Non-hydrocarbon gas replaces natural gas high temperature and high pressure multi-cycle experiment system and method

Abstract

The present application is suitable for oil and gas storage and development technical field, provide a kind of non-hydrocarbon gas replacement natural gas high temperature high pressure multi-cycle experiment system and method, the experimental system includes gas supply unit, displacement system unit, pump control unit, auxiliary equipment unit, data acquisition and processing unit and power supply unit.This experimental system can realize the continuous dynamic monitoring of the pressure change and pressure difference of core two ends in displacement process, and can real-time acquisition outlet gas component, concentration, flow and other multi-dimensional data.System can simulate the multi-cycle injection-production process of non-hydrocarbon gas such as carbon dioxide replacing methane, dynamically record each round injection-production behavior, component change and pressure response.Through the joint analysis of recovery efficiency evolution, gas mixing and storage characteristics, the displacement efficiency and storage efficiency of non-hydrocarbon gas in reservoir are evaluated, which provides experimental basis and engineering reference for gas storage operation and enhanced gas reservoir development.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas storage and development technology, and particularly relates to a high-temperature, high-pressure, multi-cycle experimental system and method for replacing natural gas with non-hydrocarbon gases. Background Technology

[0002] In current gas storage peak-shaving operations, using suitable cushion gas can improve reservoir pressure support and natural gas recovery efficiency. Currently, most operating gas storage facilities use CH4 itself as cushion gas, typically accounting for 15%-75% of the total gas volume. This portion of CH4 remains trapped in the reservoir for extended periods, making it difficult to utilize. Therefore, there is an urgent need for an additional non-hydrocarbon cushion gas to replace this portion of CH4 and allow it to remain as the long-term cushion gas, thereby improving the effective recovery rate of natural gas.

[0003] CO2, as a cushion gas, can not only replenish formation energy in multi-cycle injection and production but also achieve staged displacement of residual natural gas and geological storage effects. However, the supercritical properties, mixing behavior, and seepage characteristics of CO2 are significantly different from those of CH4, and N2, as an alternative cushion gas, also faces challenges such as calorific value dilution and recovery difficulties. Therefore, a repeatable experimental system with adjustable upper and lower pressure limits is needed to simulate the replacement process of methane and CO2 at the same injection port and different injection ports, revealing the evolution of the gas mixing front, replacement efficiency, and CO2 retention behavior under cyclic injection and production conditions. This would provide experimental verification and parameter support for the coupling of flexible peak shaving and carbon sequestration in gas storage facilities. Summary of the Invention

[0004] The purpose of this invention is to provide a non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system and method suitable for injection and production cycle conditions, aiming to solve the problems mentioned in the background art.

[0005] The present invention is implemented as follows: a high-temperature and high-pressure multi-cycle experimental system for replacing natural gas with non-hydrocarbon gas includes a gas supply unit, a displacement system unit, a pump control unit, an auxiliary equipment unit, a data acquisition and processing unit, and a power supply unit.

[0006] The gas supply unit is used to supply methane and carbon dioxide / nitrogen to the displacement system unit;

[0007] The displacement system unit includes a methane intermediate buffer container, a bottom gas intermediate buffer container, a water collection tank, a core sleeve, a core sample, a core holder, and a back pressure valve. The core sample is installed in the core holder, and the core sleeve covers the core sample. Both the methane intermediate buffer container and the bottom gas intermediate buffer container are connected to the gas supply unit, and they are also connected to the methane injection port and bottom gas injection port at both ends of the core holder, respectively. A back pressure valve is configured at the outlet end of the core holder.

[0008] The pump control unit includes a hand-cranked confining pressure pump, a displacement pump, and a back pressure pump. The displacement pump is connected to the liquid inlet at the lower end of the methane intermediate buffer container and the bottom gas intermediate buffer container via pipelines. The back pressure pump is connected to the outlet end of the core holder. The hand-cranked confining pressure pump is connected to the core holder.

[0009] The auxiliary equipment unit includes a vacuum pump, a gas flow meter, a gas chromatograph, and a gas collection bag; the vacuum pump is connected to the pipeline between the outlet end of the core holder and the back pressure valve via a four-way valve; the gas flow meter is connected to the back pressure valve for real-time monitoring and recording of the volumetric flow rate of the produced gas; the gas chromatograph is connected to the gas flow meter for analyzing the components of the mixed gas and their changes; the gas collection bag is connected to the gas chromatograph for collecting the gas;

[0010] The data acquisition and processing unit is used to monitor experimental parameters in real time and perform digital storage and remote data management of multiple parameters.

[0011] The power supply unit is used to continuously provide stable power to the experimental system.

[0012] In a further technical solution, the gas supply unit includes a methane cylinder, a carbon dioxide / nitrogen cylinder, and a gas leak detection device. The methane cylinder and the carbon dioxide / nitrogen cylinder are respectively connected to the methane intermediate buffer container and the bottom gas intermediate buffer container in the displacement system unit through a high-pressure valve and a pressure regulating valve.

[0013] In a further technical solution, the displacement system unit is installed in a constant temperature oven with a mobile function, and the constant temperature oven is used to provide a stable and controlled temperature environment for the displacement system unit.

[0014] In a further technical solution, the methane intermediate buffer container and the bottom gas intermediate buffer container are made of 316L stainless steel, with a single volume of 1000 mL, a pressure resistance rating of 70 MPa, and an internal gas-liquid isolation piston structure.

[0015] The piston structure in the intermediate buffer container of the bottom gas is made of a material resistant to CO2 corrosion.

[0016] In a further technical solution, the core sample is a real reservoir core with a size of φ38×100 mm;

[0017] The angle adjustment range of the core holder is 0~90°;

[0018] The core sleeve has dimensions of φ39×φ46×300 mm and is made of CO2-resistant material. An aluminum foil layer can be placed between the sleeve and the core to enhance sealing and corrosion resistance.

[0019] In a further technical solution, the components in the displacement system unit are connected by quick connectors.

[0020] In a further technical solution, the pump control unit also includes a water tank and an air compressor;

[0021] The water tank is connected to both the displacement pump and the back pressure pump to provide liquid supply;

[0022] The air compressor is also connected to both the displacement pump and the back pressure pump to provide continuous power.

[0023] In a further technical solution, the data acquisition and processing unit includes a pressure acquisition module, a temperature acquisition module, and an intelligent acquisition system;

[0024] The temperature acquisition module is installed in a constant temperature oven and is used to monitor the system operating temperature;

[0025] Pressure acquisition modules are installed on the pipelines between the methane cylinder and the methane intermediate buffer container, the pipelines between the carbon dioxide / nitrogen cylinder and the cushion gas intermediate buffer container, the pipelines between the methane intermediate buffer container and the core holder, the pipelines between the cushion gas intermediate buffer container and the core holder, the pipelines between the hand-cranked confining pressure pump and the core holder, the output pipeline of the displacement pump, and the output pipeline of the back pressure pump.

[0026] The gas flow meter, temperature acquisition module, and each pressure acquisition module are all connected to the intelligent acquisition system, which is used for continuous data acquisition and digital storage.

[0027] Another objective of this invention is to provide a high-temperature, high-pressure, multi-cycle experimental method for replacing natural gas with non-hydrocarbon gas, based on the aforementioned experimental system, comprising the following steps:

[0028] Step 1: Core sample preparation and pretreatment;

[0029] Core samples with the required geological conditions are selected, cut, and polished to prepare standard columnar specimens; after completion, they are cleaned, dried, and cooled in sequence to ensure that there are no impurities left in the core pores and to simulate real reservoir conditions.

[0030] Step 2: Determination of core physical parameters;

[0031] The processed core samples were subjected to mass determination, and the dry weight, length, and diameter were recorded. Gas permeability was also measured to obtain basic porosity and permeability.

[0032] Step 3: Connecting and leak-checking the experimental system;

[0033] Connect each unit to form a closed loop to ensure the pipeline is airtight. After the initial connection is completed, purge the system with N2 gas to remove residual air and impurities. Then close the system outlet valve, pressurize by filling with N2 and let it stand. Observe the pressure change. If the system pressure is basically constant within the set time, it is considered to have good airtightness.

[0034] Step 4: System vacuuming and core loading;

[0035] The pretreated core samples are assembled into the core holder, and the core holder is used to simulate gas displacement behavior under different geological structural conditions. According to the experimental design requirements, a single core or multiple core segments formed by different permeability combinations can be selected. After the core samples are loaded, the outlet valve of the intermediate buffer container is closed, and the vacuum pump is started to evacuate the system.

[0036] Step 5: Constant temperature preheating and system stabilization;

[0037] Turn on the constant temperature oven, set the target experimental temperature, and preheat the core sample and system pipeline; after the system temperature stabilizes to the set value, proceed to the next step.

[0038] Step 6: Gas filling and pressurization of the intermediate container;

[0039] The required gas is sequentially introduced into the methane intermediate buffer container and the bottom gas intermediate buffer container, the outlet valve is closed, and the gas in the intermediate buffer container is pressurized by a constant speed and constant pressure displacement pump until the preset injection pressure is reached.

[0040] Step 7: CH4 saturation of core samples;

[0041] Set the upper and lower pressure limits of the system, and adjust the back pressure valve and hand-cranked confining pressure pump to maintain stable confining pressure conditions. Open the valves at the outlet of the methane intermediate buffer container and the inlet of the core holder, and inject CH4 into the core sample until it is completely saturated by pushing the piston with the displacement pump. After allowing the pressure to stabilize, open the CH4 extraction outlet valve to discharge the CH4 gas, and measure the discharged volume using a gas flow meter to obtain the saturated volume V1 of the core sample. Subsequently, to obtain control data, CH4 is injected into the core again to saturate it and stabilize it at the set upper pressure limit. After closing the injection valve, open the gas extraction outlet valve to perform simulated gas extraction, extracting the core pressure from the upper pressure limit to the lower pressure limit. During this process, the volume of extracted gas is recorded using a gas flow meter and denoted as V2, which is used to characterize the gas extraction capacity under pure CH4 conditions and serves as a reference for subsequent CO2 replacement efficiency.

[0042] Step 8: Injecting gas to replace the underside;

[0043] Switch back to the CO2 injection path and open the outlet valve of the intermediate buffer container for the cushion gas. With all other valves in the system closed, inject CO2 as cushion gas into the core sample using a displacement pump at constant pressure or constant flow rate. This gradually increases the core pressure from the lower limit to the set upper limit, providing the driving force for the subsequent methane replacement process. The volume of injected water can be indirectly converted into the injected CO2 volume, and then converted into the gas volume V3 under standard conditions using the equation of state.

[0044] Step 9: Gas collection and component analysis;

[0045] A gas chromatograph and a gas collection bag were connected to the outlet end of the core holder to perform online component analysis and sampling detection of the produced gas, obtaining a curve of CH4 / CO2 concentration changing over time. Simultaneously, the cumulative volume of the produced gas was recorded in real time using a gas flow meter at the outlet end, and combined with the volume fractions of each component measured by chromatography, the volume of CH4 replaced (V4) and the volume of CO2 produced (V5) were calculated.

[0046] Step 10: Multiple rounds of cyclic injection and extraction;

[0047] To simulate the multi-cycle injection and production process of a gas storage facility in actual operation, after the first round of gas displacement experiment was completed, subsequent cycles were repeated according to the following steps: First, the outlet valve of the core holder was closed, the CH4 injection path was reopened, and CH4 was injected into the core through the methane intermediate buffer container and displacement pump until the reservoir pressure returned to the set upper limit; then, after standing for a period of time, the outlet valve was opened again to produce CH4, while the outlet pressure was adjusted to the set lower limit through the back pressure pump, and the produced gas volume and flow rate were recorded;

[0048] Step 11: After the multi-round gas production phase is completed, the CO2 injection path can be reopened based on the gas production volume and purity of the previous round. CO2 is injected into the core through the intermediate buffer container of the underlying gas to replace the CH4 or residual underlying gas that was not used in the previous round of gas production. The injection process continues until the reservoir pressure recovers to the upper limit pressure, and then the next round of gas production is carried out until the lower limit pressure is reached. Based on the CO2 injection volume and the composition analysis results of the produced gas in each cycle, the actual CO2 consumption of that round is calculated. Before entering the next round of gas injection, the corresponding volume of CO2 is replenished as needed to ensure the stability of the underlying gas content in the reservoir. At the same time, the CH4 produced volume, CO2 injection volume and residual gas content of each round are recorded for comprehensive analysis of the impact of the number of cycles on natural gas recovery rate, CO2 replacement efficiency and storage efficiency.

[0049] Step 12: System venting and core sample unloading;

[0050] After all cyclic injection and production experiments are completed, close all gas source valves and gradually release the internal pressure of the system to atmospheric pressure. After the pressure is completely released, disassemble the core holder, take out the core sample, and perform subsequent characterization as needed to analyze changes in pore structure or gas distribution characteristics.

[0051] Step 13: Data processing and result analysis;

[0052] The data collected during each injection and production stage of the experiment were organized and recorded in each stage, including CH4 production volume, CO2 injection and consumption volume. The cumulative displacement efficiency, storage efficiency and displacement effect of each cycle were calculated and summarized. The displacement efficiency was calculated according to the formula η1 = V4 / V1 and the storage efficiency was calculated according to the formula η2 = 1 - V5 / V3.

[0053] The present invention provides a high-temperature, high-pressure, multi-cycle experimental system and method for replacing natural gas with non-hydrocarbon gases, the beneficial effects of which are as follows:

[0054] (1) It can fully simulate the entire process of enhanced extraction of various underlying gases under the real high temperature and high pressure conditions of gas storage, and the experimental conditions are closer to the actual reservoir environment.

[0055] (2) The experimental system has precise pressure, flow and temperature control capabilities, and combined with an adjustable back pressure valve to simulate different injection and extraction pressure windows, realize real-time monitoring and dynamic adjustment of multiple parameters, and ensure the accuracy and repeatability of the experiment;

[0056] (3) Through systematic research, the displacement characteristics, mixing mechanism, front advancement and retention law of different cushion gases under cyclic injection and production have been clarified, providing detailed and reliable theoretical basis for actual gas storage injection and production schemes and CO2 sealing strategies;

[0057] (4) The system has a high degree of modularity, good scalability and multi-cycle capability, supports the comparison of multiple schemes under different types of gas storage (such as structural type, water-soluble gas reservoir type, etc.) and heterogeneous reservoir conditions, and is suitable for exploring the synergistic effect of bottom gas management and carbon sequestration under complex injection and production modes. It has broad prospects for promotion and engineering application. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of a high-temperature, high-pressure, multi-cycle experimental system for replacing natural gas with non-hydrocarbon gas, provided in an embodiment of the present invention.

[0059] Figure 2 A schematic diagram of the internal structure of a constant temperature oven in a high-temperature, high-pressure, multi-cycle experimental system for replacing natural gas with non-hydrocarbon gas is provided in an embodiment of the present invention.

[0060] Figure 3A flowchart of a high-temperature, high-pressure, multi-cycle experimental method for replacing natural gas with non-hydrocarbon gas is provided in this embodiment of the invention.

[0061] Figure 4 This is a schematic diagram of the experimental operating conditions control.

[0062] Figure 5 A comparison chart of gas extraction behavior and total gas storage during multiple injection-production cycles under different base gas injection pressures (left side shows gas extraction behavior, right side shows total gas storage).

[0063] In the attached diagram: Gas supply unit I; Displacement system unit II; Pump control unit III; Auxiliary equipment unit IV; Data acquisition and processing unit V; Power supply unit VI; Methane cylinder 1; Carbon dioxide / nitrogen cylinder 2; High-pressure valve 3; Pressure regulating valve 4; Gas leak detection device 5; Methane intermediate buffer container 6; Underfill gas intermediate buffer container 7; Water collection tank 8; Core sleeve 9; Core sample 10; Core holder 11; Three-way valve 12; Quick connector 13; Four-way valve 14; Back pressure valve 15; Vacuum pump 16; Gas flow meter 17; Gas chromatograph 18; Gas collection bag 19; Hand-cranked confining pressure pump 20; Displacement pump 21; Back pressure pump 22; Water tank 23; Air compressor 24; Pressure acquisition module 25; Temperature acquisition module 26; Constant temperature oven 27; Intelligent acquisition system 28; Main control power module 29. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0065] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0066] like Figure 1 and Figure 2 As shown, a non-hydrocarbon gas replacement natural gas high temperature and high pressure multi-cycle experimental system according to an embodiment of the present invention includes a gas supply unit I, a displacement system unit II, a pump control unit III, an auxiliary equipment unit IV, a data acquisition and processing unit V, and a power supply unit VI.

[0067] The gas supply unit I is used to supply methane and carbon dioxide / nitrogen to the displacement system unit II;

[0068] The displacement system unit II includes a methane intermediate buffer container 6, a bottom gas intermediate buffer container 7, a water collection tank 8, a core sleeve 9, a core sample 10, a core holder 11, and a back pressure valve 15. The core sample 10 is installed in the angle-adjustable core holder 11, and the core sleeve 9 covers the core sample 10 to ensure the system's sealing and chemical stability under high-pressure carbon dioxide displacement conditions. The methane intermediate buffer container 6 and the bottom gas intermediate buffer container 7 are connected to the gas supply unit I to receive methane and carbon dioxide / nitrogen from the gas supply unit I. The methane intermediate buffer container 6 and the bottom gas intermediate buffer container 7 are also connected to the methane injection port and the bottom gas injection port at both ends of the core holder 11, respectively, to provide a stable gas source for the subsequent injection process. The outlet end of the core holder 11 is equipped with a back pressure valve 15, which can withstand pressures up to 70 MPa, to simulate the back pressure of the gas wellbore and maintain a stable displacement pressure differential.

[0069] The pump control unit III includes a hand-cranked confining pressure pump 20, a displacement pump 21, and a backpressure pump 22, which are used to achieve constant pressure / constant speed gas injection, confining pressure control of the core holder 11, and backpressure adjustment of the system outlet, respectively. The displacement pump 21 is connected to the liquid inlet at the lower end of the methane intermediate buffer container 6 and the cushion gas intermediate buffer container 7 through pipelines, and is used to apply hydraulic pressure to maintain the stability of the injected gas pressure. The backpressure pump 22 is connected to the outlet end of the core holder 11, and is used to precisely adjust the gas production back pressure during the displacement process. The hand-cranked confining pressure pump 20 is connected to the core holder 11, and is used to apply a confining pressure higher than the injection pressure to the outer sheath of the core holder 11 to simulate the formation stress state.

[0070] The auxiliary equipment unit IV includes a vacuum pump 16, a gas flow meter 17, a gas chromatograph 18, and a gas collection bag 19. The vacuum pump 16 is connected to the pipeline between the outlet end of the core holder 11 and the back pressure valve 15 via a four-way valve 14. It is used for system evacuation at the beginning of the experiment, assists in the airtightness detection of the system, and ensures that the device is in a good initial state. The gas flow meter 17 is connected to the back pressure valve 15 and is used to monitor and record the volumetric flow rate of the produced gas in real time to ensure accurate flow control during the experiment. The gas chromatograph 18 is connected to the gas flow meter 17 and is used to analyze the components of the mixed gas and their changes, and to assist in the evaluation of gas migration and mixing behavior. The gas collection bag 19 is connected to the gas chromatograph 18 and is used to collect natural gas and CO2 for gas component detection, and to calculate the displacement efficiency in combination with the gas volume detected by the gas flow meter 17.

[0071] The data acquisition and processing unit V is used to monitor key experimental parameters (such as pressure, temperature, flow rate, and differential pressure) in real time, and to perform digital storage and remote data management of multiple parameters.

[0072] The power supply unit VI includes a main control power module 29, which is used to continuously provide stable power to the experimental system, support the long-term continuous operation of each unit, and ensure the safe and efficient conduct of the experiment.

[0073] In this embodiment of the invention, the confining pressure applied by the hand-cranked confining pressure pump 20 to the outer jacket of the core holder 11 is generally set to be 3 MPa higher than the pore pressure. The gas collecting bag 19 is a 100L Teflon (polytetrafluoroethylene) gas collecting bag.

[0074] like Figure 1 As shown, in a preferred embodiment of the present invention, the gas supply unit I includes a methane cylinder 1, a carbon dioxide / nitrogen cylinder 2, and a gas leak detection device 5. The methane cylinder 1 and the carbon dioxide / nitrogen cylinder 2 are respectively connected to the methane intermediate buffer container 6 and the bottom gas intermediate buffer container 7 in the displacement system unit II through a high-pressure valve 3 and a pressure regulating valve 4.

[0075] In this embodiment of the invention, the gas leak detection device 5 is used to check the sealing of the gas source system and pipelines before the experiment begins, to prevent high-pressure gas leakage from affecting the experimental results or equipment safety. After pressure regulation and leak detection, the gas flow flows to the methane intermediate buffer container 6 and the bottom gas intermediate buffer container 7, respectively, to provide a stable gas source for the subsequent injection process.

[0076] like Figure 1 and Figure 2 As shown, in a preferred embodiment of the present invention, the displacement system unit II is installed in a constant temperature oven 27 with a movable function to provide a stable and controlled temperature environment (temperature range: room temperature to 80°C) for the displacement system unit II, ensuring that the experiment is carried out under the set thermodynamic conditions.

[0077] In a preferred embodiment of the present invention, the methane intermediate buffer container 6 and the bottom gas intermediate buffer container 7 are made of 316L stainless steel, with a single volume of 1000 mL and a pressure resistance rating of 70 MPa. They are equipped with a gas-liquid isolation piston structure inside. The gas pressure is controlled by injecting liquid pressure through a high-precision constant pressure and constant speed displacement pump 21 to achieve constant pressure (maximum pressure 70 MPa) or constant speed (0.01~25 mL / min) displacement. The piston structure in the bottom gas intermediate buffer container 7 is made of a CO2 corrosion resistant material.

[0078] In a preferred embodiment of the present invention, the core sample 10 is a real reservoir core with a size of φ38×100 mm.

[0079] The angle of the core holder 11 is adjustable from 0 to 90°.

[0080] The core sleeve 9 has a specification of φ39×φ46×300 mm and is made of CO2-resistant materials such as fluororubber. It can be wrapped with aluminum foil to further reduce CO2 penetration, so as to ensure the system's sealing and chemical stability under high-pressure carbon dioxide displacement conditions.

[0081] like Figure 1 As shown, in a preferred embodiment of the present invention, the components in the displacement system unit II are connected by quick connectors 12, which facilitates disassembly and modular replacement.

[0082] like Figure 1 As shown, in a preferred embodiment of the present invention, the pump control unit III further includes a water tank 23 and an air compressor 24;

[0083] The water tank 23 is connected to both the displacement pump 21 and the back pressure pump 22 to provide liquid supply.

[0084] The air compressor 24 is also connected to the displacement pump 21 and the back pressure pump 22 to provide continuous power and ensure that the experiment can be carried out continuously and stably.

[0085] like Figure 1 As shown, in a preferred embodiment of the present invention, the data acquisition and processing unit V includes a pressure acquisition module 25, a temperature acquisition module 26, and an intelligent acquisition system 28.

[0086] The temperature acquisition module 26 is installed in the constant temperature oven 27 to monitor the system operating temperature and, together with the constant temperature oven 27, to control the temperature of the core clamping area, ensuring that the experiment is carried out stably under the set thermodynamic conditions.

[0087] Pressure acquisition modules 25 are installed on the pipelines between methane cylinder 1 and methane intermediate buffer container 6, between carbon dioxide / nitrogen cylinder 2 and cushion gas intermediate buffer container 7, between methane intermediate buffer container 6 and core holder 11, between cushion gas intermediate buffer container 7 and core holder 11, between hand-cranked confining pressure pump 20 and core holder 11, the output pipeline of displacement pump 21, and the output pipeline of back pressure pump 22.

[0088] The gas flow meter 17, temperature acquisition module 26, and each pressure acquisition module 25 are all connected to the intelligent acquisition system 28. The intelligent acquisition system 28 is used to continuously acquire and digitally store multiple parameters such as pressure, temperature, flow rate, and differential pressure, providing complete and reliable data support for experimental process evaluation and subsequent result analysis.

[0089] like Figure 3As shown, another embodiment of the present invention provides a high-temperature, high-pressure, multi-cycle experimental method for replacing natural gas with non-hydrocarbon gas. Based on the above-described experimental system, it includes the following steps:

[0090] Step 1: Core sample preparation and pretreatment;

[0091] Core samples with the required geological conditions are selected, cut, and ground to prepare standard columnar specimens (e.g., approximately φ3.8 cm in diameter and 7.5 cm in length). After completion, pretreatment processes such as cleaning, drying, and cooling are performed sequentially to ensure that no impurities remain in the core pores, simulating near-real reservoir conditions.

[0092] Step 2: Determination of core physical parameters;

[0093] The processed core samples were subjected to mass determination, and geometric parameters such as dry weight, length, and diameter were recorded. Gas permeability was also measured to obtain physical property parameters such as basic porosity and permeability, which were used as a reference for subsequent experimental calculations.

[0094] Step 3: Connecting and leak-checking the experimental system;

[0095] Connect each unit to form a closed loop to ensure pipeline sealing. After the initial connection is completed, purge the system with N2 gas to remove residual air and impurities; then close the system outlet valve, pressurize by filling with N2 and let it stand, observe the pressure change. If the system pressure remains basically constant within a set time, it is considered to have good airtightness.

[0096] Step 4: System vacuuming and core loading;

[0097] Pretreated core samples are assembled into core holder 11, which simulates gas displacement behavior under different geological structures (such as faults, dip reservoirs, etc.). Depending on the experimental design requirements, a single core or cores with different permeabilities (such as...) can be used. Figure 2 Multiple core samples (k1, k2, k3) are formed by combinations shown to enhance the simulation capability of reservoir heterogeneity. After the core samples are loaded, the outlet valve of the intermediate buffer container is closed, and the vacuum pump 16 is started to evacuate the system. The evacuation process includes evacuating the entire system, including the core holder 11 and connecting pipelines, to remove residual gas, reduce initial gas interference, and ensure that subsequent CH4 and CO2 injection experiments are as close as possible to the original pore state of the actual formation. The temperature acquisition module 26 and the intelligent acquisition system 28 can synchronously record the experimental environment, improving experimental controllability and data reliability.

[0098] Step 5: Constant temperature preheating and system stabilization;

[0099] Turn on the constant temperature oven 27 and set the target experimental temperature (e.g., 20~80℃) to preheat the core sample and system pipelines. After the system temperature stabilizes to the set value, proceed to the next step to ensure that the displacement experiment is carried out under constant temperature conditions.

[0100] Step 6: Gas filling and pressurization of the intermediate container;

[0101] The required gas is sequentially introduced into the methane intermediate buffer container 6 and the bottom gas intermediate buffer container 7 (taking CO2 as an example), the outlet valve is closed, and the gas in the intermediate buffer container is pressurized by the constant speed and constant pressure displacement pump 21 until the preset injection pressure is reached (for experiments that require CO2 to be kept in a supercritical state, ensure that the internal temperature of the intermediate container is not lower than 31.1℃ and the pressure is not lower than 7.38MPa).

[0102] Step 7: CH4 saturation of core samples;

[0103] Set the upper and lower pressure limits for the system (e.g., upper limit 10 MPa, lower limit 7 MPa). Figure 4 As shown. Adjust the back pressure valve 15 and the hand-cranked confining pressure pump 20 to maintain stable confining pressure conditions (e.g., back pressure 11 MPa, confining pressure 13 MPa). Open the valves at the outlet of the methane intermediate buffer container 6 and the inlet of the core holder 11, and use the displacement pump 21 to push the piston to inject CH4 into the core sample until it is completely saturated. After allowing it to stand and stabilize, open the CH4 outlet valve to discharge the CH4 gas, and measure the discharged volume using the gas flow meter 17 to obtain the saturated volume V1 of the core sample. If necessary, the vacuuming and saturation operations can be repeated to ensure that the core sample is fully saturated. Inject CH4 again to saturate the core sample, and increase the pressure to the upper limit pressure, then close the valve of the methane intermediate buffer container 6. Then open the outlet valve to perform a simulated gas extraction operation from the upper limit pressure to the lower limit pressure, and record the extracted volume under pure CH4 conditions as V2 for comparison analysis.

[0104] Step 8: Injecting gas to replace the underside;

[0105] Switch to the CO2 injection path and open the outlet valve of the intermediate buffer container 7 for the cushion gas. Ensuring all other system valves are closed, inject CO2 as cushion gas into the core sample using the displacement pump 21 at constant pressure or constant flow rate. This gradually increases the core pressure from the lower limit to the preset upper limit, providing the driving force for the subsequent CH4 replacement process. During injection, record the actual CO2 injection volume using the volume of the injected liquid (e.g., water) from the displacement pump, and convert it to the standard volume V3 using the equation of state. To simulate different cushion gas ratios, the upper limit pressure of the CO2 injection can be set as a variable, adjusting the pressure difference between it and the initial CH4 saturation pressure. Figure 4 The experimental setup for bed gas replacement under different CO2 injection pressure conditions is shown.

[0106] Step 9: Gas collection and component analysis;

[0107] Open the CH4 extraction valve to begin collecting the produced gas. Connect a gas chromatograph 18 and a gas collection bag 19 to the outlet of the core holder 11 to perform online component analysis and sampling detection of the produced gas, thereby obtaining the CH4 / CO2 concentration change curve over time. Simultaneously, record the cumulative outlet flow rate in real time using a gas flow meter 17, and calculate the volume of CH4 displaced (V4) and the volume of CO2 produced (V5) based on the component volume fractions.

[0108] Step 10: Multiple rounds of cyclic injection and extraction;

[0109] To simulate the multi-cycle injection and production process of a gas storage facility in actual operation, after completing the first round of gas displacement experiment, subsequent cycles were repeated according to the following steps: First, the outlet valve of the core holder 11 was closed, and the CH4 injection path was reopened. CH4 was injected into the core through the methane intermediate buffer container 6 and the displacement pump 21 until the reservoir pressure returned to the set upper limit (e.g., 10 MPa). After a period of settling, the outlet valve was reopened for CH4 extraction. Simultaneously, the outlet pressure was adjusted to the set lower limit (e.g., 7 MPa) using the backpressure pump 22, and the extracted gas volume and flow rate were recorded. (See [link to relevant documentation]). Figure 5 The pressure control and flow rate change process is shown.

[0110] Step 11: After the multi-round gas production phase, the CO2 injection path can be reopened based on the gas production volume and purity of the previous round. CO2 is injected into the core through the intermediate buffer container 7 to replace the unused CH4 or residual cushion gas from the previous round. The injection process continues until the reservoir pressure recovers to the upper limit pressure, then the next round of gas production is carried out until the lower limit pressure is reached. Based on the CO2 injection volume and the composition analysis results of the produced gas in each cycle, the actual CO2 consumption for that round is calculated. Before entering the next round of gas injection, the corresponding volume of CO2 can be replenished as needed to ensure the stability of the cushion gas content in the reservoir and achieve the continuity and repeatability of the replacement effect. The number of multi-round cycles can be flexibly set according to the experimental plan. At the same time, the CH4 production volume, CO2 injection volume, and residual gas content of each round are recorded for comprehensive analysis of the impact of the number of cycles on natural gas recovery, CO2 replacement efficiency, and storage efficiency.

[0111] Step 12: System venting and core sample unloading;

[0112] After all cyclic injection and production experiments are completed, close all gas source valves and gradually release the internal pressure of the system to atmospheric pressure. After the pressure is completely released, disassemble the core holder 11, take out the core sample, and perform subsequent characterization (such as CT scan, nuclear magnetic resonance, etc.) as needed to analyze changes in pore structure or gas distribution characteristics.

[0113] Step 13: Data processing and result analysis;

[0114] Data on pressure, flow rate, and gas composition collected during each injection and production phase of the experiment were compiled. Key parameters such as CH4 production volume, CO2 injection volume, and consumption volume were recorded for each phase. The cumulative displacement efficiency, storage efficiency, and trends of displacement effects across multiple cycles were calculated. The displacement efficiency was calculated using the formula η1 = V4 / V1, and the storage efficiency was calculated using the formula η2 = 1 - V5 / V2.

[0115] In this embodiment of the invention, the process of this method has strong adaptability and scalability. It can flexibly adjust key variables such as upper and lower limit pressure, upper limit pressure of injected gas, injection flow rate, fluid physical parameters (such as the state of CO2 or N2) and number of cycles according to experimental research needs, so as to adapt to the simulation requirements of different reservoir conditions and injection and production strategies, and further enrich the research depth and scope of application of reservoir injection and production process and bottom gas displacement behavior.

[0116] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature, high-pressure, multi-cycle experimental system for replacing natural gas with non-hydrocarbon gases, characterized in that, It includes a gas supply unit, a displacement system unit, a pump control unit, an auxiliary equipment unit, a data acquisition and processing unit, and a power supply unit; The gas supply unit is used to supply methane and carbon dioxide / nitrogen to the displacement system unit; The displacement system unit includes a methane intermediate buffer container, a bottom gas intermediate buffer container, a water collection tank, a core sleeve, a core sample, a core holder, and a back pressure valve. The core sample is installed in the core holder, and the core sleeve covers the core sample. Both the methane intermediate buffer container and the bottom gas intermediate buffer container are connected to the gas supply unit, and they are also connected to the methane injection port and bottom gas injection port at both ends of the core holder, respectively. A back pressure valve is configured at the outlet end of the core holder. The pump control unit includes a hand-cranked confining pressure pump, a displacement pump, and a back pressure pump. The displacement pump is connected to the liquid inlet at the lower end of the methane intermediate buffer container and the bottom gas intermediate buffer container via pipelines. The back pressure pump is connected to the outlet end of the core holder. The hand-cranked confining pressure pump is connected to the core holder. The auxiliary equipment unit includes a vacuum pump, a gas flow meter, a gas chromatograph, and a gas collection bag; the vacuum pump is connected to the pipeline between the outlet end of the core holder and the back pressure valve via a three-way valve; the gas flow meter is connected to the back pressure valve for real-time monitoring and recording of the volumetric flow rate of the produced gas; the gas chromatograph is connected to the gas flow meter for analyzing the components of the mixed gas and their changes; the gas collection bag is connected to the gas chromatograph for collecting the gas. The data acquisition and processing unit is used to monitor experimental parameters in real time and perform digital storage and remote data management of multiple parameters. The power supply unit is used to continuously provide stable power to the experimental system.

2. The non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system according to claim 1, characterized in that, The gas supply unit includes a methane cylinder, a carbon dioxide / nitrogen cylinder, and a gas leak detection device. The methane cylinder and the carbon dioxide / nitrogen cylinder are respectively connected to the methane intermediate buffer container and the bottom gas intermediate buffer container in the displacement system unit through a high-pressure valve and a pressure regulating valve.

3. The non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system according to claim 2, characterized in that, The displacement system unit is installed in a mobile constant temperature oven, which provides a stable and controlled temperature environment for the displacement system unit.

4. The non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system according to claim 1, characterized in that, The methane intermediate buffer container and the bottom gas intermediate buffer container are made of 316L stainless steel, with a single volume of 1000 mL and a pressure resistance rating of 70 MPa. They are equipped with a gas-liquid isolation piston structure inside. The piston structure in the intermediate buffer container of the bottom gas is made of a material resistant to CO2 corrosion.

5. The non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system according to claim 1, characterized in that, The core sample used was a real reservoir core with a size of φ38×100 mm. The angle adjustment range of the core holder is 0~90°; The core sleeve has dimensions of φ39×φ46×300 mm and is made of a CO2-resistant material.

6. The non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system according to claim 1, characterized in that, The components in the displacement system unit are connected by quick connectors.

7. The non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system according to claim 1, characterized in that, The pump control unit also includes a water tank and an air compressor; The water tank is connected to both the displacement pump and the back pressure pump to provide liquid supply; The air compressor is also connected to both the displacement pump and the back pressure pump to provide continuous power.

8. The non-hydrocarbon gas replacement natural gas high-temperature and high-pressure multi-cycle experimental system according to claim 3, characterized in that, The data acquisition and processing unit includes a pressure acquisition module, a temperature acquisition module, and an intelligent acquisition system; The temperature acquisition module is installed in a constant temperature oven and is used to monitor the system operating temperature; Pressure acquisition modules are installed on the pipelines between the methane cylinder and the methane intermediate buffer container, the pipelines between the carbon dioxide / nitrogen cylinder and the cushion gas intermediate buffer container, the pipelines between the methane intermediate buffer container and the core holder, the pipelines between the cushion gas intermediate buffer container and the core holder, the pipelines between the hand-cranked confining pressure pump and the core holder, the output pipeline of the displacement pump, and the output pipeline of the back pressure pump. The gas flow meter, temperature acquisition module, and each pressure acquisition module are all connected to the intelligent acquisition system, which is used for continuous data acquisition and digital storage.

9. A high-temperature, high-pressure, multi-cycle experimental method for replacing natural gas with non-hydrocarbon gases, based on the high-temperature, high-pressure, multi-cycle experimental system for replacing natural gas with non-hydrocarbon gases as described in claim 8, characterized in that, Includes the following steps: Step 1: Core sample preparation and pretreatment; Core samples with the required geological conditions are selected, cut, and polished to prepare standard columnar specimens; after completion, they are cleaned, dried, and cooled in sequence to ensure that there are no impurities left in the core pores and to simulate real reservoir conditions. Step 2: Determination of core physical parameters; The processed core samples were subjected to mass determination, and the dry weight, length, and diameter were recorded. Gas permeability was also measured to obtain basic porosity and permeability. Step 3: Connecting and leak-checking the experimental system; Connect each unit to form a closed loop to ensure the pipeline is airtight. After the initial connection is completed, purge the system with N2 gas to remove residual air and impurities. Then close the system outlet valve, pressurize by filling with N2 and let it stand. Observe the pressure change. If the system pressure is basically constant within the set time, it is considered to have good airtightness. Step 4: System vacuuming and core loading; Pretreated core samples were assembled into a core holder, and the gas displacement behavior under different geological structural conditions was simulated using the core holder. According to the experimental design requirements, a single core or multiple core segments formed by combinations of different permeabilities are selected; after the core samples are loaded, the outlet valve of the intermediate buffer container is closed, and the vacuum pump is started to perform a vacuuming operation on the system. Step 5: Constant temperature preheating and system stabilization; Turn on the constant temperature oven, set the target experimental temperature, and preheat the core sample and system pipeline; after the system temperature stabilizes to the set value, proceed to the next step. Step 6: Gas filling and pressurization of the intermediate container; The required gas is sequentially introduced into the methane intermediate buffer container and the bottom gas intermediate buffer container, the outlet valve is closed, and the gas in the intermediate buffer container is pressurized by a constant speed and constant pressure displacement pump until the preset injection pressure is reached. Step 7: CH4 saturation of core samples; Set the upper and lower limit pressures of the system, and adjust the back pressure valve and the hand-cranked confining pressure pump to maintain stable confining pressure conditions; open the valves at the outlet of the methane intermediate buffer container and the inlet of the core holder, and use the displacement pump to push the piston to inject CH4 into the core sample until it is completely saturated; after allowing it to stand and stabilize, open the CH4 extraction outlet valve to discharge CH4 gas, and measure the discharged volume using a gas flow meter to obtain the saturated volume V1 of the core sample; subsequently, to obtain control data, CH4 is injected into the core again to saturate it and stabilize it to the set upper limit pressure; after closing the injection valve, open the gas extraction outlet valve to perform simulated gas extraction operation, and extract the core pressure from the upper limit pressure to the lower limit pressure; during this process, the volume of extracted gas is recorded using a gas flow meter and denoted as V2, which is used to characterize the gas extraction capacity under pure CH4 conditions and serves as a reference for subsequent CO2 replacement efficiency; Step 8: Injecting gas to replace the underside; Switch back to the CO2 injection path and open the outlet valve of the intermediate buffer container for the cushion gas. With all other valves in the system closed, inject CO2 as cushion gas into the core sample using a displacement pump at constant pressure or constant flow rate. Gradually increase the core pressure from the lower limit to the set upper limit to provide the driving force for the subsequent methane replacement process. The injection volume of CO2 is indirectly calculated from the volume of injected water and then converted to the gas volume V3 under standard conditions using the equation of state. Step 9: Gas collection and component analysis; A gas chromatograph and a gas collection bag are connected to the outlet end of the core holder to perform online component analysis and sampling detection of the produced gas, and obtain the CH4 / CO2 concentration change curve over time. At the same time, the cumulative volume of the produced gas is recorded in real time by the gas flow meter at the outlet end, and the volume of CH4 replaced (V4) and the volume of CO2 produced along with it are calculated by combining the volume fraction of each component measured by chromatography. Step 10: Multiple rounds of cyclic injection and extraction; To simulate the multi-cycle injection and production process of a gas storage facility in actual operation, after the first round of gas displacement experiment was completed, subsequent cycles were repeated according to the following steps: First, the outlet valve of the core holder was closed, the CH4 injection path was reopened, and CH4 was injected into the core through the methane intermediate buffer container and displacement pump until the reservoir pressure returned to the set upper limit; then, after standing for a period of time, the outlet valve was opened again to produce CH4, while the outlet pressure was adjusted to the set lower limit through the back pressure pump, and the produced gas volume and flow rate were recorded; Step 11: After the multi-round gas production phase, based on the gas production volume and purity of the previous round, the CO2 injection path is reopened. CO2 is injected into the core through the intermediate buffer container of the underlying gas to replace the CH4 or residual underlying gas that was not used in the previous round of gas production. The injection process continues until the reservoir pressure recovers to the upper limit pressure, and then the next round of gas production is carried out until the lower limit pressure is reached. Based on the CO2 injection volume and the composition analysis results of the produced gas in each cycle, the actual CO2 consumption of that round is calculated. Before entering the next round of gas injection, the corresponding volume of CO2 is replenished as needed to ensure the stability of the underlying gas content in the reservoir. At the same time, the CH4 produced volume, CO2 injection volume and residual gas content of each round are recorded for comprehensive analysis of the impact of the number of cycles on natural gas recovery rate, CO2 replacement efficiency and storage efficiency. Step 12: System venting and core sample unloading; After all cyclic injection and production experiments are completed, close all gas source valves and gradually release the internal pressure of the system to atmospheric pressure. After the pressure is completely released, disassemble the core holder, take out the core sample, and perform subsequent characterization as needed to analyze changes in pore structure or gas distribution characteristics. Step 13: Data processing and result analysis; The data collected during each injection and production stage of the experiment were organized and recorded in each stage, including CH4 production volume, CO2 injection and consumption volume. The cumulative displacement efficiency, storage efficiency and displacement effect of each cycle were calculated and summarized. The displacement efficiency was calculated according to the formula η1 = V4 / V1 and the storage efficiency was calculated according to the formula η2 = 1 - V5 / V3.

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