Liquid nitrogen and microwave synergistic induction shale gas reservoir three-dimensional fracture network forming device and method

Abstract

The application relates to the field of auxiliary rock breaking technology, in particular to a liquid nitrogen and microwave cooperative induced shale gas reservoir three-dimensional fracture network forming device and method, wherein the device comprises a liquid nitrogen tank storing liquid nitrogen; and a fracture cutter connected with the liquid nitrogen tank, wherein the fracture cutter is lowered into the shale gas reservoir, the fracture cutter comprises a microwave emitter and a jet nozzle, liquid nitrogen stored in the liquid nitrogen tank is sprayed by the jet nozzle to form a fracture at the end of the fracture cutter, and the microwave emitter is used for emitting microwaves to expand and extend the fracture; and a control console connected with the fracture cutter and used for controlling the jet nozzle and the microwave emitter of the fracture cutter to cooperate multiple times, so that a three-dimensional fracture network of the induced shale gas reservoir is formed in the shale gas reservoir. Therefore, the problems in the prior art that the hydraulic fracturing cannot form a large-scale fracture network and the fracturing cracks are randomly expanded, a large number of "blank mining areas" exist in the shale gas reservoir, and the working efficiency is low are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of auxiliary rock breaking, and in particular relates to a device and method for forming a three-dimensional fracture network of a shale gas reservoir by using liquid nitrogen and microwaves. BACKGROUND

[0002] Shale gas, as a clean and high-quality energy source, plays an important role in the composition of world energy. Due to the self-generation and self-storage characteristics of shale gas reservoirs, the permeability is low and most of the shale gas is adsorbed on the shale, increasing the difficulty of exploitation.

[0003] In related technologies, shale gas exploitation mainly uses hydraulic fracturing methods. The traditional hydraulic fracturing has many shortcomings: (1) low efficiency: the permeability of shale is extremely low, and even if the traditional hydraulic fracturing method is used, a large-scale fracture network cannot be formed, and the random expansion of the fracturing cracks leads to the existence of a large number of "blank exploitation areas" in the shale gas reservoir. (2) Water source problem: shale gas reservoirs in China are mainly distributed in hilly and mountainous areas and northern semi-arid regions, and the serious shortage of water resources limits the use of hydraulic fracturing technology, and it is impossible to increase production by simply increasing water consumption. SUMMARY

[0004] The present application provides a device and method for forming a three-dimensional fracture network of a shale gas reservoir by using liquid nitrogen and microwaves to solve the problems in related technologies that hydraulic fracturing cannot form a large-scale fracture network and the random expansion of fracturing cracks leads to the existence of a large number of "blank exploitation areas" in the shale gas reservoir, and low work efficiency.

[0005] The first aspect of the present application provides a device for forming a three-dimensional fracture network of a shale gas reservoir by using liquid nitrogen and microwaves, comprising: a liquid nitrogen tank storing liquid nitrogen; a fracture cutter connected to the liquid nitrogen tank, wherein the fracture cutter is lowered into the shale gas reservoir, the fracture cutter comprises a microwave emitter and a jet nozzle, the liquid nitrogen stored in the liquid nitrogen tank is sprayed by the jet nozzle to form a fracture at the end of the fracture cutter, and the microwave emitter is used to emit microwaves to extend and extend the fracture; and a control console connected to the fracture cutter for controlling the jet nozzle and the microwave emitter of the fracture cutter to act in coordination multiple times to form a three-dimensional fracture network of the shale gas reservoir in the shale gas reservoir.

[0006] Optionally, in one embodiment of the present application, the slitting device further comprises a magnetron, a waveguide, a cable, a liquid nitrogen delivery pipe, a pump, a motor and a telescopic rod; one end of the magnetron is connected to the cable, the other end is connected to the waveguide, the other end of the waveguide is connected to the microwave emitter, the microwave emitter is arranged in a ring shape along the surface of the slitting device; the other end of the cable is connected to the control console and the power supply; one end of the liquid nitrogen delivery pipe is connected to the valve of the liquid nitrogen tank, the other end is connected to the pump, one end of the pump is connected to the motor, the other end of the motor is connected to the telescopic rod, and the telescopic rod is uniformly provided with the jet nozzles.

[0007] Optionally, in one embodiment of the present application, the microwave emitter comprises a circulator and a microwave feed.

[0008] Optionally, in one embodiment of the present application, further comprising a cable, wherein the cable is wrapped with the cable, the liquid nitrogen delivery pipe and the cold insulation layer.

[0009] The second aspect embodiment of the present application provides a method for forming a three-dimensional fracture network in a shale gas reservoir by using liquid nitrogen and microwave cooperation, which is applied to the liquid nitrogen and microwave cooperation device for inducing a three-dimensional fracture network in a shale gas reservoir, and the method comprises the following steps: obtaining the current position of the slitting device; if the current position is at the starting end of the shale gas reservoir to be slitted, controlling the slitting device to perform a first slitting action, and after a preset time interval, detecting whether the current slitting meets a preset condition, if the preset condition is met, stopping the first slitting action, and continuously and cyclically advancing the slitting device according to a preset advancing distance until a slitting array is formed in the entire slitting section to be slitted; if the current position reaches the end of the shale gas reservoir to be slitted, controlling the slitting device to perform a second slitting action, and after a preset time interval, continuously and cyclically retreating the slitting device according to a preset advancing distance until the starting end of the slitting section to be slitted; repeatedly performing the first slitting action and the second slitting action according to the slitting position to control the slitting device, until a three-dimensional fracture network is formed in the slitting section to be slitted in the shale gas reservoir.

[0010] Optionally, in one embodiment of the present application, the control of the slitting device to perform the first slitting action comprises: controlling the control valve of the liquid nitrogen tank to be opened, the telescopic rod of the slitting device to be popped out, and high-pressure liquid nitrogen rotating jet to be emitted.

[0011] Optionally, in one embodiment of the present application, the control of the slitting device to perform the second slitting action comprises: controlling the built-in magnetron of the slitting device to generate microwaves, transmitting the microwaves to the microwave emitter through the waveguide, and emitting the microwaves by using the microwave emitter.

[0012] Optionally, in an embodiment of the present application, the continuously advancing the slit cutter according to the preset advancing distance until the whole to-be-slit section forms a slit array comprises: identifying a preset advancing distance of each slit under the current working condition; controlling the slit cutter to advance according to the preset advancing distance, and controlling the slit cutter to perform a first slitting action when the preset advancing distance is reached.

[0013] Optionally, in an embodiment of the present application, before the controlling the slit cutter to advance according to the preset advancing distance, it comprises: controlling the control valve of the liquid nitrogen tank to be closed, the retracting rod of the slit cutter to be retracted, and the high-pressure liquid nitrogen rotating jet to be paused.

[0014] Optionally, in an embodiment of the present application, before the obtaining the current position of the slit cutter, it comprises: connecting the slit cutter with the control console, the power supply and the liquid nitrogen tank by a cable; lowering the slit cutter into the shale gas reservoir through the cable and advancing to the starting end of the to-be-slit section.

[0015] Optionally, in an embodiment of the present application, the three-dimensional fracture network refers to a network of cracks that are interconnected with each other after the secondary cracks are fully developed.

[0016] Therefore, the present application has at least the following beneficial effects:

[0017] (1) The embodiment of the present application uses liquid nitrogen and microwave to cooperatively induce the shale gas reservoir to form a three-dimensional fracture network, which can greatly improve the efficiency of forming the fracture network, the efficiency of shale exploitation and the efficiency of subsequent fracturing.

[0018] (2) The embodiment of the present application uses high-pressure jet slitting technology to form fractures in shale before fracturing, which can induce the formation of directional cracks and improve the efficiency of fracturing.

[0019] (3) The embodiment of the present application uses liquid nitrogen instead of water-based jet, which avoids the pollution of the gas reservoir and at the same time plays the low-temperature effect of liquid nitrogen.

[0020] (4) The embodiment of the present application uses the method of microwave and liquid nitrogen working cooperatively, which uses microwave irradiation to deteriorate the next slitting section while the liquid nitrogen jet is slitting, increases the temperature gradient and thermal stress to generate new secondary cracks on the basis of the initial slitting, and each secondary crack will be interconnected, which can induce the shale gas reservoir to form a three-dimensional fracture network, greatly improve the fracture density and the efficiency of subsequent fracturing, and thus improve the shale gas production.

[0021] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings of which:

[0023] Figure 1 A block schematic diagram of a device for forming a three-dimensional fracture network in a shale gas reservoir using liquid nitrogen and microwave radiation according to an embodiment of the present application;

[0024] Figure 2 A schematic diagram of a device for forming a three-dimensional fracture network in a shale gas reservoir using liquid nitrogen and microwave radiation according to an embodiment of the present application;

[0025] Figure 3 An internal schematic diagram of a device for forming a three-dimensional fracture network in a shale gas reservoir using liquid nitrogen and microwave radiation according to an embodiment of the present application;

[0026] Figure 4 A layout schematic diagram of a microwave emitter according to an embodiment of the present application;

[0027] Figure 5 A cross-sectional schematic diagram of a microwave emitter according to an embodiment of the present application;

[0028] Figure 6 A cross-sectional schematic diagram of a cable according to an embodiment of the present application;

[0029] Figure 7 A flowchart of a method for forming a three-dimensional fracture network in a shale gas reservoir using liquid nitrogen and microwave radiation according to an embodiment of the present application;

[0030] Figure 8 A schematic diagram of the formation of initial fractures according to an embodiment of the present application;

[0031] Figure 9 A schematic diagram of the formation of secondary fractures according to an embodiment of the present application;

[0032] Figure 10 A perspective view of a three-dimensional fracture network according to an embodiment of the present application;

[0033] Figure 11 A schematic diagram of the extension of fractures according to an embodiment of the present application;

[0034] Figure 12 A schematic diagram of the formation of a three-dimensional fracture network according to an embodiment of the present application;

[0035] Figure 13 A plan view of a three-dimensional fracture network according to an embodiment of the present application.

[0036] Explanation of reference signs: liquid nitrogen tank 1, valve 2, power supply 3, control console 4, cable 5, cold insulation layer 51, overburden 6, high-pressure liquid nitrogen jet 7, secondary fracture 8, fracture cutter 9, magnetron 91, waveguide 92, pump 93, motor 94, microwave transmitter 95, circulator 951, microwave feed 952, telescopic rod 96, jet nozzle 97, shale gas reservoir 10, cable 11, liquid nitrogen delivery pipe 12, initial fracture 13. DETAILED DESCRIPTION

[0037] Embodiments of the present application are described in detail below with reference to examples illustrated in 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 intended to explain the present application, and cannot be understood as a limitation of the present application.

[0038] In recent decades, high-pressure jet cutting technology has been widely used around the world, and is a high-tech that integrates mechanics, machinery, computers, and other disciplines. Currently, this technology is used to improve the rock breaking efficiency when cutting rock. If high-pressure jet cutting technology is used to cut a uniform radial slot in a shale gas reservoir at a high speed before fracturing the low-transparency reservoir, the stress in the reservoir is released and fractures are generated, thereby improving the permeability of the shale and the subsequent fracturing efficiency.

[0039] With the popularization and in-depth research of liquid nitrogen, the auxiliary rock breaking technology using the low-temperature effect of liquid nitrogen has also been paid more and more attention. The temperature of liquid nitrogen at normal pressure is as low as -196°C. When it is injected into a shale gas reservoir, a large temperature gradient is formed, and the thermal stress generated will further develop the fractures to form a complex fracture network, thereby improving the production of shale gas. In addition, liquid nitrogen is a colorless, odorless, and non-corrosive inert liquid, which can prevent the reservoir from being damaged and to some extent alleviate the environmental problems caused by water-based liquids. Therefore, liquid nitrogen jet has a broader application prospect than ordinary water jet.

[0040] Microwave refers to electromagnetic waves with a frequency in the range of 300 MHz-300 GHz, and in the use of microwave, a thermal effect is caused. When a dielectric is subjected to microwave radiation, the dipoles in the dielectric will produce swings and friction at a rate of hundreds of millions per second, so that the microwave energy is converted into heat energy of the dielectric, which is macroscopically manifested as an increase in the temperature of the dielectric. The temperature rise caused by microwave has a bulk heating property, i.e., the inside and outside of the material can be heated and raised in temperature at the same time, thereby greatly shortening the heat conduction time in conventional heating and reducing energy loss. In addition, shale as a whole has strong microwave absorption capacity, fast heating rate, and is easy to form high-temperature thermal fractures. Moreover, due to the difference in microwave absorption capacity of different minerals in shale, thermal stress will be generated at the grain boundaries and inside, further causing damage.

[0041] Therefore, the microwave-liquid nitrogen combined treatment fuses the commonness of both based on thermal effect, generates greater temperature gradient and thermal stress. Meanwhile, with the help of high pressure jet, it induces the shale gas reservoir to form dense three-dimensional fracture network in a targeted manner, reduces the "blank mining area" in the shale gas reservoir, and improves the shale gas production.

[0042] The liquid nitrogen and microwave combined device for inducing three-dimensional fracture network of shale gas reservoir and the method thereof are described below with reference to the accompanying drawings. Figure 1 The block diagram of the liquid nitrogen and microwave combined device for inducing three-dimensional fracture network of shale gas reservoir provided by the embodiment of the present application is shown.

[0043] As shown in Figures 1-3 , the liquid nitrogen and microwave combined device for inducing three-dimensional fracture network of shale gas reservoir 100 comprises a liquid nitrogen tank 1, a fracturing device 9, and a control console 4.

[0044] The liquid nitrogen tank 1 stores liquid nitrogen; the fracturing device 9 is connected to the liquid nitrogen tank 1, wherein the fracturing device 9 is lowered into the shale gas reservoir 10, the fracturing device 9 comprises a microwave emitter 95 and a jet nozzle 97, the jet nozzle 97 is used to spray the liquid nitrogen stored in the liquid nitrogen tank to form a fracture at the end of the fracturing device 9, and the microwave emitter 95 is used to emit microwaves to expand and extend the fracture; the control console 4 is connected to the fracturing device 9 and is used to control the multiple coordinated actions of the jet nozzle 97 and the microwave emitter 95 of the fracturing device 9, so as to form a three-dimensional fracture network in the shale gas reservoir 10.

[0045] It can be understood that, in the present embodiment, the liquid nitrogen jet fracturing can be combined with microwave irradiation to deteriorate the next fracturing section at the same time, so as to increase the temperature gradient and thermal stress, thereby generating new secondary fractures on the basis of the initial fracture 13, the secondary fractures will be connected to each other, the shale gas reservoir 10 is induced to form a three-dimensional fracture network, the fracture density and subsequent fracturing efficiency can be greatly improved, and the shale gas production can be improved.

[0046] In the present embodiment, as shown in Figure 3 and Figure 4 , the fracturing device 9 further comprises a magnetron 91, a waveguide 92, a cable 11, a liquid nitrogen delivery pipe 12, a pump 93, a motor 94, and an extension rod 96.

[0047] The one end of the magnetron 91 is connected to the cable 11, and the other end is connected to the waveguide 92, the other end of the waveguide 92 is connected to the microwave emitter 95, the microwave emitter 95 is arranged in a ring shape along the surface of the fracturing device 9; the other end of the cable 11 is connected to the control console 4 and a power supply 3; the one end of the liquid nitrogen delivery pipe 12 is connected to the valve 2 of the liquid nitrogen tank 1, and the other end is connected to the pump 93, the one end of the pump 93 is connected to the motor 94, the other end of the motor 94 is connected to the extension rod 96, and the extension rod 96 is uniformly provided with the jet nozzle 97.

[0048] It can be understood that the shale has strong microwave absorption capacity, the heating rate is fast, and high-temperature thermal cracks are easy to form, the microwave emitter 95 and the waveguide 92 can emit microwaves, and the slotted cutter 9 is internally provided with the pump 93 and the motor 94.

[0049] It should be noted that the slotted cutter 9 can rotate and stretch to emit the high-pressure liquid nitrogen jet 7 of more than 50 MPa, the overall pressure bearing can reach 100 MPa, and the low-temperature environment of liquid nitrogen can be tolerated; the temperature of liquid nitrogen under normal pressure is as low as -196 DEG C, and the injection of liquid nitrogen into the shale gas reservoir can form a large temperature gradient, and the thermal stress generated can make the cracks further develop to form a complex fracture network, thereby improving the yield of shale gas; the temperature rise generated by the microwave has a body heating property, that is, the inside and outside of the material can be heated and raised at the same time, thereby greatly shortening the heat conduction time in conventional heating and reducing energy loss, and the shale has strong microwave absorption capacity, the heating rate is fast, and high-temperature thermal cracks are easy to form.

[0050] In the embodiment of the application, as shown in Figure 5 The microwave emitter includes a circulator 951 and a microwave feed port 952.

[0051] It can be understood that the microwave emitter of the embodiment of the application contains the circulator 951 and the microwave feed port 952, and is arranged in a ring shape along the surface of the slotted cutter, which can uniformly and fully irradiate the surface of the complete shale gas reservoir and form a ring-shaped initial cutting gap, thereby greatly improving the cutting efficiency and the shale exploitation efficiency.

[0052] In the embodiment of the application, as shown in Figure 6 It also includes a cable 5.

[0053] The cable 5 is internally wrapped with a cable 11, a liquid nitrogen delivery pipe 12 and a cold insulation layer 51.

[0054] It can be understood that the cable 5 in the embodiment of the application is internally wrapped with the cable 11, the liquid nitrogen delivery pipe 12 and the cold insulation layer 51, wherein the cable 11 is used for power transmission and communication signal transmission, the liquid nitrogen delivery pipe 12 is used for transporting liquid nitrogen from the liquid nitrogen tank 1 to the slotted cutter 9, and the cold insulation layer is a heat insulation material wrapped around the liquid nitrogen delivery pipe, which mainly functions to minimize the evaporation and temperature rise of liquid nitrogen during the transportation process; the cold insulation layer can maintain the low-temperature state of the liquid nitrogen, ensure that the liquid nitrogen still has sufficient low-temperature efficiency when it reaches the operation point, thereby improving the cutting efficiency and safety.

[0055] It should be noted that the liquid nitrogen delivery pipe uses copper cables wrapped with cross-linked polyethylene (XLPE) and high-density polyethylene (HDPE), and is wrapped with a cold insulation layer of nitrile rubber and diene foam (LT+LTD) on the outside. The connection points are also equipped with secondary protective cables to overcome the problem of maintaining the low temperature of liquid nitrogen.

[0056] According to the liquid nitrogen and microwave synergistic shale gas reservoir three-dimensional fracture network formation device proposed in the embodiments of this application, microwave irradiation is used to degrade the next cut segment while liquid nitrogen jet cutting is being performed. This improves efficiency, increases the temperature gradient and thermal stress, thereby generating new secondary fractures on the basis of the initial cut. The secondary fractures will be interconnected, inducing the formation of a three-dimensional fracture network in the shale gas reservoir. This can greatly improve the fracture density and subsequent fracturing efficiency, thereby increasing shale gas production.

[0057] Next, referring to the accompanying drawings, a method for forming a three-dimensional fracture network in shale gas reservoirs using liquid nitrogen and microwave synergistic induction according to embodiments of this application is described.

[0058] like Figure 7 As shown, the method for forming a three-dimensional fracture network in a shale gas reservoir by synergistic induction of liquid nitrogen and microwave is applied to the liquid nitrogen and microwave synergistic induction device for forming a three-dimensional fracture network in a shale gas reservoir as described in the above embodiment. The method includes the following steps:

[0059] In step S101, the current position of the slit cutter is obtained.

[0060] It is understood that the embodiments of this application can obtain the current position of the slit cutter in order to perform corresponding operations based on the current position of the slit cutter.

[0061] In this embodiment of the application, before obtaining the current position of the slotter, the process includes: connecting the slotter to the control console, power supply, and liquid nitrogen tank using a cable; lowering the slotter into the shale gas reservoir using the cable and advancing it forward to the starting end of the section to be slotted.

[0062] It is understood that, in the embodiments of this application, a cable can be used to connect the slotter to the control console, power supply, and liquid nitrogen tank; the slotter can be lowered into the shale gas reservoir via the cable and advanced forward to the beginning of the section to be slotted, so that the slotter can be controlled to perform corresponding operations from the beginning of the section to be slotted.

[0063] Specifically, the equipment setup steps are as follows: a control console, liquid nitrogen tank, power supply, and other equipment are set up near the hydraulic fracturing wellhead. The slotter is then connected to the control console, power supply, and liquid nitrogen tank via cables. After that, the equipment is debugged before construction to ensure that the equipment is safe and reliable. Then, the slotter is lowered into the shale gas reservoir via cables and advanced to the beginning of the section to be slotted.

[0064] In step S102, if the current position is at the starting end of the shale gas reservoir to be slotted, the slotted control device performs the first slotted action, and after a preset time interval, detects whether the current slot meets the preset condition. If the preset condition is met, the first slotted action is stopped, and the slotted device is continuously and cyclically advanced by a preset advancing distance until the entire slotted section forms a slot array.

[0065] The preset time interval can be 3-8 minutes, the preset condition can be that an initial slot array is formed at the starting end of the shale gas reservoir to be slotted, and the preset advancing distance can be 0.5-2 meters, which can be set according to actual needs and is not limited.

[0066] It can be understood that the embodiments of the present application can control the slotted device to perform the first slotted action when the current position is at the starting end of the shale gas reservoir to be slotted, and stop the first slotted action when the current slot meets the preset condition after a preset time interval. The slotted device is continuously and cyclically advanced by a preset advancing distance until the entire slotted section forms a slot array. The high-pressure jet slotting technology is used to form a directional slot in shale before fracturing, which can induce directional fractures in fracturing and improve fracturing efficiency.

[0067] In the embodiments of the present application, controlling the slotted device to perform the first slotted action includes: opening the control valve of the liquid nitrogen tank, extending the telescopic rod of the slotted device, and emitting high-pressure liquid nitrogen rotating jet.

[0068] It can be understood that the embodiments of the present application can control the control valve of the liquid nitrogen tank to be opened, the telescopic rod of the slotted device to be extended, and high-pressure liquid nitrogen rotating jet to be emitted, so that a directional slot is formed in shale before fracturing, which can induce directional fractures in fracturing and improve fracturing efficiency. In addition, liquid nitrogen is used instead of water-based jet, which avoids pollution of the gas reservoir and also plays the low-temperature effect of liquid nitrogen.

[0069] In the embodiments of the present application, the slotted device is continuously and cyclically advanced by a preset advancing distance until the entire slotted section forms a slot array, which includes: identifying a preset advancing distance corresponding to each slotting under the current working condition; controlling the slotted device to advance forward according to the preset advancing distance, and controlling the slotted device to perform the first slotted action when the preset advancing distance is reached.

[0070] It can be understood that the embodiments of the present application can control the slotted device to advance forward by a preset advancing distance according to the specific working condition requirements, and control the slotted device to perform the first slotted action when the preset advancing distance is reached. In this way, the slotted device is cyclically advanced until an initial slot array with a preset advancing distance is formed in the entire slotted section, so that a directional slot is formed in shale before fracturing, which can induce directional fractures in fracturing and improve fracturing efficiency.

[0071] Specifically, the liquid nitrogen jetting step: open the valve, pop up the telescopic rod by means of the ground console, assisted by the built-in pump and motor, the slotted cutter will emit high-pressure liquid nitrogen rotating jet, after 3-8 minutes, a set of initial slotted holes in radial arrangement is formed at the starting end of the shale gas reservoir to be slotted, then according to the specific working condition requirements, it is pushed back 0.5-2 meters, the slotted hole is continued to be cut for 3-8 minutes and the process is circulated and pushed forward, until the initial crack array with a spacing of 0.5-2 meters is formed in the entire slotted section.

[0072] In the embodiment of the present application, before the slotted cutter is controlled to advance according to the preset advancing distance, it includes: controlling the control valve of the liquid nitrogen tank to be closed, the telescopic rod of the slotted cutter to be retracted, and the high-pressure liquid nitrogen rotating jet to be temporarily stopped.

[0073] It can be understood that the control valve of the liquid nitrogen tank can be controlled to be closed, the telescopic rod of the slotted cutter can be retracted, and the high-pressure liquid nitrogen rotating jet can be temporarily stopped, so as to facilitate the forward advancement of the slotted cutter and protect the slotted cutter from being damaged.

[0074] Specifically, the valve is closed and the telescopic rod is retracted, the liquid nitrogen jet is temporarily stopped, and the slotted cutter is pushed to the initial slotted hole at the end of the slotted section.

[0075] In step S103, if the current position reaches the end of the shale gas reservoir to be slotted, the slotted cutter is controlled to perform a second slotted action, and after a preset time interval, the slotted cutter is continuously circulated and retreated according to the preset advancing distance until the starting end of the slotted section.

[0076] It can be understood that the current position reaches the end of the shale gas reservoir to be slotted, the slotted cutter is controlled to perform a second slotted action, and after a preset time interval, the slotted cutter is continuously circulated and retreated according to the preset advancing distance until the starting end of the slotted section, while the liquid nitrogen jetting slotted hole, the next slotted section is deteriorated by microwave irradiation, which improves the efficiency while increasing the temperature gradient and thermal stress, thereby generating new secondary cracks on the basis of the initial slotted hole, each secondary crack will be connected to each other, and the shale gas reservoir will form a three-dimensional crack network, which can greatly improve the crack density and subsequent fracturing efficiency, thereby improving the shale gas production.

[0077] Specifically, the microwave-nitrogen combined step is: the ground control console remotely controls the slitting device, the built-in magnetron of the slitting device generates microwaves, the microwaves are transmitted to the microwave emitter through the waveguide, the slitting device irradiates microwaves to heat the shale, the initial cracks are deteriorated for 3-8 minutes, then the slitting device is pulled back 0.5-2 meters to the previous initial slit, at this time, the valve is opened and the telescopic rod is ejected, a high-temperature high-pressure liquid nitrogen jet is emitted to impact the high-temperature initial crack to form a secondary crack, further extend the fracture, at the same time, the microwave irradiates the next initial slit, and the cycle is repeated, after all the initial cracks and secondary cracks are fully developed, the liquid nitrogen valve and the magnetron are closed, the telescopic rod is retracted, the microwave-nitrogen combination stops, and finally the slitting device is withdrawn by using the cable, so that the shale gas reservoir is successfully induced to form a ring-shaped three-dimensional slit network with a spacing of 0.5-2 meters and a radius of 3-4 meters.

[0078] In the embodiment of the present application, the control of the slitting device to perform the second slitting action includes: controlling the built-in magnetron of the slitting device to generate microwaves, and transmitting the microwaves to the microwave emitter through the waveguide, and emitting the microwaves by the microwave emitter.

[0079] It can be understood that the built-in magnetron of the slitting device can be controlled to generate microwaves, and the microwaves can be transmitted to the microwave emitter through the waveguide, and the microwaves can be emitted by the microwave emitter, the microwave irradiation can be used to deteriorate, the efficiency can be improved, the temperature gradient can be increased, the thermal stress can be increased, and thus new secondary cracks can be generated on the basis of the initial slits, the secondary cracks will be connected to each other, the three-dimensional slit network of the shale gas reservoir can be induced, the fracture density and the subsequent fracturing efficiency can be greatly improved, and thus the shale gas production can be improved.

[0080] In step S104, the first slitting action and the second slitting action are repeatedly performed according to the slitting position to control the slitting device until the three-dimensional slit network is formed in the shale gas reservoir.

[0081] The three-dimensional slit network refers to the fracture network connected to each other after the secondary cracks are fully developed.

[0082] It can be understood that the first slitting action and the second slitting action can be repeatedly performed according to the slitting position to control the slitting device until the three-dimensional slit network connected to each other is generated in the shale gas reservoir, the three-dimensional slit network of the shale gas reservoir can be induced, the fracture density and the subsequent fracturing efficiency can be greatly improved, and thus the shale gas production can be improved.

[0083] The method for forming a three-dimensional fracture network of a shale gas reservoir by using liquid nitrogen and microwaves according to the embodiment of the present application utilizes the thermal coupling of microwaves and liquid nitrogen on rocks to generate new secondary fractures on the basis of original fractures, and on the basis of reasonable planning of fracture spacing, each secondary fracture is connected to each other, thereby inducing the shale gas reservoir to form a three-dimensional fracture network, while reducing reservoir pollution, greatly improving the fracture efficiency and subsequent fracturing efficiency, and further improving the shale gas production.

[0084] The method and device for forming a three-dimensional fracture network of a shale gas reservoir by using liquid nitrogen and microwaves will be described in detail below. Figures 1-13 The method and device for forming a three-dimensional fracture network of a shale gas reservoir by using liquid nitrogen and microwaves will be described in detail below.

[0085] Step 1, equipment erection step:

[0086] The equipment such as the control console 4, the liquid nitrogen tank 1, and the power supply 3 is erected near the hydraulic fracturing wellhead of the shale gas reservoir 10 which has penetrated the overburden 6, the cable 5 which comprises a copper cable 11 wrapped by crosslinked polyethylene (XLPE) and a liquid nitrogen delivery pipe 12 made of high-density polyethylene (HDPE) is used to connect the fracturing device 9 with the control console 4, the power supply 3, and the liquid nitrogen tank 1, then the equipment is debugged before construction to ensure the safety and reliability of the equipment, and then the fracturing device 9 is lowered into the shale gas reservoir 10 through the cable 5 and pushed forward to the end of the section to be fractured.

[0087] Step 2, liquid nitrogen jet step:

[0088] The valve 2 is opened, the telescopic rod 96 is ejected by the ground control console 4, and the built-in pump 93 and motor 94 are used, the fracturing device 9 emits a high-pressure liquid nitrogen rotating jet 7, a radial initial fracture 13 is formed at the starting end of the section to be fractured in the shale gas reservoir 10, then the fracturing device 9 is pushed forward by 0.5-2 meters according to the specific working conditions, the fracturing process is continued and the fracturing device 9 is pushed forward in a cycle, until an initial fracture array with a spacing of 0.5-2 meters is formed in the entire section to be fractured (as shown in Figure 8 ).

[0089] Step 3, microwave-liquid nitrogen coordination step:

[0090] The valve 2 is closed and the telescopic rod 96 is retracted, the liquid nitrogen jet 7 is temporarily stopped, the fracturing device 9 is pushed to the initial fracture 13 at the end of the section to be fractured, the built-in magnetron 91 of the fracturing device 9 generates microwaves which are transmitted to the microwave emitter 95 through the waveguide 92 by remote control of the ground control console 4, so that the fracturing device 9 irradiates microwaves to heat the shale and degrade the initial fracture 9 for 3-8 minutes (as shown in Figure 9As shown), then the slotted device 9 is pulled back 0.5-2 meters to the previous initial slit, at this time the valve 2 is opened and the telescopic rod 96 is ejected, the low-temperature high-pressure liquid nitrogen jet 7 is launched to impact the slit after microwave radiation, forming a secondary slit, further expanding the extended fracture, while the next initial slit is radiated by microwave (as shown) Figure 11 As shown), and the cycle is repeated (as shown) Figure 12 As shown), and the cycle is repeated (as shown) Figure 10 、 13 As shown).

[0091] It should be noted that the cable 5 includes: a cross-linked polyethylene (XLPE) wrapped copper cable 11, a high-density polyethylene (HDPE) material liquid nitrogen delivery pipe 12, a cold insulation layer 5 made of nitrile rubber and diene foam (LT+LTD), and secondary protection is provided at the connection.

[0092] The slotted device 9 includes: a magnetron 91, a waveguide 92, a cable 11, a liquid nitrogen delivery pipe 12, a pump 93, a motor 94, a microwave emitter 95, a telescopic rod 96, a jet nozzle 97, and other electrical equipment, which can radiate microwaves and rotate the telescopic emitter to emit a high-pressure liquid nitrogen jet of 50MPa or more. The overall device can withstand a pressure of 100MPa and can withstand the low-temperature environment of liquid nitrogen.

[0093] The microwave emitter 95 contains a circulator 951 and a microwave feed 952, and is arranged in a ring along the surface of the slotted device, which can uniformly and fully radiate the entire shale gas reservoir surface to form a ring-shaped initial slit.

[0094] In summary, the present application utilizes the thermal coupling effect of microwave and liquid nitrogen on rock to produce new secondary slits on the basis of the original cracks, and on the basis of reasonable planning of the slotted distance, each secondary slit will be connected to each other, thereby inducing the shale gas reservoir to form a three-dimensional fracture network. This reduces the pollution of the reservoir while greatly improving the slotted efficiency and subsequent fracturing efficiency, thereby improving the shale gas production.

[0095] In the description of the application, reference to "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that a particular feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. The illustrative appearances of the above-mentioned terms in various places in the specification are not necessarily referred to the same embodiment or example. Moreover, specific features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. Furthermore, in non-contradictory cases, those skilled in the art can combine and combine the features of different embodiments or examples described in the specification and the features of different embodiments or examples.

[0096] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the application, the meaning of "N" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0097] Any process or method descriptions or descriptions of the flow diagrams in the specification can be understood as representing code modules, segments or portions of code which include one or more executable instructions for implementing the specified logic function or process. It should also be understood that the preferred embodiments of the application include the combination of hardware and software configured to effect the functions described in the specification and illustrated in the drawings.

[0098] It should be understood that parts of the application can be implemented in hardware, software, firmware or a combination thereof. In the above-described embodiments, N steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. As in another embodiment, if implemented in hardware, any of the following technologies known in the art can be used in combination: discrete logic circuit with logic gate circuit for implementing logic functions on data signals, application specific integrated circuit with suitable combination logic gate circuit, programmable gate array (PGA), field programmable gate array (FPGA) and the like.

[0099] Those skilled in the art of the present technology can understand that all or part of the steps carried out by the above-mentioned embodiment method can be completed by program instructions to the relevant hardware. The program can be stored in a computer readable storage medium, and the program includes one or a combination of steps of the method embodiments when executed.

Claims

1. A device for forming a three-dimensional fracture network in a shale gas reservoir using liquid nitrogen and microwaves, the device comprising: a microwave generator; a liquid nitrogen source; a microwave applicator; and a shale gas reservoir. The application relates to a device for forming a three-dimensional fracture network in a shale gas reservoir by using liquid nitrogen and microwaves, which comprises the following parts: a liquid nitrogen tank storing liquid nitrogen; a slotted device connected with the liquid nitrogen tank, wherein the slotted device is lowered into the shale gas reservoir, the slotted device comprises a microwave emitter and a jet nozzle, liquid nitrogen stored in the liquid nitrogen tank is sprayed by the jet nozzle to form a slot at the end of the slotted device, and the microwave emitter is used to emit microwaves to expand and extend the slot; a control console connected with the slotted device, which is used to control the jet nozzle and the microwave emitter of the slotted device to act repeatedly to form a three-dimensional fracture network in the shale gas reservoir, wherein the slotted device further comprises a magnetron, a waveguide, a cable, a liquid nitrogen delivery pipe, a pump, a motor and an extension rod, one end of the magnetron is connected with the cable, the other end of the magnetron is connected with the waveguide, the other end of the waveguide is connected with the microwave emitter, the microwave emitter is arranged in a ring shape along the surface of the slotted device, the other end of the cable is connected with the control console and a power supply, one end of the liquid nitrogen delivery pipe is connected with a valve of the liquid nitrogen tank, the other end of the liquid nitrogen delivery pipe is connected with the pump, one end of the pump is connected with the motor, the other end of the motor is connected with the extension rod, and the extension rod is uniformly provided with the jet nozzles.

2. The device according to claim 1, wherein, The microwave emitter comprises a circulator and a microwave feed.

3. The device according to claim 1, wherein, The application further comprises: a cable, wherein the cable is internally provided with the cable, the liquid nitrogen delivery pipe and a cold insulation layer.

4. A method for forming a three-dimensional fracture network in a shale gas reservoir by using liquid nitrogen and microwaves, characterized in that, The method is applied to the device for forming a three-dimensional fracture network in a shale gas reservoir by using liquid nitrogen and microwaves, and the method comprises the following steps: acquiring a current position of the slotted device; if the current position is at a starting end of a shale gas reservoir to be slotted, a first slotting action is controlled to be performed on the slotted device, a preset time interval is set, and whether the current slot meets a preset condition is detected, if the preset condition is met, the first slotting action is stopped, and the slotted device is continuously and cyclically pushed forward by a preset pushing distance until a slot array is formed in the shale gas reservoir to be slotted; if the current position reaches an ending end of the shale gas reservoir to be slotted, a second slotting action is controlled to be performed on the slotted device, a preset time interval is set, and the slotted device is continuously and cyclically retreated by a preset pushing distance until the starting end of the shale gas reservoir to be slotted; the first slotting action and the second slotting action are repeatedly performed on the slotted device according to a slot position until a three-dimensional fracture network is formed in the shale gas reservoir to be slotted, wherein the first slotting action comprises the following steps: controlling a control valve of the liquid nitrogen tank to be opened, controlling the extension rod of the slotted device to be popped out and controlling high-pressure liquid nitrogen rotating jet flow to be emitted, and the second slotting action comprises the following steps: controlling the magnetron built in the slotted device to generate microwaves, controlling the microwaves to be transmitted to the microwave emitter through the waveguide and controlling the microwave emitter to emit microwaves.

5. The method of claim 4, wherein the method further comprises the step of: The continuously and cyclically pushing the slotted device by the preset pushing distance until the slot array is formed in the shale gas reservoir to be slotted comprises the following steps: identifying a preset pushing distance corresponding to each slotting under a current working condition; controlling the slotted device to be pushed forward according to the preset pushing distance, and controlling the slotted device to perform the first slotting action when the preset pushing distance is reached.

6. The method of claim 5, wherein the method further comprises the step of: Before the forward pushing of the slitter according to the preset pushing distance, comprising: controlling the control valve of the liquid nitrogen tank to be closed, the telescopic rod of the slitter to be retracted, and the high-pressure liquid nitrogen rotating jet to be paused.

7. The method of claim 4, wherein the method further comprises the step of: Before the current position of the slitter is acquired, comprising: ​ connecting the slitter with the control console, the power supply and the liquid nitrogen tank by a cable; lowering the slitter into the shale gas reservoir by the cable and pushing it forward to the starting end of the section to be slitted.

8. The method of claim 4-7, wherein the method further comprises, The three-dimensional network of cracks refers to the network of cracks connected with each other formed by the interlacing of each secondary crack after full development.

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