Deep coal hydraulic breaking physical fluidization mining method

Abstract

The invention discloses a deep coal hydraulic breaking physical fluidization mining method. A vertical main shaft and an opposite horizontal well are arranged; the high-pressure water pump is connected with the sand tank and the water tank, the console and the high-pressure water pump are connected, the console and the ultrahigh-pressure water injector are connected, and the ultrahigh-pressure water injector is connected with the oscillating abrasive water jet drilling and slotting integrated tool to form drilling and slotting operation equipment; drilling an opposite fishbone well network; the oscillating jet flow spray head is combined with the slotting unit to perform slotting and cave forming operation; coal around the fishbone well is continuously mined in a fluidized form; fracture expansion is induced, and a high-quality complex fracture network is formed in the target coal seam; the extraction operation of desorption gas of the coal seam is completed by utilizing the mutually communicated complex fracture networks; injecting an oxidizing agent, igniting or detonating a methane-air mixture in the complex fracture network through electric shock ignition, and converting the coal into combustible gases such as hydrogen, methane and carbon monoxide in situ. By means of the method, fluidization mining operation of deep coal can be efficiently achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of unconventional natural gas mining, and specifically is a deep coal hydraulic fracturing physical fluidization mining method. Background Art

[0002] As the main component of energy resources, coal supports the development of my country's economy and society. However, with the continuous exploitation and utilization of coal by humans, the shallow coal resources of the earth have gradually become exhausted. The development of coal resources needs to continue to move to the deep earth, and kilometer-level mine mining will become the norm. From the perspective of my country's energy development strategy, coal will remain the main energy and basic energy of my country for a considerable period of time in the future, and nearly 70% of my country's coal resources are distributed at a depth of more than 2000m. Therefore, deep coal resource mining is imperative. However, according to the existing mining methods, the level of mining technology development, and the level of mine disaster awareness and prevention, the mining depth of coal resources cannot be extended infinitely to the deep. The traditional mining methods and the current technical level are no longer sufficient to support the mining process of deep coal resources. Based on this, Academician Xie Heping proposed in 2012 that the future development of deep coal should realize the mining technology idea of ​​ecological mines with "no coal out of the ground, no people underground, underground ore dressing, combustion power generation and underground gasification integration". The academic concept of fluidized mining of deep coal resources was first proposed in 2014, and a preliminary technical framework for deep in-situ fluidized mining of coal was formed.

[0003] Among them, physical crushing fluidized mining technology refers to the use of deep high stress, through drilling and water jet rock breaking, inducing deep coal body protrusion to form mixed fluid materials such as particle flow, gas, and liquid, forming a particle size that meets the pipeline transmission, and then achieving the purpose of pipeline negative pressure fluidization to the surface, so as to carry out ground extraction operations. However, a large number of studies have shown that most coal seams in China are low-permeability coal seams, and usually the number of pores and cracks inside these coal seams is limited. With the increase in the depth of coal seam mining, the ground stress continues to rise, the permeability of the coal seam is further reduced, and the difficulty of coalbed methane extraction increases accordingly. Therefore, the permeability enhancement technology of low-permeability coal seams has become one of the keys to coalbed methane extraction research. In recent years, ultra-high pressure hydraulic cutting and decompression and permeability enhancement technology has developed rapidly. This technology uses high-pressure water flow to cut and flush rocks, and by changing the stress distribution of rocks around the borehole, the cracks are enlarged, and finally the rock pressure relief and permeability enhancement are achieved. However, this technology has problems such as unsatisfactory hole expansion effect, low hole protection efficiency, and small improvement in the permeability of the explosion layer gas. In order to effectively solve the above technical problems, it is urgent to provide a new type of deep coal hydraulic crushing physical fluidization mining method. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a physical fluidized mining method for deep coal hydraulic crushing. The method has a simple implementation process, and can conveniently and efficiently realize the fluidized mining operation of deep coal. At the same time, it can effectively improve the hole expansion efficiency and significantly improve the permeability of the coal seam. It can effectively solve the problem of fluidized mining inducing coal body outburst and can greatly and significantly improve the extraction efficiency of coalbed methane.

[0005] In order to achieve the above object, the present invention provides a deep coal hydraulic fracturing physical fluidization mining method, which specifically comprises the following steps:

[0006] Step 1: Preparation;

[0007] Analyze the structure and density of the coal seam according to the geological parameters and exploration data of the underground coal seam, and determine the well layout section of the coal seam and the drilling position of the fishbone well according to the logging data, and design specific construction parameters;

[0008] Step 2: Arrangement of the vertical main wellbore and the opposite horizontal well;

[0009] Arranging a well pattern body in the coal seam, wherein the well pattern body is composed of two groups of composite well bodies distributed on both sides of the coal seam, wherein a plurality of composite well bodies in each group of composite well bodies are sequentially spaced and distributed along the length direction of the coal seam, and a plurality of composite well bodies in the two groups of composite well bodies are staggered and distributed in an intersecting manner along the length direction of the coal seam;

[0010] Each composite well body is composed of a vertical well and a double-layer horizontal well connected to the lower part of the vertical well. The double-layer horizontal wells are located in different coal seams and are aligned vertically. At the same time, they form opposing wells with adjacent horizontal wells in the same coal seam. At the same time, the four vertical wells in four adjacent composite well bodies form a parallelogram layout, and along the length direction of the coal seam, the double-layer horizontal wells in multiple composite well bodies are aligned horizontally.

[0011] Step 3: Arrange ground drilling and cutting equipment;

[0012] S31: Arranging ground equipment and a control platform on the ground, wherein the ground equipment and the control platform include a sand tank, a water tank, a high-pressure water pump, a control console and a drilling rig frame;

[0013] S32: connecting the liquid inlet end of the high-pressure water pump to the outlet end of the sand tank and the outlet end of the water tank through pipelines, establishing a connection between the inlet end of the control panel and the liquid outlet end of the high-pressure water pump by using a section of ultra-high pressure hose, establishing a connection between the outlet end of the control panel and the liquid inlet end of the ultra-high pressure water injector by using another section of ultra-high pressure hose, and then connecting the ultra-high pressure water injector to the oscillating abrasive water jet drilling and slitting integrated tool to form a drilling and slitting operation equipment;

[0014] Among them, the oscillating abrasive water jet drilling and slitting integrated tool includes a drill rod, an oscillating jet nozzle combined slitting tool, a drilling rig and a drill bit; the interior of the drill rod is a hollow structure and is provided with a guide tube, the head end of the drill rod is fixedly connected to the water outlet end of the ultra-high pressure water injector, and the inlet end of the guide tube is connected to the liquid inlet end of the ultra-high pressure water injector; the oscillating jet nozzle combined slitting tool includes a guide tube interface and a plurality of oscillating jet nozzles, the guide tube interface is fixedly installed at the end of the drill rod, and its inner cavity is connected to the liquid outlet end of the guide tube; three oscillating jet nozzles are fixedly installed on the outer wall of the guide tube interface evenly in the circumferential direction, and are connected through a reserved connecting passage. The channel is connected with the inner cavity of the guide pipe interface; the centers of the two ends of the oscillating jet nozzle in the length direction have relatively distributed nozzle inlets and nozzle outlets, and at the same time, the inner center area of ​​the oscillating jet nozzle is provided with an oscillation cavity connecting the nozzle inlet and the nozzle outlet, and at the same time, the interior of the oscillating jet nozzle is symmetrically provided with two feedback channels on both sides of the oscillation cavity, and the feedback channels are bent channels, and the two ends thereof are respectively connected with the head and tail ends of the oscillation cavity; the cross section of the inner cavity of the nozzle outlet is in the shape of a fan of 120°, and the small end is connected with the oscillation cavity, and the large end is located on the outside; the drilling rig is installed at the end of the drill rod; the drill bit is installed at the output end of the drilling rig;

[0015] S33: Establishing a connection between the drilling rig frame and the drill rod 9;

[0016] Step 4: Drilling opposite fishbone wells;

[0017] S41: lowering the oscillating jet drilling and slotting integrated tool into the horizontal well of the coal seam, and controlling the operation of the drilling rig through the console, using the drilling rig to drive the drill bit to rotate at high speed for drilling operations, and drilling multiple horizontal branch wells in sequence at different positions along the length direction of the horizontal well, while ensuring that the multiple horizontal branch wells and the axis of the horizontal well are located in the same plane, and that the horizontal well and the multiple horizontal branch wells are distributed in a fishbone shape as a whole, thereby forming a fishbone well; in this process, multiple horizontal branch wells of different fishbone wells in the same coal seam are arranged in a staggered layout, forming a staggered opposite fishbone well network in the same coal seam;

[0018] S42: After the drilling of the herringbone well is completed, the oscillating jet drilling and slotting integrated tool is first withdrawn from the wellbore, and then the branch horizontal well is washed and desludged, followed by pumping operations to ensure that there is no water accumulation in the herringbone well;

[0019] Step 5: Water jet rock breaking and cutting operation;

[0020] S51: once again, the oscillating jet drilling and slotting integrated tool is moved deep into the set slotting position in the horizontal branch well;

[0021] S52: Start the slotting and cavitation function to perform high-pressure swing abrasive water jet slotting operations; start the high-pressure water pump through the control console, and synchronously provide negative pressure to the water tank and the sand tank, so that the water in the water tank and the sand in the sand tank enter the high-pressure water pump in proportion and mix to form a sand-containing water flow, and then supply the oscillating jet nozzle combined slotting tool through the ultra-high pressure water injector and the guide pipe in the drill pipe, and the three oscillating jet nozzles oscillate the jets to form an annular high-pressure jet surrounding the wellbore, and use the high-pressure jet to penetrate and cut the surrounding rock in the horizontal branch well, and then form an annular slot in the fishbone well;

[0022] Step 6: fluidization extraction of coal particles;

[0023] The rock breaking and cutting operation is used to induce coal body protrusion to form a mixed fluid material that meets the particle size of pipeline transmission. At the same time, the fluidized transportation effect generated by the negative pressure of the pipeline is used to continuously mine the coal around the fishbone well in a fluidized form; at the same time, several interlaced and connected seams are used to promote the formation of goafs;

[0024] Step 7: Induce crack expansion in goaf area;

[0025] By utilizing the induction effect of the seams and goaf, cracks are formed in the coal seams around the fishbone wells to release the stress of the coal seams. During the stress release process of the coal seams, the cracks are further induced to expand, so that the cracks around the staggered fishbone wells communicate with each other, thereby forming a high-quality complex crack network in the target coal seam.

[0026] Step 8: Use coal seam fissures to extract coal seam gas;

[0027] The complex fracture network constructed is used to improve the permeability of the coal seam and the desorption efficiency of the coal seam gas. At the same time, the complex fracture network that communicates with each other is used to complete the extraction of the desorbed gas from the coal seam;

[0028] Step 9: Remaining coal gasification operation;

[0029] S91: After the extraction operation is completed, the gasification pipe string is lowered to the end of the horizontal well and an oxidant is injected to ignite or detonate the methane-air mixture in the complex fracture network by electric shock ignition. The high temperature conditions generated by the combustion and explosion process are used to evaporate the residual water in the coal seam to form water vapor, and the coal and water vapor are prompted to continue to react chemically to produce hydrogen and carbon monoxide, which further promotes the hydrogen, carbon monoxide and coal to continue to react chemically to produce methane;

[0030] S92: Recover the gasification string upward to complete the gasification operation of all horizontal well sections.

[0031] Preferably, in step one, the construction parameters include well layout orientation, drilling depth, slit position and slit spacing.

[0032] Furthermore, in order to provide a reliable power supply to the drilling rig and to facilitate real-time monitoring of the operating status of the drilling rig, in step three S32, the power supply cable and signal cable connected to the drilling rig are extended to the position of the console through the annular cavity inside the drill pipe and connected to the console.

[0033] Furthermore, in order to further improve the efficiency of the water jet rock breaking and cutting operation and to form a more ideal annular groove, in step three S32, the cross-section of the inner cavity of the nozzle inlet is an isosceles trapezoid, with the large diameter end located on the outside and the small diameter end connected to the oscillation cavity.

[0034] Preferably, in step six, the mixed fluid substance includes granular fluid, gas and liquid.

[0035] Furthermore, in order to enable the drill rod to meet the ultra-high pressure requirements, in step three S32, the drill rod is an ultra-high pressure sealed drill rod.

[0036] The present invention proposes a deep coal hydraulic fracturing physical fluidization mining method, which aims to realize the pressure relief and permeability enhancement and physical fluidization mining operations of low-permeability deep coal seams. First, multiple composite well bodies are arranged in an interlaced manner in the length direction of the coal seam, and the upper and lower horizontal wells in the adjacent composite well bodies are formed into opposite wells. On this basis, a network of opposite fishbone wells is directionally drilled in the same coal seam, which can ensure that the constructed opposite fishbone well network can effectively cover the coal seam area to be mined, and at the same time, ensure that the constructed fluidized mining network basic framework can provide reliable guarantees for the full and comprehensive mining of the coal seam to be mined. Secondly, an oscillating abrasive water jet drilling and slitting integrated tool with a drilling rig and an oscillating jet nozzle combined slitting tool is selected as a drilling and slitting operation equipment. On the one hand, the drilling rig can be used to drive the drill bit to conveniently and efficiently perform the drilling operation of the fishbone well. On the other hand, the oscillating jet nozzle combined slitting tool can also be used to perform convenient and efficient jet rock breaking and slitting operations, realizing the multi-purpose use of the same operation tool, effectively reducing the operation process, and significantly improving the operation efficiency. When performing jet rock breaking and cutting operations, a high-pressure water pump is used to synchronously absorb the sand in the sand tank and the water in the water tank. The sand can be entrained by the high-pressure water flow to form a sand-containing water flow, which is then supplied to the oscillating jet nozzle combined cutting tool. In this way, the surrounding rock can be cut using conventional abrasive water jet cutting technology. In particular, the present invention has a special structural design for the oscillating jet nozzle combined slitting tool (oscillating jet nozzle and its internal structure), so that the interior of the oscillating jet nozzle is provided with an oscillation cavity, and dual feedback channels are provided on both sides of the oscillation cavity, so that a self-excited oscillation structure can be formed, and then the abrasive water jet can be induced to perform continuous sweeping motion during the jetting process. After a large number of tests, the deflection angle of the outlet jet of a single oscillating jet nozzle can reach about 120°. Specifically, for each oscillating jet nozzle, when the jet flows into the nozzle inlet, the main jet will become unstable when entering the oscillation cavity with a larger space, and it will deflect to both sides of the oscillation cavity. Due to the "Coanda effect", the main jet will stick to the side wall after being unstable, and flow along the wall surface, so as to flow out from the nozzle outlet. Part of the jet will enter the feedback channels on both sides, and then flow back to the inlet throat of the nozzle inlet, so that the main jet can be induced to deflect to the other side, and the cycle will be repeated to form a sweeping oscillating jet at the nozzle outlet. On this basis, the oscillating jet nozzle combined cutting tool formed by the combination of three oscillating jet nozzles can realize the annular cutting operation along the side wall of the main borehole; compared with the conventional hydraulic cutting technology, it can complete the expansion of multi-layer radial annular slots and the physical crushing process of the coal seam, effectively promoting the communication of each layer of cracks and forming a higher quality complex network of cracks; at the same time, it can induce the coal body to protrude through the cutting operation to form a mixed fluid material with a particle size that meets the pipeline transmission requirements, thereby enabling fluidized pipeline transportation of coal seam particles, and promoting the formation of a three-dimensional cutting goaf through a number of interlaced slots.The formation of three-dimensional slotted goaf can effectively induce the generation of tensile shear fractures, thereby significantly improving the efficiency of coalbed methane extraction and building a fluidized mining network for particle flow, gas, solid and other materials in deep low-permeability coal seams. With the further expansion of induced fractures, the permeability of coal seams can be significantly improved, which is conducive to the efficient extraction of coalbed methane. Through the chemical reaction of water vapor and coal in the fishbone well and fracture network under high temperature environment, the coal is converted into combustible gases such as hydrogen, methane and carbon monoxide in situ, achieving the purpose of in-situ fluidized mining, and at the same time, effectively improving the efficiency of fluidized mining and conversion.

[0037] The present invention adopts a technical method that combines water jet rock breaking and cutting in low-permeability coal seams with physical fluidized mining. The implementation process is simple, and it can effectively improve the hole expansion efficiency while ensuring the hole expansion effect. The three-dimensional cutting holes and grooves formed produce a pressure relief effect in the axial direction and induce the formation of cracks, thereby significantly improving the permeability of the coal seam, solving the problem of fluidized mining inducing coal body outburst, and effectively improving the coalbed methane extraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a distribution diagram of the vertical main wellbore and the opposite horizontal well in the present invention;

[0039] Figure 2 It is a distribution diagram of the opposite fishbone wells in the present invention;

[0040] Figure 3 It is a schematic diagram of the assembly of the ground equipment, control platform and drilling and slitting operation tool in the present invention;

[0041] Figure 4 It is a schematic diagram of the structure of the oscillating jet nozzle combined slitting tool of the present invention;

[0042] Figure 5 It is a schematic diagram of the three-dimensional structure of the oscillating jet nozzle in the present invention;

[0043] Figure 6 is a cross-sectional view of an oscillating jet nozzle in the present invention;

[0044] Figure 7 The principle of the oscillating jet swing in the present invention is Figure 1 ;

[0045] Figure 8 The principle of the oscillating jet swing in the present invention is Figure 2 ;

[0046] Fig. 9 It is a schematic diagram of the extraction state of broken coal and rock in the goaf area of ​​the present invention;

[0047] Fig.10 Schematic diagram of the present invention using coal seam fissures to extract coal seam gas;

[0048] Fig.11 It is a schematic diagram of coal gasification operation in the present invention.

[0049] In the figure: 1, coal seam, 2, vertical well, 3, horizontal well, 4, fishbone well, 5, oscillating abrasive water jet drilling and slitting integrated tool, 6, drill bit, 7, drilling rig, 8, oscillating jet nozzle combined slitting tool, 9, drill pipe, 10, guide tube, 11, high-pressure water pump, 12, water tank, 13, sand pot, 14, control console, 15, ultra-high pressure hose, 16, ultra-high pressure water injector, 17, oscillating jet nozzle, 18, guide tube interface, 19, oscillation cavity, 20, nozzle outlet, 21, nozzle inlet, 22, feedback channel, 23, mixed fluid material, 24, goaf, 25, slot, 26, coal seam desorption gas, 27, fracture, 28 gasification pipe column, 29, oxidant, 30, horizontal branch well, 31, composite well body. DETAILED DESCRIPTION

[0050] The present invention proposes a physical fluidization mining method for deep coal hydraulic fracturing, which uses a directional drilling method to drill opposite fishbone wells, and completes the physical crushing of the target coal seam by combining the low-permeability coal seam water jet rock breaking and cutting with physical fluidization mining technology, thereby forming a particle size that meets the pipeline transmission requirements, and realizing fluidized pipeline transportation of coal body particles; at the same time, through the formation of three-dimensional cutting goaf areas, it effectively induces the generation of shear fractures, further improves the coalbed methane extraction efficiency, and constructs a fluidization mining network for particle flow, gas, solid and other materials in deep low-permeability coal seams.

[0051] The following is a more detailed description of a deep coal physical crushing fluidized mining method of the present invention in conjunction with the accompanying drawings and specific embodiments. The following embodiments only describe the general process of implementing this method in a coal mine, and are not targeted at a specific mine. Therefore, the various parameters described below are only qualitatively described and are not intended to limit the present invention.

[0052] like Figures 1 to 11 As shown, the deep coal hydraulic fracturing physical fluidization mining method provided by the present invention specifically includes the following steps:

[0053] Step 1: Preparation;

[0054] Analyze the structure and density of the coal seam 1 according to the geological parameters and exploration data of the underground coal seam 1, and determine the well layout layer section of the coal seam 1 and the drilling position of the fishbone well 4 according to the well logging data, and at the same time, design specific construction parameters;

[0055] Step 2: Arrangement of the vertical main wellbore and the opposite horizontal well;

[0056] A well pattern body is arranged in the coal seam 1, wherein the well pattern body is composed of two groups of composite well bodies 31 distributed on both sides of the coal seam 1, wherein a plurality of composite well bodies 31 in each group of composite well bodies 31 are sequentially spaced along the length direction of the coal seam 1, and a plurality of composite well bodies 31 in the two groups of composite well bodies 31 are staggeredly distributed along the length direction of the coal seam 1 in an intersecting manner; Figure 1 The schematic diagram of the layout of the main well pattern is shown in FIG.

[0057] Each composite well body 31 is composed of a vertical well 2 and a double-layer horizontal well 3 connected to the lower part of the vertical well 2. The double-layer horizontal wells 3 are respectively located in different coal seams 1 and are aligned with each other up and down. At the same time, they form opposing wells with adjacent horizontal wells 3 in the same coal seam 1. At the same time, the four vertical wells 2 in four adjacent composite well bodies 31 form a parallelogram layout, and along the length direction of the coal seam 1, the double-layer horizontal wells 3 in multiple composite well bodies 31 are aligned in the horizontal direction.

[0058] Step 3: Arrange ground drilling and cutting equipment;

[0059] S31: Arrange ground equipment and control platform on the ground, such as Figure 3 As shown, the ground equipment and control platform include a sand tank 13, a water tank 12, a high-pressure water pump 11, a control console 14 and a drilling rig frame;

[0060] S32: The liquid inlet end of the high-pressure water pump 11 is connected to the outlet end of the sand tank 13 and the outlet end of the water tank 12 through pipelines, and a section of ultra-high pressure hose 15 is used to establish a connection between the inlet end of the control panel 14 and the liquid outlet end of the high-pressure water pump 11, and another section of ultra-high pressure hose 15 is used to establish a connection between the outlet end of the control panel 14 and the liquid inlet end of the ultra-high pressure water injector 16, and then the ultra-high pressure water injector 16 is connected to the oscillating abrasive water jet drilling and slitting integrated tool 5 to form a drilling and slitting operation equipment;

[0061] In order to enhance the connectivity of each layer of cracks and construct a higher quality network fracture structure, under the condition that the coal seam characteristics and pump pressure are determined, the oscillating jet nozzle combined slitting tool 8, the oscillating jet nozzle 17 and their internal structure are optimized as follows to ensure that they achieve the best performance: wherein, the oscillating abrasive water jet drilling and slitting integrated tool 5 includes a drill rod 9, an oscillating jet nozzle combined slitting tool 8, a drilling rig 7 and a drill bit 6, as shown in FIG. Figures 3 to 8As shown; the interior of the drill rod 9 is a hollow structure, and is provided with a guide tube 10, the head end of the drill rod 9 is fixedly connected to the water outlet end of the ultra-high pressure water injector 16, and the inlet end of the guide tube 10 is connected to the liquid inlet end of the ultra-high pressure water injector 16, and the ultra-high pressure water injector 16 can realize ultra-high pressure water supply to the guide tube 10; the oscillating jet nozzle combination slitting tool 8 includes a guide tube interface 18 and a plurality of oscillating jet nozzles 17, the guide tube interface 18 is fixedly installed at the end of the drill rod 9, and its inner cavity is connected to the liquid outlet end of the guide tube 10; three oscillating jet nozzles 17 are fixedly installed on the outer side wall of the guide tube interface 18 evenly in the circumferential direction, and are connected to the inner cavity of the guide tube interface 18 through a reserved connecting channel; the centers of the two ends of the oscillating jet nozzle 17 in the length direction have relatively distributed nozzle inlets 21 and nozzle outlets 20, and at the same time, the oscillating jet nozzle 17 An oscillation cavity 19 connecting the nozzle inlet 21 and the nozzle outlet 20 is arranged in the inner central area. Meanwhile, two feedback channels 22 are symmetrically arranged on both sides of the oscillation cavity 19 inside the oscillation jet nozzle 17. The feedback channel 22 is a curved channel, and its two ends are connected to the head and tail ends of the oscillation cavity 19 respectively; the cross section of the inner cavity of the nozzle outlet 20 is in the shape of a 120° fan, and the small end is connected to the oscillation cavity 19, and the large end is located on the outside, wherein the 120° fan-shaped extension surface of the nozzle outlet 20 is perpendicular to the axis of the wellbore in which it is located. As a further preference, the width of the small end of the nozzle outlet 20 is 1 mm, and the two ends of the large end extend 1 mm outward from the center of the small end; the drilling rig 7 is installed at the end of the drill pipe 9. As a preference, the drilling rig 7 and the drill pipe 9 are connected in a detachable installation manner; the drill bit 6 is installed at the output end of the drilling rig 7;

[0062] As a preferred embodiment, the guide pipe interface 18 is a hollow cylindrical tube with an outer diameter of 40 mm and an inner diameter of 30 mm, the upper end of which is open and fixedly connected to the lower end of the drill rod 9, and the lower end of which is closed by an end plate.

[0063] As a preferred embodiment, the oscillating jet nozzle 17 has a length of 22 mm, a width of 18 mm, and a thickness of 4 mm.

[0064] As a preferred embodiment, the oscillation cavity 19 is a flat cavity, the width of which is greater on the side close to the nozzle outlet 20 than on the side close to the nozzle inlet 21, and the maximum width of the oscillation cavity 19 is 8 mm and the minimum width is 4 mm;

[0065] As a preferred embodiment, the feedback channel 22 is a flat cavity in an L-shape, wherein the transverse section is a main section, the length of the main section is 11 mm, the width is 3 mm, and the longitudinal section is an auxiliary section;

[0066] S33: Establishing a connection between the drilling rig frame and the drill rod 9;

[0067] Step 4: Drilling opposite fishbone wells;

[0068] S41: Figure 2 As shown, the oscillating abrasive water jet drilling and slitting integrated tool 5 is lowered into the horizontal well 3 of the coal seam 1, and the operation of the drilling rig 7 is controlled by the console 14, and the drilling rig 7 is used to drive the drill bit 6 to rotate at high speed for drilling operations, and multiple horizontal branch wells 30 are drilled in sequence at different positions along the length direction of the horizontal well 3. At the same time, it is ensured that the multiple horizontal branch wells 30 and the axis of the horizontal well 3 are located in the same plane, and the horizontal well 3 and the multiple horizontal branch wells 30 are distributed in a fishbone shape as a whole, so as to form a fishbone well 4; in this process, the multiple horizontal branch wells 30 of different fishbone wells 4 in the same coal seam 1 are arranged in a staggered manner, forming a staggered opposite fishbone well network in the same coal seam 1;

[0069] S42: After the drilling of the herringbone well 4 is completed, the oscillating abrasive water jet drilling and slotting integrated tool 5 is first withdrawn from the wellbore, and then the branch horizontal well 3 is washed and deslagging is processed, and then a pumping operation is performed to ensure that there is no water accumulation in the herringbone well 4;

[0070] Step 5: Water jet rock breaking and cutting operation;

[0071] S51: once again, the oscillating abrasive water jet drilling and slotting integrated tool 5 is moved deep into the set slotting position in the horizontal branch well 30;

[0072] S52: Figure 3 The schematic diagram of rock breaking and slotting is shown in the figure. After the opposite fishbone well is drilled, the high-pressure swing abrasive water jet slotting operation is carried out;

[0073] Start the slotting and cavitation function; when the inlet and outlet ends of the high-pressure water pump 11 are respectively connected to the water inlet valve and the water outlet valve, first open the water inlet valve and the water outlet valve, and then start the high-pressure water pump 11 through the control console 14, and synchronously provide negative pressure to the water tank 12 and the sand tank 13, so that the water in the water tank 12 and the sand in the sand tank 13 enter the high-pressure water pump 11 in proportion and mix to form a sand-containing water flow. In this process, the sand in the sand tank 13 will be entrained by the high-pressure water flow and enter the ultra-high pressure water injector 16 together; then the oscillating jet nozzle combined slotting tool 8 is supplied through the ultra-high pressure water injector 16 and the guide tube 10 in the drill pipe 9, and the oscillating jet is swung through three oscillating jet nozzles 17 to form an annular high-pressure jet surrounding the wellbore, and the high-pressure jet is used in the horizontal branch well 30 to penetrate and cut the surrounding rock, thereby forming an annular slot 25 in the fishbone well 4;

[0074] The principle diagram of the oscillation jet swing is as follows: when the jet flows in from the nozzle inlet 21, the main jet will become unstable when entering the larger oscillation cavity 19, and then deflect to the two sides of the oscillation cavity 19. Due to the "Coanda effect", the main jet will stick to the side wall after being unstable, flow along the wall, and then flow out from the nozzle outlet 20. However, due to the flow limiting effect of the nozzle outlet 20, part of the jet enters the feedback channels 22 on both sides and flows back to the inlet throat. By stimulating the main jet, the main jet is induced to deflect to the other side, thereby pushing the main jet to the other feedback channel 22, and repeating the cycle. A sweeping oscillating jet is formed at the nozzle outlet 20, as shown in FIG. Figure 7 and Figure 8 As a preferred embodiment, the deflection angle of the jet can be effectively increased by adjusting the length of the feedback channel 18 inside the oscillating jet nozzle 17 and the size of the oscillating cavity 19. The oscillating jet nozzle combined slotting tool 8 composed of three oscillating jet nozzles 17 can realize an annular slot 25 along the main borehole.

[0075] Step 6: fluidization extraction of coal particles;

[0076] The rock breaking and cutting operation is used to induce the coal body to protrude and form a mixed fluid material 23 that meets the particle size of the pipeline transmission. At the same time, the fluidized transportation effect generated by the negative pressure of the pipeline is used to continuously mine the coal around the fishbone well 4 in a fluidized form; at the same time, a number of interlaced slots 25 are used to promote the formation of the goaf 24, such as Fig. 9 As shown;

[0077] Step 7: Induce crack expansion in goaf area;

[0078] By utilizing the induction effect of the seam slots 25 and the goaf 24, cracks 27 are formed in the coal seam around the herringbone wells 4. The cracks 27 are mainly tensile shear cracks, which release the stress of the coal seam. In the process of releasing the stress of the coal seam, the cracks 27 are further induced to expand, so that the cracks around the staggered herringbone wells 4 communicate with each other, thereby forming a high-quality complex crack network in the target coal seam 1, such as Fig.10 As shown;

[0079] Step 8: Use coal seam fissures to extract coal seam gas;

[0080] The complex fracture network constructed is used to improve the permeability of the coal seam and the desorption efficiency of the coal seam gas. At the same time, the complex fracture network that communicates with each other is used to complete the extraction operation of the coal seam desorption gas 26, such as Fig.10 As shown;

[0081] Step 9: Remaining coal gasification operation;

[0082] S91: Fig.11As shown, after the extraction operation is completed, the gasification pipe column 28 is lowered to the end of the horizontal well 3, and the oxidant 29 is injected to ignite or detonate the methane-air mixture in the complex fracture network by electric shock ignition. The high temperature conditions generated by the combustion and explosion process are used to evaporate the residual water in the coal seam 1 to form water vapor, and the coal and water vapor are prompted to continue to react chemically to produce hydrogen and carbon monoxide, and further promote the hydrogen, carbon monoxide, and coal to continue to react chemically to produce methane;

[0083] S92: Recover the gasification pipe string 28 upward to complete the gasification operation of all horizontal well sections 3.

[0084] As a preferred embodiment, in step one, the construction parameters include well layout orientation, drilling depth, slit position and slit spacing, etc.

[0085] In order to provide a reliable power supply to the drilling rig 7 and to facilitate real-time monitoring of the operating status of the drilling rig 7, in step three S32, the power supply cable and signal cable connected to the drilling rig 7 are extended to the position of the console 14 through the annular cavity inside the drill pipe 9 and are connected to the console 14.

[0086] In order to further improve the efficiency of water jet rock breaking and cutting operations and form a more ideal annular groove, such as Figures 6 to 8 As shown, in step 3 S32, the cross section of the inner cavity of the nozzle inlet 21 is an isosceles trapezoid, with the large diameter end located on the outside and the small diameter end connected to the oscillation cavity 19. As a preferred embodiment, the length of the inner cavity of the nozzle inlet 21 is 3 mm, the inner diameter of the small diameter end is 2 mm, and the inner diameter of the large diameter end is 4 mm;

[0087] As a preference, in step six, the mixed fluid substance 23 includes granular fluid, gas, liquid and the like.

[0088] In order to enable the drill rod 9 to meet the requirements of ultra-high pressure operation, in step three S32, the drill rod 9 is an ultra-high pressure sealed drill rod.

[0089] The present invention proposes a deep coal hydraulic fracturing physical fluidization mining method, which aims to realize the pressure relief and permeability enhancement and physical fluidization mining operations of low-permeability deep coal seams. First, multiple composite well bodies are arranged in an interlaced manner in the length direction of the coal seam, and the upper and lower horizontal wells in the adjacent composite well bodies are formed into opposite wells. On this basis, a network of opposite fishbone wells is directionally drilled in the same coal seam, which can ensure that the constructed opposite fishbone well network can effectively cover the coal seam area to be mined, and at the same time, ensure that the constructed fluidized mining network basic framework can provide reliable guarantees for the full and comprehensive mining of the coal seam to be mined. Secondly, an oscillating abrasive water jet drilling and slitting integrated unit with a drilling rig and an oscillating jet nozzle combined slitting tool is selected as the drilling and slitting operation equipment. On the one hand, the drilling rig can be used to drive the drill bit to conveniently and efficiently perform the drilling operation of the fishbone well. On the other hand, the oscillating jet nozzle combined slitting tool can also be used to perform convenient and efficient jet rock breaking and slitting operations, realizing the multi-purpose use of the same operation tool, effectively reducing the operation process, and significantly improving the operation efficiency. When performing jet rock breaking and cutting operations, a high-pressure water pump is used to synchronously absorb the sand in the sand tank and the water in the water tank. The sand can be entrained by the high-pressure water flow to form a sand-containing water flow, which is then supplied to the oscillating jet nozzle combined cutting tool. In this way, the surrounding rock can be cut using conventional abrasive water jet cutting technology. In particular, the present invention has a special structural design for the oscillating jet nozzle combined slitting tool (oscillating jet nozzle and its internal structure), so that the interior of the oscillating jet nozzle is provided with an oscillation cavity, and dual feedback channels are provided on both sides of the oscillation cavity, so that a self-excited oscillation structure can be formed, and then the abrasive water jet can be induced to perform continuous sweeping motion during the jetting process. After a large number of tests, the deflection angle of the outlet jet of a single oscillating jet nozzle can reach about 120°. Specifically, for each oscillating jet nozzle, when the jet flows into the nozzle inlet, the main jet will become unstable when entering the oscillation cavity with a larger space, and it will deflect to both sides of the oscillation cavity. Due to the "Coanda effect", the main jet will stick to the side wall after being unstable, and flow along the wall surface, so as to flow out from the nozzle outlet. Part of the jet will enter the feedback channels on both sides, and then flow back to the inlet throat of the nozzle inlet, so that the main jet can be induced to deflect to the other side, and the cycle will be repeated to form a sweeping oscillating jet at the nozzle outlet. On this basis, the oscillating jet nozzle combined cutting tool formed by the combination of three oscillating jet nozzles can realize the annular cutting operation along the side wall of the main borehole; compared with the conventional hydraulic cutting technology, it can complete the expansion of multi-layer radial annular slots and the physical crushing process of the coal seam, effectively promoting the communication of each layer of cracks and forming a higher quality complex network of cracks; at the same time, it can induce the coal body to protrude through the cutting operation to form a mixed fluid material with a particle size that meets the pipeline transmission requirements, thereby enabling fluidized pipeline transportation of coal seam particles, and promoting the formation of a three-dimensional cutting goaf through a number of interlaced slots.The formation of three-dimensional slotted goaf can effectively induce the generation of tensile shear fractures, thereby significantly improving the efficiency of coalbed methane extraction and building a fluidized mining network for particle flow, gas, solid and other materials in deep low-permeability coal seams. With the further expansion of induced fractures, the permeability of coal seams can be significantly improved, which is conducive to the efficient extraction of coalbed methane. Through the chemical reaction of water vapor and coal in the fishbone well and fracture network under high temperature environment, the coal is converted into combustible gases such as hydrogen, methane and carbon monoxide in situ, achieving the purpose of in-situ fluidized mining, and at the same time, effectively improving the efficiency of fluidized mining and conversion.

[0090] The present invention adopts a technical method that combines water jet rock breaking and cutting in low-permeability coal seams with physical fluidized mining. The implementation process is simple, and it can effectively improve the hole expansion efficiency while ensuring the hole expansion effect. The three-dimensional cutting holes and grooves formed produce a pressure relief effect in the axial direction and induce the formation of cracks, thereby significantly improving the permeability of the coal seam, solving the problem of fluidized mining inducing coal body outburst, and effectively improving the coalbed methane extraction efficiency.

Claims

1. A deep coal hydraulic crushing physical fluidization mining method, characterized in that: The specific steps include: Step 1: Preparation; Analyze the structure and density of the coal seam (1) according to the geological parameters and exploration data of the underground coal seam (1), determine the well layout section of the coal seam (1) and the drilling position of the fishbone well (4) according to the well logging data, and design specific construction parameters; Step 2: Arrangement of the vertical main wellbore and the opposite horizontal well; A well pattern main body is arranged in the coal seam (1), wherein the well pattern main body is composed of two groups of composite well bodies (31) distributed on both sides of the coal seam (1), wherein a plurality of composite well bodies (31) in each group of composite well bodies (31) are sequentially spaced along the length direction of the coal seam (1), and a plurality of composite well bodies (31) in the two groups of composite well bodies (31) are staggeredly distributed in an intersecting manner along the length direction of the coal seam (1); Each composite well body (31) is composed of a vertical well (2) and a double-layer horizontal well (3) connected to the lower part of the vertical well (2); the double-layer horizontal wells (3) are respectively located in different coal seams (1) and are aligned vertically, and at the same time, form a facing well with the adjacent horizontal well (3) in the same coal seam (1); at the same time, the four vertical wells (2) in four adjacent composite well bodies (31) form a parallelogram layout, and along the length direction of the coal seam (1), the double-layer horizontal wells (3) in multiple composite well bodies (31) are all aligned horizontally; Step 3: Arrange ground drilling and cutting equipment; S31: Arranging ground equipment and a control platform on the ground, wherein the ground equipment and the control platform include a sand tank (13), a water tank (12), a high-pressure water pump (11), a control console (14) and a drilling rig frame; S32: connecting the liquid inlet end of the high-pressure water pump (11) to the outlet end of the sand tank (13) and the outlet end of the water tank (12) through pipelines, establishing a connection between the inlet end of the control panel (14) and the liquid outlet end of the high-pressure water pump (11) by using a section of ultra-high pressure hose (15), establishing a connection between the outlet end of the control panel (14) and the liquid inlet end of the ultra-high pressure water injector (16) by using another section of ultra-high pressure hose (15), and then connecting the ultra-high pressure water injector (16) to the oscillating abrasive water jet drilling and slitting integrated tool (5) to form a drilling and slitting operation equipment; The oscillating abrasive water jet drilling and slitting integrated tool (5) comprises a drill rod (9), an oscillating jet nozzle combined slitting tool (8), a drilling machine (7) and a drill bit (6); the interior of the drill rod (9) is a hollow structure and is provided with a guide tube (10); the head end of the drill rod (9) is fixedly connected to the water outlet end of an ultra-high pressure water injector (16), and the inlet end of the guide tube (10) is communicated with the liquid inlet end of the ultra-high pressure water injector (16); the oscillating jet nozzle combined slitting tool (8) comprises a guide tube interface (18) and a plurality of oscillating jet nozzles (17); the guide tube interface (18) is fixedly mounted at the end of the drill rod (9), and its inner cavity is connected to the liquid outlet end of the guide tube (10); three oscillating jet nozzles (17) are fixedly mounted on the outer wall of the guide tube interface (18) evenly in the circumferential direction, and are connected to the guide tube interface (18) through a reserved communication channel. The inner cavity of the flow tube interface (18) is connected; the centers of the two ends of the oscillating jet nozzle (17) in the length direction have relatively distributed nozzle inlets (21) and nozzle outlets (20); at the same time, an oscillation cavity (19) connecting the nozzle inlet (21) and the nozzle outlet (20) is provided in the inner center area of ​​the oscillating jet nozzle (17); at the same time, two feedback channels (22) are symmetrically provided on both sides of the oscillation cavity (19) inside the oscillating jet nozzle (17); the feedback channels (22) are bent channels, and the two ends thereof are respectively connected to the head and tail ends of the oscillation cavity (19); the cross section of the inner cavity of the nozzle outlet (20) is in the shape of a fan of 120°, and the small end is connected to the oscillation cavity (19), and the large end is located on the outside; the drilling rig (7) is installed at the end of the drill rod (9); the drill bit (6) is installed at the output end of the drilling rig (7); S33: Establishing a connection between the drilling rig frame and the drill rod (9); Step 4: Drilling opposite fishbone wells; S41: lowering the oscillating jet drilling and slitting integrated tool (5) into the horizontal well (3) of the coal seam (1), and controlling the operation of the drilling rig (7) through the control console (14), using the drilling rig (7) to drive the drill bit (6) to rotate at high speed to perform drilling operations, and drilling a plurality of horizontal branch wells (30) in sequence at different positions along the length direction of the horizontal well (3), while ensuring that the axes of the plurality of horizontal branch wells (30) and the horizontal well (3) are located in the same plane, and that the horizontal well (3) and the plurality of horizontal branch wells (30) are arranged in a fishbone shape as a whole, thereby forming a fishbone well (4); in this process, the plurality of horizontal branch wells (30) of different fishbone wells (4) in the same coal seam (1) are arranged in a staggered arrangement, forming a staggered opposing fishbone well network in the same coal seam (1); S42: After the drilling of the herringbone well (4) is completed, the oscillating jet drilling and slotting integrated tool (5) is first withdrawn from the wellbore, and then the branch horizontal well (3) is washed and desludged, and then a pumping operation is performed to ensure that there is no water accumulation in the herringbone well (4); Step 5: Water jet rock breaking and cutting operation; S51: once again, the integrated oscillating jet drilling and slotting tool (5) is moved deep into the horizontal branch well (30) to the set slotting position; S52: Start the slotting and cavitation function to perform high-pressure oscillating abrasive water jet slotting operation; start the high-pressure water pump (11) through the control console (14), and synchronously provide negative pressure to the water tank (12) and the sand tank (13), so that the water in the water tank (12) and the sand in the sand tank (13) enter the high-pressure water pump (11) in proportion and mix to form a sand-containing water flow, and then supply the oscillating jet nozzle combined slotting tool (8) through the ultra-high pressure water injector (16) and the guide pipe (10) in the drill pipe (9), and the three oscillating jet nozzles (17) oscillate the jet to form an annular high-pressure jet surrounding the wellbore, and use the high-pressure jet to penetrate the surrounding rock in the horizontal branch well (30) to perform a slotting operation, thereby forming an annular slot (25) in the fishbone well (4); Step 6: fluidization extraction of coal particles; The rock breaking and cutting operation is used to induce coal body protrusion to form a mixed fluid material (23) that meets the particle size of pipeline transmission. At the same time, the fluidized transportation effect generated by the negative pressure of the pipeline is used to continuously mine the coal around the fishbone well (4) in a fluidized form; at the same time, a plurality of interlaced and connected seams (25) are used to promote the formation of the goaf (24); Step 7: Induce crack expansion in goaf area; By utilizing the inductive effect of the seams (25) and the goaf (24), cracks (27) are formed in the coal seam around the herringbone wells (4), so as to release the stress of the coal seam. In the process of releasing the stress of the coal seam, the cracks (27) are further induced to expand, so that the cracks around the staggered herringbone wells (4) communicate with each other, thereby forming a high-quality complex crack network in the target coal seam (1); Step 8: Use coal seam fissures to extract coal seam gas; The permeability of the coal seam and the desorption efficiency of the coal seam gas are improved by using the constructed complex fracture network, and at the same time, the extraction operation of the desorbed gas (26) of the coal seam is completed by using the interconnected complex fracture network; Step 9: Remaining coal gasification operation; S91: After the extraction operation is completed, the gasification pipe column (28) is lowered to the end of the horizontal well (3), and an oxidant (29) is injected to ignite or detonate the methane-air mixture in the complex fracture network by electric shock ignition. The high temperature conditions generated by the combustion and explosion process are used to evaporate the residual water in the coal seam (1) to form water vapor, and the coal and water vapor are further chemically reacted to produce hydrogen and carbon monoxide, which further promotes the hydrogen, carbon monoxide and coal to continue to chemically react to produce methane; S92: Recover the gasification pipe string (28) upwards to complete the gasification operation of all horizontal well sections (3).

2. A deep coal hydraulic fracturing physical fluidization mining method according to claim 1, characterized in that: In step one, the construction parameters include well layout orientation, drilling depth, slit position and slit spacing.

3. A deep coal hydraulic fracturing physical fluidization mining method according to claim 1, characterized in that: In step three S32, the power supply cable and the signal cable connected to the drilling rig (7) are extended to the position of the control console (14) through the annular cavity inside the drill pipe (9) and connected to the control console (14).

4. A deep coal hydraulic fracturing physical fluidization mining method according to claim 3, characterized in that: In step three S32, the cross-section of the inner cavity of the nozzle inlet (21) is an isosceles trapezoid, with the large diameter end located on the outside and the small diameter end connected to the oscillation cavity (19).

5. A deep coal hydraulic fracturing physical fluidization mining method according to claim 4, characterized in that: In step six, the mixed fluid substance (23) includes granular fluid, gas and liquid.

6. A deep coal hydraulic fracturing physical fluidization mining method according to claim 5, characterized in that: In step three S32, the drill pipe (9) is an ultra-high pressure sealed drill pipe.

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