j , the gas pressure B in the coal seam j , the porosity P of the coal pillar j , where j = 1, 2, 3, 4…, establish a formula relationship based on the on-site test data. Given the change rate A of the gas pressure in the hole wall j , the porosity P of the coal pillar j obtain the gas pressure B in the coal seam j .

2. The method for predicting the gas pressure of the original coal seam according to claim 1, characterized in that: Central gas drainage hole A and surrounding gas drainage holes B i The hole diameter is 94 mm for all, the hole depth is 20 m, and they are arranged perpendicular to the working face.

3. The method for predicting the gas pressure of the original coal seam according to claim 1, characterized in that: The hole sealing method is capsule hole sealing.

4. The method for predicting the gas pressure of the original coal seam according to claim 1, characterized in that: Peripheral drainage hole B i is arranged in a circular pattern.

5. The method for predicting the gas pressure of the original coal seam according to claim 1, characterized in that: The central drainage hole A and the surrounding drainage holes B around it i are 1.5 m apart.

6. The method for predicting the gas pressure of the original coal seam according to claim 1, characterized in that: The central drainage hole A and the surrounding drainage holes B i are formed by drilling with a drilling rig.

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