Crack tracking and pressure feedback physical simulation test system and use method

Abstract

The present invention provides a crack tracking and pressure feedback physical simulation test system and a test use method. The test system comprises: a similar material model used for simulating rock mass in a mining area, wherein a grating and an optical fiber used for acquiring a stress-strain signal are arranged in a horizontal hole, the grating and the optical fiber are connected to a static stress-strain acquisition instrument; a test bench used for placing the similar material model; and hydraulic devices used for applying stress to the similar material model, wherein the hydraulic devices include a top hydraulic device and a lateral hydraulic device, the top hydraulic device is arranged at the top of the similar material model, and the lateral hydraulic device is arranged at a side surface of the similar material model. In the present invention, the propagation of fractures during a fracturing process of an ore body can be truly reflected, and on the basis of test results, optimal design can be made for the in-situ fracturing range of the ore body, a rock mass cracking mode, and a fluid pressure, thereby minimizing the disturbance to the surrounding rock while ensuring mining recovery efficiency, and thus ensuring the safe and stable progression of projects.

Description

Crack Tracking and Pressure Feedback Physical Simulation Test System and its Usage Technical Field

[0001] This invention relates to the field of gas fracturing technology, and more particularly to a crack tracking and pressure feedback physical simulation test system and its usage method. Background Technology

[0002] In recent years, gas fracturing, as a novel fracturing method without explosives or water, has emerged as a green, environmentally friendly, and highly efficient approach to rock mass fracturing due to its unique advantages in flow, transport, and penetration. However, existing experimental equipment and methods primarily analyze whether pressure values ​​can induce rock mass fracturing, and cannot provide experimental equipment for tracking crack initiation and pressure feedback.

[0003] Traditional mine fracturing monitoring mainly relies on fiber optic grating sensors, which are usually placed at or near high-pressure fluid or gas fracturing wells. They can only obtain single-point pressure data and cannot comprehensively monitor the entire process and area of ​​ore body mining. Furthermore, they are difficult to monitor and track fracturing cracks in real time, and it is even more difficult to achieve real-time feedback on the fracturing status, which has limitations.

[0004] Patent CN202410016049.X discloses a real-time fracturing monitoring system based on fiber optic distributed sensing. This device receives and analyzes feedback optical signals from high-pressure fluids or gases to sense and monitor the flow rate of the flowback fluid, monitor temperature and pressure parameters, identify abnormal signals to monitor pressure parameters within the monitoring area, and issue an alarm when an abnormal signal is detected. It then controls the pressurization pressure based on the flow rate of the flowback fluid, thus achieving automatic control. However, this device does not yet include crack tracking during the fracturing process, acoustic emission fracture signal monitoring and feedback devices, or post-processing methods for optimizing the in-situ fracture range, rock mass fracturing mode, and fluid pressure based on the monitoring results.

[0005] Research on the mechanisms of crack propagation during hydraulic fracturing is still in its early stages. Especially in engineering fracturing operations, a complete theoretical framework for crack direction and fracture extent is lacking, requiring guidance and data support from laboratory tests. By adjusting pressure values ​​based on feedback information from injected pressure and rock mass fracturing during laboratory tests, we can not only study the mechanisms of high-pressure fluid-induced rock mass fracturing but also propose various countermeasures and optimize fracturing effects for field operations. Summary of the Invention

[0006] This invention discloses a crack tracking and pressure feedback physical simulation test system and its usage method. By real-time monitoring of crack initiation and propagation in the model and controlling the fracturing technology through a feedback system, it solves the technical challenge of accurately controlling the crack range. The constructed crack tracking and pressure feedback physical simulation test device can achieve a scale upgrade from laboratory to field, combining the crack propagation location and fracture pressure value obtained from similar material tests in the laboratory with numerical analysis simulation results, and applying them to the monitoring of the failure stress threshold and the delineation of fracture danger zones. This provides services for scientific research on mechanisms and applications.

[0007] The apparatus of the present invention is as follows:

[0008] A crack tracking and pressure feedback physical simulation test system includes:

[0009] A similar material model is used to simulate the rock mass in the mining area; the similar material model has a simulated borehole inside, which is a horizontal borehole, and a perforation cluster is connected around the horizontal borehole. A sleeve is installed inside the simulated borehole, and a fracturing fluid delivery mechanism is connected to the upper part of the sleeve. The fracturing fluid delivery mechanism is connected to a gas storage tank; a fiber optic grating sensor for collecting stress and strain signals is installed inside the horizontal borehole, and the fiber optic grating sensor is connected to a static stress and strain acquisition instrument; an acoustic emission sensor is installed on the surface of the similar material model to monitor and collect fracture signals.

[0010] A test bench for placing similar material models;

[0011] A hydraulic device for applying stress to a similar material model; the hydraulic device includes a top hydraulic device and a side hydraulic device, the top hydraulic device being disposed on the top of the similar material model and the side hydraulic device being disposed on the side of the similar material model.

[0012] This invention also provides a crack tracking and pressure feedback physical simulation test method, implemented based on any of the above-mentioned crack tracking and pressure feedback physical simulation test systems, comprising the following steps:

[0013] S1. Based on the geological conditions of the mining area, prepare a rock mass model of the mining area, place the model on the test system platform, and attach fiber optic grating sensors and acoustic emission sensors to the model.

[0014] S2. Activate the top hydraulic device and the side hydraulic device to apply pressure to the model to simulate the stress of the on-site geology;

[0015] S3. Start the gas storage tank to inject liquid fracturing gas and pressurize it. The liquid gas is then transported to the perforation cluster inside the capsule in the similar material model through the fracturing fluid delivery mechanism. At this time, cracks are generated in the similar material model around the perforation cluster. After the cracks have fully developed, ceramic is added as a proppant to prevent the cracks from closing. At the same time, a fluorescent agent is added to track the cracks. After loading is completed and the proppant fixes the cracks, a complete image of the cracks is obtained by drilling and imaging.

[0016] S4. A fiber optic grating sensor attached to the surface of the model collects stress and strain signals, and a static stress and strain acquisition instrument connected to the fiber optic grating sensor collects fracturing information; the fracturing information includes the tensile strength and uniaxial compressive strength of the rock.

[0017] S5. Acoustic emission sensors installed on the model surface collect the model fracture signal during the fracturing process and send it to the acoustic emission instrument to realize the location and tracking of fractures during the model fracturing process, and to locate and monitor the fracture area in the model.

[0018] S6. Based on the fracturing information monitored by the acoustic emission system, damage variables are derived, and a rock damage model is established in the data processing terminal computer based on the damage variables.

[0019] Furthermore, S1 specifically includes the following steps:

[0020] Based on the on-site geological conditions, rock samples from the mining area were tested to obtain the mechanical parameters of the rock samples;

[0021] The mechanical parameters of the rock sample are set as the mechanical parameters of the similar material model, and the cementing material and aggregate of the similar material are selected based on the mechanical parameters of the similar material model;

[0022] Similar material models were prepared using cementitious materials and aggregates of similar materials.

[0023] Furthermore, the mechanical parameters include density, compressive strength, Poisson's ratio, and elastic modulus.

[0024] Furthermore, the complete image of the crack is used to create a deep learning dataset and train a model. The specific steps are as follows:

[0025] In the complete image of the crack, the object edge is defined by multi-segment coils to obtain the closed boundary, and a labeled dataset is created. The dataset is randomly divided into a training set and a validation set in an 8:2 ratio and put into an image segmentation neural network for training and validation to achieve image learning and segmentation.

[0026] Specifically, the steps include the following:

[0027] Apply rock damage models to actual field operations; deduce possible scenarios in actual fracturing operations based on complete images of fractures and fracturing information, and optimize fracturing operation design accordingly;

[0028] Based on fracturing information, it is determined whether the rock has undergone tensile or shear failure, where the variable for tensile failure is F. s The shear failure variable is F. t F s =-σ3-f s0 (1)

[0029] Among them, f s0 f is the tensile strength of the rock. t0 σ1 represents the uniaxial compressive strength of the rock, in MPa; σ2 and σ3 represent the major and minor principal stresses of the rock, in MPa. The friction angle within the rock mass; the tensile direction is defined as negative;

[0030] The damage variable D of the rock is defined using tensile failure variables and shear failure variables:

[0031] Where, ε s0 ε is the maximum tensile strain of the rock. t0 ε is the maximum compressive strain of the rock, in MPa; ε1 and ε are the principal strains of the rock, and D is the damage variable of the rock;

[0032] Based on the elastoplastic damage theory, a rock damage model is established: E=(1-D)E0 (4)

[0033] In the formula, E is the real-time elastic modulus of the rock, and E0 is the initial modulus of the rock;

[0034] The statistical method for the failure zone of rocks in similar material models is as follows:

[0035] The tensile failure variables, shear failure variables, damage variables, and rock damage model are imported into the Comsol Multiphysics (version 5.4) numerical analysis program. The tensile strength and uniaxial compressive strength of the rock in the similar material model are defined. Other rock parameters obtained from laboratory tests are input into the Comsol Multiphysics (version 5.4) numerical analysis program to calculate the plastic deformation and failure curve of the similar material model and obtain the damage factor D.

[0036] The rock region with a damage factor D greater than 0 is defined as the damaged zone, and the region with a damage factor D equal to 0 is defined as the non-damaged safe zone.

[0037] The obtained damage factor D was applied to actual field work, and the damaged area of ​​the rock was reflected by updating the elastic modulus of the rock in real time.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] This invention can realistically reflect the relationship between crack propagation and injected gas pressure during the gas-induced fracturing process in hard rock masses. It can simulate the fracturing phenomenon of hard and brittle rock masses in engineering fields such as pillar recovery under high stress, oil and gas injection and production in areas prone to casing damage, and tunnel excavation under complex geological conditions. Based on the test results, it can optimize the design of actual fracturing operations, minimize the disturbance to the surrounding rock while ensuring safe excavation, and ensure the safe and stable progress of the project. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 is a diagram of the test system of the present invention.

[0042] Figure 2 is the left view of the AA section of Figure 1.

[0043] Figure 3 is a top view of the BB section of Figure 1.

[0044] Figure 4 is a front view of the test bench of the present invention.

[0045] Figure 5 is a similar material model diagram of an embodiment of the present invention.

[0046] In the diagram: 1. Similar material model; 2. Test bench; 3. Top hydraulic device; 4. Lateral hydraulic device; 5. Horizontal hole; 6. Fiber optic grating sensor; 7. Double-sided partition; 8. Encapsulated capsule; 9. Perforation cluster; 10. Acoustic emission sensor; 11. Gas storage tank; 12. Fracturing fluid delivery mechanism; 13. Acoustic emission instrument; 14. Data processing terminal computer; 15. Counterweight; 16. Support platform; 17. Ground surface. Detailed Implementation

[0047] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0050] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0051] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0052] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0053] This invention develops an indoor physical simulation test system for crack tracking and pressure feedback control during the fluid pressure fracturing process in hard and brittle rock masses. The system includes strain sensors, stress sensors, and a computer with built-in simulation programs.

[0054] First, a similar material model is prepared based on similarity theory, and fiber optic grating sensors are arranged in the flow pressure fracturing region of the similar material model. Then, boundary loading, including the top and sides, is performed using a similar material test bench. Third, a proppant is added to fix the gas diffusion path after fracturing, and a fluorescent agent is added to track the crack. Finally, after loading is completed, the strain and failure of the overall test model are observed, and the crack morphology is observed through drilling and imaging.

[0055] A crack tracking and pressure feedback physical simulation test system, as shown in Figures 1-4, includes:

[0056] A similar material model 1 is used to simulate the rock mass in the mining area; the similar material model 1 has a simulated borehole 5 inside; the double-sided partition 7 installed on both sides of the similar material model contains a capsule 8 in the middle, and the horizontal borehole 5 inside the capsule 8 is surrounded by a perforation cluster 9; a lateral fracturing delivery device is connected to one end of the horizontal borehole 5; a sleeve is installed inside the simulated borehole, and a fracturing fluid delivery mechanism 12 is connected to the upper part of the sleeve, which is connected to a gas storage tank 11; a fiber optic grating sensor 6 for collecting stress and strain signals is installed inside the horizontal borehole 5, and the fiber optic grating sensor 6 is connected to a static stress and strain acquisition instrument; acoustic emission sensors 10 are evenly distributed on the surface of the similar material model, and the acoustic emission sensors 10 are connected to an acoustic emission instrument 13.

[0057] In the perforation cluster 9, the perforations are directed at the oil or gas layer, delivering gas or liquid at a certain pressure to create radial holes of a certain depth within the formation. This allows for the collection of oil and gas from the formation or oil / gas layer to the surface via tubing or casing. A cluster refers to a group of interconnected perforating guns. These perforating guns are connected in series or parallel to allow for multiple perforation operations in the same well section, thereby increasing production capacity. Here, the "perforation cluster" refers to rows of perforations around the horizontal well used for introducing fracturing fluid. In one embodiment, the fracturing fluid delivery mechanism 12 is a SNIPER-Ⅱ type directional hydraulic jet for fracturing, and the static stress-strain acquisition instrument is a DH3816N with 36 channels.

[0058] The test platform 2 is used to place the similar material model 1, and counterweights 15 are placed on both sides of the test platform;

[0059] The model is placed on the platform 16 of the test bench 2, and the test bench 2 is placed on the horizontal ground surface 17. A hydraulic device is used to apply stress to the similar material model. The hydraulic device includes a top hydraulic device 3 and a side hydraulic device 4. The top hydraulic device 3 is located on the top of the similar material model 1, and the side hydraulic device 4 is located on the side of the similar material model 1.

[0060] This invention also provides a crack tracking and pressure feedback physical simulation test method, which is implemented based on a crack tracking and pressure feedback physical simulation test system. The principle is shown in Figure 2, and includes the following steps:

[0061] S1. Based on the on-site geological conditions, rock samples from the mining area are tested to obtain their mechanical parameters, such as density, compressive strength, Poisson's ratio, and elastic modulus. According to the three similarity theorems in the principle of similarity, the mechanical parameters of the similar material model are set. Based on this, the cementing materials and aggregates for the similar material are selected. Commonly used cementing materials include gypsum, cement, rosin, paraffin wax, lime, and water glass. Commonly used aggregates include sand, mica, iron powder, clay, sawdust, and barite powder. Based on the mechanical properties of the target rock sample, one or more similar material models are selected to prepare the model. Generally, multiple model samples are obtained through different proportions. Mechanical tests are conducted on the samples to test the mechanical parameters. Finally, the final proportion of the similar material is determined from the multiple proportion samples. On the similar material test bench, the model of the hard and brittle rock mass is prepared through steps such as pre-setting mold holes, filling, curing, and demolding. During the model casting process, horizontal holes and perforation clusters are pre-set using pre-embedded molds.

[0062] S2. Simulate the actual wellbore setup in engineering projects. Fiber optic sensors are placed in horizontal boreholes to collect stress and strain signals, and fracturing information is collected through a connected static stress and strain acquisition instrument. The fracturing zone is determined based on the on-site engineering conditions. The top hydraulic system and lateral hydraulic system are activated to apply pressure to a similar material model to simulate the stress in the on-site geological conditions.

[0063] S3. The gas storage tank is activated, injecting liquid fracturing gas and pressurizing it. The liquid gas is then delivered to the perforation cluster via the fracturing fluid delivery mechanism. At this time, cracks appear in the similar material model around the perforation cluster. These cracks are generated by the liquid fracturing delivered from the perforation cluster to the similar material model, resulting in fracturing near the perforation cluster. After the cracks have fully developed, ceramic is added as a proppant to prevent crack closure, and a fluorescent agent is added to track the cracks. After loading is complete and the proppant has fixed the cracks, a complete image of the cracks is obtained using a borehole camera.

[0064] S4. A fiber optic grating sensor acquires stress-strain signals, and a static stress-strain acquisition instrument connected to the fiber optic grating sensor collects fracturing information; the fracturing information includes rock tensile strength and uniaxial compressive strength.

[0065] S5. Location and tracking of fractures in similar material models during fracturing: Acoustic emission sensors installed on the model surface are used to collect fracture signals during fracturing and send them to an acoustic emission instrument to locate and monitor the fracture area in the model.

[0066] S6. Based on the fracturing information monitored by the acoustic emission system, damage variables are obtained, and a rock damage model is established in the data processing terminal computer based on the damage variables.

[0067] S7. Apply the rock damage model to actual field work;

[0068] S8. Based on the complete image of the fracture and fracturing information, deduce the possible situations in actual fracturing operations and optimize the fracturing operation design accordingly.

[0069] S5 and S6 specifically include: combining the tensile criterion and Mohr's Coulomb's law to determine whether the rock has experienced tensile or shear failure. The tensile failure variable and the shear failure variable can be expressed as: F s and F t F s =-σ3-f s0 (1)

[0070] Among them, f s0 f represents the tensile strength of the rock (the "rock" in the similar material model). t0 σ1 represents the uniaxial compressive strength of the rock, in MPa; σ1 and σ3 represent the major and minor principal stresses of the rock, in MPa; the tensile direction is defined as negative.

[0071] The damage variable D of the rock is defined using tensile failure variables and shear failure variables:

[0072] In the formula, ε s0 ε is the maximum tensile strain of the rock. t0 ε is the maximum compressive strain of the rock, in MPa; ε1 and ε are the principal strains of the rock; and D is the damage variable of the rock.

[0073] Based on the elastoplastic damage theory, a rock damage model is established: E=(1-D)E0 (4)

[0074] In the formula, E is the real-time elastic modulus of the rock, and E0 is the initial modulus of the rock.

[0075] The statistical method for determining the failure zone of rock in a similar material model is as follows: First, formulas 1, 2, 3, and 4 are entered into the large-scale finite element software COMSOL numerical analysis program. The tensile strength and uniaxial compressive strength of the "rock" in the similar material model are defined. Other rock parameters obtained from laboratory tests, such as the internal friction angle, are input into the COMSOL numerical analysis program to calculate the plastic deformation and failure curve of the similar material model, thus obtaining the damage factor D. The rock region with a damage factor D greater than 0 is defined as the failure zone, and the region with a damage factor D equal to 0 is defined as the non-failure safe zone. The obtained damage factor D is applied to actual field work, and the rock's elastic modulus is updated in real time to reflect the rock's damage zone.

[0076] The main purpose of similar material testing is to deduce the possible scenarios in actual engineering by analyzing the strain of the model, and to optimize and adjust the project accordingly. Through the four steps described, the strain and cracking of the similar material model after loading can be obtained. This allows for the deduction of the actual cracking conditions that may occur in the project. Based on this, adjustments and optimizations can be made to the fracturing design, finding a balance between safety and economy, controlling the deformation range as much as possible, and ensuring fracturing is carried out under safe conditions.

[0077] Example

[0078] An experiment on the relationship between gas-induced fracturing pressure and fracture propagation during the recovery process of a column in a panel of an underground metal mine:

[0079] 1) Based on the actual geological parameters of the ore body between the disk and the column, a similar material model of the ore body between the disk and the column is prepared by combining similarity theorems.

[0080] ①Based on the hard and brittle characteristics and mechanical parameters of the column rock in a certain underground metal mine, see Table 1, physical simulation tests were carried out using cement as the main material for similarity.

[0081] Table 1. Rock Mass Physical and Mechanical Parameters

[0082] ②Based on the geometric dimensions (2.4m*1.2m*0.2m) of the test bench (loading area) and the structural parameters of the disk area, the geometric similarity ratio C of this test is... L =200, density similarity ratio Cγ=2, stress similarity ratio C σ =C L ·C γ =400, the dimensionless similarity ratio is 1 (strain ratio, Poisson's ratio, friction angle ratio), that is, Cε=Cμ=Cφ=1. At the same time, the size of the model, the similar test materials, and the field prototype are geometrically similar, and the initial and boundary conditions are similar, see Figure 5.

[0083] ③ Under the premise of satisfying the similarity ratio, design the similar material ratio and use mechanical tests to determine its mechanical parameters.

[0084] 2) After the similar material model is prepared, place the similar material model on the test bench (specific location), and install stress, strain, and acoustic emission sensors near the fracturing borehole area on the model.

[0085] 3) Start the hydraulic device on the top and side of the test bench to apply pressure to the prepared similar material model to simulate the stress conditions of the geological site of the column in the mine panel. After 6 hours of loading, and once the internal stress field of the similar material has stabilized, the subsequent test will begin.

[0086] 4) According to the panel mining design plan, each stope is mined one by one in the order of alternating mining and cementing and tailings backfilling is carried out until the entire panel is mined. After the model test is completed, it is left to stand still for 6 hours to allow the internal stress field of similar materials to be rebalanced.

[0087] 5) According to the panel pillar recovery design plan, fluid fracturing boreholes are laid out, and liquid fracturing gas is injected through the gas storage tank. After the fractures have fully developed, proppant and fluorescent agent are added to track the fracture rupture. After loading is completed and the proppant fixes the fractures, the complete image of the fracture is obtained by using borehole cameras. The initiation pressure and the expansion range of microcracks of the model are determined by acoustic emission monitoring equipment, and the panel stress is obtained by using a fiber optic stress monitoring system.

[0088] 6) Collect fracturing information of similar material models using fiber optic stress and strain acquisition instruments and acoustic emission instruments, including parameters such as rock tensile strength, uniaxial compressive strength, acoustic emission ring count, and energy release value, as well as fracturing images.

[0089] 7) Based on the fracturing information obtained from the similar material model, and combined with the damage variables of the similar material model calculated through numerical analysis and similarity theory, a field rock damage model for the column in the mine panel is established.

[0090] 8) Based on the complete fracture images and fracturing information obtained in steps 4-6, deduce the possible scenarios of the columnar rock mass in the mining panel during actual fracturing operations. Guide actual mining operations on-site based on the derived actual fracturing feedback mechanism; and conduct targeted optimization of fracturing operation design.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A crack tracking and pressure feedback physical simulation test system, characterized in that, include: A similar material model is used to simulate the rock mass in the mining area; the similar material model has simulated boreholes inside, which are horizontal holes, and a perforation cluster is connected around the horizontal holes. A sleeve is installed inside the simulated boreholes, and a fracturing fluid delivery mechanism is connected to the upper part of the sleeve. The fracturing fluid delivery mechanism is connected to a gas storage tank; a fiber optic grating sensor for collecting stress and strain signals is installed inside the horizontal holes, and the fiber optic grating sensor is connected to a static stress and strain acquisition instrument; an acoustic emission sensor for monitoring model fracture signals is placed on the surface of the similar material model; bidirectional partitions placed on the front and rear sides of the model and a sealing capsule in the middle of the bidirectional partitions are used to encapsulate the similar material model; A test bench for placing similar material models; A hydraulic device for applying stress to a model; the hydraulic device includes a top hydraulic device and a side hydraulic device, the top hydraulic device being disposed on the top of the similar material model and the side hydraulic device being disposed on the side of the similar material model.

2. A crack tracking and pressure feedback physical simulation test method, implemented based on the crack tracking and pressure feedback physical simulation test system described in claim 1, characterized in that, Includes the following steps: S1. Based on the geological conditions of the mining area, prepare a rock mass model of the mining area, place the model on the test system platform, and attach fiber optic grating sensors and acoustic emission sensors to the model. S2. Activate the top hydraulic device and the side hydraulic device to apply the desired pressure to the model; S3. Start the gas storage tank to inject liquid fracturing gas and pressurize it. The liquid gas is then transported to the perforation cluster inside the capsule in the similar material model through the fracturing fluid delivery mechanism. At this time, cracks are generated in the model around the perforation cluster. After the cracks have fully developed, ceramic is added as a proppant to prevent the cracks from closing. At the same time, a fluorescent agent is added to track the cracks. After loading is completed and the proppant fixes the cracks, a complete image of the cracks is obtained by drilling and imaging. S4. A fiber optic grating sensor attached to the surface of the model collects stress and strain signals, and a static stress and strain acquisition instrument connected to the fiber optic grating sensor collects fracturing information; the fracturing information includes the tensile strength and uniaxial compressive strength of the rock. S5. Acoustic emission sensors installed on the model surface collect the model fracture signal during the fracturing process and send it to the acoustic emission instrument to realize the location and tracking of fractures during the model fracturing process, and to locate and monitor the fracture area in the model. S6. Based on the fracturing information monitored by the acoustic emission system, damage variables are derived, and a rock damage model is established in the data processing terminal computer based on the damage variables.

3. The crack tracking and pressure feedback physical simulation test method according to claim 1, characterized in that, S1 specifically includes the following steps: Based on the on-site geological conditions, rock samples from the mining area were tested to obtain the mechanical parameters of the rock samples; The mechanical parameters of the rock sample are set as the mechanical parameters of the similar material model, and the cementing material and aggregate of the similar material are selected based on the mechanical parameters of the similar material model; Similar material models were prepared using cementitious materials and aggregates of similar materials.

4. The crack tracking and pressure feedback physical simulation test method according to claim 2, characterized in that, The mechanical parameters include density, compressive strength, Poisson's ratio, and elastic modulus.

5. The crack tracking and pressure feedback physical simulation test method according to claim 2, characterized in that, Specifically, the steps include the following: Apply rock damage models to actual field operations; deduce possible scenarios in actual fracturing operations based on complete images of fractures and fracturing information, and optimize fracturing operation design accordingly; Based on fracturing information, it is determined whether the rock has undergone tensile or shear failure, where the variable for tensile failure is F. s The shear failure variable is F. r ; F s =-σ3-f s0 (1) Among them, f s0 f is the tensile strength of the rock. t0 σ1 represents the uniaxial compressive strength of the rock, in MPa; σ1 and σ3 represent the major and minor principal stresses of the rock, in MPa; the tensile direction is defined as negative. The damage variable D of the rock is defined using tensile failure variables and shear failure variables: Where, ε S0 ε is the maximum tensile strain of the rock. t0 ε1 represents the maximum compressive strain of the rock, in MPa; ε2 and ε3 represent the principal strains of the rock; and D represents the damage variable of the rock. Based on the elastoplastic damage theory, a rock damage model is established: E=(1-D)E0 (4) In the formula, E is the real-time elastic modulus of the rock, and E0 is the initial modulus of the rock; The statistical method for the failure zone of rocks in similar material models is as follows: The tensile failure variables, shear failure variables, damage variables, and rock damage model are imported into the COMSOL numerical analysis program. The tensile strength and uniaxial compressive strength of the rock in the similar material model are defined. Other rock parameters obtained from laboratory tests are input into the COMSOL numerical analysis program. The plastic deformation and failure curve of the similar material model are calculated, and the damage factor D is obtained. The rock region with a damage factor D greater than 0 is defined as the damaged zone, and the region with a damage factor D equal to 0 is defined as the non-damaged safe zone. The obtained damage factor D was applied to actual field work, and the damaged area of ​​the rock was reflected by updating the elastic modulus of the rock in real time.

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