Coal bed methane production simulation device based on inert gas tracing and phase distinction method

Abstract

The present application relates to a coal bed methane production simulation device based on inert gas tracing and a phase state distinguishing method, comprising a gas injection module, a sample clamping assembly, a back pressure control module and a mass spectrometry monitoring module, the gas injection module comprises a methane gas cylinder, a tracer gas cylinder and a reference tank, the methane and the tracer gas are first input into the reference tank, mixed and then input into the sample clamping assembly; the sample clamping assembly comprises an external pressure-resistant container and an internal sample bin, the pressure-resistant container provides a deep coal bed simulation environment for the sample bin; the sample bin is placed with a coal sample, the coal sample is saturated with methane adsorption, the tracer gas is not adsorbed by the coal sample and exists in the free gas in the sample bin; the back pressure control module controls the pressure at the outlet end of the sample clamping assembly, after the coal sample is saturated with methane adsorption, the coal bed gas depletion development process is simulated, the gas produced by the coal sample is discharged to the mass spectrometry monitoring module, the tracer gas concentration in the produced gas is analyzed in real time, and the proportion of the adsorbed methane and the original free methane is obtained.

Description

Technical Field

[0001] This invention belongs to the field of deep coalbed methane production analysis technology, specifically relating to a coalbed methane production simulation device based on inert gas tracers and a phase differentiation method. Background Technology

[0002] Coalbed methane (CBM) is primarily composed of methane, existing mainly in adsorbed and free states within coal seams. Adsorbed methane is mainly found on the coal matrix surface and requires gradual desorption into the free phase as pressure decreases before it can be produced. Free methane refers to methane existing in the pores and fractures of the coal matrix, not adsorbed on the coal surface, and existing as a free gas; it is the primary source of initial CBM production. Therefore, the free methane in its original state can be called primary free gas. In deep coal seam CBM extraction, the dynamic production ratio of adsorbed gas and primary free gas directly determines the shape of the gas production curve and the differences in stage divisions during the depletion development process. Therefore, accurately quantifying the real-time contribution of free gas versus adsorbed gas is a crucial prerequisite for developing reasonable operating procedures, predicting recoverable reserves, and optimizing deep CBM development plans.

[0003] Currently, conventional methods for determining the ratio of adsorbed gas to pristine free gas production mainly include gas geochemical analysis, adsorption isotherm analysis, production capacity numerical simulation, and microscopic molecular simulation. Gas geochemical analysis, through isotope fractionation enrichment trends, can provide qualitative judgments on the increase or decrease of adsorbed or pristine free gas, but it is difficult to establish a quantitative correspondence between isotope differences and specific percentage contents. Adsorption isotherm analysis, under equilibrium conditions in the laboratory, obtains the Langmuir volume and pressure constants, simulating the instantaneous production ratio of adsorbed gas to pristine free gas under non-equilibrium conditions during gas production, which is difficult to capture in real time. Therefore, it is often used for static theoretical reserve prediction. Production capacity numerical simulation separates free gas and desorbed gas by fitting historical gas production curves; its results are greatly affected by the model input parameters and are prone to multiple solutions. Microscopic molecular simulation is an important means of revealing gas adsorption-desorption mechanisms and phase ratios at the nanoscale. Currently, it cannot directly match the macroscopic production ratio and is mostly used in the mechanism explanation stage.

[0004] In summary, existing methods for determining the ratio of adsorbed gas to original free gas during coalbed methane production generally suffer from problems such as low quantification, high equipment and experimental costs, and difficulty in engineering application. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a coalbed methane production simulation device and phase differentiation method based on inert gas tracers. This device enables continuous and quantitative characterization of the production ratio of adsorbed gas and original free gas on a high-temperature, high-pressure displacement platform. During research on actual deep coalbed methane production, the inventors discovered a correlation between the concentration of inert gases in deep coal seams and the total amount of coalbed methane produced. Furthermore, some inert gases are not adsorbed by the coal seam and exist only in the free gas. This discovery spurred in-depth research into inert gases in coalbed methane, ultimately leading to the technical solution of this invention. This invention introduces a non-adsorbed inert gas as a tracer. By combining this with the stable initial concentration of the tracer in the original free gas of the coal sample after methane adsorption saturation, and incorporating the tracer's mass conservation relationship, this invention achieves real-time and quantitative characterization of the contributions of original free gas and adsorbed / desorbed gas during the depletion development of deep coalbed methane. This provides a reliable theoretical basis for the division of gas production stages, optimization of development regimes, and prediction of recoverable reserves during the development of deep coalbed methane.

[0006] In the first aspect, the coalbed methane production simulation device based on inert gas tracer includes a gas injection module, a sample clamping assembly, a back pressure control module, and a mass spectrometry monitoring module. The gas injection module includes a methane cylinder, a tracer gas cylinder, a premixed tank, and a reference storage tank. Methane and tracer gas are first fed into the premixed tank for mixing, then fed into the reference storage tank, measured, and then fed into the sample clamping assembly.

[0007] The sample clamping assembly includes an external pressure-resistant container and an internal sample chamber. The pressure-resistant container is connected to a temperature and pressure servo module, which inputs and outputs a high-temperature and high-pressure circulating medium to the pressure-resistant container, providing a simulated environment of deep coal seams for the sample.

[0008] The sample chamber contains a coal sample, and pressure-bearing pipes are installed at both ends of the sample chamber. The pressure-bearing pipes extend out of the pressure-resistant container and are connected to the reference storage tank and the back pressure control module, respectively. The coal sample adsorbs methane until it is saturated, and the tracer gas is not adsorbed by the coal sample, but exists in the free phase gas in the sample chamber.

[0009] The back pressure control module is used to control the outlet pressure of the sample clamping assembly. After the coal sample is saturated with adsorbed methane, the coalbed methane depletion development process is simulated. The gas produced by the coal sample is discharged to the mass spectrometry monitoring module. The mass spectrometry monitoring module can analyze the concentration of tracer gas in the produced gas in real time, and thus calculate the total output of inert tracer gas, thereby obtaining the proportion of adsorbed methane and original free methane in the produced gas.

[0010] The mass spectrometry monitoring module includes a gas flow meter and a mass spectrometer, used to measure the flow rate, composition, and concentration of the tracer gas.

[0011] The free phase gas includes free methane in the sample chamber after the coal sample has been saturated with adsorbed methane, and inert tracer gas. After the coal sample is saturated with adsorbed methane, it is in an initial equilibrium state. The free methane in the sample chamber under this state is called the original free methane, which is distinct from the methane phase released from the coal sample during coalbed methane depletion development. During gas production, the molar ratio of original free methane to inert tracer gas remains constant; therefore, the production rate of original free methane can be determined by the production rate of inert tracer gas.

[0012] Optionally, the gas filling module also includes a first booster pump and a gas filling control valve. The outlet pipes of the methane cylinder and the tracer gas cylinder are each equipped with a check valve to prevent the gas in the pipes from flowing back into the cylinders. The outlets of the two cylinders are respectively connected to the inlet of the premixing tank through high-pressure hoses for premixing methane and inert tracer gas.

[0013] The outlet of the premix tank is connected to the reference storage tank via a first booster pump, which injects the pressurized mixed gas into the reference storage tank, so that the reference storage tank has sufficient gas pressure to allow gas to enter the sample chamber until the coal sample is saturated with adsorption. The outlet of the reference storage tank is connected to the sample clamping assembly via a gas injection pipeline, which is equipped with a gas injection control valve to precisely control the injection volume and injection rate of the mixed gas.

[0014] Optionally, the sample clamping assembly is cylindrical in shape, with the pressure-resistant container and the sample chamber arranged concentrically. The pressure-resistant container includes a main container and removable plugs at both ends of the main container. The main container is hollow inside and open at both ends to accommodate the sample chamber. The side walls at both ends of the main container are respectively provided with liquid inlet and liquid outlet for inputting and outputting the circulating medium of the temperature and pressure servo module. The inner walls at both ends of the main container are provided with internal threads, and the outer surfaces of the plugs are provided with external threads, which are connected to each other by thread engagement.

[0015] The plug has a high-pressure sealing through hole in the middle, which is parallel to the central axis of the sample clamping assembly. The pressure-bearing tube at the end of the sample clamping assembly extends out of the plug through the high-pressure sealing through hole.

[0016] Optionally, the sample chamber includes an inlet plug, a sealing pipe, and an outlet plug in sequence along its axial direction. The inlet plug and the outlet plug are symmetrically arranged. The coal sample is located inside the sealing pipe. The two ends of the coal sample face the inner end faces of the inlet plug and the outlet plug, respectively. The outer ends of the inlet plug and the outlet plug are respectively connected to a pressure-bearing pipe. The two plugs are provided with flow channels inside to connect the two pressure-bearing pipes with the space where the coal sample is located.

[0017] Alternatively, the sealing fitting is cylindrical and is a heat-shrinkable tube that can tightly wrap around the outside of the coal sample. This facilitates the application of temperature and pressure of the circulating medium inside the pressure vessel to the coal sample, thus simulating the environment of deep coal seams.

[0018] Further optionally, the end plug is provided with a main air passage and an expansion air passage. The expansion air passage is conical and its inner diameter gradually increases towards the coal sample.

[0019] The small inner diameter end of the extended air passage is connected to the main air passage, and the large inner diameter end is connected to the pressure-bearing plane. The two end faces of the coal sample abut against the pressure-bearing planes of the two end plugs respectively. The surface of the pressure-bearing plane is evenly covered with through holes.

[0020] The sum of the areas of all the through holes on the pressure-bearing plane accounts for 10%-18% of the total area of ​​the pressure-bearing plane, which makes the mixed gas flow uniformly along the coal sample axis, avoids end-face effects, and improves the accuracy of detection.

[0021] Secondly, the phase differentiation method provided by the present invention includes: placing a coal sample into a sample chamber, applying pressure and temperature simulating a deep coal seam to the coal sample, introducing methane and inert tracer gas into a reference storage tank through a premixing tank, and measuring the total amount of gas and the concentration of each component in the reference storage tank.

[0022] The mixed gas in the reference tank is then introduced into the sample chamber until the coal sample is saturated with adsorbed methane. The inert tracer gas is not adsorbed by the coal sample and exists only in the free gas. After the coal sample is saturated with adsorbed methane, the free gas in the sample chamber is sampled. The free gas includes free methane and inert tracer gas. The concentration of inert tracer gas in the free gas is measured and recorded as the original concentration.

[0023] The gas path at the outlet of the sample clamping assembly is opened by a back pressure valve to simulate the coalbed methane depletion development process. The coal sample gas production is input into the mass spectrometry monitoring module. The coal sample gas production includes adsorbed methane and the free gas. The concentration of inert tracer gas in the free gas remains unchanged and is the original concentration. The mass spectrometry monitoring module analyzes the concentration of inert tracer gas in the gas production in real time, and then combines it with the original concentration to determine the amount of free methane produced in real time, and then determines the amount of adsorbed methane produced in real time.

[0024] The methane produced from the coal sample includes desorbed adsorbed methane and original free methane. The inert tracer gas exists only in the free phase and is not adsorbed by the coal; therefore, all produced tracer gases originate from the free phase. Based on the original tracer gas concentration in the free phase at adsorption equilibrium (i.e., the original concentration), combined with the system's tracer gas mass conservation, the cumulative free methane production can be determined. Then, by subtracting the cumulative free methane production from the cumulative total methane production, the cumulative adsorbed methane production is obtained, achieving dynamic quantitative analysis of the free and adsorbed gas production.

[0025] Optionally, the phase differentiation method specifically includes:

[0026] S1: Free volume calibration and pore volume test: The coal sample to be tested is installed in the sample chamber. The specified confining pressure and experimental temperature are applied to the pressure vessel using the temperature and pressure servo module. The inlet pipeline volume, coal sample pore volume and outlet pipeline volume are measured.

[0027] S2: Adsorption saturation test: Two gas cylinders inject high-pressure mixed gas into the reference tank through a premixing tank, and measure the initial pressure, initial temperature and initial tracer gas concentration of the reference tank.

[0028] Close the outlet of the pressure-bearing pipe on the downstream side of the pressure-resistant container, open the gas injection control valve, and inject the mixed gas in the reference storage tank into the sample chamber. After the coal sample has absorbed methane to equilibrium, measure the equilibrium pressure and equilibrium tracer gas concentration in the sample chamber. The equilibrium tracer gas concentration in the sample chamber is the concentration of inert tracer gas in the free gas.

[0029] Based on the principle of conservation of mass, determine the total amount of injected methane, the total amount of free methane inside the coal sample, and the total amount of methane adsorbed by the coal sample.

[0030] S3: Depletion Development Simulation: Close the gas injection control valve, open the back pressure valve, and use the back pressure pump to control the pressure drop at the outlet of the downstream pressure pipe to simulate the coalbed methane depletion development process; monitor the pressure and tracer gas concentration at the inlet of the sample clamping assembly, the pressure and tracer gas concentration at the outlet of the sample clamping assembly, and the cumulative gas output of the sample clamping assembly in real time through the mass spectrometry monitoring module.

[0031] By utilizing the conservation of inert tracer gas and the ideal gas law, the amount of inert tracer gas produced from the coal sample is determined. Then, combined with the original concentration, the amount of original free methane and adsorbed methane during the coal sample production process is determined.

[0032] S4: Convert the cumulative output of free methane and adsorbed methane from the coal sample into standard state volumes, determine the contribution ratios of the original free methane and adsorbed methane, and obtain the dynamic output curve.

[0033] Optionally, in step S3, the amount of original free methane in the coal sample gas production process is quantified by the amount of inert tracer gas produced, which is equal to the amount of inert tracer gas produced from the coal sample × (1 - the original concentration) / the original concentration.

[0034] The amount of adsorbed methane in the coal sample gas production process = the total amount of methane produced - the original free methane produced from the coal sample.

[0035] This invention, by introducing an inert gas tracer, avoids dependence on indirect parameters and enables dynamic quantification of the ratio of adsorbed gas to original free gas production directly based on experimental monitoring data. Furthermore, the equipment is highly versatile, with low experimental costs, eliminating the need for high-cost equipment and significantly reducing experimental investment, thus possessing excellent prospects for engineering application. This invention has a wide range of applicable sizes, allowing for the customization of sample chambers of different sizes according to coal samples or cores of varying sizes, making it particularly suitable for physical simulation experiments of large-size cores from deep coalbed methane. This invention can help researchers in the field reveal the dynamic contribution patterns of original free gas and adsorbed gas during the depletion and development of deep coalbed methane, providing clear experimental support for gas production stage division, development scheme optimization, and recoverable reserve prediction. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a coalbed methane production simulation device based on inert gas tracers.

[0037] Figure 2 This is a schematic diagram of the sample clamping assembly.

[0038] Figure 3 The curves showing the changes in the amount of tracer gas, original free methane, and adsorbed methane produced from coal samples at different times;

[0039] Figure 4 The curves show the dynamic changes in the production volume and corresponding ratio of the original free methane and adsorbed methane under standard conditions.

[0040] Among them, 1-methane cylinder, 2-tracer gas cylinder, 3-reference storage tank, 4-pressure resistant container, 5-sample chamber, 6-coal sample, 7-pressure bearing pipe, 8-gas flow meter, 9-mass spectrometer, 10-premixing tank, 11-first booster pump, 12-second booster pump, 13-gas injection control valve, 14-gas collection device, 15-liquid storage container, 16-circulation pump, 17-plug, 18-main container, 19-first edge, 20-second edge, 21-third edge, 22-sealing cone, 23-inlet end plug, 24-outlet end plug, 25-sealing fitting, 26-pressure bearing plane, 27-connector, 28-main gas channel, 29-expansion gas channel, 30-backpressure valve, 31-buffer container, 32-backpressure pump, 33-pressure relief valve. Detailed Implementation

[0041] Example 1

[0042] The coalbed methane production simulation device based on inert gas tracing in this embodiment, such as... Figures 1-2As shown, the system includes a gas preparation module, a sample clamping assembly, a back pressure control module, and a mass spectrometry monitoring module. The gas preparation module includes a methane cylinder 1, a tracer gas cylinder 2, a premixing tank 10, and a reference storage tank 3. Methane and tracer gas are first mixed in the premixing tank 10, then mixed in the reference storage tank 3, measured, and finally fed into the sample clamping assembly. The sample clamping assembly includes an external pressure-resistant container 4 and an internal sample chamber 5. The pressure-resistant container 4 is connected to a temperature and pressure servo module, which provides a high-temperature and high-pressure circulating medium for inputting and outputting into the pressure-resistant container 4, providing a simulated environment of deep coal seams for the sample. A coal sample 6 is placed in the sample chamber 5. Two pressure-bearing pipes 7 are provided at both ends of the sample chamber 5, extending out of the pressure-resistant container 4 and used to connect to the reference storage tank 3 and the back pressure control module, respectively. The coal sample adsorbs methane until saturation, while the tracer gas is not adsorbed by the coal sample but exists in the free phase gas in the sample chamber.

[0043] The back pressure control module is used to control the outlet pressure of the sample clamping assembly. After the coal sample is saturated with adsorbed methane, the coalbed methane depletion development process is simulated. The gas produced by the coal sample is discharged to the mass spectrometry monitoring module. The mass spectrometry monitoring module can analyze the concentration of tracer gas in the produced gas in real time, and thus calculate the total output of tracer gas, thereby obtaining the proportion of adsorbed methane and original free methane in the produced gas.

[0044] The mass spectrometry monitoring module includes a gas flow meter 8 and a mass spectrometer 9, which are used to measure the flow rate, composition, and concentration of the tracer gas.

[0045] The gas filling module also includes a first booster pump 11 and a gas filling control valve 13. The outlet pipes of the methane cylinder 1 and the tracer gas cylinder 2 are respectively equipped with one-way valves to prevent the gas in the pipes from flowing back into the cylinders. The outlets of the two cylinders are respectively connected to the inlet of the premixing tank 10 through high-pressure hoses for premixing methane and inert tracer gas.

[0046] The outlet of the premix tank 10 is connected to the reference storage tank 3 through the first booster pump 11, which injects the pressurized mixed gas into the reference storage tank 3, so that the reference storage tank has sufficient gas pressure to allow gas to enter the sample chamber until the coal sample is saturated. The outlet of the reference storage tank 3 is connected to the sample clamping assembly through the gas injection pipeline, which is equipped with a gas injection control valve 13 for precisely controlling the injection volume and injection rate of the mixed gas.

[0047] Both the premix tank 10 and the reference storage tank 3 are equipped with sampling interfaces, which can be used to sample and detect the concentration of each component of the gas in the premix tank 10 and the reference storage tank 3.

[0048] Reference tank 3 is a high-pressure resistant container of known volume, equipped with pressure and temperature sensors for accurately measuring the total amount of gas injected into the sample clamping assembly.

[0049] The gas mixing module of this invention is used to premix methane and inert tracer gas to a preset concentration and then pressurize and inject the mixture into the sample clamping assembly. Methane cylinder 1 stores high-pressure methane gas (purity greater than 99.9%), and tracer gas cylinder 2 stores inert tracer gas (purity greater than 99.9%). Premixing tank 10 receives and premixes methane and inert tracer gas; after sampling and testing at the sampling interface of premixing tank 10, the initial concentration of the mixed gas can be obtained. A first booster pump 11 pressurizes the mixed gas to the pressure required for testing, and then injects the pressurized mixed gas into reference storage tank 3.

[0050] The inert tracer gas is selected from helium, neon or argon. In this example, helium is used. The amount of inert tracer gas adsorbed on the coal matrix surface is negligible compared to methane and is easily identified by the mass spectrometer 9.

[0051] The temperature and pressure servo module includes a liquid storage container 15, a second booster pump 12, and a circulation pump 16. The liquid storage container 15 is equipped with a temperature control device to control the temperature of the circulating medium inside the liquid storage container 15. The outlet of the liquid storage container 15 is connected to the second booster pump 12 through the circulation pump 16. The second booster pump 12 is connected in parallel to the inlet of the pressure-resistant container 4 and the inlet of the liquid storage container 15 to provide a circulating medium with a certain temperature and pressure to the pressure-resistant container 4, so as to apply confining pressure and temperature to the sample chamber 5 to simulate the high temperature and high pressure environment of deep strata. The outlet of the pressure-resistant container 4 is connected to another inlet of the liquid storage container 15 to realize the circulation of the circulating medium between the temperature and pressure servo module and the sample clamping assembly.

[0052] The liquid storage container 15 is used to store the circulating medium, which is selected from high-temperature resistant silicone oil or a mixture of deionized water and ethylene glycol. The operating temperature range is 20-150℃, and it can maintain chemical stability and low compressibility within this temperature range.

[0053] The temperature and pressure servo module of this invention provides a circulating medium with the required temperature and pressure for testing into the pressure vessel 4. This circulating medium acts uniformly on the outside of the sample chamber 5, i.e., uniformly on the outside of the coal sample 6, simulating the temperature and pressure environment of a deep coal seam. The storage container 15 contains the circulating medium and its temperature can be controlled. The circulating medium, after passing through the circulation pump 16 and the second booster pump 12, reaches a certain pressure at a certain temperature and enters the pressure vessel 4, applying confining pressure to the sample chamber 5, and then returns to the storage container 15, forming a closed loop.

[0054] The first booster pump 11 and the second booster pump 12 are both electric servo plunger pumps with an output pressure range of 0-70MPa and a control accuracy of not less than ±0.1MPa. They are also equipped with a high-pressure safety relief valve. The temperature control device of the liquid storage container 15 controls the temperature of the circulating medium within the range of ±0.5℃ of the preset value.

[0055] The sample clamping assembly is cylindrical in shape, with the pressure container 4 and the sample chamber 5 arranged concentrically. The pressure container 4 includes a main container 18 and detachable plugs 17 at both ends of the main container 18. The main container 18 is hollow inside and open at both ends to accommodate the sample chamber 5. The side walls at both ends of the main container are respectively provided with liquid inlet and liquid outlet for inputting and outputting the circulating medium of the temperature and pressure servo module. The inner walls at both ends of the main container 18 are provided with internal threads, and the outer side of the plugs is provided with external threads, which are connected to each other by thread engagement.

[0056] The plug 17 has a high-pressure sealing through hole in its middle, which is parallel to the central axis of the sample clamping assembly. The pressure-bearing tube at the end of the sample clamping assembly extends through the high-pressure sealing through hole and passes through the plug. The high-pressure sealing through hole penetrates the corresponding plug.

[0057] The main container 18 is divided into three parts along its own axis. The inner diameters of the two end parts are equal and larger than the inner diameter of the middle part, so that the connection between the end part and the middle part forms a first edge 19 protruding into the main container 18. The plug is divided into three parts along its own axis. The outer diameter of the plug gradually decreases from the outside to the inside of the main container 18, so that the connection between every two parts of the plug forms a second edge 20 protruding outward from the plug. The third edge 21 is the second edge 20 and the third edge 21, respectively, from the outside to the inside of the main container 18.

[0058] The second edge 20 faces the outer end face of the main container 18; the third edge 21 faces the first edge 19, and a sealing ring is provided between the third and first edges 19. The plug and the main container 18 are sealed by the double seal of the thread and the sealing ring. The sealing ring is deformed by the axial pressure generated by tightening the plug 17, forming a reliable static seal; the end face with the smallest outer diameter of the plug 17 faces the sample chamber 5.

[0059] The high-pressure sealing through hole of the plug is provided with a sealing cone 22, and the pressure-bearing pipe 7 can pass through the sealing cone 22; the sealing cone 22 includes a clamping nut and a conical sealing sleeve, and the sealing sleeve is inserted into the high-pressure sealing through hole from the outside; the outer end of the sealing sleeve is connected to the clamping nut, and the clamping nut is located outside the plug; the inner end of the sealing sleeve abuts against the limiting part inside the plug through a sealing gasket.

[0060] When the compression nut is tightened from the outside, the sealing sleeve is deformed under pressure, causing the inner wall of the sealing sleeve to grip the outer wall of the pressure-bearing pipe. At the same time, the outer wall of the sealing sleeve is tightly fitted with the inner wall of the high-pressure sealing through hole, thus forming a dynamic seal between the pressure-bearing pipe and the plug. This allows the pressure-bearing pipe to maintain airtightness relative to the plug under pressure, preventing the circulating medium from leaking from the gap between the pressure-bearing pipe and the high-pressure sealing through hole. It also allows the pressure-bearing pipe to move axially within a certain range to adapt to installation requirements.

[0061] The sample chamber 5 includes, along its axial direction, an inlet plug 23, a sealing pipe 25, and an outlet plug 24. The inlet plug 23 and the outlet plug 24 are symmetrically arranged. The coal sample 6 is located inside the sealing pipe 25. The two ends of the coal sample 6 face the inner end faces of the inlet plug 23 and the outlet plug 24, respectively. The outer ends of the inlet plug 23 and the outlet plug 24 are respectively connected to a pressure-bearing pipe. The two plugs are provided with flow channels inside to connect the two pressure-bearing pipes with the space where the coal sample 6 is located.

[0062] The sealing tube 25 is cylindrical and is a heat-shrinkable tube that can tightly wrap around the outside of the coal sample 6. This facilitates the application of temperature and pressure of the circulating medium inside the pressure vessel to the coal sample, simulating the environment of deep coal seams. Both ends of the sealing tube 25 can be fastened to the outer walls of two end plugs, coaxially fixing the coal sample 6 between the two end plugs to form a sealed axial flow channel. The sealing tube is a heat-shrinkable tube with high thermal conductivity and high pressure transmission capacity, possessing excellent thermal conductivity and pressure transmission performance.

[0063] The inlet plug 23 and the outlet plug 24 have the same structure, but are in opposite directions. Taking the inlet plug 23 as an example, the inlet plug 23 is a stainless steel columnar structure. Its inner end face is provided with a pressure-bearing plane 26 that fits against the end face of the coal sample 6. The pressure-bearing plane 26 is set vertically and its area is not less than the area of ​​the end face of the coal sample 6.

[0064] The outer surface of the inlet plug 23 is provided with several annular grooves for placing the sealing ring. The end of the sealing tube 25 is sleeved on the outside of the grooved part of the inlet plug 23 to enhance the sealing and fixation between the inlet plug 23 and the sealing tube 25.

[0065] The end plug has an internal threaded hole at the center of the end furthest from the sealing tube 25 for connecting the connector 27. One end of the connector 27 is connected to the internal threaded hole through an external threaded tube, and the other end is connected to the pressure tube. The pressure tube, the connector 27 and the internal threaded hole form a gas channel.

[0066] The end plug has a main air passage 28 and an expansion air passage 29 inside. The expansion air passage 29 is conical and faces the coal sample 6. The inner diameter of the expansion air passage 29 gradually increases. The two ends of the main air passage 28 are connected to the internal threaded hole and the small inner diameter end of the expansion air passage 29, respectively. The large inner diameter end of the expansion air passage 29 is connected to the pressure bearing plane 26. The two end faces of the coal sample abut against the pressure bearing planes of the end plugs on both sides. The surface of the pressure bearing plane 26 is evenly covered with through holes, so that the space where the coal sample 6 is located is connected to the pressure bearing plane 26, the expansion air passage 29 and the internal threaded hole of the main air passage 28 in sequence, allowing the test gas to pass through the coal sample 6 axially and then be discharged from the sample chamber 5.

[0067] The sample chamber 5 of this invention is located at the center of the pressure vessel 4. The pressure-bearing pipe of the inlet plug 23 passes through the high-pressure sealing through-hole and sealing cone of the upstream plug. This pressure-bearing pipe is connected to the gas dispensing module through a pipeline connector and is equipped with inlet pressure and tracer concentration measuring points. The pressure-bearing pipe of the outlet plug 24 passes through the high-pressure sealing through-hole and sealing cone of the downstream plug, extends to the outside of the sample clamping assembly, and is then connected to the back pressure control module through a pipeline connector. It is also equipped with outlet pressure and tracer concentration measuring points. After the plugs at both ends are tightened, the coal sample 6 is suspended at the axial center of the pressure vessel 4. The circulating medium delivered by the temperature and pressure servo module enters the annular space between the inner wall of the pressure vessel 4 and the outer wall of the sample chamber 5, applying uniform confining pressure to the coal sample 6, while simultaneously regulating the experimental temperature through heat transfer.

[0068] The pressure-bearing pipe is made of small-diameter high-pressure stainless steel with an inner diameter of no more than 2 mm and a length as short as possible to reduce the dead volume of the inlet and outlet pipelines and reduce the deduction error in the calculation of the gas production of coal sample 6.

[0069] The sum of the areas of all the through holes in the pressure-bearing plane 26 accounts for 10% of the total area of ​​the pressure-bearing plane 26, which makes the mixed gas flow uniformly along the axial direction of the coal sample 6. This is conducive to the uniform adsorption of methane in all parts of the coal sample, avoids uneven gas dispersion in the coal sample, minimizes dead zones in the coal sample, and accelerates the adsorption of methane in the coal sample.

[0070] The back pressure control module includes a back pressure valve 30, a buffer container 31 and a back pressure pump 32 connected in sequence, which are used to control the pressure at the gas outlet of the sample clamping component to simulate the pressure reduction condition during the coalbed methane depletion development process.

[0071] The inlet end of the back pressure valve 30 is connected to the pressure-bearing pipe at the outlet end of the sample clamping assembly via a pipeline. The outlet end of the back pressure valve 30 is connected in parallel to the buffer container 31 and the mass spectrometry monitoring module. A sampling interface and a rapid pressure relief branch are provided between the back pressure valve 30 and the pressure-bearing pipe. The sampling interface is used to determine the concentration of tracer gas in the produced gas. A pressure relief valve 33 is provided on the rapid pressure relief branch. That is, the pressure relief valve 33 is set in parallel with the back pressure valve 30 and is used for rapid pressure relief when the experiment ends or an emergency shutdown occurs.

[0072] The back pressure pump 32 is connected to the back pressure valve 30 through the buffer container 31 to provide a stable pressure source to drive the set pressure adjustment of the back pressure valve 30; the buffer container 31 can absorb pressure pulsation to ensure stable back pressure.

[0073] The back pressure valve 30 is a pneumatic or electrically controlled precision pressure regulating valve that can set and maintain the back pressure at the outlet of the sample clamping assembly.

[0074] The back pressure pump 32 is a precision plunger pump or gas booster pump with stable output pressure and is equipped with a safety relief valve to prevent overpressure; the back pressure valve 30 has a pressure adjustment range of 0-40MPa, a control accuracy of not less than ±0.05MPa, and a minimum adjustable pressure drop rate of 0.01MPa / min.

[0075] The mass spectrometry monitoring module includes a gas flow meter 8 and a mass spectrometer 9, which are used to measure the flow rate, composition and concentration of tracer gas produced by the sample clamping assembly.

[0076] The outlet end of the back pressure valve 30 is connected to the gas flow meter 8, which is used to directly output the cumulative gas production and instantaneous gas production rate under standard conditions. The gas flow meter 8 is a mass flow meter or a standard state volume flow meter.

[0077] Alternatively, if the mass spectrometer 9 operates in automatic continuous monitoring mode, the outlet of the gas flow meter 8 is connected to the mass spectrometer 9 through the sample inlet line. The sample inlet line is equipped with a micro-flow control valve to introduce the produced gas into the ion source of the mass spectrometer 9 at a constant micro-flow rate. The mass spectrometer 9 automatically collects and analyzes the gas components at set time intervals and determines the mole fraction (concentration) of the tracer gas in the produced gas during each time period.

[0078] Alternatively, if the mass spectrometer 9 operates in offline sampling mode, the outlet of the gas flow meter 8 is connected to the mass spectrometer 9 via a gas collection device 14. The gas collection device 14 includes several sampling gas cylinders or aluminum-plastic composite gas bags, used to manually collect the produced gas at set time points, seal and preserve the produced gas samples, and then connect the produced gas samples to the offline mass spectrometer 9 for batch analysis to determine the mole fraction (concentration) of inert tracer gas in each sample. The sampling gas cylinders or aluminum-plastic composite gas bags are equipped with sealing valves and are pre-vacuum treated to eliminate residual air interference.

[0079] The mass spectrometry monitoring module also includes a data acquisition unit and a standard gas calibration unit. The data acquisition unit is connected to the gas flow meter 8 and the online mass spectrometer 9, or to the timed switching valve and the gas flow meter 8, to synchronously record the gas production, sampling time and corresponding gas component data, and transmit them to the central numerical control system.

[0080] The standard gas calibration unit includes inert tracer gas standard gas cylinders of known concentrations, used for periodic concentration calibration of the mass spectrometer 9.

[0081] Both the methane cylinder 1 and the tracer gas cylinder 2 are equipped with pressure gauges at their openings. The reference storage tank 3 is equipped with a thermometer and a pressure gauge. A pressure gauge and a sampling interface are provided between the gas injection control valve 13 and the pressure-bearing pipe opening on the upstream side of the sample clamping assembly. A pressure gauge and a sampling interface are provided between the pressure-bearing pipe opening on the downstream side of the sample clamping assembly and the back pressure valve 30. This facilitates the measurement of gas pressure in the pipelines at corresponding locations and facilitates sampling.

[0082] The central numerical control system adopts existing technologies, such as an industrial computer, a data acquisition card, a control output interface, and a human-machine interface, to realize the coordinated automated control, data acquisition, and processing of various modules.

[0083] The industrial control computer is connected to the signal output terminals of each sensor, pressure gauge, and flow meter via a data acquisition card. The industrial control computer is connected to the control terminals of each actuator via a control output interface, and sends control commands to the one-way valve of the gas injection module, the first booster pump 11 and the gas injection control valve 13, the second booster pump 12 of the temperature and pressure servo module, the circulation pump 16 and the temperature control device, the back pressure valve 30 and the back pressure pump 32 of the back pressure control module, and the gas flow meter 8 of the mass spectrometry monitoring module to realize the automatic adjustment of gas injection rate, confining pressure, temperature and back pressure.

[0084] The central numerical control system coordinates the sequential operation of each module according to the preset experimental plan, synchronously records time series data, and collects the following parameters in real time: gas source pressure, reference storage tank 3 pressure, inlet and outlet pressure of the sample clamping component, confining pressure, temperature, back pressure, output gas volume, and tracer gas concentration at the inlet and outlet of the sample clamping component.

[0085] The industrial control computer has a built-in phase state calculation program module, which can perform the following calculations based on the collected data: the amount of methane adsorbed by the sample and the amount of original free methane during the adsorption process, the amount of original free methane produced by the sample during the depletion development process, the amount of adsorbed methane produced by the sample and the proportion of phase state produced, and generate a dynamic production curve based on the calculation results.

[0086] The human-computer interaction interface is used to display real-time curves of various parameters, dynamic change curves of phase output ratio, set experimental schemes, and alarm prompts.

[0087] The central numerical control system is equipped with emergency safety protection logic. When any parameter of the confining pressure, temperature, or inlet / outlet pressure of the sample clamping assembly is detected to be out of limit or abnormal, the gas injection control valve 13 and the first booster pump 11 are automatically shut off, the pressure relief valve 33 is activated, and an audible and visual alarm is triggered.

[0088] Example 2

[0089] The coalbed methane production simulation device based on inert gas tracer in this embodiment is the same as that in Embodiment 1, except that the inlet end plug does not have a main gas channel and an extension gas channel. Instead, it is replaced by six independent horizontal gas channels. The six horizontal gas channels are evenly distributed on the longitudinal section of the inlet end plug, and the upstream end of each gas channel is connected to the connector of the inlet end plug. However, the methane adsorption saturation time of the coal sample in this embodiment is twice as long as that of the coal sample in Embodiment 1. Too many gas channels not only increase the processing cost, but also affect the strength and stability of the end plug.

[0090] Example 3

[0091] The coalbed methane production simulation device based on inert gas tracer in this embodiment is the same as that in Embodiment 1, except that the sum of the areas of all through holes on the pressure-bearing plane accounts for 18% of the total area of ​​the pressure-bearing plane.

[0092] Example 4

[0093] The coalbed methane production simulation device based on inert gas tracer in this embodiment is the same as that in Embodiment 1, except that the sum of the areas of all through holes on the pressure-bearing plane accounts for 9% of the total area of ​​the pressure-bearing plane.

[0094] Example 5

[0095] The coalbed methane production simulation device based on inert gas tracing in this embodiment is the same as that in Embodiment 1, except that the sum of the areas of all through holes on the pressure-bearing plane accounts for 19% of the total area of ​​the pressure-bearing plane.

[0096] Table 1. Comparison of the time taken for adsorbed methane to reach equilibrium in coal samples of Examples 1, 3, 4, and 5.

[0097] project Time (days) for coal sample to reach methane adsorption equilibrium Example 1 6.5 Example 3 6.2 Example 4 7.0 Example 5 6.1

[0098] A suitable pore area on the pressure-bearing surface is beneficial for the coal sample to quickly reach methane adsorption equilibrium.

[0099] Example 6

[0100] The coalbed methane production phase differentiation method based on inert gas tracer in this embodiment includes: placing a coal sample into a sample chamber, applying pressure and temperature simulating deep coal seams to the coal sample, introducing methane and inert tracer gas into a reference tank through a premixing tank, and measuring the total amount of gas and the concentration of each component in the reference tank.

[0101] The mixed gas in the reference tank is then introduced into the sample chamber until the coal sample is saturated with adsorbed methane. The inert tracer gas is not adsorbed by the coal sample and exists only in the free gas. After the coal sample is saturated with adsorbed methane, the free gas in the sample chamber is sampled. The free gas includes free methane and inert tracer gas. The concentration of inert tracer gas in the free gas is measured and recorded as the original concentration.

[0102] The gas path at the outlet of the sample clamping assembly is opened by a back pressure valve to simulate the coalbed methane depletion development process. The coal sample gas production is input into the mass spectrometry monitoring module. The coal sample gas production includes adsorbed methane and the free gas. The concentration of inert tracer gas in the free gas remains unchanged and is the original concentration. The mass spectrometry monitoring module analyzes the concentration of inert tracer gas in the gas production in real time, and then combines it with the original concentration to determine the amount of free methane produced in real time, and then determines the amount of adsorbed methane produced in real time.

[0103] The phase differentiation method is specifically as follows:

[0104] S1: Free volume calibration and pore volume test: The coal sample to be tested is installed in the sample chamber. The specified confining pressure and experimental temperature are applied to the pressure vessel using the temperature and pressure servo module. The inlet pipeline volume, coal sample pore volume and outlet pipeline volume are measured.

[0105] S2: Adsorption saturation test: Two gas cylinders inject high-pressure mixed gas into the reference tank through a premixing tank, and measure the initial pressure, initial temperature and initial tracer gas concentration of the reference tank.

[0106] Close the outlet of the pressure-bearing pipe on the downstream side of the pressure-resistant container, open the gas injection control valve, and inject the mixed gas in the reference storage tank into the sample chamber. After the coal sample has absorbed methane to equilibrium, measure the equilibrium pressure and equilibrium tracer gas concentration in the sample chamber. The equilibrium tracer gas concentration in the sample chamber is the concentration of inert tracer gas in the free gas.

[0107] Based on the principle of conservation of mass, determine the total amount of injected methane, the total amount of free methane inside the coal sample, and the total amount of methane adsorbed by the coal sample.

[0108] S3: Depletion Development Simulation: Close the gas injection control valve, open the back pressure valve, and use the back pressure pump to control the pressure drop at the outlet of the downstream pressure pipe to simulate the coalbed methane depletion development process; monitor the pressure and tracer gas concentration at the inlet of the sample clamping assembly, the pressure and tracer gas concentration at the outlet of the sample clamping assembly, and the cumulative gas output of the sample clamping assembly in real time through the mass spectrometry monitoring module.

[0109] By utilizing the conservation of inert tracer gas and the ideal gas law, the amount of inert tracer gas produced from the coal sample is determined. Then, combined with the original concentration, the amount of original free methane and adsorbed methane during the coal sample production process is determined.

[0110] S4: Convert the cumulative output of free methane and adsorbed methane from the coal sample into standard state volumes, determine the contribution ratios of the original free methane and adsorbed methane, and obtain the dynamic output curve.

[0111] Step S1 specifically includes:

[0112] (1) First, the coal sample is processed into a standard φ25×50mm cylindrical plunger sample. The diameter of the end face of the coal sample is slightly smaller than the pressure bearing plane of the plug. After the coal sample is dried and weighed, the sealing pipe is wrapped around the outside of the coal sample, the sample chamber is assembled, and then the sample chamber is installed between the two plugs and fixed in an airtight manner. In this embodiment, the sample mass is 34.308g.

[0113] (2) Inject circulating medium into the pressure vessel through the temperature and pressure servo module, apply a specified confining pressure of 25 MPa and keep the sample chamber at the target experimental temperature T. sys=343.15K, placing the coal sample in a simulated formation environment;

[0114] (3) The inlet pipeline volume V is determined using the existing helium expansion method. in Coal sample pore volume V samp and the volume V of the outlet pipeline out In this embodiment, V in V samp and V out The values ​​were 4.82 mL, 0.85 mL, and 5.5 mL, respectively.

[0115] In step (3), the inlet pipeline volume refers to the sum of the volumes of all gas passages from the gas injection control valve to the upstream end of the coal sample, and the outlet pipeline volume refers to the sum of the volumes of all gas passages from the downstream end of the coal sample to the back pressure valve.

[0116] Step S2 is as follows:

[0117] (4) Simultaneously inject gas into the premixing tank from both the methane cylinder and the tracer gas cylinder. After sampling and analysis, once the component concentration of the mixed gas in the premixing tank has stabilized to the set concentration, start the first booster pump to inject gas into the reference storage tank. After the pressure gauge and thermometer readings of the reference storage tank have stabilized, record the initial pressure P of the reference storage tank. ref,0 The pressure is 22.12 MPa, and the initial temperature is T. ref,0 The initial tracer gas concentration C was measured at 296.15 K from a sample taken from a reference tank. ref,0 The value is 3.02%; the gas injection control valve remains closed during this step.

[0118] (5) Close the pipeline downstream of the back pressure valve through the back pressure valve, shut off the gas path between the premix tank and the reference tank, open the gas injection control valve, perform throttling control, and slowly inject the mixed gas in the reference tank into the sample clamping assembly, and monitor the pressure P at the inlet of the reference tank. in and tracer gas concentration C in The pressure P at the outlet of the reference storage tank out and tracer gas concentration C out Simultaneously monitor the internal pressure P of the reference storage tank. ref ;

[0119] (6) When the pressure at the inlet of the pressure-bearing tubes at both ends of the sample clamping assembly and the concentration of the tracer gas are stable and tend to be consistent, the coal sample is determined to have reached adsorption equilibrium; in this embodiment, the equilibrium pressure P of the sample chamber is... eq The pressure is 20.12 MPa, and the tracer gas equilibrium concentration C in the sample chamber is... eq The concentration is 3.05%, which is the original concentration.

[0120] Close the gas injection control valve and record the equilibrium pressure P of the reference storage tank. ref,eqand equilibrium tracer gas concentration C ref,eq The values ​​were 20.32 MPa and 3.05%, respectively.

[0121] (7) According to the law of conservation of mass, the total amount of methane injected into the simulation device is determined by the following formula based on the initial and equilibrium states of the reference storage tank:

[0122]

[0123] in, V represents the total amount of methane injected into the simulation device. ref The reference storage tank volume is 785.40 mL; R is the ideal gas constant, 8.314 J / mol·K; Z ref,0 The compressibility factor of the mixed gas in the initial state of the reference storage tank is 0.8479; Z ref,eq The compressibility factor of the mixed gas in the reference storage tank after balancing is 0.8381;

[0124] The initial total amount of free methane in the simulation device is determined using the following formula:

[0125]

[0126] in, The total amount of free methane injected into the simulation device; C eq P represents the equilibrium tracer gas concentration in the sample chamber when the coal sample reaches adsorption equilibrium. eq Z represents the target adsorption pressure in the sample chamber when the coal sample reaches adsorption equilibrium. eq The compressibility factor of the mixed gas in the system containing the coal sample in equilibrium is 0.9249.

[0127] According to the law of conservation of mass, the amount of adsorbed methane and the amount of original free methane in the coal sample can be determined using the following formulas:

[0128]

[0129]

[0130] in, This represents the amount of methane adsorbed by the coal sample. This represents the amount of original free methane within the coal sample.

[0131] Based on the ideal gas law, the volume of adsorbed methane and the volume of free methane inside the coal sample under standard conditions are determined using the following formulas:

[0132]

[0133]

[0134] in, The volume of methane adsorbed by the coal sample under standard conditions, in mL; Z represents the initial free methane volume inside the coal sample under standard conditions, in mL; std The compressibility factor of methane gas under standard conditions is 0.9976; T std The temperature of the gas under standard conditions is 273.15 K; P std The pressure of the gas under standard conditions is 0.1 MPa.

[0135] In this embodiment, at adsorption equilibrium, the volume of adsorbed methane was 657.32 mL, and the volume of the original free methane was 146.55 mL.

[0136] Step S3 is as follows:

[0137] (8) Total amount of gaseous substances produced, n pro (t) The cumulative amount of inert tracer gas produced, converted from standard state volume, n TG,pro (t) The tracer gas concentration C at the outlet of the reference storage tank, continuously measured at time intervals Δt by a gas flow meter. out,i and the corresponding gas output ΔV during the time period std,i Accumulation determines, that is:

[0138]

[0139]

[0140] Among them, V std (t) represents the cumulative standard-state gas volume produced by the sample clamping assembly after correction. It is a set of numbers representing the cumulative methane produced by the sample clamping assembly at each time point, converted to the volume under standard conditions (i.e., 0°C and 1 atmosphere), where the volume increases with time. t represents the actual simulated gas production time in seconds; i represents the number of samples; n represents the total number of samples; Z std,i The compressibility factor of the gas mixture under standard conditions at sampling time point i;

[0141] For example, if sampling is performed every 2 seconds, then the sampling times within 10 seconds are the 2nd, 4th, 6th, 8th, and 10th seconds, with i being 1, 2, 3, 4, and 5 respectively, and n=5.

[0142] Total amount of methane produced for:

[0143]

[0144] Because the system is closed, according to the law of conservation of mass, the total amount of methane produced in the coal sample is... for:

[0145]

[0146] in, The amount of methane produced by the inlet pipeline; The amount of methane produced by the outlet pipeline;

[0147] According to the ideal gas law and Determined by the following formula:

[0148]

[0149]

[0150] in, The initial amount of methane in the inlet pipeline is determined by the following formula:

[0151]

[0152] The initial amount of methane in the outlet pipeline is determined by the following formula:

[0153]

[0154] The amount of residual methane in the inlet pipeline is determined by the following formula:

[0155]

[0156] The amount of residual methane in the outlet pipeline is determined by the following formula:

[0157]

[0158] Among them, P in (t) represents the pressure at the inlet of the sample clamping assembly; P our (t) represents the pressure at the outlet of the sample clamping assembly; these two pressure values ​​are measured in real time by pressure gauges in the pipelines at both ends of the sample clamping assembly.

[0159] C in (t) represents the concentration of the tracer gas at the inlet of the sample clamping assembly; C out (t) represents the tracer gas concentration at the outlet of the sample clamping assembly; these two gas concentration values ​​are obtained by real-time sampling and analysis by the samplers at both ends of the sample clamping assembly.

[0160] Z in (t) is the compressibility factor of the mixed gas in the inlet pipeline at time t; Z out (t) represents the compressibility factor of the mixed gas in the outlet pipeline at time t; these two compressibility factors can be determined by querying the corresponding P, T, and C parameters using REFPROP software.

[0161] (9) The amount of inert tracer gas produced from the coal sample, n TG,samp,pro (t) is determined by the following formula:

[0162]

[0163] Where, n TG,samp,eq The amount of initial inert tracer gas in the coal sample is determined using the ideal gas law and the conservation of inert tracer gas in the system:

[0164]

[0165] n TG,samp (t) represents the amount of residual inert tracer gas in the coal sample, determined by the ideal gas law and the conservation of inert tracer gas in the system:

[0166]

[0167] Where, n TG,sys,0 The total amount of initial inert tracer gas in the system is obtained using the ideal gas law:

[0168]

[0169] n TG,in (t) represents the total amount of inert tracer gas in the inlet pipeline, obtained using the ideal gas law:

[0170]

[0171] n TG,out (t) represents the total amount of inert tracer gas in the outlet pipeline, obtained using the ideal gas law:

[0172]

[0173] n TG,pro (t) represents the measured total amount of inert gas produced, including the total amount of inert gas produced in the inlet pipeline, outlet pipeline, and sample.

[0174] Based on the characteristic that inert tracer gases exist only in free gases, the amount of original free methane produced can be determined by conserving the amount of inert tracer gas. It is determined by the following formula:

[0175]

[0176] According to the law of conservation of mass, the amount of adsorbed methane produced... Determined by the following formula:

[0177] ;

[0178] Step S4 is as follows:

[0179] Based on the ideal gas law, the volumes of free methane and adsorbed methane produced by coal samples at different time periods under standard conditions can be obtained (e.g., Figure 3 (as shown)

[0180]

[0181]

[0182] in, The compressibility factor of methane gas under standard conditions is 0.9976; based on the above formula, the contribution ratio of the original free methane in the methane produced from the coal sample at time t is... Determined by the following formula:

[0183]

[0184] The proportion of adsorbed methane in the methane produced from the coal sample at time t Determined by the following formula:

[0185]

[0186] According to different times and Plotting time on the x-axis and contribution ratio on the y-axis, we obtain the dynamic change curves of the original free methane production ratio and the adsorbed methane production ratio (e.g., Figure 4 As shown in the figure, this enables continuous quantitative characterization of the contribution ratio of adsorbed gas and original free gas during the production of deep coalbed methane.

[0187] In this invention, all temperature parameters are in Kelvin (K), and all gas volume parameters are in cm³. 3 All gas concentrations are expressed in %, all gaseous amounts of substance (n) are expressed in mol, and all compressibility factor parameters can be determined by querying the corresponding P, T, and C parameters using REFPROP software.

Claims

1. A coalbed methane production simulation device based on inert gas tracing, comprising a gas injection module, a sample clamping assembly, a back pressure control module, and a mass spectrometry monitoring module, characterized in that, The gas dispensing module includes a methane cylinder, a tracer gas cylinder, a premixing tank, and a reference storage tank. Methane and tracer gas are first mixed in the premixing tank, then mixed in the reference storage tank, measured, and finally fed into the sample clamping assembly. The sample clamping assembly includes an external pressure-resistant container and an internal sample chamber. The pressure-resistant container is connected to a temperature and pressure servo module to provide a simulated environment of deep coal seams for the sample chamber. The sample chamber contains a coal sample. Two pressure-bearing pipes are installed at both ends of the sample chamber. The two pressure-bearing pipes extend out of the pressure-resistant container and are connected to the reference storage tank and the back pressure control module, respectively. The coal sample adsorbs methane until it is saturated. The tracer gas is not adsorbed by the coal sample, but exists in the free phase gas in the sample chamber. The back pressure control module is used to control the outlet pressure of the sample clamping assembly. After the coal sample is saturated with adsorbed methane, the coalbed methane depletion development process is simulated. The gas produced by the coal sample is discharged to the mass spectrometry monitoring module. The mass spectrometry monitoring module can analyze the concentration of tracer gas in the produced gas in real time, thereby obtaining the proportion of adsorbed methane and original free methane in the produced gas.

2. The simulation device according to claim 1, characterized in that, The gas dispensing module also includes a first booster pump and a gas injection control valve. The outlet pipes of the methane cylinder and the tracer gas cylinder are each equipped with their own one-way valves. The outlets of both cylinders are connected to a premixing tank for premixing methane and inert tracer gas. The outlet of the premix tank is connected to the reference storage tank via a first booster pump, which injects the pressurized mixed gas into the reference storage tank, so that the reference storage tank has sufficient gas pressure to allow gas to enter the sample chamber until the coal sample is saturated with adsorption. The outlet of the reference storage tank is connected to the sample clamping assembly via a gas injection pipeline, which is equipped with a gas injection control valve.

3. The simulation device according to claim 2, characterized in that, The sample clamping assembly is cylindrical in shape, and the pressure-resistant container and the sample chamber are concentrically arranged. The pressure-resistant container includes a main container and removable plugs at both ends of the main container. The main container is hollow inside and open at both ends to accommodate the sample chamber. The side walls at both ends of the main container are respectively provided with liquid inlet and liquid outlet for inputting and outputting the circulating medium of the temperature and pressure servo module. The plug has a high-pressure sealing through hole in the middle, which is parallel to the central axis of the sample clamping assembly. The pressure-bearing tube at the end of the sample chamber extends out of the plug through the high-pressure sealing through hole.

4. The simulation device according to claim 3, characterized in that, The sample chamber includes an inlet plug, a sealing pipe, and an outlet plug along its axial direction. The inlet plug and the outlet plug are symmetrically arranged. The coal sample is located inside the sealing pipe. The two ends of the coal sample face the inner end faces of the inlet plug and the outlet plug, respectively. The outer ends of the inlet plug and the outlet plug are respectively connected to a pressure-bearing pipe. Both end plugs have flow channels inside to connect the two pressure-bearing pipes with the space where the coal sample is located.

5. The simulation device according to claim 4, characterized in that, The sealing fitting is cylindrical and is a heat-shrinkable tube that can tightly wrap around the outside of the coal sample. This facilitates the application of temperature and pressure of the circulating medium inside the pressure vessel to the coal sample, thus simulating the environment of deep coal seams.

6. The simulation device according to claim 5, characterized in that, The end plug is provided with a main air passage and an expansion air passage. The expansion air passage is conical and its inner diameter gradually increases towards the coal sample. The small inner diameter end of the extended air passage is connected to the main air passage, and the large inner diameter end is connected to the pressure-bearing plane. The two end faces of the coal sample abut against the pressure-bearing planes of the two end plugs respectively. The surface of the pressure-bearing plane is evenly covered with through holes. The sum of the areas of all through holes on the pressure-bearing plane accounts for 10%-18% of the total area of ​​the pressure-bearing plane.

7. A method for phase differentiation of coalbed methane production based on inert gas tracing, implemented using the simulation device described in claim 6, wherein a coal sample is placed in a sample chamber, and pressure and temperature simulating deep coal seams are applied to the coal sample, characterized in that... Methane and inert tracer gas were introduced into a reference storage tank through a premixing tank, and the total amount of gas and the concentration of each component in the reference storage tank were measured. The mixed gas in the reference tank is then introduced into the sample chamber until the coal sample is saturated with adsorbed methane. The inert tracer gas is not adsorbed by the coal sample and exists only in the free gas. After the coal sample is saturated with adsorbed methane, the free gas in the sample chamber is sampled. The free gas includes the original free methane and the inert tracer gas. The concentration of the inert tracer gas in the free gas is measured and recorded as the original concentration. The gas path at the outlet of the sample clamping assembly is opened by a back pressure valve to simulate the coalbed methane depletion development process. The coal sample gas production is input into the mass spectrometry monitoring module. The coal sample gas production includes adsorbed methane and the free gas. The concentration of inert tracer gas in the free gas remains unchanged and is the original concentration. The mass spectrometry monitoring module analyzes the concentration of inert tracer gas in the gas production in real time, and then combines it with the original concentration to determine the amount of free methane produced in real time, and then determines the amount of adsorbed methane produced in real time.

8. The phase differentiation method according to claim 7, characterized in that, include: S1: Install the coal sample to be tested in the sample chamber, and use the temperature and pressure servo module to apply the specified confining pressure and experimental temperature to the pressure vessel to measure the inlet pipeline volume, coal sample pore volume and outlet pipeline volume. S2: High-pressure mixed gas is injected into the reference tank through the methane cylinder and tracer gas cylinder via the premixing tank, and the initial pressure, initial temperature and initial tracer gas concentration of the reference tank are measured. Close the outlet of the pressure-bearing pipe on the downstream side of the pressure-resistant container, open the gas injection control valve, and inject the mixed gas in the reference storage tank into the sample chamber. After the coal sample has absorbed methane to equilibrium, measure the equilibrium pressure and equilibrium tracer gas concentration in the sample chamber. The equilibrium tracer gas concentration in the sample chamber is the concentration of inert tracer gas in the free gas. Based on the principle of conservation of mass, determine the total amount of injected methane, the amount of free methane inside the coal sample, and the amount of methane adsorbed by the coal sample. S3: Close the gas injection control valve, open the back pressure valve, and the back pressure pump controls the pressure drop at the outlet of the downstream pressure pipe to simulate the coalbed methane depletion development process; monitor the pressure and tracer gas concentration at the inlet of the sample clamping component, the pressure and tracer gas concentration at the outlet of the sample clamping component, and the cumulative gas output of the sample clamping component in real time through the mass spectrometry monitoring module. By utilizing the conservation of inert tracer gas and the ideal gas law, the amount of inert tracer gas produced from the coal sample is determined. Then, combined with the original concentration, the amount of original free methane produced and the amount of adsorbed methane produced during the coal sample production process are determined. S4: Convert the cumulative output of free methane and adsorbed methane from the coal sample into standard state volumes, determine the contribution ratios of the original free methane and adsorbed methane, and obtain the dynamic output curve.

9. The phase differentiation method according to claim 8, characterized in that, In step S3, the amount of initial free methane in the coal sample gas production process is equal to the amount of inert tracer gas produced from the coal sample × (1 - the initial concentration) / the initial concentration; The amount of adsorbed methane in the coal sample gas production process = the total amount of methane produced - the original free methane produced from the coal sample.

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