Rock in-situ high temperature pyrolysis and permeability test system and method based on CT scanning

Abstract

This invention discloses a system and method for in-situ high-temperature pyrolysis and permeability testing of rocks based on CT scanning, belonging to the field of clean mining technology for underground resources. The testing system includes a high-precision pressure loading mechanism, an electromagnetic heating and temperature control mechanism, and a permeability testing mechanism. The high-precision pressure loading mechanism forms an upper and lower clamp for the specimen, without affecting the CT scanning path. The permeability testing mechanism includes a movable confining wall, which can continue high-temperature in-situ permeability testing after the real-time CT scan is completed. This invention can simultaneously realize four functions: in-situ stress simulation, high-temperature pyrolysis, real-time CT scanning, and permeability testing. It can complete multi-parameter testing without transferring the specimen, avoiding data deviations caused by structural changes during specimen transfer.

Description

Technical Field

[0001] This invention belongs to the field of clean mining technology of underground resources, specifically a system and method for in-situ high-temperature pyrolysis and permeability testing of rocks based on CT scanning. Background Technology

[0002] Unconventional petroleum resources mainly include shale oil, oil sands, heavy oil, and coalbed methane-to-oil. Their reservoir conditions are complex, and extraction is difficult, requiring specialized technologies and management models for efficient development. As my country's conventional petroleum resource supply enters a stable period, the exploration and development of unconventional petroleum resources has become one of the core directions for ensuring national energy security. Organic rocks (including oil shale and anthracite) are abundant unconventional resources that, under high-temperature pyrolysis conditions, can generate large quantities of refined oil products that can replace conventional petroleum, possessing significant strategic reserve value. Currently, organic rock extraction methods are divided into traditional surface dry distillation and underground in-situ extraction. In-situ extraction, due to its advantages such as no need for surface stripping, lower pollutant emissions, and lower overall costs, is internationally recognized as a technology with potential for large-scale industrial application.

[0003] However, perfecting the in-situ mining mechanism of organic rocks still faces core technological bottlenecks: the evolution of the microscopic pore and fracture structure of organic rocks, changes in macroscopic permeability, and the coupling relationship with temperature and stress in the underground in-situ environment are not yet clear. Existing experimental devices have significant limitations: most devices can only achieve high-temperature pyrolysis, CT scanning, or permeability testing independently, and cannot simulate in-situ stress-temperature coupling conditions, nor can they simultaneously acquire dynamic data on the microstructure and seepage characteristics during pyrolysis; some integrated devices have problems such as poor heating uniformity, insufficient stress loading accuracy, X-ray scanning obstruction, and low high-temperature sealing reliability, resulting in large deviations in experimental data and failing to provide accurate theoretical basis for field mining.

[0004] Therefore, there is an urgent need to design an integrated, high-precision experimental system to accurately simulate the in-situ stress-high temperature pyrolysis environment, simultaneously complete real-time CT scanning and permeability testing, accurately capture the dynamic evolution of the microstructure and seepage characteristics of organic rocks, and provide technical support for optimizing the in-situ mining process of organic rocks. Summary of the Invention

[0005] This invention overcomes the shortcomings of existing technologies by proposing a CT-based in-situ high-temperature pyrolysis and permeability testing system and method for rocks. It can simultaneously conduct real-time CT scanning of the high-temperature pyrolysis process and post-pyrolysis permeability testing on three types of organic rock specimens: intact rock, fractured rock, and fissured rock, under simulated in-situ underground stress conditions. This enables multi-parameter coordinated monitoring of stress, temperature, microstructure, and permeability characteristics, improving the accuracy and correlation of experimental data.

[0006] This invention is achieved through the following technical solution:

[0007] A CT scan-based in-situ high-temperature pyrolysis and permeability testing system for rocks includes a high-precision pressure loading mechanism, an electromagnetic heating and temperature control mechanism, and a permeability testing mechanism. The high-precision pressure loading mechanism includes an axial pressure head for applying axial pressure to the specimen. The axial pressure head is slidably positioned within an upper pressure frame, with a lower pressure frame positioned below it, clamping the specimen between the axial pressure head and the lower pressure frame. The electromagnetic heating and temperature control mechanism includes superconducting electromagnetic heating coils, symmetrically positioned at the bottom of the axial pressure head and the top of the lower pressure frame. The electromagnetic heating coil contacts the specimen; the penetrant testing mechanism includes a movable confining pressure wall, an annular cavity arranged axially inside the axial pressure head, the bottom of the cavity communicating with the bottom of the axial pressure head; the cavity is connected to the first constant pressure single-cylinder pump through the drive source inlet; the movable confining pressure wall is slidably arranged inside the cavity, and a confining pressure chamber is arranged inside the movable confining pressure wall, which is connected to the cavity; the upper pressure frame is provided with a confining pressure injection port, the inner side of which communicates with the cavity, and a seepage channel is arranged inside the upper pressure frame, which passes through the axial pressure head and communicates with the bottom of the axial pressure head.

[0008] Furthermore, the high-precision pressure loading mechanism also includes a servo motor, a harmonic reducer, a coupling, a ball screw, and an electric cylinder thrust rod. The output end of the servo motor is connected to the harmonic reducer, the harmonic reducer is connected to the coupling, the coupling is connected to the ball screw, the ball screw is connected to the electric cylinder thrust rod, and the electric cylinder thrust rod is connected to the shaft pressure head.

[0009] Furthermore, a load sensor is installed within the lower pressure frame; the electric cylinder thrust rod drives the axial pressure head to apply pressure to the specimen, and the load sensor collects the loading force value in real time and feeds it back to the control system.

[0010] Furthermore, it also includes a non-contact fastening connection mechanism, which is used to achieve non-contact fastening between the upper and lower pressure frames, ensuring that there are no metal or non-metal obstructions in the X-ray path.

[0011] Furthermore, the non-contact fastening connection mechanism includes upper and lower magnetic components and an electromagnetic control module; the upper magnetic component is installed at the bottom of the upper pressure frame, and the lower magnetic component is installed at the top of the lower pressure frame. Neither the upper nor lower magnetic components have direct contact with the specimen.

[0012] Furthermore, a high-pressure chamber is provided at the upper end of the shaft pressure head, and the top of the cavity is connected to the high-pressure chamber; a drive source inlet is provided on the upper pressure frame; the high-pressure chamber is connected to one end of the drive source inlet through a telescopic pipe, and the other end of the drive source inlet is connected to the first constant pressure single-cylinder pump through a pipe.

[0013] Furthermore, the inner wall of the movable confining wall is connected to a copper sleeve, the inner diameter of which matches the outer diameter of the specimen.

[0014] Furthermore, a high-temperature resistant graphite sealing ring is provided on the top surface of the lower pressure frame, and the high-temperature resistant graphite sealing ring is coaxially arranged with the superconducting electromagnetic heating coil and the test piece.

[0015] Furthermore, the outer side of the confining pressure injection port is connected to the second constant pressure single-cylinder pump through a pipeline; high-pressure deionized water is injected into the confining pressure injection port through the second constant pressure single-cylinder pump; the seepage channel is connected to the inert gas source through a pipeline; a seepage outlet is provided inside the lower pressure frame, one end of the seepage outlet passes through the lower pressure frame and is connected to the top of the lower pressure frame, the seepage outlet is located at the bottom of the specimen, and the other end of the seepage outlet is connected to a gas flow meter.

[0016] The method for in-situ high-temperature pyrolysis and permeability testing of rocks based on CT scanning, employing the aforementioned CT scanning-based in-situ high-temperature pyrolysis and permeability testing system, includes the following steps:

[0017] S1. Place the specimen between the lower pressure frame and the axial pressure head; complete the non-contact fastening of the upper and lower pressure frames, at which point the X-ray path of the CT scan is unobstructed.

[0018] S2. Start the high-precision pressure loading mechanism to apply in-situ stress to the specimen, and keep it constant after reaching the target load so that the specimen is in an in-situ stress state.

[0019] S3. Start the electromagnetic heating and temperature control mechanism to perform in-situ pyrolysis of the specimen;

[0020] S4. Start the CT scanner and perform a full-range scan of the pyrolysis specimen;

[0021] S5. Start the first constant pressure single cylinder pump, which drives the movable confining wall to move axially downward through the drive source inlet until it presses the lower pressure frame. At this time, the movable confining wall covers the surface of the specimen and fits tightly.

[0022] S6. Inject confining pressure medium into the confining pressure chamber through the confining pressure injection port to apply confining pressure to the specimen;

[0023] S7. Permeability test is performed by introducing a permeation medium into the specimen through the permeation channel.

[0024] The beneficial effects of this invention compared to the prior art are as follows:

[0025] 1. Multi-condition adaptability: It is compatible with three types of organic rock specimens: intact rock, broken rock, and fractured rock. It can simultaneously realize four functions: in-situ stress simulation, high-temperature pyrolysis, real-time CT scanning, and permeability testing. Multi-parameter testing can be completed without transferring specimens, avoiding data deviation caused by structural changes during specimen transfer.

[0026] 2. Guaranteed Scanning Accuracy: The non-contact magnetic clamping design completely removes obstructions in the X-ray path. Combined with the lightweight titanium alloy structure and synchronous rotation of the CT sample stage, it significantly improves the clarity and dynamic capture accuracy of CT scan images and can identify microscopic pores and cracks ≥5μm.

[0027] 3. Precise heating and stress control: Superconducting electromagnetic heating combined with an adaptive electromagnetic field control algorithm achieves uniform heating and precise temperature control in high-temperature environments; the high-precision pressure loading device can simulate stress at a burial depth of 5000m, with high precision in load and loading rate control, meeting the requirements for accurate replication of in-situ environments.

[0028] 4. Sealing and Testing Reliability: The composite sealing structure of movable confining wall and embedded copper sleeve allows for continued high-temperature in-situ permeation testing after real-time CT scanning, making it suitable for high-temperature and high-pressure environments and ensuring high sealing reliability; the dual-pump synergistic loading and inert gas permeation test design ensure the accuracy and repeatability of permeability test data. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the CT scan-based in-situ high-temperature pyrolysis and permeability testing system for rocks described in this invention;

[0030] Figure 2 for Figure 1 Enlarged view of point A in the middle;

[0031] Figure 3 This is a schematic diagram of the confining pressure injection port.

[0032] Figure 4 A plan view showing the arrangement of the superconducting electromagnetic heating coil and the high-temperature resistant graphite sealing ring;

[0033] Figure 5 A connection diagram of an inert gas source, a first constant-pressure single-cylinder pump, a second constant-pressure single-cylinder pump, and a gas flow meter;

[0034] Explanation of the labels in the diagram:

[0035] 1-Servo motor; 2-Harmonic reducer; 3-Coupling; 4-Ball screw; 5-Electric cylinder thrust rod; 6-Seepage channel; 7-High pressure chamber; 8-Drive source inlet; 9-Containing pressure injection port; 10-Movable confining pressure wall; 11-Magnetic component; 12-Superconducting electromagnetic heating coil; 13-High temperature resistant graphite sealing ring; 14-Seepage outlet; 15-Load sensor; 16-Inert gas source; 18-First constant pressure single-cylinder pump; 19-Second constant pressure single-cylinder pump; 20-Gas flow meter; 21-Shaft pressure head; 22-Specimen; 23-Upper pressure frame; 24-Lower pressure frame. Detailed Implementation

[0036] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0037] See Figures 1 to 5 This embodiment proposes an in-situ high-temperature pyrolysis and permeability testing system for rocks based on CT scanning. The system includes a high-precision pressure loading mechanism, an electromagnetic heating and temperature control mechanism, a non-contact fastening connection mechanism, and a permeability testing mechanism. These mechanisms work together to accurately simulate the in-situ environment and complete multi-parameter tests. The CT scanner used for scanning is a conventional external device. Figures 1 to 5 Not shown in the diagram; the structure, function, and technical parameters of each mechanism are as follows:

[0038] (a) High-precision pressure loading mechanism

[0039] A high-precision pressure loading mechanism is used to apply axial pressure to specimen 22 (organic rock) to accurately simulate the in-situ stress state at different burial depths underground, providing a stable mechanical environment for the experiment. Its core components include a servo motor 1, a harmonic reducer 2, a coupling 3, a ball screw 4, an electric cylinder thrust rod 5, and a shaft pressure head 21. Each component adopts a series transmission structure from top to bottom. Specifically, the output end of the servo motor 1 is connected to the harmonic reducer 2, the harmonic reducer 2 is connected to the coupling 3, the coupling 3 is connected to the ball screw 4, the ball screw 4 is connected to the electric cylinder thrust rod 5, and the electric cylinder thrust rod 5 is connected to the shaft pressure head 21. The shaft pressure head 21 is slidably disposed within the upper pressure frame 23, and a lower pressure frame 24 is disposed below the upper pressure frame 23. Specimen 22 is placed on top of the lower pressure frame 24 and is clamped between the shaft pressure head 21 and the lower pressure frame 24. A load sensor 15 is disposed within the lower pressure frame 24.

[0040] The power transmission path of the high-precision pressure loading mechanism is as follows: servo motor 1 outputs power → harmonic reducer 2 reduces speed and increases torque → coupling 3 buffers and dampens vibration and transmits power to ball screw 4 → ball screw 4 converts rotational motion into linear motion → drives electric cylinder thrust rod 5 to drive shaft pressure head 21 to apply pressure to specimen 22 → load sensor 15 collects loading force value in real time and feeds it back to the control system.

[0041] The technical parameters of the high-precision pressure loading mechanism are as follows:

[0042] 1. Load and stress performance: The maximum load can reach 1t. For a columnar bearing specimen 22 with a diameter of 10mm, it can provide a maximum axial stress of 125MPa, corresponding to the in-situ stress environment of organic rock buried at a depth of 5000m (calculated based on a rock density of 25kN / m³). The load control accuracy reaches 0.1%FS (full scale), which can effectively avoid the interference of stress fluctuations on the structure of specimen 22. The effective stroke is 50mm, which can meet the loading requirements of specimens 22 of different heights (5-25mm).

[0043] 2. Loading rate control: The motor speed is collected in real time by the encoder of the servo motor 1. Combined with the pitch of the ball screw 4 (preset to 5mm) and the rotation angle, the displacement and loading rate of the axial pressure head 21 are accurately calculated. The loading rate can be continuously adjusted from 0.01-5MPa / s to meet the mechanical property testing needs of different types of organic rocks.

[0044] 3. Material and Compatibility: The main structure of the high-precision pressure loading mechanism (including the electric cylinder thrust rod 5, axial pressure head 21, upper pressure frame 23, and lower pressure frame 24) is made of titanium alloy, with a tensile strength ≥860MPa and a density of only 4.5g / cm³. 3 While meeting mechanical strength requirements, it significantly reduces its own weight (overall weight ≤30kg), and can rotate synchronously with the CT machine sample stage (rotation angle 0-360°) without additional inertial interference, ensuring the continuity and accuracy of CT scans.

[0045] (ii) Electromagnetic heating and temperature control mechanism

[0046] The electromagnetic heating and temperature control mechanism is used to rapidly and uniformly heat the specimen 22, accurately control the pyrolysis temperature and heating rate, and simulate the temperature environment of in-situ pyrolysis of organic rocks. The core components include superconducting electromagnetic heating coils 12 arranged symmetrically on the upper and lower sides, a high-frequency inverter power supply, and an intelligent controller. The superconducting electromagnetic heating coils 12 are connected to the high-frequency inverter power supply and the intelligent controller. A superconducting electromagnetic heating coil 12 is symmetrically arranged at the bottom of the axial pressure head 21 and the top of the lower pressure frame 24, and the superconducting electromagnetic heating coil 12 is in contact with the specimen 22. The superconducting electromagnetic heating coil 12 is made of yttrium barium copper oxide (YBCO) high-temperature superconducting material, and its resistance is close to zero at room temperature. The resistance loss is reduced by more than 90% compared with traditional copper coils, and the heating efficiency is increased to more than 85%. The coil is wrapped with a 3mm thick corundum heat insulation pad, which can withstand temperatures above 800℃ and effectively prevent heat from being transferred to the pressure loading device. When the experimental temperature exceeds 600℃, a liquid nitrogen cooling device can be connected (liquid nitrogen is introduced through the cooling channel reserved in the coil) to achieve rapid temperature control and meet the requirements of extreme high-temperature pyrolysis experiments (the maximum heating temperature can reach 1000℃).

[0047] The intelligent controller incorporates an adaptive electromagnetic field control algorithm based on a magnetic-thermal multiphysics coupling model and machine learning optimization strategies. It can intelligently match the optimal heating path according to the material properties (thermal conductivity, specific heat capacity), geometric dimensions (diameter, height), and target temperature of the specimen 22. By real-time acquisition of the current of the superconducting electromagnetic heating coil 12 and the surface temperature of the specimen 22 (built-in thermocouple, temperature measurement accuracy ±1℃), it dynamically adjusts the magnetic field distribution of the superconducting electromagnetic heating coil 12 to ensure that the radial temperature difference of the specimen 22 is ≤5℃ and the axial temperature difference is ≤3℃, thereby achieving uniform heating of the complex-shaped specimen 22 and maximizing the utilization efficiency of thermal effects.

[0048] The high-frequency inverter power supply adopts an improved full-bridge resonant circuit with a working frequency range of 10-50kHz and an output power that is continuously adjustable from 0-5kW. The circuit has a built-in wideband response module and overcurrent, overvoltage, and overheat protection mechanisms, which can operate stably under high power and high frequency conditions. The energy transfer efficiency is ≥92%, avoiding the impact of power fluctuations on heating uniformity.

[0049] Both the high-frequency inverter and the intelligent controller are existing devices.

[0050] (iii) Non-contact fastening connection mechanism

[0051] This mechanism is used to achieve non-contact fastening of the upper pressure frame 23 and the lower pressure frame 24, ensuring that there are no metal or non-metal obstructions in the X-ray path, avoiding X-ray intensity attenuation caused by obstructions, and ensuring the clarity and accuracy of CT scan images. Its core components include two magnetic components 11 and an electromagnetic control module. The upper magnetic component 11 is installed at the bottom of the upper pressure frame 23, and the lower magnetic component 11 is installed at the top of the lower pressure frame 24. Neither the upper nor lower magnetic component 11 has direct contact with the specimen 22.

[0052] The technical parameters of the non-contact fastening connection mechanism are as follows:

[0053] 1. Structure of magnetic component 11: Each magnetic component 11 is composed of a samarium cobalt permanent magnet and an electromagnetic coil. The samarium cobalt permanent magnet is of model Sm2Co17, which can withstand high temperatures up to 350℃. By adjusting the ratio of samarium and cobalt elements (Sm:Co=2:17), the high temperature stability is improved, and a basic clamping force of 500N can be provided. The electromagnetic coil is wound around the outside of the permanent magnet. The magnetic field direction is switched by changing the direction of the coil current (forward and reverse). The magnetic field strength is dynamically adjusted by adjusting the current magnitude (0-5A). The clamping force adjustment range is 100-1000N, which can adapt to the clamping requirements under different stress loading conditions.

[0054] 2. Linkage Protection Mechanism: The electromagnetic control module and the load sensor 15 of the high-precision pressure loading mechanism are linked to collect the axial load data of the specimen 22 in real time. When the load changes abruptly (fluctuation > 5%FS), it is determined that the specimen 22 may break. The controller immediately adjusts the current of the electromagnetic coil, reduces the clamping force (to 50% of the basic clamping force), and finely adjusts the direction of the magnetic field to avoid rigid impact between the upper pressure frame 23 and the lower pressure frame 24 due to the breakage of the specimen 22, while protecting the CT scanning components from damage.

[0055] The electromagnetic control module is an existing device.

[0056] (iv) Penetration testing organizations

[0057] The permeation testing mechanism is used to test the permeability of specimen 22 after high-temperature pyrolysis. Its core components include a movable confining wall 10, a first constant pressure single-cylinder pump 18, a second constant pressure single-cylinder pump 19, an inert gas source 16, a gas flow meter 20, and a sealing assembly.

[0058] An annular cavity is provided axially within the axial pressure head 21, with the bottom of the cavity communicating with the bottom of the axial pressure head 21. A high-pressure chamber 7 is provided at the upper end of the axial pressure head 21, and the top of the cavity communicates with the high-pressure chamber 7. A drive source inlet 8 is provided on the upper pressure frame 23. The high-pressure chamber 7 is connected to one end of the drive source inlet 8 via a telescopic pipe, and the other end of the drive source inlet 8 is connected to the first constant-pressure single-cylinder pump 18 via a pipe. A movable confining wall 10 is slidably disposed within the cavity. A copper sleeve is connected to the inner wall of the movable confining wall 10, and the inner diameter of the copper sleeve matches the outer diameter of the specimen 22. A confining cavity is provided inside the movable confining wall 10, and the confining cavity is connected to the cavity. The pressure source is output to the high-pressure chamber 7 through the first constant pressure single-cylinder pump 18, which pushes the movable confining wall 10 downward. The inner wall of the copper sleeve fits against the outer wall of the specimen 22. Finally, the bottom of the movable confining wall 10 fits tightly against the top of the lower pressure frame 24, and the outer wall of the specimen 22 is tightly covered by the movable confining wall 10.

[0059] The movable confining wall 10 adopts an axially sliding design. The outer side is equipped with a high-temperature resistant, low-friction guide rail (made of silicon nitride, with a friction coefficient ≤0.02), which can achieve smooth axial movement in an environment of 20-800℃. The inner side is embedded with an oxygen-free copper sleeve with a thickness of 2mm (ductility ≥35%, high temperature resistance ≥500℃). The copper sleeve is tightly fitted to the surface of the specimen 22. It can undergo radial plastic deformation during confining pressure loading, so as to achieve uniform radial coverage and sealing of the specimen 22 and avoid high-pressure fluid leakage.

[0060] To improve the sealing performance of the movable confining wall 10, a high-temperature resistant graphite sealing ring 13 is provided at the contact point between the movable confining wall 10 and the lower pressure frame 24; specifically, the high-temperature resistant graphite sealing ring 13 is provided on the top surface of the lower pressure frame 24 and is coaxially arranged with the superconducting electromagnetic heating coil 12 and the test piece 22.

[0061] The upper pressure frame 23 is provided with a confining pressure injection port 9. The inner side of the confining pressure injection port 9 is connected to the cavity, and the outer side of the confining pressure injection port 9 is connected to the second constant pressure single cylinder pump 19 through a pipeline. The confining pressure medium (high pressure deionized water) is injected into the confining pressure injection port 9 through the second constant pressure single cylinder pump 19. The confining pressure medium enters the confining pressure cavity through the cavity and applies confining pressure to the sample 22.

[0062] A seepage channel 6 is provided inside the upper pressure frame 23. The seepage channel 6 passes through the axial pressure head 21 and is connected to the bottom of the axial pressure head 21. The seepage channel 6 is connected to the inert gas source 16 through a pipeline. A seepage outlet 14 is provided inside the lower pressure frame 24. One end of the seepage outlet 14 passes through the lower pressure frame 24 and is connected to the top of the lower pressure frame 24. The seepage outlet 14 is located at the bottom of the specimen 22. The other end of the seepage outlet 14 is connected to the gas flow meter 20.

[0063] The mechanism of penetration testing is as follows:

[0064] 1. Dual-pump coordinated confining pressure loading: A first constant-pressure single-cylinder pump 18 and a second constant-pressure single-cylinder pump 19 form a collaborative loading system. The first constant-pressure single-cylinder pump 18 serves as the driving source for the movable confining pressure wall 10, with an output pressure range of 0-10 MPa. It drives the movable confining pressure wall 10 to move axially downwards through the driving source inlet 8 until it compresses the high-temperature resistant graphite sealing ring 13 (sealing temperature ≤800℃, sealing pressure ≤20 MPa), completing the initial sealing of the permeation experiment. The second constant-pressure single-cylinder pump 19 serves as the confining pressure loading source, with an output pressure range of 0-50 MPa. It injects high-pressure deionized water into the confining pressure chamber through the confining pressure injection port 9, compressing the embedded copper sleeve and uniformly transferring the confining pressure to the circumference of the specimen 22. The confining pressure control accuracy is ±0.1 MPa, which can simulate the confining pressure environment corresponding to different burial depths. The two pumps are linked by a control system to achieve sequential loading (sealing is completed before confining pressure is applied), avoiding structural damage or sealing failure of the specimen 22 due to sudden changes in confining pressure.

[0065] 2. Permeability Testing Procedure Design: Nitrogen gas (chemically stable and does not react with the pyrolyzed specimen 22) is selected as the inert gas source 16. The pressure is adjusted to the target osmotic pressure (0.1-5MPa continuously adjustable) via a pressure reducing valve and introduced into the specimen 22 through the permeation channel 6. The permeation outlet 14 is connected to a high-precision gas flow meter 20 (measurement range 0-100mL / min, accuracy ±0.01mL / min). After the reading of the gas flow meter 20 stabilizes (fluctuation ≤1%), the flow rate data is recorded. The permeability of the specimen 22 is calculated using Darcy's Law (K=QμL / (AΔP), where K is the permeability, Q is the flow rate, μ is the gas viscosity, L is the specimen length, A is the cross-sectional area of ​​the specimen, and ΔP is the osmotic pressure difference), thus achieving accurate permeability testing under in-situ stress-pyrolysis temperature coupling conditions.

[0066] The system described in this invention can perform in-situ high-temperature pyrolysis real-time CT scanning and permeability testing on organic rock specimens of different burial depths and types. The operation process is described in detail below through two specific embodiments. All operations are completed inside the CT machine to ensure the continuity of the testing process.

[0067] Example 1: Testing of columnar oil shale specimens (φ10×20mm) at a burial depth of 300m;

[0068] S1. Specimen Installation and Fastening: Place a cylindrical oil shale specimen (φ10×20mm with a smooth surface and no obvious defects) at the center of the superconducting electromagnetic heating coil 12 of the lower pressure frame 24 of the holder. Adjust the posture of the specimen 22 so that its axis coincides with the axis of the superconducting electromagnetic heating coil 12. Place the center of the superconducting electromagnetic heating coil 12 at the bottom of the upper pressure frame 23 directly above the specimen 22. Activate the non-contact fastening connection mechanism. Adjust the current of the electromagnetic control module to 2A so that the magnetic component 11 generates a fastening force of 500N, completing the non-contact fastening of the upper pressure frame 23 and the lower pressure frame 24. At this time, the X-ray path is unobstructed.

[0069] S2. In-situ stress loading: The high-precision pressure loading mechanism parameters are set through the control system: loading rate 0.5MPa / s, target load 7.5MPa (corresponding to stress at a burial depth of 300m, calculated according to σ=ρgh, ρ=25kN / m). 3 g=10m / s 2 (h=300m), load holding time 3h; start the high-precision pressure loading mechanism, servo motor 1 drives ball screw 4 to drive shaft pressure head 21 to apply pressure, load sensor 15 provides real-time feedback of force value, and after reaching the target load, it remains constant, so that the specimen 22 is in the in-situ stress state.

[0070] S3. High-temperature pyrolysis control: Set the heating parameters of the superconducting electromagnetic heating coil 12: target temperature 400℃ (the optimal pyrolysis temperature range of oil shale), heating rate 5℃ / min, and holding time 2h; start the electromagnetic heating and temperature control mechanism, the high-frequency inverter power supply output power 3kW, the adaptive electromagnetic field control algorithm matches the heating path according to the thermal conductivity of oil shale (0.8W / (m·K)), the thermocouple collects the specimen temperature in real time and provides feedback adjustment, and after heating to 400℃, it is kept at a stable temperature to complete the in-situ pyrolysis of specimen 22.

[0071] S4. Real-time CT Scan: After pyrolysis, start the CT scanner and set the scanning parameters: 10μm scanning resolution, 5 frames / min scanning speed, and the scanning range covers the entire specimen 22. The CT scanner rotates around the specimen 22 to scan and simultaneously record the microstructure images of the specimen after pyrolysis. It can clearly identify the development morphology and distribution pattern of pores and cracks. During the scanning process, the high-precision pressure loading mechanism maintains a constant load, and the non-contact fastening connection mechanism remains in working condition.

[0072] S5. Preparation for Penetration Test Sealing: After the CT scan is completed, keep the axial load at 7.5MPa and start the first constant pressure single cylinder pump 18. Set the output pressure to 5MPa and drive the movable confining pressure wall 10 to move axially downward along the guide slide rail through the drive source inlet 8 until it presses the high temperature resistant graphite sealing ring 13 to form an initial seal. At this time, the embedded copper sleeve is tightly fitted to the surface of the specimen 22 without gaps.

[0073] S6. Confining pressure loading: Start the second constant pressure single cylinder pump 19, set the output pressure to 9MPa (corresponding to the confining pressure at a burial depth of 300m, which is 1.2 times the axial stress), inject high-pressure deionized water into the confining pressure chamber through the confining pressure injection port 9, compress the embedded copper sleeve to cause radial plastic deformation, uniformly cover the specimen 22 and transfer the confining pressure, and maintain a constant pressure after reaching the target confining pressure, with stable sealing pressure and no leakage.

[0074] S7. Permeability Test: Turn on the inert gas source 16 (permeation medium, nitrogen is used in this embodiment), and adjust the permeation pressure sequentially to 3MPa, 2.5MPa, 2MPa, 1.5MPa, and 1MPa through the pressure reducing valve (gradual pressure reduction to avoid pressure sudden changes that could damage the structure of the specimen 22). Nitrogen gas is introduced into the interior of the specimen 22 through the seepage channel 6. The high-precision gas flow meter 20 at the seepage outlet 14 monitors the flow rate in real time. After each level of permeation pressure stabilizes for 30 minutes, the flow rate data is recorded (fluctuation ≤1% is considered stable). Calculate the permeability at each permeation pressure according to Darcy's law, and take the average value as the permeability of the oil shale under this stress-temperature condition. After the test is completed, turn off the gas source, unload the confining pressure and axial load, and remove the specimen 22.

[0075] Example 2: Testing of columnar anthracite specimens (φ10×20mm) at a burial depth of 1000m;

[0076] S1. Installation and fastening of specimen 22: Place the cylindrical anthracite specimen with dimensions of φ10×20mm (with a small crack reserved to simulate natural fractured rock) at the center of the superconducting electromagnetic heating coil 12 of the lower pressure frame 24 of the holder, and adjust the axis alignment; place the upper pressure frame 23 above the specimen 22, activate the non-contact fastening connection mechanism, adjust the current to 3A to generate a fastening force of 800N, and complete the non-contact fastening of the upper pressure frame 23 and the lower pressure frame 24 to ensure that the X-ray path is unobstructed.

[0077] S2. In-situ stress loading: Set the pressure loading parameters: loading rate 1MPa / s, target load 25MPa (corresponding to stress at a burial depth of 1000m), holding time 3h; start the high-precision pressure loading mechanism, stabilize after reaching the target load, so that the specimen 22 is in an in-situ stress state, and the load sensor 15 monitors in real time to avoid stress fluctuations.

[0078] S3. High-temperature pyrolysis control: Set the heating parameters of the superconducting electromagnetic heating coil 12: target temperature 300℃ (the pyrolysis temperature range of anthracite), heating rate 3℃ / min (anthracite has low thermal conductivity, so slow down the heating rate to avoid local overheating), and holding time 2h; start the electromagnetic heating and temperature control mechanism, and adjust the magnetic field distribution according to the thermal conductivity of anthracite (0.4W / (m·K)) to ensure that the axial and radial temperature difference of the specimen 22 is ≤3℃. After heating to 300℃, hold the temperature to complete the in-situ pyrolysis.

[0079] S4. Real-time CT scan: Start the CT machine, set the scanning resolution to 8μm and the scanning speed to 3 frames / min, and perform a full-range scan on the pyrolysis specimen 22, focusing on capturing crack propagation and pore connectivity. During the scan, maintain stress and temperature stability and store CT image data synchronously.

[0080] S5. Penetration Test Sealing and Confining Pressure Loading: After the CT scan, keep the axial load constant at 25MPa, start the first constant pressure single-cylinder pump 18, output pressure of 8MPa to drive the movable confining pressure wall 10 to press the high-temperature resistant graphite sealing ring 13; start the second constant pressure single-cylinder pump 19, inject high-pressure deionized water to raise the confining pressure to 30MPa (corresponding to the confining pressure at a burial depth of 1000m), keep the confining pressure stable, and ensure reliable sealing.

[0081] S6. Permeability Test: Turn on the nitrogen gas source, and adjust the osmotic pressure sequentially to 3MPa, 2.5MPa, 2MPa, 1.5MPa, and 1MPa using the pressure reducing valve. After each pressure is stabilized for 30 minutes, record the reading of the gas flow meter 20. Calculate the permeability according to Darcy's law. After the test is completed, unload the osmotic pressure, confining pressure, and axial load sequentially, turn off all devices, remove the specimen 22, organize the CT images and permeability data, and complete the experiment.

[0082] The above embodiments verify the feasibility and stability of the system. The test data are accurate and reliable, and can effectively reflect the evolution of microstructure and seepage characteristics during the in-situ pyrolysis of organic rock, providing core experimental basis for optimizing the in-situ mining process of organic rock.

[0083] To provide the public with a thorough understanding of the present invention, specific details have been described in detail in the above preferred embodiments. However, those skilled in the art can fully understand the invention even without these detailed descriptions. Several improvements and modifications can be made without departing from the principles of the invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A CT scan-based in-situ high-temperature pyrolysis and permeability testing system for rocks, characterized in that, The system includes a high-precision pressure loading mechanism, an electromagnetic heating and temperature control mechanism, a penetration testing mechanism, and a non-contact fastening connection mechanism. The high-precision pressure loading mechanism includes an axial pressure head (21) for applying axial pressure to the specimen (22). The axial pressure head (21) is slidably disposed within an upper pressure frame (23), and a lower pressure frame (24) is disposed below the upper pressure frame (23). The specimen (22) is clamped between the axial pressure head (21) and the lower pressure frame (24). The non-contact fastening connection mechanism is used to achieve non-contact fastening between the upper pressure frame (23) and the lower pressure frame (24), ensuring that there are no metal or non-metal obstructions in the X-ray path. The electromagnetic heating and temperature control mechanism includes a superconducting electromagnetic heating coil (12), which is symmetrically disposed at the bottom of the axial pressure head (21) and the top of the lower pressure frame (24). The electromagnetic heating coil (12) is in contact with the specimen (22); the permeation test mechanism includes a movable confining wall (10), the inner wall of which is connected to a copper sleeve, the inner diameter of which matches the outer diameter of the specimen (22); an annular cavity is provided in the axial pressure head (21), the bottom of which is connected to the bottom of the axial pressure head (21); the cavity is connected to the first constant pressure single cylinder pump (18) through the drive source inlet (8); the movable confining wall (10) is slidably disposed in the cavity, a confining cavity is provided in the movable confining wall (10), and the confining cavity is connected to the cavity; the upper pressure frame (23) is provided with a confining pressure injection port (9), the inner side of which is connected to the cavity; a seepage channel (6) is provided in the upper pressure frame (23), the seepage channel (6) passes through the axial pressure head (21) and is connected to the bottom of the axial pressure head (21); The confining pressure injection port (9) is connected to the second constant pressure single cylinder pump (19) through a pipeline on the outside; high pressure deionized water is injected into the confining pressure injection port (9) through the second constant pressure single cylinder pump (19); the seepage channel (6) is connected to the inert gas source (16) through a pipeline; a seepage outlet (14) is provided in the lower pressure frame (24), one end of the seepage outlet (14) passes through the lower pressure frame (24) and is connected to the top of the lower pressure frame (24), the seepage outlet (14) is located at the bottom of the specimen (22), and the other end of the seepage outlet (14) is connected to the gas flow meter (20).

2. The in-situ high-temperature pyrolysis and permeability testing system for rocks based on CT scanning according to claim 1, characterized in that, The high-precision pressure loading mechanism also includes a servo motor (1), a harmonic reducer (2), a coupling (3), a ball screw (4), and an electric cylinder thrust rod (5). The output end of the servo motor (1) is connected to the harmonic reducer (2), the harmonic reducer (2) is connected to the coupling (3), the coupling (3) is connected to the ball screw (4), the ball screw (4) is connected to the electric cylinder thrust rod (5), and the electric cylinder thrust rod (5) is connected to the shaft pressure head (21).

3. The in-situ high-temperature pyrolysis and permeability testing system for rocks based on CT scanning according to claim 2, characterized in that, A load sensor (15) is installed inside the lower pressure frame (24); the electric cylinder push rod (5) drives the shaft pressure head (21) to apply pressure to the specimen (22), and the load sensor (15) collects the loading force value in real time and feeds it back to the control system.

4. The in-situ high-temperature pyrolysis and permeability testing system for rocks based on CT scanning according to claim 1, characterized in that, The non-contact fastening connection mechanism includes two magnetic components (11) and an electromagnetic control module. The upper magnetic component (11) is installed at the bottom of the upper pressure frame (23), and the lower magnetic component (11) is installed at the top of the lower pressure frame (24). Neither the upper nor lower magnetic components (11) are in direct contact with the specimen (22).

5. The in-situ high-temperature pyrolysis and permeability testing system for rocks based on CT scanning according to claim 1, characterized in that, A high-pressure chamber (7) is provided at the upper end of the axial pressure head (21), and the top of the cavity is connected to the high-pressure chamber (7); a drive source inlet (8) is provided on the upper pressure frame (23); the high-pressure chamber (7) is connected to one end of the drive source inlet (8) through a telescopic pipe, and the other end of the drive source inlet (8) is connected to the first constant pressure single cylinder pump (18) through a pipe.

6. The in-situ high-temperature pyrolysis and permeability testing system for rocks based on CT scanning according to claim 1, characterized in that, A high-temperature resistant graphite sealing ring (13) is provided on the top surface of the lower pressure frame (24), and the high-temperature resistant graphite sealing ring (13) is coaxially arranged with the superconducting electromagnetic heating coil (12) and the test piece (22).

7. A method for in-situ high-temperature pyrolysis and permeability testing of rocks based on CT scanning, characterized in that, The method employs the CT scan-based in-situ high-temperature pyrolysis and permeability testing system for rocks as described in any one of claims 1-6, and includes the following steps: S1. Place the specimen (22) between the lower pressure frame (24) and the axial pressure head (21); complete the non-contact fastening of the upper pressure frame (23) and the lower pressure frame (24), at which time the X-ray path of the CT scan is unobstructed. S2. Start the high-precision pressure loading mechanism to load the specimen (22) in situ with stress, and keep it constant after reaching the target load so that the specimen (22) is in situ stress state. S3. Start the electromagnetic heating and temperature control mechanism to perform in-situ pyrolysis on the specimen (22); S4. Start the CT scanner and perform a full-range scan on the pyrolysis specimen (22); S5. Start the first constant pressure single cylinder pump (18), drive the movable confining wall (10) to move axially downward through the drive source inlet (8) until the lower pressure frame (24) is pressed. At this time, the movable confining wall (10) covers the surface of the specimen (22) and fits tightly. S6. Inject confining pressure medium into the confining pressure cavity through the confining pressure injection port (9) to apply confining pressure to the specimen (22); S7. Permeability test is performed by introducing the permeation medium into the specimen (22) through the permeation channel (6).

Images