Test system and method for simulating in-situ reservoir electric detonation fracturing through gas-liquid coupling pressure application

Abstract

The invention provides a test system and method for simulating in-situ reservoir electric detonation fracturing through gas-liquid coupling pressure application. The test system comprises a pressure chamber used for installing a test piece, a stress loading device, a gas-liquid coupling device and a high-voltage electric detonation fracturing device with a discharge electrode. A detonation hole is formed in the top of the test piece; the stress loading device is connected with the pressure chamber and is used for applying axial pressure and confining pressure to the test piece in the pressure chamber to simulate ground stress; the gas-liquid coupling device can inject water, gas, water and gas into the pressure chamber; and a discharge electrode of the high-voltage electric detonation cracking device can be arranged in a detonation hole of the test piece to crack the test piece. The device has the characteristic of being capable of applying axial pressure and confining pressure, controllable explosion energy can be achieved, coupling of multiple physical fields and high accuracy of energy output are guaranteed, and self-water injection, self-gas injection and up-down water pumping and draining are achieved through the gas-liquid coupling device; and accurate and in-depth research on the hole fracture development law, gas migration, permeability and the like after the in-situ reservoir high-voltage electric pulse technology is realized is facilitated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electric detonation and the field of unconventional natural gas development, and particularly relates to a test system and method for simulating in-situ reservoir electric detonation fracturing through gas-liquid coupling pressure application. BACKGROUND

[0002] The key to efficient development of oil and gas resources is not only an important clean energy related to social and economic development, but also an important strategic resource for bottom-up guarantee of national security and stability. Efficient development of unconventional natural gas resources such as coalbed methane (gas) and shale gas is one of the most realistic ways to supplement natural gas resources. At present, electric detonation technology has gradually matured and can break through the technical bottleneck of small fracturing range of electric pulse technology, and is expected to be widely used in unconventional natural gas development engineering practice, greatly improving the development efficiency of unconventional natural gas and solving the exploitation problems faced by low-permeability unconventional reservoirs.

[0003] Traditional electric detonation tests only simulate laboratory site environments and cannot simulate in-situ test pieces during the test process, and the formed fracturing characteristics are not enough to represent the damage in the in-situ environment.

[0004] After searching, no similar technical solutions of the present application have been disclosed. SUMMARY

[0005] To solve the technical problems in the prior art, the first aspect of the present application provides a test system for simulating in-situ reservoir electric detonation fracturing through gas-liquid coupling pressure application. The second aspect, based on the same inventive concept, the present application also provides a test method based on the aforementioned test system for simulating in-situ reservoir electric detonation fracturing through gas-liquid coupling pressure application.

[0006] In the present application, the test system for simulating in-situ reservoir electric detonation fracturing through gas-liquid coupling pressure application comprises a pressure chamber for installing a test piece, a stress loading device, a gas-liquid coupling device, and a high-voltage electric detonation fracturing device with a discharge electrode; the top of the test piece is provided with a detonation hole; the stress loading device is connected with the pressure chamber and is used for applying axial pressure and confining pressure to the test piece in the pressure chamber to simulate ground stress; the gas-liquid coupling device can inject water, gas, pump water and exhaust gas into the pressure chamber to realize gas-liquid coupling; the discharge electrode of the high-voltage electric detonation fracturing device can be placed in the detonation hole of the test piece, and the high-voltage electric detonation fracturing device performs high-voltage pulse discharge through the discharge electrode immersed in water to fracture the test piece.

[0007] The test method of the embodiment of the present application is realized based on the test system for simulating in-situ reservoir electric detonation fracturing by gas-liquid coupling, and comprises the following steps: step a: building the test system, installing and debugging; step b: preparing the test piece, installing the test piece into the pressure chamber, and sealing the upper end and the lower end of the pressure chamber; step c: static experiment stage, establishing the initial saturation condition, vacuumizing the pressure chamber through the gas-liquid coupling device, ensuring that there is no residual air in the test piece, slowly injecting water into the pressure chamber through the gas-liquid coupling device to soak the test piece, making the test piece fully saturated by absorbing water, standing for a period of time to stabilize the pore fluid distribution of the test piece, and extracting the water in the pressure chamber through the gas-liquid coupling device; step d: applying axial pressure and confining pressure to the test piece through the stress loading device to simulate the original stress environment of the oil and gas well field; step e: injecting water and gas into the pressure chamber through the gas-liquid coupling device, injecting water from the upper end of the pressure chamber to flow downward, and injecting gas from the lower end of the pressure chamber to flow upward, controlling the injection rate of water and gas, performing basic gas-liquid coupling seepage experiment, and recording the initial seepage characteristics; step f: dynamic experiment stage, immersing the discharge electrode in the water of the detonation hole, and performing high-voltage pulse discharge through the discharge electrode by operating the high-voltage electric detonation fracturing device to fracture the test piece; step g: restoring the seepage experiment, and observing the flow recovery characteristics of the fluid in the test piece; and step h: analyzing and observing the influence of electric detonation on the seepage characteristics of the test piece.

[0008] Compared with the prior art, the beneficial effects of the preferred technical solutions of the present application include:

[0009] 1. The present application provides a high-strength electric detonation fracturing experiment system capable of applying axial pressure and confining pressure, which can simulate electric detonation fracturing experiments under different ground stresses and different voltages, truly simulate high-strength electric detonation volume fracturing experiments under the action of gas-liquid coupling in the oil and gas well field, and perform observation, which is beneficial to the study of the seepage and dynamic behavior of liquid and gas in the oil and gas well field based on high-strength electric detonation technology, can provide reliable technical support for high-strength electric detonation fracturing gas-bearing reservoir technology and its basic research, and can deeply understand the electric detonation volume fracturing mechanism, optimize the stimulation measures, and improve the oil and gas field recovery efficiency.

[0010] 2. The present application adopts a multi-stage sliding rod combined with an oil cylinder to provide axial pressure loading to the test piece from top to bottom, ensures the sliding cooperation with the pressure chamber through the first sliding rod with a larger diameter, and reduces the influence of pipe wall friction on axial pressure loading through the smaller sliding rod, adopts the oil cylinder side wall opening axial pressure channel and realizes the transmission of axial pressure through the multi-stage sliding rod, which is convenient for the processing and replacement of a single sliding rod and facilitates the disassembly and assembly of the test piece during the test process; an opening is formed in the upper end and the lower end of the side wall of the pressure chamber as a confining pressure channel, and is combined with a separation rubber sleeve and a sealing ring to prevent hydraulic oil from being immersed into the test piece through the separation rubber sleeve, which has the advantages of simple structure and reliable loading. The axial pressure loading skillfully utilizes the side wall opening of the oil cylinder, and the confining pressure loading skillfully utilizes the side wall opening of the pressure chamber, so that the whole layout is reasonable, compact, simple and easy to control.

[0011] 3、The water injection and pumping of the system is realized by the water pressure pump, the upper water pumping pump, the upper water pressure pipeline and the upper water gas passage in the upper end of the test piece, and the exhaust is realized by the vacuum pump and the upper water gas passage; similarly, the gas injection and water pumping are realized by the lower water pumping pump and the gas cylinder in the lower end of the test piece. The precise coupling and circulation control of the gas-liquid medium are realized by the bidirectional fluid control.

[0012] 4、The test system of the application is a coupling test system with wide simulation range and simpler operation. The characteristics of the axial pressure and confining pressure and the controllable explosion energy of the high-voltage electric energy storage box can be realized by using the test system, which ensures the high accuracy of the coupling of multiple physical fields and the energy output. The self-water injection, self-gas injection and up-down water pumping are realized by using the gas-liquid coupling device, which is beneficial to the accurate and in-depth research on the pore and fracture development law, gas migration and permeability after the action of the in-situ reservoir high-voltage electric pulse technology, and reveals the internal mechanism and essence of the multi-field coupling such as electric field and stress field in the action process. The high-voltage electric shock volume fracturing and permeability improvement based on the liquid-electric effect are used to meet the research needs of the electric shock technology to solve the plugging effect, perfect the basic theory and optimize the electric shock technology, and provide theoretical support and engineering parameter guidance for improving the exploitation efficiency of the gas in the gas reservoir. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a structural schematic diagram of the test system for simulating the electric shock fracturing of the in-situ reservoir by the gas-liquid coupling pressure in example one.

[0014] Figure 2 is a structural schematic diagram of the gas-liquid coupling device in example one.

[0015] Figure 3 is a schematic diagram of the movement and fracturing of the test piece by the discharge electrode in the pressure chamber.

[0016] Figure 4 is a flowchart of the test method for simulating the electric shock fracturing of the in-situ reservoir by the gas-liquid coupling pressure in example two.

[0017] The reference signs in the drawings of the specification include: test piece 1, detonation hole 1a, pressure chamber 2, axial pressure pump 3, confining pressure pump 4, axial pressure pipeline 5, confining pressure pipeline 6, stop valve 7, oil cylinder 8, first sliding rod 9, second sliding rod 10, third sliding rod 11, fourth sliding rod 12, isolation rubber sleeve 13, high-voltage power supply 14, high-voltage electric energy storage box 15, output control cabinet 16, discharge electrode 17, oscilloscope 18, intelligent millisecond switch 19, first section transmission cable 20a, second section transmission cable 20b, third section transmission cable 20c, gas-liquid coupling device 21, hose 22, upper water gas pipeline 23a, lower water gas pipeline 23b, upper gas pipeline 24a, lower gas pipeline 24b, upper water pressure pipeline 25a, lower water pressure pipeline 25b, flow detection meter 26, pressure detection meter 27, valve 28, vacuum pump 29, water pressure pump 30, water tank 31, upper water pump 32a, lower water pump 32b, upper water gas collection tank 33a, lower water gas collection tank 33b, gas storage cylinder 34, data acquisition system 35. DETAILED DESCRIPTION

[0018] Embodiments of the present application are described in detail below with reference to the accompanying drawings, in which the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are only used to explain the present application and cannot be understood as a limitation of the present application.

[0019] Embodiment One

[0020] The present embodiment provides a test system for simulating in-situ reservoir electric detonation fracturing by gas-liquid coupling pressure application, as shown in Figure 1 In a preferred embodiment, the test system includes a pressure chamber 2 for mounting a test piece 1, a stress loading device, a gas-liquid coupling device 21, and a high-voltage electric detonation fracturing device with a discharge electrode 17. The pressure chamber 2 is a circular tubular structure that fits the test piece 1, and the test piece 1 is centrally mounted in the pressure chamber 2. The top of the test piece 1 is provided with a detonation hole 1a for placing the discharge electrode 17 of the high-voltage electric detonation fracturing device.

[0021] The stress loading device is connected to the pressure chamber 2 and is used to apply axial pressure and confining pressure to the test piece 1 in the pressure chamber 2 to simulate ground stress, simulating the original stress environment of the oil and gas well site. The gas-liquid coupling device 21 can inject water, gas (experimental gas such as methane gas), pump water, and exhaust gas into the pressure chamber 2 to achieve gas-liquid coupling. By injecting gas, it also plays a displacement role when simulating well site drainage. The discharge electrode 17 of the high-voltage electric detonation fracturing device can be placed in the detonation hole 1a of the test piece 1. The high-voltage electric detonation fracturing device performs high-voltage pulse discharge through the discharge electrode 17 immersed in water to fracture the test piece 1.

[0022] The application can simulate the electric explosion cracking experiment under different stress and different voltage conditions by setting the stress loading device, the high-voltage electric explosion cracking device and the gas-liquid coupling device 21, and can realize self-water injection, self-gas injection and water pumping and draining by using the gas-liquid coupling device 21, which is beneficial to accurately and deeply study the pore and fracture development law, gas migration and permeability of the reservoir after the action of the high-voltage electric explosion cracking technology, and reveals the internal mechanism and essence of the multi-field coupling of electric field and stress field in the action process, thereby providing theoretical support and engineering parameter guidance for using the high-voltage electric explosion cracking based on the liquid-electric effect to increase the permeability and improve the gas recovery efficiency of the gas reservoir.

[0023] In the application, the stress loading device comprises an axial pressure loading module and a confining pressure loading module, and the vertical stress and the lateral pressure in the underground environment of the rock layer or soil under the actual oil and gas well field geological conditions are simulated by applying axial pressure and confining pressure.

[0024] As shown in Figure 1 and Figure 3 , wherein the axial pressure loading module comprises two oil cylinders 8 provided with multi-stage sliding rods, an axial pressure pump 3, an axial pressure pipeline 5 and a stop valve 7 arranged on the axial pressure pipeline 5, for example, the multi-stage sliding rods comprise a fourth sliding rod 12 connected with the oil cylinder 8, a third sliding rod 11 in sliding connection with the fourth sliding rod 12, a second sliding rod 10 in sliding connection with the third sliding rod 11 and a first sliding rod 9 in sliding connection with the second sliding rail, the first sliding rod 9 is the terminal end of the multi-stage sliding rod and has a diameter larger than that of the other sliding rods, the first sliding rod 9 can be inserted into the pressure chamber 2 and is in sliding connection with the inner wall of the pressure chamber 2, the first sliding rod 9, the second sliding rod 10, the third sliding rod 11 and the fourth sliding rod 12 are high-density insulating rods, and the axial pressure pump 3 adopts a displacement precision injection pump with a servo control system. The two oil cylinders 8 are arranged in an upper-lower relative mode, the axial pressure pump 3 (an oil tank connected with the axial pressure pump 3 is not shown in the figure) is connected with the axial pressure channels (holes in the side wall of the oil cylinder 8) in the side wall of the two oil cylinders 8 through two axial pressure pipelines 5 arranged in parallel, the upper and lower ends of the test piece 1 are connected with the first sliding rods 9 at the terminal ends of the two multi-stage sliding rods, respectively, and the axial pressure pump 3 delivers hydraulic oil to the oil cylinder 8 through the axial pressure pipeline 5 to push the multi-stage sliding rods to provide the test piece 1 with equal axial pressure from the top and bottom. When the axial pressure is loaded, the hydraulic oil flowing out of the axial pressure pump 3 flows through the axial pressure pipeline 5 to the oil cylinder 8, and the hydraulic oil reaching the oil cylinder 8 pushes the first sliding rod 9, the second sliding rod 10, the third sliding rod 11 and the fourth sliding rod 12 to act, thereby transmitting the hydraulic pressure to the test piece 1 to provide the test piece 1 with equal axial pressure from the top and bottom.

[0025] The confining pressure loading module comprises a confining pressure pump 4, a confining pressure pipeline 6, and a stop valve 7 arranged on the confining pressure pipeline 6, and the upper end and the lower end of the side wall of the pressure chamber 2 are each provided with a confining pressure passage (as an opening on the side wall of the pressure chamber 2), and the shaft pressure pump 3 is connected to the inside of the pressure chamber 2 through the confining pressure pipeline 6 and the two confining pressure passages, respectively, and the confining pressure pump 4 sends hydraulic oil into the pressure chamber 2 through the confining pressure pipeline 6 to provide confining pressure for the periphery of the test piece 1. When the confining pressure is provided, the hydraulic oil flows through the confining pressure pipeline 6 to the pressure chamber 2 through the confining pressure pump 4, the confining pressure passage is closed after the hydraulic oil fills the pressure chamber 2, and the hydraulic oil with pressure exerts confining pressure on the periphery of the test piece 1 in the pressure chamber 2.

[0026] Preferably, the pressure chamber 2 is further provided with an isolation rubber sleeve 13, and the isolation rubber sleeve 13 is wrapped around the test piece 1 and the ends of the two multi-stage sliding rods, and the isolation rubber sleeve 13 is arranged to prevent the hydraulic oil from being immersed into the test piece 1 through the upper and lower ends of the isolation rubber sleeve 13.

[0027] As shown in Figure 1 In the present application, the high-voltage electric detonation cracking device comprises a high-voltage power supply 14, a high-voltage electric energy storage box 15 connected to the high-voltage power supply 14 through a first section of transmission cable 20a, an output control cabinet 16 connected to the high-voltage electric energy storage box 15 through a second section of transmission cable 20b, and a discharge electrode 17 connected to the output control cabinet 16 through a third section of transmission cable 20c, and the first section of transmission cable 20a and the third section of transmission cable 20c are each provided with an intelligent millisecond switch 19. The high-voltage power supply 14 charges the high-voltage electric energy storage box 15 through the first section of transmission cable 20a under the action of the intelligent millisecond switch 19, and when the charging voltage reaches a working threshold value, the charging voltage reaches the output control cabinet 16 through the second section of transmission cable 20b, which transmits the stored electric energy to both ends of the discharge electrode 17 through the third section of transmission cable 20c, and when the field strength between the two poles of the discharge electrode 17 reaches the water medium breakdown field strength, a discharge channel is formed between the two poles of the discharge electrode 17 to generate a water shock wave effect.

[0028] The present application can adjust the discharge gap position of the discharge electrode 17 through the third section of transmission cable 20c, so that the two poles of the discharge electrode 17 correspond to different positions of the detonation hole 1a. In addition, for the test piece 1 with multiple layers of reservoirs, the discharge electrode 17 can also be moved up and down in the detonation hole 1a by pulling the third section of transmission cable 20c, and the volume cracking of electric detonation in different layers can be realized by adjusting the up and down position of the discharge electrode 17.

[0029] Preferably, the detonation hole 1a is further provided with a protective sleeve, which is an inflatable sleeve or an air bag and is telescopic. The volume of the protective sleeve decreases when it is contracted, which is beneficial to placing it in the detonation hole 1a, and the volume of the protective sleeve increases when it is expanded, and the outer wall of the protective sleeve tightly adheres to the wall of the detonation hole 1a to fix the discharge electrode 17.

[0030] As shown in Figure 1As shown in another preferred embodiment, the high-voltage electric detonation fracturing device further comprises an oscilloscope 18 connected with the third section transmission cable 20c.

[0031] As shown in another preferred embodiment, the high-voltage electric detonation fracturing device further comprises an oscilloscope 18 connected with the third section transmission cable 20c. Figure 1 and Figure 2 As shown in another preferred embodiment, the high-voltage electric detonation fracturing device further comprises an oscilloscope 18 connected with the third section transmission cable 20c. The gas-liquid two-phase module injects, pumps and discharges water from the upper end of the pressure chamber 2 through the upper water gas pipeline 23a, and injects and pumps water from the lower end of the pressure chamber 2 through the lower water gas pipeline 23b.

[0032] The present application injects, pumps and discharges water from the upper end of the pressure chamber 2, and injects and pumps gas from the lower end of the pressure chamber 2, so as to realize precise coupling and circulation control of the gas-liquid medium through bidirectional fluid control.

[0033] The data acquisition module is used for collecting the water injection flow, gas injection flow, water discharge flow, gas discharge flow and gas discharge pressure of the gas-liquid two-phase module, so as to determine the pressure change, seepage rate and relative permeability through the data acquisition module, and analyze and observe the seepage characteristics of the fluid in the test piece 1.

[0034] Specifically, the gas-liquid two-phase module comprises a vacuum pump 29 connected to the upper water-gas pipe 23a through the upper gas pipe 24a, a water pressure pump 30 and an upper water pump 32a connected to the upper water-gas pipe 23a through the upper water pressure pipe 25a and arranged in parallel, a water tank 31 connected to the inlet of the water pressure pump 30, an upper water-gas collection tank 33a connected to the outlet of the upper water pump 32a, a gas storage cylinder 34 connected to the lower water-gas pipe 23b through the lower gas pipe 24b, a lower water pump 32b connected to the lower water-gas pipe 23b through the lower water pressure pipe 25b, and a lower water-gas collection tank 33b connected to the outlet of the lower water pump 32b. Valves 28 are arranged on the upper gas pipe 24a, the upper water pressure pipe 25a, the lower gas pipe 24b and the lower water pressure pipe 25b, and the valves 28 are on-off stop valves 7. Preferably, non-return valves are further arranged on the upper gas pipe 24a, the upper water pressure pipe 25a, the lower gas pipe 24b and the lower water pressure pipe 25b.

[0035] The data acquisition module comprises flow detection meters 26 for monitoring flow and pressure detection meters 27 for monitoring pressure arranged on the upper gas pipe 24a, the lower gas pipe 24b, the upper water pressure pipe 25a and the lower water pressure pipe 25b, and the signal output ends of the flow detection meters 26 and the pressure detection meters 27 are connected to the input end of the data acquisition system 35.

[0036] With the technical scheme, the vacuum pump 29 is connected to the upper water-gas pipe 23a through the upper gas pipe 24a, and the vacuum pump 29 can be used to extract the gas in the pressure chamber 2 from the upper end of the pressure chamber 2 or to create a vacuum in the pressure chamber 2. The water pressure pump 30 is connected to the upper water-gas pipe 23a through the upper water pressure pipe 25a, and the water pressure pump 30 can be used to inject the water in the water tank 31 into the pressure chamber 2 from the upper end of the pressure chamber 2 (the water is injected into the explosion hole through the hose 22 and then overflows from the explosion hole 1a into the pressure chamber 2), thereby realizing self-water injection. The upper water pump 32a is connected to the upper water-gas pipe 23a through the upper water pressure pipe 25a, and the upper water pump 32a can be used to extract the water in the pressure chamber 2 from the upper end of the pressure chamber 2 to the upper water-gas collection tank 33a. When the seepage experiment is performed, the water and the gas in the pressure chamber 2 can also enter the upper water-gas collection tank 33a from the upper water pressure pipe 25a. The gas storage cylinder 34 is connected to the lower water-gas pipe 23b through the lower gas pipe 24b, and the gas storage cylinder 34 can be used to inject the gas in the gas storage cylinder 34 into the pressure chamber 2 from the lower end of the pressure chamber 2, thereby realizing self-gas injection. The lower water pump 32b is connected to the lower water-gas pipe 23b through the lower water pressure pipe 25b, and the lower water pump 32b can be used to extract the water in the pressure chamber 2 from the lower end of the pressure chamber 2 to the lower water-gas collection tank 33b, thereby draining the water in the pressure chamber 2.

[0037] Preferably, the upper water pressure pipeline 25a comprises an upper main water pressure pipeline connected with the upper gas pipeline 23a and two upper branch water pressure pipelines connected with the upper main water pressure pipeline in parallel, the water pressure pump 30 and the upper water pump 32a are respectively arranged on the two upper branch water pressure pipelines, the flow detector 26 and the pressure detector 27 are arranged on the upper main water pressure pipeline, and the valve 28 is arranged on each of the two upper branch water pressure pipelines. Since the water injection and water pumping at the upper end of the pressure chamber 2 are performed at different times, one flow detector 26 and one pressure detector 27 are not arranged on each of the two upper branch water pressure pipelines, but are arranged on the upper branch water pressure pipelines, thereby reducing the number of flow detectors 26 and pressure detectors 27 to reduce the cost.

[0038] Embodiment Two

[0039] The embodiment provides a test method for simulating in-situ reservoir electric detonation fracturing by gas-liquid coupling pressure, which is realized based on the test system for simulating in-situ reservoir electric detonation fracturing by gas-liquid coupling pressure in the embodiment one, as shown in the following figure, and includes the following steps: Figure 4

[0040] Step a: build the test system, install and connect the pipelines between systems and debug. After installation, perform the air tightness test, and test the stability of the pipeline connection by increasing the pressure.

[0041] Step b: prepare the test piece 1 (the test piece 1 is a cylindrical structure matched with the inside of the pressure chamber 2), perform physical test and drying treatment on the test piece 1, install the test piece 1 into the pressure chamber 2, and close the upper end and the lower end of the pressure chamber 2 by the two first sliding rods 9 to ensure the closed environment of the pressure chamber 2.

[0042] Step c: static experiment stage, establish the initial saturation condition, perform vacuumization on the pressure chamber 2 by the gas-liquid coupling device 21 to ensure that there is no residual air in the test piece 1, slowly inject water into the pressure chamber 2 by the gas-liquid coupling device 21 to soak the test piece 1, make the test piece 1 fully saturated by absorbing water, stand for a period of time to stabilize the pore fluid distribution of the test piece 1, and then extract the water in the pressure chamber 2 by the gas-liquid coupling device 21.

[0043] Specifically, step c includes the following processes:

[0044] c1: open the valve 28 on the upper gas pipeline 24a, start the vacuum pump 29 to perform vacuumization on the pressure chamber 2 to remove the air in the test piece 1, and then close the vacuum pump 29 and the valve 28 on the upper gas pipeline 24a.

[0045] c2: open the valve 28 on the upper water pressure pipeline 25a, start the water pressure pump 30, pressurize the water in the water tank 31 by the water pressure pump 30, flow the water through the upper water pressure pipeline 25a to the upper water gas passage, and then enter the pressure chamber 2 to establish the water medium environment for the test piece 1 to self-supply water.​

[0046] c3: After the water saturation of the test piece 1 is completed, it is left to stand for 12-24 hours to stabilize the pore fluid distribution of the test piece 1.

[0047] c4: The valve 28 on the lower water pressure pipeline 25b is opened, and the lower water pump 32b is started to discharge the water in the pressure chamber 2 from the lower end thereof through the lower water gas passage and the lower water pressure pipeline 25b to the lower water gas collection tank 33b.

[0048] Step d: The axial pressure and confining pressure are applied to the test piece 1 by the stress loading device to simulate the original stress environment of the oil and gas well site.

[0049] Specifically, step d includes the following processes:

[0050] d1: The confining pressure is gradually applied, and the confining pressure pump 4 outputs hydraulic oil, which flows through two different confining pressure pipelines 6 to the pressure chamber 2. After the pressure chamber 2 is filled with hydraulic oil, the stop valve 7 on the confining pressure passage is closed, and the hydraulic oil with pressure applies confining pressure to the test piece 1 around the pressure chamber 2. It should be noted that the hydraulic oil of the confining pressure is outside the test piece 1, and the pressure is applied through the gel sleeve. The injected water and gas are inside the core pores of the test piece 1, so the hydraulic oil will not enter the core pores by mistake.

[0051] d2: The axial pressure slightly larger than the confining pressure is applied, and the axial pressure pump 3 outputs hydraulic oil, which flows through two different axial pressure pipelines 5 to the oil cylinder 8 and pushes the multi-pole multi-stage sliding rod to work to reach the set axial pressure value. The axial pressure is gradually applied to ensure that the test piece 1 is not damaged or deformed. After the confining pressure and axial pressure are stable and do not fluctuate, the subsequent steps can be continued.

[0052] Step e: The water and gas are injected into the pressure chamber 2 through the gas-liquid coupling device 21. The water in the water tank 31 is pressurized by the water pressure pump 30 and injected into the pressure chamber 2 through the upper water pressure pipeline 25a and the upper water gas pipeline 23a. The water flows downward from the upper end of the pressure chamber 2. The gas in the gas storage bottle 34 is injected into the pressure chamber 2 through the lower gas pipeline 24b and the lower water gas pipeline 23b, and the gas flows upward from the lower end of the pressure chamber 2. The injection rate of water and gas is controlled, the basic gas-liquid coupling seepage experiment (i.e., the experimental steps before electric shock-induced cracking, that is, steps a-e) is carried out, and the initial seepage characteristics are recorded.

[0053] Step f: Dynamic experiment stage, the discharge electrode 17 is immersed in the water of the shock hole 1a, and the high-voltage electric shock-induced cracking device is operated to perform high-voltage pulse discharge through the discharge electrode 17 to crack the test piece 1.

[0054] Specifically, step f includes the following processes:

[0055] f1: open the high-voltage power supply 14, and charge the high-voltage energy storage box 15 through the first section of the transmission cable 20a until the working threshold of the intelligent millisecond switch 19 on the third section of the transmission cable 20c is reached.

[0056] f2: when the working threshold of the intelligent millisecond switch 19 on the third section of the transmission cable 20c is reached, the intelligent millisecond switch 19 on the third section of the transmission cable 20c is turned on, and the energy stored in the high-voltage energy storage box 15 is transmitted to both ends of the discharge electrode 17. When the field strength between the two poles of the discharge electrode 17 reaches the water medium breakdown field strength, the positive and negative poles of the discharge electrode 17 are turned on and a discharge channel is formed between the two poles to crack the test piece 1 by high-voltage electric shock.

[0057] f3: operate the oscilloscope 18 to record the curve of pulse voltage and current during high-voltage pulse discharge.

[0058] Preferably, when the high-voltage pulse discharge is performed on the test piece 1 through the discharge electrode 17, the following formula is used to adjust the parameters of the operated high-voltage electric shock cracking device:

[0059]

[0060] In the formula, P m is the peak pressure of the water shock wave generated by the high-voltage pulse, which is similar to the process of underwater explosion of explosives; U is the discharge voltage of the discharge electrode 17, which can be adjusted; d is the electrode spacing of the discharge electrode 17, which is the distance between the positive and negative poles of the discharge electrode 17, and is generally fixed, but can be adjusted according to the situation to obtain the influence of different electrode spacings on the experiment; L is the discharge distance of the discharge electrode 17, which is the distance of the water shock wave generated by the high-voltage pulse, and can be determined according to the experimental or empirical value; and the decimal in the formula is the data obtained by fitting.

[0061] Through the above formula, the parameters of the operated high-voltage electric shock cracking device can be adjusted, and the peak pressure of the water shock wave is stably improved with the increase of the discharge voltage within a certain range, and the peak pressure of the water shock wave decreases in the form of a power function with the increase of the discharge distance.

[0062] Step g: restore the seepage experiment, and monitor the flow, pressure and fluid proportion at the output end through the data acquisition module to observe the flow recovery characteristics of the fluid in the test piece 1.

[0063] Specifically, step g includes the following processes:

[0064] g1: gradually release the axial stress and confining stress applied to the test piece 1 by injecting gas (specifically, open the valve 28 on the gas storage bottle 34 and the lower gas pipeline 24b, and the gas in the gas storage bottle 34 enters the pressure chamber 2 through the lower gas pipeline 24b and the lower water-gas pipeline 23b) from the lower end of the pressure chamber 2 and keeping the gas injection;

[0065] g2: measure the residual saturation and the change of permeability by displacing the residual fluid in the pressure chamber 2 by the gas injected from the lower end of the pressure chamber 2 (the specific measurement and calculation method is prior art, which is not described here).

[0066] g3: observe the recovery of the seepage capacity and the flow characteristics by injecting water from the upper end of the pressure chamber 2 through the gas-liquid coupling device 21 (the water injection process is the same as step c2, which is not described here) to inject water vapor, and gradually restore the confining stress and axial stress applied to the test piece 1 by the stress loading device.

[0067] Step h: analyze the influence of electric detonation on the seepage characteristics of the test piece 1. Before step f and after step g, measure the pressure change, seepage rate and relative permeability by the data acquisition module (the specific measurement and calculation method is prior art, which is not described here), analyze the seepage characteristics of the fluid in the test piece 1, and compare the data before and after the two steps, for example, the change of permeability can be analyzed, and the specific characteristics are analyzed, which is prior art. The test system is to obtain the change of characteristics by simulating the environment.

[0068] Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and purposes of the present application, and the scope of the present application is defined by the claims and their equivalents.

Claims

1. A test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure, characterized by: It includes a pressure chamber for installing the test piece, a stress loading device, a gas-liquid coupling device and a high-voltage electric detonation cracking device with a discharge electrode; A detonation hole is provided on the top of the test piece; The stress loading device is connected to the pressure chamber and is used to apply axial pressure and confining pressure to the test piece in the pressure chamber to simulate ground stress; The gas-liquid coupling device is capable of injecting water, injecting gas, pumping water and exhausting gas into the pressure chamber to achieve gas-liquid coupling; The discharge electrode of the high-voltage electric detonation and cracking device can be placed in the detonation hole of the test piece. The high-voltage electric detonation and cracking device performs high-voltage pulse discharge through the discharge electrode immersed in water to crack the test piece.

2. The test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to claim 1 is characterized in that: The stress loading device includes an axial pressure loading module and a confining pressure loading module; The axial pressure loading module includes two oil cylinders with multi-stage slide rods, an axial pressure pump, an axial pressure pipeline and a shut-off valve provided on the axial pressure pipeline. The two oil cylinders are arranged opposite to each other, one above and one below. The axial pressure pump is connected to the two oil cylinders through the axial pressure pipelines. The upper and lower ends of the test piece are respectively connected to the ends of the two multi-stage slide rods. The axial pressure pump delivers hydraulic oil to the oil cylinders through the axial pressure pipelines to push the multi-stage slide rods to provide equal axial pressure on the upper and lower parts of the test piece. The confining pressure loading module includes a confining pressure pump, a confining pressure pipeline and a stop valve arranged on the confining pressure pipeline. A confining pressure channel is respectively provided at the upper and lower ends of the side wall of the pressure chamber. The axial pressure pump is connected to the two confining pressure channels through the confining pressure pipeline and connected to the interior of the pressure chamber. The confining pressure pump transports hydraulic oil into the pressure chamber through the confining pressure pipeline to provide confining pressure around the specimen.

3. The test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to claim 2 is characterized in that: An isolation rubber sleeve is further provided in the pressure chamber, and the isolation rubber sleeve is wrapped around the test piece and the ends of the two multi-stage sliding rods.

4. The test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to claim 1 is characterized in that: The high-voltage electric detonation and fracturing device includes a high-voltage power supply, a high-voltage electric energy storage box connected to the high-voltage power supply via a first section of a transmission cable, an output control cabinet connected to the high-voltage electric energy storage box via a second section of a transmission cable, and a discharge electrode connected to the output control cabinet via a third section of a transmission cable. Intelligent millisecond switches are provided on both the first section of the transmission cable and the third section of the transmission cable.

5. The test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to claim 4 is characterized in that: The high-voltage electric detonation and fracturing device further comprises an oscilloscope connected to the third section of the transmission cable.

6. The test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to any one of claims 1 to 5, characterized in that: The gas-liquid coupling device includes a gas-liquid two-phase module and a data acquisition module; The gas-liquid two-phase module is connected to the upper end of the pressure chamber through an upper water-gas pipeline, and the upper water-gas pipeline is connected to a hose extending into the detonation hole. The gas-liquid two-phase module injects, extracts and exhausts water into the pressure chamber from the upper end of the pressure chamber through the upper water-gas pipeline; The gas-liquid two-phase module is also connected to the lower end of the pressure chamber through a water-gas pipeline, and the gas-liquid two-phase module injects gas and pumps water into the pressure chamber from the lower end of the pressure chamber through the water-gas pipeline; The data acquisition module is used to collect the water injection flow, gas injection flow, drainage flow, exhaust flow, drainage pressure and exhaust pressure of the gas-liquid two-phase module.

7. The test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to claim 6, characterized in that: The gas-liquid two-phase module includes a vacuum pump connected to the upper water-gas pipeline through an upper gas pipeline, a water pressure pump and an upper water pump arranged in parallel connected to the upper water-gas pipeline through an upper water pressure pipeline, a water tank connected to the inlet of the water pressure pump, an upper water-gas collecting box connected to the outlet of the upper water pump, a gas storage bottle connected to the lower water-gas pipeline through a lower gas pipeline, a lower water pump connected to the lower water-gas pipeline through a lower water pressure pipeline, and a lower water-gas collecting box connected to the outlet of the lower water pump, and valves are provided on the upper gas pipeline, the upper water pressure pipeline, the lower gas pipeline and the lower water pressure pipeline; The data acquisition module includes a flow meter for monitoring flow and a pressure meter for monitoring pressure, which are arranged on the upper gas pipeline, the upper water pressure pipeline of the lower gas pipeline, and the lower water pressure pipeline. The signal output ends of the flow meter and the pressure meter are connected to the input end of the data acquisition system.

8. The test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to claim 7, characterized in that: The upper water pressure pipeline includes an upper main water pressure pipeline connected to the upper water and gas pipeline and two upper branch water pressure pipelines connected to the upper main water pressure pipeline and arranged in parallel. The water pressure pump and the upper water pump are respectively arranged on the two upper branch water pressure pipelines. A flow meter and a pressure meter are set on the upper main water pressure pipeline, and valves are provided on the two upper branch water pressure pipelines.

9. An experimental method for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure, characterized in that: The method is implemented based on the test system for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure as described in any one of claims 1 to 8, comprising the following steps: Step a: Building the test system, installing and debugging it; Step b: Prepare the test piece, install the test piece into the pressure chamber, and seal the upper and lower ends of the pressure chamber; Step c: Static test phase: establish initial saturation conditions, evacuate the pressure chamber using a gas-liquid coupling device to ensure that there is no residual air inside the specimen, slowly inject water into the pressure chamber using the gas-liquid coupling device to soak the specimen until it is fully saturated with water, let it stand for a period of time to stabilize the pore fluid distribution of the specimen, and then pump out the water in the pressure chamber using the gas-liquid coupling device; Step d: Apply axial pressure and confining pressure to the specimen through a stress loading device to simulate the original stress environment of the oil and gas well site. Step e: Inject water and gas into the pressure chamber through the gas-liquid coupling device. Water is injected from the upper end of the pressure chamber and flows downward, and gas is injected from the lower end of the pressure chamber and flows upward. The injection rates of water and gas are controlled to conduct a basic gas-liquid coupling seepage experiment and record the initial seepage characteristics. Step f: In the dynamic experiment stage, the discharge electrode is immersed in the water in the detonation hole, and the high-voltage electric detonation cracking device is operated to adjust the peak pressure of the water shock wave by adjusting the discharge voltage of the discharge electrode, the distance between the electrodes, and the discharge distance of the discharge electrode, so as to perform high-voltage pulse discharge and crack the test piece; Where, P m is the peak pressure of the water shock wave generated by the high-voltage electric pulse; U is the discharge voltage of the discharge electrode; d is the electrode spacing of the discharge electrode, which is the distance between the positive and negative electrodes of the discharge electrode; L is the discharge distance of the discharge electrode, which is the distance the water shock wave generated by the high-voltage electric pulse travels; the decimals in the formula are the data obtained by fitting; Step g: restore the seepage experiment to observe the flow recovery characteristics of the fluid in the specimen; Step h: Analyze and observe the effect of electric detonation on the seepage characteristics of the specimen.

10. The test method for simulating in-situ reservoir electric explosion fracturing by gas-liquid coupling pressure according to claim 9, characterized in that: Step g includes the following steps: g1: Inject gas into the pressure chamber through the gas-liquid coupling device and maintain gas injection, gradually releasing the axial pressure and confining pressure applied to the specimen. g2: Displace residual fluid by injected gas and measure the residual saturation and permeability changes; g3: Inject water into the pressure chamber through the gas-liquid coupling device to inject water gas. By gradually restoring the confining pressure and axial pressure applied to the specimen, observe the recovery of the seepage capacity and the flow characteristics.

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