Sandstone internal dynamic crystallization controllable system and method based on force-flow coupling driving

Abstract

In order to solve the problem of accurate simulation of sandstone fracture evolution and dynamic crystallization in geotechnical engineering experiment monitoring, the invention provides a sandstone internal dynamic crystallization controllable system and method based on force-flow coupling driving, and four defects of out-of-control crystallization position, confining pressure distortion, transportation blockage and monitoring limitation are solved. The system integrates core packaging, solution conveying, stress applying, crystallization restraining and fracture monitoring functions. A core packaging unit adopts a molecular sieve composite membrane to reduce interference, and an annular ERT electrode realizes millimeter-level fracture positioning; the capillary transport unit drives the solution to be directionally transported by using gradient ceramic layer aperture gradual change; the axial loading module realizes uniform confining pressure through cooperation of a weight and an elastic film; dry nitrogen is introduced into the evaporative crystallization module to constrain the crystallization range. The method comprises the steps of packaging, communication, solution injection, stress application, crystallization control and crack monitoring. A reliable platform is provided for complex engineering scene fracture evolution research, the experimental research range is expanded, and the correlation research comprehensiveness of sandstone is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical engineering experiment monitoring, and particularly relates to a sandstone internal dynamic crystallization controllable system and method based on force-flow coupling driving. BACKGROUND

[0002] In the field of geotechnical engineering experiment monitoring, the study of the mechanical properties and damage mechanism of sandstone has always been the core. As a widely distributed rock type in underground water environment, saline soil area and various types of geotechnical engineering, the mechanical property degradation process of sandstone under the influence of crystallization and confining pressure is directly related to the safety and stability of engineering. However, due to technical limitations, the traditional experimental device is difficult to accurately simulate the crack evolution and dynamic crystallization process of sandstone in a complex environment, resulting in a significant deviation between the experimental results and the actual engineering scene, which has become a key bottleneck restricting the study of sandstone damage mechanism.

[0003] The existing sandstone crack experiment technology mainly relies on the static seepage method. Its typical device includes a rigid hydraulic cylinder confining pressure loading system, a glass tube or a homogeneous channel solution transport module, and a CT scan and other invasive monitoring means. The vertical confining pressure is applied by the hydraulic cylinder, the salt solution is transported by the glass tube, and the crack propagation trajectory is captured by the CT scan. There is also a method of simulating groundwater seepage by artificial dripping, and monitoring the crack area resistivity change by resistivity meter. The core principle of this technology is to drive the solution flow by external pressure or gravity, and to indirectly infer the crack evolution state by combining imaging or electrical means. However, four key defects have been exposed in its application: 1. The problem of uncontrollable crystallization position is prominent The traditional liquid injection method (such as artificial dripping or glass tube transportation) leads to random distribution of crystallization, which cannot simulate the capillary transport process of groundwater in rock layers. The glass tube transport system is blocked by sodium sulfate crystallization within 24 hours when transporting 10% % of solution, and the experimental repeatability is less than 40%. The hydraulic cylinder loading device can only realize vertical confining pressure control, ignoring the stress distribution in the horizontal direction, resulting in a deviation of more than 30% between the crack initiation pressure and the actual engineering. For example, CN118226006A mentions controlling the state of carbon dioxide through a booster system, but does not solve the problem of crystallization positioning under multi-physical field coupling; CN120233067A uses an air compressor to drive seepage, but relies on a single seepage port at the bottom, which cannot achieve precise control of the three-dimensional space of the crystallization position.

[0004] 2. The confining pressure control distortion phenomenon is serious The boundary stress concentration problem is prominent when the rigid hydraulic cylinder applies confining pressure, and it is impossible to realize synchronous crack electrical monitoring. In the existing technology, when the hydraulic cylinder is loaded, the stress concentration coefficient of the core edge area can reach more than 1.5 when the confining pressure is more than 5 MPa, and the crack propagation trajectory inversion error is more than 15%; at the same time, the intervention type monitoring such as CT scanning needs to interrupt the experimental process, and the high-energy rays may cause secondary damage to the internal structure of the sandstone, which violates the authenticity principle of damage research. For example, CN118226006A simulates the formation temperature by heating the whole reaction kettle, but does not solve the problem of uneven confining pressure distribution; CN120233067A uses an air compressor to adjust the seepage pressure, but the confining pressure loading and seepage control are independent of each other, and it is impossible to realize the real simulation of stress-seepage coupling.

[0005] 3. Frequent blockage of transport channels Homogeneous transport channels (such as glass tubes or single-aperture ceramic layers) are prone to interruption of experiments due to crystallization during salt solution transport. The blockage rate of glass tube systems is as high as 60% when transporting high-concentration solutions, and single-aperture ceramic layers can partially alleviate the blockage, but cannot achieve directional solution transport, resulting in the diffusion of the crystallization range to the entire core surface, causing distortion of the monitoring data. For example, the direct connection design of the gas storage tank and the reaction kettle in CN118226006A has the risk of incomplete liquefaction of carbon dioxide, which easily leads to pipe icing; although the seepage pipeline of CN120233067A is equipped with a flowmeter, it does not solve the problem of crystallization and deposition of high-salinity solutions on the pipe wall, and the long-term experimental stability is insufficient.

[0006] 4. Significant limitations of monitoring methods Traditional CT scanning and other invasive methods have high destructive power and cannot achieve in-situ non-destructive monitoring of the crack evolution process. CT scanning requires the core to be removed from the experimental device, which causes the cracks to close during unloading, resulting in a distortion rate of more than 30% in the monitoring data; although resistivity instrument monitoring can achieve in-situ detection, the electrode layout in the existing technology is not reasonable, and the crack propagation trajectory inversion error is more than 15%. For example, CN118226006A indirectly infers damage through temperature sensors, lacking direct crack observation means; CN120233067A introduces temperature and humidity sensors, but can only monitor the local environment at the bottom, and cannot comprehensively reflect the coordinated evolution of core internal crystallization and cracks.

[0007] In addition, the existing technology also has the following defects and deficiencies: 1. Insufficient functional integration CN118226006A focuses on the single factor of supercritical carbon dioxide and does not consider the multi-field coupling of seepage-crystallization-stress; CN120233067A realizes seepage-crystallization coupling, but lacks real-time stress field regulation and monitoring, and cannot reproduce the real stress state of deep formations.

[0008] 2. Control precision defects CN118226006A realizes automatic pressure stabilization through electrode point pressure gauge, but temperature control relies on bottom heater, and there is longitudinal temperature gradient; CN120233067A adopts directional drying with hair dryer, but the temperature and humidity field is unevenly distributed, resulting in significant spatial difference in crystallization rate.

[0009] 3. Limited scope of application CN118226006A is dedicated to supercritical carbon dioxide environment and cannot be expanded to salt solution or acidic corrosion scene; CN120233067A supports multiple solution systems, but does not solve the problem of heterogeneous core (such as fractured sandstone) seepage-crystallization difference simulation.

[0010] To solve the above problems, the present application provides a system and method for realizing controllable dynamic crystallization in sandstone by force-flow coupling driving. The technology adopts a composite structure of gradient ceramic layer and hydrophobic coating, generates directional capillary force based on pore size gradient (100 μm→10 μm), realizes stable solution delivery and accurate control of crystallization position; through the synergistic action of vertical pressure of weight and lateral pressure of elastic membrane, realizes uniform confining pressure control (stress concentration coefficient <1.05), and synchronously integrates annular ERT electrode array, realizes three-dimensional electrical tomography scanning and in-situ nondestructive monitoring of fracture expansion trajectory; combined with air compressor driven solution circulation and dry gas to restrict crystallization range, solves the problem of transport blockage, so that crystallization only occurs in the top center area of the core (diameter Ø15±2mm). This technology is closer to the capillary rise phenomenon of underground water in rock layers, and provides a new solution for precise monitoring of fracture evolution process in scenes such as seepage-crystallization damage of groundwater in saline soil area and erosion of shale gas reservoir fracturing fluid.

[0011] In the field of geotechnical engineering experimental monitoring, the mechanical properties and damage mechanism of sandstone always occupy a core position. As a kind of rock type widely distributed in underground water environment, saline soil area and various types of geotechnical engineering, the mechanical property degradation process of sandstone under the influence of crystallization and confining pressure is directly related to the safety and stability of engineering. However, due to the technical limitations of traditional experimental devices, it is difficult to accurately simulate the fracture evolution and dynamic crystallization process of sandstone in complex environment, resulting in significant deviation between experimental results and actual engineering scene, which becomes a key bottleneck restricting the research of sandstone damage mechanism. SUMMARY

[0012] The technical problem to be solved by the present application is to provide a sandstone internal dynamic crystallization controllable system and method based on force-flow coupling driving, to solve the technical problem of accurate simulation of sandstone fracture evolution and dynamic crystallization process in the field of rock-soil engineering experiment monitoring, and to overcome the four core defects of uncontrollable crystallization position, distorted confining pressure control, blocked transport channel and limited monitoring means in the prior art.

[0013] To achieve the above-mentioned target, the present application adopts the following technical solutions: a comprehensive system and method integrating core packaging, solution transportation, stress application, crystallization constraint and fracture monitoring are constructed, and the system structure and functions are as follows: 1. Core packaging unit: used for realizing confining pressure generation and fracture monitoring, the sandstone core is packaged in the core packaging unit, which includes a sandstone core, the outer surface of which is coated with a molecular sieve composite membrane, an annular ERT electrode is arranged on the outer ring, the outer surface is further coated with a silicone oil layer, and the outer periphery of the silicone oil layer is coated with a FEP elastic film. The molecular sieve composite membrane uses molecular sieve to adsorb water vapor to reduce electrode interference and prolongs the service life of the composite membrane by the corrosion resistance of PTFE; the annular ERT electrode is attached in a four-quadrant symmetric layout, which can realize millimeter-level fracture positioning.

[0014] 2. Capillary transport unit: used for realizing directional transportation of solution to the inside of the core packaging unit, including a solution storage tank, a metal mesh substrate, a gradient ceramic layer and a hydrophobic nano coating. The gradient ceramic layer has a gradually decreasing pore size from bottom to top, which drives the solution to rise through capillary force gradient, and cooperates with the high-porosity metal mesh substrate and the super-hydrophobic hydrophobic nano coating to realize efficient directional transportation of the solution.

[0015] 3. Axial loading module: used for providing vertical stress, composed of a water-permeable stone, a pressure-bearing plate and a weight, and realizing uniform confining pressure loading through the cooperation of the weight and the elastic film.

[0016] 4. Solution driving module: used for controlling solution injection, the solution storage device is connected to the solution storage tank of the capillary transport unit through a pipeline, and is provided with a pressure closed-loop control system, which can accurately control the replenishment and stable supply of the solution.

[0017] 5. Evaporative crystallization module: connected to an external gas supply system, dry nitrogen is introduced into the top of the sandstone core through an adjustable flow nozzle to form a local low-humidity area to constrain the crystallization range.

[0018] The method comprises the following steps: Step 1: packaging the sandstone core in the core packaging unit; Step 2: The capillary transport unit, axial loading module, solution driving module and evaporation crystallization module are respectively communicated with the core packaging unit; Step 3: Start the solution driving module, inject the solution in the solution storage device into the solution storage tank of the capillary transport unit through the pipeline, and the solution is transported to the gradient ceramic layer through the metal mesh substrate, and is transported along the gradient ceramic layer to the inside of the core packaging unit; Step 4: Start the axial loading module to apply a vertical stress to the sandstone core; Step 5: Start the evaporation crystallization module, and introduce dry nitrogen into the top of the sandstone core to form a local low humidity area at the top of the sandstone core to constrain the crystallization range; Step 6: Real-time monitoring of the fracture of the sandstone core is realized by the annular ERT electrode, and the monitoring data is processed by the resistivity inversion algorithm to generate a three-dimensional fracture distribution map.

[0019] The sandstone internal dynamic crystallization controllable system and method based on force-flow coupling driving provided by the application have the following beneficial effects: 1. The application effectively solves the technical problem of accurate simulation of sandstone fracture evolution and dynamic crystallization process in the field of geotechnical engineering experiment monitoring. In view of the four core defects of uncontrolled crystallization position, distorted confining pressure, blocked transport channel and limited monitoring means in the prior art, the limitations of traditional experimental devices that cannot realize accurate control of the crystallization position, uniform loading of the confining pressure, directional transport of the solution and in-situ non-destructive monitoring of the fracture are overcome. By integrating multiple functional modules, directional transport of the solution and accurate control of the crystallization position are realized, and the confining pressure generation and fracture monitoring are cooperated, which provides a reliable experimental platform for the fracture evolution research of complex engineering scenes such as groundwater seepage-crystallization damage in saline soil area and shale gas reservoir fracturing fluid erosion.

[0020] 2. The crystallization position deviation is reduced from ±10mm in the traditional technology to ±1mm by the gradient ceramic layer and hydrophobic coating composite structure, which is closer to the groundwater seepage path in the actual engineering, and provides more reliable experimental basis for the sandstone damage mechanism research. At the same time, the force-flow coupling driving mode is used to solve the problem that the traditional experimental device cannot accurately control the crystallization position, and the gradient ceramic layer and hydrophobic nano coating are used to realize directional transport of the solution and accurate control of the crystallization position.

[0021] 3. The application successfully solves the problem of confining pressure distortion. Specifically, when the traditional rigid hydraulic cylinder applies confining pressure, the boundary stress is concentrated, and only the vertical pressure is considered, the pressure in other directions in the actual engineering is ignored, and the fracture electrical monitoring cannot be realized synchronously.

[0022] 4、The weight and the elastic film of the application are cooperatively loaded to reduce the stress concentration coefficient from 1.5 or above to 1.05 or below, and the error of the crack initiation pressure test is reduced from 30% or above to 5% or below, thereby significantly improving the coincidence degree of the experimental results and the actual engineering.

[0023] 5、The application adopts the weight and the elastic film cooperatively loaded and the annular ERT electrode monitoring to solve the problem that the uniformity of the previous confining pressure control is difficult to guarantee, and realizes the uniform confining pressure loading and the in-situ nondestructive monitoring of the crack.

[0024] 6、The solution circulation supply and the dry gas restraint module of the application reduce the blockage rate of the transport channel from 60% to 0%, and the experimental repeatability is improved from 40% to 95% or above, thereby greatly reducing the experimental cost and time consumption. The pressure closed-loop control of the solution driving module and the dry nitrogen restraint of the evaporation crystallization module solve the problem of the transport channel blockage. The traditional homogeneous transport channel (such as a glass tube) is easy to be blocked due to crystallization in the salt solution transport, and the experimental process is interrupted, and the problem is effectively solved by the application.

[0025] 7、The annular ERT electrode array of the application realizes the in-situ nondestructive monitoring of the crack propagation trajectory, and the resistivity inversion error is reduced from 15% to 5% or below, and the experimental process is not interrupted, and the secondary damage problem of the intervention means such as CT scanning is avoided. Through the annular ERT electrode monitoring and data processing, the limitations of the traditional monitoring means are overcome, and a more effective crack monitoring method is provided. The annular ERT electrode is attached in a four-quadrant symmetrical layout, realizes millimeter-level crack positioning, and the monitoring data is processed by the resistivity inversion algorithm to generate a three-dimensional crack distribution map, providing a quantitative basis for research.

[0026] 8、The application constructs a comprehensive system integrating core packaging, solution transport, stress application, crystallization restraint and crack monitoring, and realizes the cooperative work of multiple functions, and such overall architecture is less seen in the prior art.

[0027] 9、The core packaging unit of the application is improved to adopt a PTFE-molecular sieve composite membrane to coat the sandstone core, uses the molecular sieve to adsorb water vapor to reduce electrode interference, and uses the corrosion resistance of PTFE to prolong the service life of the composite membrane.

[0028] 10、The gradient ceramic layer aperture of the capillary transport unit is gradually reduced from bottom to top, the solution is driven to rise by the capillary force gradient, and the high-porosity metal mesh base and the super-hydrophobic hydrophobic nano coating are matched to realize efficient directional transport of the solution.

[0029] 11、The evaporation crystallization module of the application introduces dry nitrogen into the top of the sandstone core through an adjustable flow nozzle to form a local low-humidity area to restrain the crystallization range.

[0030] 12、The solution driving module of the present application adopts a pressure closed-loop control system to accurately control the replenishment and stable supply of the solution.

[0031] 13、The units of the present application work in coordination, the solution driving module provides the solution for the capillary transport unit, the capillary transport unit delivers the solution to the sandstone core of the core packaging unit, the axial loading module applies stress, the evaporation crystallization module controls the crystallization range, and at the same time, the annular ERT electrode of the core packaging unit monitors the fractures, forming an organic whole.

[0032] 14、The present application not only can carry out the conventional sandstone fracture monitoring and crystallization control experiment, but also can study the influence of different factors on the damage mechanism of sandstone by changing the solution composition (such as using mixed solution with different concentrations) and stress conditions (such as applying dynamic vertical stress), which expands the range and depth of experimental research and provides a more comprehensive technical means for sandstone related research.

[0033] 15、The technical effects of the present application have been fully verified by comparative experiments and experimental effects, under the same experimental conditions (confining pressure 5MPa, solution concentration 10% ), the key indicators such as crystallization position deviation, stress concentration coefficient, plugging rate and monitoring error of the device of the present application are significantly better than those of the traditional technology, which provides a new solution for the research of sandstone fracture evolution. BRIEF DESCRIPTION OF DRAWINGS

[0034] The present application will be further described below in combination with the drawings and embodiments: Fig. 1 It is a schematic diagram of the overall structure of the present application; Fig. 2 It is a schematic diagram of the three-dimensional structure of the core packaging of the present application; Fig. 3 It is a schematic diagram of the annular ERT electrode structure of the present application; Fig. 4 It is a schematic diagram of the structure of the solution driving module of the present application; In the figure: core packaging unit 1, capillary transport unit 2, axial loading module 3, solution driving module 4, evaporation crystallization module 5, sandstone core 11, molecular sieve composite membrane 12, annular ERT electrode 13, silicone oil layer 14, FEP elastic film 15, hydrophobic nano coating 21, gradient ceramic layer 22, metal mesh substrate 23, solution storage tank 24, weight 31, pressure bearing plate 32, water-permeable stone 33, air compressor 41, solution storage device 42, electrode 131, small part of tapered hole 221, large part of tapered hole 222, hole top 231, hole bottom 232. DETAILED DESCRIPTION

[0035] The technical solutions in the present application will be further described below in combination with the drawings and embodiments: Embodiment 1 As shown in the figure, the embodiment provides a force-flow coupling driven internal dynamic crystallization controllable system of sandstone, which comprises a core packaging unit 1, a capillary transport unit 2, an axial loading module 3, a solution driving module 4 and an evaporation crystallization module 5. Figs. 1 to 4 In the core packaging unit 1, the sandstone core 11 is taken as a damage carrier and is coated by a PTFE (Polytetrafluoroethylene)-molecular sieve composite film 12. The PTFE-molecular sieve composite film 12 can not only reduce electrode interference by adsorbing water vapor through the molecular sieve, but also has corrosion resistance, which can prolong its service life. The annular ERT (Electrical Resistance Tomography) electrode 13 is attached to the outside of the PTFE-molecular sieve composite film 12 in the form of a 16-electrode array. The 16 electrodes 131 are distributed at equal angles along the core circumference, and the adjacent electrodes have an included angle of 22.5°, forming a four-quadrant symmetric layout. The millimeter-level fracture positioning is realized through a 5mm spacing. The silicone oil layer 14 is pressed to push the FEP (Fluorinated Ethylene Propylene) elastic film 15 outward, which eliminates the boundary stress concentration. The FEP elastic film 15 contacts the thick encapsulation silicone oil medium and transmits the confining pressure to the sandstone core 11 through shrinkage deformation.

[0036] In the capillary transport unit 2, the hole bottom 232 and the hole top 231 of the metal mesh substrate 23 are both high-porosity structures. The substrate is immersed in the solution storage tank 24, and the solution can be quickly dispersed through the high porosity. The gradient ceramic layer 22 has a gradually decreasing pore size from the large cone portion 222 to the small cone portion 221. In this embodiment, the pore size gradient ranges from 100μm (pore size of the large cone portion 222) to 10μm (pore size of the small cone portion 221), which drives the solution to rise to the interior of the sandstone through the capillary force gradient. The hydrophobic nano coating 21 adopts a super-hydrophobic nano structure, which prevents blockage and conducts the solution to the interior of the sandstone through sub-micron pores. The upper end of the gradient ceramic layer 22 is in contact with the bottom of the sandstone core 11 in the core packaging unit 1.

[0037] In the axial loading module 3, the weight 31 provides vertical pressure through gravity, and the pressure range is 5~20MPa. The pressure value can be adjusted by increasing or decreasing the number of weights, which simulates the one-way vertical pressure of the rock. The pressure plate structure 32 disperses the weight pressure through surface contact to avoid stress concentration. The water-permeable stone 33 provides a vapor escape path to ensure the uniformity of pressure transmission. The pressure of the weight 31 and the pressure transmitted by the horizontal silicone oil form a triaxial pressure of the actual environment. The weight 31 uniformly applies vertical stress to the sandstone core 11 through the pressure plate structure 32 and the water-permeable stone 33.

[0038]

[0039] ​The solution driving module 4 comprises an air compressor and a solution storage device 42, and the solution driving module 4 is provided with a pressure closed-loop control system. The air compressor 41 is connected to the solution storage device 42 through a pipeline, and the solution storage device 42 is connected to the solution storage tank 24 of the capillary transport unit 2 through a pipeline. The pressure closed-loop control system has a pressure regulation range of 0.1-0.5 MPa, and the accuracy is ±0.01 MPa. Through the system, the solution in the solution storage device 42 is accurately controlled and timely supplemented to the storage tank 24.

[0040] In the evaporation crystallization module 5, the adjustable flow nozzle is connected to dry nitrogen gas towards the top of the sandstone core 11. The nitrogen gas is an inert gas, which avoids affecting the experiment. In this embodiment, the humidity of the dry nitrogen gas ranges from 0 to 30% RH, and the flow rate ranges from 0.1 to 1.0 L / min, which is accurately controlled by a mass flow meter. The nozzle is at a certain distance from the surface of the core, and by controlling the gas humidity and flow rate, a local low-humidity area is formed, which restricts the crystallization range to the top center area.

[0041] The cooperative working process of each unit is as follows: the solution driving module 4 delivers the solution to the solution storage tank 24 of the capillary transport unit 2. After the solution is quickly dispersed through the metal mesh base 23, it rises to the inside of the sandstone core 11 through the capillary force gradient of the gradient ceramic layer 22. The axial loading module 3 applies vertical stress to the sandstone core 11, and at the same time, the core packaging unit 1 transmits horizontal confining pressure through silicone oil, forming a triaxial pressure environment. Under the action of solution delivery and pressure, the sandstone may produce cracks, and the annular ERT electrode 13 in the core packaging unit 1 monitors the crack situation in real time. The evaporation crystallization module 5 introduces dry nitrogen gas to the top of the sandstone core 11 to restrict the crystallization range.

[0042] Example 2 In another preferred embodiment, based on example 1, this embodiment provides a controllable system for dynamic crystallization inside sandstone based on force-flow coupling driving, which is composed of a core packaging unit 1, a capillary transport unit 2, an axial loading module 3, a solution driving module 4, and an evaporation crystallization module 5.

[0043] In the core encapsulation unit 1, the sandstone core 11 is tightly wrapped by the PTFE molecular sieve composite membrane 12. The molecular sieve composite membrane 12 not only can effectively reduce the electrode interference by adsorbing water vapor through the molecular sieve, but also has excellent corrosion resistance, which can significantly prolong its service life. The annular ERT electrode 13 is composed of 16 electrodes 131, which are attached to the outer surface of the molecular sieve composite membrane 12 in an array form, and are distributed along the circumference of the sandstone core 11 at equal angles. The adjacent electrodes are at an angle of 22.5°, forming a four-quadrant symmetric layout. With a 5mm electrode spacing, millimeter-scale fracture positioning is achieved. The silicone oil layer 14 will push the FEP elastic film 15 to expand outward when it is under pressure, thereby eliminating the boundary stress concentration phenomenon. The FEP elastic film 15 contacts the thick encapsulation silicone oil medium, and transmits the confining pressure to the sandstone core 11 through shrinkage deformation.

[0044] The solution storage device 42 of the solution driving module 4 is connected to the solution storage tank 24 of the capillary transport unit 2 through a pipeline, providing a solution source for capillary transport. The pressure closed-loop control system of this module accurately controls the pressure adjustment range to be 0.1~0.5MPa, with an accuracy of ±0.01MPa, which can ensure stable and continuous supply of solution.

[0045] The capillary transport unit 2 is responsible for directing the solution to the inside of the core encapsulation unit 1. The metal mesh base 23 is provided in the solution storage tank 24, and the metal mesh base 23 is covered with a plurality of holes, the hole bottom 232 is communicated with the solution storage tank 24, and the hole top 231 is connected with the gradient ceramic layer 22. The gradient ceramic layer 22 is provided with a plurality of tapered holes, the large part 222 of the tapered hole is connected with the hole top 231 of the metal mesh base 23, and the small part 221 of the tapered hole is communicated with the hydrophobic nano coating 21. The pore size of the gradient ceramic layer 22 gradually changes from 100μm at the lower end to 10μm at the upper end, which ensures efficient directional transport of the solution. The hydrophobic nano coating 21 adopts super-hydrophobic nano structure, which can prevent clogging through sub-micron pores and smoothly conduct the solution to the inside of the sandstone. The top of the hydrophobic nano coating 21 is tightly attached to the bottom of the sandstone core 11 of the core encapsulation unit 1.

[0046] The axial loading module 3 is installed on the top of the sandstone core 11 of the core encapsulation unit 1, which is composed of a water-permeable stone 33, a pressure plate 32 and a weight 31. The water-permeable stone 33 is placed on the top of the sandstone core 11 to provide a path for the vapor to escape. The pressure plate 32 is located on the top of the water-permeable stone 33, which is used to disperse the pressure of the weight 31 to avoid stress concentration. The weight 31 can provide a pressure of 5~20MPa, and the pressure value can be adjusted by increasing or decreasing the number of weights. The weight 31 uniformly applies vertical stress to the sandstone core 11 through the pressure plate 32 and the water-permeable stone 33, and together with the horizontal pressure transmitted by the silicone oil in the core encapsulation unit 1, it creates a triaxial pressure environment.

[0047] The evaporation crystallization module 5 is connected with an external gas supply system and is provided with an adjustable flow nozzle. The adjustable flow nozzle is directed towards the top of the sandstone core 11 and is kept at a certain distance from the surface of the sandstone core 11. Dry nitrogen is introduced into the top of the sandstone core 11 through the nozzle. The humidity of the dry nitrogen is controlled in the range of 0-30% RH, and the flow rate is controlled in the range of 0.1-1.0 L / min, which is accurately controlled by a mass flow meter, so as to form a local low-humidity area at the top of the sandstone core 11 and restrict the crystallization range to the central area at the top.

[0048] The cooperation process of each unit is as follows: after the solution driving module 4 is started, the air compressor 41 works, and the solution in the solution storage device 42 is accurately delivered to the solution storage tank 24 of the capillary transport unit 2 through the pressure closed-loop control system. After the solution enters the solution storage tank 24, it is quickly dispersed through the metal mesh base 23, and then rises under the action of the capillary force gradient of the gradient ceramic layer 22, and is directionally transported into the sandstone core 11 through the hydrophobic nano coating 21. At the same time, the axial loading module 3 starts to work, and the weight 31 applies vertical stress to the sandstone core 11 through the pressure-bearing plate 32 and the water-permeable stone 33, and forms a triaxial pressure environment together with the horizontal confining pressure in the core packaging unit 1. Under the dual influence of solution delivery and pressure action, the sandstone may produce cracks, and at this time the annular ERT electrode 13 in the core packaging unit 1 monitors the crack situation in real time. The evaporation crystallization module 5 is started, dry nitrogen is introduced into the top of the sandstone core 11 through the adjustable flow nozzle, and the crystallization range is restricted.

[0049] Example 3 In another preferred embodiment, based on examples 1 and 2, the present embodiment provides a controllable system for dynamic crystallization in sandstone based on force-flow coupling driving, which also includes a core packaging unit 1, a capillary transport unit 2, an axial loading module 3, a solution driving module 4 and an evaporation crystallization module 5.

[0050] The structure of the core packaging unit 1 is consistent with that of examples 1 and 2. The sandstone core 11 is covered by a PTFE molecular sieve composite membrane 12, and the annular ERT electrode 13 is attached outside the molecular sieve composite membrane 12. The silicon oil layer 14 and the FEP elastic film 15 are sequentially covered outside the annular ERT electrode 13, and each part cooperates to realize the functions of confining pressure generation and crack monitoring.

[0051] In the solution driving module 4, the solution storage device 42 is connected with the solution storage tank 24 of the capillary transport unit 2 through a pipeline, and the pressure closed-loop control system provided therein can accurately control the solution delivery. The pressure adjustment range is 0.1-0.5 MPa, and the accuracy is ±0.01 MPa. The difference is that the solution storage device 42 stores a mixed solution mixed in different proportions, which is used to study the influence of different solution components on the sandstone crack and crystallization process. 、 The mixed solution mixed in different proportions is used to study the influence of different solution components on the sandstone crack and crystallization process.

[0052] In the capillary transport unit 2, the structure and function of the metal mesh substrate 23, the gradient ceramic layer 22 and the hydrophobic nano-coating 21 are the same as those in Embodiment 3. The pore size gradient of the gradient ceramic layer 22 is 100 μm (pore size of the large part of the tapered hole 222) to 10 μm (pore size of the small part of the tapered hole 221), which ensures efficient directional transport of the solution.

[0053] In the axial loading module 3, the combination of the weight 31, the pressure-bearing plate 32 and the water-permeable stone 33 can apply a vertical stress to the sandstone core 11. In this embodiment, a special control system is used to make the weight 31 apply a dynamically changing vertical stress, simulating more complex actual geological conditions, with a pressure change range of 5-20 MPa.

[0054] The adjustable flow nozzle of the evaporation crystallization module 5 can accurately control the humidity (0-30% RH) and flow rate (0.1-1.0 L / min) of dry nitrogen, forming a local low-humidity area at the top of the sandstone core 11 and restricting the crystallization range.

[0055] The working process of each unit is as follows: The solution driving module 4 transports the mixed solution of different components from the solution storage device 42 to the solution storage tank 24 of the capillary transport unit 2 according to the preset program. After the solution is dispersed by the metal mesh substrate 23, rises in the gradient ceramic layer 22 and is conducted by the hydrophobic nano-coating 21, it enters the interior of the sandstone core 11. The axial loading module 3 applies a vertical stress to the sandstone core 11 according to the set dynamic change mode, together with the horizontal confining pressure, to form a dynamic triaxial pressure environment. Under the combined action of the solution and the stress, the sandstone produces cracks, and the annular ERT electrode 13 of the core packaging unit 1 monitors the crack situation in real time. The evaporation crystallization module 5 continuously introduces dry nitrogen into the top of the sandstone core 11 to restrict the crystallization range.

[0056] Embodiment 4 In another preferred embodiment, based on Embodiment 1, this embodiment provides a controllable method for dynamic crystallization in sandstone based on force-flow coupling driving, which uses the controllable system for dynamic crystallization in sandstone based on force-flow coupling driving described in Embodiment 1 to monitor the in-situ cracks of sandstone, and the specific steps are as follows: 1. Core packaging: The sandstone core 11 is packaged in the core packaging unit 1, the PTFE-molecular sieve composite membrane 12 is wrapped around the sandstone core 11, the annular ERT electrode 13 is attached, and the silicone oil layer 14 and the FEP elastic film 15 are installed.

[0057] 2. Solution delivery: Start the solution driving module 4, the air compressor 41 applies pressure, and the solution in the solution storage device 42 is supplemented to the reservoir 24 of the capillary transport unit 2 through the pressure closed-loop control system; after the solution is quickly dispersed through the metal mesh substrate 23, it is directionally transported to the inside of the sandstone core 11 under the action of the capillary force gradient of the gradient ceramic layer 22.

[0058] 3. Stress application: Start the axial loading module 3, increase or decrease the number of weights 31 according to experimental requirements, adjust the pressure value in the range of 5-20 MPa, and uniformly apply vertical stress to the sandstone core 11 through the pressure-bearing plate structure 32 and the water-permeable stone 33, together with the pressure transmitted by the horizontal silicon oil to form a triaxial pressure environment.

[0059] 4. Crystallization constraint: Start the evaporation crystallization module 5, adjust the adjustable flow nozzle to control the humidity of dry nitrogen in the range of 0-30% RH, and the flow rate in the range of 0.1-1.0 L / min, and introduce dry nitrogen into the top of the sandstone core 11 to form a local low-humidity area, and constrain the crystallization range in the top center area.

[0060] 5. Fracture monitoring: During the experiment, the annular ERT electrode 13 in the core packaging unit 1 monitors the fracture propagation trajectory of the sandstone core 11 in real time, and the monitoring data is processed by resistivity inversion algorithm to generate a three-dimensional fracture distribution map, providing a quantitative basis for sandstone damage mechanism research.

[0061] Example 5 In another preferred embodiment, based on example 2, this embodiment provides a controllable method for dynamic crystallization inside sandstone based on force-flow coupling driving, which uses the controllable system for dynamic crystallization inside sandstone based on force-flow coupling driving described in example 2 to conduct in-situ monitoring of sandstone fractures, and the specific steps are as follows: Step 1: Carefully place the sandstone core 11 in the molecular sieve composite membrane 12 made of PTFE material to ensure tight wrapping. Then, the annular ERT electrode 13 composed of 16 electrodes 131 is accurately attached to the outer surface of the molecular sieve composite membrane 12 in an array form, ensuring equal-angle distribution along the circumference of the sandstone core 11, with adjacent electrodes at an angle of 22.5°, forming a four-quadrant symmetric layout. Then, install the silicon oil layer 14 and the FEP elastic film 15 in sequence to complete the assembly of the core packaging unit 1.

[0062] Step 2: The solution driving module 4 and the capillary transport unit 2 are arranged and connected according to the design drawings. The solution storage device 42 of the solution driving module 4 is connected to the solution storage tank 24 of the capillary transport unit 2 through a pipeline. The assembled core packaging unit 1 is carefully placed on the hydrophobic nano-coating 21 of the capillary transport unit 2, ensuring that the bottom of the sandstone core 11 is tightly attached to the hydrophobic nano-coating 21. The evaporation crystallization module 5 is installed on the top side of the sandstone core 11. The position of the adjustable flow nozzle is adjusted to face the top of the sandstone core 11.

[0063] Step 3: Start the air compressor 41 of the solution driving module 4, and turn on the pressure closed-loop control system. The pressure closed-loop control system stably transports the solution in the solution storage device 42 to the solution storage tank 24 of the capillary transport unit 2 through the pipeline according to the set parameters. After the solution enters the solution storage tank 24, it quickly spreads on the metal mesh substrate 23, then rises under the capillary force of the gradient ceramic layer 22, and finally is transported directionally to the inside of the sandstone core 11 through the hydrophobic nano-coating 21.

[0064] Step 4: Place the water-permeable stone 33, pressure-bearing plate 32 and weight 31 in sequence on the top of the sandstone core 11 to form the axial loading module 3. According to the experimental requirements, the number of weights 31 is accurately increased or decreased to adjust the vertical stress to a set value within the range of 5-20 MPa. The weight 31 uniformly applies vertical stress to the sandstone core 11 through the pressure-bearing plate 32 and the water-permeable stone 33, forming a triaxial pressure environment together with the horizontal confining pressure inside the core packaging unit 1.

[0065] Step 5: Start the external gas source and introduce dry nitrogen gas into the top of the sandstone core 11 through the adjustable flow nozzle of the evaporation crystallization module 5. The humidity of the dry nitrogen gas is accurately adjusted to be within the range of 0-30% RH and the flow rate is within the range of 0.1-1.0 L / min using a mass flow meter, so that a stable local low-humidity area is formed on the top of the sandstone core 11, and the crystallization range is restricted to the central area on the top.

[0066] Step 6: Turn on the monitoring system of the annular ERT electrode 13 to monitor the fracture propagation trajectory of the sandstone core 11 in real time. The monitoring data is transmitted to the data processing center in real time and processed by resistivity inversion algorithm to generate a three-dimensional fracture distribution map, providing accurate quantitative basis for sandstone damage mechanism research.

[0067] Example 6 In another preferred embodiment, based on examples 3 and 5, this embodiment provides a controllable method for dynamic crystallization inside sandstone based on force-flow coupling driving, which uses the controllable system for dynamic crystallization inside sandstone based on force-flow coupling driving in example 3 to monitor the fracture in situ of sandstone. The specific steps are as follows: Step 1: Assemble the core package unit 1 according to the procedure in Step 1 of Method Example 5.

[0068] Step 2: Prepare the mixed solution according to the specified ratio 、 Mix the solution and inject it into the solution storage device 42 of the solution driving module 4. Connect the solution driving module 4 and the capillary transport unit 2 according to the layout, and connect the solution storage device 42 to the solution storage tank 24 of the capillary transport unit 2 through the pipeline. Place the core package unit 1 on the hydrophobic nano-coating 21 of the capillary transport unit 2, and ensure that the bottom of the sandstone core 11 is tightly attached to the hydrophobic nano-coating 21. Place the evaporation crystallization module 5 on the side of the top of the sandstone core 11, and adjust the position and angle of the adjustable flow nozzle.

[0069] Step 3: Start the air compressor 41 and the pressure closed-loop control system of the solution driving module 4. The pressure closed-loop control system accurately controls the pressure in the range of 0.1-0.5 MPa according to the characteristics of the mixed solution and the transportation requirements, and stably transports the mixed solution to the solution storage tank 24 of the capillary transport unit 2 through the pipeline. The solution in the capillary transport unit 2 passes through the metal mesh substrate 23 dispersion, the gradient ceramic layer 22 rising and the hydrophobic nano-coating 21 conduction in turn, and finally enters the inside of the sandstone core 11.

[0070] Step 4: Place the water-permeable stone 33, the pressure-bearing plate 32 and the weight 31 in sequence on the top of the sandstone core 11 to form the axial loading module 3. Through a special control system, set the dynamic pressure change mode of the weight 31, so that the weight 31 applies a dynamically changing vertical stress in the range of 5-20 MPa according to the preset program, simulating the stress change under actual geological conditions.

[0071] Step 5: Start the external gas source, and pass dry nitrogen gas into the top of the sandstone core 11 through the adjustable flow nozzle of the evaporation crystallization module 5. Use the mass flow meter to accurately adjust the humidity of the dry nitrogen gas in the range of 0-30% RH and the flow rate in the range of 0.1-1.0 L / min, to form a stable local low-humidity area, and constrain the crystallization range to the central area of the top of the sandstone core 11.

[0072] Step 6: Turn on the monitoring system of the annular ERT electrode 13 to monitor the fracture propagation trajectory of the sandstone core 11 under different mixed solution compositions and dynamic stress conditions in real time. The monitoring data are transmitted to the data processing center in real time, processed by the resistivity inversion algorithm, and a three-dimensional fracture distribution map is generated to analyze the influence of different solution compositions and dynamic stress on the damage mechanism of sandstone.

[0073] Compared with the prior art, the significant difference of the present application is that the in-situ monitoring of sandstone fractures and the controllable crystallization process are realized. The prior art often has problems such as uncontrolled crystallization position, distorted confining pressure control, blocked transport channel and limited monitoring means.

[0074] The present application realizes solution directional transportation and precise control of crystallization position through the gradient ceramic layer 22 and the hydrophobic nano coating 21; realizes uniform confining pressure loading and in-situ nondestructive monitoring of fractures through the cooperation of the weight 31 and the elastic film and the monitoring of the annular ERT electrode 13; solves the problem of transportation channel blockage and controls the crystallization range through the pressure closed-loop control of the solution driving module 4 and the dry nitrogen restriction of the evaporation crystallization module 5, and effectively improves the accuracy and reliability of the experiment.

[0075] In the preferred scheme, the core packaging unit 1 includes a sandstone core 11, the outer surface of the sandstone core 11 is coated with a molecular sieve composite film 12, the outer ring of the molecular sieve composite film 12 is provided with an annular ERT electrode 13, the outer surface of the annular ERT electrode 13 is coated with a silicone oil layer 14, and the outer periphery of the silicone oil layer 14 is coated with a FEP elastic film 15; the above settings effectively isolate the interference of the external environment on the sandstone core 11, the molecular sieve composite film 12 improves the permeability and selectivity of the core, the annular ERT electrode 13 facilitates resistivity imaging testing, the silicone oil layer 14 enhances the sealing property and reduces friction, and the FEP elastic film 15 provides good flexibility and chemical stability.

[0076] In the preferred scheme, the annular ERT electrode 13 includes a plurality of electrodes 131, the electrode array is attached to the outer surface of the molecular sieve composite film 12, is uniformly distributed along the circumference of the sandstone core 11, and is arranged in a four-quadrant symmetry to realize fracture positioning; the above settings can significantly improve the accuracy and efficiency of ERT monitoring and ensure accurate capture of internal fractures of the sandstone core 11; at the same time, the cooperative work between the electrodes 131 can provide real-time feedback of dynamic changes of the fractures, and provide reliable data support for geological exploration and oil and gas resource development.

[0077] In the preferred scheme, the capillary transportation unit 2 is used to realize directional transportation of the solution to the inside of the core packaging unit 1, and includes a solution storage tank 24, the inside of the solution storage tank 24 is provided with a metal mesh substrate 23, the top of the metal mesh substrate 23 is installed with a gradient ceramic layer 22, the top of the gradient ceramic layer 22 is provided with a hydrophobic nano coating 21, the top of the hydrophobic nano coating 21 places the core packaging unit 1, and the bottom of the sandstone core 11 is closely attached to the hydrophobic nano coating 21; the above settings ensure that the solution can penetrate along the metal mesh substrate 23 and the gradient ceramic layer 22 to the hydrophobic nano coating 21, and be directionally guided to the bottom of the sandstone core 11 by using the hydrophobic property of the coating, realizing efficient and uniform solution transportation and enhancing the accuracy and stability of experimental control.

[0078] In the preferred scheme, the metal mesh substrate 23 is provided with a plurality of holes, the hole bottom 232 is communicated with the solution storage tank 24, and the hole top 231 is communicated with the gradient ceramic layer 22; the gradient ceramic layer 22 is provided with a plurality of tapered holes, the large part 222 of the tapered hole is communicated with the hole top 231 of the metal mesh substrate 23, and the small part 221 of the tapered hole is communicated with the hydrophobic nano coating 21; the above arrangement enables the solution to smoothly enter the tapered hole of the gradient ceramic layer 22 from the solution storage tank 24 through the metal mesh substrate 23, and flow upward along the tapered hole to the hydrophobic nano coating 21, effectively improving the penetration efficiency and uniform distribution of the solution, and enhancing the performance of the overall structure.

[0079] In the preferred scheme, the monitoring data of the annular ERT electrode 13 is processed by resistivity inversion algorithm to generate a three-dimensional fracture distribution map, providing a quantitative basis for sandstone damage mechanism research; the above arrangement effectively improves the accuracy and efficiency of fracture detection, and further analyzes the fracture expansion trend in combination with the geomechanical model, providing a scientific basis for engineering stability evaluation and disaster prevention.

[0080] In the preferred scheme, the axial loading module 3 includes a water permeable stone 33, which is placed on the top of the sandstone core 11 of the core packaging unit 1, the top of the water permeable stone 33 is provided with a pressure bearing plate 32, and the top of the pressure bearing plate 32 is placed with a weight 31; the above arrangement applies pressure to the pressure bearing plate 32 through the weight 31, and then uniformly transmits the pressure to the sandstone core 11 through the water permeable stone 33, realizes axial loading, simulates the vertical stress suffered by the underground rock stratum, and thus performs performance tests such as permeability or strength of the core.

[0081] In the preferred scheme, the solution driving module 4 includes a solution storage device 42, which is communicated with the solution storage tank 24 of the capillary transport unit 2 through a pipeline, and is communicated with an air compressor 41 through a pipeline; the above arrangement enables the air compressor 41 to pressurize the solution in the solution storage device 42, so as to smoothly flow into the solution storage tank 24 of the capillary transport unit 2, ensuring stable supply of the solution and normal operation of the system.

[0082] In the preferred scheme, the evaporation crystallization module 5 is communicated with an external gas supply system and is provided with an adjustable flow nozzle, through which dry gas is introduced into the top of the sandstone core 11, and the dry gas is nitrogen; the above arrangement ensures that the moisture inside the sandstone core can be efficiently and uniformly evaporated and removed, and at the same time, as an inert gas, nitrogen effectively avoids possible chemical effects on the sandstone core during the evaporation process, ensuring the accuracy of the experimental results.

[0083] In the preferred embodiment, the molecular sieve composite membrane 12 is made of PTFE and covers the core 11. The molecular sieve absorbs water vapor to reduce electrode interference, while the composite membrane is corrosion-resistant, extending its lifespan. The silicone oil layer 14, under pressure, pushes the FEP membrane 15 outward, eliminating boundary stress concentration. The FEP elastic membrane 15 contacts the thick encapsulating silicone oil medium and transmits the confining pressure through contraction and deformation. This arrangement effectively improves the sealing and stability of the packaging structure. Furthermore, the silicone oil layer 14 has excellent thermal conductivity, which helps dissipate heat and ensures stable operation of the device in high-temperature environments. The high elasticity of the FEP membrane 15 ensures a good fit under varying pressure conditions.

[0084] In the preferred embodiment, the hydrophobic nanocoating 21 adopts a super-hydrophobic nanostructure, which prevents blockage and conducts the solution to the interior of the sandstone through submicron pores; the above setting can ensure that the coating forms a uniform and lasting protective layer on the surface of the sandstone, effectively resisting water penetration, while not hindering the natural breathing of the sandstone, maintaining its good air permeability and structural stability.

[0085] In the preferred solution, the pore size gradient range of the gradient ceramic layer 22 is 100 μm (pore size of the large conical hole 222) to 10 μm (pore size of the small conical hole 221), ensuring the directional transport efficiency of the solution; the above setting can greatly improve the penetration rate and uniformity of the solution in the gradient ceramic layer. At the same time, the gradual design of the conical hole structure effectively reduces the fluid resistance, further ensuring the overall transmission efficiency of the system.

[0086] In the preferred solution, the pressure range of the weight 31 is 5~20MPa, and the pressure value is adjusted by increasing or decreasing the number of weights; the above setting ensures the flexibility and accuracy of the pressure conditions during the experiment, meets the performance testing requirements of different materials under different pressure environments, and effectively improves the reliability and practicality of the experimental data.

[0087] In the preferred solution, the solution driving module 4 is provided with a pressure closed-loop control system for controlling the solution in the solution storage tank to be replenished into the solution storage tank 24, so as to realize timely replenishment of the solution storage tank 24, and the air compressor 41 is connected to the solution storage tank 24 of the solution storage device 2 through a pipeline to realize a stable supply of solution; the above settings ensure the efficient operation of the system; at the same time, the solution driving module 4 is also equipped with an intelligent sensor to monitor the liquid level of the solution storage tank 24 in real time. Once the liquid level is lower than the preset value, the replenishment mechanism is automatically triggered to maintain the stability and adequacy of the solution reserves.

[0088] In the preferred scheme, the pressure regulating range of the pressure closed-loop control system is 0.1-0.5 MPa, and the accuracy is ±0.01 MPa; the above settings ensure that the system can stably operate in a wide and accurate pressure range, effectively cope with various working condition requirements, improve the stability and response speed of the overall control, and lay a solid foundation for long-term and efficient operation of the equipment.

[0089] In the preferred scheme, the evaporation crystallization module 5 can adjust the flow nozzle towards the top of the sandstone core 11 at a certain distance from the surface of the sandstone core 11, and sprays dry nitrogen to form a local low-humidity area at the top of the sandstone core 11 by controlling the humidity and flow of the gas, so as to restrict the crystallization range to the central area at the top; the above settings aim to promote the efficient evaporation and concentrated crystallization of solutes in the solution at the top of the sandstone core, while avoiding unnecessary impact on the overall structure of the core, ensuring the accuracy and repeatability of the experimental results, and providing strong support for subsequent geological storage or resource development research.

[0090] In the preferred scheme, the humidity of the dry nitrogen ranges from 0 to 30% RH, and the flow rate ranges from 0.1 to 1.0 L / min, which is accurately controlled by a mass flow meter; the above settings ensure a low-humidity and stable airflow in the experimental environment, effectively preventing the sample from getting wet, and at the same time, the high-precision regulation of the mass flow meter makes the experimental conditions highly repeatable, improving the accuracy and reliability of the data.

[0091] In summary, the present application proposes a controllable system and method for dynamic crystallization in sandstone based on force-flow coupling driving, which effectively solves the technical problems of precise simulation of sandstone fracture evolution and dynamic crystallization process in the field of geotechnical engineering experiment monitoring.

[0092] In view of the four core defects of uncontrollable crystallization position, distorted confining pressure control, blocked transport channel and limited monitoring means in the prior art, the present application successfully overcomes the limitations of traditional experimental devices, and provides a reliable experimental platform for the research on fracture evolution in complex engineering scenarios such as salted soil area groundwater seepage-crystallization damage and shale gas reservoir fracturing fluid erosion.

[0093] In the system design, a comprehensive system integrating core packaging, solution delivery, stress application, crystallization restriction and fracture monitoring is constructed, the overall architecture is novel, and the cooperative work of solution directional delivery and precise control of crystallization position, confining pressure generation and fracture monitoring is realized. Among them, the core packaging unit 1 adopts PTFE-molecular sieve composite membrane 12 to cover the sandstone core 11, which has the functions of reducing electrode interference and prolonging service life, and the annular ERT electrode 13 is arranged in four quadrants, realizing millimeter-level fracture positioning; the gradient ceramic layer 22 of the capillary transport unit 2 has a gradually changing aperture, which cooperates with the metal mesh base and the hydrophobic nano coating to realize efficient directional delivery of the solution; the evaporation crystallization module 5 forms a local low-humidity area by introducing dry nitrogen to restrict the crystallization range.

[0094] In technical means, the annular ERT electrode 13 monitors the data to generate a three-dimensional fracture distribution map, providing a quantitative basis for research, and the pressure closed-loop control system of the solution driving module 4 can accurately control the solution supply. Through force-flow coupling driving, the gradient ceramic layer 22 and the hydrophobic nano coating 21 solve the problem of uncontrollable crystallization position, the weight 31 and the elastic film are cooperatively loaded, and the annular ERT electrode 13 is used to improve the confining pressure control and monitoring means, and the pressure closed-loop control and dry nitrogen restriction are used to solve the problem of transport channel blockage and control the crystallization range. Each unit works together to form an organic whole.

[0095] In addition, the present application can also study the influence of different factors on the damage mechanism of sandstone by changing the solution composition and stress conditions, expand the experimental research range and depth, and provide more comprehensive technical means for related research of sandstone.

Claims

1. A controllable system for dynamic crystallization of sandstone based on force-fluid coupling, characterized by: The invention comprises a core packaging unit (1) for realizing confining pressure generation and crack monitoring and a solution driving module (4) for controlling solution injection. The solution storage device (42) of the solution driving module (4) is connected to the solution storage tank (24) in the capillary transport unit (2) through a pipeline, providing a solution source for the capillary transport unit (2). The capillary transport unit (2) directionally transports the solution to the sandstone core (11) of the core packaging unit (1). An axial loading module (3) is provided on the sandstone core (11) to provide vertical stress. An evaporation crystallization module (5) is provided on the top side of the sandstone core (11). The units work together to realize in-situ monitoring of sandstone cracks and controllable crystallization process.

2. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 1 is characterized in that: The core packaging unit (1) comprises a sandstone core (11), the outer surface of the sandstone core (11) is coated with a molecular sieve composite membrane (12), an annular ERT electrode (13) is provided on the outer ring of the molecular sieve composite membrane (12), the outer surface of the annular ERT electrode (13) is coated with a silicone oil layer (14), and the outer periphery of the silicone oil layer (14) is coated with an FEP elastic membrane (15).

3. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 2 is characterized in that: The annular ERT electrode (13) includes a plurality of electrodes (131), the electrode array being attached to the outer surface of the molecular sieve composite membrane (12), and being evenly distributed along the circumference of the sandstone core (11), with a four-quadrant symmetrical layout to achieve crack positioning.

4. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 3 is characterized by: The capillary transport unit (2) is used to realize the directional transport of the solution into the core packaging unit (1), and comprises a solution storage tank (24). A metal mesh base (23) is provided inside the solution storage tank (24). A gradient ceramic layer (22) is installed on the top of the metal mesh base (23). A hydrophobic nano coating (21) is provided on the top of the gradient ceramic layer (22). The core packaging unit (1) is placed on the top of the hydrophobic nano coating (21). The bottom of the sandstone core (11) is in close contact with the hydrophobic nano coating (21).

5. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 4 is characterized in that: The metal mesh base (23) is provided with a plurality of holes, the hole bottoms (232) are connected to the solution storage tank (24), and the hole tops (231) are connected to the gradient ceramic layer (22); the gradient ceramic layer (22) is provided with a plurality of conical holes, the large parts (222) of the conical holes are connected to the hole tops (231) of the metal mesh base (23), and the small parts (221) of the conical holes are connected to the hydrophobic nano coating (21).

6. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 5 is characterized in that: The monitoring data of the annular ERT electrode (13) is processed by a resistivity inversion algorithm to generate a three-dimensional crack distribution map, providing a quantitative basis for the study of sandstone damage mechanism.

7. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 6, characterized in that: The axial loading module (3) comprises a permeable stone (33), which is placed on the top of the sandstone core (11) of the core packaging unit (1), a pressure plate (32) is provided on the top of the permeable stone (33), and a weight (31) is placed on the top of the pressure plate (32).

8. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 7 is characterized in that: The solution driving module (4) comprises a solution storage device (42), the solution storage device (42) being connected to the solution storage tank (24) of the capillary transport unit (2) via a pipeline, and the solution storage device (42) being connected to an air compressor (41) via a pipeline.

9. The controllable system for dynamic crystallization of sandstone based on force-fluid coupling drive according to claim 8, characterized in that: The evaporation crystallization module (5) is connected to an external gas supply system and is provided with an adjustable flow nozzle, through which dry gas is introduced into the top of the sandstone core (11), and the dry gas is nitrogen.

10. A method for controlling dynamic crystallization of sandstones based on force-fluid coupling is a method for in-situ monitoring of sandstone fractures using the controllable system for dynamic crystallization of sandstones based on force-fluid coupling as described in claim 9, characterized in that: The following steps are involved: Step 1: Encapsulate the sandstone core (11) in the core encapsulation unit (1); Step 2: connect the solution driving module (4) and the capillary transport unit (2) according to the arrangement shown in the figure, place the core encapsulation unit (1) in the liquid storage tank (24) of the capillary transport unit (2), and set the evaporation crystallization module (5) on the top side of the sandstone core (11); Step 3: Start the air compressor (41) of the solution driving module (4) to directionally transport the solution in the solution storage device (42) to the interior of the sandstone through the capillary transport unit (2); Step 4: placing an axial loading module (3) on top of the sandstone core (11) to apply vertical stress, and the weight (33) uniformly applies pressure to the sandstone core (11) through the pressure plate structure (32) and the permeable stone (31); Step 5: Start the external gas source, introduce dry nitrogen through the evaporation crystallization module (5) to constrain the crystallization range, and spray dry nitrogen toward the top of the sandstone core (11) through the adjustable flow nozzle; Step 6: Monitor the crack propagation trajectory in real time through the annular ERT electrode (13) and generate a three-dimensional crack distribution map.

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