Device and method for simulating huff and puff of sand-carrying foam of heterogeneous reservoir

Abstract

The invention discloses a device and a method for simulating huff and puff of heterogeneous reservoir sand-carrying foam. The device comprises an injection mechanism, a rock core simulation mechanism and a flowback mechanism, can realize preparation and flow distribution of sand-carrying foam, simulates heterogeneous conditions on parallel rock cores, and performs independent separation and component detection on each path of output fluid. According to the method, systematic research is carried out through the steps of establishing an initial state, carrying out benchmark comparison, optimizing flow distribution, evaluating differential influence of fluid parameters and the like. The technical problem that an existing experimental device cannot simulate heterogeneity-homogeneity is solved, the effectiveness of the flow control technology can be quantitatively evaluated, the interaction rule of a fluid formula and reservoir physical properties is revealed, and a scientific basis is provided for field yield increasing operation.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction simulation experiments, and in particular to an apparatus and method for simulating the sand-carrying foam intrusion of heterogeneous reservoirs. Background Technology

[0002] As an important strategic alternative resource, the efficient development of shale oil is crucial for ensuring energy security. However, after hydraulic fracturing and commissioning, shale oil reservoirs generally face severe challenges such as rapid production decline and low recovery rates, urgently requiring new development methods such as replenishing formation energy to improve efficiency.

[0003] Against this backdrop, carbon dioxide (CO2) huff and puff technology has become a hot research topic in the industry due to its dual potential in enhancing shale oil recovery and achieving CO2 geological sequestration (CCUS). Compared with conventional water injection development, CO2 fluid has better injection capabilities, can be miscible with crude oil, and effectively restores well productivity through multiple mechanisms such as replenishing formation energy, extracting light and intermediate components from crude oil, reducing crude oil viscosity, and increasing its expansibility. It is a highly promising enhanced oil recovery (EOR) medium.

[0004] Despite its promising prospects, CO2 huff and puff and storage technologies for shale oil reservoirs are still in the exploratory stage, facing multiple challenges in both theory and practice. One of the core difficulties in developing real oil and gas reservoirs is the heterogeneity of the reservoirs. In actual formations, oil and gas wells often encounter multiple layers with vastly different permeability and other physical properties. When displacing fluids such as CO2 foam are injected, the fluid tends to preferentially flow into the high-permeability "dominant channels," forming "channeling," resulting in low sweep efficiency of the injected fluid and severely limiting the utilization of medium- and low-permeability layers and overall recovery rate.

[0005] To address this issue, while field operations have begun to explore the application of technologies such as Inflow Control Devices (ICDs) to actively regulate flow distribution among multiple layers, the evaluation of effectiveness and optimization of solutions are severely limited by insufficient experimental methods. Existing laboratory physical simulation studies are mostly based on homogenized "point" models constructed from single core samples. This oversimplification fails to reproduce the complex interlayer disturbances and fluid distribution patterns in heterogeneous reservoirs. Furthermore, both the immaturity of numerical simulation techniques and the lack of physical simulation methods result in a lack of clarity regarding the differentiated interaction mechanisms between CO2 foam and its proppant materials (such as ceramsite and quartz sand) with reservoirs of varying physical properties. Therefore, both academia and industry currently lack a comprehensive experimental platform capable of realistically simulating heterogeneous reservoir conditions in the laboratory, quantitatively evaluating and optimizing flow control technologies, and deeply revealing the influence of key process parameters. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and to propose an apparatus and method for simulating the sand-carrying foam huff and puff of heterogeneous reservoirs.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0008] This invention provides an apparatus for simulating the proppant-carrying foam huff and puff of heterogeneous reservoirs, comprising:

[0009] An injection mechanism for preparing and injecting experimental fluid includes a foam generating unit, a sand dispenser, a mixer, a main injection pump, a main injection pipe, and a flow distribution module. The outlet of the foam generating unit is connected to the first inlet of the mixer, the outlet of the sand dispenser is connected to the second inlet of the mixer, the outlet of the mixer is connected to the inlet of the main injection pump, and the outlet of the main injection pump is connected to one end of the main injection pipe. The flow distribution module includes several flow control valves, one end of each of the flow control valves being connected to the other end of the main injection pipe.

[0010] The core simulation mechanism includes several triaxial core holders, one end of each triaxial core holder is connected to the other end of the corresponding flow control valve, and each triaxial core holder is used to hold core samples with different physical properties.

[0011] The return flow mechanism, whose inlet end is connected to the outlet end of each of the core simulation mechanisms, is used to perform gas-liquid separation on the fluid returned from each core sample and to individually detect the content of each component in the separated gas.

[0012] In some embodiments, the mixer includes a tank, an agitator disposed within the tank, and a weighing device for supporting the tank and monitoring its total mass in real time. The outlet of the tank is connected to the inlet of the main injection pump. The weighing device is used to acquire real-time data on the mass of the material in the tank for calculating the foam or proppant content.

[0013] In some embodiments, the foam generating unit includes a gas supply component, a liquid supply component, and a foam generator. The gas supply component includes a carbon dioxide tank, a gas pump, and a gas supply pipe. The inlet of the gas pump is connected to the carbon dioxide tank, the outlet of the gas pump is connected to one end of the gas supply pipe, and the other end of the gas supply pipe is connected to the gas input end of the foam generator. A pressure gauge, a first flow meter, and a gas supply valve are provided on the gas supply pipe. The liquid supply component includes a liquid filling cylinder, a piston, a liquid pump, and a liquid supply pipe. The piston is slidably disposed inside the liquid filling cylinder, dividing the liquid filling cylinder into a liquid storage chamber and a piston driving chamber. The outlet of the liquid pump is connected to the piston driving chamber. The liquid storage chamber is connected to the liquid input end of the foam generator through the liquid supply pipe. A second flow meter and a liquid supply valve are provided on the liquid supply pipe. The outlet of the foam generator is connected to the tank body.

[0014] In some embodiments, the sand feeder includes a sand storage hopper for storing proppant, a screw conveyor disposed below the sand storage hopper, and a drive motor. The inlet of the screw conveyor is connected to the outlet of the sand storage hopper, and the outlet of the screw conveyor is connected to the tank body. The drive motor is used to drive the screw conveyor to rotate. By controlling the rotational speed of the drive motor, the proppant discharge rate can be adjusted.

[0015] In some embodiments, the apparatus for simulating sand-carrying foam huff and puff in a heterogeneous reservoir further includes a methane displacement unit, which includes a methane tank, a displacement pump, and a displacement pipe. The inlet of the displacement pump is connected to the outlet of the methane tank, the outlet of the displacement pump is connected to one end of the displacement pipe, the other end of the displacement pipe is connected to the main injection pipe, and a displacement valve is provided on the displacement pipe.

[0016] In some embodiments, the triaxial core holder includes a hollow cylindrical cylinder, a flexible sleeve for wrapping the core sample, a first end piston and a second end piston respectively placed at both ends of the flexible sleeve, and an axial pressure application component. The flexible sleeve is coaxially disposed inside the cylinder. The first end piston and the second end piston are used to seal and apply axial pressure to the core sample. The cylinder is provided with a confining pressure inlet for injecting pressurized fluid into the annular space between the cylinder and the flexible sleeve to apply confining pressure. Simultaneously, one end of the first end piston abuts against the cylinder and the other end of the first end piston abuts against one end of the core sample. The first end piston is provided with a through first axial fluid channel, which is connected to the other end of the corresponding flow control valve. One end of the second end piston abuts against the other end of the core sample and is provided with a through second axial fluid channel, which is connected to the inlet end of the return flow mechanism. The axial pressure application component includes a pressure cylinder, and the output shaft of the pressure cylinder is connected to the second end piston.

[0017] The core simulation mechanism also includes a confining pressure pump and an axial pressure pump. The outlet of the confining pressure pump is connected to the confining pressure inlet of each of the three-axis core holders, and the outlet of the axial pressure pump is connected to the gas input end of the pressure cylinder of each of the three-axis core holders.

[0018] In some embodiments, the core simulation mechanism further includes a constant temperature chamber, and each of the triaxial core holders is disposed inside the constant temperature chamber.

[0019] In some embodiments, the return mechanism includes return components that correspond one-to-one with each of the triaxial core holders. Each return component includes a back pressure valve, a gas-liquid separator, a gas discharge pipe, a liquid discharge pipe, a third flow meter, and a gas composition detector. The input end of the back pressure valve is connected to the outlet of the corresponding triaxial core holder, and the output end of the back pressure valve is connected to the inlet of the gas-liquid separator. The gas outlet of the gas-liquid separator is connected to one end of the gas discharge pipe, and the liquid outlet of the gas-liquid separator is connected to one end of the liquid discharge pipe. The third flow meter is installed in the gas discharge pipe, and the gas composition detector is used to detect the gas composition and content within the gas discharge pipe.

[0020] In some embodiments, the backflow mechanism further includes a recovery tank connected to the other end of each of the liquid discharge pipes.

[0021] The present invention also provides a method for simulating proppant-carrying foam huff and puff in heterogeneous reservoirs, applicable to the aforementioned apparatus for simulating proppant-carrying foam huff and puff in heterogeneous reservoirs, and comprising the following steps:

[0022] a) Initial state establishment steps: Initial physical property measurements are performed on multiple core samples with different physical properties that are respectively loaded into the core simulation mechanism, and the operation of saturating simulated formation water and then displacing them with methane gas to the bound water state is performed in sequence to determine the initial methane reserves of each core sample.

[0023] b) Baseline Experiment Procedure: Set the multiple flow control valves in the flow distribution module to a unified baseline state, and using a baseline fluid formula, sequentially perform the following injection-soaking-return operation through the injection mechanism and the return mechanism:

[0024] b1) Injection stage: A predetermined volume of reference fluid is injected into the core simulation mechanism through the injection mechanism;

[0025] b2) Soaking stage: Close all valves of the injection mechanism and the return mechanism, so that the injected fluid interacts with the core sample at the set temperature and pressure for a predetermined time;

[0026] b3) Backflow stage: The backflow mechanism is activated to reduce the pressure during mining with the set production pressure difference until the backflow process meets the preset cutoff conditions. During this process, the fluid backflowed from each core sample is independently measured.

[0027] c) Flow control optimization step: Keep the reference fluid formula unchanged, only adjust the opening degree of at least one flow control valve in the flow distribution module, repeat the injection, soaking and backflow operations described in step b), and record the methane content in the fluid returned from the core sample, and analyze the impact of the flow distribution module on the overall production increase effect of the system.

[0028] d) Evaluation steps for the differential impact of key parameters: Keeping the optimized flow control valve setting in step c) unchanged, systematically change the foam content and / or proppant concentration of the fluid prepared by the injection mechanism, and conduct at least two sets of experiments at different parameter levels. For each set of experiments, repeat the injection, soaking, and backflow operations described in step b). By comparing and analyzing the different degrees of improvement in the recovery rate of core samples with different physical properties caused by the change of this key parameter, the differential impact of this parameter on different physical properties and lithologies can be quantitatively evaluated.

[0029] Compared with existing technologies, the beneficial effects of the apparatus and method for simulating sand-carrying foam huff and puff in heterogeneous reservoirs provided by this invention include:

[0030] (1) By using multiple sets of triaxial core holders in parallel, core samples with different properties can be loaded at the same time, and the flow distribution module can be used to precisely control the liquid inlet of each core. This fundamentally overcomes the defect that traditional single core devices cannot simulate reservoir heterogeneity and can truly reproduce the competitive injection and ripple process of injected fluid in different permeability layers.

[0031] (2) This device can physically simulate and verify the core production enhancement mechanism in the CO2 huff and puff process. By independently measuring and analyzing the composition of each flowback fluid, it is possible to directly study how reservoir heterogeneity affects the replenishment of formation energy, the extraction of crude oil by CO2, swelling and viscosity reduction, etc., providing reliable physical evidence for a deeper understanding of its mechanism.

[0032] (3) The method of this invention, through systematic steps such as setting up benchmark experiments, optimizing flow control, and evaluating key parameters, can quantitatively evaluate the effectiveness of inflow control technology (simulated by adjusting the flow control valve). Simultaneously, it can systematically study the influence of key process parameters such as injection timing, injection volume, well-keeping time, foam quality, and proppant concentration on the oil enhancement effect and CO2 sequestration in different physical property zones. This corresponds to the main controlling factors such as injection volume found in numerical simulation studies, providing direct experimental basis for on-site operation optimization.

[0033] (4) Through this invention, CO2 foam systems and proppant schemes that match the heterogeneous characteristics of specific reservoirs can be accurately screened and designed. This avoids the "one-size-fits-all" approach to technology application and helps to "tailor-make" the best production enhancement measures for reservoirs with different physical properties, thereby maximizing the recovery rate while improving CO2 storage efficiency and project economics. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of a device for simulating sand-carrying foam ingestion and release in a heterogeneous reservoir according to an embodiment of the present invention;

[0035] Figure 2 yes Figure 1 A schematic diagram of the injection mechanism;

[0036] Figure 3 yes Figure 2 Schematic diagram of the structure of the sander and mixer;

[0037] Figure 4 yes Figure 1 Schematic diagram of the core simulation mechanism and the backflow mechanism;

[0038] Figure 5 yes Figure 4 A schematic diagram of the cross-sectional structure of a single triaxial core holder;

[0039] Explanation of reference numerals in the attached drawings: 1. Injection mechanism; 11. Foam generation unit; 111. Gas supply assembly; 1111. Carbon dioxide gas cylinder; 1112. Air pump; 1113. Gas supply pipe; 1114. Barometer; 1115. First flow meter; 1116. Gas supply valve; 112. Liquid supply assembly; 1121. Liquid filling cylinder; 1122. Piston; 1123. Liquid pump; 1124. Liquid supply pipe; 1125. Second flow meter; 1126. Liquid supply valve; 113. Foam generator; 12. Sand adder; 121. Sand storage hopper; 122. Screw conveyor; 123. Drive motor; 13. Mixer; 131. Tank body; 132. Agitator; 133. Weighing device; 14. Main injection pump; 15. Main injection pipe; 16. 1. Flow distribution module; 161. Flow control valve; 2. Core simulation mechanism; 21. Triaxial core holder; 211. Cylinder liner; 212. Flexible sleeve; 213. First end piston; 214. Second end piston; 215. Axial pressure component; 2151. Pressure cylinder; 22. Confining pressure pump; 23. Axial pressure pump; 24. Constant temperature chamber; 3. Return mechanism; 31. Return assembly; 311. Back pressure valve; 312. Gas-liquid separator; 313. Gas discharge pipe; 314. Liquid discharge pipe; 315. Third flow meter; 316. Gas composition detector; 32. Recovery tank; 4. Methane displacement unit; 41. Methane tank; 42. Displacement pump; 43. Displacement pipe; 44. Displacement valve; 5. Core sample. Detailed Implementation

[0040] The technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The described embodiments are only possible technical implementations of the present invention, but are not limited thereto. Other embodiments obtained by those skilled in the art in conjunction with the embodiments of the present invention without creative effort are also within the protection scope of the present invention.

[0041] This application primarily employs a simulated CO2 foam injection experimental system for heterogeneous reservoirs, aiming to address the problems of low sweep efficiency and low recovery rates caused by reservoir heterogeneity in unconventional oil and gas reservoir development, such as shale oil. This device can accurately simulate the entire process of CO2 proppant-carrying foam injection and flushing under heterogeneous reservoir conditions, from injection and well shut-in to flowback, providing experimental support for optimizing production enhancement processes and assessing CO2 storage potential, and promoting the large-scale application of this technology. The following is a further detailed description of this application.

[0042] Example 1

[0043] Please refer to Figures 1-5The apparatus for simulating sand-carrying foam injection in heterogeneous reservoirs provided in this application includes an injection mechanism 1, a core simulation mechanism 2, and a flowback mechanism 3. The injection mechanism 1 is used to prepare and inject experimental fluid; the core simulation mechanism 2 is used to simulate reservoirs with different physical properties; and the flowback mechanism 3 is used to perform gas-liquid separation on the fluid flowback from each core sample 5 and to individually detect the content of each component in the separated gas. Additionally, a methane displacement unit 4 can be optionally installed to saturate the core sample 5 before the experiment. These four mechanisms work together to realistically simulate the entire process from initial formation establishment, fluid preparation, heterogeneous reservoir injection to production flowback.

[0044] For details, please refer to Figure 1 and Figure 2 The injection mechanism 1 includes a foam generation unit 11, a sand adder 12, a mixer 13, a main injection pump 14, a main injection pipe 15, and a flow distribution module 16.

[0045] The foam generating unit 11 includes an air supply assembly 111, a liquid supply assembly 112, and a foam generator 113. The air supply assembly 111 includes a carbon dioxide tank 1111, an air pump 1112, and an air supply pipe 1113. The carbon dioxide tank 1111 stores carbon dioxide gas. The inlet of the air pump 1112 is connected to the carbon dioxide tank 1111, and its outlet is connected to one end of the air supply pipe 1113, used to deliver carbon dioxide gas to the foam generator 113. The air supply pipe 1113 is equipped with a barometer 1114, a first flow meter 1115, and an air supply valve 1116. The barometer 1114 measures the air pressure within the air supply pipe 1113, the first flow meter 1115 measures the flow rate of the carbon dioxide gas, and the air supply valve 1116 controls the supply of carbon dioxide gas. The liquid supply assembly 112 includes a liquid filling cylinder 1121, a piston 1122, a liquid pump 1123, and a liquid supply pipe 1124. The liquid filling cylinder 1121 is used to hold liquid. The piston 1122 is slidably disposed inside the liquid filling cylinder 1121, dividing the liquid filling cylinder 1121 into a liquid storage chamber and a piston drive chamber. The outlet of the liquid pump 1123 is connected to the piston drive chamber. The liquid storage chamber is connected to the liquid input end of the foam generator 113 through the liquid supply pipe 1124. When the liquid pump 1123 is working, it pushes the piston 1122, so that the liquid in the liquid storage chamber is delivered to the foam generator 113 through the liquid supply pipe 1124. A second flow meter 1125 and a liquid supply valve 1126 are provided on the liquid supply pipe 1124. The second flow meter 1125 is used to measure the flow rate of the liquid, and the liquid supply valve 1126 is used to control the supply of liquid. The foam generator 113 mixes carbon dioxide gas and liquid to generate foam, and its outlet is connected to the tank 131 of the mixer 13. Here, the air pump 1112 in the air supply assembly 111 can also be replaced by a compressor to provide higher pressure; the liquid filling cylinder 1121 can also be replaced by a liquid storage tank with a liquid level gauge for easy observation of the liquid level.

[0046] Please refer to Figures 1-3 The sand feeder 12 includes a sand storage hopper 121 for storing proppant, a screw conveyor 122 disposed below the sand storage hopper 121, and a drive motor 123. The sand storage hopper 121 stores proppant. The inlet of the screw conveyor 122 is connected to the outlet of the sand storage hopper 121, and the outlet is connected to the tank 131 of the mixer 13. The drive motor 123 drives the screw conveyor 122 to rotate. By controlling the rotation speed of the drive motor 123, the proppant discharge rate can be adjusted. The screw conveyor 122 ensures that the proppant is uniformly and stably delivered to the mixer 13. Alternatively, a vibrating feeder can be used instead of the screw conveyor 122, and the discharge rate of the proppant can be controlled by adjusting the vibration frequency.

[0047] Please refer to Figures 1-3 The mixer 13 includes a tank 131, an agitator 132 disposed within the tank 131, and a weighing device 133 for supporting the tank 131 and monitoring its total mass in real time. The tank 131 contains foam and proppant. The agitator 132 rotates within the tank 131 to thoroughly mix the foam and proppant. The weighing device 133 acquires real-time data on the mass of the material within the tank 131 for calculating the foam or proppant content. The agitator 132 can be a paddle agitator or a turbine agitator to improve the mixing effect.

[0048] Please refer to Figures 1-3 The outlet of mixer 13 is connected to the inlet of main injection pump 14, and the outlet of main injection pump 14 is connected to one end of main injection pipe 15. Flow distribution module 16 includes several flow control valves 161, one end of each flow control valve 161 being connected to the other end of main injection pipe 15. Main injection pump 14 delivers the mixed experimental fluid to flow distribution module 16 through main injection pipe 15. Flow control valves 161 can adjust the flow rate of each branch. Flow control valves 161 can be electric or pneumatic, facilitating remote or automatic control as needed.

[0049] These components are combined together. First, foam is generated by the foam generation unit 11, proppant is added by the sand adder 12, and the mixture is fully mixed in the mixer 13. Then, it is delivered by the main injection pump 14 and the flow distribution module 16 distributes the flow so that the experimental fluid can be injected into the core simulation mechanism 2 at a suitable flow rate and ratio.

[0050] For details, please refer to Figure 1 and Figure 4The core simulation mechanism 2 includes several triaxial core holders 21, a confining pressure air pump 22, an axial pressure air pump 23, and a constant temperature chamber 24. The triaxial core holders 21 are configured such that the inlet of each holder is connected to a branch outlet of the flow distribution module 16. Before the experiment, core samples 5 with high, medium, and low physical properties are placed in each holder.

[0051] Please refer to Figure 5 The triaxial core holder 21 includes a hollow cylindrical cylinder liner 211, a flexible sleeve 212 for wrapping the core sample 5, a first end piston 213 and a second end piston 214 respectively located at both ends of the flexible sleeve 212, and an axial pressure application element 215. The flexible sleeve 212 is coaxially disposed inside the cylinder liner 211. The first end piston 213 and the second end piston 214 are used to seal and apply axial pressure to the core sample 5. The cylinder liner 211 is provided with a confining pressure inlet for injecting pressurized fluid into the annular space between the cylinder liner 211 and the flexible sleeve 212 to apply confining pressure. One end of the first end piston 213 abuts against the cylinder liner 211, and the other end abuts against one end of the core sample 5. The first end piston 213 is provided with a through first axial fluid channel, which is connected to the other end of the corresponding flow control valve 161. One end of the second end piston 214 abuts against the other end of the core sample 5. The second end piston 214 has a through-hole second axial fluid channel, which communicates with the inlet end of the return flow mechanism 3. The axial pressure application component 215 includes a pressure cylinder 2151, the output shaft of which is connected to the second end piston 214. Axial pressure can be applied to the core sample 5 through the pressure cylinder 2151. The flexible sleeve 212 can be a rubber sleeve, providing good flexibility and sealing. The pressure cylinder 2151 can also be a hydraulic cylinder to provide greater pressure.

[0052] Please refer to Figures 1-5 The outlet of the confining pressure air pump 22 is connected to the confining pressure inlet of each triaxial core holder 21, and is used to inject pressurized fluid into the annular space between the cylinder liner 211 and the flexible sleeve 212 to apply confining pressure. The outlet of the axial pressure air pump 23 is connected to the gas input end of the pressure cylinder 2151 of each triaxial core holder 21, and is used to provide power to the pressure cylinder 2151 to apply axial pressure.

[0053] Each triaxial core holder 21 is placed inside a constant temperature chamber 24, which can keep the core sample 5 at a constant temperature during the experiment, simulating the actual temperature environment of the formation.

[0054] These components combined allow the triaxial core holder 21 to simulate the stress state of the core sample 5 in the formation, while the confining pressure pump 22 and axial pressure pump 23 provide pressure, and the constant temperature chamber 24 provides a stable temperature, so that the core sample 5 is in an environment close to the actual formation, which facilitates the entry of experimental fluid into the core sample 5 for related experiments.

[0055] Specifically, the return mechanism 3 includes a return assembly 31 that corresponds to each of the triaxial core holders 21 and a recovery tank 32.

[0056] Please refer to Figure 1 and Figure 4 The backflow assembly 31 includes a back pressure valve 311, a gas-liquid separator 312, a gas discharge pipe 313, a liquid discharge pipe 314, a third flow meter 315, and a gas composition detector 316. The input end of the back pressure valve 311 is connected to the outlet of the corresponding triaxial core holder 21, and the output end of the back pressure valve 311 is connected to the inlet of the gas-liquid separator 312. In this embodiment, the back pressure valve 311 can continuously control the back pressure; for example, a pneumatically controlled back pressure valve can be used, whose back pressure is controlled by air pressure and can be arbitrarily adjusted within a set air pressure range. The gas-liquid separator 312 separates the backflowed fluid into gas and liquid components; its gas outlet is connected to one end of the gas discharge pipe 313, and its liquid outlet is connected to one end of the liquid discharge pipe 314. The third flow meter 315 is installed in the gas discharge pipe 313 to measure the flow rate of the discharged gas, and the gas composition detector 316 is used to detect the gas composition and content within the gas discharge pipe 313.

[0057] Specifically, gas composition detection can be achieved in two ways: first, a miniature gas chromatograph is independently configured on each runoff branch to achieve simultaneous online analysis of gases from each stream; second, a multi-channel injection valve is used in conjunction with a high-performance gas chromatograph, and the sampling channels are switched sequentially and periodically under program control to achieve time-sharing and independent detection of gases from each stream. Both methods can accurately obtain dynamic change data of the composition (such as CH4 and CO2) of gases produced during the runoff process of each core sample 5.

[0058] The recovery tank 32 is connected to the other end of each liquid discharge pipe 314 for recovering the separated liquid.

[0059] These components are combined, with the backflow assembly 31 performing gas-liquid separation and component analysis on the fluid backflowed from the core sample 5, and the recovery tank 32 collecting the separated liquid, thus achieving effective treatment and analysis of the backflowed fluid.

[0060] The implementation principle of this embodiment is as follows: This device for simulating the injection and release of proppant-carrying foam in heterogeneous reservoirs prepares and distributes experimental fluid through injection mechanism 1, core simulation mechanism 2 simulates reservoir environments with different physical properties, and flowback mechanism 3 processes and analyzes the flowback fluid. It can realistically simulate the entire process of CO2 foam injection under heterogeneous reservoir conditions. Compared with existing technologies, it overcomes the limitation of single-core sample experimental devices in simulating heterogeneity. It can be used to evaluate the effectiveness of flow control technology, help reveal the migration, plugging, and modification patterns of CO2 foam and its carried proppant in reservoirs with different physical properties, and thus accurately select and design matching CO2 foam systems and proppant schemes based on the specific geological characteristics of the target reservoir, providing strong experimental support for improving oil recovery and CO2 storage.

[0061] Please refer to Figure 2 The methane displacement unit 4 is a key component in establishing the initial formation state before conducting gas-bearing reservoir simulation experiments. The methane displacement unit 4 includes a methane tank 41, a displacement pump 42, and a displacement pipe 43. The inlet of the displacement pump 42 is connected to the outlet of the methane tank 41, and the outlet of the displacement pump 42 is connected to one end of the displacement pipe 43. The other end of the displacement pipe 43 is connected to the main injection pipe 15, and a displacement valve 44 is installed on the displacement pipe 43.

[0062] Function: In the initial state establishment phase of the experiment, other parts of the injection mechanism 1 are closed, the displacement valve 44 is opened, and the displacement pump 42 is started to inject methane gas into the water-saturated core sample 5 through the main injection pipe 15 and the flow distribution module 16 until no more water is produced. This establishes a specific and calculable initial methane saturation and bound water saturation in the core sample 5, providing accurate initial reserve data for subsequent recovery calculations.

[0063] Example 2

[0064] The method for simulating proppant-carrying foam huff and puff in heterogeneous reservoirs provided in this application embodiment, with shale oil reservoirs as the application background, focuses on studying the impact of heterogeneity on CO2 huff and puff performance through physical simulation and optimizing relevant process parameters. Specifically, it includes the following steps:

[0065] S1, Initial state establishment steps: including:

[0066] S11, Physical property measurement: The dried high, medium and low permeability core samples 5 were weighed and their pore volume was measured using a porosimeter and a permeability meter.

[0067] S12, Saturated water: After vacuuming each core sample 5, it is immersed in simulated formation water until it is completely saturated. The saturated core sample 5 is then placed into the triaxial core holder 21 in the core simulation mechanism 2 and brought to a preset temperature in the constant temperature chamber 24. Simulated in-situ stress is then applied by the confining pressure air pump 22 and the axial pressure air pump 23.

[0068] S13, Methane Displacement: Close the liquid supply valve 1126 and sand feeder 12 of injection mechanism 1. Open the displacement valve 44 of methane displacement unit 4, start the displacement pump 42, and inject methane gas into core sample 5 through main injection pipe 15 and flow distribution module 16 to displace the movable water therein. Continuously monitor at the outlet end of return mechanism 3. When no more water is produced, stop injection and close displacement valve 44.

[0069] S14, Initial Reserve Calculation: Accurately record the discharged water volume (Vw), then the initial methane gas volume in each core sample 5 is: V CH4_initial =PV-Vw, this value is the benchmark for subsequent calculation of recovery rate.

[0070] S2, Benchmark Experiment Procedure: Includes:

[0071] S21, Parameter Setting: Set all flow control valves 161 in the flow distribution module 16 to the fully open state. Set the reference fluid formula in the injection mechanism 1 (e.g., foam mass 85%, proppant content 10%).

[0072] S22, Injection Stage: Start the injection mechanism 1 and inject a predetermined volume (e.g., 0.5 PV) of reference CO2 foam into each core simulation mechanism 2 through the main injection pump 14.

[0073] S23, Soaking stage: Close all valves of injection mechanism 1 and return mechanism 3, and soak for a predetermined time (e.g., 24 hours) under constant temperature and pressure to allow CO2 to fully dissolve, diffuse and react.

[0074] S24, Backflow Stage: Gradually reduce the back pressure of the back pressure valve 311 of the backflow mechanism 3 to achieve a pressure reduction extraction at a set production pressure difference (e.g., 5 MPa). Independently and continuously record the gas production of each backflow branch, and analyze the concentrations of CH4 and CO2 in the gas using a gas composition detector 316 until production ends.

[0075] S3, Flow Control Optimization Step: Keeping the baseline fluid formulation unchanged, only adjust the opening degree of at least one flow control valve 161 in the flow distribution module 16 (for example, reduce the valve opening corresponding to the high-permeability core sample 5 by 50%), repeat the injection, soaking, and flowback operations described in step S2, and record the methane content in the fluid flowback from core sample 5 to analyze the impact of the flow distribution module 16 on the overall system production enhancement effect. By changing the opening degree of the flow control valve 161, observe the changes in the recovery rate of core sample 5 under different flow distributions to find the optimal flow distribution scheme.

[0076] S4, Evaluation of the Differential Impact of Key Parameters: Keeping the optimized flow control valve 161 setting from step S3 unchanged, systematically change the foam content and / or proppant concentration of the fluid prepared by injection mechanism 1, conducting at least two sets of experiments at different parameter levels. For each set of experiments, repeat the injection, soaking, and backflow operations described in step S2. Quantitatively evaluate the differential impact of this parameter on different lithological properties by comparing and analyzing the different degrees of improvement in the recovery rate of core samples 5 with varying physical properties. For example, gradually increase the foam content or proppant concentration and observe how the recovery rate of core samples 5 with different physical properties changes to determine the optimal foam content and proppant concentration.

[0077] For example, two independent experiments were conducted with proppant contents of 1% and 5%, respectively.

[0078] In each group of experiments, the complete injection, soaking, and backflow operations described in step S2 were repeated.

[0079] Analysis: By comparing the results of the two sets of experiments, the focus is on analyzing the differences in the improvement in recovery rate of high, medium, and low permeability core samples 5 when the proppant content increases from 1% to 5%. For example, if it is found that increasing the proppant content mainly improves the recovery rate of medium permeability core sample 5, while having little effect on high and low permeability core samples 5, then it can be concluded that "under these reservoir conditions, a medium concentration of proppant is more conducive to establishing effective support in the medium permeability section."

[0080] In this embodiment, the formula for calculating the recovery factor (RF) is as follows:

[0081]

[0082] Where i represents core samples with different physical properties (high, medium, and low permeability), V CH4_produced，i V represents the cumulative volume of methane returned from the i-th core sample. CH4_initial，i Let be the initial methane volume of the i-th core sample. This method allows for precise matching of optimal fluid formulations to formations with different physical properties.

[0083] The implementation principle of this embodiment is as follows: This method for simulating proppant-carrying foam injection in heterogeneous reservoirs, through steps such as establishing initial conditions, conducting benchmark experiments, optimizing flow control, and evaluating the differential effects of key parameters, can comprehensively and systematically study the role of CO2 foam in heterogeneous reservoirs. Compared with existing technologies, it can more accurately assess the effectiveness of flow control technology and the impact of different parameters on the recovery rate of core samples with different physical properties. This provides a scientific basis for selecting appropriate CO2 foam systems and proppant schemes in actual oil and gas field development, and helps to improve recovery rate and achieve CO2 sequestration.

[0084] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A device for simulating the proppant-carrying foam huff and puff of heterogeneous reservoirs, characterized in that, include: An injection mechanism for preparing and injecting experimental fluid includes a foam generating unit, a sand dispenser, a mixer, a main injection pump, a main injection pipe, and a flow distribution module. The outlet of the foam generating unit is connected to the first inlet of the mixer, the outlet of the sand dispenser is connected to the second inlet of the mixer, the outlet of the mixer is connected to the inlet of the main injection pump, and the outlet of the main injection pump is connected to one end of the main injection pipe. The flow distribution module includes several flow control valves, one end of each of the flow control valves being connected to the other end of the main injection pipe. The core simulation mechanism includes several triaxial core holders, one end of each triaxial core holder is connected to the other end of the corresponding flow control valve, and each triaxial core holder is used to hold core samples with different physical properties. The return flow mechanism, whose inlet end is connected to the outlet end of each of the core simulation mechanisms, is used to perform gas-liquid separation on the fluid returned from each core sample and to individually detect the content of each component in the separated gas.

2. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 1, characterized in that, The mixer includes a tank, an agitator disposed within the tank, and a weighing device for supporting the tank and monitoring its total mass in real time. The outlet of the tank is connected to the inlet of the main injection pump. The weighing device is used to acquire real-time data on the mass of the material inside the tank for calculating the foam or proppant content.

3. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 2, characterized in that, The foam generating unit includes an air supply component, a liquid supply component, and a foam generator. The air supply component includes a carbon dioxide tank, an air pump, and an air supply pipe. The inlet of the air pump is connected to the carbon dioxide tank, and the outlet of the air pump is connected to one end of the air supply pipe. The other end of the air supply pipe is connected to the gas input end of the foam generator. A barometer, a first flow meter, and an air supply valve are installed on the air supply pipe. The liquid supply component includes a liquid filling cylinder, a piston, a liquid pump, and a liquid supply pipe. The piston is slidably disposed inside the liquid filling cylinder, dividing the liquid filling cylinder into a liquid storage chamber and a piston driving chamber. The outlet of the liquid pump is connected to the piston driving chamber. The liquid storage chamber is connected to the liquid input end of the foam generator through the liquid supply pipe. A second flow meter and a liquid supply valve are installed on the liquid supply pipe. The outlet of the foam generator is connected to the tank body.

4. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 2, characterized in that, The sand feeder includes a sand storage hopper for storing proppant, a screw conveyor disposed below the sand storage hopper, and a drive motor. The inlet of the screw conveyor is connected to the outlet of the sand storage hopper, and the outlet of the screw conveyor is connected to the tank body. The drive motor is used to drive the screw conveyor to rotate. By controlling the rotation speed of the drive motor, the proppant discharge rate can be adjusted.

5. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 1, characterized in that, It also includes a methane displacement unit, which includes a methane tank, a displacement pump and a displacement pipe. The inlet of the displacement pump is connected to the outlet of the methane tank, the outlet of the displacement pump is connected to one end of the displacement pipe, the other end of the displacement pipe is connected to the main injection pipe, and a displacement valve is provided on the displacement pipe.

6. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 1, characterized in that, The triaxial core holder includes a hollow cylindrical cylinder, a flexible sleeve for wrapping the core sample, a first end piston and a second end piston respectively placed at both ends of the flexible sleeve, and an axial pressure application component. The flexible sleeve is coaxially disposed inside the cylinder. The first end piston and the second end piston are used to seal and apply axial pressure to the core sample. The cylinder is provided with a confining pressure inlet for injecting pressurized fluid into the annular space between the cylinder and the flexible sleeve to apply confining pressure. At the same time, one end of the first end piston abuts against the cylinder and the other end of the first end piston abuts against one end of the core sample. The first end piston is provided with a through first axial fluid channel, which is connected to the other end of the corresponding flow control valve. One end of the second end piston abuts against the other end of the core sample and is provided with a through second axial fluid channel, which is connected to the inlet end of the return flow mechanism. The axial pressure application component includes a pressure cylinder, and the output shaft of the pressure cylinder is connected to the second end piston. The core simulation mechanism also includes a confining pressure pump and an axial pressure pump. The outlet of the confining pressure pump is connected to the confining pressure inlet of each of the three-axis core holders, and the outlet of the axial pressure pump is connected to the gas input end of the pressure cylinder of each of the three-axis core holders.

7. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 1, characterized in that, The core simulation mechanism also includes a constant temperature chamber, and each of the triaxial core holders is installed inside the constant temperature chamber.

8. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 1, characterized in that, The return mechanism includes return components that correspond one-to-one with each of the triaxial core holders. Each return component includes a back pressure valve, a gas-liquid separator, a gas discharge pipe, a liquid discharge pipe, a third flow meter, and a gas composition detector. The input end of the back pressure valve is connected to the outlet of the corresponding triaxial core holder, and the output end of the back pressure valve is connected to the inlet of the gas-liquid separator. The gas outlet of the gas-liquid separator is connected to one end of the gas discharge pipe, and the liquid outlet of the gas-liquid separator is connected to one end of the liquid discharge pipe. The third flow meter is installed in the gas discharge pipe, and the gas composition detector is used to detect the gas composition and content in the gas discharge pipe.

9. The apparatus for simulating sand-carrying foam huff and puff in heterogeneous reservoirs according to claim 8, characterized in that, The return mechanism also includes a recovery tank, which is connected to the other end of each of the liquid discharge pipes.

10. A method for simulating the proppant-carrying foam huff and puff of heterogeneous reservoirs, characterized in that, An apparatus suitable for simulating sand-carrying foam huff and puff in heterogeneous reservoirs as described in any one of claims 1-9, comprising the following steps: a) Initial state establishment steps: Initial physical property measurements are performed on multiple core samples with different physical properties that are respectively loaded into the core simulation mechanism, and the operation of saturating simulated formation water and then displacing them with methane gas to the bound water state is performed in sequence to determine the initial methane reserves of each core sample. b) Baseline Experiment Procedure: Set the multiple flow control valves in the flow distribution module to a unified baseline state, and using a baseline fluid formula, sequentially perform the following injection-soaking-return operation through the injection mechanism and the return mechanism: b1) Injection stage: A predetermined volume of reference fluid is injected into the core simulation mechanism through the injection mechanism; b2) Soaking stage: Close all valves of the injection mechanism and the return mechanism, so that the injected fluid interacts with the core sample at the set temperature and pressure for a predetermined time; b3) Backflow stage: The backflow mechanism is activated to reduce the pressure during mining with the set production pressure difference until the backflow process meets the preset cutoff conditions. During this process, the fluid backflowed from each core sample is independently measured. c) Flow control optimization step: Keep the reference fluid formula unchanged, only adjust the opening degree of at least one flow control valve in the flow distribution module, repeat the injection, soaking and backflow operations described in step b), and record the methane content in the fluid returned from the core sample, and analyze the impact of the flow distribution module on the overall production increase effect of the system. d) Evaluation steps for the differential impact of key parameters: Keeping the optimized flow control valve setting in step c) unchanged, systematically change the foam content and / or proppant concentration of the fluid prepared by the injection mechanism, and conduct at least two sets of experiments at different parameter levels. For each set of experiments, repeat the injection, soaking, and backflow operations described in step b). By comparing and analyzing the different degrees of improvement in the recovery rate of core samples with different physical properties caused by the change of this key parameter, the differential impact of this parameter on different physical properties and lithologies can be quantitatively evaluated.

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