Large-scale true triaxial co2 storage caprock mechanical property testing device and method based on three-field conversion

Abstract

The application discloses a large-scale true triaxial CO2 storage caprock mechanical property testing device and method based on three-field conversion and relates to the technical field of carbon capture, utilization and storage. The device comprises a shell, an inner container, a current rod, a baffle, a control device and a data acquisition device. The shell is filled with demagnetization materials to form a shielding cavity; the inner container comprises a cubic frame and six baffles, the baffles are composed of X-shaped elastic connecting strips, elastic connecting frames, triangular baffle pieces and electromagnetic conversion devices, and can form independent electromagnet areas; the current rod is arranged in six directions, and outputs current to drive magnetic field conversion; the control device realizes linkage between stress and CO2 injection parameters, and the data acquisition device synchronously monitors mechanical and CO2 migration data; the method evaluates the stability of the caprock through parameter setting, multi-field coupling testing, dynamic adjustment and data processing. The application can accurately simulate non-uniform stress field, pressure pulsation and chemical-mechanical coupling effect, and provides a basis for storage safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon capture and storage, and particularly relates to a CO2 storage caprock mechanical property testing device and method based on three-field conversion. BACKGROUND

[0002] In the CO2 geological storage project, the caprock is a key barrier to prevent CO2 from escaping upward, and its mechanical stability directly determines the safety and long-term effectiveness of storage. The migration of supercritical CO2 (Sc-CO2) at the bottom of the caprock will cause multiple complex mechanical effects: first, the high flowability of Sc-CO2 causes the pressure in different regions of the caprock to change in a pulse manner over time, such as the pressure fluctuation frequency near the injection well, which can reach 1-5 Hz; second, a significant pressure difference can be formed between the CO2 enrichment area and the unimpinged area, which can be more than 20 MPa, causing the stress field of the caprock to present a clear gradient distribution; third, the dissolution of Sc-CO2 to rock minerals will weaken the mechanical properties of the caprock, accelerate the initiation and propagation of internal cracks, and further aggravate the risk of caprock integrity failure.

[0003] The existing testing device has obvious limitations in simulating the special mechanical environment of CO2 storage. The traditional triaxial testing device mostly uses a uniform hydraulic loading method, which cannot reproduce the non-uniform stress gradient and pulse pressure field caused by CO2 migration, and it is difficult to capture the damage characteristics caused by local stress concentration in the caprock. At the same time, the sample size of the existing device is generally small, usually less than 100 mm, which cannot reflect the influence of natural fractures in large-scale caprock on CO2 channeling paths, resulting in a large deviation between the test results and the actual situation. In addition, most of the devices lack CO2-stress coupling test function, which cannot accurately simulate the degradation law of the mechanical properties of the caprock under the long-term erosion of Sc-CO2, and it is difficult to meet the test demand of caprock stability evaluation in CO2 storage engineering.

[0004] With the engineering promotion of CCUS technology, higher requirements are put forward for the precision and scene restoration of caprock mechanical property testing. It is urgent to develop a large-scale true triaxial testing device that can reproduce the special mechanical environment of CO2 storage, to accurately simulate the three-dimensional non-uniform stress field, Sc-CO2 pressure pulsation and chemical-mechanical coupling effect, and to realize the dynamic monitoring of the mechanical behavior of the caprock under complex conditions such as elastic deformation, plastic yield and crack propagation, so as to provide reliable test basis for CO2 storage site selection, caprock integrity evaluation and risk warning. SUMMARY

[0005] In order to solve the above technical problems, the present application provides a large-scale true triaxial CO2 storage caprock mechanical property testing device and method based on three-field conversion, which can accurately simulate complex environments and dynamically monitor the mechanical behavior of the caprock, providing reliable test basis for CO2 storage safety evaluation.

[0006] The technical scheme adopted by the present application to solve its technical problems is: a CO2 storage caprock mechanical property testing device based on three-field conversion, comprising a shell, an inner container, a current rod, a baffle, a control device, and a data acquisition device;

[0007] The shell is a cuboid, filled with demagnetization material to form a closed cavity, and the closed cavity has magnetic field shielding performance;

[0008] The inner container is arranged inside the shell and is made of CO2 corrosion-resistant material, and has a reserved Sc-CO2 injection interface on the surface, and distributed sensing optical fibers are arranged on the contact surface between the inner container and the rock sample;

[0009] The inner container includes a cubic frame and six baffles arranged on each side of the cubic frame; the baffles include X-shaped elastic connecting strips, an elastic connecting frame, four independent triangular baffle pieces, and four electromagnetic conversion devices;

[0010] The elastic connecting frame is connected to the opening edge of the side wall of the cubic frame, the X-shaped elastic connecting strips are integrally formed at the diagonal lines of the elastic connecting frame, the adjacent side edges between the baffle pieces are connected by the X-shaped elastic connecting strips, and the outer side edges are connected to the elastic connecting frame;

[0011] The electromagnetic conversion devices correspond one-to-one to the baffle pieces, and the electromagnetic conversion devices are arranged at the center of the outer side wall of the corresponding baffle piece; the baffle is divided into four independent electromagnet regions, each baffle piece corresponds to an electromagnet region, and a single electromagnet region has a predetermined bearing capacity and can simulate the stress difference between the CO2 enrichment zone and the depletion zone;

[0012] The current rods are arranged in six directions between the shell and the inner container, and four current rods are arranged in each direction, and the four current rods are uniformly distributed along the center of the corresponding inner wall surface of the shell; the current rods are made of high-conductivity material and have adjustable lengths to adapt to stress gradients of caprocks of different depths, and can output a predetermined range of current to drive magnetic field conversion;

[0013] The control device is signal-connected to the current rods and the Sc-CO2 injection interface of the inner container, and includes an initial pressure setting module, a pressure fluctuation setting module, and a CO2-stress coupling control unit; the initial pressure setting module is used to simulate a predetermined range of overburden pressure, the pressure fluctuation setting module is used to reproduce pressure pulsations of a predetermined frequency range caused by CO2 migration, and the control device is externally connected to control software to realize multi-field coupling loading programming;

[0014] The data acquisition device is integrated with a fiber optic demodulator, a CO2 permeability monitoring module, and a stress and strain recording unit, can synchronously acquire mechanical parameters and CO2 migration data, and is bidirectionally signal-connected to the control device.

[0015] Further, the shell comprises an upper end cover which is covered on the top of the shell, adopts a quick-release buckle structure, and is provided with a CO2 sealing gasket.

[0016] Further, the electromagnetic conversion device comprises an iron core and a CO2 corrosion resistant coil which are fixed to the center of the triangle of the baffle, can convert electric current into a magnetic field with a predetermined intensity range, and simulate the magnetic field force of different structural positions of the cap layer.

[0017] Further, the demagnetization material is a permalloy, the CO2 corrosion resistant material is stainless steel, the iron core is an electrotechnical pure iron core, and the CO2 corrosion resistant coil adopts a polytetrafluoroethylene insulation layer.

[0018] Further, the four areas of the baffle can independently adjust the magnetic field intensity, can form a predetermined value of stress difference in a single plane, and simulate the pressure gradient of the edge and center of the CO2 gas reservoir.

[0019] Further, the distributed sensing optical fiber is a Bragg grating sensing optical fiber and is arranged in the inner side wall of the baffle in a quadrature grid.

[0020] Further, the Sc-CO2 injection interface is arranged at the bottom of the cubic frame of the inner container, a square gas distribution pipeline is embedded in the inner side wall of the bottom of the cubic frame, the gas distribution pipeline is in communication with the Sc-CO2 injection interface, and a plurality of gas holes are formed in the gas distribution pipeline.

[0021] Further, the inner container also reserves an exhaust port, and the inner wall surface is provided with a CO2 pressure sensor.

[0022] Further, the baffle at the top wall of the inner container is detachably connected with the cubic frame.

[0023] The application also provides a CO2 storage cap layer mechanical property test method, which utilizes the CO2 storage cap layer mechanical property test device based on three-field conversion.

[0024] S1: test preparation: select a cap layer rock sample and process it into a cubic test sample with a size suitable for the inner container, after demagnetization treatment and component detection, place the test sample in the inner container so that the surface of the test sample is attached to the distributed sensing optical fiber;

[0025] S2: parameter setting and environment simulation: set three-dimensional initial stress parameters through the control device, simulate the overburden and tectonic stress, drive the six-way current rod to output corresponding current, generate a gradient magnetic field through the electromagnetic conversion device, so that the baffle applies a preset stress to the test sample; inject supercritical CO2 through the Sc-CO2 injection interface, set the injection pressure and rate, and simulate the CO2 contact environment of the cap layer.

[0026] S3: Multi-field coupling test: Start the pressure fluctuation setting module, output alternating current through the current rod, realize the baffle pressure pulsation through the electromagnetic conversion device to reproduce the CO2 migration effect; simultaneously open the data acquisition device, collect the mechanical parameters and CO2 migration data of the sample through the sensing optical fiber, CO2 permeability monitoring module and stress and strain recording unit;

[0027] S4: Dynamic adjustment and damage monitoring: According to the real-time collected data, adjust the current output and CO2 injection parameters through the CO2-stress coupling control unit, capture the elastic deformation, plastic yield and crack propagation process of the sample, until the sample is damaged or the preset test period is reached;

[0028] S5: Data processing: Based on the collected stress-strain, permeability and CO2 partial pressure data, analyze the mechanical performance degradation law and damage characteristics of the cap rock under the action of multi-field coupling, and evaluate the stability of the cap rock.

[0029] The beneficial effects of the present application are:

[0030] 1. The device realizes precise simulation of three-dimensional non-uniform stress field, Sc-CO2 pressure pulsation and chemical-mechanical coupling effect through the electric-magnetic-force three-field conversion mechanism; compared with the traditional hydraulic loading device, the non-contact force transmission avoids the interference of the pipeline to the CO2 migration path, and the large-scale sample is suitable for 1×1×1m 3 Large size rock sample can reflect the influence of natural fracture on CO2 channeling, and the deviation of test results from actual field is significantly reduced.

[0031] 2. Distributed Bragg grating sensing optical fiber, CO2 permeability monitoring module and stress-strain recording unit synchronously collect data, combined with CO2-stress coupling control unit, can dynamically adjust current output and Sc-CO2 injection parameters, and real-time capture the whole process of crack initiation, expansion and rock sample damage.

[0032] 3. The inner container is made of corrosion-resistant material, which cooperates with the air distribution pipeline to realize uniform injection of Sc-CO2; the baffle realizes independent micro-motion through X-shaped elastic connecting strips, and the bearing capacity of a single electromagnet area reaches the predetermined value, which can accurately simulate the difference between CO2 enrichment zone and depletion zone; the shell is filled with permalloy, and the upper end cover is fastened with CO2 sealing gasket, which takes into account the magnetic field shielding, high pressure sealing and sample loading and unloading convenience.

[0033] 4. Output gradient current through six-direction current rod, convert into directional magnetic field force through electromagnetic conversion device, drive four independent triangular baffles of baffle to apply non-uniform pressure; this mechanism breaks through the uniformity limitation of traditional hydraulic loading, and for the first time realizes the simulation of stress difference ≥20MPa in a single plane, and accurately reproduces the pressure gradient between CO2 enrichment zone and edge. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the overall structure schematic diagram of the present application.

[0035] Figure 2 is the front view of the present application for embodying the internal structure of the shell.

[0036] Figure 3 is the top view of the present application for embodying the internal structure of the shell.

[0037] Figure 4 is the structure schematic diagram of the inner container in the present application.

[0038] Figure 5 is the partial exploded view of the present application for embodying the structure of the inner container.

[0039] In the figure: 1, shell; 11, upper end cover; 12, current rod; 2, inner container; 21, baffle; 211, X-shaped elastic connecting strip; 212, elastic connecting frame; 213, baffle piece; 214, electromagnetic conversion device; 22, cubic frame; 221, air diffusing pipeline; 222, injection interface; 3, initial pressure setting module; 4, pressure fluctuation setting module; 5, data acquisition device. DETAILED DESCRIPTION

[0040] The present application will be further described in detail below in combination with the drawings.

[0041] The application discloses a CO2 storage caprock mechanical property testing device based on three-field conversion.

[0042] Referring to Figures 1 to 5 A CO2 storage caprock mechanical property testing device based on three-field conversion, comprising a shell 1, an inner container 2, a current rod 12, a control device and a data acquisition device 5.

[0043] The shell 1 is a cuboid, filled with a demagnetization material of 1J85 permalloy inside to form a closed cavity, and the closed cavity has magnetic field shielding effectiveness; the shell 1 comprises an upper end cover 11, which is covered on the top of the shell 1 and adopts a quick-release buckle structure and is equipped with a CO2 sealing gasket. The inner container 2 is arranged inside the shell 1 and is made of a CO2 corrosion-resistant material, and a Sc-CO2 injection interface 222 is reserved on the surface of the inner container 2, and the contact surface of the inner container 2 and the rock sample is provided with a distributed sensing optical fiber.

[0044] Referring to Figure 4 and Figure 5 The inner container 2 comprises a cubic frame 22 and six baffles 21 arranged on each side of the cubic frame 22; each baffle 21 comprises an X-shaped elastic connecting strip 211, an elastic connecting frame 212, four independent triangular baffle pieces 213 and four electromagnetic conversion devices 214.

[0045] The elastic connecting frame 212 is square, connected and fixed to the edges of the square openings of the side walls of the cubic frame 22, and the X-shaped elastic connecting strips 211 are integrally formed at the diagonal lines of the elastic connecting frame 212. The elastic connecting frame 212 and the X-shaped elastic connecting strips 211 can be made of 6061-T6 aluminum alloy or TC4 titanium alloy; preferably TC4 titanium alloy, which has an elastic modulus of 110 GPa, a yield strength of ≥895 MPa, an elongation of ≥10%, a recovery rate of ≥95%, and more excellent corrosion resistance. The baffle 213 is made of 316L stainless steel material, which has excellent CO2 corrosion resistance. The adjacent side edges between the four baffles 213 are connected by the X-shaped elastic connecting strips 211, and the outer side edges are connected to the elastic connecting frame 212, so that the baffle 213 can produce micro-motion in the direction perpendicular to the plane to press the sample. The distributed sensing optical fiber is a Bragg grating sensing optical fiber, which is arranged in a orthogonal grid on the inner side wall of the baffle 21; and the spatial resolution is ≤10mm.

[0046] The electromagnetic conversion device 214 corresponds to the baffle 213 one by one, and the electromagnetic conversion device 214 is arranged at the center of the outer side wall of the corresponding baffle 213; so that the baffle 21 is divided into four independent electromagnet areas, each baffle 213 corresponds to an electromagnet area, and each electromagnet area has a predetermined bearing capacity, which can simulate the stress difference between the CO2 enrichment area and the depletion area; the electromagnetic conversion device 214 includes a core and a CO2 corrosion resistant coil, the core is an electrical pure iron core, and the CO2 corrosion resistant coil adopts a polytetrafluoroethylene insulation layer. The electromagnetic conversion device 214 is fixed to the triangular center of the baffle 213, can convert current into a 0-2T magnetic field, and simulate the magnetic field force of different structural positions of the cover layer.

[0047] The current rod 12 is arranged along six directions between the shell 1 and the inner container 2, and four current rods 12 are arranged in each direction. The four current rods 12 are uniformly distributed along the center of the corresponding inner wall surface of the shell 1; the current rod 12 is coaxially arranged with the corresponding electromagnetic conversion device 214, the current rod 12 is made of high-conductivity material, the length can be adjusted to adapt to the stress gradient of the cover layer of different depths, and can output a predetermined range of current to drive the magnetic field conversion.

[0048] The current rod 12 is made of high-conductivity red copper alloy with a conductivity of ≥95% IACS, and the surface is treated with silver plating to reduce the contact resistance and ensure that the current transmission efficiency is not affected by the telescopic structure. The current rod 12 includes a hollow main rod and a telescopic section slidingly arranged in the hollow main rod. The outer wall of the telescopic section is attached to the inner wall of the hollow main rod. A spring is arranged in the hollow main rod and abuts against the telescopic section, so that the telescopic section of the current rod 12 is in contact with the outer wall of the inner container 2.

[0049] The four areas of the baffle 21 can independently adjust the magnetic field strength, and can form a predetermined value of stress difference in a single plane to simulate the pressure gradient of the edge and center of the CO2 gas reservoir.

[0050] The Sc-CO2 injection interface 222 is arranged at the bottom of the cuboid frame 22 of the inner container 2 and is connected with a special gas supply device outside. A recess is arranged in the inner side wall at the bottom of the cuboid frame 22, and a square gas distribution pipeline 221 is embedded in the recess. The Sc-CO2 injection interface 222 is in communication with the gas distribution pipeline 221. A plurality of gas holes are arranged in the gas distribution pipeline 221 and are inclined at an angle of 45° towards the bottom of the rock sample, so that the Sc-CO2 is diffused in a fan shape after being sprayed out of the gas holes, avoiding local pressure concentration caused by single-point gas injection. The Sc-CO2 injection interface 222 is arranged at the lower part of the inner container 2 and corresponds to the fracture development area at the bottom of the rock sample, simulating the actual migration path of CO2 from the reservoir to the overlying layer. The inner container 2 also has an exhaust port and a CO2 pressure sensor arranged on the inner wall surface.

[0051] The control device is in signal connection with the electric current rod 12 and the Sc-CO2 injection interface 222 of the inner container 2, and includes an initial pressure setting module 3, a pressure fluctuation setting module 4 and a CO2-stress coupling control unit. The initial pressure setting module 3 is used to simulate the pressure of the overlying rock layer in a predetermined range. The pressure fluctuation setting module 4 is used to reproduce the pressure pulsation in a predetermined frequency range caused by CO2 migration. The inner CO2 channeling simulation mode can generate a non-sinusoidal pressure pulse with a frequency of 0.1-10 Hz and a peak coefficient of 1.5, reproducing the instantaneous impact when the Sc-CO2 breaks through the fracture. The CO2-stress coupling control unit can set the linkage relationship between the Sc-CO2 injection pressure and the stress loading, such as increasing the regional stress by 5 MPa for each increase of 1 MPa of the CO2 partial pressure, simulating the stress uplift caused by CO2 accumulation in the actual storage. The control device is externally connected with MATLAB / LabVIEW control software to realize the programming of multi-field coupling loading.

[0052] The data acquisition device 5 is integrated with a fiber optic demodulator, a CO2 permeability monitoring module and a stress and strain recording unit, can synchronously acquire the mechanical parameters and CO2 migration data, and is in bidirectional signal connection with the control device. The sampling frequency of the fiber optic demodulator is ≥1 kHz, the measurement range of the CO2 permeability monitoring module is 10 -6 ~10 -3 μm 2 .

[0053] The baffle 21 at the top wall of the inner container 2 is detachably connected with the cuboid frame 22. In this embodiment, the outer side of the elastic connecting frame 212 of the baffle 21 at the top wall is also fixedly connected with a flange surrounding edge, and the flange surrounding edge is detachably connected with the cuboid frame 22 through bolts. In some embodiments, the top baffle 21 and the cuboid frame 22 can also be connected by buckling, as long as the structure can guarantee the sealing and detachable functions.

[0054] It should be noted that the test device of the present application is not suitable for strong magnetic cover layer rocks with iron content > 30% or residual magnetization > 500A / m.

[0055] The working principle of the CO2 storage caprock mechanical property test device based on three-field conversion of the present application is as follows: through the hierarchical mechanism of dynamic conversion of electric-magnetic-force three fields and multi-physical field synergistic coupling, the device reproduces the complex stress and material action process of the caprock under the CO2 geological storage environment, and the specific implementation path is as follows:

[0056] The control device generates differentiated current signals through the initial pressure setting module 3 and the pressure fluctuation setting module 4 based on the field parameters of the CO2 storage project, such as the overburden pressure corresponding to the target reservoir burial depth, the pressure gradient formed by the planar distribution of the gas reservoir, etc. Among them, in view of the stress difference of different structural regions of the caprock such as the center and the edge of the gas reservoir, the six-way current rod 12 outputs adjustable current of 0-5A according to the preset gradient, forming a current field distribution matched with the actual geological conditions, and providing accurate energy input for subsequent magnetic field conversion. At the same time, the CO2-stress coupling control unit realizes the linkage of current output and Sc-CO2 injection parameters through MATLAB / LabVIEW programming, simulating the stress uplift effect caused by CO2 accumulation.

[0057] The six electromagnetic conversion devices 214 serve as the energy conversion core, which converts the current signal into a spatial gradient magnetic field. Based on the principle of magnetic field superposition, through independent regulation and control of the electromagnetic devices outputting at the center position of the cubic triangle, a three-dimensional non-uniform magnetic field distribution is formed around the rock sample: the magnetic field strength is the highest in the area corresponding to the center of the gas reservoir, and decreases linearly to the edge, simulating the natural gradient of tectonic stress. Compared with the traditional hydraulic loading, this non-contact force transmission mechanism can avoid the physical obstruction of pipeline connection to the CO2 migration path, making the permeation process of Sc-CO2 along the natural fractures of the rock sample closer to the actual field.

[0058] The baffle 21 generates directional pressure under the action of the gradient magnetic field, and the four-zone independent magnetic field adjustment of a single baffle 21 can form an in-plane stress difference ≥20MPa, accurately reproducing the pressure difference between the CO2 enrichment area and the depletion area. At the same time, the inner container 2 injects supercritical fluid into the rock sample pores through the Sc-CO2 injection interface 222, and cooperates with the stress field; the dissolution of Sc-CO2 weakens the strength of rock minerals, and the increase of pore pressure offsets part of the effective stress, both of which accelerate crack initiation and expansion, realizing dynamic simulation of the long-term degradation process of the caprock.

[0059] The distributed Bragg grating sensing optical fiber and the CO2 permeability monitoring module constitute a global monitoring network, and real-time collection of rock sample strain distribution, crack propagation rate and CO2 migration parameters is realized. The data acquisition device 5 feeds back the monitoring data to the control device, and the current output and the CO2 injection parameters are dynamically adjusted through the preset algorithm: ensure that the test scene is highly consistent with the chain effect in the actual storage, and realize the quantitative evaluation of the mechanical behavior of the caprock.

[0060] The application further discloses a CO2 storage caprock mechanical property testing method, which utilizes the CO2 storage caprock mechanical property testing device based on three-field conversion.

[0061] S1: test preparation: select a caprock sample and process it into a cubic sample with a size suitable for the inner container 2, after demagnetization treatment and composition detection, place the sample in the inner container 2, and make the sample surface adhere to the distributed sensing optical fiber; the residual magnetization of the sample after demagnetization treatment is less than or equal to 500 A / m.

[0062] S2: parameter setting and environment simulation: set the three-dimensional initial stress parameters through the control device, simulate the overburden and tectonic stress, drive the six-way current rod 12 to output corresponding current, generate a gradient magnetic field through the electromagnetic conversion device 214, and make the baffle 21 apply a preset stress to the sample;

[0063] Inject supercritical CO2 through the Sc-CO2 injection interface 222, set the injection pressure and rate, simulate the CO2 contact environment of the caprock; the Sc-CO2 injection pressure is 0-30 MPa, the injection rate is 0.1-10 mL / min, and the three-dimensional initial stress setting range is 0-200 MPa

[0064] S3: multi-field coupling test: start the pressure fluctuation setting module 4, output alternating current through the current rod 12, realize pressure pulsation of the baffle 21 through the electromagnetic conversion device 214, and reproduce the CO2 migration effect; simultaneously start the data acquisition device 5, collect the mechanical parameters and CO2 migration data of the sample through the sensing optical fiber, the CO2 permeability monitoring module and the stress and strain recording unit; wherein the pressure pulsation frequency is 0.1-10 Hz, the sampling frequency of the data acquisition device 5 is greater than or equal to 1 kHz, and the synchronous acquisition time error is less than or equal to 10 ms.

[0065] S4: dynamic adjustment and damage monitoring: according to the real-time collected data, adjust the current output and the CO2 injection parameters through the CO2-stress coupling control unit, capture the elastic deformation, plastic yield and crack propagation process of the sample, and stop until the sample is damaged or the preset test period is reached; when the sample strain rate is greater than 100 με / min, automatically improve the current output accuracy and the data sampling frequency, and focus on the stress change in the crack propagation area.

[0066] S5: Data processing: Based on the collected stress-strain, permeability and CO2 partial pressure data, the mechanical property degradation law and failure characteristics of the cap rock sample under the action of multi-field coupling are analyzed, and the stability of the cap rock is evaluated.

[0067] Taking a certain sandstone cap rock sample as an example, the device simulates the mechanical behavior evolution after CO2 injection through multi-field coupling loading, and the specific process is as follows:

[0068] Sc-CO2 injection and stress gradient establishment stage: control device starts CO2-stress coupling control program, through inner container 2 injection interface 222 to 1 × 1 × 1 m 3 Sandstone sample injected with Sc-CO2, temperature 40℃, initial injection pressure 10MPa, synchronous driving six-way current rod 12 output gradient current: upper current rod 12 simulates overburden load, outputs 3A current, which is converted into 20MPa vertical pressure by electromagnetic conversion device 214; lower current rod 12 simulates reservoir pressure gradient, outputs 1-3A linearly increasing current, corresponding to generate 10-30MPa gradient pressure field, matching the stress characteristics of CO2 enrichment area.

[0069] After the electromagnetic conversion device 214 converts the current signal into a gradient magnetic field, it applies a non-uniform pressure of 10-30MPa to the rock sample through the four independent areas of the lower baffle 21, which drives the rock sample to produce compressive deformation along the vertical direction. In this stage, Sc-CO2 gradually penetrates along the natural fractures of the rock sample, and its permeability increases from the initial 1 × 10 -4 μm 2 to 5 × 10 -4 μm 2 ; distributed Bragg grating sensing optical fiber monitoring shows that when the crack tip strain increases to 5με / s, it indicates that local stress concentration has started crack initiation.

[0070] Pressure pulsation simulation stage: the device switches to CO2 channeling simulation mode, the front current rod 12 outputs 1±0.5A alternating current, frequency 2Hz, after electromagnetic conversion, the front baffle 21 generates 5±2.5MPa periodic pressure pulsation, accurately reproducing the periodic scouring effect of Sc-CO2 along the fracture on the bottom of the cap rock.

[0071] Rock sample multi-field coupling response stage:

[0072] Pore pressure effect: Sc-CO2 continues to accumulate in the fracture, causing local pore pressure to rise by 5MPa, according to the principle of effective stress, offsetting part of the external load, making the rock yield strength in this area decrease from 60MPa to 52MPa, and the mechanical properties deteriorate.

[0073] Fatigue damage accumulation: the pressure fluctuation at 2 Hz makes the crack tip bear cyclic stress, and the crack length expands from 5 mm to 20 mm within 30 min; the sensing optical fiber captures the stepwise increase of strain amplitude with the number of cycles, and each cycle increases by 5 με, reflecting the nonlinear characteristics of crack propagation.

[0074] Chemical-mechanical coupling weakening: the dissolution of feldspar minerals in sandstone by Sc-CO2 reduces the roughness of the crack wall, and the crack propagation rate increases from the initial 0.1 mm / min to 0.3 mm / min, accelerating the destruction of the integrity of the rock sample.

[0075] Rock sample failure stage: when the pressure in the lower high stress area rises to 35 MPa and the CO2 pore pressure reaches 15 MPa, the internal cracks of the rock sample are connected, forming a CO2 channeling channel. Real-time monitoring by the sensing optical fiber shows that the stress in this area instantaneously drops by 15 MPa, and the CO2 permeability breaks through 10 -3 μm 2 , and the control device triggers the automatic unloading protection program to terminate loading.

[0076] The failure characteristics are as follows: a directional shear failure surface is formed along the Sc-CO2 permeation path, the rock sample in the 30-35 MPa high stress area is broken into pieces with a size of ≤30 mm, and the 10-20 MPa low stress area is broken into pieces with a size of ≤100 mm, which is highly consistent with the non-uniform failure mode caused by CO2 breakthrough in the field caprock, verifying the simulation capability of the device for actual engineering scenarios.

[0077] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined by the scope of the claims.

Claims

1. A device for testing the mechanical properties of a CO2sequestration cap rock based on three-field conversion, characterized in that: The device comprises a shell (1), an inner container (2), a current rod (12), a baffle (21), a control device and a data acquisition device (5); The shell (1) is a cuboid, filled with demagnetizing material to form a closed cavity with magnetic field shielding performance; The inner container (2) is arranged inside the shell (1) and made of CO2 corrosion resistant material, with a reserved Sc-CO2 injection interface (222) on the surface, and distributed sensing optical fibers arranged on the contact surface of the inner container (2) and the rock sample; The inner container (2) comprises a cubic frame (22) and six baffles (21) arranged on each side of the cubic frame (22); the baffle (21) comprises an X-shaped elastic connecting strip (211), an elastic connecting frame (212), four independent triangular baffle pieces (213) and four electromagnetic conversion devices (214); The elastic connecting frame (212) is connected to the opening edge of the side wall of the cubic frame (22), the X-shaped elastic connecting strip (211) is integrally formed at the diagonal of the elastic connecting frame (212), the adjacent side edges between the baffle pieces (213) are connected through the X-shaped elastic connecting strip (211), and the outer side edges are connected to the elastic connecting frame (212); The electromagnetic conversion device (214) corresponds to the baffle piece (213) one by one, and the electromagnetic conversion device (214) is arranged at the center of the outer side wall of the corresponding baffle piece (213); so that the baffle (21) is divided into four independent electromagnet areas, each baffle piece (213) corresponds to an electromagnet area, and a single electromagnet area has a predetermined bearing capacity and can simulate the stress difference between the CO2 enrichment area and the depletion area; The current rod (12) is arranged in six directions between the shell (1) and the inner container (2), and four current rods (12) are arranged in each direction, and the four current rods (12) are uniformly distributed along the center of the corresponding inner wall surface of the shell (1); the current rod (12) is made of high-conductivity material and has a length adjustable to adapt to different depth of cover stress gradient, and can output a predetermined range of current to drive the magnetic field conversion; The control device is signal connected with the current rod (12) and the Sc-CO2 injection interface (222) of the inner container (2), and comprises an initial pressure setting module (3), a pressure fluctuation setting module (4) and a CO2-stress coupling control unit; the initial pressure setting module (3) is used to simulate a predetermined range of overburden pressure, the pressure fluctuation setting module (4) is used to reproduce a predetermined frequency range of pressure pulsation caused by CO2 migration, and the control device is externally connected with control software to realize multi-field coupling loading programming; The data acquisition device (5) is integrated with a fiber demodulator, a CO2 permeability monitoring module and a stress and strain recording unit, can synchronously collect mechanical parameters and CO2 migration data, and is bidirectionally signal connected with the control device.

2. The device for testing mechanical properties of a CO2sequestration cap rock based on three-field conversion according to claim 1, characterized in that: The shell (1) comprises an upper end cover (11), the upper end cover (11) covers the top of the shell (1), adopts a quick release buckle structure, and is provided with a CO2 sealing gasket.

3. The device for testing mechanical properties of a CO2 storage cap rock based on three-field conversion according to claim 2, characterized in that: The electromagnetic conversion device (214) includes a core and a CO2 corrosion resistant coil, is fixed to the triangular center of the baffle (213), can convert current into a magnetic field with a predetermined intensity range, and simulates the magnetic field force of different structural positions of the cap layer.

4. The device for testing mechanical properties of a CO2sequestration cap rock based on three-field conversion according to claim 3, characterized in that: The demagnetization material is a permalloy, the CO2 corrosion resistant material is a stainless steel, the core is an electrotechnical pure iron core, and the CO2 corrosion resistant coil adopts a polytetrafluoroethylene insulation layer.

5. The device for testing mechanical properties of a CO2sequestration cap rock based on three-field conversion according to claim 1, characterized in that: The four areas of the baffle (21) can independently adjust the magnetic field intensity, can form a stress difference with a predetermined value in a single plane, and simulates the pressure gradient of the edge and center of the CO2 gas reservoir.

6. The device for testing mechanical properties of a CO2sequestration cap rock based on three-field conversion according to claim 1, characterized in that: The distributed sensing optical fiber is a Bragg grating sensing optical fiber and is arranged in a quadrature grid on the inner side wall of the baffle (21).

7. The device for testing mechanical properties of a CO2 storage cap rock based on three-field transformation according to any one of claims 1-6, characterized in that: The Sc-CO2 injection interface (222) is arranged at the bottom of the cubic frame (22) of the inner container (2), a square gas distribution pipeline (221) is embedded in the inner side wall of the bottom of the cubic frame (22), the gas distribution pipeline (221) is in communication with the Sc-CO2 injection interface (222), and a plurality of gas holes are formed in the gas distribution pipeline (221).

8. The device for testing mechanical properties of a CO2sequestration cap rock based on three-field conversion according to claim 7, characterized in that: The inner container (2) also has a reserved exhaust port, and the inner wall surface is provided with a CO2 pressure sensor.

9. The device for testing mechanical properties of a CO2sequestration cap rock according to claim 8, wherein: The baffle (21) at the top wall of the inner container (2) is detachably connected with the cubic frame (22).

10. A method of testing the mechanical properties of a CO2 storage cap rock, characterized by: The CO2 storage cap layer mechanical property testing device based on three-field conversion of claim 9 comprises the following steps: S1: test preparation: select a cap rock sample and process it into a cubic sample suitable for the size of the inner container (2), after demagnetization treatment and composition detection, place it in the inner container (2), and make the sample surface adhere to the distributed sensing optical fiber; S2: parameter setting and environment simulation: set the three-dimensional initial stress parameters through the control device, simulate the overburden and tectonic stress, drive the six-way current rod (12) to output the corresponding current, generate a gradient magnetic field through the electromagnetic conversion device (214), and make the baffle (21) apply a preset stress to the sample; inject supercritical CO2 through the Sc-CO2 injection interface (222), set the injection pressure and rate, and simulate the CO2 contact environment of the cap layer; S3: multi-field coupling test: start the pressure fluctuation setting module (4), output alternating current through the current rod (12), realize the pressure pulsation of the baffle (21) through the electromagnetic conversion device (214), and reproduce the CO2 migration effect; simultaneously start the data acquisition device (5), collect the mechanical parameters and CO2 migration data of the sample through the sensing optical fiber, the CO2 permeability monitoring module, and the stress and strain recording unit; S4: dynamic adjustment and damage monitoring: according to the real-time collected data, adjust the current output and CO2 injection parameters through the CO2-stress coupling control unit, capture the elastic deformation, plastic yield, and crack propagation process of the sample, until the sample is damaged or the preset test period is reached; S5: data processing: based on the collected stress-strain, permeability, and CO2 partial pressure data, analyze the mechanical performance degradation law and damage characteristics of the cap rock sample under the action of multi-field coupling, and evaluate the stability of the cap layer.

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