A coal reservoir shaped charge penetration and fracturing test method

Abstract

The invention relates to a coal reservoir shaped energy perforating bullet penetration and fracturing test method, comprising: casting a simulated coal seam material in a bullet target mold, and removing the bullet target mold after curing and forming to obtain a columnar target; arranging an oil bag in a target shell, and then placing the columnar target and a stress sensing sheet to form a bullet target assembly; installing a simulated coal seam casing and a bracket on a base, the bullet target assembly is horizontally arranged on the corresponding bracket, and the front end of each bullet target assembly is butted against a corresponding butt seat on the side of the simulated coal seam casing; inputting hydraulic oil into the oil bag to simulate the formation pressure of an actual coal reservoir; placing a perforating gun into the simulated coal seam casing, and each perforating bullet of the perforating gun corresponds to a butt seat; performing perforation, and the stress sensing sheet detects in real time the stress change data of the corresponding columnar target when being shot by the perforating bullet; after the perforating bullet is shot, the perforating gun is retracted; injecting fracturing fluid into the simulated coal seam casing to perform a fracturing test, and the stress sensing sheet detects in real time the stress change data of the corresponding columnar target when being fractured.

Description

Technical Field

[0001] The invention belongs to the technical field of coal reservoir perforating charge testing, and in particular relates to a coal reservoir shaped-energy perforating charge penetration and fracturing testing method. Background Art

[0002] Perforating coalbed methane wells is one of the key technologies to open and penetrate coalbed methane reservoirs. The quality of perforating directly affects the expected production capacity of coalbed methane wells and the protection of coal seams. At present, the perforating bullets used in coalbed methane development are penetrating bullets. In order to clarify the influence and control factors of rock and coal seam fracture and crack extension under the action of penetrating bullets, it is necessary to conduct penetrating bullet target shooting experiments on the developed perforating bullets.

[0003] At present, the perforating elastic performance test methods recommended by domestic and foreign standards mainly include: ground column-mounted penetration steel target test, ground simulated gun-mounted penetration API columnar concrete target test, ground simulated well whole gun penetration casing test and ground whole gun penetration annular concrete target test. Among them, the ground whole gun penetration annular concrete target test can realize the penetration depth, aperture and cracking test of perforating bullets under formation conditions. However, the production cycle of cement targets is long, the cost is high, and the maintenance workload is large. In addition, due to the influence of factors such as pouring, curing, and mixing, defects such as uneven solidification and uneven strength are prone to occur, which affects the test of perforating bullets. In addition, when testing perforating bullets, cement columnar targets and column-mounted steel targets are generally not loaded with guns, but are placed on the target material for firing. There are problems such as low efficiency, poor accuracy, and the test effect is greatly interfered by external factors. Summary of the invention

[0004] In view of the above problems, the present invention provides a coal reservoir shaped charge penetration and fracturing test method, comprising the following steps:

[0005] S1: Casting simulated coal seam materials in several target molds respectively, and removing the target molds after curing and forming to obtain several columnar targets;

[0006] S2: An oil bag is arranged on the inner wall of the target shell, and then a columnar target and a plurality of stress sensing sheets are placed to form a projectile-target assembly;

[0007] S3: A vertical simulated coal seam casing and several vertical brackets are installed on the base, and the target assembly is installed on the corresponding bracket and kept horizontal. The front end of each target assembly is docked with the corresponding docking seat on the side of the simulated coal seam casing; hydraulic oil is input into the oil bag to simulate the formation pressure of the actual coal reservoir in the target shell;

[0008] S4: lowering the perforating gun into the simulated coal seam casing, each perforating bullet of the perforating gun corresponds to a docking seat and a bullet target assembly, fixing the position of the perforating gun;

[0009] S5: Perform perforation. The stress sensing sheet in the target assembly detects in real time the stress change data of the corresponding columnar target when the perforating bullet is fired. After the perforating bullets of the perforating gun have been fired, the perforating gun is lifted up and retracted.

[0010] S6: Inject fracturing fluid into the simulated coal seam casing, perform fracturing tests on all target components, and use stress sensing sheets to detect stress change data of corresponding columnar targets during fracturing in real time;

[0011] After the fracturing experiment, the fracturing fluid is pumped back.

[0012] The beneficial effects of the present invention are as follows: compared with the traditional ground perforation test device, the present invention adopts the form of installing multiple target assemblies corresponding to a simulated coal seam casing, and can place a perforating gun in the simulated coal seam casing to test multiple perforating bullets at one time, which greatly improves the test efficiency. Since the perforating bullet position on the perforating gun is fixed, several target assemblies can be installed in advance, and each perforating bullet can be perforated for the corresponding target assembly; it is only necessary to install the perforating bullets under different experimental conditions to the ammunition position of the perforating gun characteristics, and multiple perforating bullets can be tested at the same time. In addition, the target assembly of the present invention provides pressure through hydraulic oil to simulate the formation pressure of the real underground coal reservoir. The pressure has a great influence on the internal / external mechanical changes of the columnar target when receiving the perforating bullet shooting. By filling and discharging the hydraulic oil in the oil bag, it is convenient to provide pressure for the columnar target, and avoid direct contact of the hydraulic oil with the columnar target, and prevent the oil from entering the cracks of the columnar target (the cracks are formed inside or outside the columnar target after the perforating bullet is shot, or formed during fracturing) to bring a large error to the test result. The present invention can implement the perforation and fracturing experiments of a single-shot perforating bullet at one time, that is, the fracturing experiment is carried out after perforation, avoiding the influence of disassembly and assembly of traditional experimental equipment and the influence of pressure applied in the middle, and can also collect perforation and fracturing data separately, thereby improving the test efficiency and accuracy. In this field, there is little research on the relationship between the pores formed after perforating bullets and subsequent fracturing. Previously, perforation and fracturing were studied as two separate steps (modules), but in fact, perforation and fracturing influence each other and are closely related. The testing method of the present invention is to connect the two steps in series, study the internal connection and law of perforation and fracturing, and provide theoretical data and models for practical operations.

[0013] Optionally, in step S1, the target mold is cylindrical, with one end closed and the other end open, and is used for casting simulated coal seam materials; the closed end of the target mold is provided with an openable and closable lid, and the upper surface of the lid is provided with a sealing ring. During casting, the lid is closed and the sealing ring prevents material leakage; after curing and molding, the lid is opened, at which time both ends of the target mold are open, and the columnar target is pushed out forcefully at either end to complete demolding.

[0014] Optionally, the simulated coal seam material includes coal, sandstone, clay, and cement. Due to the heterogeneity of coal reservoirs in different regions, according to the composition of actual drilling core samples, coal, sandstone, clay, and cement are used in proportion to make columnar targets similar to the coal reservoir material.

[0015] In traditional target shooting tests, concrete is used to prepare the target material, which can ensure the strength of the target material. However, the adhesion of concrete is too good, which is different from the geological structure of the actual coal reservoir. The inventors found that adding an appropriate proportion of coal, sand, and clay to cement, combined with the corresponding formation pressure, can more accurately simulate the perforation and fracturing of underground coal reservoirs, especially in terms of perforation depth and fracturing effect.

[0016] Optionally, in step S2, the target shell is cylindrical, with an open front end and a closed rear end, and is used to accommodate a cylindrical target, and the diameter of the target shell is larger than the diameter of the cylindrical target;

[0017] A row of movable supports is provided on one side of the inner wall of the target shell, and a plurality of movable supports are evenly arranged along the length direction of the target shell; a row of fixed supports is provided on the other side, and a plurality of fixed supports are evenly arranged along the length direction of the target shell; the movable supports correspond to the fixed supports one by one, and are respectively arranged on opposite sides of the inner wall of the target shell, and the columnar target is placed between the movable supports and the fixed supports, so that the side of the columnar target does not contact the inner wall of the target shell, so as to avoid the force of the columnar target being constrained by the inner wall of the target shell when being shot or fracturing, thereby affecting the detection result.

[0018] Further optionally, since the movable supports / fixed supports are arranged in rows and at intervals, a number of oil bags are provided in the target shell, and the oil bags and the supports do not affect each other. After the oil bags are filled with hydraulic oil, the adjacent oil bags expand to fill the space around the supports, so that the support rods of the supports are in close contact with the surrounding oil bags; the oil bags are evenly arranged, and after being filled with oil and expanded, they can fill the gap between the columnar target and the inner wall of the target shell; the oil filling port of the oil bag passes through the target shell.

[0019] Further optionally, stress sensing sheets are provided on the end faces of the movable support and the fixed support facing the columnar target, the other end of the movable support passes through the target shell and has a handle, the part of the movable support close to its own handle is provided with an external thread, and the part of the target shell side wall corresponding to the movable support is provided with an internal thread, the internal and external threads cooperate with each other, and the movable support can be rotated into or out of the target shell.

[0020] The present invention does not arrange the stress sensing sheet between the columnar target and the oil bag. Considering the fluidity of hydraulic oil, after the oil bag is filled with oil, the slight flow of the hydraulic oil will be captured by the stress sensing sheet, thereby affecting the detection of the columnar target.

[0021] In step S2, an oil bag is first laid on the inner wall of the target shell, and then a stress sensing sheet is arranged on the end faces of the movable support and the fixed support in the target shell, and then the columnar target is installed between a row of movable supports and a row of fixed supports; the target shell is placed horizontally, and the fixed support is at the bottom of the target shell, supporting the columnar target upward, and the length of the fixed support is the same, so that the columnar target and the target shell are arranged concentrically; the movable support is at the top of the target shell, and the handle of the movable support is rotated to rotate the movable support downward until the stress sensing sheet at the bottom of the movable support contacts the surface of the columnar target and can measure a non-zero value, and the stress sensing sheets of all movable supports have the same measured values, indicating that a row of movable supports exert a balanced force on the columnar target. The target shell of the present invention can be used repeatedly.

[0022] Optionally, in step S3, the base is fixed on the ground to provide stable support, and the base includes a center plate and several surrounding support plates, the center plate is circular, the support plates are rectangular, and a circle of screw holes are evenly arranged on the edge of the center plate for connecting the support plates; the number of support plates is equal to the number of perforating bullets and the number of target assemblies, and the angle of the support plate corresponds to the shooting angle of the perforating bullet on the perforating gun; at least one bracket is arranged on each support plate for setting up the target assembly.

[0023] Further optionally, the simulated coal seam casing is a concrete hollow cylindrical tube, simulating an actual mined coal seam gas well, and the bottom of the simulated coal seam casing is fixed at the center of the center plate;

[0024] A plurality of docking seats are arranged on the outer side of the simulated coal seam casing, and the docking seats correspond to the positions of the perforating bullets on the perforating gun one by one.

[0025] In step S3, according to the number and position of perforating bullets on the perforating gun, a support plate is connected around the center plate, and then a bracket is fixed on the support plate;

[0026] The front end of the target shell is inserted into the through hole of the docking seat, and hydraulic oil is injected into the oil bag through the oil filling port. The air in the target shell is discharged through the front end. When the surface of the oil bag contacts the surface of the columnar target, most of the air in the target shell has been discharged. The through hole is filled with sealing material (such as a sealing gasket), and the flange is connected to the docking seat to complete the sealed connection between the target assembly and the simulated coal seam casing.

[0027] While continuing to inject hydraulic oil into each oil bag, at least two pressure gauges are arranged on the target shell to measure the pressure inside the target shell. When the pressure reaches the formation pressure of the simulated coal reservoir, the oil filling is stopped and the oil filling port is closed.

[0028] Optionally, in step S4, a flexible detonating cord is provided on the outer side of the perforating gun, a plurality of fracturing drug grooves are provided on the detonating cord, fracturing drugs are contained in the fracturing drug grooves, and perforating bullets are provided on the outer side of the fracturing drug grooves;

[0029] On the detonating cord, at least one fracturing groove is provided at the same height, and the fracturing grooves are evenly arranged along the downward spiral direction. For example, along the clockwise downward spiral direction, a fracturing groove is arranged by rotating a certain angle (for example, 90 degrees) on the surface of the detonating cord and descending a certain height at the same time. Along the clockwise downward spiral direction, the angles between two adjacent fracturing grooves are equal, and the vertical spacings are equal.

[0030] Optionally, in step S5, the perforating gun fires perforating bullets in sequence from top to bottom, and the corresponding stress sensing sheets simulating the side walls of the coal seam casing and the stress sensing sheets of the columnar targets are detected in real time, the resistance of the strain sheets is measured, and the detection data is transmitted to professional processing software for processing and calculation to obtain stress and strain data of the area covered by the stress sensing sheets, so as to observe the stress distribution and strain of the side walls of the coal seam casing and the columnar targets after perforating, and judge the damage and deformation of the side walls of the coal seam casing and the depth and deformation of the cracks in the columnar targets.

[0031] Optionally, in step S6, a sealing plate is installed on the top of the simulated coal seam casing, and a fracturing fluid port and a pressure port are provided on the sealing plate. The fracturing fluid port is connected to an external fracturing fluid tank to inject fracturing fluid into the simulated coal seam casing, and the pressure port is connected to an external gas supply device to provide pressure for the simulated coal seam casing, thereby simulating the fracturing pressure of a real deep coalbed methane well.

[0032] After the pressure inside the simulated coal seam casing reaches the standard, the stress sensing plates on the side walls of the simulated coal seam casing and the stress sensing plates on the columnar targets are tested in real time, and the test data are transmitted to professional processing software for processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of a test device used in the embodiments;

[0034] Figure 2 is a schematic diagram of a perforating gun;

[0035] Figure 3 is a schematic diagram of the base;

[0036] Figure 4 A schematic diagram of a target assembly;

[0037] Figure 5 It is a schematic diagram of the cooperation between the support plate and the lifting rod;

[0038] Figure 6 It is a schematic diagram of a docking mode between a projectile target assembly and a simulated coal seam casing;

[0039] Figure 7 A schematic diagram of another docking mode between a target assembly and a simulated coal seam casing.

[0040] In the accompanying drawings, 1-columnar target, 2-oil bag, 3-stress sensing sheet, 4-target assembly, 5-base, 6-simulated coal seam casing, 7-bracket, 8-docking seat, 9-perforating gun, 10-perforating bullet, 11-target shell, 12-movable support, 13-fixed support, 14-sealing material, 15-handle, 16-center plate, 17-support plate, 18-through hole, 19-flange, 20-fracturing agent, 21-sealing plate, 22-fracturing fluid port, 23-pressure port, 24-support plate, 25-lifting rod, 26-liquid collecting box, 27-first butt joint, 28-second butt joint, 29-pouring port. DETAILED DESCRIPTION

[0041] This embodiment provides a coal reservoir shaped charge penetration and fracturing test method, such as Figure 1-Figure 7 As shown, the following steps are included:

[0042] S1: Casting simulated coal seam materials in a plurality of target molds, removing the target molds after curing and forming, and obtaining a plurality of columnar targets 1;

[0043] S2: An oil bag 2 is arranged on the inner wall of the target shell 11, and then a columnar target 1 and a plurality of stress sensing sheets 3 are placed to form a projectile-target assembly 4;

[0044] S3: A vertical simulated coal seam casing 6 and a plurality of vertical brackets 7 are installed on the base 5, and the target assembly 4 is installed on the corresponding bracket 7 and kept horizontal, and the front end of each target assembly 4 is docked with the corresponding docking seat 8 on the side of the simulated coal seam casing 6; hydraulic oil is input into the oil bag 2 to simulate the formation pressure of the actual coal reservoir in the target shell 11;

[0045] S4: lowering the perforating gun 9 into the simulated coal seam casing 6, each perforating bullet 10 of the perforating gun 9 corresponds to a docking seat 8 and a bullet target assembly 4, and fixing the position of the perforating gun 9;

[0046] S5: Perform perforation. The stress sensing sheet 3 in the target assembly 4 detects in real time the stress change data of the corresponding columnar target 1 when the perforating bullet 10 is fired. After the perforating bullets 10 of the perforating gun 9 have finished firing, the perforating gun 9 is lifted up and retracted.

[0047] S6: injecting fracturing fluid into the simulated coal seam casing 6, performing fracturing tests on all target assemblies 4, and the stress sensing sheet 3 real-time detecting stress change data of the corresponding columnar target 1 during fracturing;

[0048] After the fracturing experiment, the fracturing fluid is pumped back.

[0049] In step S1, the target mold is cylindrical, with one end closed and the other end open, and is used for casting simulated coal seam materials; the closed end of the target mold is provided with an openable and closable lid, and the upper surface of the lid is provided with a sealing ring. During casting, the lid is closed, and the sealing ring prevents material leakage; after curing and molding, the lid is opened, and at this time, both ends of the target mold are open, and the columnar target 1 is pushed out forcefully at any end to complete demoulding.

[0050] The simulated coal seam materials include coal, sand, gravel, clay and cement.

[0051] In step S2, the target shell 11 is cylindrical, with an open front end and a closed rear end, and is used to accommodate the columnar target 1. The diameter of the target shell 11 is larger than the diameter of the columnar target 1;

[0052] A row of movable supports 12 is provided on one side of the inner wall of the target shell 11, and a plurality of movable supports 12 are evenly arranged along the length direction of the target shell 11; a row of fixed supports 13 is provided on the other side, and a plurality of fixed supports 13 are evenly arranged along the length direction of the target shell 11; the movable supports 12 correspond to the fixed supports 13 one by one, and are respectively arranged on the opposite sides of the inner wall of the target shell 11, and the columnar target 1 is placed between the movable supports 12 and the fixed supports 13, so that the side of the columnar target 1 does not contact the inner wall of the target shell 11, so as to avoid the force of the columnar target 1 being constrained by the inner wall of the target shell 11 when it is shot or fracturing, thereby affecting the detection result.

[0053] Since the movable supports 12 / fixed supports 13 are arranged in rows and at intervals, a plurality of oil bags 2 are arranged in the target shell 11, and the oil bags 2 and the supports do not affect each other. After the oil bags 2 are filled with hydraulic oil, the adjacent oil bags 2 expand to fill the space around the supports, so that the support rods of the supports are in close contact with the surrounding oil bags 2; the oil bags 2 are evenly arranged, and after being filled with oil and expanded, they can fill the gap between the columnar target 1 and the inner wall of the target shell 11; the oil filling port of the oil bag 2 passes through the target shell 11.

[0054] The rear end of the target shell 11 is not provided with an oil bag 2. During the experiment, the rear end of the columnar target 1 is in close contact with the rear end of the target shell 11 to position the columnar target 1 and simulate the actual coal reservoir. The rear end of the target shell 11 is not provided with an oil bag 2 to prevent the impact of the columnar target 1 from causing the rear end oil bag 2 to rupture and leak oil.

[0055] The movable support 12 and the fixed support 13 are provided with a stress sensing sheet 3 on one end surface facing the columnar target 1, and the other end of the movable support 12 passes through the target shell 11 and has a handle 15. The portion of the movable support 12 close to its own handle 15 is provided with an external thread, and the portion of the side wall of the target shell 11 corresponding to the movable support 12 is provided with an internal thread. The internal and external threads cooperate with each other, so that the movable support 12 can be rotated into or out of the target shell 11.

[0056] In step S2, the oil bag 2 is first laid on the inner wall of the target shell 11, and then the stress sensing sheet 3 is arranged on the end faces of the movable support 12 and the fixed support 13 in the target shell 11, and then the columnar target 1 is installed between a row of movable supports 12 and a row of fixed supports 13; the target shell 11 is placed horizontally, and the fixed support 13 is at the bottom of the target shell 11, supporting the columnar target 1 upward, and the length of the fixed support 13 is the same, so that the columnar target 1 and the target shell 11 are arranged concentrically; the movable support 12 is at the top of the target shell 11, and the movable support 12 is rotated downward by rotating the handle 15 of the movable support 12 until the stress sensing sheet 3 at the bottom of the movable support 12 contacts the surface of the columnar target 1 and can measure a non-zero value, and the values ​​measured by the stress sensing sheets 3 of all the movable supports 12 are the same, indicating that a row of movable supports 12 exert a balanced force on the columnar target 1.

[0057] In order to ensure the sealing of the movable support 12 penetrating the target shell 11, when the movable support 12 is about to be rotated into place, a sealing gasket is placed under the handle 15, and then the handle 15 is continued to be rotated, and the handle 15 presses the gasket to seal.

[0058] In step S3, the base 5 is fixed on the ground to provide a stable support. The base 5 includes a center plate 16 and a plurality of surrounding support plates 17. The center plate 16 is circular and the support plates 17 are rectangular. A circle of screw holes is evenly arranged on the edge of the center plate 16 for connecting the support plates 17. The number of support plates 17 is equal to the number of perforating bullets 10 and the number of target assemblies 4. The angle of the support plate 17 corresponds to the shooting angle of the perforating bullet 10 on the perforating gun 9. At least one bracket 7 is arranged on each support plate 17 for setting up the target assembly 4.

[0059] The simulated coal seam casing 6 is a concrete hollow cylindrical tube, simulating an actual mined coal seam gas well, and the bottom of the simulated coal seam casing 6 is fixed at the center of the center plate 16;

[0060] The outer side of the simulated coal seam casing 6 is provided with a plurality of docking seats 8, and the docking seats 8 correspond to the positions of the perforating bullets 10 on the perforating gun 9. The present invention provides two forms of docking seats, as follows.

[0061] The first docking seat 8 protrudes toward the outside of the simulated coal seam casing 6 and is integrally formed with the simulated coal seam casing 6; a through hole 18 is provided at the center of the docking seat 8, and the front end of the target assembly 4 is inserted into the through hole 18 and directly abuts against the outer wall of the simulated coal seam casing 6, and a sealing material is filled between the inner wall of the through hole 18 and the front end of the target assembly 4 to prevent leakage of the fracturing fluid;

[0062] The through hole 18 is concentrically arranged with the target shell 11, and the bullet of the perforating bullet 10 is shot at the center of the through hole 18 and then hits the center of the cylindrical target 1;

[0063] A circle of flange 19 is provided on the outer surface of the target shell 11, and bolt holes are provided on the side of the docking seat 8 facing the flange 19, which correspond one to one with the through holes on the flange 19. The target shell 11 is connected to the docking seat 8 through the flange 19 and bolts.

[0064] A sealing ring may be provided between the front end of the target shell 11 and the outer wall of the simulated coal seam casing 6 , and the sealing ring covers part of the oil bag 2 , leaving only the front end face of the columnar target 1 to prevent a large amount of fracturing fluid from impacting the oil bag 2 .

[0065] The second docking seat 8 includes a first docking tube 27 and a second docking tube 28. One end of the first docking tube 27 is welded to the outer wall of the simulated coal seam casing 6, and the other end is connected to one end of the second docking tube 28 through a flange. The other end of the second docking tube 28 is used to connect the plugging material 14.

[0066] The first butt joint 27 and the second butt joint 28 are respectively provided with through holes, the two through holes are concentrically arranged and have the same diameter, the front end of the target assembly 4 is inserted into the two through holes and directly abuts against the outer wall of the simulated coal seam casing 6;

[0067] A pouring port is provided on the side of the second butt joint pipe 28 , and the pouring port is connected to the through hole in the second butt joint pipe 28 .

[0068] The inner diameter of the through hole of the first butt joint pipe 27 and the second butt joint pipe 28 is slightly larger than the outer diameter of the target shell. After the first butt joint pipe 27 and the second butt joint pipe 28 are connected by flanges, the target assembly 4 is inserted into the through hole and abuts against the outer wall of the simulated coal seam casing 6. According to the plugging material 14, the second butt joint pipe 28 is blocked away from the opening of the simulated coal seam casing 6, and the plugging material 14 is close to the outside of the target shell to prevent the concrete in the docking seat from flowing out; then concrete is poured into the docking seat through the pouring port 29 so that the concrete fills the space between the target shell and the inner wall of the docking seat; then the pouring port 29 is sealed, and after the concrete in the docking seat is cured, the target assembly 4 can be sealed and firmly connected with the docking seat.

[0069] The above two forms of docking sockets can be selected according to actual conditions. The first one is simple and convenient, and the experiment can be started directly after installation. Although the second one needs to wait for maintenance time after installation, it has better stability and sealing.

[0070] In step S3, according to the number and position of the perforating bullets 10 on the perforating gun 9, the support plate 17 is connected around the central plate 16, and then the bracket 7 is fixed on the support plate 17. For example, one target assembly 4 corresponds to two brackets 7, which can keep the target shell 11 in a horizontal state. The two brackets 7 are evenly arranged along the length direction of the corresponding support plate 17 (that is, the extension direction of the support plate 17 and the shooting direction of the perforating bullet 10);

[0071] The front end of the target shell 11 extends into the through hole 18 of the docking seat 8, and hydraulic oil is injected into the oil bag 2 through the oil filling port. The air in the target shell 11 is discharged through the front end. When the surface of the oil bag 2 contacts the surface of the columnar target 1, most of the air in the target shell 11 has been exhausted. A sealing material (such as a sealing gasket) is filled in the through hole 18, and the flange 19 is connected to the docking seat 8 to complete the sealed connection between the target assembly 4 and the simulated coal seam casing 6.

[0072] While continuing to inject hydraulic oil into each oil bag 2, at least two pressure gauges are provided on the target shell 11 to measure the pressure inside the target shell 11. When the pressure reaches the formation pressure of the simulated coal reservoir, the oil filling is stopped and the oil filling port is closed. The length of the front end of the target shell 11 extending into the through hole 18 is not too large, for example, accounting for 5-10% of the length of the target shell 11.

[0073] In step S4, a flexible detonating cord is provided on the outer side of the perforating gun 9, and a plurality of fracturing drug grooves are provided on the detonating cord. The fracturing drug grooves contain fracturing drugs 20, and the outer side of the fracturing drug grooves contains perforating bullets 10;

[0074] On the detonating cord, at least one fracturing groove is provided at the same height, and the fracturing grooves are evenly arranged along the downward spiral direction. For example, along the clockwise downward spiral direction, a fracturing groove is arranged by rotating a certain angle (for example, 90 degrees) on the surface of the detonating cord and descending a certain height at the same time. Along the clockwise downward spiral direction, the angles between two adjacent fracturing grooves are equal, and the vertical spacings are equal.

[0075] The following operation is also included before step S4: at least one stress sensing sheet is provided at the position of each through hole 18 on the inner wall of the simulated coal seam casing 6 to detect the impact of the perforating bullet 10 on the casing side wall when the perforating bullet 10 penetrates the casing side wall.

[0076] In step S5, the perforating gun 9 fires perforating bullets 10 in sequence from top to bottom, and the corresponding stress sensing sheets of the simulated coal seam casing 6 side walls and the stress sensing sheets of the columnar target 1 are detected in real time, and the resistance of the strain sheets is measured. The detection data is transmitted to professional processing software for processing and calculation, and the stress and strain data of the area covered by the stress sensing sheets are obtained, so as to observe the stress distribution and strain of the coal seam casing side walls and the columnar target after perforation, and judge the damage and deformation of the coal seam casing side walls and the crack penetration depth and deformation in the columnar target.

[0077] In step S6, a sealing plate 21 is installed on the top of the simulated coal seam casing 6. A fracturing fluid port 22 and a pressure port 23 are provided on the sealing plate 21. The fracturing fluid port 22 is connected to an external fracturing fluid tank to inject fracturing fluid into the simulated coal seam casing 6. The pressure port 23 is connected to an external gas supply device to provide pressure for the simulated coal seam casing 6, simulating the fracturing pressure of a real deep coal seam methane well.

[0078] When simulating deep formations, the length of the coalbed methane well is relatively long (up to 1000-2000 meters). When the fracturing fluid is input into the bottom or lower part of the coalbed methane well, the fracturing fluid above is pressurized. During the ground experiment, the simulated coalbed casing 6 is relatively short and cannot simulate the pressure in the coalbed methane well. The present invention blocks and seals the top pipe opening of the simulated coalbed casing 6, and can inject fracturing fluid and air separately. For example, the fracturing fluid is injected first, and a certain distance (for example, 1-5 cm) is left between the liquid level and the pipe opening, and then the air is injected to pressurize the simulated coalbed casing 6 and the connected target shell 11, so that the pressure in the simulated coalbed casing 6 reaches the pressure of the simulated deep coalbed methane well;

[0079] After the pressure inside the simulated coal seam casing 6 reaches the standard, the stress sensing sheets on the side walls of the simulated coal seam casing 6 and the stress sensing sheets on the columnar target 1 are tested in real time, and the test data are transmitted to professional processing software for processing.

[0080] In the test of step S6, bullet holes and bullet grooves appear inside the columnar target 1 after being shot by the perforating bullet 10, and then fracturing is performed. When the pressure is high, some columnar targets 1 may be broken or partially broken, especially the columnar targets 1 shot by the powerful perforating bullet 10. When the columnar target 1 is broken, the debris may slide into the surrounding oil bag 2, and the leakage of hydraulic oil will pollute the inside of the target shell 11. In view of this problem, the present invention proposes the following solution.

[0081] In step S4, the charge amount of the perforating bullets 10 arranged in the perforating gun 9 from top to bottom gradually increases;

[0082] The center plate 16 has a liftable support plate 24 inside. The support plate 24 is circular and has a diameter equal to the inner diameter of the simulated coal seam casing 6. The support plate 24 can be lifted and lowered in the simulated coal seam casing 6. A hard rubber sheet is provided on the edge of the support plate 24, and the hard rubber sheet is tightly attached to the inner wall of the simulated coal seam casing 6.

[0083] The bottom of the support plate 24 is connected to a lifting rod 25 , which is connected to a lifting device below the base 5 . A liquid collecting box 26 is provided on the lifting rod 25 . The liquid collecting box 26 is located below the support plate 24 and moves together with the lifting rod 25 .

[0084] For example, the base 5 is fixed on a fixed table top, a through hole is provided on the table top, the diameter of the through hole is smaller than the diameter of the center plate 16 , the center plate 16 covers the through hole, and the lifting device is provided under the table top without affecting the base 5 .

[0085] In step S6, the fracturing fluid is input into the coal seam casing 6 to fractur the columnar target 1 in the target tube. The perforating bullet 10 and the fracturing fluid are borne by the target assembly 4 at the bottom, and the columnar target 1 is most likely to be broken or fragmented.

[0086] When the stress sensing sheet of the bottom columnar target 1 detects the predetermined stress before the columnar target 1 is broken, the bottom support plate 24 is raised, and the support plate 24 supports the fracturing fluid and rises together to prevent the fracturing fluid from leaking. After the support plate 24 is higher than the bottom target assembly 4, the target assembly 4 is not under pressure to prevent it from breaking, and the residual fracturing fluid in it flows into the liquid collecting box 26;

[0087] When the support plate 24 rises, it squeezes the fracturing fluid in the simulated coal seam casing 6. At this time, the air injected into the pressure port 23 is adjusted or part of the air is extracted from the pressure port 23 to maintain the pressure in the space above the support plate 24 in the simulated coal seam casing 6 at a constant value.

Claims

1. A coal reservoir shaped charge penetration and fracturing test method, characterized in that: The following steps are involved: S1: Casting simulated coal seam materials in several target molds respectively, removing the target molds after curing and forming, and obtaining several columnar targets; S2: An oil bag is arranged on the inner wall of the target shell, and then a columnar target and a plurality of stress sensing sheets are placed to form a projectile-target assembly; S3: A vertical simulated coal seam casing and several vertical brackets are installed on the base, and the target assembly is installed on the corresponding bracket and kept horizontal. The front end of each target assembly is docked with the corresponding docking seat on the side of the simulated coal seam casing; hydraulic oil is input into the oil bag to simulate the formation pressure of the actual coal reservoir in the target shell; S4: lowering the perforating gun into the simulated coal seam casing, each perforating bullet of the perforating gun corresponds to a docking seat and a bullet target assembly, fixing the position of the perforating gun; S5: Perform perforation. The stress sensing sheet in the target assembly detects in real time the stress change data of the corresponding columnar target when the perforating bullet is fired. After the perforating bullets of the perforating gun have been fired, the perforating gun is lifted up and retracted. S6: Inject fracturing fluid into the simulated coal seam casing, perform fracturing tests on all target components, and use stress sensing sheets to detect stress change data of corresponding columnar targets during fracturing in real time; After the fracturing experiment, the fracturing fluid is pumped back.

2. The coal reservoir shaped charge penetration and fracturing test method according to claim 1, characterized in that: In step S1, the target mold is cylindrical, with one end closed and the other end open, and is used for casting simulated coal seam materials; the closed end of the target mold is provided with an openable and closable lid, and the upper surface of the lid is provided with a sealing ring. During casting, the lid is closed and the sealing ring prevents material leakage; after curing and molding, the lid is opened, at which time both ends of the target mold are open, and the columnar target is pushed out forcefully at either end to complete demoulding.

3. The coal reservoir shaped charge penetration and fracturing test method according to claim 1, characterized in that: In step S2, the target shell is cylindrical, with an open front end and a closed rear end, and is used to accommodate a cylindrical target. The diameter of the target shell is larger than the diameter of the cylindrical target. A row of movable supports is provided on one side of the inner wall of the target shell, and a plurality of movable supports are evenly arranged along the length direction of the target shell; a row of fixed supports is provided on the other side, and a plurality of fixed supports are evenly arranged along the length direction of the target shell; the movable supports correspond to the fixed supports one by one, and are respectively arranged on the opposite sides of the inner wall of the target shell, and the columnar target is placed between the movable supports and the fixed supports, so that the side of the columnar target does not contact the inner wall of the target shell; A number of oil bags are arranged in the target shell. The oil bags and the support do not affect each other. After the oil bags are filled with hydraulic oil, the adjacent oil bags expand to fill the space around the support, so that the support rods of the support are in close contact with the surrounding oil bags; the oil bags are evenly arranged and can fill the gap between the columnar target and the inner wall of the target shell after being filled with oil and expanded; the oil filling port of the oil bag passes through the target shell.

4. The coal reservoir shaped charge penetration and fracturing test method according to claim 3, characterized in that: The movable support and the fixed support are provided with stress sensing sheets on their end surfaces facing the columnar target, the other end of the movable support passes through the target shell and has a handle, the part of the movable support close to its own handle is provided with an external thread, and the part of the target shell side wall corresponding to the movable support is provided with an internal thread, the internal and external threads cooperate with each other, and the movable support can be rotated into or out of the target shell.

5. The coal reservoir shaped charge penetration and fracturing test method according to claim 4, characterized in that: In step S2, an oil bag is first laid on the inner wall of the target shell, and then a stress sensing sheet is arranged on the end surface of the movable support and the fixed support in the target shell, and then a columnar target is installed between a row of movable supports and a row of fixed supports; the target shell is placed horizontally, and the fixed support is at the bottom of the target shell to support the columnar target upward, and the length of the fixed support is the same, so that the columnar target and the target shell are arranged concentrically; The movable support is located at the top of the target shell. By turning the handle of the movable support, the movable support is turned downward until the stress sensing sheet at the bottom of the movable support contacts the surface of the cylindrical target and a non-zero value can be measured. The values ​​measured by the stress sensing sheets of all movable supports are the same, indicating that a row of movable supports exerts balanced force on the cylindrical target.

6. The coal reservoir shaped charge penetration and fracturing test method according to claim 1, characterized in that: In step S3, the base is fixed on the ground to provide a stable support. The base includes a center plate and a plurality of surrounding support plates. The center plate is circular and the support plates are rectangular. A circle of screw holes is evenly arranged on the edge of the center plate for connecting the support plates. The number of support plates is equal to the number of perforating bullets and the number of target assemblies. The angle of the support plate corresponds to the shooting angle of the perforating bullet on the perforating gun. At least one bracket is arranged on each support plate for setting up the target assembly. The simulated coal seam casing is a concrete hollow cylindrical tube, simulating an actual mined coal seam gas well, and the bottom of the simulated coal seam casing is fixed at the center of the center plate; A plurality of docking seats are arranged on the outer side of the simulated coal seam casing, and the docking seats correspond to the positions of the perforating bullets on the perforating gun one by one.

7. The coal reservoir shaped charge penetration and fracturing test method according to claim 6, characterized in that: In step S3, according to the number and position of perforating bullets on the perforating gun, a support plate is connected around the center plate, and then a bracket is fixed on the support plate; The front end of the target shell is inserted into the through hole of the docking seat, and hydraulic oil is injected into the oil bag through the oil filling port. The air in the target shell is discharged through the front end. When the surface of the oil bag contacts the surface of the columnar target, most of the air in the target shell has been discharged. The sealing material is filled in the through hole, and the flange is connected to the docking seat to complete the sealed connection between the target assembly and the simulated coal seam casing. While continuing to inject hydraulic oil into each oil bag, at least two pressure gauges are arranged on the target shell to measure the pressure inside the target shell. When the pressure reaches the formation pressure of the simulated coal reservoir, the oil filling is stopped and the oil filling port is closed.

8. The coal reservoir shaped charge penetration and fracturing test method according to claim 1, characterized in that: In step S5, the perforating gun fires perforating charges in order from top to bottom, and the corresponding stress sensing sheets of the simulated coal seam casing sidewalls and the stress sensing sheets of the columnar targets are detected in real time.

9. The coal reservoir shaped charge penetration and fracturing test method according to claim 1, characterized in that: In step S6, a sealing plate is installed on the top of the simulated coal seam casing, and a fracturing fluid port and a pressure port are provided on the sealing plate. The fracturing fluid port is connected to an external fracturing fluid tank to inject fracturing fluid into the simulated coal seam casing, and the pressure port is connected to an external gas supply device to provide pressure for the simulated coal seam casing, simulating the fracturing pressure of a real deep coal seam methane well; After the pressure inside the simulated coal seam casing reaches the standard, the stress sensing plates on the side walls of the simulated coal seam casing and the stress sensing plates on the columnar targets are tested in real time.

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