Physical simulation device and method for hydraulic fracture propagation of multi-thin-layer reservoir

Abstract

The invention discloses a multi-thin-layer reservoir hydraulic fracture propagation physical simulation device and method. The device comprises a simulation box, a sample stacking body is formed by stacking a plurality of transparent micropore layered modules, and through holes are aligned to form a simulation shaft. The vertical loading mechanism applies vertical stress, the horizontal differential loading mechanism applies spatial non-uniform horizontal stress to the side face through an air bag array and a multi-channel air pump, a complex stress barrier is constructed, and stress parameters can be digitally set to achieve closed-loop control to achieve decoupling. The fluid injection mechanism comprises an injection tubular column and a fracturing fluid pumping assembly. The controllable filtration mechanism independently sets an equivalent filtration coefficient for each module through active suction and gets rid of dependence on material permeability. The monitoring mechanism comprises a high-speed camera and an acoustic emission sensor. The control module cooperatively controls the mechanisms and collects and processes data. According to the design, the real geological condition is highly restored, the experiment authenticity, flexibility and reliability are improved, and powerful support is provided for fracturing research.

Description

Technical Field

[0001] This invention relates to the field of hydraulic fracturing simulation, specifically to a physical simulation device and method for hydraulic fracture propagation in multi-thin reservoirs. Background Technology

[0002] Hydraulic fracturing is a core technology for developing unconventional resources such as shale oil and gas, and it is of great significance. With the deepening development of unconventional resources, the complexity of reservoir geological conditions is becoming increasingly apparent, especially the presence of multiple thin interbedded lithologies vertically, which makes the propagation behavior of hydraulic fractures extremely complex. Research on fracture propagation laws helps to better understand the hydraulic fracturing process, optimize fracturing design, and improve the development efficiency of unconventional resources; therefore, it has always been a research focus in this field.

[0003] Currently, numerical simulation is the primary method used to study crack propagation. However, physical experiments are also employed to verify many parameters and assumptions within the numerical models. Traditionally, physical simulations utilize monolithic rock samples, either made from cement or real rock cores. When controlling key geological and engineering parameters, traditional methods lack effective means to address differences in stress and filtration coefficients, often hindering precise control and flexible adjustment.

[0004] However, existing physical simulation methods have many limitations. Monolithic rock samples prepared using cement or real rock cores are complex to prepare, requiring significant time and effort, resulting in high costs and poor repeatability; the results of each experiment can vary considerably. Traditional equipment struggles to flexibly and independently control key geological and engineering parameters. For example, it cannot accurately reproduce stress differences between different rock layers (stress barriers), simulate differences in filtration coefficients between different strata, or achieve targeted fracturing of specific strata. This leads to experimental conditions that deviate significantly from actual geological conditions, limiting the guiding significance of the simulation results. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and to propose a physical simulation device and method for hydraulic fracture propagation in multi-thin reservoirs.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: This invention provides a physical simulation device for the propagation of hydraulic fractures in multi-thin reservoirs, comprising: A simulation chamber, wherein a transparent observation window is provided on the simulation chamber; The sample stack includes multiple layered modules stacked within the simulation chamber. Each layered module is made of a transparent material and has micropores. Each layered module has a through hole at its center. When all the through holes of the layered modules are aligned, they together form a simulated well. A vertical loading mechanism is used to apply vertical stress to the top surface of the sample stack. A horizontal differential loading mechanism is used to apply a spatially uneven horizontal stress to at least one side of the sample stack to form a predetermined interlayer stress difference at different layered modules inside the sample stack. The fluid injection mechanism includes an injection string that can be placed inside the simulated wellbore and a fracturing fluid pumping assembly. The injection string is provided with at least one jet orifice and at least two packers for sealing the annular space between the simulated wellbore and the injection string. The packers are capable of limiting the jet orifice to the height range of at least one target layered module. A controllable filtration mechanism, which is capable of extracting fluid from at least one layered module at a preset rate to simulate the filtration coefficient of the module; The monitoring mechanism includes at least one high-speed camera and several acoustic emission sensors. The high-speed camera is positioned facing the transparent observation window and is used to capture the crack propagation morphology of the sample stack. The acoustic emission sensors are installed inside the simulation chamber and are used to monitor the acoustic emission signals generated during crack propagation. The control module is communicatively connected to the vertical loading mechanism, the horizontal differential loading mechanism, the fluid injection mechanism, the controllable filtration mechanism, and the monitoring mechanism. It is used to control the coordinated operation of each mechanism according to a preset program, and to collect, process, and display monitoring data.

[0007] In some embodiments, a flexible gasket with a preset coefficient of friction is placed between two adjacent layered modules to simulate a specific bonding strength at the interface.

[0008] In some embodiments, the vertical loading mechanism includes a pressure plate, several mounting boxes, several vertical cylinders, and a pressure sensor. The pressure plate is pressed onto the uppermost layered module. The pressure plate has clearance holes corresponding to the through holes. The mounting boxes are fixed to the top surface of the simulation box. The fixed end of the vertical cylinder is fixed inside the mounting box. The output shaft of the vertical cylinder abuts against the pressure plate via the corresponding pressure sensor.

[0009] In some embodiments, the horizontal differential loading mechanism includes a first baffle, a second baffle, a plurality of airbags, and a multi-channel air pump. The first baffle and the second baffle are both fixed inside the simulation chamber and are located on both sides of the sample stack. The first baffle abuts against one side of the sample stack, and the second baffle has a gap with the other side of the sample stack. Each airbag is disposed between the second baffle and the corresponding layered module. The multi-channel air pump individually adjusts the air pressure at each output end. Each output end of the multi-channel air pump is connected to the inlet and outlet of each airbag via a plurality of first connecting pipes.

[0010] In some embodiments, the packer includes a packer body and a packer bladder. The packer body is fixed to the injection string, and the two packer bodies are respectively located on both sides of the jet orifice. The packer bladder is fixedly sleeved on the packer body. The fluid injection mechanism further includes a packer drive assembly, which includes an air pipe and a packer pump. The air pipe is connected to the inlet and outlet of both packer airbags, and the outlet of the packer pump is connected to the air pipe to inflate the two packer airbags so that they are sealed against the inner wall of the simulated wellbore.

[0011] In some embodiments, the fracturing fluid injection assembly includes a preparation tank, a delivery pump, and a delivery pipe. The preparation tank is used to prepare fracturing fluid. The inlet of the delivery pump is connected to the outlet of the preparation tank. The outlet of the delivery pump is connected to one end of the delivery pipe, and the other end of the delivery pipe is connected to the injection string. The delivery pipe is equipped with a pressure sensor and a flow meter.

[0012] In some embodiments, a liquid collection tank is provided at the position where the first baffle contacts each of the layered modules, and a plurality of liquid suction ports communicating with each of the liquid collection tanks are provided on the first baffle. The controllable filtration mechanism includes a multi-channel suction pump, which can independently adjust the suction negative pressure of each suction end. Each suction end is connected to each suction port via several second connecting tubes.

[0013] In some embodiments, a sealing groove is provided at the position where the first baffle contacts each of the layered modules, and a sealing ring is provided in the sealing groove to seal the gap between the layered module and the first baffle.

[0014] In some embodiments, the pore diameter of the micropores is between 1 micrometer and 500 micrometers.

[0015] The present invention also provides a physical simulation method for the propagation of hydraulic fractures in multi-thin-layer reservoirs, applicable to the physical simulation device for the propagation of hydraulic fractures in multi-thin-layer reservoirs, and includes the following steps: a) Stack multiple layered modules inside the simulation box to form a sample stack with a simulated wellbore; b) Apply a vertical stress to the sample stack using the vertical loading mechanism; c) Apply uneven horizontal stress to the sample stack using the horizontal differential loading mechanism to establish a preset interlayer stress difference; d) Insert the injection string into the simulated wellbore and position the jet holes on it to the height of the target layered module; e) Activate the packer to seal the annulus space within the simulated wellbore and isolate the target layered module; f) Using the fluid injection mechanism, high-pressure fluid is injected into the target layered module through the jet orifice to initiate and propagate hydraulic fractures; g) While step f) is being performed, fluid is extracted from at least one layered module at a preset rate using the controllable filtration mechanism to simulate the formation filtration effect; h) Use the monitoring device to monitor and collect data on the crack propagation process in real time.

[0016] Compared with existing technologies, the beneficial effects of the physical simulation device and method for hydraulic fracture propagation in multi-thin reservoirs provided by this invention are as follows: The horizontal differential loading mechanism, through its airbag array and multi-channel air pump, can apply different horizontal stresses to different layers of the sample stack, thereby flexibly and accurately constructing arbitrarily complex "stress barrier" profiles; the magnitudes of vertical stress, horizontal stress, and interlayer stress differences can all be independently digitally set and closed-loop controlled by the control module, achieving decoupling of stress parameters and facilitating single-factor sensitivity analysis; the controllable filtration mechanism, through the "active suction" principle, can independently set and precisely control the equivalent filtration coefficient of each layered module. This completely eliminates the traditional method that relies on the material's own permeability, making it possible to study the impact of filtration differences at different layers on fracture propagation. This series of designs makes the experimental conditions highly realistic geological conditions, greatly improving the realism, flexibility, and reliability of the physical simulation experiment, and providing strong experimental support for verifying numerical models and optimizing fracturing design. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the physical simulation device for hydraulic fracture propagation in multi-thin reservoirs provided in an embodiment of the present invention.

[0018] Figure 2 yes Figure 1The schematic diagram of the physical simulation device for the propagation of hydraulic fractures in multi-thin reservoirs, omitting the fluid injection mechanism, controllable filtration mechanism, and monitoring mechanism.

[0019] Figure 3 yes Figure 2 A magnified view of a portion of region A in the middle.

[0020] Figure 4 yes Figure 2 A magnified view of a portion of region B in the middle.

[0021] Explanation of reference numerals in the attached drawings: 1. Simulation chamber; 2. Sample stack; 21. Layered module; 22. Simulated wellbore; 23. Flexible gasket; 3. Vertical loading mechanism; 31. Pressure plate; 32. Mounting box; 33. Vertical cylinder; 34. Pressure sensor; 4. Horizontal differential loading mechanism; 41. First baffle; 411. Liquid collection tank; 412. Liquid suction port; 42. Second baffle; 43. Airbag; 44. Multi-channel air pump; 45. First connecting pipe; 5. Fluid injection mechanism; 51. Injection string; 511. Jet orifice; 52. Separator 521. Packer body; 522. Packer airbag; 523. Fracturing fluid pumping assembly; 5231. Preparation tank; 5232. Transfer pump; 5233. Transfer pipe; 5234. Pressure detection device; 5235. Flow meter; 524. Packer drive assembly; 5241. Air pipe; 5242. Packer air pump; 6. Controllable filtration mechanism; 61. Multi-channel suction pump; 62. Sealing ring; 63. Second connecting pipe; 64. Waste liquid pipe; 65. Waste liquid tank; 7. Monitoring mechanism; 71. High-speed camera; 72. Acoustic emission sensor. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The described embodiments are only possible technical implementations of the present invention, but are not limited thereto. Other embodiments obtained by those skilled in the art in conjunction with the embodiments of the present invention without creative effort are also within the protection scope of the present invention.

[0023] This application mainly adopts modular design and multi-system collaborative control, which achieves a high degree of simulation of real geological and engineering conditions, and improves the realism, flexibility and reliability of physical simulation experiments. The following is a further detailed description of this application.

[0024] Example 1 Please refer to Figures 1-4The physical simulation device for hydraulic fracture propagation in multi-thin reservoirs provided in this application includes a simulation chamber 1, a sample stack 2, a vertical loading mechanism 3, a horizontal differential loading mechanism 4, a fluid injection mechanism 5, a controllable filtration mechanism 6, a monitoring mechanism 7, and a control module. The simulation chamber 1 provides a relatively stable experimental space for the entire device. The sample stack 2 is placed inside the simulation chamber 1. The vertical loading mechanism 3 applies vertical stress to the sample stack 2, and the horizontal differential loading mechanism 4 applies uneven horizontal stress to the sample stack 2, thereby forming a preset interlayer stress within the sample stack 2. Due to the force difference, the fluid injection mechanism 5 can inject high-pressure fluid into the target layered module 21, the controllable filtration mechanism 6 can extract fluid from the layered module 21 to simulate the filtration coefficient, the monitoring mechanism 7 monitors the fracture propagation process, and the control module coordinates the collaborative work of each mechanism and processes the monitoring data. This achieves the effect of accurately simulating the hydraulic fracture propagation process of multi-thin reservoirs, making the experimental conditions closer to the real geological conditions, and improving the reliability of the simulation results. This is because each mechanism cooperates with each other and can independently and accurately control multiple key parameters such as multi-thin geological models, triaxial stress fields, interlayer cementation strength, fixed-point injection, and interlayer filtration differences.

[0025] For details, please refer to Figure 1 and Figure 2 The simulation chamber 1 is equipped with a transparent observation window. The simulation chamber 1 is typically made of high-strength metal materials, such as stainless steel, to ensure its structural stability and durability. The transparent observation window can be made of high-strength transparent glass or plexiglass, allowing the high-speed camera 71 to easily photograph the crack propagation morphology of the sample stack 2. In some special cases, transparent plastic sheets can also be used as the observation window material, as long as they meet the requirements for transparency and strength.

[0026] For details, please refer to Figure 1 and Figure 2The sample stack 2 comprises multiple layered modules 21 stacked within the simulation chamber 1. Each layered module 21 is made of a transparent material, such as transparent plastic or resin, to facilitate observation of internal fracture propagation. The layered modules 21 have micropores with diameters ranging from 1 micrometer to 500 micrometers. These micropores simulate the pore structure and permeability of rocks; this range is significant because it covers permeability characteristics ranging from tight reservoirs (such as shale, with pores mostly at the micrometer level) to conventional reservoirs (such as sandstone, with pores reaching hundreds of micrometers). By combining modules with different pore sizes, the stacking of formations with different permeabilities can be simulated. Each layered module 21 has a central through-hole; when all the through-holes of the layered modules 21 are aligned, they together form a simulated wellbore 22. A flexible gasket 23 with a preset friction coefficient is placed between two adjacent layered modules 21. The flexible gasket 23 can be made of rubber material to simulate the specific bonding strength of the interface. By changing the material and thickness of the gasket, different interface conditions from weak bonding to strong bonding can be simulated. At the same time, the flexible gasket 23 should be densely covered with fine pores to facilitate fluid passage.

[0027] For details, please refer to Figure 1 and Figure 2 The vertical loading mechanism 3 includes a pressure plate 31, several mounting boxes 32, several vertical cylinders 33, and a pressure sensor 34. The pressure plate 31 is pressed onto the uppermost layered module 21. The pressure plate 31 has clearance holes corresponding to the through holes to avoid the simulated well shaft 22. The pressure plate 31 is usually made of metal to ensure sufficient strength to transmit pressure. The mounting boxes 32 are fixed to the top surface of the simulation box 1. The mounting boxes 32 can be fixed by welding or bolting to provide a stable installation environment for the vertical cylinders 33. The fixed end of the vertical cylinder 33 is fixed inside the mounting box 32. The output shaft of the vertical cylinder 33 abuts against the pressure plate 31 via the corresponding pressure sensor 34. The pressure sensor 34 can measure the magnitude of the vertical stress in real time, thereby realizing the accurate application and measurement of the vertical stress. A hydraulic jack can also be used to replace the vertical cylinder 33, which can also achieve the function of applying vertical stress.

[0028] For details, please refer to Figures 1-4The horizontal differential loading mechanism 4 includes a first baffle 41, a second baffle 42, several airbags 43, and a multi-channel air pump 44. The first baffle 41 and the second baffle 42 are both fixed inside the simulation chamber 1 and are located on opposite sides of the sample stack 2. The first baffle 41 abuts against one side of the sample stack 2, while the second baffle 42 has a gap with the other side of the sample stack 2. Each airbag 43 is positioned between the second baffle 42 and the corresponding layered module 21. The multi-channel air pump 44 individually adjusts the air pressure at each output end, and each output end of the multi-channel air pump 44 is connected to the inlet and outlet of each airbag 43 via several first connecting pipes 45. By controlling the inflation pressure of the multi-channel air pump 44 on different airbags 43, different horizontal stresses can be applied to different layers of the sample, precisely constructing a "stress barrier."

[0029] In this embodiment, the control module instructs the multi-channel air pump 44 to fill different air bags 43 with different air pressures according to a preset stress profile. For example, to simulate a high-stress layer, a higher air pressure can be filled into the air bag 43 corresponding to the layer; to simulate a low-stress reservoir, a lower air pressure is filled. In this way, arbitrarily complex stepped stress distributions can be applied to the side of the sample flexibly and accurately, realistically reproducing the stress difference between strata.

[0030] In a preferred embodiment, to more comprehensively simulate the three-dimensional stress state of a real stratum, the horizontal differential loading mechanism 4 can be configured in two sets, acting orthogonally on two adjacent sides of the sample stack 2. One set is used to simulate the maximum horizontal principal stress (σH), and the other set is used to simulate the minimum horizontal principal stress (σh). By independently controlling these two sets of mechanisms, not only can an interlayer stress difference be constructed in the direction of the minimum horizontal principal stress, but different stress values ​​can also be applied in the two horizontal directions, thereby achieving a realistic simulation of any triaxial stress state, greatly expanding the applicability and simulation accuracy of the device.

[0031] For details, please refer to Figure 1 and Figure 2 The fluid injection mechanism 5 includes a fracturing fluid pumping assembly 523 and an injection string 51. The fracturing fluid pumping assembly 523 includes a preparation tank 5231, a delivery pump 5232, and a delivery pipe 5233. The preparation tank 5231 is used to prepare fracturing fluid. The inlet of the delivery pump 5232 is connected to the outlet of the preparation tank 5231, and the outlet of the delivery pump 5232 is connected to one end of the delivery pipe 5233. The other end of the delivery pipe 5233 is connected to the injection string 51. The delivery pipe 5233 is equipped with a pressure sensor 5234 and a flow meter 5235. The pressure sensor 5234 can monitor the pressure of the fracturing fluid in real time, and the flow meter 5235 can measure the flow rate of the fracturing fluid.

[0032] Please refer to Figures 1-3The injection string 51 can be lowered into the simulated wellbore 22, which is provided with at least one jet orifice 511 and at least two packers 52 for sealing the annular space between the simulated wellbore 22 and the injection string 51. The packer 52 includes a packer body 521 and a packer airbag 522. The packer body 521 is fixed to the injection string 51, and the two packer bodies 521 are respectively located on both sides of the jet orifice 511. The packer airbag 522 is fixedly sleeved on the packer body 521. The fluid injection mechanism 5 also includes a sealing drive assembly 524, which includes an air pipe 5241 and a sealing air pump 5242. The air pipe 5241 is connected to the inlet and outlet of the two sealing air bags 522. The outlet of the sealing air pump 5242 is connected to the air pipe 5241 to inflate the two sealing air bags 522, so that they are sealed and fitted against the inner wall of the simulated wellbore 22, thus isolating the jet hole 511 at the target layer.

[0033] In this embodiment, the packer airbag 522 is inflated by the packer drive assembly 524 (packer air pump 5242), causing it to expand and tightly adhere to the inner wall of the simulated wellbore 22, thereby completely sealing the wellbore above and below the jet orifice 511. In this way, the high-pressure fracturing fluid pumped in by the delivery pump 5232 cannot flow vertically; it can only be ejected at high speed from the jet orifice 511, precisely acting on the well wall of the target layered module 21 to induce fractures.

[0034] For details, please refer to Figures 1-4 The controllable filtration mechanism 6 includes a multi-channel suction pump 61. A liquid collection tank 411 is provided at each contact point between the first baffle 41 and each layered module 21. Several suction ports 412 communicating with each liquid collection tank 411 are provided on the first baffle 41. To prevent interlayer crossflow, a circumferentially arranged sealing groove is provided at each contact point between the first baffle 41 and each layered module 21, surrounding the liquid collection tank 411. A sealing ring 62 is provided within the sealing groove to seal the gap between the layered module 21 and the first baffle 41. All suction ports 412 are connected to the multi-channel suction pump 61 via pipelines. The multi-channel suction pump 61 can independently adjust the suction negative pressure at each suction end. Each suction end is connected to each suction port 412 via several second connecting pipes 63. This suction pump can independently control the suction rate (negative pressure) for each layer, thereby actively and controllably simulating the filtration coefficients of different formations. The outlet of the multi-channel suction pump 61 is connected to the waste liquid tank 65 via the waste liquid pipe 64.

[0035] In this embodiment, please refer to Figures 1-4The controllable filtration mechanism 6 operates on the principle of active suction. On the first baffle 41, which contacts the sample, corresponding to each layered module 21, are a liquid collection tank 411 and a suction port 412 for collecting the filtrated liquid. To prevent interlayer flow of liquid between the baffle and the sample surface, a sealing groove and a sealing ring 62 are provided around the liquid collection tank 411. All suction ports 412 are connected to a multi-channel suction pump 61 via pipelines. During the experiment, when the liquid portion of the fracturing fluid in the fracture permeates into the micropores of the layered module 21 due to high pressure and finally reaches the liquid collection tank 411 at the first baffle 41, the multi-channel suction pump 61 starts working. The solid components in the fracturing fluid remain in the fracture, forming a "mud cake." The control module can instruct the pump to draw liquid from different layers at different suction rates (i.e., adjust the suction negative pressure of each channel). This suction rate directly corresponds to the filtration coefficient of that layer. This active and controllable suction method can accurately simulate the filtration characteristics of different formations and study their impact on fracture propagation.

[0036] Specifically, the monitoring unit 7 includes at least one high-speed camera 71 and several acoustic emission sensors 72. The high-speed camera 71 is positioned facing a transparent observation window to capture the crack propagation morphology of the sample stack 2. The acoustic emission sensors 72 are installed inside the simulation chamber 1 to monitor the acoustic emission signals generated during crack propagation. The high-speed camera 71 can quickly and clearly record the crack propagation process, while the acoustic emission sensors 72 can capture the high-frequency sound wave signals generated when the crack ruptures, in order to analyze the dynamic process of crack propagation. By analyzing the energy, amplitude, and location of the acoustic emission signals, the dynamic process, velocity, and microscopic rupture mechanism of crack propagation can be reconstructed, complementing macroscopic observations.

[0037] Specifically, the control module is communicatively connected to the vertical loading mechanism 3, the horizontal differential loading mechanism 4, the fluid injection mechanism 5, the controllable filtration mechanism 6, and the monitoring mechanism 7. It is used to control the coordinated operation of each mechanism according to a preset program, and to collect, process, and display monitoring data. The control module can be a computer system, and corresponding programs can be written to achieve precise control and data processing of each mechanism. The control module is the brain of the entire device, responsible for precisely coordinating and controlling the start-up, shutdown, pressure, flow, and other parameters of each mechanism according to the preset program by the experimenter, and for collecting, processing, and displaying data returned by all sensors in real time, thereby automating and digitizing the experimental process.

[0038] The implementation principle of this embodiment is as follows: This physical simulation device, through modular design, independently controls multiple key parameters such as multi-layer geological models, triaxial stress fields, interlayer cementation strength, targeted injection, and interlayer filtration differences. Each mechanism works closely together under the coordination of the control module. The vertical loading mechanism 3 and the horizontal differential loading mechanism 4 accurately simulate the triaxial stress of the formation; the fluid injection mechanism 5 achieves targeted fracturing; the controllable filtration mechanism 6 simulates formation filtration; and the monitoring mechanism 7 monitors the fracture propagation process in real time. This series of designs ensures that the experimental conditions highly replicate real geological conditions, greatly improving the realism, flexibility, and reliability of the physical simulation experiment, and providing strong experimental support for verifying numerical models and optimizing fracturing designs.

[0039] Example 2 The physical simulation method for hydraulic fracture propagation in multi-thin reservoirs provided in this application includes the following steps: S1, multiple layered modules 21 are stacked inside the simulation chamber 1 to form a sample stack 2 with a simulated wellbore 22. During stacking, ensure that the through-holes of each layered module 21 are aligned to form the simulated wellbore 22. Simultaneously, according to experimental requirements, flexible gaskets 23 with a preset coefficient of friction are placed between adjacent layered modules 21 to simulate interlayer bonding strength. During operation, specialized fixtures can be used to assist in stacking the layered modules 21, ensuring stacking accuracy.

[0040] S2, apply a vertical stress to the sample stack 2 using the vertical loading mechanism 3. Activate the vertical cylinder 33, and monitor the magnitude of the vertical stress in real time using the pressure sensor 34, ensuring the vertical stress reaches the preset value. If a hydraulic jack is used instead of the vertical cylinder 33, it is equally important to control the applied pressure to ensure the accuracy of the experiment.

[0041] S3, using the horizontal differential loading mechanism 4, non-uniform horizontal stress is applied to the sample stack 2 to establish a preset interlayer stress difference. If the airbag 43 scheme is adopted, the inflation pressure of each airbag 43 is adjusted by the multi-channel air pump 44.

[0042] S4, the injection string 51 is placed into the simulated wellbore 22, and the jet orifice 511 on it is positioned at the height of the target layered module 21. Specialized positioning tools can be used to ensure the accurate position of the injection string 51 and prevent the jet orifice 511 from deviating from the target layer.

[0043] S5, activate packer 52 to seal the annulus space within the simulated wellbore 22 and isolate the target layered module 21. Activate packer air pump 5242 to inflate packer airbag 522 through air pipe 5241, causing packer airbag 522 to expand and seal against the inner wall of simulated wellbore 22.

[0044] S6, using the fluid injection mechanism 5, high-pressure fluid is injected into the target layered module 21 through the jet orifice 511 to initiate and propagate hydraulic fractures. The delivery pump 5232 is started to deliver the fracturing fluid from the preparation tank 5231 to the injection string 51 through the delivery pipe 5233, and then inject it into the target layered module 21 through the jet orifice 511. Simultaneously, the pressure and flow rate of the fracturing fluid are monitored in real time using the pressure sensor 5234 and the flow meter 5235.

[0045] S7. Simultaneously with step S6, a controllable filtration mechanism 6 is used to extract fluid from at least one layered module 21 at a preset rate to simulate the formation filtration effect. A multi-channel suction pump 61 is started, and the suction negative pressure at each suction end is adjusted according to the preset rate to extract fluid from the layered module 21 through the suction port 412 and the liquid collection tank 411.

[0046] S8, the monitoring mechanism 7 is used to monitor and collect data on the crack propagation process in real time. A high-speed camera 71 captures the crack propagation morphology through a transparent observation window, and an acoustic emission sensor 72 monitors the acoustic emission signals generated during crack propagation. The control module processes and displays the data collected by the monitoring mechanism 7 for easy analysis by experimental personnel.

[0047] The implementation principle of this embodiment is as follows: This physical simulation method is designed strictly according to the actual process of hydraulic fracture propagation in multi-thin reservoirs, with each step closely centered on simulating real geological conditions and engineering requirements. By precisely controlling parameters in each step, such as stress magnitude, injection pressure, and filtration rate, combined with real-time monitoring by monitoring unit 7, the propagation process of hydraulic fractures in multi-thin reservoirs can be accurately simulated. This method provides a scientific and reliable experimental means for studying the mechanism of hydraulic fracturing, verifying numerical models, and optimizing fracturing design, thereby improving the understanding and application capabilities of hydraulic fracturing technology in unconventional resource development.

[0048] The physical simulation device and method for hydraulic fracture propagation in multi-thin reservoirs provided by this invention have the following significant advantages compared with the prior art: 1. The horizontal differential loading mechanism 4, through its array of airbags 43 and multi-channel air pump 44, can apply different horizontal stresses to different layers of the sample stack 2, thereby flexibly and accurately constructing arbitrarily complex "stress barrier" profiles. This overcomes the major technical challenge of traditional devices being unable to effectively simulate interlayer stress differences, providing key boundary conditions for studying the longitudinal propagation behavior of cracks.

[0049] 2. The magnitudes of vertical stress, horizontal stress, and interlayer stress difference can all be independently set digitally and controlled in a closed loop by the control module, which decouples the stress parameters and facilitates single-factor sensitivity analysis.

[0050] 3. The controllable filtration mechanism 6, through the principle of "active suction," can independently set and precisely control the equivalent filtration coefficient of each layered module 21. This completely eliminates the traditional method that relies on the material's own permeability, making it possible to study the impact of filtration differences in different layers on crack propagation.

[0051] 4. The monitoring unit 7 employs both a high-speed camera 71 and an acoustic emission sensor 72. The former, through a transparent observation window, can macroscopically and intuitively record the complete geometric morphology and propagation path of the crack; the latter can capture microscopic fracture events within the material during crack propagation. The combination of these two provides comprehensive observational data across scales, from macroscopic morphology to microscopic mechanisms. The process is completely transparent: thanks to the transparent layered module 21 and the observation window of the simulation box 1, the entire process of crack initiation, propagation, translayering, or reversal in the three-dimensional stress field is clearly visible, transforming the original "black box" experiment into a fully visualized scientific study, which helps in discovering new physical phenomena and verifying theoretical models.

[0052] In summary, through a series of structural and methodological innovations, this invention has constructed a physical simulation platform that can highly reproduce real geological conditions, accurately control key parameters, provide comprehensive process visualization, and operate flexibly and efficiently. It solves many pain points of existing technologies in the simulation of fracturing in complex multi-thin-layer formations, and has significant technological progress and important application value.

[0053] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A physical simulation apparatus for hydraulic fracture propagation in a multi-lamella reservoir, comprising: The simulation box is provided with a transparent observation window. A sample stack is arranged in the simulation box, and comprises a plurality of layered modules arranged in a stack, each of which is made of transparent material and has micropores, and each of which has a through hole in the center, and the through holes of all the layered modules are aligned to form a simulation wellbore. A vertical loading mechanism is used to apply vertical stress to the top surface of the sample stack. A horizontal differential loading mechanism is used to apply spatially uneven horizontal stress to at least one side surface of the sample stack to form a preset interlayer stress difference at different layered modules inside the sample stack. A fluid injection mechanism comprises an injection string that can be placed in the simulation wellbore and a fracturing fluid pumping assembly, the injection string is provided with at least one jet hole and at least two packers for sealing the annular space between the simulation wellbore and the injection string, and the packers can limit the jet hole within the height range of at least one target layered module. A controllable fluid loss mechanism can draw fluid from at least one layered module at a preset rate to simulate the fluid loss coefficient of the module. A monitoring mechanism comprises at least one high-speed camera and a plurality of acoustic emission sensors, the high-speed camera is arranged towards the transparent observation window to capture the crack propagation morphology of the sample stack, and the acoustic emission sensors are installed in the simulation box to monitor the acoustic emission signals generated during crack propagation. A control module is in communication connection with the vertical loading mechanism, the horizontal differential loading mechanism, the fluid injection mechanism, the controllable fluid loss mechanism and the monitoring mechanism, and is used to control the coordinated work of the mechanisms according to a preset program, and collect, process and display monitoring data. A flexible gasket with a preset friction coefficient is placed between two adjacent layered modules to simulate the specific cementation strength of the interface.

2. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 1, wherein, The vertical loading mechanism comprises a pressing plate, a plurality of mounting boxes, a plurality of vertical cylinders and pressure sensors, the pressing plate is arranged on the uppermost layered module, the pressing plate is provided with a clearance hole corresponding to the through hole, the mounting boxes are fixed to the top surface of the simulation box, the fixed end of the vertical cylinder is fixed in the mounting box, and the output shaft of the vertical cylinder abuts against the pressing plate through the corresponding pressure sensor.

3. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 1, wherein, The horizontal differential loading mechanism comprises a first baffle, a second baffle, a plurality of air bags and a multi-channel air pump, the first baffle and the second baffle are fixed in the simulation box and are located on the two sides of the sample stack respectively, the first baffle abuts against one side of the sample stack, the second baffle has a gap with the other side of the sample stack, each air bag is arranged between the second baffle and the gap of each corresponding layered module, the multi-channel air pump individually adjusts the air pressure of each output end, and each output end of the multi-channel air pump is in corresponding communication with the air inlet and outlet of each air bag through a plurality of first connecting pipes.

4. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 1, wherein, ​ 5. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 1, wherein, The packer comprises a packer body and a packer air bag, the packer body is fixed to the injection string, two packer bodies are respectively located on both sides of the jet hole, and the packer air bag is fixedly sleeved on the packer body. The fluid injection mechanism further comprises a packer driving assembly, the packer driving assembly comprises an air pipe and a packer air pump, the air pipe is in communication with the air inlet and outlet of the two packer air bags, and the air outlet end of the packer air pump is in communication with the air pipe.

6. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 1, wherein, The fracturing fluid pump injection assembly comprises a preparation tank, a delivery pump and a delivery pipe, the preparation tank is used for preparing fracturing fluid, the inlet of the delivery pump is in communication with the outlet of the preparation tank, the outlet of the delivery pump is in communication with one end of the delivery pipe, the other end of the delivery pipe is in communication with the injection string, and the delivery pipe is provided with a pressure detection member and a flowmeter.

7. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 4, wherein, The first baffle is provided with a liquid collecting groove at a position in contact with each layer module, and a plurality of liquid suction openings are formed in the first baffle and in communication with the liquid collecting grooves. The controllable fluid loss mechanism comprises a multi-channel suction pump, the multi-channel suction pump can independently adjust the suction negative pressure of each suction end, and each suction end is in communication with each liquid suction opening through a plurality of second connecting pipes.

8. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 7, wherein, The first baffle is provided with a sealing groove arranged in a circumferential direction around the liquid collecting groove at a position in contact with each layer module, and a sealing ring is arranged in the sealing groove, the sealing ring is used for sealing the gap between the layer module and the first baffle.

9. The multi-lamella reservoir hydraulic fracture propagation physical modeling apparatus of claim 1, wherein, The pore diameter of the micropore is between 1 micrometer and 500 micrometers.

10. A method of physical modeling of hydraulic fracture propagation in a multi-lamella reservoir, characterized by, The method is suitable for the multi-layer reservoir hydraulic fracture propagation physical simulation device according to any one of claims 1-9, and comprises the following steps: a) stacking a plurality of layer modules in the simulation box to form a sample stack with a simulated wellbore; b) applying a vertical stress to the sample stack by using the vertical loading mechanism; c) applying an uneven horizontal stress to the sample stack by using the horizontal differential loading mechanism to establish a preset interlayer stress difference; d) placing the injection string into the simulated wellbore and positioning the jet hole on the injection string to the height of the target layer module; e) starting the packer to seal the annular space in the simulated wellbore and isolate the target layer module; f) injecting high-pressure fluid into the target layer module through the jet hole by using the fluid injection mechanism to initiate and expand the hydraulic fracture; g) while step f) is being performed, using the controllable fluid loss mechanism to extract fluid from at least one layer module at a preset rate to simulate the formation fluid loss effect; h) using the monitoring mechanism to monitor the expansion process of the fracture in real time and collect data.

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