Hard top horizontal well porous fracturing pressure-flow intelligent regulation experiment system and method

Abstract

The present application relates to the technical field of coal mining, and provides a hard top horizontal well porous fracturing pressure-flow intelligent regulation and control experiment system and method, the experiment system comprises a transparent sample, a true three-dimensional loading servo control system of ground stress, a hydraulic servo pump pressure system and a hydraulic fracture information visualization monitoring system; a simulation wellbore is arranged in the transparent sample from the end face to the inside on one side, a plurality of perforations intersecting and communicating with the simulation wellbore are prearranged in the transparent sample at intervals, and a pressure and flow dynamic distribution regulation and control system is connected to one end of the perforation close to the simulation wellbore; the pressure and flow dynamic distribution regulation and control system is used for collecting the pressure and flow information of the perforation, and adjusting the pressure and flow size of the perforation according to the pressure-flow dynamic distribution control mechanism. The present scheme can simulate the real situation of horizontal well multi-perforation fracturing, provide a scientific basis for coal mining, and achieve uniform expansion of multiple fractures through real-time dynamic distribution of multi-perforation pressure and flow.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, specifically to an experimental system and method for intelligent control of pressure and flow rate in multi-hole fracturing of hard-roofed horizontal wells. Background Technology

[0002] In coal mining, the control of the hard overlying roof directly affects mine safety. Hard roofs are characterized by high strength, large fracture steps, wide impact range, and complex mechanical behavior, posing a major challenge to coal mine roof control. Especially as coal seam mining progresses deeper, the typical "three highs" (high temperature, high humidity, and high temperature) environment of deep rock masses results in exceptionally complex rock strata fracture mechanical behavior over large areas of the overlying strata, leading to frequent engineering disasters that are difficult to predict and effectively control. Therefore, even higher requirements are placed on the control of thick, hard roofs.

[0003] Modifying the overburden structure in deep coal mines is a key technological approach for disaster prevention and control. Hydraulic fracturing technology, which eliminates the need for blasting operations, reduces costs, improves construction efficiency, and is an effective means of modifying thick, hard coal seams with high roof strength. Horizontal well multi-cluster simultaneous fracturing technology, by creating multiple clusters of perforations within the same fracturing section, simultaneously opens numerous dense fractures extending along the direction of maximum principal stress. This effectively divides relatively intact, hard strata into smaller "pieces," reducing rock mass strength and energy storage capacity, thereby mitigating the risk of disasters.

[0004] However, experimental data shows that 30% or more of the fractures fail to achieve the designed production effect. During the propagation of hydraulic fractures, the initiation, extension, direction, and penetration of fractures are influenced by multiple factors, including lithology, formation conditions, geostress levels, and fracturing parameters. It is generally believed that during the synchronous propagation of multiple fractures, mutual interference between adjacent fractures causes some fractures to lose propagation stability. Due to limitations in current technology, the understanding of the propagation process of multiple fractures remains inaccurate. The propagation process of multiple fractures is influenced by the coupling of multiple factors, such as stress shadowing effects, and its propagation direction and length are dynamically changing. Microseismic monitoring used in the field is limited by its own accuracy, making it difficult to accurately locate the fracture trajectory. Numerical studies still face challenges, especially in considering the coupling between in-situ stress and lithology to determine the complex behavior of fracture propagation. Acoustic emission monitoring can determine the location of crack events in experiments, but it is difficult to accurately reconstruct the fracture morphology from the data. CT scans are difficult to capture fracture propagation in real time due to equipment and cost limitations. The geometry of hydraulic fractures is usually obtained by splitting the rock after a fracturing test. Therefore, the lack of experimental studies on the dynamic propagation process of multiple cracks limits our understanding of their competition and mutual interference mechanisms.

[0005] Moreover, relevant studies have shown that pressure and flow rate parameters in multi-perforation horizontal wells are key parameters affecting fracture propagation paths. Currently, there is a lack of research on pressure and flow rate changes and control methods in multi-perforation horizontal well fracturing. There is also a lack of correct understanding of the mechanisms that cause synchronous propagation and interactive response of multiple fractures. It is urgent to solve the influence of multi-perforation pressure and flow rate changes and regulation on multi-fracture propagation, so as to achieve dynamic allocation and achieve the goal of uniform propagation of multiple fractures. Summary of the Invention

[0006] To address the problems existing in the background technology, this invention proposes an intelligent control experimental system and method for pressure-flow rate of multi-perforation fracturing in hard-top horizontal wells. This system can simulate the real situation of multi-perforation fracturing in horizontal wells, and intuitively monitor the multi-fracture propagation process and mutual disturbance of perforations inside the sample. It helps to understand the effect of multi-perforation pressure and flow rate changes on fracture propagation, providing a scientific basis for coal mining. Through real-time dynamic distribution of multi-perforation pressure and flow rate, uniform propagation of multiple fractures can be achieved.

[0007] To achieve the above objectives, the present invention adopts the following scheme: a hard-top horizontal well multi-hole fracturing pressure-flow intelligent control experimental system, including a transparent sample, a true three-dimensional in-situ stress loading servo control system, a hydraulic servo pump pressure system, and a hydraulic fracture information visualization monitoring system; a simulated wellbore is provided on one side of the transparent sample from the end face inward, and multiple perforations that intersect and communicate with the simulated wellbore are preset at intervals inside the transparent sample, and a pressure and flow dynamic distribution control system is connected to one end of the perforation near the simulated wellbore, and the pressure and flow dynamic distribution control system is electrically connected to the hydraulic servo pump pressure system;

[0008] The pressure and flow dynamic distribution and control system is used to collect the pressure and flow information of the perforation and adjust the pressure and flow of the perforation according to the pressure and flow dynamic distribution control mechanism. The pressure and flow dynamic distribution and control system includes a pressure and flow regulator, a pressure and flow sensor, and a pressure and flow control system. The pressure and flow regulator and the pressure and flow sensor are disposed at one end of the perforation near the simulated wellbore. The pressure and flow regulator is electrically connected to the pressure and flow control system through the pressure and flow sensor. The pressure and flow dynamic distribution control mechanism includes:

[0009] The sum of the injection flows from all perforations equals the total injection flow, expressed as:

[0010] ;

[0011] The relationship between pressure and flow rate within each perforation is as follows:

[0012] ;

[0013] Among them, Q0 and Q i These represent the total injection flow rate and the injection flow rate of the i-th perforation, respectively; N is the total number of perforations. Set resistance for pressure and flow regulators; For perforation pressure; To simulate the pressure inside the wellbore; The friction coefficient of the perforation; To simulate the pressure inside the wellbore;

[0014] The true three-dimensional loading servo control system for ground stress includes a true triaxial pressure loading test machine, pressure plates, and a pressure loading control system. During the experiment, the transparent sample is placed inside the true triaxial pressure loading test machine. Multiple pressure plates are provided, and the multiple pressure plates act on the peripheral and top ends of the transparent sample through the pressure loading control system.

[0015] The hydraulic servo pump system is used to pump fracturing fluid at a set flow rate into the transparent sample;

[0016] The hydraulic fracture information visualization monitoring system is used to monitor, record, and process the dynamic propagation process of fractures, pumping pressure information, and stress evolution process on the surface of transparent samples during the fracturing process.

[0017] Preferably, the pressure loading control system includes a vertical pressure loading control system, a lateral pressure loading control system, a pressure controller, and pressure control software. The pressure plates acting on the peripheral ends of the transparent specimen are respectively disposed opposite to each other on the peripheral sidewalls of the true triaxial pressure loading testing machine, and the pressure plate acting on the top of the transparent specimen is disposed on the top wall of the true triaxial pressure loading testing machine. The pressure plate located on the top wall is connected to the vertical pressure loading control system, and the pressure plate located on the peripheral sidewalls is connected to the lateral pressure loading control system. The vertical pressure loading control system and the lateral pressure loading control system are electrically connected to the pressure control software through the pressure controller.

[0018] Preferably, the hydraulic servo pump pressure system includes a plunger pump, a plunger pump controller, and a plunger pump control system. The output end of the plunger pump is connected to the simulated wellbore through a pumping pipeline. The plunger pump is connected to the plunger pump control system through the plunger pump controller. The plunger pump control system is electrically connected to the pressure and flow control system.

[0019] Preferably, the pressure plate is a transparent plate, and a measuring element is provided in the reserved hole on the side of the pressure plate near the transparent sample.

[0020] Preferably, the hydraulic fracture information visualization monitoring system includes a high-speed camera, a DIC digital image monitoring system, an acoustic emission monitoring system, and a multi-element information processor. The high-speed camera, DIC digital image monitoring system, and acoustic emission monitoring system are electrically connected to the multi-element information processor. The high-speed camera and DIC digital image monitoring system are set at a preset position close to the transparent sample via a mobile device. The high-speed camera and DIC digital image monitoring system are used to monitor the crack propagation and full-field stress evolution process on the surface of the transparent sample. The acoustic emission monitoring system is electrically connected to the measuring element and is used to monitor the internal crack changes of the transparent sample during fracturing. The multi-element information processor is used to visualize, monitor, record, store, and analyze the internal and surface crack information of the transparent sample.

[0021] Preferably, the dynamic distribution control conditions for the flow rates of the multiple perforations are as follows:

[0022] ,

[0023] Among them, Q0 and Q i These represent the total injection flow rate and the injection flow rate of the i-th perforation, respectively; N is the total number of perforations; the... This represents the relative flow rate into the perforation hole.

[0024] An experimental method for intelligent control of pressure-flow rate in hard-top horizontal well fracturing includes the following steps:

[0025] Step 1: Prepare a transparent sample that meets the mechanical parameter requirements and has a multi-perforated horizontal well.

[0026] Step 2: Install the entire experimental system;

[0027] Step 3, conduct the experiment: First, activate the hydraulic fracture information visualization monitoring system and input the corresponding specimen number and time information into the multi-element information processor; then, activate the pressure and flow dynamic distribution control system, simultaneously fill the prepared fracturing fluid into the plunger pump of the hydraulic servo pump system, and activate the hydraulic servo pump system to pump fracturing fluid into the transparent specimen according to the set flow rate; after the hydraulic fracturing experiment begins, when the plunger pump control system observes that the pump pressure-time curve decreases instantaneously and stabilizes near a certain pressure value, the hydraulic fracturing physical simulation experiment ends. The dynamic control method of the pressure and flow dynamic distribution control system is as follows: at time t, the pressure in perforation a reaches the specimen fracturing condition, at which time the pressure and flow rate of perforation a are P(a) and Q(a), respectively, and the pressure and flow rate of perforation b are P(a) and Q(b), respectively, and P(a)...<P(b)、Q(a)> Q(b), at this point, the pressure and flow regulator feeds back the pressure and flow information to the pressure and flow control system through the pressure and flow sensor, and the pressure and flow regulator adjusts... Additional resistance to the flow into the crack at any moment , so that P(a)+ =P(b), the flow rate pumped into each crack is the same;

[0028] Step 4: After the experiment, dismantle the entire experimental system in sequence;

[0029] Step 5: Processing and analyzing experimental data: After the experiment, observe the morphology and trend of hydraulic cracks on the surface of the transparent sample and record the data using a camera; cut and observe the transparent sample and record the data using a camera after cutting; analyze the morphology of hydraulic cracks using pump pressure-time curves, capture the complete process of multi-perforation crack propagation using a high-speed camera, obtain stress information during the fracture process of the transparent sample based on DIC digital image monitoring technology; scan and reconstruct the internal crack morphology of the transparent sample based on CT scanning technology, and compare and analyze it with the internal crack information obtained by the acoustic emission monitoring system; summarize and analyze the pressure and flow distribution control mechanism under different combinations of fracturing parameters.

[0030] Preferably, the transparent sample is prepared by: setting at least four perforated precast pipes at intervals on the simulated wellbore precast pipe, placing the simulated wellbore precast pipe in the mold, filling the mold with sample material selected according to the mechanical characteristics of the simulated rock strata, and curing for 24 days.

[0031] Preferably, the method for installing the entire experimental system is as follows: the transparent sample is placed in a true triaxial pressure loading testing machine, and pressure plates with pre-drilled holes are placed on the left and right opposite sides, front and back opposite sides, and top side of the transparent sample. Measuring elements are placed in the pre-drilled holes of the pressure plates and connected to the acoustic emission monitoring system; the simulated well in the transparent sample is connected to the hydraulic servo pump system and the pressure and flow dynamic distribution control system through the pumping pipeline; the high-speed camera and DIC digital image monitoring system are moved to a position where the complete transparent sample surface can be clearly captured and connected to the multi-element information processor; the true three-dimensional loading servo control system for ground stress applies pressure to the axial and lateral sides of the transparent sample according to the stress scheme.

[0032] After the experiment, the entire experimental system was dismantled sequentially as follows: the hydraulic fracture information visualization monitoring system, the hydraulic servo pump system, and the pressure and flow dynamic distribution control system were shut down; the fracturing fluid injection pipeline was disconnected from the hydraulic servo pump system and the pressure and flow dynamic distribution control system; the true three-dimensional stress loading servo control system was shut down, and the simulated stress loading was stopped; the pressure plate was removed, and then the measuring elements in the pre-drilled holes of the pressure plate were removed; the transparent sample was removed; and the pressure plate, the true triaxial pressure loading test machine, and related wiring were cleaned and then cured.

[0033] The beneficial effects of this invention are as follows: First, based on the technology of horizontal well multi-perforation hydraulic fracturing, this method can reveal the synchronous propagation law and interaction mechanism of fractures in multiple perforations within a sample under true three-dimensional conditions. This not only overcomes the limitations of traditional single-well fracturing and multi-vertical-perforation fracturing tests, but also provides a more realistic and intuitive means of monitoring the fracture propagation process, providing a scientific basis for coal mining.

[0034] Moreover, by adopting a dynamic pressure and flow distribution control system, it is possible not only to accurately monitor the pressure and flow changes entering each perforation and to more accurately understand the impact of pressure and flow changes on fracture propagation under multi-perforation conditions, but also to adjust the pressure and flow of each perforation in real time according to the dynamic pressure and flow distribution control mechanism, ensuring that multiple fractures are evenly distributed during the propagation process. This helps to improve the connectivity of the fracture network, promote the effective mining of coal resources, and reduce unnecessary energy consumption.

[0035] In addition, the use of multiple technologies to achieve visual monitoring: combining acoustic emission positioning, high-speed cameras, DIC digital imaging technology and transparent similar materials, it is possible to achieve real-time dynamic propagation process of multiple cracks inside rocks and full-field stress disturbance characteristics, providing a powerful tool for in-depth research on crack propagation mechanisms and helping to discover new scientific laws.

[0036] In summary, this scheme can conduct experimental research on the influence of multiple factors on different rock types and geological conditions. This not only helps to propose a theory for optimizing the mechanism of synchronous multi-cluster fracture propagation, but also provides important technical support for practical engineering applications. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of the experimental system in an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the transparent sample structure in an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the transparent sample workflow in an embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram of the dynamic pressure and flow distribution control system in an embodiment of the present invention;

[0041] Figure 5 This is a schematic diagram of the control process of the pressure and flow dynamic distribution control system in an embodiment of the present invention;

[0042] Figure 6 This is a schematic diagram of the simulation results before the dynamic adjustment of synchronous fracturing pressure and flow rate in an embodiment of the present invention;

[0043] Figure 7 This is a schematic diagram of the simulation results after the synchronous fracturing pressure and flow rate are dynamically adjusted in an embodiment of the present invention.

[0044] Labels in the diagram: 1. Simulated wellbore; 2. Perforation; 3. Pressure and flow regulator; 4. Pressure and flow sensor; 5. Transparent specimen; 6. Pressure plate; 7. Acoustic emission monitoring system; 8. High-speed camera; 9. DIC digital image monitoring system; 10. Multi-element information processor; 11. True triaxial pressure loading testing machine; 12. Vertical pressure loading control system; 13. Pressure controller; 14. Pressure control software; 15. Lateral pressure loading control system; 16. Plunger pump; 17. Plunger pump controller; 18. Plunger pump control system; 19. Pressure and flow regulation system. Detailed Implementation

[0045] To make the present invention clearer and more understandable, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the given embodiments are only one implementation method and do not represent all embodiments.

[0046] Example 1

[0047] Combination Figures 1-7 This embodiment provides an experimental system for intelligent control of pressure and flow rate in multi-hole fracturing of hard-top horizontal wells, including a transparent sample 5, a true three-dimensional loading servo control system for in-situ stress, a hydraulic servo pump pressure system, and a hydraulic fracture information visualization monitoring system. A simulated wellbore 1 is provided on one side of the transparent sample 5 from the end face inward. Multiple perforations 2 are pre-set at intervals inside the transparent sample 5 and are intersecting and communicating with the simulated wellbore 1. A pressure and flow rate dynamic distribution control system is connected to one end of the perforation 2 near the simulated wellbore 1. The pressure and flow rate dynamic distribution control system is electrically connected to the hydraulic servo pump pressure system.

[0048] The pressure and flow dynamic distribution and control system is used to collect the pressure and flow information of the perforation 2, and adjust the pressure and flow of the perforation 2 according to the pressure and flow dynamic distribution control mechanism, wherein the pressure and flow dynamic distribution control mechanism includes:

[0049] The sum of the injection flow rates from all perforations 2 equals the total injection flow rate, expressed as:

[0050] ;

[0051] Since the pressure inside the simulated wellbore is almost constant, the relationship between the pressure at the fracture inlet and the flow rate is as follows:

[0052] ;

[0053] Due to reservoir heterogeneity and different fracture propagation stages, the pressure p required for the continuous propagation of each fracture is different. i The flow rate also differs, leading to uneven distribution, which is detrimental to the balanced propagation of the crack. Therefore, the key to controlling the flow rate distribution lies in balancing the difference in propagation resistance by adjusting the resistance of the perforation 2. After setting the dynamic regulator, the relationship between pressure and flow rate in each perforation 2 is as follows:

[0054] ,

[0055] The dynamic flow distribution control conditions for the multiple perforations 2 are as follows:

[0056] ,

[0057] The above formula illustrates the dynamic control of the dominant fracture. During the simultaneous fracturing process of multiple perforations 2, pressure and flow information are dynamically fed back to the high-precision pressure and flow sensor 4 in real time. If the pressure in perforation a reaches the sample cracking condition at time t, the pressure and flow rate of perforation a are P(a) and Q(a), respectively, and the pressure and flow rate of perforation b are P(a) and Q(b), respectively, and P(a) = Q(b).<P(b)、Q(a)> Q(b), at this time, the pressure and flow regulator 3 feeds back the pressure and flow information to the pressure and flow control system 19 through the pressure and flow sensor 4, and the pressure and flow regulator 3 adjusts... Additional resistance to the flow into the crack at any moment , so that P(a)+ =P(b), the flow rate pumped into each crack is the same, and the pressure and flow information continues to be dynamically fed back to the pressure and flow sensor 4. The pressure and flow sensor 4 simultaneously feeds back the pressure and flow information to the pressure and flow control system 19. After analysis, the pressure and flow control system 19 sends a control signal to the pressure and flow regulator 3. The pressure and flow regulator 3 adjusts the fluid pressure and flow to achieve dynamic distribution of pressure and flow so that the cracks can expand uniformly.

[0058] Among them, Q0 and Q i These are the total injection flow rate and the injection flow rate of the i-th perforation, respectively. The relative flow rate into the perforation holes; N is the total number of perforations; Set resistance for pressure and flow regulators; For perforation pressure; To simulate the pressure inside the wellbore; The friction coefficient of the perforation; To simulate the pressure inside the wellbore.

[0059] The true three-dimensional stress loading servo control system includes a true triaxial pressure loading test machine 11, pressure plates 6, and a pressure loading control system. During the experiment, the transparent sample 5 is placed inside the true triaxial pressure loading test machine 11. Multiple pressure plates 6 are provided, and the multiple pressure plates 6 act on the peripheral and top ends of the transparent sample 5 respectively through the pressure loading control system. The hydraulic servo pump system is used to pump fracturing fluid of a set flow rate into the transparent sample 5. The hydraulic fracture information visualization monitoring system is used to monitor, record, and process the dynamic propagation process of fractures, pumping pressure information, and surface stress evolution process of the transparent sample 5 during the fracturing process.

[0060] The experimental system in this embodiment mainly includes a transparent sample 5, a true three-dimensional in-situ stress loading servo control system, a hydraulic servo pump system, a hydraulic fracture information visualization monitoring system, and a pressure and flow dynamic distribution and control system. Visual experiments on multi-perforation 2 simultaneous fracturing based on high-speed cameras and transparent materials can solve problems such as uneven fracture propagation during multi-perforation 2 simultaneous fracturing in horizontal wells with hard overlying coal seams. This helps to reveal the dynamic propagation competition mechanism of multiple fractures and achieve effective control of the synchronous propagation path of multi-perforation 2 fractures.

[0061] Specifically, the pressure loading control system includes a vertical pressure loading control system 12, a lateral pressure loading control system 15, a pressure controller 13, and pressure control software 14. The pressure plates 6 acting on the peripheral ends of the transparent specimen 5 are respectively disposed opposite to each other on the peripheral sidewalls of the true triaxial pressure loading testing machine 11. The pressure plate 6 acting on the top of the transparent specimen 5 is disposed on the top wall of the true triaxial pressure loading testing machine 11. The pressure plate 6 on the top wall is connected to the vertical pressure loading control system 12, and the pressure plate 6 on the peripheral sidewalls is connected to the lateral pressure loading control system 15. The vertical pressure loading control system 12 and the lateral pressure loading control system 15 are electrically connected to the pressure control software 14 through the pressure controller 13. During the experiment, the vertical pressure loading control system 12 and the lateral pressure loading control system 15 are used to achieve servo loading of vertical and horizontal stresses on the transparent specimen 5.

[0062] Specifically, the pressure and flow dynamic distribution and control system includes a pressure and flow regulator 3, a pressure and flow sensor 4, and a pressure and flow control system 19. The pressure and flow regulator 3 and the pressure and flow sensor 4 are disposed within the perforation 2 near one end of the simulated wellbore 1. The pressure and flow regulator 3 is electrically connected to the pressure and flow control system 19 via the pressure and flow sensor 4. The pressure and flow regulator 3 is used to collect pressure and flow information entering each perforation 2 in real time and adjust the pressure and flow rate. The pressure and flow sensor 4 is used to collect pressure and flow information of each perforation 2 in real time and transmit the information to the pressure and flow control system 19.

[0063] Specifically, the hydraulic servo pumping system includes a plunger pump 16, a plunger pump controller 17, and a plunger pump control system 18. One end of the plunger pump 16 is connected to the simulated wellbore 1 via a pumping pipeline, and the other end of the plunger pump 16 is connected to the plunger pump control system 18 via the plunger pump controller 17. The plunger pump control system 18 is electrically connected to the pressure and flow control system 19 to achieve controllable intelligent pumping of the multi-perforation 2 of the fracturing sample. The plunger pump control system 18 is used to record information such as the pump pressure-time curve in real time.

[0064] Specifically, the pressure plate 6 is a transparent plate, specifically an acrylic transparent plate, to facilitate observation of the changes in the simulated wellbore 1 during the experiment. A pre-drilled hole for a measuring element is provided on the side of the pressure plate 6 near the transparent sample 5, and a measuring element is installed within the pre-drilled hole. In this embodiment, the measuring element is an acoustic emission sensor. The hydraulic fracture information visualization monitoring system includes a high-speed camera 8, a DIC digital image monitoring system 9, an acoustic emission monitoring system 7, and a multi-element information processor 10. The high-speed camera 8, the DIC digital image monitoring system 9, and the acoustic emission monitoring system 7 are electrically connected to the multi-element information processor 10. The high-speed camera 8 and the DIC digital image monitoring system 9 are positioned at a preset location near the transparent sample 5 via a moving device. The high-speed camera 8 and the DIC digital image monitoring system 9 are used to monitor the surface crack propagation and full-field stress evolution process of the transparent sample 5. The acoustic emission monitoring system 7 is electrically connected to the measuring element and is used to monitor the internal crack changes of the transparent sample 5 during fracturing. The multi-element information processor 10 is used to visualize, monitor, record, store, and analyze the internal and surface crack information of the transparent sample 5.

[0065] Example 2

[0066] This embodiment provides an experimental method for intelligent control of pressure-flow rate in hard-top horizontal well fracturing, including the following steps:

[0067] Step 1: Fabricate a transparent sample 5 with multiple perforations 2 in a horizontal well that meets the mechanical parameter requirements. First, obtain the physical and mechanical parameters of the hard roof rock. Then, develop a rock-like material mix to obtain a material ratio consistent with the physical and mechanical parameters of the hard roof rock. Simultaneously, synthesize a transparent material with consistent mechanical parameters using chemical materials such as polymethyl methacrylate (PMMA) as the mold filling material. Specifically, at least four prefabricated perforation 2 pipes are spaced apart on the prefabricated pipe of the simulated wellbore 1. The prefabricated pipe of the simulated wellbore 1 is placed inside the mold. The mold is filled with mold filling material and cured for 24 days to form a 200mm × 200mm × 200mm cubic rock-like material model, i.e., the transparent sample 5. The length of the configured simulated wellbore 1 is 150mm and the diameter is 12mm. The perforations 2 are 6mm in diameter. Considering the interference of pressure and flow distribution among the multiple perforations 2, four to six perforations 2 are set for dynamic intelligent adjustment to reflect the control effect of multi-perforation 2 fracturing in a real formation horizontal well.

[0068] Step 2, install the entire experimental system, specifically: place the transparent sample 5 in the true triaxial pressure loading test machine 11, and place pressure plates 6 with reserved holes on the left and right opposite sides, front and back opposite sides and the top side of the transparent sample 5 respectively. Place acoustic emission sensors in the reserved holes of the pressure plates 6 and connect them to the acoustic emission monitoring system 7; connect the simulated well 1 in the transparent sample 5 to the hydraulic servo pump pressure system and the pressure and flow dynamic distribution control system using the pump injection pipeline; move the high-speed camera 8 and the DIC digital image monitoring system 9 to a position that clearly captures the surface of the complete transparent sample 5 and connect them to the multi-element information processor 10; use the true three-dimensional loading servo control system for ground stress to apply pressures of 8MPa, 3MPa and 5MPa to the axial and lateral sides of the transparent sample 5 respectively according to the stress scheme.

[0069] Step 3, conduct the experiment: First, activate the hydraulic fracture information visualization monitoring system and input the corresponding specimen number, time, and other information into the multi-element information processor 10; then, start the pressure and flow dynamic distribution control system, and simultaneously fill the prepared fracturing fluid into the plunger pump 16 of the hydraulic servo pump system, and start the hydraulic servo pump system to pump fracturing fluid into the transparent specimen 5 at a flow rate of 100 ml / min; after the hydraulic fracturing experiment begins, when the plunger pump control system 18 observes that the pump pressure-time curve drops instantaneously and stabilizes near a certain pressure value, the hydraulic fracturing physical simulation experiment ends.

[0070] Step 4: After the experiment, dismantle the entire experimental system in sequence. Shut down the hydraulic fracture information visualization monitoring system, the hydraulic servo pump system, and the pressure and flow dynamic distribution control system; disconnect the fracturing fluid injection pipeline from the hydraulic servo pump system and the pressure and flow dynamic distribution control system; shut down the true three-dimensional stress loading servo control system and stop simulating stress loading; remove the pressure plate 6, and then remove the measuring elements from the pre-drilled holes in the pressure plate 6; remove the transparent sample 5; clean the pressure plate 6, the true triaxial pressure loading testing machine 11, and related wiring, and then perform maintenance treatment.

[0071] Step 5: Processing and analyzing experimental data: After the experiment, observe the morphology and trend of hydraulic cracks on the surface of transparent sample 5 and record the data using a camera; cut and observe transparent sample 5 and record the data using a camera after cutting; analyze the morphology of hydraulic cracks using pump pressure-time curves, capture the complete process of crack propagation in multi-perforation 2 using high-speed camera 8, obtain stress information during the rupture process of transparent sample 5 based on DIC digital image monitoring technology; scan and reconstruct the internal crack morphology of transparent sample 5 based on CT scanning technology, and compare and analyze it with the internal crack information obtained by acoustic emission monitoring system 7; summarize and analyze the crack propagation evolution law, geometric morphology and induced stress evolution law caused by different pressure and flow rate changes in perforation 2 under the action of dynamic pressure and flow rate distribution, and propose a pressure and flow rate distribution control mechanism under different fracturing parameter combinations.

[0072] The specific embodiments of the present invention have been described in detail above with reference to the figures, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A hard-top horizontal well porous fracturing pressure-flow intelligent regulation experiment system, characterized in that: The device comprises a transparent sample (5), a true three-dimensional loading servo control system, a hydraulic servo pump pressure system and a hydraulic fracture information visualization monitoring system; one side of the transparent sample (5) is internally provided with a simulated wellbore (1) from the end face, a plurality of perforations (2) intersecting and communicating with the simulated wellbore (1) are pre-provided in the transparent sample (5) at intervals, a pressure and flow dynamic distribution control system is connected to one end of the perforation (2) close to the simulated wellbore (1), and the pressure and flow dynamic distribution control system is electrically connected with the hydraulic servo pump pressure system; ​ The pressure and flow dynamic distribution control system is used for collecting pressure and flow information of the perforation (2) and adjusting the pressure and flow size of the perforation (2) according to a pressure flow dynamic distribution control mechanism, and the pressure and flow dynamic distribution control system comprises a pressure and flow regulator (3), a pressure and flow sensor (4) and a pressure and flow control system (19); the pressure and flow regulator (3) and the pressure and flow sensor (4) are arranged at one end of the perforation (2) close to the simulated wellbore (1), and the pressure and flow regulator (3) is electrically connected with the pressure and flow control system (19) through the pressure and flow sensor (4), wherein the pressure flow dynamic distribution control mechanism comprises: The sum of injection flow rates of all perforations (2) is equal to the total injection flow rate, and the expression is: ； The relationship between pressure and flow in each perforation (2) is: ； wherein, and Qi is the total injection flow rate and the injection flow rate of the i-th perforation, respectively; N is the total number of perforations; is the set resistance of the pressure and flow rate regulator; is the perforation pressure; is the perforation friction coefficient; is the simulated pressure in the wellbore; The true three-dimensional loading servo control system comprises a true triaxial pressure loading testing machine (11), a pressure plate (6) and a pressure loading control system; during the experiment, the transparent sample (5) is placed in the true triaxial pressure loading testing machine (11), and a plurality of pressure plates (6) are arranged on the circumferential side and the top end of the transparent sample (5) through the pressure loading control system; The hydraulic servo pump pressure system is used for pumping the fracturing fluid with a set flow rate into the transparent sample (5); The hydraulic fracture information visualization monitoring system is used for monitoring, recording and processing the crack dynamic expansion process, the pump injection pressure information and the surface stress evolution process of the transparent sample (5) in the fracturing process.

2. The hard-top horizontal well porous fracturing pressure-flow intelligent regulation experiment system according to claim 1, characterized in that: The pressure loading control system comprises a vertical pressure loading control system (12), a lateral pressure loading control system (15), a pressure controller (13) and pressure control software (14); the pressure plates (6) arranged on the circumferential side of the transparent sample (5) are arranged on the circumferential wall of the true triaxial pressure loading testing machine (11) oppositely, the pressure plates (6) arranged on the top end of the transparent sample (5) are arranged on the top wall of the true triaxial pressure loading testing machine (11), the pressure plates (6) on the top wall are connected with the vertical pressure loading control system (12), the pressure plates (6) on the circumferential wall are connected with the lateral pressure loading control system (15), and the vertical pressure loading control system (12) and the lateral pressure loading control system (15) are electrically connected with the pressure controller (13) and the pressure control software (14).

3. The hard-top horizontal well multi-pore fracturing pressure-flow intelligent regulation experiment system according to claim 1, characterized in that: The hydraulic servo pump pressure system comprises a plunger pump (16), a plunger pump controller (17) and a plunger pump control system (18), the output end of the plunger pump (16) is connected with the simulated wellbore (1) through a pump injection pipeline, and the plunger pump (16) is connected with the plunger pump control system (18) through the plunger pump controller (17); and the plunger pump control system (18) is electrically connected with the pressure and flow control system (19).

4. The hard-top horizontal well multi-pore fracturing pressure-flow intelligent regulation experiment system according to claim 3, characterized in that: The pressing plate (6) is a transparent plate, and a reserved hole is formed in the side of the pressing plate (6) close to the transparent sample (5), and a measuring element is arranged in the reserved hole.

5. The hard-top horizontal well multi-pore fracturing pressure-flow intelligent regulation experiment system according to claim 4, characterized in that: The hydraulic fracture information visual monitoring system comprises a high-speed camera (8), a DIC digital image monitoring system (9), an acoustic emission monitoring system (7) and a multi-element information processor (10), the high-speed camera (8), the DIC digital image monitoring system (9) and the acoustic emission monitoring system (7) are electrically connected with the multi-element information processor (10) respectively, the high-speed camera (8) and the DIC digital image monitoring system (9) are arranged at a preset position close to the transparent sample (5) through a moving device, the high-speed camera (8) and the DIC digital image monitoring system (9) are used for monitoring the crack expansion and full-field stress evolution process of the transparent sample (5), the acoustic emission monitoring system (7) is electrically connected with the measuring element and is used for monitoring the crack change process of the transparent sample (5) in the fracturing process through the measuring element, and the multi-element information processor (10) is used for visual monitoring, recording, storing and analyzing the internal and surface crack information of the transparent sample (5).

6. The hard-top horizontal well multi-pore fracturing pressure-flow intelligent regulation experiment system according to claim 1, characterized in that: The multiple perforations (2) flow dynamic distribution control condition is that: ， wherein, and Qi is the total injection flow rate and the injection flow rate of the i-th perforation (2); N is the total number of perforations (2); and Qi is the relative flow rate into the i-th perforation (2).

7. An experimental method using the hard-top horizontal well porous fracturing pressure-flow intelligent regulation experimental system of claim 5, characterized in that, The method comprises the following steps: Step 1, a transparent sample (5) meeting the mechanical parameter requirements and having multiple perforations (2) is prepared; Step 2, the entire experimental system is installed; Step 3, implement the experiment: first enable hydraulic fracture information visualization monitoring system, and input corresponding test piece number, time information on the multi-element information processor (10); then start the pressure and flow dynamic distribution control system, at the same time fill the configured fracturing fluid into the plunger pump (16) of the hydraulic servo pumping system, and start the hydraulic servo pumping system and pump the fracturing fluid into the transparent sample (5) at the set flow rate; after the hydraulic fracturing experiment starts, the plunger pump control system (18) observes that the pump pressure-time curve instantaneously decreases and stabilizes around a certain pressure value, and the hydraulic fracturing physical simulation experiment ends, wherein the dynamic distribution control method of the pressure and flow dynamic distribution control system is: at time t, the pressure in perforation a reaches the sample cracking condition, at this time, the pressure and flow rate of perforation a are P(a) and Q(a) respectively, the pressure and flow rate of perforation b are P(a) and Q(b) respectively, and P(a) < P(b), Q(a) > Q(b), at this time, the pressure and flow regulator (3) feeds back the pressure and flow information to the pressure and flow control system (19) through the pressure and flow sensor (4), the pressure and flow regulator (3) adjusts the additional resistance of the inflow fracture at time t so that P(a) + Q(a) = P(b) + Q(b), the flow rates pumped into each fracture are the same; ​ Step 4, after the experiment is completed, the entire experimental system is removed in sequence; Step 5, the experimental data are processed and analyzed: after the experiment is completed, the hydraulic fracture shape and trend of the transparent sample (5) are observed, and the transparent sample (5) is photographed and recorded by using a camera; the transparent sample (5) is cut and observed, and the cut transparent sample (5) is photographed and recorded by using a camera; the hydraulic fracture shape is analyzed by using a pump pressure-time curve, the complete crack expansion process of the multiple perforations (2) is captured by using a high-speed camera (8), stress information in the crack process of the transparent sample (5) is obtained based on a DIC digital image monitoring technology; the crack shape inside the transparent sample (5) is scanned and reconstructed based on a CT scanning technology, and the internal crack information obtained by the acoustic emission monitoring system (7) is compared and analyzed; and the pressure flow distribution control mechanism under the action of different fracturing parameter groups is summarized and analyzed.

8. The hard-top horizontal well multi-pore fracturing pressure-flow intelligent regulation experiment method according to claim 7, characterized in that: The transparent sample (5) is prepared by: arranging at least four perforation (2) prefabricated pipes on the simulated wellbore (1) prefabricated pipe at intervals, arranging the simulated wellbore (1) prefabricated pipe in a mold, filling the mold with a sample material selected according to the mechanical characteristics of the simulated rock stratum, and curing for 24 days.

9. The hard-top horizontal well multi-pore fracturing pressure-flow intelligent regulation experiment method according to claim 8, characterized in that: The method for installing the whole experimental system is as follows: the transparent sample (5) is placed in a true triaxial pressure loading testing machine (11), and a pressure plate (6) provided with a reserved hole is arranged on the left and right opposite sides, the front and back opposite sides and the upper side of the transparent sample (5), the measuring element in the reserved hole of the pressure plate (6) is placed and connected with the acoustic emission monitoring system (7); the simulated wellbore (1) in the transparent sample (5) is connected with a hydraulic servo pump pressure system and a pressure and flow dynamic distribution control system by using a pump injection pipeline; a high-speed camera (8) and a DIC digital image monitoring system (9) are moved to clearly capture the surface of the complete transparent sample (5) and are connected with a multi-element information processor (10); the true three-dimensional stress servo control system is used to apply pressure to the axial and lateral directions of the transparent sample (5) according to a stress scheme; After the experiment is completed, the method for dismounting the whole experimental system in sequence is as follows: the hydraulic fracture information visualization monitoring system, the hydraulic servo pump pressure system and the pressure and flow dynamic distribution control system are closed, the fracturing fluid pump injection pipeline is disconnected from the hydraulic servo pump pressure system and the pressure and flow dynamic distribution control system; the true three-dimensional stress servo control system is closed, and the simulated ground stress loading is stopped; the pressure plate (6) is removed, and then the measuring element in the reserved hole of the pressure plate (6) is removed; the transparent sample (5) is removed; the pressure plate (6), the true triaxial pressure loading testing machine (11) and related lines are cleaned and maintained.

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