Rock permeability testing system in high-temperature and high-pressure environment and use method thereof

Abstract

The invention discloses a rock permeability testing system in a high-temperature and high-pressure environment and a using method thereof, and belongs to the technical field of geothermal development or coal in-situ gasification mining. The test system is composed of a stress loading system, a test kettle assembly and a magnetic particle imaging system. When in use, the stress loading system and the test kettle assembly provide conditions such as high temperature, high pressure, seepage fluid and the like for a test piece; and detecting the spatial distribution state of the nano magnetic induction particles added in the seepage fluid through a magnetic particle imaging system to observe the pore and crack distribution characteristics in the test piece or detecting the nano magnetic induction particles added in the pollutant solution to observe the pollutant migration condition. The test system is scientific in design, simple in structure and easy to operate and maintain, can monitor pore fracture distribution and pollutant migration conditions in the test piece in real time under high-temperature and high-pressure conditions, provides accurate dynamic observation data, and provides important technical support for reservoir assessment and optimization in a complex environment.

Description

Technical Field

[0001] The invention belongs to the technical field of geothermal development or in-situ coal gasification mining, and particularly relates to a rock permeability testing system in a high-temperature and high-pressure environment and a using method thereof. Background Art

[0002] With the rapid development of China's economy, the energy demand continues to increase. However, the output of conventional energy in China has approached its peak, so it is urgent to accelerate the development of supplementary energy for conventional energy. China has rich organic rock resources (such as medium-low maturity rocks like coal, shale oil and gas, etc.) and relatively rich geothermal resources. The development and utilization of these resources are of great significance for meeting the energy demand. Especially in the development of organic rocks with large burial depths, in-situ heat injection mining is considered to be one of the most promising utilization methods; for geothermal resources, cold water can be injected from the ground into the geothermal reservoir, and by using the heat exchange process between the cold water and the high-temperature rock mass, high-temperature water or steam can be produced, thereby realizing effective development and utilization.

[0003] The development and utilization of the above deep-earth resources require a full study and understanding of the high-temperature and high-pressure rock seepage mechanical properties of the resource reservoir and its confining pressure. Especially the pore and fracture distribution of the rock, as an important parameter of the rock and underground reservoir characteristics, directly affects the storage and fluidity of the resources. Therefore, accurately mastering the distribution of pores and fractures inside the rock is crucial for improving the resource recovery efficiency and ensuring mining safety.

[0004] At present, rock permeability testing mainly relies on conventional experimental devices, but in a high-temperature and high-pressure environment, existing equipment generally has some limitations. Especially in permeability testing or pollutant migration tests, it is difficult to simultaneously monitor the pore and fracture distribution of the rock under high-temperature and high-pressure conditions in real time. Traditional permeability testing methods cannot accurately observe the dynamic distribution of pores and fractures inside the rock, nor can they track the migration process of pollutants in the rock in real time.

[0005] Therefore, there is an urgent need for a new type of experimental device that can conduct rock permeability testing or pollutant migration tests under high-temperature and high-pressure conditions and effectively monitor the distribution of pores and fractures inside the rock and the migration of pollutants. Summary of the Invention

[0006] The purpose of the invention is to solve the deficiencies of the existing real-time high-temperature and high-pressure permeability testing technology in the above-mentioned prior art, and provide a rock permeability testing system in a high-temperature and high-pressure environment. The testing system has a simple structure and reliable performance, and can conduct permeability testing or pollutant migration tests under high-temperature and high-pressure conditions.

[0007] The invention is realized through the following technical solutions: A rock permeability testing system for high-temperature and high-pressure environments, comprising a stress loading system, a test kettle assembly, a specimen, and a magnetic particle imaging system.

[0008] The stress loading system includes a hydraulic pump, a confining pressure constant current and constant pressure pump, a ring cylinder cooling device, a ring cylinder, a shaft cylinder, an experimental operation table, and a servo hydraulic control frame; the hydraulic pump is connected to the ring cylinder and the shaft cylinder through pipelines to provide power for them; the confining pressure constant current and constant pressure pump is connected to the test kettle assembly through pipelines to apply a constant confining pressure to the specimen; the ring cylinder cooling device is coated on the outer surface of the ring cylinder, and a water flow channel is provided inside the ring cylinder cooling device to prevent the ring cylinder from overheating and being damaged by injecting low-temperature circulating water; the experimental operation table is arranged on the servo hydraulic control frame.

[0009] The test kettle assembly includes a kettle body. A through cavity penetrating the upper and lower parts of the kettle body is opened along the axial direction of the kettle body. The outside of the kettle body is coated with a heating and insulation jacket. Temperature and pressure monitoring holes and confining pressure injection ports that penetrate the heating and insulation jacket and the kettle body and communicate with the through cavity are opened on both sides of the whole heating and insulation jacket and the kettle body. The temperature and pressure monitoring holes are connected to temperature and pressure sensors, and the confining pressure injection ports are connected to the confining pressure constant current and constant pressure pump through pipelines. A kettle base is installed at the bottom of the kettle body. A sample table extending upward is fixed at the center position of the top of the kettle base. The sample table extends into the bottom cavity opening of the through cavity. A seepage fluid injection port penetrating the upper and lower parts of the kettle base and the sample table is opened along the axial direction of the whole kettle base and the sample table for applying pore pressure to the specimen during permeability testing. A ring-shaped pressure head is installed at the top of the kettle body. The lower part of the ring-shaped pressure head extends into the top cavity opening of the through cavity. A through hole penetrating the upper and lower parts of the ring-shaped pressure head is opened along the axial direction of the ring-shaped pressure head; a ring-shaped pressure transfer cushion block is provided at the top of the ring-shaped pressure head. A through hole penetrating the upper and lower parts of the ring-shaped pressure transfer cushion block is opened along the axial direction of the ring-shaped pressure transfer cushion block; a shaft pressure head is inserted into the through holes of the ring-shaped pressure head and the ring-shaped pressure transfer cushion block. The lower part of the shaft pressure head extends into the through cavity. A seepage fluid outlet penetrating the upper and lower parts of the shaft pressure head is opened along the axial direction of the shaft pressure head. The top end of the shaft pressure head is connected to a high-pressure pipeline for collecting permeated fluid; a shaft pressure transfer cushion block is provided at the top of the shaft pressure head. The shaft pressure transfer cushion block is located in the through hole of the ring-shaped pressure transfer cushion block. A groove for the extension of the high-pressure pipeline is reserved at the position where the bottom of the shaft pressure transfer cushion block contacts the shaft pressure head. A transverse through hole connecting low-temperature circulating water is provided in the upper part of the shaft pressure transfer cushion block.

[0010] The test piece is arranged in the through cavity of the autoclave body and clamped between the top of the sample stage and the bottom end of the axial pressure head. The outside of the test piece is covered with a confining pressure seal sleeve. The bottom of the confining pressure seal sleeve is connected to the sample stage in a wrapping manner, and the top of the confining pressure seal sleeve is connected to the axial pressure head in a wrapping manner. The test piece is completely covered at the middle position inside the confining pressure seal sleeve. A porous tube is sleeved outside the confining pressure seal sleeve, and fine holes for the flow of the confining pressure liquid are provided on the side surface of the porous tube. An upper graphite seal ring and a lower graphite seal ring are arranged in the through cavity of the autoclave body. The upper graphite seal ring is sleeved on the axial pressure head, and the lower graphite seal ring is sleeved on the sample stage. The porous tube is clamped between the upper graphite seal ring and the lower graphite seal ring.

[0011] The magnetic particle imaging system includes a radio frequency coil for wrapping the test piece and a magnetic particle imaging device for observing the distribution of nano magnetic induction particles inside the test piece. The radio frequency coil is covered outside the porous tube, and the end of the radio frequency coil extends out from the seepage fluid outlet on the axial pressure head and is connected to the magnetic particle imaging device.

[0012] As a preferred technical solution, a slotted opening communicating with its through hole is provided on the side wall of the annular pressure transmission cushion block, and the high-pressure pipeline and the low-temperature circulating water pipe are led out from the slotted opening.

[0013] As a preferred technical solution, bolt holes corresponding to each other in position are provided on the outer side of the bottom of the autoclave body and on the outer side of the autoclave base, and the autoclave body and the autoclave base are fixedly connected by bolts.

[0014] As a preferred technical solution, the axial pressure transmission cushion block, the axial pressure head, the test piece and the sample stage have the same diameter.

[0015] As a preferred technical solution, the material of the confining pressure seal sleeve is a metal with a high melting point and excellent ductility, and the height of the confining pressure seal sleeve is at least 3 times the height of the test piece.

[0016] As a preferred technical solution, the porous tube is made of a high-strength quartz tube or ceramic tube. The inner diameter of the porous tube is larger than the outer diameter of the confining pressure seal sleeve, its outer diameter is smaller than the diameter of the through cavity, and the height of the porous tube is at least 1.5 times the height of the test piece, but does not exceed 0.6 times the height of the confining pressure seal sleeve.

[0017] As a preferred technical solution, high-power resistance wires and heat-insulating cotton are provided inside the heating and heat-insulating sleeve, and the test piece can be heated and insulated at a maximum temperature of 550 °C.

[0018] As a preferred technical solution, the radio frequency coil is used to generate a detection magnetic field change, and the magnetic particle imaging device is used to detect and image the nano magnetic induction particles. The distribution of the nano magnetic induction particles is used to reflect the pore and crack distribution inside the test piece, or the nano magnetic induction particles added in advance as a tracer in the pollutant solution are detected by magnetic resonance imaging to reflect the internal pollutant migration situation.

[0019] Furthermore, the present invention also provides a method for using the above rock permeability testing system in a high-temperature and high-pressure environment, comprising the following steps: S1: Place the cut specimen on the sample stage, put the confining pressure sealing sleeve on the specimen and the sample stage, and insert the axial pressure head from the upper part into the confining pressure sealing sleeve and press against the upper surface of the specimen.

[0020] S2: Fit the kettle body onto the kettle base from top to bottom, place the specimen in the through cavity of the kettle body, and fixedly connect the kettle body and the kettle base through bolt holes and bolts.

[0021] S3: Place the lower graphite sealing ring at the gap between the through cavity of the kettle body and the sample stage, with the filling height of the lower graphite sealing ring being flush with the bottom of the specimen. Then, fit the porous pipe outside the confining pressure sealing sleeve and wrap it with a radio frequency coil; place the upper graphite sealing ring at the gap between the through cavity of the kettle body and the axial pressure head, with the filling height of the upper graphite sealing ring being higher than the upper end of the confining pressure sealing sleeve; fit the annular pressure head onto the axial pressure head and install and connect it to the kettle body; fit the heating and insulation sleeve onto the kettle body.

[0022] S4: Place the assembled test kettle assembly on the experimental operation table, extend the radio frequency coil outwards from the seepage fluid outlet and connect it to the magnetic particle imaging device; install the annular pressure transfer pad and the axial pressure transfer pad, connect the confining pressure constant current and constant pressure pump to the confining pressure injection port, connect the ring cylinder cooling device and the axial pressure transfer pad to the low-temperature circulating water respectively, and connect the temperature and pressure sensor to the temperature and pressure monitoring hole.

[0023] S5: Fix the specimen by applying a pressure of 0.1 MPa to the specimen through the axial cylinder, apply a downward pressure to the upper graphite sealing ring and the lower graphite sealing ring through the ring cylinder, so that the upper graphite sealing ring and the lower graphite sealing ring extrude the confining pressure sealing sleeve under the action of pressure and form a sealed space at the position of the porous pipe.

[0024] S6: Apply axial pressure and confining pressure to the specimen through the axial cylinder and the ring cylinder to the specified pressure, turn on the heating and insulation sleeve, heat the specimen to the specified temperature, inject the seepage fluid that has been previously added with nano magnetic induction particles and reaches the specified pressure from the seepage fluid injection port after maintaining the specified duration, collect and record the flow rate of the seepage fluid from the high-pressure pipeline connected to the seepage fluid outlet, calculate and obtain the permeability of the tested specimen under real-time high temperature and high pressure, and simultaneously observe the pore and fracture distribution inside the specimen through the magnetic particle imaging device.

[0025] Furthermore, when used to detect pollutant migration, the seepage fluid in step S6 is replaced with a pollutant solution pre-added with nano magnetic particles, and a magnetic particle imaging device is used to observe the pollutant migration inside the specimen. At the same time, by virtue of the magnetic material characteristics of the nano magnetic particles, directional guidance or tracking in a specific direction or position is carried out through an external magnetic field, and the nano magnetic particles can be controlled to be repeatedly tested in a specific area.

[0026] A rock permeability test system and its usage method under high temperature and high pressure environments provided by the present invention belong to the category of research on efficient and clean exploitation of resources and energy related to high temperature and high pressure rock seepage mechanics such as underground in-situ coal gasification mining, in-situ heating exploitation of medium-low maturity shale oil and gas, or dry hot rock exploitation, and can perform permeability tests or pollutant migration experiments under high temperature and high pressure conditions. The device of the present invention observes the distribution state of nano magnetic particles to monitor in real time the distribution of pores and fractures inside the rock sample and the migration process of pollutants. Through the action of an external magnetic field, the nano magnetic particles can also be directionally guided or tracked, enabling these nano magnetic particles to be repeatedly tested in a specific area, which is very beneficial for tracking the diffusion, accumulation, and transfer paths of pollutants, thereby providing more accurate and dynamic experimental data for permeability tests and pollutant migration research.

[0027] Compared with the prior art, the technical features of the present invention include the following points: 1) The present invention conducts high temperature and high pressure permeability tests by transmitting pressure through a porous tube, focuses on permeability tests in geothermal development and underground in-situ coal gasification mining, emphasizes simplicity of structure and reliability of performance, and is applicable to high temperature and high pressure permeability tests of various rock samples, with a wide range of applications.

[0028] 2) In the present invention, the ring cylinder, shaft cylinder, hydraulic pump, etc. constitute a stress loading system, and the confining pressure seal sleeve, upper graphite seal ring, lower graphite seal ring, etc. constitute a sealing system. Through the stress loading system and the sealing system, permeability tests under high temperature and high pressure conditions are achieved. The structural design has stronger pressure transmission and sealing performance, and is very suitable for the geothermal and coal mining fields.

[0029] 3) The rock permeability test simulated by the present invention is for high-temperature and high-pressure environments, mainly focusing on the permeability performance of rocks and fluid interactions under extreme conditions; magnetic particle imaging is mainly used to observe the distribution of nano-magnetic-sensing particles in the fluid of the specimen, and then infer the characteristics of pore fractures inside the rock. Compared with existing PIV particles, nano-magnetic-sensing particles have significant advantages in real-time detection of pore fracture distribution and pollutant migration. First, the size of nano-magnetic-sensing particles is relatively small (usually at the nano level), which can enter the tiny pores and fractures in the rock, thus providing higher-resolution fracture distribution images. They can accurately track the migration paths of fluids and pollutants in tiny fractures, enabling nano-magnetic-sensing particles to provide more detailed and accurate flow information than PIV particles. Second, nano-magnetic-sensing particles have excellent stability, can remain stable under extreme environments such as high temperature and high pressure, and their interaction with fluids is not easily disturbed by the external environment. In addition, nano-magnetic-sensing particles are monitored through magnetic induction imaging technology, and real-time flow data of fluids in tiny fractures can be obtained. PIV particles mainly rely on larger-sized particles that cannot enter tiny fractures, resulting in limitations in monitoring fine fractures. Therefore, nano-magnetic-sensing particles show stronger advantages in occasions with complex pore structures and high requirements for fluid flow accuracy, and in the observation of pollutant migration, which involves high-temperature and high-pressure rock permeability tests, especially applied to geothermal development or in-situ coal gasification mining, mainly to solve the problem of testing rock permeability under high-temperature and high-pressure conditions.

[0030] The beneficial effects of the present invention mainly include the following points: 1) The test system of the present invention can perform real-time permeability tests on various rock specimens under normal temperature to 550°C high-temperature conditions.

[0031] 2) The test system of the present invention can be used to study the migration characteristics of pollutants in soil or rock-like porous media under different temperature and pressure conditions.

[0032] 3) The test system of the present invention is scientifically designed, has a simple structure, and is easy to operate and maintain.

[0033] 4) By combining nano-magnetic-sensing particles with magnetic particle imaging equipment, the test system of the present invention can monitor the pore fracture distribution and pollutant migration inside the specimen in real time under high-temperature and high-pressure conditions, provide accurate dynamic observation data, and provide important technical support for reservoir evaluation and optimization in complex environments. Description of the Drawings

[0034] The drawings here are used to provide further illustration of the present invention, form a part of this application, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention, and do not constitute an improper limitation to the present invention.

[0035] Figure 1 This is a schematic structural diagram of the stress loading system in the present invention.

[0036] Figure 2 This is a schematic structural diagram of the test autoclave assembly in the present invention.

[0037] Figure 3 This is an assembly schematic diagram of the test piece and the confining pressure sealing sleeve inside the test autoclave assembly.

[0038] Figure 4 This is an assembly schematic diagram of the porous tube and the radio frequency coil.

[0039] In the figure: 1 - hydraulic pump, 2 - confining pressure constant current and constant pressure pump, 3 - ring cylinder cooling device, 4 - ring cylinder, 5 - shaft cylinder, 6 - experimental operation table, 7 - servo hydraulic control frame, 8 - annular pressure transmitting pad, 9 - axial pressure transmitting pad, 10 - axial pressure head, 11 - annular pressure head, 12 - experimental autoclave body, 13 - upper graphite sealing ring, 14 - heating and heat preservation sleeve, 15 - porous tube, 16 - temperature and pressure monitoring hole, 17 - bolt hole, 18 - autoclave base, 19 - seepage fluid injection port, 20 - confining pressure injection port, 21 - seepage fluid outlet, 22 - lower graphite sealing ring, 23 - test piece, 24 - confining pressure sealing sleeve, 25 - sample stage, 26 - radio frequency coil, 27 - slot, 28 - fine hole. Detailed implementation manners

[0040] In order to enable those skilled in the art to better understand the present invention, the present invention will be further clearly and completely described below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, without conflict, the implementation manners and the features in the embodiments in the present application can be combined with each other. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] In the description of this embodiment, it should be understood that the orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", etc. is the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this embodiment and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention. Embodiment 1

[0042] As Figures 1 to 4 shown, this embodiment provides a rock permeability testing system in a high temperature and high pressure environment, including a stress loading system, a test autoclave assembly, a test piece 23 and a magnetic particle imaging system.

[0043] The stress loading system includes a hydraulic pump 1, a confining pressure constant current and constant pressure pump 2, a ring cylinder cooling device 3, a ring cylinder 4, a shaft cylinder 5, an experimental operation table 6, and a servo hydraulic control frame 7; the hydraulic pump 1 is connected to the ring cylinder 4 and the shaft cylinder 5 through pipelines. The ring cylinder 4 and the shaft cylinder 5 are two concentric shaft cylinders, and the two-way hydraulic pump 1 provides power for them respectively; the confining pressure constant current and constant pressure pump 2 is connected to the test kettle assembly through a pipeline to apply a constant confining pressure to the specimen 23; the ring cylinder cooling device 3 is coated on the outer surface of the ring cylinder 4. There is a water flow channel inside the ring cylinder cooling device 3, and low-temperature circulating water is injected to prevent the ring cylinder 4 from overheating and being damaged; the experimental operation table 6 is arranged on the servo hydraulic control frame 7.

[0044] The test kettle assembly includes a kettle body 12. A through cavity penetrating the upper and lower parts of the kettle body 12 along its axis direction is provided on the kettle body 12. The outside of the kettle body 12 is coated with a heating and heat preservation sleeve 14. High-power resistance wires and heat preservation cotton are arranged inside the heating and heat preservation sleeve 14, which can heat and keep warm the specimen 23 at a maximum temperature of 550 °C ± 5 °C; temperature and pressure monitoring holes 16 and confining pressure injection ports 20 that penetrate the heating and heat preservation sleeve 14 and the kettle body 12 and communicate with the through cavity are provided on both sides of the whole heating and heat preservation sleeve 14 and the kettle body 12. The temperature and pressure monitoring holes 16 are connected to temperature and pressure sensors, and the confining pressure injection ports 20 are connected to the confining pressure constant current and constant pressure pump 2 through pipelines. A kettle base 18 is installed at the bottom of the kettle body 12. Specifically, bolt holes 17 corresponding in position are provided on the outer side of the bottom of the kettle body 12 and the outer side of the kettle base 18, and the kettle body 12 and the kettle base 18 are fixedly connected by bolts inserted into the bolt holes 17; a sample table 25 extending upward is fixed at the central position of the top of the kettle base 18. The sample table 25 extends into the bottom cavity opening of the through cavity. A seepage fluid injection port 19 penetrating the upper and lower parts of the kettle base 18 and the sample table 25 along their axis direction is provided, which is used to apply pore pressure to the specimen 23 during permeability testing. A ring-shaped pressure head 11 is installed at the top of the kettle body 12. The lower part of the ring-shaped pressure head 11 extends into the top cavity opening of the through cavity. A through hole penetrating the upper and lower parts of the ring-shaped pressure head 11 along its axis direction is provided; a ring-shaped pressure transfer cushion block 8 is provided at the top of the ring-shaped pressure head 11. A through hole penetrating the upper and lower parts of the ring-shaped pressure transfer cushion block 8 along its axis direction is provided; a shaft pressure head 10 is inserted into the through holes of the ring-shaped pressure head 11 and the ring-shaped pressure transfer cushion block 8. The lower part of the shaft pressure head 10 extends into the through cavity. A seepage fluid outlet 21 penetrating the upper and lower parts of the shaft pressure head 10 along its axis direction is provided. The top end of the shaft pressure head 10 is connected to a high-pressure pipeline for collecting seepage fluid; a shaft pressure transfer cushion block 9 is provided at the top of the shaft pressure head 10. The shaft pressure transfer cushion block 9 is located in the through hole of the ring-shaped pressure transfer cushion block 8. A groove for the extension of the high-pressure pipeline is reserved at the position where the bottom of the shaft pressure transfer cushion block 9 contacts the shaft pressure head 10. A transverse through hole connecting low-temperature circulating water is provided in the upper part of the shaft pressure transfer cushion block 9; a slot 27 communicating with its through hole is provided on the side wall of the ring-shaped pressure transfer cushion block 8, and the high-pressure pipeline and the low-temperature circulating water pipe are led out from the slot 27.

[0045] The test piece 23 is arranged in the through cavity of the kettle body 12 and clamped between the top end of the sample stage 25 and the bottom end of the axial pressure head 10. The test piece 23, the sample stage 25, the axial pressure head 10 and the axial pressure transfer cushion block 9 have the same diameter; the outside of the test piece 23 is coated with a confining pressure sealing sleeve 24. The bottom of the confining pressure sealing sleeve 24 is wrapped and connected with the sample stage 25, and the top of the confining pressure sealing sleeve 24 is wrapped and connected with the axial pressure head 10. The test piece 23 is completely coated in the middle position inside the confining pressure sealing sleeve 24; the material of the confining pressure sealing sleeve 24 is a metal with a high melting point and excellent ductility. The height of the confining pressure sealing sleeve 24 is at least 3 times the height of the test piece 23, and the wall thickness of the confining pressure sealing sleeve 24 is as thin as possible on the premise of ensuring ductility and strength; a porous tube 15 is sleeved outside the confining pressure sealing sleeve 24, and fine holes 28 for the flow of the confining pressure liquid are arranged on the side surface of the porous tube 15; the porous tube 15 is made of a high-strength quartz tube or ceramic tube to avoid the influence of the porous tube 15 on observing the nano magnetic induction particles inside the test piece 23; the inner diameter of the porous tube 15 is larger than the outer diameter of the confining pressure sealing sleeve 24, and its outer diameter is smaller than the diameter of the through cavity. The height of the porous tube 15 is at least 1.5 times the height of the test piece 23, but does not exceed 0.6 times the height of the confining pressure sealing sleeve 24; an upper graphite sealing ring 13 and a lower graphite sealing ring 22 are arranged in the through cavity of the kettle body 12. The upper graphite sealing ring 13 is sleeved on the axial pressure head 10, and the lower graphite sealing ring 22 is sleeved on the sample stage 25. The porous tube 15 is clamped between the upper graphite sealing ring 13 and the lower graphite sealing ring 22. The fine holes 28 on the side of the porous tube 15 are convenient for the confining pressure liquid to flow to the periphery of the confining pressure sealing sleeve 24, so as to apply confining pressure to the test piece 23. At the same time, the porous tube 15 plays a role in transmitting the vertical pressure of the annular pressure head 11, and at the same time extrudes the upper graphite sealing ring 13 and the lower graphite sealing ring 22 to ensure the sealing performance at both ends of the confining pressure sealing sleeve 24. The axial cylinder 5 applies axial stress to the test piece 23 through the axial pressure transfer cushion block 9 and the axial pressure head 10, and the annular cylinder 4 applies downward pressure to the upper graphite sealing ring 13, the lower graphite sealing ring 22 and the porous tube 15 through the annular pressure transfer cushion block 8 and the annular pressure head 11. After the upper graphite sealing ring 13 receives the axial pressure from the annular pressure head 11, on the one hand, it will undergo lateral deformation, squeeze the upper end of the confining pressure sealing sleeve 24 and make it close to the axial pressure head 10. On the other hand, the upper graphite sealing ring 13 will transmit the axial pressure from the annular pressure head 11 to the lower graphite sealing ring 22 through the porous tube 15. The lower graphite sealing ring 22 is compressed and undergoes lateral deformation, squeezes the lower end of the confining pressure sealing sleeve 24 and makes it close to the sample stage 25. The upper and lower ends of the confining pressure sealing sleeve 24 are sealed against the test piece 23 under the extrusion of the upper graphite sealing ring 13 and the lower graphite sealing ring 22.After the upper graphite sealing ring 13 and the lower graphite sealing ring 22 are axially pressed by the annular indenter 11, they are extruded and deformed to seal the upper and lower ends of the porous tube 15, so that a sealed space is formed at the position where the porous tube 15 is located. A pressure liquid with a specified pressure is filled into this sealed space through the confining pressure injection port 20. The pressure liquid enters the outer surface of the confining pressure sealing sleeve 24 through the fine holes 28 on the side of the porous tube 15, and the confining pressure is applied to the specimen 23 through the confining pressure sealing sleeve 24.

[0046] The magnetic particle imaging system includes an RF coil 26 for wrapping the test piece 23 and a magnetic particle imaging device for observing the distribution of nano-magnetic-sensing particles inside the test piece 23. The RF coil 26 is coated outside the porous tube 15, and the end of the RF coil 26 extends out from the seepage fluid outlet 21 on the axial press head 10 and is connected to the magnetic particle imaging device. The RF coil 26 is used to generate a detection magnetic field change, and the magnetic particle imaging device is used to detect and image nano-magnetic-sensing particles, which has high sensitivity and high resolution, and is particularly suitable for the tracking and quantitative analysis of nano-particles in vivo. By generating a strong magnetic field to excite the nano-magnetic-sensing particles and then processing the response signal generated by the nano-magnetic-sensing particles under the action of an alternating magnetic field, the distribution state of the nano-magnetic-sensing particles added in advance to the seepage fluid is detected to reflect the pore and fracture distribution inside the test piece 23, or the nano-magnetic-sensing particles added in advance to the pollutant solution as a tracer are detected by magnetic resonance imaging to reflect the internal pollutant migration situation. The nano-magnetic-sensing particles with a nano-scale particle size have a very small size, can enter the tiny voids in the rock pores or fractures and can migrate in even tinier fractures, and interact precisely with the fluid; at the same time, the particles can more easily remain stable under high-temperature and high-pressure environments. In rocks, especially in extreme environments such as geothermal or coal gasification, the nano-magnetic-sensing particles are not easily damaged by the fluid environment, can exist stably for a long time and migrate with the fluid, thus accurately reflecting the propagation path of pollutants in the rock; these particles can be tracked in real time through magnetic induction imaging technology, and can display the migration of pollutants in the fluid in real time, especially in terms of the diffusion, distribution of pollutants in the fluid and the interaction with rock pores, providing a more intuitive and accurate analysis; due to the magnetic properties of the nano-magnetic-sensing particles, the position change of the nano-magnetic-sensing particles can be detected in real time through magnetic field imaging, and the propagation of pollutants or fluids can be shown in real-time dynamic monitoring; due to their very small particle size, the nano-magnetic-sensing particles have almost no interference or influence on the fluid flow. They can be embedded into the fluid silently without affecting the flow law of the fluid or the permeability test of the rock mass; the nano-magnetic-sensing particles can not only help monitor the macroscopic flow path of the fluid, but also penetrate into the microscopic fractures of the rock, and track the diffusion process of pollutants in the tiny pores through magnetic field imaging technology. This makes the nano-magnetic-sensing particles have unique advantages in monitoring the microscopic migration of pollutants, especially in complex fracture networks, and it can reflect the dynamic changes of the fluid at the microscopic scale. Example 2

[0047] This embodiment provides a method of using the test system of Example 1 to perform a real-time high-temperature and high-pressure permeability test on cylindrical shale oil, which specifically includes the following steps: S1: Place the cut shale oil specimen 23 on the sample stage 25, put the confining pressure seal sleeve 24 over the specimen 23 and the sample stage 25, and insert the axial pressure head 10 from above into the confining pressure seal sleeve 24 and press against the upper surface of the specimen 23.

[0048] S2: Fit the kettle body 12 over the kettle base 18 from top to bottom, place the specimen 23 in the through cavity of the kettle body 12, and fixedly connect the kettle body 12 and the kettle base 18 through the bolt holes 17 and bolts.

[0049] S3: Place the lower graphite sealing ring 22 at the gap between the through cavity of the kettle body 12 and the sample stage 25, with the filling height of the lower graphite sealing ring 22 being flush with the bottom of the specimen 23. Then, fit the porous tube 15 outside the confining pressure seal sleeve 24 and wrap it with the radio frequency coil 26; place the upper graphite sealing ring 13 in the through cavity of the kettle body 12 at the gap with the axial pressure head 10, with the filling height of the upper graphite sealing ring 13 being higher than the upper end of the confining pressure seal sleeve 24; fit the annular pressure head 11 over the axial pressure head 10 and install and connect it to the kettle body 12; fit the heating and insulation sleeve 14 outside the kettle body 12.

[0050] S4: Place the assembled components on the experimental operation table 6, extend the radio frequency coil 26 outwards from the seepage fluid outlet 21 and connect it to the magnetic particle imaging device; install the annular pressure transfer cushion block 8 and the axial pressure transfer cushion block 9, connect the confining pressure constant current and constant pressure pump 2 to the confining pressure injection port 20, connect the ring cylinder cooling device 3 and the axial pressure transfer cushion block 9 to the low-temperature circulating water respectively, and connect the temperature and pressure sensor to the temperature and pressure monitoring hole 16.

[0051] S5: Apply a pressure of 0.1 MPa to the specimen 23 through the axial cylinder 5 to fix the specimen 23, apply a downward pressure to the upper graphite sealing ring 13 and the lower graphite sealing ring 22 through the ring cylinder 4, so that the upper graphite sealing ring 13 and the lower graphite sealing ring 22 squeeze the confining pressure seal sleeve 24 under the action of pressure and form a sealed space at the position of the porous tube 15.

[0052] S6: Apply axial pressure and confining pressure to the specimen 23 through the axial cylinder 5 and the ring cylinder 4 to the specified pressure, turn on the heating and insulation sleeve 14, heat the specimen 23 to the specified temperature, after keeping warm for the specified duration, inject the seepage fluid that has been previously added with nano magnetic induction particles and reaches the specified pressure from the seepage fluid injection port 19, collect and record the flow rate of the seepage fluid from the high-pressure pipeline connected to the seepage fluid outlet 21, calculate and obtain the permeability of the tested specimen 23 under real-time high temperature and high pressure, and simultaneously observe the pore and fracture distribution inside the specimen 23 through the magnetic particle imaging device. Example 3

[0053] This embodiment provides a method for using the test system of Embodiment 1 to study the migration characteristics of pollutants in the roof and floor of coal seams during in-situ underground coal gasification, which specifically includes the following steps: S1: Place the cut roof and floor specimens 23 of the coal seam on the sample stage 25, put the confining pressure seal sleeve 24 on the specimens 23 and the sample stage 25, and insert the axial pressure head 10 from the upper part into the confining pressure seal sleeve 24 to press against the upper surface of the specimens 23.

[0054] S2: Set the kettle body 12 on the kettle base 18 from top to bottom, place the specimens 23 in the through cavity of the kettle body 12, and fixedly connect the kettle body 12 and the kettle base 18 through the bolt holes 17 and bolts.

[0055] S3: Place the lower graphite sealing ring 22 at the gap between the through cavity of the kettle body 12 and the sample stage 25. The filling height of the lower graphite sealing ring 22 is flush with the bottom of the specimens 23. Then, put the porous tube 15 outside the confining pressure seal sleeve 24 and wrap it with the radio frequency coil 26; place the upper graphite sealing ring 13 at the gap between the through cavity of the kettle body 12 and the axial pressure head 10. The filling height of the upper graphite sealing ring 13 is higher than the upper end of the confining pressure seal sleeve 24; set the annular pressure head 11 on the axial pressure head 10 and install and connect it with the kettle body 12; set the heating and insulation sleeve 14 outside the kettle body 12.

[0056] S4: Place the assembled components on the experimental operation table 6, extend the radio frequency coil 26 outwards from the seepage fluid outlet 21 and connect it with the magnetic particle imaging device; install the annular pressure transfer spacer 8 and the axial pressure transfer spacer 9, connect the confining pressure constant current and constant pressure pump 2 with the confining pressure injection port 20, connect the annular cylinder cooling device 3 and the axial pressure transfer spacer 9 with the low-temperature circulating water respectively, and connect the temperature and pressure sensor with the temperature and pressure monitoring hole 16.

[0057] S5: Apply a pressure of 0.1 MPa to the specimens 23 through the axial cylinder 5 to fix the specimens 23, apply a downward pressure to the upper graphite sealing ring 13 and the lower graphite sealing ring 22 through the annular cylinder 4, so that the upper graphite sealing ring 13 and the lower graphite sealing ring 22 squeeze the confining pressure seal sleeve 24 under the action of pressure and form a sealed space at the position of the porous tube 15.

[0058] S6: Apply axial pressure and confining pressure to the specimen 23 through the axial cylinder 5 and the annular cylinder 4 until the specified pressure is reached. Turn on the heating and insulation jacket 14, heat the specimen 23 to the specified temperature, and after maintaining the temperature for the specified duration, inject the pollutant solution with pre-added nano-magnetic induction particles and reaching the specified pressure from the seepage fluid injection port 19 and maintain the pressure for the specified duration. Collect the outflowing pollutant solution from the high-pressure pipeline connected to the seepage fluid outlet 21. After the experiment is completed, take out the specimen 23, monitor the pollutant content of the pollutant solution at the outlet end, the pollutant solution at the injection end, and the specimen 23 at different distances from the injection end inside the specimen 23 to obtain the migration law of pollutants in the coal seam roof and floor under specified temperature and pressure conditions. At the same time, observe the pollutant migration inside the specimen 23 through a magnetic particle imaging device. In addition, by virtue of the fact that the nano-magnetic induction particles are magnetic materials, according to the experimental requirements, perform directional guidance or tracking in a specific direction or position through an external magnetic field. These nano-magnetic induction particles can be controlled to be repeatedly tested in a specific area, which is very beneficial for tracking the diffusion, accumulation, and transfer paths of pollutants.

[0059] The above-described embodiments only represent the optimal implementation modes of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A rock permeability testing system for high-temperature and high-pressure environments, characterized in that: It includes a stress loading system, a test kettle assembly, a specimen (23), and a magnetic particle imaging system; The stress loading system includes a hydraulic pump (1), a confining pressure constant current and constant pressure pump (2), an annular cylinder cooling device (3), an annular cylinder (4), a shaft cylinder (5), an experimental operation table (6), and a servo hydraulic control frame (7); the hydraulic pump (1) is connected to the annular cylinder (4) and the shaft cylinder (5) through pipelines; the confining pressure constant current and constant pressure pump (2) is connected to the test kettle assembly through pipelines; the annular cylinder cooling device (3) is coated on the outer surface of the annular cylinder (4), and a water flow channel is arranged inside the annular cylinder cooling device (3) to prevent the annular cylinder (4) from being damaged by overheating through injecting low-temperature circulating water; the experimental operation table (6) is arranged on the servo hydraulic control frame (7); The test kettle assembly includes a kettle body (12). A through cavity penetrating the upper and lower parts of the kettle body (12) is provided along its axis direction. The outside of the kettle body (12) is covered with a heating and heat preservation jacket (14). Temperature and pressure monitoring holes (16) and confining pressure injection ports (20) that penetrate the heating and heat preservation jacket (14) and the kettle body (12) and communicate with the through cavity are provided on both sides of the whole heating and heat preservation jacket (14) and the kettle body (12). The temperature and pressure monitoring holes (16) are connected to temperature and pressure sensors, and the confining pressure injection ports (20) are connected to a confining pressure constant current and constant pressure pump (2) through pipelines. A kettle base (18) is installed at the bottom of the kettle body (12). A sample table (25) extending upward is fixed at the central position of the top of the kettle base (18). The sample table (25) extends into the bottom cavity opening of the through cavity. A seepage fluid injection port (19) penetrating the upper and lower parts of the kettle base (18) and the sample table (25) along their axis directions is provided for applying pore pressure to the specimen (23) during permeability testing. A ring-shaped pressure head (11) is installed at the top of the kettle body (12). The lower part of the ring-shaped pressure head (11) extends into the top cavity opening of the through cavity. A through hole penetrating the upper and lower parts of the ring-shaped pressure head (11) along its axis direction is provided. A ring-shaped pressure transmission cushion block (8) is provided at the top of the ring-shaped pressure head (11). A through hole penetrating the upper and lower parts of the ring-shaped pressure transmission cushion block (8) along its axis direction is provided. An axial pressure head (10) is inserted into the through holes of the ring-shaped pressure head (11) and the ring-shaped pressure transmission cushion block (8). The lower part of the axial pressure head (10) extends into the through cavity. A seepage fluid outlet (21) penetrating the upper and lower parts of the axial pressure head (10) along its axis direction is provided. The top end of the axial pressure head (10) is connected to a high-pressure pipeline for collecting seepage fluid. An axial pressure transmission cushion block (9) is provided at the top of the axial pressure head (10). The axial pressure transmission cushion block (9) is located in the through hole of the ring-shaped pressure transmission cushion block (8). A groove for the extension of the high-pressure pipeline is reserved at the position where the bottom of the axial pressure transmission cushion block (9) contacts the axial pressure head (10). A horizontal through hole for connecting low-temperature circulating water is provided in the upper part of the axial pressure transmission cushion block (9). The specimen (23) is arranged in the through cavity and clamped between the top end of the sample table (25) and the bottom end of the axial pressure head (10). The outside of the specimen (23) is covered with a confining pressure sealing sleeve (24). The bottom of the confining pressure sealing sleeve (24) is wrapped and connected to the sample table (25), and the top of the confining pressure sealing sleeve (24) is wrapped and connected to the axial pressure head (10). A porous pipe (15) is sleeved outside the confining pressure sealing sleeve (24). Fine holes (28) for the flow of confining pressure liquid are provided on the side of the porous pipe (15). An upper graphite sealing ring (13) and a lower graphite sealing ring (22) are arranged in the through cavity of the kettle body (12). The upper graphite sealing ring (13) is sleeved on the axial pressure head (10), and the lower graphite sealing ring (22) is sleeved on the sample table (25). The porous pipe (15) is clamped between the upper graphite sealing ring (13) and the lower graphite sealing ring (22). The magnetic particle imaging system includes a radio frequency coil (26) and a magnetic particle imaging device. The radio frequency coil (26) is wrapped outside the porous tube (15), and the end of the radio frequency coil (26) extends from the seepage fluid outlet (21) on the axial pressure head (10) and is connected to the magnetic particle imaging device.

2. The rock permeability testing system for high-temperature and high-pressure environments according to claim 1, characterized in that: A slotted opening (27) communicating with its through hole is provided on the side wall of the annular pressure transmitting pad (8), and the high-pressure pipeline and the low-temperature circulating water pipe are led out from the slotted opening (27).

3. The rock permeability testing system for high-temperature and high-pressure environments according to claim 1, characterized in that: Bolt holes (17) corresponding in position are provided on the outer side of the bottom of the kettle body (12) and on the outer side of the kettle base (18), and the kettle body (12) and the kettle base (18) are fixedly connected by bolts.

4. The rock permeability testing system for high-temperature and high-pressure environments according to claim 1, characterized in that: The axial pressure transmitting pad (9), the axial pressure head (10), the test piece (23) and the sample stage (25) all have the same diameter.

5. The rock permeability testing system for high-temperature and high-pressure environments according to claim 1, characterized in that: The material of the confining pressure sealing sleeve (24) is a metal with a high melting point and excellent ductility, and the height of the confining pressure sealing sleeve (24) is at least 3 times the height of the test piece (23).

6. The rock permeability testing system for high-temperature and high-pressure environments according to claim 1, characterized in that: The porous tube (15) is made of a quartz tube or a ceramic tube. The inner diameter of the porous tube (15) is larger than the outer diameter of the confining pressure sealing sleeve (24), and its outer diameter is smaller than the diameter of the through cavity. The height of the porous tube (15) is at least 1.5 times the height of the test piece (23), but does not exceed 0.6 times the height of the confining pressure sealing sleeve (24).

7. The rock permeability testing system for high-temperature and high-pressure environments according to claim 1, characterized in that: The heating and heat preservation sleeve (14) is internally provided with high-power resistance wires and heat preservation cotton, and can heat and keep the temperature of the test piece (23) at a maximum temperature of 550 °C.

8. The rock permeability testing system for high-temperature and high-pressure environments according to claim 1, characterized in that: The magnetic particle imaging device is used to detect and image nano magnetic-sensitive particles, and reflects the pore and crack distribution inside the test piece (23) through the distribution state of the nano magnetic-sensitive particles, or detects the nano magnetic-sensitive particles added in advance as a tracer in the pollutant solution through magnetic resonance imaging to reflect the internal pollutant migration situation; the radio frequency coil (26) is used to generate a detection magnetic field change.

9. A method for using the rock permeability testing system for high-temperature and high-pressure environments according to any one of claims 1-8, characterized in that, It includes the following steps: S1: Place the cut test piece (23) on the sample stage (25), put the confining pressure sealing sleeve (24) on the test piece (23) and the sample stage (25), and insert the axial pressure head (10) from above into the confining pressure sealing sleeve (24) and press against the upper surface of the test piece (23). S2: Put the kettle body (12) on the kettle base (18) from top to bottom, place the test piece (23) in the through cavity of the kettle body (12), and fixedly connect the kettle body (12) and the kettle base (18) by bolts. S3: Place the lower graphite sealing ring (22) in the gap between the through cavity of the kettle body (12) and the sample stage (25), and the filling height of the lower graphite sealing ring (22) is flush with the bottom of the test piece (23). Then, put the porous tube (15) on the outside of the confining pressure sealing sleeve (24) and wrap it with the radio frequency coil (26); place the upper graphite sealing ring (13) in the gap between the through cavity of the kettle body (12) and the axial pressure head (10), and the filling height of the upper graphite sealing ring (13) is higher than the upper end of the confining pressure sealing sleeve (24); put the annular pressure head (11) on the axial pressure head (10) and install and connect it to the kettle body (12); put the heating and heat preservation sleeve (14) on the kettle body (12). S4: Place the assembled test autoclave assembly on the experimental operation table (6), extend the radiofrequency coil (26) outwards from the seepage fluid outlet (21) and connect it to the magnetic particle imaging device; install the annular pressure transmission spacer block (8) and the axial pressure transmission spacer block (9), connect the confining pressure constant current and constant pressure pump (2) to the confining pressure injection port (20), connect the annular cylinder cooling device (3) and the axial pressure transmission spacer block (9) to the low-temperature circulating water respectively, and connect the temperature and pressure sensor to the temperature and pressure monitoring hole (16); S5: Apply a pressure of 0.1 MPa to the specimen (23) through the axial cylinder (5) to fix the specimen (23), apply a downward pressure to the upper graphite sealing ring (13) and the lower graphite sealing ring (22) through the annular cylinder (4), so that the upper graphite sealing ring (13) and the lower graphite sealing ring (22) squeeze the confining pressure sealing sleeve (24) under the action of pressure and form a sealed space at the position of the porous tube (15); S6: Apply axial pressure and confining pressure to the specimen (23) through the axial cylinder (5) and the annular cylinder (4) to the specified pressure, turn on the heating and insulation jacket (14), heat the specimen (23) to the specified temperature, after keeping the temperature for the specified duration, inject the seepage fluid that has been previously added with nano magnetic induction particles and reaches the specified pressure from the seepage fluid injection port (19), collect and record the flow rate of the seepage fluid from the high-pressure pipeline connected to the seepage fluid outlet (21), calculate and obtain the permeability of the specimen (23) under real-time high temperature and high pressure, and at the same time observe the pore and fracture distribution inside the specimen (23) through the magnetic particle imaging device.

10. The method for using the rock permeability testing system for high-temperature and high-pressure environments according to claim 9, characterized in that: When used for detecting pollutant migration, replace the seepage fluid in step S6 with a pollutant solution that has been previously added with nano magnetic induction particles, and observe the pollutant migration inside the specimen (23) through the magnetic particle imaging device; at the same time, relying on the magnetic material characteristics of the nano magnetic induction particles, conduct directional guidance or tracking in a specific direction or position through an external magnetic field, and the nano magnetic induction particles can be controlled to be repeatedly tested in a specific area.

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