A micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil

Abstract

This invention provides a micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil, relating to the field of oil and gas exploration and development. It includes: a framework section, a core, an axial confining pressure boosting section, a radial confining pressure boosting section, and a pre-tightening buffer section. The core is installed within the framework section. The axial confining pressure boosting sections are installed on both sides of the framework section, increasing the axial confining pressure of the core. The radial confining pressure boosting sections are installed within the framework section, increasing the radial confining pressure of the core. The pre-tightening buffer sections are installed on both axial sides of the core. This device can fully encompass the core, ensuring balanced stress on the core and improving the accuracy of data acquisition. Furthermore, by utilizing such triaxial pressurization, it can more accurately simulate the actual confining pressure experienced by the core.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration and development, specifically to a micro-flow core holder for measuring the flow patterns of tight reservoirs and shale oil. Background Technology

[0002] Core holders are core equipment in geological exploration, oil and gas development, and rock mechanics research. Their function is to fix core samples in a laboratory environment and simulate the temperature, pressure, and fluid environment of underground strata to test the physical properties (such as permeability and porosity), mechanical properties (such as compressive strength and elastic modulus), and fluid transport laws of the core.

[0003] Currently used core holders simulate confined pressure on cores by inputting the pressurizing medium at a single point. However, this single-point input results in significant spatial and temporal differences in medium diffusion: pressure builds up earlier near the input point, while pressure is lower at farther points due to longer paths and greater losses, affecting testing accuracy. This leads to uneven stress on the core, generating additional shear stress, causing low-strength cores to fracture and high-strength cores to develop microcracks. It also exacerbates localized wear on the elastic sleeve, creating a vicious cycle that increases cost and error.

[0004] Based on this, the present invention is proposed. Summary of the Invention

[0005] According to embodiments of the present invention, a micro-flow core holder is provided for determining the flow patterns of tight reservoirs and shale oil. This addresses the problems existing in the background.

[0006] In a first aspect of the invention, a micro-flow core holder is provided for determining the flow patterns of tight reservoirs and shale oil.

[0007] The micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil includes: a skeleton section, a core, an axial confining pressure boosting section, a radial confining pressure boosting section, and a pre-tightening buffer section;

[0008] The core is installed inside the skeleton; the axial confining pressure boosting part is installed on both sides of the skeleton, and the axial confining pressure boosting part can increase the axial confining pressure of the core; the radial confining pressure boosting part is installed inside the skeleton, and the radial confining pressure boosting part can increase the radial confining pressure of the core; the pre-tightening buffer part is installed on both sides of the core along its axial direction.

[0009] Preferably, the skeleton part includes: a metal skeleton, a stainless steel end cap, a pressure cap, and screws;

[0010] The metal frame is a rectangular hollow structure, and a perfluoroether rubber composite sealing ring is installed on one side of each end; there are two stainless steel end caps, which are installed at both ends of the metal frame and connected to the outer wall of the metal frame by screws; there are two pressure caps, which are respectively set on both sides of the metal frame.

[0011] Preferably, the radial confining pressure boosting section includes: a confining pressure interface and a stainless steel well casing;

[0012] There are two confining pressure interfaces, which are symmetrically installed on the upper and lower sides of the metal frame. The stainless steel wellbore is detachably installed inside the metal frame, and the two confining pressure interfaces communicate with the inner cavity of the stainless steel wellbore. The core is located at the center of the inner cavity of the stainless steel wellbore. A perfluoroether rubber sleeve is installed inside the stainless steel wellbore, and the core is located in the perfluoroether rubber sleeve. A guide hole corresponding to the confining pressure interface is opened on the stainless steel wellbore.

[0013] Preferably, the axial confining pressure boosting unit includes: an injection pipe, a stainless steel interface, a sealing ring, an output pipe, a core cylinder metal cover, and a guide plate;

[0014] The injection and output pipes are symmetrically arranged relative to the metal frame, with their opposite ends penetrating the outer walls of both ends of the metal frame and extending into the inner cavity of the metal frame. There are two stainless steel interfaces, symmetrically installed at both ends of the metal frame, with the injection and output pipes passing through the two stainless steel interfaces respectively. There are two core tube metal covers, movably installed at both ends of the stainless steel wellbore. There are two guide plates, installed on opposite sides of the two core tube metal covers. The guide plates have guide grooves for fluid passage. There are two sealing rings, installed at the connection points of the two core tube metal covers and the guide plates, and in contact with the inner wall of the metal frame. The injection and output pipes pass through the center of the two core tube metal covers and the sealing rings respectively.

[0015] Preferably, it also includes: a heating wire;

[0016] The stainless steel wellbore is spirally equipped with heating wires, which are arranged around the outside of the rock core.

[0017] Preferably, the pre-tightening buffer includes: a spring;

[0018] The spring is installed between the metal frame and the metal cover of the core cylinder.

[0019] Preferably, a positioning buckle;

[0020] The positioning buckle is installed inside the metal frame.

[0021] In a second aspect of the invention, an experimental apparatus is provided for determining the flow patterns of tight reservoirs and shale oil.

[0022] The equipment includes: a micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil, as well as: an injection system, a measurement system, an insulation box, and an integrated data acquisition unit;

[0023] The injection system, confining pressure simulation system, and measurement system are installed inside the insulated box. The injection system is used to input the pressurized medium into the micro-flow core holder used to determine the flow characteristics of tight reservoirs and shale oil, thereby increasing the confining pressure on the core. The measurement system is used to measure data such as fluid pressure, pressure difference, mass, and temperature.

[0024] Preferably, the injection system includes a dual-piston micro-metering pump and a differential pressure sensor;

[0025] The injection pipe and the two confining pressure ports are respectively connected to a dual-piston micro-metering pump via hydraulic oil circuits; a differential pressure sensor is installed on the output pipe.

[0026] Preferably, the measurement system includes a pressure sensor, a temperature sensor, and a mass flow meter;

[0027] A pressure sensor is installed on the injection pipe, the output pipe, and the two confining pressure ports respectively; there are several temperature sensors, which are connected to the stainless steel end cap, the rock core, and the stainless steel well barrel respectively; and a mass flow meter is installed on the output pipe.

[0028] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0029] 1. The present invention provides a micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil. The core is encased in a stainless steel wellbore and a perfluoroether rubber sleeve. When confining pressure is applied, the core is fully enclosed, ensuring balanced stress on the core and protecting it from damage, thus improving the accuracy of data acquisition.

[0030] 2. A micro-flow core holder for measuring the flow patterns of tight reservoirs and shale oil in this invention can provide radial pressure to the core through a confining pressure interface, and can ensure that the core is subjected to radial confining pressure symmetrically and uniformly. Axial confining pressure to the core can be achieved through an injection pipe. By using such triaxial pressurization, the actual confining pressure on the core can be simulated more accurately.

[0031] 3. The experimental device for determining the flow law of tight reservoirs and shale oil in this invention can stably and accurately control the enhancement of core confining pressure through the injection system, accurately acquire data from various parts of the core during the experiment through the measurement system, and accurately organize and present the data using the integrated data acquisition unit.

[0032] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0033] The above and other features, advantages, and aspects of the various embodiments of the present invention will become more apparent from the accompanying drawings and the following detailed description. In the drawings, the same or similar reference numerals denote the same or similar elements, wherein:

[0034] Figure 1 A system framework diagram of an experimental apparatus for determining the flow characteristics of tight reservoirs and shale oil according to an embodiment of the present invention is shown.

[0035] Figure 2 A flowchart of an experimental setup for determining the flow characteristics of tight reservoirs and shale oil according to an embodiment of the present invention is shown.

[0036] Figure 3 A schematic diagram of a micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil according to an embodiment of the present invention is shown.

[0037] The attached figures are labeled as follows:

[0038] 1. Injection pipe; 2. Stainless steel interface; 3. Metal frame; 4. Sealing ring; 5. Confining pressure interface; 6. Core; 7. Positioning buckle; 8. Output pipe; 9. Stainless steel end cap; 10. Spring; 11. Core tube metal cover; 12. Stainless steel well shaft; 13. Heating wire; 14. Guide plate; 15. Pressure cap; 16. Screw. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0041] like Figure 3 As shown, the micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil includes: an injection pipe 1, a stainless steel interface 2, a metal skeleton 3, a sealing ring 4, a confining pressure interface 5, a core 6, a positioning buckle 7, an output pipe 8, a stainless steel end cap 9, a spring 10, a core tube metal cover 11, a stainless steel wellbore 12, a heating wire 13, a flow guide plate 14, a pressure cap 15, and a screw 16.

[0042] The metal skeleton 3 is a rectangular hollow structure with a prism or cylinder in the hollow cavity. In this embodiment, a cylinder is used as an example. The metal skeleton 3 is made of stainless steel with a 5-10μm electroless nickel plating to enhance corrosion resistance and provide rigid support for the seal, preventing the internal material from being squeezed out under high pressure. The main body dimensions are 350mm×200mm×400mm. Fixed caps are fixedly installed at both ends. The fixed caps and the main body of the metal skeleton 3 form a complete sealing system. Perfluoroether rubber composite sealing rings are installed on opposite sides of the two fixed caps. The rubber is a high-performance rubber with a fluorine content of >70%, a thickness of 1-3mm, a Shore hardness of 70-90A, and has a wide temperature adaptability of -20~300℃ and strong chemical compatibility. It can withstand acid, alkali and hydrocarbon media. It fills the sealing gap through elastic deformation to achieve the main seal. At the same time, the perfluoroether rubber composite sealing rings of the metal skeleton 3 form an axial pressure compensation device with a compensation range of ±3mm. Under the conditions of 0-100MPa confining pressure and room temperature to 150℃, the leakage is ≤0.05μL / h, which improves the sealing stability by 10 times compared with traditional rubber seals, and the replacement cycle of the seal is extended to more than 50 tests. The injection pipe 1 and the output pipe 8 are symmetrically arranged relative to the metal frame 3, with their opposite ends penetrating the outer walls of both ends of the metal frame 3 and extending into the inner cavity of the metal frame 3. Two stainless steel interfaces 2 are symmetrically installed at both ends of the metal frame 3. The injection pipe 1 and the output pipe 8 pass through the two stainless steel interfaces 2 and are fixed to each other, ensuring stable installation of the injection pipe 1 and the output pipe 8. Two stainless steel end caps 9 are installed at both ends of the metal frame 3 and connected to the outer wall of the metal frame 3 by at least two screws 16. The stainless steel end caps 9 reinforce the stainless steel interfaces 2, injection pipe 1, and output pipe 8, ensuring a stable overall structure with the metal frame 3. Two pressure caps 15 are located on both sides of the metal frame 3, reinforcing the connection between the two end faces of the metal frame 3 and the main body. Two confining pressure interfaces 5 are symmetrically installed in the middle of the upper and lower sides of the metal frame 3, with hollow channels inside the confining pressure interfaces 5. The stainless steel well casing 12 is detachably installed within the metal frame 3, and the two confining pressure ports 5 communicate with the inner cavity of the stainless steel well casing 12. The core 6 is located at the center of the inner cavity of the stainless steel well casing 12, serving as the experimental subject for simulation testing. A perfluoroether rubber sleeve, a highly elastic material, is installed inside the stainless steel well casing 12. After the core 6 is placed inside the perfluoroether rubber sleeve, it undergoes elastic deformation under the action of external confining pressure media, such as hydraulic oil, water, or mechanical force, tightly wrapping the surface of the core 6. The material's own elasticity adapts to the dimensional errors or minor irregularities in the shape of the core 6, ensuring that the core 6 can uniformly withstand the external confining pressure, thereby obtaining accurate experimental data. The stainless steel well casing 12 has guide holes corresponding to the confining pressure ports 5. These guide holes are used to pour the confining pressure media between the stainless steel well casing 12 and the perfluoroether rubber sleeve, thereby increasing the radial confining pressure received by the core 6.There are two core tube metal covers 11, which are movably installed at both ends of the stainless steel wellbore 12. There are two guide plates 14, which are installed on opposite sides of the two core tube metal covers 11. The guide plates 14 are conical, made of copper, and have a low thermal conductivity. It has strong thermal conductivity and the ability to heat evenly across the surface. With a cone angle of 30°, the guide plate 14 has a guide groove for fluid passage, ensuring that the contact area between the guide plate 14 and the end face of the core 6 is ≥90%, compressing the dead volume (excluding the volume of the guide groove) to <10μL. Combined with the output mass flow meter and differential pressure sensor, it eliminates the "edge effect" and flow deviation of low-permeability cores. Two sealing rings 4 are installed at the connection points of the two core cylinder metal covers 11 and the guide plate 14. The sealing rings 4 are perfluoroether O-rings, contacting the inner wall of the metal frame 3 to ensure the stainless steel wellbore 12 is in a relatively closed space. The injection pipe 1 and the output pipe 8 pass through the center of the two core cylinder metal covers 11 and the sealing rings 4, respectively, using the sealing effect of the two sealing rings 4 to ensure the internal space of the stainless steel wellbore 12 is relatively closed. When fluid flows through the guide grooves on the core tube metal cover 11, sealing ring 4, and guide plate 14 into the space between the two guide plates 14, it increases the axial confining pressure received by the core 6. A heating wire 13 is spirally arranged inside the stainless steel wellbore 12, surrounding the outside of the core 6. The heating wire 13 heats up when energized, thus heating the core 6. In this embodiment, the stainless steel wellbore 12, guide plate 14, core tube metal cover 11, and sealing ring 4 constitute a pressure-boosting section for increasing axial and radial confining pressure. The entire assembly of the guide plate 14, core tube metal cover 11, and sealing ring 4 can slide relative to the metal frame 3, allowing adjustment to accommodate stainless steel wellbores 12 and cores 6 of different sizes. A spring 10 is installed between the metal frame 3 and the core tube metal cover 11. The spring 10 serves as a pre-tensioning structure, using its elasticity to compensate for the deformation of the core 6. Spring 10 is made of beryllium bronze or nickel-based alloy, with a preload of 50~500N, which can be selected according to actual needs. It compensates for a stroke of ±3mm, which can prevent the influence of device assembly errors or temperature expansion. The linear stiffness is 100~500N / mm, which continuously provides sealing pressure and counteracts the relaxation of the sealing surface caused by the axial deformation of the core 6.

[0043] Furthermore, the positioning buckle 7 is installed inside the metal frame 3 and is fixedly connected to the metal frame 3 to form an integral structure. It is a ring-shaped structure used to limit the irregular rock core 6 and ensure its stable position. Its specific structure is a ring-shaped rubber structure with a circular through hole in the middle. The rock core 6 is inserted into it, so that the inner wall of the positioning buckle 7 is compressed. At the same time, the positioning buckle 7 is used to limit the irregular shape of the rock core 6.

[0044] It is worth noting that in this embodiment, the inner walls of all pipes and channels that allow fluid to pass through are nano-polished and coated with a high-temperature durable oleophobic coating to ensure that the contact angle with the fluid is >150°, reduce the adsorption of heavy oil, and avoid microcrack blockage.

[0045] Furthermore, the core 6 is suitable for regular and slightly irregular shapes with a diameter of 10-50mm and a length of 30-150mm; the working pressure range is 0~100MPa, and the medium is hydraulic oil; the working temperature range is room temperature~150℃, and the device temperature control accuracy is ±0.5℃, which can be controlled in conjunction with the heating wire 13 and the external sensor.

[0046] In addition, refer to Figure 1 The present invention also provides an experimental apparatus for determining the flow patterns of tight reservoirs and shale oil, comprising: the aforementioned micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil, and further comprising: an injection system, a confining pressure simulation system, a measurement system, and an integrated data acquisition unit. The injection system is used to input the medium required for pressurization into the confining pressure simulation system, increasing the confining pressure on the core 6. The measurement system is used to measure data such as fluid pressure, pressure difference, mass, and temperature. It is worth noting that the injection system, confining pressure simulation system, and measurement system are all located inside an insulated chamber to ensure that the temperature during the experiment remains stable. Through the integrated data acquisition unit, parameters such as pressure and temperature can be acquired synchronously, avoiding the errors caused by manual recording and subsequent data splicing required in traditional devices.

[0047] refer to Figure 2The injection system includes a dual-piston micro-metering pump and a differential pressure sensor. Injection pipe 1 and two confining pressure ports 5 are connected to the dual-piston micro-metering pump via hydraulic circuits. The dual-piston micro-metering pump allows for the input of hydraulic oil through injection pipe 1 and the two confining pressure ports 5 as needed, for loading axial and radial pressures onto the core 6. Each hydraulic circuit is independently equipped with a high-pressure plunger pump with a displacement of 1-5 L / min and a maximum pressure of 100 MPa, and is equipped with a 5-10 L accumulator to achieve independent control of hydraulic oil input for each path, avoiding mutual interference when loading the core 6 in multiple axes. The inner walls of the hydraulic circuits are nano-polished and coated with a high-temperature durable oleophobic coating to reduce viscous oil adsorption and prevent blockage of microcracks. A differential pressure sensor is installed on the output pipe 8. In this embodiment, the dual-piston micro-metering pump is an existing device driven by a high-precision stepper motor. Its specifications include a piston diameter of 0.5-5mm, a pump chamber volume of 10μL-1mL, and a dead volume of <0.5μL. The selected model is designed to detect flow rates ranging from 0.001-100μL / min for micro-flows and 0.1-100mL / min for large-flows, with an accuracy of ±0.5%FS. It is equipped with a miniature six-way valve with a dead volume of <1μL, a switching time of ≤50ms, and a zero-dead-volume conical sealing joint. The differential pressure sensor is a high-sensitivity sensor with a range of 0.1Pa-10MPa, a resolution of 0.1Pa, an accuracy of ±0.05%FS, and a response time of <10ms. This design solves the problem of traditional devices being unable to detect flow rates ≤0.1μL / min, making it particularly suitable for flow testing of ultra-low permeability cores from shale oil.

[0048] refer to Figure 2 The confining pressure simulation system mainly consists of a micro-flow core holder for measuring the flow patterns of tight reservoirs and shale oil. It is designed with an injection pipe 1 and two confining pressure interfaces 5, which together form an integrated triaxial independent hydraulic loading unit. An axial loading system consisting of a dual-piston micro-metering pump and injection pipe 1 is linked with a fine-tuning unit. The fine-tuning unit is a piezoelectric ceramic valve installed on injection pipe 1, which enables precise fluid regulation. The piezoelectric ceramic valve compensates for axial pressure fluctuations in real time, simulating horizontal ground stress. The hydraulic circuit system is an independent oil supply circuit, and high-precision proportional relief valves, proportional throttle valves, and accumulators are configured on both the axial and radial pressure boosting paths. The proportional relief valve has a control accuracy of ±0.01MPa and a sampling frequency of 100Hz; the proportional throttle valve covers a flow range of 0.1~10L / min with a response time of <20ms, ensuring a stable loading rate and a pressure control resolution of 0.01MPa; the accumulator uses a 3~5L bladder-type accumulator, which can absorb pump pulsation with a pressure fluctuation of <±0.02MPa, while compensating for minor system leakage, ensuring long-term pressure stability during loading, and a pressure holding accuracy of ±0.05MPa / 24h. The proportional relief valve, proportional throttle valve, and accumulator work together to eliminate pressure pulsation.

[0049] refer to Figure 2 The measurement system includes pressure sensors, temperature sensors, and mass flow meters. A pressure sensor is installed on each of the injection pipe 1, output pipe 8, and two confining pressure ports 5. These pressure sensors have a range of 0-100 MPa and an accuracy of ±0.01%FS, monitoring pressure distribution in real time to help control the uniform stress on the core 6. Several temperature sensors are connected to the stainless steel end caps 9, the core 6, and the stainless steel wellbore 12. Two temperature sensors measure the temperature of the two stainless steel end caps 9; two temperature sensors measure the temperature of two different points on the surface of the core 6; and two other temperature sensors measure the temperature of two points on the inner wall of the stainless steel wellbore 12, thus constructing a temperature gradient field based on the temperatures at different points. In addition, temperature sensors are installed on the hydraulic circuit path to monitor the oil temperature in real time, ensuring that the hydraulic oil temperature does not exceed 60 degrees Celsius. This helps operators to cool the oil when the temperature exceeds 60 degrees Celsius, preventing changes in hydraulic oil viscosity from affecting loading accuracy. The mass flow meter is installed on output pipe 8. It integrates a micro flow meter and a large flow meter to form a parallel dual-meter structure, achieving a flow rate of 0.001 μL / min to 100 mL / min. It has a wide range of measurement coverage and a built-in temperature compensation algorithm to collect fluid temperature in real time, correct for density changes, and ensure flow accuracy across the entire temperature range.

[0050] The integrated data acquisition unit is existing technology. It receives data and controls components via a data acquisition card, and presents the data through an external monitor. Relevant data is calculated using Darcy permeability-stress coupling analysis and non-Darcy flow coefficient. Parameter thresholds can also be preset to ensure that pressure fluctuations exceeding set values ​​automatically trigger audible and visual alarms and record anomalies. The injection system, pressure sensor, temperature sensor, and mass flow meter mentioned in this embodiment are all electrically connected to the integrated data acquisition unit, enabling real-time data transmission.

[0051] Furthermore, this invention also provides a test method for determining the flow patterns of tight reservoirs and shale oil:

[0052] Step 1, Core Pretreatment: Screen tight reservoir / shale oil core 6 and determine basic parameters such as porosity, permeability, and diameter tolerance; for irregular cores, use a pre-tightening structure composed of springs 10 and self-adaptive clamping with positioning buckles 7, and use a stainless steel wellbore 12 with a built-in perfluoroether rubber sleeve to ensure that the core is completely covered; after cleaning, drying, and simulating formation fluid saturation (pre-charge with a large flow rate using a dual-piston micro-metering pump), eliminate initial fluid interference.

[0053] Step 2, Device Commissioning: Sealing Performance Verification: Preload a 5MPa confining pressure through the confining pressure interface 5 and test the leakage rate of the sealing ring 4; select the indicated spring 10 according to the actual situation to ensure that it can compensate for the axial deformation of the core.

[0054] Step 3: Sensor Calibration: Perform standard source calibration on pressure sensors, confining pressure sensors, temperature sensors, differential pressure sensors, and mass flow meters to ensure measurement accuracy.

[0055] Step 4: Temperature Loading in the Multi-Field Environmental Simulation Stage: Heating wire 13 is activated, and temperature is controlled by a constant temperature chamber. The target temperature is 25~150℃ (i.e., simulated formation temperature), with a heating rate ≤2℃ / min to avoid thermal damage to the shale. The conical guide plate 14 is designed for heat homogenization, ensuring the internal temperature difference of the core is ≤±1℃. Hydraulic oil is injected through the confining pressure port 5, utilizing symmetrical oil supply through multiple ports. In conjunction with the overflow valve, proportional throttle valve, and energy storage regulator, a radial confining pressure of 0~100MPa is precisely applied, with a circumferential pressure difference <±0.05MPa, to simulate vertical ground stress. An axial force of 0~500kN is applied to injection pipe 1 to simulate vertical ground stress.

[0056] Step 5, Initial Saturation of Micro-Flow Test Stage: Switch all sensors to high flow rate, inject hydraulic oil at a rate of 1~10mL / min using a dual-piston micro-metering pump, monitor the inlet and outlet pressure difference using a high-sensitivity differential pressure sensor until ΔP stabilizes (change rate <0.1% / h), complete core saturation, and record the initial pressure field; Steady-State Seepage (Micro-Flow Mode): Switch all sensors to micro-flow rate, adjust the pump speed to 0.001~100μL / min, continuously inject and simultaneously collect pressure, flow rate, temperature, and axial strain data, collecting one set every 10min until the obtained flow-pressure curve stabilizes.

[0057] Step Six: Calculation of Basic Parameters in the Data Processing and Analysis Stage

[0058] Permeability: Calculated using Darcy's law, with non-Darcy flow incorporating a starting pressure gradient for fitting;

[0059] Flow correction: Using the built-in temperature compensation algorithm of the mass flow meter, the effect of fluid viscosity changes on micro-flow rate is corrected (error ≤ ±0.5%).

[0060] Multi-field coupling law analysis: Using data acquired by the integrated data acquisition unit, curves of permeability-confining pressure, flow rate-temperature, and strain-pressure are plotted to reveal the pressure-sensitive effect of tight reservoirs and the fluid-solid coupling mechanism of shale oil.

[0061] Step 7: Core testing during post-experiment processing: After disassembly, observe the integrity of the core, determine the shale breakage rate and microcrack propagation, verify the pre-tightening effect of spring 10 and the protective effect of the perfluoroether rubber sleeve on the brittle core. A breakage rate of ≤5% is considered qualified. Clean the media flow path pipeline, calibrate the sealing components at each point, and prepare for the next experiment.

[0062] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil, characterized in that, include: The skeleton section, core, axial confining pressure boosting section, radial confining pressure boosting section, and pre-tightening buffer section; The core is installed inside the skeleton; the axial confining pressure boosting part is installed on both sides of the skeleton, and the axial confining pressure boosting part can increase the axial confining pressure of the core; the radial confining pressure boosting part is installed inside the skeleton, and the radial confining pressure boosting part can increase the radial confining pressure of the core; the pre-tightening buffer part is installed on both sides of the core along its axial direction; The skeleton includes: a metal skeleton, a stainless steel end cap, a pressure cap, and screws; The metal frame is a rectangular hollow structure, with perfluoroether rubber composite sealing rings installed on opposite sides at both ends; there are two stainless steel end caps, which are installed at both ends of the metal frame and connected to the outer wall of the metal frame by screws; there are two pressure caps, which are respectively located on both sides of the metal frame. The radial confining pressure boosting section includes: a confining pressure interface and a stainless steel well casing; There are two confining pressure interfaces, which are symmetrically installed on the upper and lower sides of the metal frame. The stainless steel wellbore is detachably installed inside the metal frame, and the two confining pressure interfaces communicate with the inner cavity of the stainless steel wellbore. The core is located at the center of the inner cavity of the stainless steel wellbore. A perfluoroether rubber sleeve is installed inside the stainless steel wellbore, and the core is located in the perfluoroether rubber sleeve. A guide hole corresponding to the confining pressure interface is opened on the stainless steel wellbore. The axial confining pressure boosting unit includes: an injection pipe, a stainless steel interface, a sealing ring, an output pipe, a core cylinder metal cover, and a flow guide plate; The injection pipe and the output pipe are symmetrically arranged relative to the metal frame, with their opposite ends penetrating the outer walls of both ends of the metal frame and extending into the inner cavity of the metal frame. There are two stainless steel interfaces, symmetrically installed at both ends of the metal frame, with the injection pipe and the output pipe passing through each of the two stainless steel interfaces. There are two core tube metal covers, movably installed at both ends of the stainless steel wellbore. There are two guide plates, installed on opposite sides of the two core tube metal covers. The guide plates have guide grooves for fluid passage. There are two sealing rings, installed at the connection points of the two core tube metal covers and the guide plates, and in contact with the inner wall of the metal frame. The injection pipe and the output pipe pass through the center of the two core tube metal covers and the sealing rings.

2. The micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil according to claim 1, characterized in that, Also includes: Heating wire; The stainless steel wellbore is spirally equipped with heating wires, which are arranged around the outside of the rock core.

3. The micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil according to claim 2, characterized in that, The pre-tightening buffer includes: a spring; The spring is installed between the metal frame and the metal cover of the core cylinder.

4. The micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil according to claim 3, characterized in that, It also includes positioning clips; The positioning buckle is installed inside the metal frame.

5. An experimental apparatus for determining the flow patterns of tight reservoirs and shale oil, comprising: The micro-flow core holder for determining the flow patterns of tight reservoirs and shale oil as described in claim 4 is characterized in that it further comprises: an injection system, a confining pressure simulation system, a measurement system, an insulation box, and an integrated data acquisition unit; The injection system, confining pressure simulation system, and measurement system are installed inside the insulation box. The injection system is used to input the medium required for pressurization into the confining pressure simulation system of the micro-flow core holder used to determine the flow law of tight reservoirs and shale oil, thereby increasing the confining pressure on the core. The measurement system is used to measure fluid pressure, pressure difference, mass, and temperature data.

6. The experimental apparatus for determining the flow patterns of tight reservoirs and shale oil according to claim 5, characterized in that, The injection system includes a dual-piston micro-metering pump and a differential pressure sensor; The injection pipe and the two confining pressure ports are respectively connected to a dual-piston micro-metering pump via hydraulic oil circuits; a differential pressure sensor is installed on the output pipe.

7. The experimental apparatus for determining the flow patterns of tight reservoirs and shale oil according to claim 6, characterized in that, The measurement system includes a pressure sensor, a temperature sensor, and a mass flow meter; A pressure sensor is installed on the injection pipe, the output pipe, and the two confining pressure ports respectively; there are several temperature sensors, which are connected to the stainless steel end cap, the rock core, and the stainless steel well barrel respectively; and a mass flow meter is installed on the output pipe.

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