Experimental device for accurately simulating gas diffusion behavior of reservoir and use method of experimental device

Abstract

The invention discloses an experimental device for accurately simulating gas diffusion behavior of a reservoir and a use method thereof, the experimental device comprises a diffusion system, a gas supply system, a vacuum system and a data acquisition system, the diffusion system is used for placing a rock sample and simulating the actual working condition of the reservoir to perform a diffusion experiment; the gas supply system is used for supplying gas required by an experiment into the diffusion system; the vacuum system is used for vacuumizing internal devices and pipelines of the diffusion system to ensure the cleanliness of the system; and the data acquisition system is used for acquiring experimental data of the diffusion system and processing the experimental data. By carrying the high-temperature and high-pressure columnar diffusion system, the natural gas diffusion behavior under the in-situ condition can be accurately simulated, so that a reliable experimental platform is provided for researching the transportation characteristics of gas in a real reservoir.

Description

Technical Field

[0001] The present invention relates to an experimental device for accurately simulating the gas diffusion behavior in a reservoir and a method for using the same, and belongs to the technical field of natural gas production. Background Art

[0002] Unconventional natural gases (such as coalbed methane and shale gas) are profoundly changing the global energy pattern due to their huge development potential and characteristics such as cleanness, high efficiency, and sustainability. The gas transport mechanism in a reservoir is a key link in natural gas development, and the process mainly includes adsorption, desorption, diffusion, and seepage. Among them, diffusion is the core link of gas transport, and the diffusion coefficient is a key parameter for measuring the gas migration ability in a reservoir. Therefore, accurately calculating the gas diffusion coefficient is crucial for deeply exploring the diffusion and evolution law of unconventional natural gas, and is also an important basis for effectively controlling mine safety problems such as coal and gas outburst and promoting the increase of natural gas reserves and production.

[0003] At present, laboratory indirect methods are generally used to measure the diffusion coefficient of gases. That is, first, the gas flux passing through the sample within a certain period of time is measured by an experimental device, and then the gas diffusion coefficient under different experimental conditions is obtained through theoretical calculation. The testing methods mainly include the steady-state method, desorption method, inverse diffusion method, etc. During the carbon dioxide replacement process, the diffusion characteristics of gases in the coal matrix are one of the key factors affecting the gas extraction rate. To deeply explore the diffusion law of coalbed methane under carbon dioxide injection conditions and reveal the mechanism of carbon dioxide improving the recovery rate of coalbed methane, researchers have developed special experimental devices to simulate the process of carbon dioxide replacing coalbed methane and carried out carbon dioxide diffusion experiments under different injection pressures and temperature conditions. These experimental results show that during the carbon dioxide injection process, the diffusion characteristics of gases in the coal matrix are the key factors affecting the recovery efficiency of coalbed methane. In addition, the study of the diffusion and evolution law of natural gas in tight oil reservoirs is of great significance for optimizing the gas injection production strategy. By deeply analyzing the diffusion law, the rapid decline of production in the initial stage of gas injection production can be effectively delayed, the recovery rate can be increased, and a scientific basis can be provided for the dynamic analysis and prediction of production effects. Therefore, a high-temperature and high-pressure oil and gas diffusion experimental device based on the pressure decay method has been developed to study the influence of permeability characteristics, pressure, porous media, and fractures on oil and gas diffusion under tight reservoir conditions [Quantitative Analysis of Natural Gas Diffusion Characteristics in Tight Oil Reservoirs Based on Experimental and Numerical Simulation Methods]. Guo et al. studied the desorption and diffusion kinetic characteristics of raw coal and tectonic coal under different gas adsorption equilibrium pressures through an improved gas desorption experimental device and found significant differences in their gas desorption rates and volumes [Experimental study on the desorption law and diffusion kinetic characteristics of gas in raw coal and tectonic coal]. To determine the diffusion coefficient of oxygen during coal spontaneous combustion in a mining area with a complex structure of porous media, relevant researchers developed a testing device for the gas diffusion coefficient of porous media and found the distribution law of gas concentration in porous media under different particle size conditions through experiments [Gas Dispersion Coefficient Test System and Dimensionless Inversion Method for Porous Media].In addition to the above-mentioned devices, some scholars have introduced high-frequency ultrasonic precision instruments based on programming algorithms that can monitor the gas diffusion kinetics in real time to improve the accuracy of experimental results [Qin, Y., Zhao, Z., Xu, H., Liu, W., Wu, F., Zhou, Y., Duan, W., 2022b. Numerical solution of three mathematical models of gas adsorption in coal particle based on finite difference method. Fuel 308, 122036.].

[0004] The existing gas diffusion devices have promoted the research on diffusion behavior to a certain extent and laid a foundation for further improving natural gas recovery and addressing a series of problems that occur during the exploitation process. However, there are still the following technical problems: (1) The experimental operation is complex and it is not easy to replace samples. (2) The airtightness is not ideal and it is prone to air leakage when the experimental pressure is too high. (3) To improve the diffusion efficiency, granular samples are mostly used, which deviates from the in-situ reservoir conditions and cannot accurately simulate the natural gas diffusion behavior under in-situ conditions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an experimental device for accurately simulating the gas diffusion behavior in a reservoir and its usage method to solve the technical problems existing in the above-mentioned prior art.

[0006] The technical solution adopted by the present invention is as follows: An experimental device for accurately simulating the gas diffusion behavior in a reservoir includes a diffusion system, a gas supply system, a vacuum system, and a data acquisition system. The diffusion system is used to place rock samples and simulate the actual working conditions of the reservoir to conduct diffusion experiments; the gas supply system is used to supply the gas required for the experiment into the diffusion system; the vacuum system is used to evacuate the internal devices and pipelines of the diffusion system to ensure the cleanliness of the system; the data acquisition system is used to collect and process the experimental data of the diffusion system.

[0007] Preferably, the diffusion system includes a core holder. A temperature measurement port and an annular pressure port are provided on the core holder. A temperature sensor is installed at the temperature measurement port to detect the temperature inside the diffusion system, and a pressure sensor is provided at the annular pressure port to detect the pressure inside the diffusion system. Both the temperature sensor and the pressure sensor are electrically connected to the data acquisition system; a heating mechanism is provided inside the diffusion system.

[0008] Preferably, the gas supply system includes a helium gas cylinder and a carbon dioxide gas cylinder. Both the helium gas cylinder and the carbon dioxide gas cylinder are internally connected to the diffusion system through pipelines. Valves and pressure gauges are provided on the pipelines connecting the helium gas cylinder and the carbon dioxide gas cylinder to the diffusion system. Carbon dioxide gas is used for the diffusion experiment of the diffusion system. The helium gas is used to detect whether the diffusion system leaks and to flush the pipelines, and also serves as a reference gas during the diffusion experiment.

[0009] Preferably, the vacuum system includes a vacuum pump. The vacuum pump is internally connected to the diffusion system through a pipeline. Valves and pressure gauges are provided on the pipeline connecting the vacuum pump to the diffusion system.

[0010] Preferably, the data acquisition system includes a control cabinet, a computer mainframe, and a display. The control cabinet is electrically connected to the computer mainframe, and the computer mainframe is electrically connected to the display. The diffusion system, the vacuum system, and the gas supplementing system are all electrically connected to the control cabinet. The operator sets the initial parameters of the temperature and pressure of the diffusion system through the mainframe. The mainframe controls the diffusion system, the gas supply system, the vacuum system, and the data acquisition system to work automatically through the control cabinet. Subsequently, the system automatically completes the acquisition and processing of data, and generates original data reports, analysis reports, and relevant curve graphs, intuitively showing the working process and experimental results of the instrument.

[0011] Preferably, the core holder includes a cylindrical pressure-bearing cylinder with its axis arranged horizontally and one end open. A U-shaped adjusting bracket is fixed on the outer periphery of the open end of the pressure-bearing cylinder. A rotating screw coaxial with the pressure-bearing cylinder is threadedly connected to the adjusting bracket. A taper sleeve for sealing the open end of the pressure-bearing cylinder is fixed on one end of the rotating screw close to the pressure-bearing cylinder. The closed end of the pressure-bearing cylinder is closed by a cylindrical screw. Sampling valves are provided at both ends of the core holder.

[0012] The present invention also discloses a usage method of the experimental device for accurately simulating the gas diffusion behavior of a reservoir, including the following steps: (1) Place a cylindrical core sample into the core holder of the diffusion system; (2) Use the vacuum system to evacuate the inside of the diffusion system; (3) Use the heating mechanism of the diffusion system to preheat the diffusion system to the experimental set temperature and maintain it; (4) Open the gas source valve of the gas supply system cylinder to supply gas to the inside of the diffusion system, and load the gas pressure to the experimental set value; (5) Open the computer software of the data acquisition system and start collecting data. The time for the diffusion experiment is 1 d; After the diffusion time ends, the experimenter collects the sampled gas taken out with a special latex or rubber airbag, then analyzes the concentration of the collected sampled gas using a GC-4000A gas chromatograph, and finally calculates the gas diffusion coefficient in the rock sample according to Fick's law.

[0013] Advantages of the present invention: Compared with the prior art, the gas diffusion device of the present invention can accurately simulate the natural gas diffusion behavior under in-situ conditions by carrying a high-temperature and high-pressure columnar diffusion system, thereby providing a reliable experimental platform for studying the gas transport characteristics in real reservoirs. Description of the Drawings

[0014] Figure 1 is a schematic diagram of the overall structure of the present invention.

[0015] Figure 2 is a schematic diagram of the core holder structure in the present invention.

[0016] The reference numerals in the accompanying drawings of the specification include: vacuum system 10, vacuum pump 11, valve 12, pressure gauge 13, diffusion system 20, core holder 21, pressure-bearing cylinder 211, adjusting bracket 212, rotating screw 213, taper sleeve 214, sampling valve 215, cylindrical screw 216, gas supply system 30, helium gas cylinder 31, carbon dioxide gas cylinder 32, pressure regulating valve 33, data acquisition system 40. Detailed Embodiments

[0017] The present invention will be further introduced below in conjunction with the accompanying drawings and specific embodiments.

[0018] Embodiment 1: An experimental device for accurately simulating the gas diffusion behavior of a reservoir, as Figure 1 shown, includes a diffusion system 20, a gas supply system 30, a vacuum system 10, and a data acquisition system 40. The diffusion system 20 is used to place rock samples and simulate the actual working conditions of the reservoir to conduct diffusion experiments; the gas supply system 30 is used to supply the gases required for the experiment into the diffusion system 20; the vacuum system 10 is used to evacuate the internal devices and pipelines of the diffusion system 20 to ensure the cleanliness of the system; the data acquisition system 40 is used to collect and process the experimental data of the diffusion system 20.

[0019] In this embodiment, the diffusion system 20 includes a core holder 21, as Figure 2As shown, the core holder 21 includes a cylindrical pressure-bearing cylinder 211 with its axis arranged horizontally and an open right end. A U-shaped adjusting bracket 212 is fixed to the outer periphery of the right end of the pressure-bearing cylinder 211. A rotating screw 213 coaxial with the pressure-bearing cylinder 211 is threadedly connected to the adjusting bracket 212. A taper sleeve 214 for sealing the right end of the pressure-bearing cylinder 211 is fixed to the left end of the rotating screw 213. The left end of the pressure-bearing cylinder 211 is closed by a cylindrical screw 216. Sampling valves 215 are provided at both ends of the core holder 21.

[0020] The core holder 21 is provided with a temperature measurement port and an annular pressure port. A temperature sensor is installed at the temperature measurement port for detecting the temperature inside the diffusion system 20, and a pressure sensor is provided at the annular pressure port for detecting the pressure inside the diffusion system 20. Both the temperature sensor and the pressure sensor are electrically connected to the data acquisition system 40. An heating mechanism is provided inside the diffusion system 20, and the heating mechanism is an electric heating plate.

[0021] There are two sets of core holders 21 in this embodiment: with dimensions of Φ25 × 25–100 mm (diameter 25 mm, height 25–100 mm) and Φ50 × 50–100 mm (diameter 50 mm, height 50–100 mm) respectively, and they are selected according to actual needs. The two sets of core holders 21 are connected in parallel.

[0022] In this embodiment, the gas supply system 30 includes a helium gas cylinder 31 and a carbon dioxide gas cylinder 32. Both the helium gas cylinder 31 and the carbon dioxide gas cylinder 32 are connected to the inside of the core holder 21 of the diffusion system 20 through pipelines. Valves 12, pressure gauges 13 and pressure regulating valves 33 are provided on the pipelines connecting the helium gas cylinder 31 and the carbon dioxide gas cylinder 32 to the diffusion system 20. Carbon dioxide gas is used for the diffusion experiment of the diffusion system 20, and helium gas is used to detect whether the diffusion system 20 leaks and to flush the pipelines, and it is also used as a reference gas during the diffusion experiment.

[0023] In this embodiment, the vacuum system 10 includes a vacuum pump 11. The vacuum pump 11 is connected to the core holder 21 inside the diffusion system 20 through a pipeline. Valves 12 and pressure gauges 13 are provided on the pipeline connecting the vacuum pump 11 to the diffusion system 20.

[0024] In this embodiment, the data acquisition system 40 includes a control cabinet, a computer mainframe and a display. The control cabinet is electrically connected to the computer mainframe, and the computer mainframe is electrically connected to the display. All the valves 12 in this embodiment are electro-controlled pneumatic valves, and all the valves 12, pressure sensors, temperature sensors, electric heating plates, vacuum pumps 11, pressure gauges 13, core holders 21, etc. are all electrically connected to the control cabinet; the operator sets the initial parameters of the temperature and pressure inside the diffusion system 20 through the host computer, and the host computer controls the diffusion system 20, the gas supply system 30, the vacuum system 10, and the data acquisition system 40 to work automatically through the control cabinet. Subsequently, the system automatically completes the acquisition and processing of data, and generates raw data reports, analysis reports, and relevant curve graphs, intuitively showing the working process and experimental results of the instrument.

[0025] In this embodiment, the maximum confining pressure provided by the manual pump of the diffusion system 20 is 25 MPa; the volume of the diffusion chamber is 10 mL / 20 mL, and the volume of the equilibrium chamber is 100 mL / 25 MPa; the lower limit of the working temperature of the diffusion system 20 is room temperature, and the upper limit is 150 °C respectively; the accuracy of the pressure sensor is 0.25%, and the differential pressure accuracy is 0.05%.

[0026] This embodiment also discloses a method for using an experimental device for accurately simulating the gas diffusion behavior of a reservoir, including the following steps: (1) Place the columnar core sample into the core holder 21 of the diffusion system 20; start the disassembly operation from the right side of the holder. First, rotate the rotating screw 213 counterclockwise to separate the adjusting bracket 212 from the holder, and then take out the taper sleeve 214 on the right side of the holder. Then rotate the cylindrical screw 216 on the left side of the holder clockwise to separate it from the pressure-bearing cylinder 211, so that the sample can be loaded into the pressure-bearing cylinder 211. After the sample is loaded, install each part of the holder back to its original position in the order of "left first and then right".

[0027] (2) Use the vacuum system 10 to evacuate the inside of the diffusion system 20; the vacuum system 10 consists of a VP750-30L type vacuum pump 11, a vacuum valve, and a vacuum hose. Before each experiment or cyclic experiment starts, it is necessary to use this system to evacuate the experimental device and its pipelines for at least 0.5 hours to remove the pollutants in the pipelines. According to the sample size and gas type, the evacuation time can be adjusted appropriately, but it shall not exceed 5 hours. During specific operation, the vacuum valve should be opened first to allow the vacuum pump 11 to circulate and extract the gas inside the system, and then the impurities should be discharged outside the pump through the vent valve to ensure the cleanliness of the system. This process follows the following steps: ① Start the vacuum valve to allow the vacuum pump 11 to access the system.

[0028] ② The vacuum pump 11 starts to work and circulates to extract the gas inside the system.

[0029] ③ Operate the vent valve in a timely manner to discharge the gas containing impurities from the system to ensure that the impurities do not flow back.

[0030] ④ Monitor the vacuum degree until the vacuum level required for the experiment is reached.

[0031] (3) Use the heating mechanism of the diffusion system 20 to preheat the diffusion system 20 to the set temperature of the experiment and maintain it. (4) Open the gas source valve of the helium gas cylinder 31 of the gas supply system 30 to supply gas into the diffusion system 20 and load the gas pressure to the set value of the experiment. (5) Open the computer software of the data acquisition system 40 to start collecting data. The diffusion experiment time is 1 d. (6) After the diffusion time ends, the experimenter collects the extracted sample gas with a special latex or rubber airbag, then analyzes the concentration of the collected sample gas with a GC-4000A gas chromatograph, and finally calculates the gas diffusion coefficient in the rock sample according to Fick's law.

[0032] In this embodiment, the gas diffusion behavior of the reservoir can be simulated at different temperatures and pressures.

[0033] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. An experimental device for accurately simulating the gas diffusion behavior of a reservoir, characterized in that: It includes a diffusion system, a gas supply system, a vacuum system and a data acquisition system. The diffusion system is used to place rock samples and simulate the actual working conditions of the reservoir for diffusion experiments. The gas supply system is used to supply the gases required for the experiments into the diffusion system. The vacuum system is used to evacuate the internal devices and pipelines of the diffusion system to ensure the cleanliness of the system. The data acquisition system is used to collect and process the experimental data of the diffusion system. The diffusion system includes a core holder. The gas supply system includes a helium gas cylinder and a carbon dioxide gas cylinder. Both the helium gas cylinder and the carbon dioxide gas cylinder are internally connected to the core holder of the diffusion system through pipelines. Valves, pressure gauges and pressure regulating valves are provided on the pipelines connecting the helium gas cylinder and the carbon dioxide gas cylinder to the diffusion system. The vacuum system includes a vacuum pump. The vacuum pump is connected to the core holder inside the diffusion system through a pipeline. Valves and pressure gauges are provided on the pipeline connecting the vacuum pump to the diffusion system. The data acquisition system includes a control cabinet, a computer mainframe and a display. The control cabinet is electrically connected to the computer mainframe, and the computer mainframe is electrically connected to the display.

2. The experimental device for accurately simulating the gas diffusion behavior of a reservoir according to claim 1, wherein: The diffusion system includes a core holder. A temperature measurement port and an annular pressure port are provided on the core holder. A temperature sensor is installed at the temperature measurement port to detect the temperature inside the diffusion system, and a pressure sensor is provided at the annular pressure port to detect the pressure inside the diffusion system. Both the temperature sensor and the pressure sensor are electrically connected to the data acquisition system. A heating mechanism is provided inside the diffusion system.

3. The experimental device for accurately simulating the gas diffusion behavior in a reservoir according to claim 1, characterized in that: The gas supply system includes a helium gas cylinder and a carbon dioxide gas cylinder. Both the helium gas cylinder and the carbon dioxide gas cylinder are connected to the inside of the diffusion system through pipelines. Valves and pressure gauges are provided on the pipelines connecting the helium gas cylinder and the carbon dioxide gas cylinder to the diffusion system. Carbon dioxide gas is used for the diffusion experiment of the diffusion system. Helium gas is used to detect whether the diffusion system leaks and to flush the pipelines, and also serves as a reference gas during the diffusion experiment.

4. The experimental device for accurately simulating the gas diffusion behavior of a reservoir according to claim 1, characterized in that: The vacuum system includes a vacuum pump. The vacuum pump is connected to the inside of the diffusion system through a pipeline. Valves and pressure gauges are provided on the pipeline connecting the vacuum pump to the diffusion system.

5. The experimental device for accurately simulating the gas diffusion behavior of a reservoir according to claim 1, characterized in that: The data acquisition system includes a control cabinet, a computer mainframe and a display. The control cabinet is electrically connected to the computer mainframe, and the computer mainframe is electrically connected to the display. The diffusion system, the vacuum system and the gas supply system are all electrically connected to the control cabinet. The operator sets the initial parameters of the temperature and pressure of the diffusion system through the mainframe. The mainframe controls the automatic operation of the diffusion system, the gas supply system, the vacuum system and the data acquisition system through the control cabinet. Subsequently, the system automatically completes the acquisition and processing of data, and generates original data reports, analysis reports and relevant curve graphs, intuitively showing the working process and experimental results of the instrument.

6. The experimental device for accurately simulating the gas diffusion behavior of a reservoir according to claim 2, characterized in that: The core holder includes a cylindrical pressure-bearing cylinder with its axis arranged horizontally and one end open. A U-shaped adjusting bracket is fixed to the outer periphery of the open end of the pressure-bearing cylinder. A rotating screw coaxial with the pressure-bearing cylinder is threadedly connected to the adjusting bracket. A taper sleeve for sealing the open end of the pressure-bearing cylinder is fixed to one end of the rotating screw close to the pressure-bearing cylinder. The closed end of the pressure-bearing cylinder is closed by a cylindrical screw. Sampling valves are provided at both ends of the core holder.

7. The method of using the experimental device for accurately simulating the gas diffusion behavior of a reservoir according to any one of claims 1-6, characterized in that: It includes the following steps: Put the columnar core sample into the core holder of the diffusion system; Use the vacuum system to evacuate the inside of the diffusion system; Use the heating mechanism of the diffusion system to preheat the diffusion system to the experimental set temperature and maintain it; Open the gas source valve of the gas supply system cylinder to supply gas into the diffusion system and load the gas pressure to the experimental set value; Open the computer software of the data acquisition system, start collecting data, and the diffusion experiment time is 1 d; After the diffusion time ends, the experimenter collects the sampled gas taken out with a special latex or rubber airbag, then analyzes the concentration of the collected sampled gas with a GC-4000A gas chromatograph, and finally calculates the gas diffusion coefficient in the rock sample according to Fick's law.

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