Gas seepage long core clamping system

Abstract

This invention discloses a long core clamping system for gas seepage, belonging to the field of experimental technology for gas seepage in deep coal seams. The system includes a long core clamp, a constant-speed and constant-pressure loading device, an air intake system, and an air exhaust system. The long core clamp can hold single or multiple sections of coal samples with a length not exceeding 500 mm, employing an axially distributed external thread structure to reduce weight and ensure strength. The constant-speed and constant-pressure loading device independently controls axial pressure and confining pressure through dual pumps, and has a built-in temperature control system to simulate coal seam temperature. The air intake system provides stable gas pressure via a pressure regulating valve and a buffer tank, while the air exhaust system achieves negative pressure extraction through a water-ring vacuum pump, with sensors monitoring parameters in real time. This invention achieves coordinated simulation of overall and segmented seepage patterns, improves operational convenience and parameter control accuracy, and can simulate gas seepage scenarios under real geological conditions in deep coal seams, providing experimental support for gas disaster prevention and resource development.

Description

Technical Field

[0001] This utility model relates to the field of experimental technology for gas seepage in deep coal seams, specifically to a long core clamping system for simulating the migration law of gas in coal bodies, which is suitable for laboratory research on coal mine gas disaster prevention and resource development. Background Technology

[0002] In the process of deep coal seam mining, gas is both a harmful gas that threatens mine safety and a clean energy source that can be utilized as a resource.

[0003] In order to understand the migration patterns of gas in coal seams, evaluate the effectiveness of gas extraction, and guide safe production, the laboratory usually adopts an integrated experimental device of "core clamping-seepage-negative pressure extraction": coal samples taken from the site are loaded into the clamp, axial pressure and confining pressure are applied by an external pump system, and a constant gas pressure is provided by the gas intake system. The gas exhaust system is connected to a vacuum pump to generate negative pressure, thereby simulating the underground extraction conditions.

[0004] This device can continuously measure key parameters of continuous seepage, such as gas permeability, desorption, and displacement efficiency, under controllable stress, gas pressure, and temperature conditions, which is of great guiding significance for the prevention and control of gas disasters and resource development in deep coal seams.

[0005] However, as deep mining enters a new stage characterized by high ground stress, high gas content, and complex geological environments, existing experimental equipment has revealed the following defects, which are directly related to the structural design of the equipment:

[0006] (i) The single clamping specification of long core / coal sample makes it impossible to take into account both overall and segmented seepage simulation.

[0007] In existing technologies, core holders generally suffer from the drawback of fixed specifications: either they only support short-sized standard coal samples (such as Φ50×100 mm), which are convenient for preparation and sealing, but cannot simulate the overall seepage law of long cores (length ≥300 mm) in deep strata; or they only support long cores of a specific length (such as Φ50×300 mm), but the preparation of long cores is difficult (easy to break, high cost), and it is impossible to simulate radial seepage or gas injection displacement processes by segment splicing, resulting in low experimental efficiency and limited applicable scenarios.

[0008] Existing technologies focus on the structural design of single-specification clamps to prioritize sealing performance and loading stability (such as mature end-face sealing technology for short coal samples and low difficulty in axial uniform loading of long cores), without considering the need for coordinated simulation of "overall seepage / displacement of long cores" and "seepage / displacement of segmented coal samples".

[0009] (ii) The core holder is large in size and heavy in weight, and its operation is not convenient enough.

[0010] Existing technologies focus on the sealing advantages of internal thread structures (the threaded surface is perpendicular to the coal sample end face, and high sealing performance can be achieved through radial compression), neglecting the impact of structural weight on operational convenience. Therefore, to ensure sealing performance and structural strength under high-pressure environments, existing core holders generally adopt internal thread connections (the thread is located on the inner wall of the holder), resulting in a large overall size and high weight (typically ≥20kg). During experiments, the installation, disassembly, and handling of long cores / coal samples require multiple people working together, leading to low operational efficiency, especially when multiple experiments are conducted consecutively, which is time-consuming and labor-intensive.

[0011] (iii) The axial pressure and confining pressure control accuracy is low and the confining pressure stability is insufficient.

[0012] Existing technologies focus on the independent control logic of axial pressure and confining pressure to simplify the design complexity of a single pressure source (e.g., a single pump only needs to drive a pressure cylinder in one direction), neglecting the coupling effect between the two during the deformation process of the coal sample. Therefore, in existing seepage experiments, the simulation of coal sample loading conditions (axial pressure and confining pressure) mostly relies on independent control systems: either using a single pump with a single pressure output (which can only load axial pressure or confining pressure), or adjusting the confining pressure through an external pressure compensation device. This presents two key problems: ① The confining pressure is prone to fluctuation during axial pressure loading, resulting in low accuracy of coordinated control (error ≥ ±0.5MPa); ② The confining pressure needs to be manually monitored and manually replenished, making it impossible to maintain a constant pressure in real time, leading to distortion of the loading condition simulation and affecting the accuracy of the seepage law.

[0013] In addition, in existing gas seepage test devices, switching between vacuum and atmospheric pressure relies on manual disassembly of pipelines, which involves many steps, is prone to leakage, and cannot quickly compare the seepage differences under negative pressure and atmospheric pressure, resulting in cumbersome switching of operating conditions.

[0014] In summary, existing gas seepage experimental devices have significant shortcomings in terms of long core / coal sample clamping specifications, ease of operation, and accuracy of load condition control. This results in an inability to efficiently and accurately simulate the complex seepage scenario of "long core under load + negative pressure extraction" in deep coal seams, hindering in-depth research on gas seepage mechanisms. Therefore, there is an urgent need to develop a long core clamping system that is compatible with coal samples of various specifications, has a lightweight structure, and is stable under confining pressure. This system would enable the simulation of continuous seepage (displacement) patterns of loaded long cores / coal samples under real geological conditions, providing experimental support for efficient coal seam gas extraction technology. Utility Model Content

[0015] The purpose of this invention is to provide a long core clamping system that can accommodate coal samples of different lengths to achieve overall and segmented seepage simulation, and to improve the convenience of handling and installation.

[0016] To achieve the above objectives, the gas seepage long core clamping system of this utility model includes a long core clamp, a constant speed and constant pressure loading device for applying axial pressure and confining pressure to the coal sample, an air intake system for providing a gas source, and an air outlet system for controlling the gas outlet state.

[0017] The constant speed and constant pressure loading device is connected to the long core holder through a loading pipeline. The air intake system is connected to the front end of the long core holder through an air intake pipe, and the air outlet system is connected to the rear end of the long core holder through an air outlet pipe. The long core holder is used to hold single-segment coal samples or multiple standard-sized coal samples with a length not exceeding 500 mm. The long core holder adopts an external thread structure, and the external thread structure is distributed along the axial direction of the long core holder.

[0018] The constant speed and constant pressure loading device consists of two constant speed and constant pressure pumps. The long core holder has a confining pressure chamber and an axial pressure chamber. One constant speed and constant pressure pump is connected to the confining pressure chamber through a loading pipeline, and the other constant speed and constant pressure pump is connected to the axial pressure chamber through a loading pipeline. The constant speed and constant pressure pumps are used to maintain constant axial pressure and confining pressure.

[0019] The long core holder has a built-in temperature control system, which includes a heating wire and a temperature sensor. The temperature control system is connected to an electronic control device and is used to control the working temperature of the long core holder within the range of room temperature to 60°C.

[0020] The air intake system includes a gas source storage tank, a pressure regulating valve, a buffer tank, and an air intake valve. The gas source storage tank is connected to the air intake pipeline in sequence through the pressure regulating valve, the buffer tank, and the air intake valve.

[0021] The gas outlet system includes an outlet valve, a gas flow meter, a negative pressure sensor, and a water ring vacuum pump. The outlet pipeline is provided with the outlet valve, gas flow meter, negative pressure sensor, and end valve in sequence from upstream to downstream. The water ring vacuum pump is connected to the downstream end of the outlet pipeline through the end valve. The outlet pipeline between the negative pressure sensor and the end valve is connected to a discharge pipe, and a discharge valve is provided on the discharge pipe.

[0022] The exhaust valve, outlet valve, and end valve are all solenoid valves; the exhaust valve, outlet valve, end valve, gas flow meter, negative pressure sensor, and water ring vacuum pump are all connected to the electronic control device.

[0023] The constant speed and constant pressure loading device includes a constant speed and constant pressure pump, a high-precision servo motor connected to the constant speed and constant pressure pump, and a display screen. The display screen is used to display the operating status, pressure, and flow parameters of the constant speed and constant pressure loading device.

[0024] The air intake pipe is equipped with an air intake valve and a gas pressure sensor. The gas pressure sensor is located between the air intake valve and the long core holder. Both the air intake valve and the air outlet valve are solenoid valves. Both the air intake valve and the gas pressure sensor are connected to the electronic control device.

[0025] This utility model has the following advantages:

[0026] By using a long core holder to hold both single-segment long coal samples (≤500 mm) and multiple standard coal samples, the shortcomings of existing technologies, such as "lack of overall seepage simulation of long cores" or "low efficiency of segmented displacement experiments" caused by the single specification, are solved. This achieves synergistic simulation of overall and segmented seepage patterns and improves the breadth of applicable experimental scenarios.

[0027] Compared to the traditional internal thread structure, the external thread structure reduces the wall thickness of the clamp, significantly reducing the overall weight and improving the ease of handling and installation. At the same time, the axial distribution of the external thread ensures the structural strength of the clamp under high pressure loading.

[0028] The dual pumps enable independent adjustment of axial pressure and confining pressure, precisely maintaining a constant state of axial pressure and confining pressure.

[0029] The temperature control system simulates the real temperature environment of the coal seam through closed-loop control of the heating wire (500W power) and the temperature sensor (accuracy ±0.5℃), ensuring the accuracy of the temperature-dependent gas seepage pattern.

[0030] The pressure regulating valve achieves inlet pressure regulation of 0.1-5MPa, and the buffer tank 4 (volume 5L) eliminates gas source pressure fluctuations, ensuring stable gas pressure entering the long core holder 7 and simulating gas pressure conditions in different coal seams.

[0031] The water ring vacuum pump 14 can provide a stable extraction negative pressure of -0.01~-0.1MPa. Combined with the gas flow meter 11 (range 0-100mL / min, accuracy ±1%FS) and the negative pressure sensor 12 (range -0.1~0MPa), it can monitor the changes in gas flow and pressure under negative pressure extraction conditions in real time and simulate the on-site extraction scenario.

[0032] The high-precision servo motor (control accuracy ±0.1 mm / min) enables precise adjustment of axial pressure / containment pressure, and the display screen (800×480 resolution) provides real-time parameter feedback, improving ease of operation and control accuracy.

[0033] Gas pressure sensor 2 (range 0-10MPa, accuracy ±0.2%FS) monitors the gas pressure entering the long core holder 7 in real time, and combined with the on / off control of the air inlet valve 5, it achieves precise regulation of the air inlet pressure. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of this utility model. Detailed Implementation

[0035] like Figure 1 As shown, the gas seepage long core clamping system of this utility model includes a long core clamp 7, a constant speed and constant pressure loading device 8 for applying axial pressure and confining pressure to the coal sample, an air intake system for providing gas source, and an air outlet system for controlling the gas outlet state.

[0036] The constant speed and constant pressure loading device 8 is connected to the long core holder 7 through a loading pipeline. The air intake system is connected to the front end (i.e., the upstream end) of the long core holder 7 through the air intake pipe 6, and the air outlet system is connected to the rear end (i.e., the downstream end) of the long core holder 7 through the air outlet pipe 9. The long core holder 7 is used to hold single-segment coal samples or multiple standard-sized coal samples with a length not exceeding 500 mm. The long core holder 7 adopts an external thread structure, and the external thread structure is distributed along the axial direction of the long core holder 7.

[0037] The main body of the long core holder 7 is made of high-strength alloy material (such as 40Cr), and the inner wall is coated with a wear-resistant coating. By using the long core holder 7 to hold both single-segment long coal samples (≤500 mm) and multiple standard coal samples, it solves the defects of existing technologies, such as "lack of overall seepage simulation of long cores" or "low efficiency of segmented displacement experiments" caused by the single specification. It achieves synergistic simulation of overall and segmented seepage patterns, improving the breadth of applicable experimental scenarios. The multiple standard-sized coal samples are cylindrical coal samples with a diameter of Φ50×100 mm, and the segments are sealed with high-temperature resistant gaskets (such as fluororubber).

[0038] Compared to traditional internal thread structures, the external thread structure reduces the wall thickness of the clamp, significantly lowering the overall weight and improving ease of handling and installation. Simultaneously, the axial distribution of the external thread ensures the structural strength of the clamp under high-pressure loading. The external thread pitch is 2 mm, and the thread accuracy grade is 6g.

[0039] Compared to traditional internal thread structures, external thread structures can reduce the wall thickness of the clamp and lower the overall weight. This principle can be explained from three core dimensions: force distribution, stress distribution, and material utilization.

[0040] I. Differences in force distribution: from "radial pressure" to "axial force transmission".

[0041] Internal thread structure:

[0042] Traditional internal threads require machining the threads on the inner wall of the clamp, with the thread profile embedded within the matrix. When the clamp is subjected to axial or confining pressure, the internal thread must simultaneously resist radial expansion forces (reaction forces from the core / coal sample) and shear forces of the threaded connection. To prevent thread stripping or matrix fracture, a relatively thick wall thickness (typically 1.5 to 2 times the nominal thread diameter) must be maintained to provide sufficient material support.

[0043] External thread structure:

[0044] External threads are machined on the outer wall of the clamp, and connection is achieved through an end cap with external threads. In this case, the load is mainly transmitted through axial force (the end cap with external threads is in contact with the end face of the clamp), and the thread only needs to withstand axial tensile or compressive forces, rather than radial expansion forces. Therefore, the base wall thickness can be significantly reduced, only needing to meet the strength requirements of the thread profile (usually 0.8 to 1.2 times the nominal thread diameter).

[0045] II. Stress distribution optimization: reduce "local stress concentration".

[0046] Stress concentration problem in internal threads:

[0047] The root and tip of internal threads are typical stress concentration areas, especially under high pressure loading (such as the "axial compression and confining pressure adjustment" mentioned in the document). The local stress in the internal thread may exceed the material's yield strength. To reduce the risk of fracture, the design needs to increase the wall thickness to distribute the stress, resulting in an increase in overall weight.

[0048] The stress dispersion advantages of external threads:

[0049] The threads of the external thread are exposed on the outer wall, and stress can be dispersed by the uniform tightening of the matching nut. In addition, the external thread structure can adopt a "fine thread" design. Fine threads have a shallower tooth profile and a greater number of teeth, which can further reduce the stress per unit area and allow for a reduction in the thickness of the base wall.

[0050] III. Improved material utilization: Reduced “ineffective structural volume”.

[0051] Material waste in internal threads:

[0052] Internal thread machining requires drilling before tapping. To ensure thread accuracy and strength, the drilled diameter must be smaller than the minor diameter of the thread, resulting in an "ineffective material layer" between the hole wall and the thread. For example, if you need to machine an M50 internal thread (minor diameter of about 48mm), you need to drill a φ45mm hole first, leaving 3mm of material on the hole wall for tapping. This part of the material contributes little to the structural strength but increases the overall weight.

[0053] Lightweight design of external threads:

[0054] External threads are machined directly on the outer wall of the gripper, eliminating the need for internal drilling and maximizing material utilization. For example, for a gripper capable of holding a Φ50×500mm coal sample, the external thread design allows the gripper's outer diameter to be controlled at φ60~φ70mm (only 10~20mm larger than the coal sample diameter), while the internal thread structure, to ensure strength, may require an outer diameter of φ80~φ90mm. This difference in wall thickness directly results in a weight reduction of approximately 40%~50%.

[0055] The constant-speed, constant-pressure loading device 8 consists of two constant-speed, constant-pressure pumps. The long core holder has a confining pressure chamber and an axial pressure chamber. One constant-speed, constant-pressure pump is connected to the confining pressure chamber through a loading pipeline, and the other constant-speed, constant-pressure pump is connected to the axial pressure chamber through a loading pipeline. The constant-speed, constant-pressure pumps are used to maintain constant axial pressure and confining pressure. The confining pressure chamber and axial pressure chamber are conventional technologies and are not shown in detail in the figure.

[0056] The constant speed and pressure pump can be mechanical (e.g., maintaining constant pressure through an overflow valve) or electronic (maintaining constant pressure through an electronic control device such as a microcontroller). A single-cylinder constant speed and pressure pump is preferred to comprehensively address requirements in terms of functionality, accuracy, size, and cost. In this embodiment, the maximum output pressure of the single-cylinder constant speed and pressure pump is 30 MPa, and the pressure response time is ≤1 second.

[0057] The dual pumps enable independent adjustment of axial pressure and confining pressure, precisely maintaining a constant state of axial pressure and confining pressure.

[0058] When using an electronic constant-speed, constant-pressure pump, it is preferable to install pressure sensors in both the axial pressure chamber and the confining pressure chamber. Each pressure sensor is connected to an electronic control device 15, which in turn is connected to the constant-speed, constant-pressure pump. The pressure sensors (accuracy ±0.01 MPa) monitor and provide feedback on confining pressure changes in real time, ensuring the stability of the coal sample's loading conditions and avoiding distortion of seepage data due to pressure fluctuations. Using a mechanical constant-speed, constant-pressure pump offers the advantage of lower cost.

[0059] The long core holder 7 has a built-in temperature control system, which includes a heating wire (500W power) and a temperature sensor (accuracy ±0.5℃). The temperature control system is connected to the electronic control device 15 and is used to control the operating temperature of the long core holder 7 within the range of room temperature to 60℃. The electronic control device 15 has a display screen for recording and displaying data and controlling components such as solenoid valves. The heating wire and temperature sensor are conventional parts and are not shown in the figure.

[0060] The temperature control system simulates the real temperature environment of the coal seam through closed-loop control of the heating wire (500W power) and the temperature sensor (accuracy ±0.5℃), ensuring the accuracy of the temperature-dependent gas seepage pattern.

[0061] The heating rate of the temperature control system is 1℃ / min, and the temperature fluctuation range is ≤±0.5℃.

[0062] The air intake system includes a gas source storage tank 1, a pressure regulating valve 3, a buffer tank 4, and an air intake valve 5. The gas source storage tank 1 is connected to the air intake pipe 6 in sequence through the pressure regulating valve 3, the buffer tank 4, and the air intake valve 5.

[0063] The pressure regulating valve 3 achieves inlet pressure regulation of 0.1-5MPa, and the buffer tank 4 (volume 5L) eliminates gas source pressure fluctuations, ensuring stable gas pressure entering the long core holder 7 and simulating gas pressure conditions in different coal seams.

[0064] The gas outlet system includes an outlet valve 10, a gas flow meter 11, a negative pressure sensor 12, and a water ring vacuum pump 14. The outlet pipe 9 is provided with the outlet valve 10, gas flow meter 11, negative pressure sensor 12, and end valve 13 in sequence from upstream to downstream. The water ring vacuum pump 14 is connected to the downstream end (rear end) of the outlet pipe 9 through the end valve 13. The outlet pipe 9 between the negative pressure sensor 12 and the end valve 13 is connected to a discharge pipe, and a discharge valve 16 is provided on the discharge pipe.

[0065] The exhaust valve 16, the outlet valve 10, and the end valve 13 are all solenoid valves; the exhaust valve 16, the outlet valve 10, the end valve 13, the gas flow meter 11, the negative pressure sensor 12, and the water ring vacuum pump 14 are all connected to the electronic control device 15.

[0066] The water ring vacuum pump 14 can provide a stable extraction negative pressure of -0.01~-0.1MPa. Combined with the gas flow meter 11 (range 0-100mL / min, accuracy ±1%FS) and the negative pressure sensor 12 (range -0.1~0MPa), it can monitor the changes in gas flow and pressure under negative pressure extraction conditions in real time and simulate the on-site extraction scenario.

[0067] The constant speed and constant pressure loading device 8 includes a constant speed and constant pressure pump, a high-precision servo motor connected to the constant speed and constant pressure pump, and a display screen. The display screen is used to display the operating status, pressure, and flow parameters of the constant speed and constant pressure loading device 8.

[0068] The high-precision servo motor (control accuracy ±0.1 mm / min) enables precise adjustment of axial pressure / containment pressure, and the display screen (800×480 resolution) provides real-time parameter feedback, improving ease of operation and control accuracy.

[0069] The air intake pipe 6 is equipped with an air intake valve 5 and a gas pressure sensor 2. The gas pressure sensor 2 is located between the air intake valve 5 and the long core holder 7. Both the air intake valve 5 and the air outlet valve 10 are solenoid valves. Both the air intake valve 5 and the gas pressure sensor 2 are connected to the electronic control device 15.

[0070] Gas pressure sensor 2 (range 0-10MPa, accuracy ±0.2%FS) monitors the gas pressure entering the long core holder 7 in real time, and combined with the on / off control of the air inlet valve 5, it achieves precise regulation of the air inlet pressure.

[0071] The working process of this utility model is described below.

[0072] I. Pre-experiment preparation stage.

[0073] 1. Coal sample preparation and installation.

[0074] Select the coal sample specifications according to experimental requirements: If simulating overall seepage of a long core, directly prepare a single-segment coal sample of Φ50×500 mm; if simulating segmented radial seepage or gas injection displacement, prepare multiple standard coal samples of Φ50×100 mm, and seal the intervals between segments with high-temperature resistant gaskets (such as fluororubber) to prevent gas leakage. Load the prepared coal sample into the clamping cavity of the long core holder 7, and tighten the end caps using the external thread structure (distributed along the axial direction of the holder) to ensure tight contact between the coal sample and the inner wall of the holder, achieving axial sealing.

[0075] The long core holder 7 supports single sections ≤500 mm or multiple sections spliced ​​together, which solves the problem of the single specification of traditional holders and improves experimental efficiency; the external thread structure reduces weight by about 50% compared with the internal thread, which facilitates the handling and operation of coal samples during installation, while the axial distribution of the external thread ensures the structural strength under high pressure loading.

[0076] 2. System connection and airtightness check.

[0077] The front end of the long core holder 7 is connected to the air intake system through the air intake pipe 6. The air intake valve 5 and the gas pressure sensor 2 are installed on the air intake pipe 6 in sequence. The rear end is connected to the air exhaust system through the air exhaust pipe 9. The air exhaust valve 10, the gas flow meter 11, and the negative pressure sensor 12 are installed on the air exhaust pipe 9 in sequence. The end valve 13 and the exhaust valve 16 are respectively connected to the atmosphere (valve 16) and the water ring vacuum pump 14 (valve 13).

[0078] Check the sealing of all pipe joints (e.g., O-ring seals), close inlet valve 5, outlet valve 10, end valve 13 and exhaust valve 16, and introduce low-pressure nitrogen (0.5MPa) into the pipes through the inlet system. Let it stand for 5 minutes. If the reading of gas pressure sensor 2 does not drop, the system is confirmed to be airtight.

[0079] The modular design of the inlet / outlet pipe connection facilitates quick assembly and maintenance; the real-time monitoring of the gas pressure sensor 2 and the negative pressure sensor 12 provides a data basis for subsequent pressure regulation, ensuring no gas leakage during the experiment and avoiding data distortion.

[0080] II. Experimental Parameter Setting Stage.

[0081] 1. Temperature control system starts.

[0082] Turn on the temperature control system of the long core holder 7 and set the target temperature (based on the simulated coal seam environment, the range is room temperature to 60℃). The temperature control system uses a built-in heating wire (power 500W) and a temperature sensor (accuracy ±0.5℃) for closed-loop control. Set the heating rate to 1℃ / min. After the temperature stabilizes (fluctuation range ≤ ±0.5℃), proceed to the next step.

[0083] The temperature control system simulates the real coal seam temperature environment, eliminates the influence of temperature on gas seepage characteristics, and ensures the authenticity of experimental data; high-precision temperature control (±0.5℃) avoids changes in gas adsorption / desorption patterns caused by temperature fluctuations.

[0084] 2. Axial compression and confining pressure loading

[0085] Two constant-speed, constant-pressure pumps connected in series are started. Axial pressure and confining pressure parameters are set via the display screen (axial pressure range 0-30 MPa, confining pressure range 0-20 MPa, depending on the simulated formation depth). The constant-speed, constant-pressure pumps inject hydraulic oil into the axial pressure and confining pressure chambers of the long core holder 7, achieving axial and radial loading of the coal sample. When the confining pressure fluctuates due to coal sample compression or leakage, the pump body automatically replenishes pressure based on the pressure detected by the pressure sensor, maintaining a constant loading pressure.

[0086] The dual-pump series connection enables independent adjustment of axial pressure and confining pressure, meeting the simulation requirements of different geostress conditions; the pressure tracking function avoids the lag of traditional manual pressure replenishment, ensuring the stability of coal sample loading conditions and providing a reliable stress environment for seepage law research.

[0087] III. Experimental Operation Phase.

[0088] 1. Gas pressure regulation of the intake system.

[0089] Open the valve of the gas source storage tank 1, and adjust the gas pressure to the target value (simulating coal seam gas pressure, range 0.1~5MPa) through the pressure regulating valve 3. After the gas pressure is stabilized in the buffer tank 4 (volume 5L), open the inlet valve 5 to allow the gas to enter the front end of the long core holder 7 through the inlet pipe 6, contact the coal sample, and begin to seep. The buffer tank 4 can eliminate gas source pressure fluctuations and ensure that the gas pressure entering the coal sample is stable (fluctuation range ≤ ±0.05MPa).

[0090] The combination of pressure regulating valve 3 and buffer tank 4 enables precise control of gas pressure and simulates different coal seam gas pressure conditions; stable inlet pressure provides a benchmark for subsequent seepage flow measurement and avoids interference of pressure fluctuations on the data of gas flow meter 11.

[0091] 2. Selection of seepage (displacement) mode and parameter monitoring.

[0092] Select the seepage mode according to experimental requirements:

[0093] Natural seepage mode: Open the control discharge valve 16 to connect to the atmosphere and close the end valve 13. At this time, the gas passes through the coal sample under the action of pressure difference and is discharged into the atmosphere from the gas outlet pipe 9 through the gas outlet valve 10. The gas flow meter 11 records the seepage flow in real time, and the negative pressure sensor 12 monitors the outlet pressure (close to atmospheric pressure).

[0094] Negative pressure extraction mode: Close the control discharge valve 16, open the end valve 13, start the water ring vacuum pump 14, adjust the vacuum pump power so that the reading of the negative pressure sensor 12 reaches the target extraction negative pressure (range -0.01~-0.1MPa), the gas passes through the coal sample under negative pressure, the gas flow meter 11 records the extraction flow rate, and the negative pressure sensor 12 provides real-time feedback on the stability of the extraction negative pressure.

[0095] The electronic control device 15 synchronously collects temperature data from the gas pressure sensor 2 (inlet pressure), the negative pressure sensor 12 (outlet negative pressure), the gas flow meter 11 (leakage flow), and the temperature control system. The sampling frequency is set to 1Hz, and the data is displayed on the screen and stored in real time.

[0096] By switching valves (13, 16), dual-mode simulation of natural seepage and negative pressure extraction is achieved, covering different engineering scenarios; the high-precision measurement of gas flow meter 11 (range 0-100mL / min, accuracy ±1%FS) and negative pressure sensor 12 provides quantitative data for seepage law analysis; the real-time recording of electrical control device 15 ensures the continuity and traceability of the seepage process.

[0097] IV. End of Experiment Phase

[0098] After the experiment reaches the preset time (or the seepage flow stabilizes), close the valve of the gas source storage tank 1, close the inlet valve 5, stop the loading of the constant speed and constant pressure pump, and shut down the temperature control system after the axial pressure and confining pressure drop to zero. If it is a negative pressure extraction mode, first shut down the water ring vacuum pump 14, open the control discharge valve 16 to connect to the atmosphere, balance the system pressure, then disassemble the long core holder 7 and take out the coal sample. Export the data stored in the electrical control device 15 for seepage (displacement) law analysis.

[0099] The step-by-step depressurization and system balancing operation prevented the coal sample from being damaged by a sudden drop in pressure, thus protecting the experimental sample. The complete data recording provided a basis for subsequent seepage curve plotting and permeability calculation, ensuring the repeatability of the experimental results.

[0100] The entire process utilizes the multi-specification compatibility of the long core holder 7, the loading pressure tracking of the constant speed and pressure pump, the environmental simulation of the temperature control system, the pressure regulation of the air intake / exhaust system, and the real-time monitoring of the data acquisition system to achieve accurate simulation of the gas seepage (displacement) law of long cores / coal samples under load conditions. The synergistic effect of various technical features solves the defects of existing technologies such as low efficiency, limited scenarios, and insufficient parameter control accuracy, providing a reliable experimental platform for the study of gas seepage mechanisms in deep coal seams.

[0101] The above embodiments are only used to illustrate and not limit the technical solutions of this utility model. Although the utility model has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the utility model without departing from the spirit and scope of the utility model. Any modifications or partial substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A gas seepage long core clamping system, characterized in that: It includes a long core holder (7), a constant speed and constant pressure loading device (8) for applying axial pressure and confining pressure to the coal sample, an air intake system for providing gas source, and an air outlet system for controlling the gas outlet state; The constant speed and constant pressure loading device (8) is connected to the long core holder (7) through a loading pipeline. The air intake system is connected to the front end of the long core holder (7) through an air intake pipe (6). The air outlet system is connected to the rear end of the long core holder (7) through an air outlet pipe (9). The long core holder (7) is used to hold single-segment coal samples or multiple standard-sized coal samples with a length not exceeding 500 mm. The long core holder (7) adopts an external thread structure, and the external thread structure is distributed along the axial direction of the long core holder (7).

2. The gas seepage long core clamping system according to claim 1, characterized in that: The constant speed and constant pressure loading device (8) consists of two constant speed and constant pressure pumps. The long core holder has a confining pressure chamber and an axial pressure chamber. One constant speed and constant pressure pump is connected to the confining pressure chamber through a loading pipeline, and the other constant speed and constant pressure pump is connected to the axial pressure chamber through a loading pipeline. The constant speed and constant pressure pump is used to maintain constant axial pressure and confining pressure.

3. The gas seepage long core clamping system according to claim 1, characterized in that: The long core holder (7) has a built-in temperature control system, which includes a heating wire and a temperature sensor. The temperature control system is connected to the electrical control device (15) and is used to control the working temperature of the long core holder (7) within the range of room temperature to 60°C.

4. The gas seepage long core clamping system according to claim 1, characterized in that: The air intake system includes a gas source storage tank (1), a pressure regulating valve (3), a buffer tank (4) and an air intake valve (5). The gas source storage tank (1) is connected to the air intake pipe (6) in sequence through the pressure regulating valve (3), the buffer tank (4) and the air intake valve (5).

5. The gas seepage long core clamping system according to claim 1, characterized in that: The gas outlet system includes an outlet valve (10), a gas flow meter (11), a negative pressure sensor (12), and a water ring vacuum pump (14). The outlet pipe (9) is provided with the outlet valve (10), gas flow meter (11), negative pressure sensor (12), and end valve (13) in sequence from upstream to downstream. The water ring vacuum pump (14) is connected to the downstream end of the outlet pipe (9) through the end valve (13). The outlet pipe (9) between the negative pressure sensor (12) and the end valve (13) is connected to a discharge pipe, and a discharge valve (16) is provided on the discharge pipe. The discharge valve (16), the outlet valve (10), and the end valve (13) are all solenoid valves; the discharge valve (16), the outlet valve (10), the end valve (13), the gas flow meter (11), the negative pressure sensor (12), and the water ring vacuum pump (14) are all connected to the electrical control device (15).

6. The gas seepage long core clamping system according to claim 1, characterized in that: The constant speed and constant pressure loading device (8) includes a constant speed and constant pressure pump, a high-precision servo motor connected to the constant speed and constant pressure pump, and a display screen. The display screen is used to display the operating status, pressure, and flow parameters of the constant speed and constant pressure loading device (8).

7. The gas seepage long core clamping system according to claim 5, characterized in that: The air intake pipe (6) is equipped with an air intake valve (5) and a gas pressure sensor (2). The gas pressure sensor (2) is located between the air intake valve (5) and the long core holder (7). The air intake valve (5) and the air outlet valve (10) are both solenoid valves. The air intake valve (5) and the gas pressure sensor (2) are both connected to the electronic control device (15).

Images