Coal seam ultra-long directional drilling gas extraction simulation experiment system and coal seam ultra-long directional drilling gas extraction simulation experiment method

Abstract

The invention discloses a coal seam ultra-long directional drilling gas extraction simulation experiment system and method.The system comprises a pipeline with the two ends closed and a plurality of coal sample tanks, the pipeline comprises an inner pipe and an outer pipe, holes are evenly formed in the pipe wall of the inner pipe, the outer pipe is coaxially arranged outside the inner pipe in a sleeving mode, and a negative pressure cavity is formed in the inner pipe; a first cavity is formed between the inner pipe and the outer pipe, a plurality of annular partition plates are arranged in the first cavity at equal intervals, and the annular partition plates divide the first cavity into a plurality of second cavities which are not communicated with one another; a gas inlet is formed in the pipe wall of the outer pipe corresponding to each second cavity, and is connected with a coal sample tank through a gas outflow pipeline; gas injection pipelines are further connected to the coal sample tanks, the gas injection pipelines of the adjacent coal sample tanks are communicated through a first pipeline, and a first valve and a first flow sensor are arranged on the first pipeline; a pressure measuring opening is formed in the gas outflow pipeline, and the pressure measuring openings of the adjacent coal sample tanks are connected through a second pipeline; a second flow sensor, a second valve and a mass flow meter are further arranged on the gas outflow pipeline; and a first pressure sensor is arranged in the negative pressure cavity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal seam gas extraction, and particularly relates to a coal seam super-long directional drilling gas extraction simulation experiment system and method. BACKGROUND

[0002] With the continuous deepening and expansion of coal mining, coal mine gas disasters are becoming increasingly serious, and gas extraction technology has become an important measure to ensure mine safety and improve coal mine production efficiency. By adopting appropriate extraction technology and methods, the risk of coal mine gas disasters can be effectively reduced, and the production efficiency and energy utilization efficiency of coal mines can be improved.

[0003] With the development of drilling technology and equipment, super-long directional drilling has been widely used. Super-long directional drilling has the advantages of controllable trajectory, long control distance, wide coverage, and high drilling utilization rate. In the actual super-long directional drilling gas extraction engineering, the gas extraction rate at the hole mouth is low, the gas extraction contribution rate at the front of the drilling is low, and the gas extraction volume is mainly provided by the deep part of the drilling. The uneven gas extraction contribution rate in the drilling is closely related to the change of positive and negative pressure in the hole. Exploring the gas pressure gradient and migration law in the super-long directional drilling is of great significance to clarify the distribution characteristics and transition mechanism of positive and negative pressure in the hole, and to realize economic, safe and efficient extraction of super-long drilling. However, due to the limitation of on-site measurement range, the distribution of negative pressure in the hole or the attenuation mechanism of negative pressure in the hole is not clear, and it is not clear whether there is a positive pressure transition mechanism from the negative pressure at the hole mouth to the deep part of the drilling. The change characteristics of negative pressure in the drilling are an important basis for affecting drilling design, extraction volume evaluation and extraction system capacity allocation, but there is a lack of simulation experiment device in the prior art that can simulate the complete gas extraction process of long drilling and further obtain the gas migration law under different conditions, which needs to be improved. SUMMARY

[0004] In view of the defects and deficiencies in the prior art, the present application provides a coal seam super-long directional drilling gas extraction simulation experiment system and method to solve the technical problem that the distribution of negative pressure in the hole or the attenuation mechanism of negative pressure in the hole is not clear in the prior art.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solution:

[0006] A coal seam super-long directional drilling gas extraction simulation experiment system, comprising a pipeline closed at both ends and a plurality of coal sample tanks, the pipeline comprising an inner tube with uniform holes on the tube wall and an outer tube coaxially sleeved outside the inner tube, a negative pressure cavity being arranged in the inner tube; a first cavity is formed between the inner tube and the outer tube, a plurality of annular partitions are arranged in the first cavity at equal intervals, and the annular partitions separate the first cavity into a plurality of second cavities that are not connected to each other;

[0007] An air inlet is arranged on the outer tube wall corresponding to each second cavity, and the air inlet is connected with the coal sample tank through a gas outlet pipeline;

[0008] The coal sample tank is further connected with a gas injection pipeline, the gas injection pipelines of adjacent coal sample tanks are communicated through a first pipeline, a first valve and a first flow sensor are arranged on the first pipeline, a pressure measuring port is arranged on the gas outlet pipeline, the pressure measuring ports of adjacent coal sample tanks are connected through a second pipeline, and a first pressure difference sensor is arranged on the second pipeline.

[0009] A second flow sensor, a second valve and a mass flow meter are further arranged on the gas outlet pipeline, and a third valve is arranged on the gas injection pipeline.

[0010] The negative pressure cavity is provided with a first pressure sensor.

[0011] The application also has the following technical features:

[0012] Specifically, the negative pressure cavity is communicated with a negative pressure pump arranged outside the pipeline assembly through a negative pressure pipeline.

[0013] Further, a booster pump is further included, the booster pump is connected with a booster pipeline, and each gas outlet pipeline is communicated with the booster pipeline.

[0014] Further, the coal sample tank comprises a tank body, a heat shrink tube is vertically arranged in the tank body, a coal sample accommodating cavity is arranged in the heat shrink tube, and plugs are detachably arranged at both ends of the heat shrink tube, a hydraulic oil cavity is formed between the tank body and the heat shrink tube, and the hydraulic oil cavity is connected with a hydraulic pump through a hydraulic oil injection pipeline.

[0015] Further, a second pressure sensor is arranged in each second cavity, and the first flow sensor, the second flow sensor, the mass flow meter, the first pressure sensor and the second pressure sensor are connected with a controller.

[0016] Further, the air inlet of the gas injection pipeline is connected with a gas cylinder through a buffer tank.

[0017] Further, a plurality of fourth pipelines, which can be communicated with the first pipeline and the second pipeline at two ends, are further included, two adjacent coal sample tanks form a coal sample tank unit, the fourth pipelines are arranged between adjacent coal sample tank units, and the number of the fourth pipelines between adjacent coal sample tank units is two.

[0018] Further, the length of the actual coal seam super-long directional drilling is X, the diameter of the actual coal seam super-long directional drilling is R, the pressure similarity ratio of the actual coal seam super-long directional drilling and the pipe assembly is 1, and the geometric similarity ratio of the actual coal seam super-long directional drilling and the pipe assembly is a, so the length of the pipe assembly is set as X / a, and the inner tube diameter is set as R / a.

[0019] A coal seam super-long directional drilling gas extraction simulation experiment method is realized by the coal seam super-long directional drilling gas extraction simulation experiment system, and includes the following steps:

[0020] Step 1, the coal seam super-long directional drilling gas extraction simulation experiment system is built;

[0021] Step 2, the air tightness of the coal seam super-long directional drilling gas extraction simulation experiment system is tested;

[0022] Step 3, according to the geological structure, stress distribution characteristics and gas occurrence law of the to-be-simulated area obtained by the previous exploration, the hydrostatic pressure applied to the outside of the coal sample and the gas pressure in the coal sample are determined; the hydraulic pump is started to apply the same value of hydrostatic pressure to the coal sample in each coal sample tank, and the hydrostatic pressure is applied to one fourth of the experimental set value; after the hydrostatic pressure is stable, each coal sample tank is pumped to vacuum by the negative pressure pump;

[0023] Step 4, the main control item of gas replenishment when extracting coal seam gas is determined:

[0024] When the endogenous gas desorption is the main control item of extraction, only the buffer tank is opened to charge gas into each coal sample tank, and the charging is stopped after reaching the preset gas pressure, and the static balance is 20-26h; the hydrostatic pressure is applied to the experimental set value;

[0025] When the exogenous fissure gas seepage is the main control item of extraction, the coal sample tank and the buffer tank are opened, and the gas is charged into each coal sample tank, and the hydrostatic pressure is applied to the experimental set value;

[0026] When the endogenous and exogenous gas comprehensive action is the main control item of extraction, the gas is charged into each coal sample tank, and the charging is stopped after reaching the preset gas pressure, and the static balance is 20-26h; the coal sample tank and the buffer tank are opened, and the gas is charged into each coal sample tank, and the hydrostatic pressure is applied to the experimental set value;

[0027] Step 5, according to the coal sample basic parameter test analysis and the pre-experiment result, in the range of 15-98 times of the desorption flow of the enlarged coal sample, the mass flowmeter control parameter is set, and the flow distribution air is input into the gas outlet pipeline;

[0028] Step 6, by controlling the opening and closing of the valve, setting different connection forms between the plurality of coal sample tanks, completing the test data acquisition, wherein the different connection forms between the plurality of coal sample tanks include:

[0029] The coal sample tank is connected to the second cavity alone to simulate the effect of segmented extraction;

[0030] The coal sample tanks are connected in parallel to simulate the radial and tangential flow of the coal seam gas;

[0031] The coal sample tanks are connected in series to simulate the influence of the slight change of the extraction negative pressure on the extraction.

[0032] Compared with the prior art, the beneficial technical effects of the present application are:

[0033] 1. The simulation experiment system of the present application can realize the simulation of the whole process of gas production, migration and extraction in an ultra-long borehole, including the process of gas flowing from the coal matrix around the borehole to the borehole under certain confining pressure conditions, and the process of borehole gas flowing from the bottom of the borehole to the orifice, etc., which provides an important means for studying the gas migration law and can be used to reveal the gas migration law under different conditions and provide theoretical support for optimizing the gas extraction effect.

[0034] 2. The method of the present application realizes real-time monitoring and analysis of parameters including pressure, pressure difference and flow rate of each monitoring section in the simulation process, so as to explore the influence of extraction negative pressure on pressure distribution change and positive and negative pressure balance point movement. Further, the gas migration law in the ultra-long borehole is clarified, the positive and negative pressure coupling gas extraction mechanism of the ultra-long directional borehole is revealed, the effective extraction radius of gas flow is determined by analyzing the flow rate data under the condition of slight change of negative pressure, and the influence of negative pressure on the gas extraction range is discussed by comparing the extraction radii under different negative pressure conditions. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a schematic diagram of the overall structure of the simulation experiment system of the present application;

[0036] Figure 2 It is a schematic diagram of the pipeline assembly structure;

[0037] Figure 3 It is a schematic diagram of the coal sample tank structure;

[0038] Figure 4 It is a schematic diagram of the connection mode between the plurality of coal sample tanks in Example 2, wherein (a) is the coal sample tank connected to the second cavity alone, (b) is the coal sample tanks connected in parallel, and (c) is the coal sample tanks connected in series;

[0039] Figure 5 It is a coal sample cumulative desorption amount curve in Example 2;

[0040] Figure 6Desorption rate curve of the coal sample in Example 2;

[0041] Figure 7 Simulation experiment results of the ultra-long directional drilling gas extraction obtained in Example 2.

[0042] Meaning of reference signs:

[0043] 1-pipeline assembly, 2-coal sample tank, 3-annular partition, 4-second cavity, 5-gas outflow pipeline, 6-gas injection pipeline, 7-first pipeline, 8-second pipeline, 9-first valve, 10-first flow sensor, 11-first differential pressure sensor, 12-second flow sensor, 13-second valve, 14-mass flow meter, 15-first pressure sensor, 16-negative pressure pipe, 17-pressure boosting pipeline, 18-hydraulic oil injection pipeline, 19-hydraulic pump, 20-second pressure sensor, 21-buffer tank, 22-gas cylinder, 23-third valve, 24-negative pressure pump, 25-pressure boosting pump, 26-third pipeline, 27-controller, 28-fourth pipeline; 101-inner pipe, 102-outer pipe; 201-tank body, 202-heat shrink tube, 203-plug, 204-hydraulic oil cavity.

[0044] The application will be described in detail below in conjunction with the accompanying drawings and specific embodiments. EMBODIMENTS

[0045] In accordance with the above technical solution, the following specific embodiments of the application are given. It should be noted that the application is not limited to the following specific embodiments, and any equivalent variations made on the basis of the technical solution of the present application fall within the scope of the application.

[0046] The terms "upper", "lower", "front", "back", "top", "bottom", etc. used in the application indicate the orientation or positional relationship only for the purpose of facilitating the description of the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation. "Inner" and "outer" refer to the inner and outer contours of the corresponding components. The above terms should not be understood as limiting the application. The head end of the main shaft is located near the first side plate, and the tail end is located near the second side plate.

[0047] In addition, the ordinal numbers "first", "second", etc. are used only for descriptive purposes and should not be understood as indicating or implying relative importance or implying the number of the indicated technical features. Therefore, the features defined with "first" and "second" can explicitly or implicitly include one or more of the features.

[0048] In the present application, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly unless otherwise stated, for example, it can be fixedly connected, or it can be detachably connected or integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0049] It should be noted that all the components involved in the present embodiment, except for the special components, are components that can be obtained by purchase in the prior art.

[0050] Embodiment 1

[0051] As shown in Figures 1 to 3 The present embodiment provides a coal seam super-long directional drilling gas extraction simulation experiment system, which comprises a pipeline assembly 1 closed at both ends and a plurality of coal sample tanks 2. The pipeline assembly 1 comprises an inner tube 101 with uniformly opened holes on the tube wall and an outer tube 102 coaxially sleeved outside the inner tube 101, and a negative pressure cavity is arranged in the inner tube 101. A first cavity is formed between the inner tube 101 and the outer tube 102, and a plurality of annular partitions 3 are arranged at equal intervals in the first cavity, which divides the first cavity into a plurality of second cavities 4 that are not connected to each other. The outer annular wall surface of the annular partition 3 is arranged in close contact with the inner wall of the outer tube 102, and the inner annular wall surface of the annular partition 3 is arranged in close contact with the outer wall of the inner tube 101. The purpose of arranging the annular partition 3 is to ensure that the gas flow state in each second cavity 4 is relatively independent and will not affect each other, so as to facilitate real-time monitoring of the gas flow state in each second cavity 4.

[0052] An air inlet is formed on the outer tube 102 wall corresponding to each second cavity 4, and the air inlet is connected to the coal sample tank 2 through a gas outflow pipeline 5. The gas transported through the gas outflow pipeline 5 can enter the second cavity 4 through the air inlet, and then enter the negative pressure cavity through the holes on the inner tube 101 wall, and finally be extracted out of the pipeline assembly 1.

[0053] The coal sample tank 2 is also connected to a gas injection pipeline 6, and the gas injection pipelines 6 of adjacent coal sample tanks 2 are communicated through a first pipeline 7, and the first pipeline 7 is provided with a first valve 9 and a first flow sensor 10. The gas injection pipeline 6 is used for injecting gas into the coal sample tank 2, and the first flow sensor 10 is used for measuring the supplement flow of the gas.

[0054] The gas outlet pipe 5 is provided with a pressure tap, and the pressure taps of adjacent coal sample cans 2 are connected through a second pipe 8, and the second pipe 8 is provided with a first differential pressure sensor 11; the first differential pressure sensor 11 is used for measuring the gas pressure difference between two adjacent coal sample cans 2, that is, the second pipe 8 is kept open circuit, the gas does not flow in the second pipe 8, and the first differential pressure sensor 11 only measures the pressure difference. An elastic diaphragm for placing gas into the second pipe 8 can be arranged on the pressure tap.

[0055] The gas outlet pipe 5 is further provided with a second flow sensor 12, a second valve 13 and a mass flow meter 14; the gas injection pipe 6 is provided with a third valve 23; wherein the second flow sensor 12 is used for measuring the outflow gas flow, and the mass flow meter 14 is used for measuring the gas flow in the gas outlet pipe 5. During the test, for the coal sample cans 2, no matter what connection mode is adopted, the injected gas can only enter from the top of the coal sample cans 2 and flow out from the bottom.

[0056] The pressure cavity is provided with a first pressure sensor 15, and the first pressure sensor 15 is used for measuring the gas pressure in the negative pressure cavity.

[0057] In the embodiment, the first flow sensor 10 is a M12V10I type flow sensor, the first differential pressure sensor 11 is a Cerabar series sensor, the second flow sensor 12 is a M12V10I type flow sensor, the mass flow meter 14 is a Bronkhorst D-6471 / 004BI flow controller, and the first pressure sensor 15 is a PMP45-GE17MBJCCDF (Cerabar M) type positive and negative pressure sensor.

[0058] As a preferred scheme of the embodiment, the negative pressure cavity is communicated with a negative pressure pump 24 arranged outside the pipe assembly 1 through a negative pressure pipe 16, the negative pressure pump 24 can provide a maximum 40kpa extraction negative pressure, and the negative pressure adjustment accuracy is ±0.5kpa; in the embodiment, the negative pressure pipe 16 is also provided with a flow sensor for monitoring the orifice flow. By adjusting the power of the negative pressure extraction pump 19, the gas migration law under different negative pressure extraction working conditions can be simulated and explored.

[0059] As a preferred scheme of the embodiment, a booster pump 25 is further included, the booster pump 25 is connected with a booster pipe 17, and each gas outlet pipe 5 is communicated with the booster pipe 17.

[0060] The booster pump 25 inputs air into the mass flow meter 14 with air as the air source to realize the function of outputting gas with different flow rates. The mass flow meter 14 is used to control the flow rate input of the booster pump 30 to the outer pipe 102 to distribute the flow rate for the coal sample tank 2 to desorb gas. The specific distribution flow rate is set as a multiple of the gas desorption amount of the coal sample tank 2. The desorption characteristics of the gas in the coal sample during extraction under experimental conditions can be amplified. The desorption amount is prevented from being too small due to the volume limitation of the coal sample, and the real gas occurrence condition of the coal reservoir cannot be restored.

[0061] As a preferred scheme of the embodiment, the coal sample tank 2 comprises a tank body 201, a heat shrink tube 202 is vertically arranged in the tank body 201, a coal sample containing cavity is arranged in the heat shrink tube 202, the coal sample containing cavity is used for placing the prepared coal sample, and a plug 203 is detachably arranged at both ends of the heat shrink tube 202. A hydraulic oil cavity 204 is formed between the tank body 201 and the heat shrink tube 202, and the hydraulic oil cavity 204 is connected to the hydraulic pump 19 through the hydraulic oil injection pipeline 18. The heat shrink tube 202 can isolate the hydraulic oil from the coal sample. The hydraulic pump 19 is a plunger hydraulic pump, which can provide the same numerical value of hydrostatic pressure for a plurality of coal sample tanks 2. The plunger hydraulic pump is connected to the coal sample tank 2 through a high-pressure-resistant and corrosion-resistant steel pipeline. The plunger hydraulic pump can apply a maximum hydrostatic pressure of 100 MPa to simulate the gas migration characteristics of the coal body under different buried depths and ground stresses. The number of hydraulic pumps 19 can be increased, that is, one hydraulic pump 19 is arranged corresponding to each coal sample tank 2. In this way, different numerical values of hydrostatic pressure can be applied to different coal sample tanks 2 to simulate the influence of uneven stress distribution of the coal reservoir on the gas extraction efficiency, more accurately reflect the complex geological structure distribution of the underground coal mine, and explore and analyze the hindering effect of the stress concentration area on the gas extraction.

[0062] In the embodiment, the coal sample is columnar, the size of the coal sample is 50 mm in diameter and 100 mm in height, and different properties of coal samples such as soft coal, hard coal, tectonic coal and primary coal can be placed in the coal sample tank 2 to discuss the influence of uneven coal distribution on gas extraction.

[0063] As a preferred scheme of the embodiment, the gas injection pipeline 6 is in communication with the coal sample containing cavity.

[0064] As a preferred scheme of the embodiment, a second pressure sensor 20 is arranged in the second cavity; the first flow sensor 10, the second flow sensor 12, the mass flow meter 14, the first pressure sensor 15 and the second pressure sensor 20 are connected to the controller 27. Each sensor can send the collected data to the controller 27.

[0065] As a preferred scheme of the embodiment, a plurality of fourth pipelines 28, each of which can be in communication with the first pipeline 7 and the second pipeline 8 at two ends, are further included. Two adjacent coal sample tanks 2 form a coal sample tank unit. The fourth pipeline 28 is arranged between the adjacent coal sample tank units, and the number of the fourth pipelines 28 between the adjacent coal sample tank units is two.

[0066] As a preferred scheme of the embodiment, the gas injection pipeline 6 is connected with the buffer tank 21 through the fourth pipeline, the buffer tank 21 is connected with the gas cylinder 22 through the third pipeline 26, and the third valve 23 is arranged on the third pipeline 26.

[0067] The buffer tank 21 is used for supplying gas to the coal sample in the coal sample tank 2, and the gas in the gas cylinder 22 can be gas or carbon dioxide or inert gas instead of gas in view of safety.

[0068] As a preferred scheme of the embodiment, the length of the actual overlength directional borehole in the coal seam is X, the diameter of the actual overlength directional borehole in the coal seam is R, the pressure similarity ratio of the actual overlength directional borehole in the coal seam to the pipeline assembly is 1, and the geometric similarity ratio of the actual overlength directional borehole in the coal seam to the pipeline assembly is a, so that the length of the pipeline assembly is set as X / a and the diameter of the inner pipeline is set as R / a.

[0069] Specifically, in the embodiment, the length of the actual overlength directional borehole in the coal seam is 1000 m, the diameter of the actual overlength directional borehole in the coal seam is 120 mm, and the geometric similarity ratio of the actual overlength directional borehole in the coal seam to the pipeline assembly is 20, so that the length of the pipeline assembly is set as 50 m and the diameter of the inner pipeline 1 is set as 6 mm, and the annular partition plate 3 is evenly divided into 10 segments with a length of 5 m.

[0070] Through the above setting, the overlength directional borehole and the surrounding coal body and gas can be simplified, the outer pipeline 102 and the coal sample tank 2 are mainly used for simulating the process of the coal seam gas flowing to the borehole, and the inner pipeline 101 is mainly used for simulating the gas flow process in the extraction borehole, so that the defect that the coal seam gas replenishment flow cannot be restored can be avoided.

[0071] The simulation experiment system of the embodiment is provided with a flow sensor and a pressure difference sensor between two adjacent coal sample tanks, the gas flow and pressure change of each segment of the simulated extraction gas pipeline unit are monitored in real time, the simulation extraction experiment is carried out under the negative pressure condition, the extraction pressure of the orifice is gradually reduced through the control system, and the change of the gas pressure in the actual extraction process is simulated.

[0072] Embodiment 2

[0073] In the embodiment, the daily flow of the overlength directional borehole in the coal seam in a certain actual site is 2989 m 3 / d, for the convenience of calculation, 2989 m 3 / d is rounded to 3000 m 3 / d, and 3000 m 3 / d is converted into per second, which is 0.347 m 3 / s; The actual diameter of the ultra-long directional borehole in the coal mine is 120 mm, and the gas velocity at the borehole opening of the ultra-long directional borehole in the coal mine is 3.07 m / s (gas velocity equals gas flow rate divided by the cross-sectional area of ​​the ultra-long directional borehole).

[0074] In this embodiment, coal powder and binder are mixed and pressed into coal samples. Analysis is performed under laboratory conditions of a confining pressure of 20 MPa and a gas equilibrium pressure of 1 MPa to obtain... Figure 5 and Figure 6 As shown in the curve, it can be seen from the figure that the desorption time can be regarded as a stable desorption period after reaching 5400s. At the desorption time of 5400s, the desorption flow rate Q = 0.029mL / s (the desorption flow rate can be obtained by differentiating the cumulative desorption amount with respect to time). In the initial 500s, the desorption flow rate can reach Q = 1.5mL / s. To ensure that the gas flow state in the simulated experimental pipeline is similar to that in the actual ultra-long directional borehole in a coal mine, assuming laminar flow, the gas velocity at the orifice of the inner tube 101 is 0.15 m / s (the gas velocity at the orifice of the inner tube 101 is equal to the gas velocity at the orifice of the actual ultra-long directional borehole in a coal mine, which is 3.07 m / s, divided by the geometric similarity ratio 20), and the flow rate of the inner tube 101 is 4.24 mL / s. Therefore, whether in the initial stage of desorption or during the stable desorption period, the desorption amount of the coal sample container 2 does not meet the flow rate required to ensure similar gas flow state. Thus, it is necessary to increase the flow rate through the booster pump 25 and the mass flow meter 14.

[0075] Then, the following simulation experiment method for gas drainage from ultra-long directional boreholes in coal seams was used to complete the simulation of gas drainage from ultra-long directional boreholes in coal mines. This method was implemented using the simulation experiment system for gas drainage from ultra-long directional boreholes in coal seams provided in Example 1, and specifically included the following steps:

[0076] Step 1: Complete the construction of the coal seam ultra-long directional borehole gas extraction simulation experimental system;

[0077] Step 2: Complete the airtightness test of the coal seam ultra-long directional borehole gas extraction simulation experimental system;

[0078] Step 3: Based on the geological structure, stress distribution characteristics and gas occurrence patterns of the area to be simulated obtained from previous exploration, determine the hydrostatic pressure applied to the outside of the coal sample and the gas pressure inside the coal sample; start the hydraulic pump to apply the same hydrostatic pressure to the coal sample in each coal sample container, and apply the hydrostatic pressure to one-quarter of the experimental set value; after the hydrostatic pressure stabilizes, use a negative pressure pump to evacuate each coal sample container.

[0079] Specifically, the hydrostatic pressure and the gas pressure inside the coal sample can be determined based on the measured ground stress and measured gas pressure in the coal mine.

[0080] Step 4, determining the main control item of gas replenishment when extracting coal seam gas:

[0081] When endogenous gas desorption is the main control item of extraction, the endogenous desorbed gas has the greatest impact on extraction at this time, only the buffer tank is opened to charge gas into each coal sample tank, the preset gas pressure is reached, and the charging is stopped, and the balance is placed for 20-26h; the hydrostatic pressure is applied as the experimental set value;

[0082] When exogenous fissure gas seepage is the main control item of extraction, the exogenous fissure gas seepage has the greatest impact on extraction at this time, the coal sample tank and the buffer tank are opened, and gas is charged into each coal sample tank, and the hydrostatic pressure is applied as the experimental set value;

[0083] When the combined action of endogenous and exogenous gas is the main control item of extraction, the combined action of endogenous and exogenous gas has the greatest impact on extraction at this time, gas is charged into each coal sample tank, the preset gas pressure is reached, and the charging is stopped, and the balance is placed for 20-26h; the coal sample tank and the buffer tank are opened, and gas is charged into each coal sample tank, and the hydrostatic pressure is applied as the experimental set value;

[0084] Step 5, according to the test analysis and pre-experiment results of the basic parameters of the coal sample, within the range of 15-98 times of the desorption flow of the enlarged coal sample, the mass flowmeter is set to control the parameters, and the flow distribution air is input into the gas outlet pipeline;

[0085] In order to make the orifice flow of the inner tube 101 in the simulation experiment meet the flow similarity condition and be adjustable, the mass flowmeter 14 is adjusted to realize that the orifice flow rate range of the inner tube 101 in the simulation experiment is 0.15m / s-1m / s, and the corresponding flow range is 4.24-28.27mL / s. According to the stable desorption section flow of the coal sample tank 2 in the laboratory test, every 5m is connected with one coal sample tank 4, and a total of 10 coal sample tanks 2 are connected. The total flow of the coal sample tank 2 is 0.29mL / s. If the flow range of 4.24mL / s-28.27mL / s is ensured, the desorption flow of the coal sample tank 2 needs to be expanded to 15-98 times of the original flow through the mass flowmeter 14.

[0086] Step 6, by controlling the opening and closing of the valve, different connection forms between multiple coal sample tanks are set, and test data collection is completed. As shown in Figure 4 , the different connection forms between multiple coal sample tanks include:

[0087] The coal sample tank is connected to the second cavity alone to simulate the effect of segmented extraction;

[0088] The coal sample tanks are connected in parallel to simulate the radial and tangential flow of coal seam gas;

[0089] The coal sample tanks are connected in series to simulate the influence of slight changes of extraction negative pressure on extraction.

[0090] In this embodiment, the results of the ultra-long directional drilling gas extraction are as shown in Figure 5 .

[0091] To sum up, the present application can determine the effective extraction radius of gas flow by collecting the flow data under the condition of negative pressure "micro change" and calculating; according to the extraction radius under different negative pressure conditions, the influence of negative pressure on the gas extraction range is analyzed. Using the data of pressure difference sensor, the pressure distribution diagram of each section of coal sample is drawn, and the pressure change characteristics of different sections are analyzed; so as to obtain the gradual attenuation and positive pressure conversion of the pressure of each section of coal sample under the condition of negative pressure. Through the data of flow sensor, the gas flow characteristics of each section of coal sample are determined, and then the change rule of flow under the condition of negative pressure "micro change" is obtained; by comparing the flow changes of different section simulation extraction gas pipeline units, it is determined which simulation extraction gas pipeline unit has greater influence on the flow of the whole pipeline, and finally the influence of negative pressure attenuation on the gas migration characteristics of each section and the whole pipeline in the process of ultra-long directional drilling extraction is determined.

[0092] The preferred embodiments of the present application are described in detail above in combination with the drawings, but the present application is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0093] In addition, any combination of various different embodiments of the present application can also be made, as long as it does not deviate from the idea of the present application, and it should also be considered as the disclosed content of the present application.

Claims

1. A simulation experimental system for gas extraction from ultra-long directional boreholes in coal seams, characterized in that, The system includes a pipe assembly (1) with closed ends and multiple coal sample containers (2). The pipe assembly (1) includes an inner pipe (101) with uniformly perforated walls and an outer pipe (102) coaxially sleeved outside the inner pipe (101). A negative pressure chamber is provided in the inner pipe (101). A first cavity is formed between the inner pipe (101) and the outer pipe (102). Multiple annular baffles (3) are provided at equal intervals in the first cavity. The annular baffles (3) divide the first cavity into multiple non-communicating second cavities (4). Each second cavity (4) has an air inlet on the wall of the outer tube (102), and the air inlet is connected to the coal sample tank (2) via the gas outlet pipe (5); The coal sample tank (2) is also connected to a gas injection pipe (6), and the gas injection pipes (6) of adjacent coal sample tanks (2) are connected through a first pipe (7). The first pipe (7) is equipped with a first valve (9) and a first flow sensor (10). A pressure measuring port is provided on the gas outflow pipe (5), and the pressure measuring ports of the adjacent coal sample tanks (2) are connected through a second pipe (8). A first differential pressure sensor (11) is provided on the second pipe (8). The gas outflow pipe (5) is also equipped with a second flow sensor (12), a second valve (13) and a mass flow meter (14); the gas injection pipe (6) is equipped with a third valve (23); The negative pressure chamber is equipped with a first pressure sensor (15).

2. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 1, characterized in that, The negative pressure chamber is connected to a negative pressure pump (24) located outside the pipe assembly (1) via a negative pressure pipe (16).

3. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 1, characterized in that, It also includes a booster pump (25), which is connected to a booster pipe (17), and each gas outlet pipe (5) is connected to the booster pipe (17).

4. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 1, characterized in that, The coal sample container (2) includes a container body (201), a heat shrink tube (202) is vertically arranged inside the container body (201), a coal sample receiving cavity is arranged inside the heat shrink tube (202), and plugs (203) are detachably arranged at both ends of the heat shrink tube (202). A hydraulic oil cavity (204) is formed between the container body (201) and the heat shrink tube (202), and the hydraulic oil cavity (204) is connected to a hydraulic pump (19) via a hydraulic oil injection pipeline (18).

5. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 4, characterized in that, The gas injection pipe (6) is connected to the coal sample accommodating cavity.

6. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 4, characterized in that, A second pressure sensor (20) is installed in the second cavity; The first flow sensor (10), the second flow sensor (12), the mass flow meter (14), the first pressure sensor (15), and the second pressure sensor (20) are all connected to the controller (27).

7. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 1, characterized in that, It also includes multiple fourth pipes (28) whose two ends can be connected to the first pipe (7) and the second pipe (8) respectively. Two adjacent coal sample tanks (2) are considered as one coal sample tank unit. The fourth pipes (28) are arranged between adjacent coal sample tank units, and there are two fourth pipes (28) between adjacent coal sample tank units.

8. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 1, characterized in that, The gas injection pipe (6) has its inlet connected to a buffer tank (21) via a fourth pipe. The buffer tank (21) is connected to a gas cylinder (22) via a third pipe (26). A third valve (23) is installed on the third pipe (26).

9. The coal seam ultra-long directional borehole gas extraction simulation experimental system as described in claim 1, characterized in that, Let the length of the actual coal seam ultra-long directional borehole be X, the diameter of the actual coal seam ultra-long directional borehole be R, the pressure similarity ratio between the actual coal seam ultra-long directional borehole and the pipeline assembly be 1, and the geometric similarity ratio between the actual coal seam ultra-long directional borehole and the pipeline assembly be a. Then, the length of the pipeline assembly is set as X / a, and the inner pipe diameter is set as R / a.

10. A simulation experimental method for gas extraction from ultra-long directional boreholes in coal seams, characterized in that, This method is implemented using the coal seam ultra-long directional borehole gas extraction simulation experimental system as described in any one of claims 1 to 9, and includes the following steps: Step 1: Complete the construction of the coal seam ultra-long directional borehole gas extraction simulation experimental system; Step 2: Complete the airtightness test of the coal seam ultra-long directional borehole gas extraction simulation experimental system; Step 3: Based on the geological structure, stress distribution characteristics and gas occurrence patterns of the area to be simulated obtained from previous exploration, determine the hydrostatic pressure applied to the outside of the coal sample and the gas pressure inside the coal sample; start the hydraulic pump to apply the same hydrostatic pressure to the coal sample in each coal sample container, and apply the hydrostatic pressure to one-quarter of the experimental set value; after the hydrostatic pressure stabilizes, use a negative pressure pump to evacuate each coal sample container. Step 4: Determine the main control items for gas replenishment during coal seam gas extraction: When endogenous gas desorption is the main control item for extraction, only the buffer tank is opened to fill each coal sample tank with gas. After reaching the preset gas pressure, the filling is stopped and the tank is allowed to stand for 20-26 hours to reach equilibrium. The hydrostatic pressure is applied as the experimental set value. When external fissure gas seepage is the main control item for extraction, open the coal sample tank and buffer tank, fill each coal sample tank with gas, and apply the hydrostatic pressure to the experimental set value. When the combined effect of internal and external gas sources is the main control factor for extraction, gas is introduced into each coal sample tank. After the preset gas pressure is reached, the introduction is stopped and the tank is allowed to stand for 20-26 hours to reach equilibrium. Then, the coal sample tank and buffer tank are opened, and gas is introduced into each coal sample tank. The hydrostatic pressure is applied to the experimental set value. Step 5: Based on the test and analysis of the basic parameters of the coal sample and the results of the preliminary experiment, within the range of 15 to 98 times the desorption flow rate of the coal sample itself, set the mass flow meter control parameters and input distribution air into the gas outlet pipeline. Step 6: By controlling the opening and closing of valves, different connection methods are set between multiple coal sample tanks to complete the test data acquisition. The different connection methods between multiple coal sample tanks include: The coal sample container is connected to a second chamber separately to simulate the effect of segmented extraction; The coal sample containers are connected in parallel to simulate the radial and tangential flow of coal seam gas; The coal sample tanks are connected in series to simulate the effect of slight changes in negative pressure during extraction.

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