Core holder, indoor simulation experiment system and method for water injection fracturing cracks

Abstract

The present invention discloses a core holder, an indoor simulation experiment system and method for simulating water injection fracturing cracks. The core holder comprises a cylinder, a rubber sleeve, a core sealing cover and a core plug. The cylinder is provided with an inner cavity along the inner center for placing the core, and openings are provided at both ends of the inner cavity, which are a water injection end and a water outlet end respectively; the rubber sleeve is circumferentially arranged in the inner cavity for circumferentially sealing the core; the present invention realizes the simulation of dynamic cracks induced by water injection in the core by modifying the existing holder; and the crack conditions inside the core can be monitored by an acoustic emission device, and a data acquisition control device can collect relevant data in real time, so as to further understand the generation mechanism, specific manifestation form and influence law of development effect of dynamic cracks induced by water injection and volume fracturing network; dynamic crack simulation can be performed for both full-diameter cores and square cores, which can simulate the actual underground conditions more realistically.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field exploration and development, and particularly relates to a core holder, an indoor simulation experiment system and a method for simulating water injection fracturing cracks. Background Art

[0002] The development of tight oil reservoirs basically requires fracturing and production, and the development faces the influence of multiple fractures: natural fractures, volume fracturing fractures, dynamic fractures induced by water injection, etc. The generation of fractures leads to rapid increase of water cut, low sweep efficiency, and low recovery degree. At present, there is a deep understanding of the static description of natural fractures, but the understanding of the characteristics of dynamic fractures and volume fracturing networks is limited to the information fed back from production phenomena. The understanding of the generation mechanism, specific manifestations, and influence of dynamic fractures and volume fracturing networks induced by water injection on the development effect is relatively preliminary.

[0003] In the prior art, the core holder for indoor simulation experiments usually adopts a traditional core holder, which is suitable for full-diameter cores. However, the square core has a larger end face and can more realistically simulate the actual underground conditions. A core holder suitable for square cores is needed to establish a more comprehensive and realistic experimental simulation environment and ensure the validity of the experimental data. Summary of the invention

[0004] In view of the above problems, the present invention discloses a core holder, which comprises:

[0005] A cylinder body, with an inner cavity provided along the inner center thereof for placing the core, and the cylinder body is provided with a water injection end and a water outlet end;

[0006] A rubber sleeve is arranged circumferentially along the inner wall of the cylinder and is used to circumferentially seal the core;

[0007] A core sealing cap, which is arranged at the water injection end and is interconnected with the side wall of the cylinder, and is used for sealing the end face of the cylinder;

[0008] A core plug is arranged at the water outlet end, the end surface of the core plug is designed corresponding to the core end surface, and the end of the core plug contacts the inner wall of the inner cavity through a sealing sleeve, so as to seal the end surface of the cylinder.

[0009] Furthermore, a plurality of threaded holes are arranged on the side wall of the water injection end of the cylinder, and a through hole is arranged on the end surface of the core sealing cover corresponding to the plurality of threaded holes, and the core sealing cover is connected to the threaded holes by fixing screws passing through the through holes.

[0010] Furthermore, a protrusion is provided on one side of the core sealing cover, and the protrusion extends into the inner cavity and contacts the core;

[0011] The outer periphery of the protrusion contacts the inner wall of the cylinder through the rubber sleeve, and an annular notch is arranged on the periphery of the protrusion, and the annular notch forms a sealing contact with the wall surface of the cylinder through an O-ring.

[0012] Furthermore, one end of the core plug is set as a contact end, the contact end is designed corresponding to the cross-sectional size of the core, the contact end extends into the inner cavity, and contacts the wall surface of the cylinder through a sealing sleeve arranged on the periphery, and the contact end is slidably connected to the sealing sleeve;

[0013] The other end of the core plug is set as an adjustment end, and a cylindrical block is provided at the center of the adjustment end for installing a tightening component.

[0014] Furthermore, the tightening assembly includes an adjusting nut and a pressing cap;

[0015] The adjusting nut is rotatably arranged on the cylindrical block;

[0016] The pressing cap is an annular structure, the interior of the annular structure is connected to the adjusting nut by a threaded connection, and the outer wall of the annular structure is provided with a first external thread;

[0017] The outer wall of the pressure cap is threadably connected to the inner wall of the water outlet end of the cylinder through the first external thread.

[0018] Furthermore, one end of the sealing sleeve presses the rubber sleeve, and the other end is fixedly connected to the pressure cap by a positioning screw.

[0019] Furthermore, a gap is provided between the rubber sleeve and the wall surface of the inner cavity, and the gap is communicated with the outside through a confining pressure inlet and a pressure relief outlet respectively provided on the wall surface of the cylinder.

[0020] Furthermore, a first through hole is provided inside the core plug, and a second through hole is provided inside the core sealing cover. Acoustic wave probe pressure caps are provided at the positions of the first through hole and the second through hole, and the acoustic wave probe pressure caps at the water injection end and the water outlet end are respectively provided with an acoustic emission sensor transmitting end and an acoustic emission sensor receiving end near the core.

[0021] Furthermore, the end surface of the core sealing cover is provided with a plurality of through holes for installing perforation blind pipes.

[0022] In addition, the present invention also discloses an indoor simulation experiment system for simulating water injection fracturing cracks, including the core clamp for clamping the core, and the system also includes:

[0023] Full diameter gripper for holding cylindrical cores;

[0024] A fixing device for fixing the full-diameter holder and the core holder;

[0025] A control cabinet is fixedly mounted on the fixing device, and the fixing device has an internal integrated configuration including:

[0026] An annular pressure tracking pump, the output end of which is connected to the confining pressure inlet of the full-diameter clamp and the core clamp through an annular pressure pipeline;

[0027] A constant speed and constant pressure pump, the output end of which is connected to the perforation blind pipe of the full diameter clamp and the core clamp through an output pipeline;

[0028] An acoustic emission device, connected to the transmitting end of the acoustic emission sensor arranged at the water injection end, for generating elastic waves;

[0029] The data acquisition control device is electrically connected to the acoustic emission sensor disposed at the receiving end of the acoustic emission sensor and is used to acquire vibration data generated by the core according to the elastic wave.

[0030] Furthermore, the present invention also discloses an indoor simulation experiment method for simulating water injection fracturing cracks. Based on the indoor simulation experiment system, the indoor simulation experiment method for simulating water injection fracturing cracks is performed. The method comprises the following steps:

[0031] An insertion hole for a perforation blind pipe is preset on the end face of the core;

[0032] Select a corresponding holder according to the type of core, and fix the core inside the holder, wherein the holder includes the core holder and a full-diameter holder;

[0033] Install a perforation blind tube on the end face of the core plug, seal the outer end of the perforation blind tube, and drill holes in the perforation blind tube in the radial direction;

[0034] Install and fix the inner end of the perforation blind pipe corresponding to the insertion hole;

[0035] The pressure relief outlet of the clamp is blocked, and the annular pressure tracking pump and the constant speed and pressure pump are respectively started to conduct a water injection fracturing fracture simulation experiment;

[0036] The elastic waves are emitted by the acoustic emission device, causing surface displacement on the surface of the core fracture;

[0037] The real-time pressure values ​​of the ring pressure tracking pump and the constant speed and constant pressure pump, the real-time values ​​of the acoustic emission signals and the vibration data of the corresponding core are collected respectively.

[0038] The present invention realizes the simulation of dynamic cracks induced by water injection in the core by modifying the existing clamp, and the simulated cracks are dynamic; and the crack conditions inside the core can be monitored by an acoustic emission device, and the data acquisition control device can collect relevant data in real time, so as to further understand the generation mechanism, specific manifestation form and influence law of the dynamic cracks induced by water injection and volume fracturing network on the development effect; at the same time, an indoor simulation experimental system for simulating water injection fracturing cracks is proposed based on the clamp, and dynamic crack simulation can be performed on full-diameter cores and cores, which can more realistically simulate the actual underground conditions.

[0039] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 A schematic structural diagram of a core holder according to an embodiment of the present invention is shown;

[0042] Figure 2 A schematic structural diagram of a tightening assembly according to an embodiment of the present invention is shown;

[0043] Figure 3 A schematic cross-sectional view of a tightening assembly according to an embodiment of the present invention is shown;

[0044] Figure 4 A schematic diagram of the assembly structure of a core holder according to an embodiment of the present invention is shown;

[0045] Figure 5 A schematic flow chart of an indoor simulation experiment system for water injection fracturing according to an embodiment of the present invention is shown.

[0046] In the attached drawings: 1. cylinder; 2. inner cavity; 3. confining pressure inlet; 4. pressure relief outlet; 5. rubber sleeve; 6. core plug; 61. contact end; 62. adjustment end; 63. first through hole; 7. O-ring; 8. sealing sleeve; 9. core sealing cover; 10. fixing screw; 11. water injection end; 12. water outlet end; 13. adjusting nut; 14. pressure cap; 141. first external thread; 15. positioning screw; 16. perforation blind pipe; 17. sonic probe pressure pipe cap; 18. acoustic emission sensor transmitting end; 19. acoustic emission sensor receiving end; 20. core; 21. rotating shaft; 22. rotating shaft frame; 23. reduction motor; 24. control cabinet. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] In one embodiment of the present invention, a conventional core holder is suitable for full-diameter cores. As for square cores that can better reflect the actual underground conditions, the installation structure of the conventional core holder is not matched, and the installation process of the square core is not convenient and fast. For this reason, the present invention proposes a core holder for fixing the square core 20 to be tested.

[0049] refer to Figure 1 As shown, the core holder includes a barrel 1, a rubber sleeve 5, a core sealing cover 9 and a core plug 6. The barrel 1 is provided with an inner cavity 2 along the inner center thereof for placing the core 20, and the barrel 1 is provided with a water injection end 11 and a water outlet end 12; the rubber sleeve 5 is arranged circumferentially along the inner wall of the barrel 1 for circumferentially sealing the core 20; the core sealing cover 9 is provided at the water injection end 11 and is interconnected with the side wall of the barrel 1 for end face sealing of the barrel 1; the core plug 6 is provided at the water outlet end 12, and the end face of the core plug 6 is designed to correspond to the end face of the core 20, and the end of the core plug 6 contacts the inner wall of the barrel 1 through the sealing sleeve 8 for end face sealing of the barrel 1.

[0050] Among them, a protrusion is provided on one side of the core sealing cover 9, and the protrusion extends into the inner cavity 2 and abuts against the core 20; the outer periphery of the protrusion abuts against the inner wall of the cylinder 1 through the rubber sleeve 5, and an annular groove is provided in the circumference of the protrusion, and the annular groove forms a sealing contact with the wall surface of the cylinder 1 through the O-ring 7.

[0051] refer to Figure 2and Figure 3 As shown, one end of the core plug 6 is set as a contact end 61, and the contact end 61 is designed corresponding to the cross-sectional size of the core 20. The contact end 61 extends into the inner cavity 2, and contacts the wall surface of the cylinder 1 through the sealing sleeve 8 arranged on the periphery, and the contact end 61 is slidably connected to the sealing sleeve 8; the other end of the core plug 6 is set as an adjustment end 62, and a cylindrical block is arranged at the center of the adjustment end 62 for installing a tightening assembly. The tightening assembly includes an adjusting nut 13 and a pressing cap 14; the adjusting nut 13 is rotatably arranged on the cylindrical block; the pressing cap 14 is an annular structure, and the interior of the annular structure is connected to the adjusting nut 13 by a threaded connection, and the outer wall of the annular structure is provided with a first external thread 141; the outer wall of the pressing cap 14 is threadedly connected to the inner wall of the water outlet end 12 of the cylinder 1 through the first external thread 141. One end of the sealing sleeve 8 presses the rubber sleeve 5, and the other end is fixedly connected to the pressing cap 14 by a positioning screw 15.

[0052] When installing and sealing the core 20, the pretreated core 20 is placed in the inner cavity 2, which is a square cavity structure. One end of the inner cavity 2 is end-face sealed by a core sealing cover 9, and in the inner cavity 2, the outer periphery of the core 20 is circumferentially sealed by a circumferentially arranged rubber sleeve 5, and a gap is provided between the rubber sleeve 5 and the cavity wall of the inner cavity 2; the core sealing cover 9 is fixedly connected to the cylinder 1 by a plurality of circumferentially arranged fixing screws 10.

[0053] The other end of the inner cavity 2 is sealed by the core plug 6. After the core 20 is placed in the inner cavity 2, the fixedly connected sealing sleeve 8 and the pressure cap 14 are first installed in the water inlet and outlet ends 12 by threaded connection along the direction of the inner cavity 2, wherein the end face of the sealing sleeve 8 is provided with a step surface, and the step surface contacts the rubber sleeve 5, and the end face of the rubber sleeve 5 contacts the wall surface of the inner cavity 2, and then the core plug 6 is slidably installed in the sealing sleeve 8 along the axial direction of the cylinder 1. , then rotate the adjusting nut 13 and place it on the cylindrical block of the adjusting end 62 of the core plug 6, rotate the adjusting nut 13, so that the adjusting nut 13 is fed along the thread direction of the pressing cap 14, and at the same time, the adjusting nut 13 squeezes the core plug 6, so that the core plug 6 moves toward the core 20 until the end face of the core plug 6 contacts the core 20; at this time, the relative position of the adjusting nut 13 and the pressing cap 14 is maintained, so that the internal core 20 maintains a fixed relative position.

[0054] In one embodiment of the present invention, the present invention also discloses an indoor simulation experimental system for water injection fracturing cracks, including the core clamp for clamping the core 20, and the system also includes a full-diameter clamp and a fixing device, the full-diameter clamp is used to clamp the columnar core; the fixing device is used to fix the full-diameter clamp and the core clamp.

[0055] refer to Figure 4 As shown, the fixing device includes a rotating shaft frame 22, on which a rotating shaft 21 is rotatably arranged, and the rotating shaft frame 22 is provided with at least two groups, each of which is fixedly connected to the full-diameter clamp and the core clamp through the rotating shaft 21, and driven by a reduction motor 23 connected to the end of the rotating shaft 21, and the reduction motor 23 is fixedly installed on the rotating shaft frame 22; and also includes a control cabinet 24, which is fixedly arranged on the rotating shaft frame 22;

[0056] In this embodiment, when the clamp is clamping the core 20, a rotating shaft 21 is fixedly connected to the side of the cylinder 1, and the rotating shaft 21 is mounted on the rotating shaft frame 22. The rotating shaft 21 is driven to rotate by the reduction motor 23. The rotation of the rotating shaft 21 can drive the cylinder 1 to rotate. When installing the core 20, the cylinder 1 can be rotated to a vertical direction first, and the core can be hoisted into the cylinder 1 through a hoisting device, and then the cylinder 1 can be rotated back to a horizontal direction, so as to facilitate the limiting and fixing of the clamp, and keep the clamp in a horizontal or vertical state during the subsequent indoor simulation experiment, so as to avoid relative movement of the clamp during the fracturing experiment, thereby interfering with the pipeline of the indoor simulation experiment system, which is beneficial to improving the stability of the subsequent indoor simulation experiment.

[0057] refer to Figure 5 As shown, the integrated arrangement inside the control cabinet 24 includes the following structures:

[0058] An annular pressure tracking pump, the output end of which is connected to the confining pressure inlet 3 of the full-diameter clamp and the core clamp through an annular pressure pipeline;

[0059] A constant speed and constant pressure pump, the output end of which is connected to the perforation blind pipe 16 of the full diameter clamp and the core clamp through an output pipeline;

[0060] An acoustic emission device, connected to an acoustic emission sensor transmitting end 18 disposed at the water injection end 11, for generating elastic waves;

[0061] The data acquisition control device is electrically connected to the acoustic emission sensor disposed at the acoustic emission sensor receiving end 19 and is used to collect vibration data generated by the core 20 according to the elastic wave.

[0062] The input ends of the annular pressure tracking pump and the constant speed and constant pressure pump are respectively connected to two groups of water storage tanks, and the output ends of the annular pressure tracking pump and the constant speed and constant pressure pump are respectively connected to the annular pressure pipeline and the output pipeline through pneumatic control valves, and the annular pressure pipeline and the output pipeline respectively control the opening and closing of the annular pressure tracking pump and the constant speed and constant pressure pump through the pneumatic control valves arranged on the corresponding pipelines. In addition, manual valves and pressure sensors are respectively arranged on the branches of the annular pressure pipeline and the output pipeline leading to the full-diameter clamp and the core clamp, and the manual valve is used to control the flow rate of the corresponding branch, and the pressure sensor is used to detect the pressure of the corresponding branch.

[0063] Buffer tanks are also provided on the annular pressure pipeline and the output pipeline respectively. The buffer tanks are provided for carrying out sand entrainment experiments, that is, sand is carried by the movement of water in the annular pressure pipeline and the output pipeline, which can reduce the pulse of the annular pressure tracking pump and the constant speed and constant pressure pump, and play a role in stabilizing the pressure of the water transported in the annular pressure pipeline and the output pipeline.

[0064] The present invention provides an indoor simulation experiment method for water injection fracturing cracks based on the indoor simulation experiment system for water injection fracturing cracks, and the method comprises the following steps:

[0065] 1. Preset an insertion hole for the perforation blind tube 16 on the end face of the core 20;

[0066] 2. Select a corresponding holder according to the type of the core 20, and fix the core 20 inside the holder, wherein the holder includes the core holder and a full-diameter holder;

[0067] 3. Install the perforation blind tube 16 on the end surface of the core plug 6, seal the outer end of the perforation blind tube 16, and drill holes in the perforation blind tube 16 in the radial direction;

[0068] 4. Install and fix the inner end of the perforation blind pipe 16 corresponding to the insertion hole;

[0069] 5. Block the pressure relief outlet 4 of the clamp, start the ring pressure tracking pump and the constant speed and pressure pump respectively, and conduct a water injection fracturing fracture simulation experiment;

[0070] 6. Using an acoustic emission device to emit elastic waves, so as to cause surface displacement on the crack surface of the core 20;

[0071] 7. Collect the real-time pressure values ​​of the ring pressure tracking pump and the constant speed and constant pressure pump, the real-time values ​​of the acoustic emission signals, and the vibration data of the corresponding core 20 respectively.

[0072] In this embodiment, the present invention simulates the actual underground environment through the indoor simulation experiment system of water injection fracturing cracks, wherein, before the core is subjected to the simulation experiment, an insertion hole for the perforation blind pipe 16 is first preset on the end face of the core 20, a suitable clamp is selected according to the structure of the core 20, and the core 20 is fixed inside the clamp, and the core 20 is sealed by the rubber sleeve 5, the sealing sleeve 8, the core plug 6 and the core sealing cover 9. In addition, the inner cavity 2 is also sealed by the O-ring 7, wherein a protrusion is provided on one side of the core sealing cover 9, and an annular notch is provided in the circumference of the protrusion, and a sealing contact is formed with the wall surface of the inner cavity 2 through the O-ring 7; of course, an annular sealing groove is also provided on the outer periphery of the sealing sleeve 8, and the inner cavity 2 is sealed by the O-ring 7 preset therein to contact the wall surface of the inner cavity 2, thereby performing auxiliary sealing on the inner cavity 2.

[0073] In this embodiment, when the clamp is selected for use, if the core 20 is a full-diameter core, the full-diameter clamp is selected to clamp the core 20, and the pipeline of the indoor simulation experiment system of water injection fracturing fracture needs to be managed, wherein the valves of the annular pressure tracking pump and the constant speed and constant pressure pump leading to the annular pressure pipeline and the output pipeline of the full-diameter clamp are opened, and the valves of the annular pressure tracking pump and the constant speed and constant pressure pump leading to the annular pressure pipeline and the output pipeline of the core clamp are closed. If the core 20 is the core 20, the core clamp is selected to clamp the core 20; at this time, the valves of the annular pressure tracking pump and the constant speed and constant pressure pump leading to the annular pressure pipeline and the output pipeline of the full-diameter clamp are closed, and the valves of the annular pressure tracking pump and the constant speed and constant pressure pump leading to the annular pressure pipeline and the output pipeline of the core clamp are opened.

[0074] The clamp simulates the formation pressure condition, and a protruding perforation blind tube 16 is added to the end face of the core plug 6, and the outer end of the perforation blind tube 16 is sealed, and holes are drilled in the radial direction. After the clamp is assembled, the perforation blind tube 16 on the end face of the core plug 6 is inserted into the preset insertion hole of the core 20 to simulate the injection well at the oil field site. Multiple perforation blind tubes 16 are set as needed, and multiple perforation blind tubes 16 are fracturing and fracture-forming at the same time or one by one to compare the fracture-forming effects under different conditions. For example, when a full-diameter core is selected, the clamp evenly distributes 3 perforation blind tubes 16 on the end face of the full-diameter core; when a square core is selected, the core clamp evenly distributes 4 perforation blind tubes 16 on the end face of the square core to make the dynamic fractures induced by water injection evenly distributed. The effective length of the perforation blind tube 16 is 50 mm.

[0075] In this embodiment, the output end of the constant speed and constant pressure pump (model FDBS-2A) is connected to the perforation blind pipe 16 of the full-diameter clamp and the core clamp through an output pipeline; the constant speed and constant pressure pump is an improved pump body improved on the basis of the original double-cylinder constant pressure and constant speed pump. Compared with the original pump body, the constant speed and constant pressure pump increases the working pressure of the pump (from the original 70MPa to 100MPa) and the flow rate range (from the original 0-60ml / min to 0-100ml / min). When the actual water injection pressure is in the range of 40-50MPa, the dense natural core can be fractured, so that the constant speed and constant pressure pump works to inject water, which increases the hydraulic pressure and instantaneous flow rate, and can quickly and effectively induce the core 20 to form dynamic cracks, thereby squeezing to form a volumetric fracture network. The annular pressure tracking pump is a single-cylinder constant pressure pump, and the pressure of the pump body always tracks the aforementioned constant speed constant pressure pump, that is, the working pressure of the annular pressure tracking pump is 100MPa, and the flow rate range is maintained at 0-100ml / min.

[0076] When conducting an indoor simulation experiment of water injection fracturing cracks, the output end of the annular pressure tracking pump is connected to the confining pressure inlet 3 of the full-diameter clamp and the core clamp through the annular pressure pipeline. At this time, the pressure relief outlet 4 is blocked, so the high-pressure water flow injected from the confining pressure inlet 3 will fill the gap between the wall of the inner cavity 2 and the rubber sleeve 5, thereby applying circumferential pressure to the core body in the circumference of the core 20 to simulate the underground core pressure environment. After the constant speed and constant pressure pump induces dynamic cracking and volume fracturing network of the core 20 through water injection, the indoor simulation experiment system of water injection fracturing cracks is non-destructively tested by an acoustic emission device. Acoustic emission is a passive dynamic inspection method and is sensitive to linear defects. During the test, the acoustic emission inspection can comprehensively detect and evaluate the generation mechanism and specific manifestations of dynamic cracks and volume fracturing network induced by water injection.

[0077] Specifically, the acoustic emission device emits elastic waves at the acoustic emission sensor transmitting end 18 of the water injection end 11. The elastic waves propagate to the crack surface of the core 20 to generate mechanical vibrations, thereby causing relative displacement at the core cracks. The acoustic emission sensor arranged at the acoustic emission sensor receiving end 19 of the water outlet end 12 performs displacement monitoring. The acoustic emission sensor converts the mechanical vibration information of the core cracks into electrical signals and transmits them to the data acquisition control device, so as to quantitatively collect the real-time core vibration data of the indoor simulation experiment of water injection fracturing cracks. Of course, the data acquisition control device will also synchronously collect the real-time pressure values ​​of the real-time ring pressure tracking pump and the constant speed and pressure pump and the real-time values ​​of the acoustic emission signal, generate data reports, and obtain analysis reports and curves based on the data report analysis. The dynamic fracture simulation experiment of the water injection-induced core is completed, and the specific situation of the internal fractures is obtained, and the database file format can also be generated for flexible use by users.

[0078] The present invention realizes the simulation of dynamic cracks induced by water injection in the core by modifying the existing clamp, and the simulated cracks are dynamic; and the internal cracks of the core can be monitored by the acoustic emission device, and the data acquisition control device can collect relevant data in real time, which can further understand the mechanism, specific manifestations, and influence on the development effect of dynamic cracks induced by water injection and volume fracturing network; at the same time, an indoor simulation experimental system for simulating water injection fracturing cracks is proposed based on the clamp, and dynamic crack simulation can be performed for full-diameter cores and square cores, which can simulate the actual underground situation more realistically. It solves the problem that the existing technology uses high-pressure water injection to open the core cracks, freeze the water in the core cracks, and use cyclic water injection freeze-thaw to induce cracks, but the cracks simulated by this method are non-dynamic and the internal crack conditions cannot be monitored.

[0079] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A core holder for fixing a square-shaped core (20) to be tested, characterized in that: The core holder comprises: A cylinder (1) is provided with an inner cavity (2) along the inner center thereof for placing the core (20), and the cylinder (1) is provided with a water injection end (11) and a water outlet end (12); A rubber sleeve (5) is arranged circumferentially along the inner wall of the cylinder (1) and is used to circumferentially seal the core (20); A core sealing cover (9), which is arranged at the water injection end (11) and is connected to the side wall of the cylinder (1) and is used to seal the end face of the cylinder (1); A core plug (6) is arranged at the water outlet end (12), the end surface of the core plug (6) is designed to correspond to the end surface of the core (20), and the end of the core plug (6) contacts the inner wall of the cylinder (1) through a sealing sleeve (8) to seal the end surface of the cylinder (1); One end of the core plug (6) is set as a contact end (61), the contact end (61) extends into the inner cavity (2), and contacts the wall surface of the cylinder (1) through a sealing sleeve (8) arranged on the outer periphery, and the contact end (61) is slidably connected to the sealing sleeve (8); The other end of the core plug (6) is set as an adjustment end (62), and a cylindrical block is provided at the center of the adjustment end (62) for installing a tightening component; The tightening assembly comprises an adjusting nut (13) and a pressing cap (14); The adjusting nut (13) is rotatably arranged on the cylindrical block; The pressing cap (14) is an annular structure, the interior of the annular structure is connected to the adjusting nut (13) by means of a threaded connection, and the outer wall of the annular structure is provided with a first external thread (141); The outer wall of the pressure cap (14) is threadedly connected to the inner wall of the water outlet end (12) of the cylinder (1) via the first external thread (141); One end of the sealing sleeve (8) presses the rubber sleeve (5), and the other end is fixedly connected to the pressure cap (14) via a positioning screw (15); the end surface of the sealing sleeve (8) is provided with a step surface, and contacts the rubber sleeve (5) via the step surface.

2. The core holder according to claim 1, characterized in that: A plurality of threaded holes are provided on the side wall of the water injection end (11) of the cylinder (1), and through holes are provided on the end surface of the core sealing cover (9) corresponding to the plurality of threaded holes. The core sealing cover (9) is connected to the threaded holes by fixing screws (10) passing through the through holes.

3. The core holder according to claim 2, characterized in that: A protrusion is provided on one side of the core sealing cover (9), and the protrusion extends into the inner cavity (2) and contacts the core (20); The outer periphery of the protrusion contacts the inner wall of the cylinder (1) through the rubber sleeve (5), and an annular groove is provided on the periphery of the protrusion, and the annular groove forms a sealing contact with the wall surface of the cylinder (1) through an O-ring (7).

4. The core holder according to claim 1, characterized in that: The contact end (61) is designed corresponding to the cross-sectional dimensions of the core (20).

5. The core holder according to claim 1, characterized in that: A gap is provided between the rubber sleeve (5) and the wall surface of the inner cavity (2), and the gap is communicated with the outside through a confining pressure inlet (3) and a pressure relief outlet (4) provided on the cylinder (1).

6. The core holder according to claim 1, characterized in that: A first through hole (63) is provided inside the core plug (6), a second through hole is provided inside the core sealing cover (9), both the first through hole (63) and the second through hole are provided with an acoustic wave probe pressure cap (17), and the acoustic wave probe pressure caps (17) at the water injection end (11) and the water outlet end (12) are provided with an acoustic emission sensor transmitting end (18) and an acoustic emission sensor receiving end (19) respectively near the core (20).

7. The core holder according to any one of claims 1 to 6, characterized in that: The end surface of the core sealing cover (9) is provided with a plurality of through holes for installing perforation blind pipes (16).

8. An indoor simulation experimental system for water injection fracturing, comprising a core holder as claimed in any one of claims 1 to 7, used for holding a core (20), characterized in that: The system further comprises: Full diameter gripper for holding cylindrical cores; A fixing device for fixing the full-diameter holder and the core holder; A control cabinet (24) is fixedly mounted on the fixing device, and the fixing device has an internal integrated configuration including: An annular pressure tracking pump, the output end of which is connected to the confining pressure inlet (3) of the full-diameter clamp and the core clamp through an annular pressure pipeline; A constant speed and constant pressure pump, the output end of which is connected to the perforation blind pipe (16) of the full diameter clamp and the core clamp through an output pipeline; An acoustic emission device connected to an acoustic emission sensor emission end (18) disposed at the water injection end (11) and used for generating elastic waves; The data acquisition control device is electrically connected to an acoustic emission sensor disposed at the acoustic emission sensor receiving end (19) of the water outlet end 12, and is used to collect vibration data generated by the core (20) according to the elastic wave.

9. An indoor simulation experiment method for water injection fracturing cracks, based on the indoor simulation experiment system according to claim 8, the indoor simulation experiment method for water injection fracturing cracks is performed, characterized in that: The method comprises the following steps: An insertion hole for a perforation blind tube (16) is preset on the end face of the core (20); Selecting a corresponding holder according to the type of the core (20), and fixing the core (20) inside the holder, wherein the holder includes the core holder and a full-diameter holder; A perforation blind tube (16) is installed on the end surface of the core plug (6), the outer end of the perforation blind tube (16) is sealed, and the perforation blind tube (16) is perforated in the radial direction; Installing and fixing the inner end of the perforating blind pipe (16) corresponding to the insertion hole; The pressure relief outlet (4) of the clamp is blocked, and the ring pressure tracking pump and the constant speed and pressure pump are respectively started to carry out a water injection fracturing fracture simulation experiment; An elastic wave is emitted through an acoustic emission device, causing surface displacement of the crack surface of the core (20); The real-time pressure values ​​of the ring pressure tracking pump and the constant speed constant pressure pump and the real-time values ​​of the acoustic emission signals as well as the vibration data of the corresponding core (20) are collected respectively.

Images