WO2024077842A1

WO2024077842A1 - Rock stratum fracturing method and equipment using variable-frequency pulse fracture network

Info

Publication number: WO2024077842A1
Application number: PCT/CN2023/078951
Authority: WO
Inventors: 黄炳香; 赵兴龙; 邵鲁英; 陈树亮; 邢岳堃
Original assignee: 中国矿业大学; 徐州佑学矿业科技有限公司
Priority date: 2022-10-14
Filing date: 2023-03-01
Publication date: 2024-04-18
Also published as: CN115749713B; CN115749713A; AU2023251557A1

Abstract

A rock stratum fracturing method and equipment using a variable-frequency pulse fracture network. The fracturing method comprises: first, determining an initial pulse pressure peak of each rock stratum according to the physical and mechanical properties and the confining pressure of each rock stratum, and determining a pulse frequency of each rock stratum according to a collision force measurement experiment for each rock stratum; then, according to the initial pulse pressure peak and the pulse frequency, designing a fracturing pumping scheme using a variable-frequency pulse fracture network, and according to different operating conditions, designing a rock stratum fracturing drill hole arrangement scheme using a variable-frequency pulse fracture network; and finally, according to the drill hole arrangement scheme, punching a fracturing hole, and performing fracturing according to the fracturing pumping scheme. The rock stratum fracturing equipment using a variable-frequency pulse fracture network comprises a pumping-mode-variable and frequency-variable fracturing pump (4), a hydraulic fracturing measurement and control instrument (13), an automatic packer (21), a mechanical rod feeding machine (19) and a two-way water injection steel pipe (20). By means of the rock stratum fracturing method and equipment using a variable-frequency pulse fracture network, a plurality of annular fracture network structures can be formed near a drill hole from near to far and stage by stage, and are finally sequentially stacked into a relatively large-range fracture network, thereby fully breaking up a relatively large-range rock mass.

Description

Rock formation variable frequency pulse network fracturing method and equipment

Technical Field

The invention relates to a rock stratum crushing method and device, and in particular to a rock stratum variable frequency pulse network fracturing method and equipment.

Background technique

In tunneling and mining projects, intact rock formations play a positive role in maintaining the stability of tunnels and mining sites. However, the slow speed of tunneling in hard rock tunnels, the difficulty of hard roof collapse during coal mining, and the difficulty of hard ore falling during natural caving mining in metal mines are technical problems that currently restrict the rapid tunneling and safe and efficient production of mines. Solving these problems involves a common core issue, which is the transformation of rock structure, artificially adding cracks in the rock formation to weaken its strength.

The main methods of forming cracks in rock formations are explosive blasting, _CO2 phase change fracturing and hydraulic fracturing. Explosive blasting is widely used in mining production. However, the safety management of weakened rock formations by explosive blasting is complicated, involving the management and transportation of explosives and detonators. Blasting must strictly implement the "three inspections for one blast" and "three-person chain blasting system"; the large amount of harmful gases such as CO generated instantly by large-scale blasting has a huge impact on the ventilation safety management of mines; for high-gas mines, explosive blasting is not suitable due to the hidden danger of gas explosion induced by blasting sparks; the single-hole blasting has a small range, so a large amount of pyrotechnics such as gunpowder and detonators are required, and the economic cost of blasting is high; when blasting deep holes, due to the influence of confining pressure, the range of blasting cracks is small and the blasting effect is limited.

_CO2 phase change fracturing uses the energy difference between supercritical _CO2 and gaseous _CO2 as the driving force for rock breaking. During fracturing, liquid _CO2 first absorbs heat and transforms into a supercritical state, then decompresses and expands to convert into high-pressure gas to break the rock layer. The entire rock fracturing process is not only spark-free, but also absorbs heat and suppresses combustion. It is a typical physical explosion and is suitable for high-gas mines. However, compared with explosive blasting, _CO2 phase change fracturing is less powerful and has a higher blasting cost.

Hydraulic fracturing is a fracturing technology that uses clean water as the fracturing fluid. Hydraulic fracturing technology was first used in the fields of oil field production increase, shale gas extraction, geothermal extraction, ground stress measurement, and rock burst control. In recent years, hydraulic fracturing technology has also been widely used in the mining industry. Hydraulic fracturing is a continuous process of working on the rock mass. Therefore, compared with explosive blasting and _CO2 phase change fracturing, hydraulic fracturing has the characteristics of longer crack length and larger control range;

However, conventional hydraulic fracturing is controlled by ground stress and the cracks formed inside the rock formation are relatively simple, so the effect in breaking the rock formation is limited.

Summary of the invention

In view of the above technical problems, the present invention proposes a rock formation variable frequency pulse fracture network fracturing method and equipment. The layer variable frequency pulse fracture network fracturing method is to change the initial pulse pressure peak and pulse frequency to adapt to different strength rock layers. During the fracturing of each rock layer, the pulse pressure peak is gradually increased to form multiple annular fracture network structures from near to far near the borehole, and finally superimposed into a large-scale fracture network in sequence, thereby fully crushing a larger range of rock mass.

In order to achieve the above technical objectives, the present invention adopts the following technical means:

A rock formation variable frequency pulse fracture network fracturing method, comprising the following steps:

S1. Adapt to different strength rock layers by changing the initial pulse pressure peak and pulse frequency; determine the initial pulse pressure peak of each rock layer according to the physical and mechanical properties and confining pressure of each rock layer, and the initial pulse pressure peak is less than the fracture pressure of the rock during constant displacement fracturing; determine the pulse frequency of each rock layer according to the collision force measurement experiment of each rock layer;

S2. Design a variable frequency pulse fracture network fracturing pumping scheme. After fracturing for 5 to 10 minutes with the initial pulse pressure peak and pulse frequency corresponding to the first rock layer, the pulse pressure peak is increased by 2 to 5 MPa. After fracturing for 5 to 10 minutes, the pulse pressure peak is increased by 2 to 5 MPa again, and so on until the fracturing of the first rock layer is completed; then, after fracturing for 5 to 10 minutes with the initial pulse pressure peak and pulse frequency corresponding to the second rock layer, the pulse pressure peak is increased by 2 to 5 MPa. After fracturing for 5 to 10 minutes, the pulse pressure peak is increased by 2 to 5 MPa again, and so on until the fracturing of the second rock layer is completed; the same method is used until the fracturing of all rock layers is completed; during the fracturing of each rock layer, the pulse pressure peak is gradually increased to form multiple annular fracture network structures from near to far near the borehole, and finally superimposed into a large-scale fracture network in sequence, thereby fully crushing a large range of rock mass;

S3. Design the rock formation variable frequency pulse network fracturing drilling arrangement plan according to different working conditions;

S4. According to the rock formation variable frequency pulse fracture network fracturing drilling arrangement plan, fracturing holes are drilled in the rock formation to be fractured, and observation holes are drilled at the edge of the designed fracture network expansion area;

S5. Fracturing is performed according to the rock formation variable frequency pulse fracture network fracturing pumping scheme, and the pumping displacement is controlled to perform high-frequency periodic fluctuations in the form of pulse waves, resulting in periodic changes in water pressure. A large number of randomly distributed micro cracks in the rock formation near the borehole undergo random fatigue damage under the action of a lower pulse cycle load, overcoming the influence of the principal stress difference of the surrounding rock and forming a dense fracture network near the borehole;

S6. Stop fracturing after fracturing fluid flows out of the observation hole;

The method for determining the peak value of the initial pulse pressure is as follows: by taking rock samples on site and testing the confining pressure, the physical and mechanical parameters of the rock formation are tested, thereby obtaining the triaxial tensile yield strength of the rock formation. The peak value of the initial pulse pressure is the triaxial tensile yield strength of the rock. The method for determining the pulse frequency is as follows: in the laboratory, different collision forces generated by a certain mass of water pumped by a fracturing pump in one cycle colliding with the on-site rock samples at different frequencies are measured, and the frequency corresponding to the tensile yield strength is selected as the pulse frequency.

Step S2 adopts the variable frequency pulse + constant displacement fracture network fracturing method, and fracturing is performed for a period of time at the initial pulse pressure and pulse frequency. After the pulse fracture network is formed, the constant displacement pumping method is used to continue fracturing, so that the tips of the dense pulse fracture network are reopened to form a At the same time, the fracture network formed by pulse fracturing changes the local stress field, slows down the interference between fractures, slows down the far-field stress control, and forms a larger fracture network.

The rock formation to be fractured in step S4 is a hard rock formation that is about to be exposed in front of the tunneling head. During the excavation of the hard rock tunnel, a central long borehole is constructed at the central position of the tunneling head along the excavation direction and pulse fracturing is performed. A dense crack network is pre-formed in the hard rock formation that is about to be exposed in front of the tunneling head, and the rock formation is fully broken so that it can fall smoothly under the cutting of the subsequent tunneling machine or under the action of blasting, thereby increasing the excavation speed; before the formal fracturing construction, a central long borehole is first drilled in the center of the tunneling head along the excavation direction, and an observation borehole parallel to and of the same length as the central long borehole is drilled on the top plate, two sides and bottom plate of the tunnel, and a humidity sensor is arranged. The central long borehole is fractured and the change of humidity in each observation borehole with the fracturing time is recorded, so as to infer the time when the crack extends to the surrounding rock of the pre-excavated tunnel, and this time is used as the subsequent pulse fracturing time.

The rock stratum to be fractured described in step S4 is the hard roof above the coal seam during the initial roof caving of the coal mining face. During the initial roof caving of the coal mining face, holes are drilled in the hard roof above the cutting eye and the two chute holes and pulse fracturing is performed to form a dense crack network in the roof. The opening position of the cutting eye drilling hole is close to the rear coal wall; the opening position of the transportation chute drilling hole and the return air chute drilling hole are at the center line position of the chute roof.

The rock formation to be fractured described in step S4 is the hard roof above the two ends of the coal mining working face during the period when the end of the coal mining working face is suspended. During the period when the end of the coal mining working face is suspended, drill holes are drilled at the end of the working face and pulse fracturing is performed to form a dense crack network in the hard roof above the end of the working face, which fully breaks up the rock formation in this area. The opening position of the drill hole at the end of the working face is at the center line of the longitudinal top plate, the drilling angle is 70°, and the drilling direction is inclined toward the goaf.

The rock formation to be fractured described in step S4 is the thick and hard interlayer gangue and thick and hard bottom plate within the mining height range during the period when the coal mining working face is too thick and hard interlayer gangue and bottom pulling. During the period when the coal mining working face is too thick and hard interlayer gangue and bottom pulling, long drill holes are constructed in the drift and pulse fracturing is performed to form a dense crack network in the interlayer gangue or bottom plate, and the gangue or bottom plate is fully broken so that the gangue or bottom plate can fall smoothly under the subsequent cutting of the coal mining machine; the opening position of the long drill hole constructed in the drift is at the center line position of the interlayer gangue of the side wall of the drift working face or the pre-cut bottom plate, and the construction is carried out along the inclined direction of the interlayer gangue or bottom plate, and the position of the drill hole falls on the side wall of the other drift working face of the working face, and the drilling hole spacing is controlled to be 4m~5m.

The rock formation to be fractured described in step S4 is a hard rock formation near the fault during the period when the coal mining face passes through the fault. During the period when the coal mining face passes through the fault, a long borehole is constructed in the drift and pulse fracturing is performed to form a dense crack network in the fault, fully breaking the fault rock formation so that the fault rock formation can fall smoothly under the cutting of the subsequent coal mining machine; the opening position of the long borehole constructed in the drift is in the middle position of the side wall of the drift working face, and is constructed along the inclined direction of the cutting eye. The position of the drill hole passes through the fault where coal is seen, and the drilling hole spacing is controlled at 4m to 5m.

The rock layer to be fractured in step S4 is a hard rock layer above the coal layer mined by the coal mining face during the prevention of rock burst. Long holes are constructed on the top plates and walls of the two chute of the coal mining face and pulse fracturing is performed to fully break the chute. The outer rock of the slot support structure and the broken surrounding rock are used to prevent the dynamic pressure of the working face from being transmitted to the slot of this working face, thereby reducing the impact risk of the advance support section of the slot of this working face; the long drill hole constructed on the roof and side wall of the two slots of the coal mining working face is 40m long, of which the range of 20m to 40m is defined as the fracturing section.

The rock layer to be fractured described in step S4 is the hard rock layer above the tunnel during double tunnel excavation. In the drift of double tunnel excavation, the old roof above the coal pillar is first subjected to multi-hole simultaneous pulse fracturing to form a resonance effect between the holes and the surrounding rock near the holes. The rock layer between the holes is preferentially broken, and finally a fracture zone is formed along the direction of the borehole connection to prevent the dynamic pressure of mining from being transmitted to the adjacent drift; then the hanging roof at the end of the working face is treated to accelerate the rotation and sinking of the roof of the goaf to avoid the formation of a hanging roof and reduce the transmission of stress in the goaf to the adjacent drift; the opening position of the old roof drill hole above the coal pillar is at the roof of the drift 0.2m close to the side wall of the coal pillar, the position of the comprehensive drilling hole is the upper surface of the old roof just above 1/3 of the width of the coal pillar, and the drilling hole spacing is controlled at 4m to 5m.

The rock formation to be fractured described in step S4 is the hard rock formation above the protective coal pillar in the main tunnel at the end of the mining face recovery. At the end of the mining face recovery, first, before the working face advances to the stop-mining line, multi-hole simultaneous pulse fracturing is performed in the main tunnel of the mining area to form a resonance effect in the surrounding rock near the holes, and the rock formation between the holes is preferentially broken, and finally a broken zone is formed along the direction of the borehole connection line, blocking the propagation path of the mining stress to the main tunnel of the disk area; then, when the working face is recovered to the stop-mining line, the hard roof above the coal seam is fractured at the stop-mining line of the working face to avoid the formation of a cantilever beam structure on the goaf side of the stop-mining line, thereby blocking the high stress in the goaf from propagating to the main tunnel of the system, and further reducing the deformation and damage degree of the main tunnel of the mining area; the position of the drill hole for cutting off the dynamic pressure should be more than 30m away from each main tunnel in the horizontal direction and not exceed the stop-mining line.

The rock formation to be fractured in step S4 is a metal ore mined by the staged natural caving method. In the project of mining metal ore by the staged natural caving method, a long borehole is constructed in the weakened tunnel and pulse fracturing is performed to form a dense crack network inside the ore, fully crush the ore, and enable the ore to fall smoothly in the subsequent mining process; the borehole spacing is controlled within the range of 4-8m.

The rock layer to be fractured described in step S4 is a metal ore mined by the single-layer caving method. In the project of mining metal ore by the single-layer caving method, fan-shaped drill holes are drilled in the vein transportation tunnel just below the working face when cutting up the mountain, and pulse fracturing is performed to weaken the hard old roof above the mining face. The fan-shaped terminal hole spacing is 5m, and covers the entire upper roof of the working face.

The rock formation to be fractured in step S4 is a low-permeability uranium-bearing aquifer. When the low permeability of the aquifer leads to high cost and low efficiency in uranium mining, pulse fracturing is performed in the injection hole to form a dense fracture network near the injection hole, thereby increasing the permeability of the uranium-bearing aquifer, thereby improving the mining efficiency of the uranium ore; when designing the fracturing boreholes, the hole spacing of the fracturing boreholes is equal to twice the distance from the sealing section to the upper and lower top and bottom plates, so that when the cracks in the two boreholes are connected, the cracks have not yet expanded to the top and bottom plates; in addition, it is necessary to accurately control the fracturing time, which is determined by field tests; before the formal fracturing construction, an observation borehole parallel to and equal in length to the fracturing borehole is drilled in the middle of the two fracturing boreholes and a humidity sensor is arranged, and one of the fracturing boreholes on both sides of the fracturing observation hole observes and records the changes in borehole humidity with fracturing time, so as to The time when the fracture extends to the observed borehole is inferred; this time is used as the subsequent pulse fracturing time.

A rock formation variable frequency pulse network fracturing equipment, comprising:

A pumping mode and variable frequency fracturing pump is used to output pulse water to fractur e rock formations and provide a constant displacement water for an automatic packer to seal holes. The motor connected to the power end of the pumping mode and variable frequency fracturing pump is a variable frequency motor. The hydraulic end of the pumping mode and variable frequency fracturing pump consists of three plungers, one of which corresponds to a discharge channel and a liquid inlet channel at a pump head, respectively, and a discharge stop valve and a liquid inlet stop valve are arranged. The working chamber corresponding to the plunger is provided with a channel connected to the outside world, and a water stop valve is arranged at the channel, and the water stop valve is connected to the water tank through a water hose.

The high-pressure hose output by the variable-frequency fracturing pump is divided into two paths by a tee. One path is used to input pulse water into the borehole to fractur e the rock formation, which is called the fracturing hose, and the other path provides a constant-displacement water for the automatic packer to seal the hole, which is called the sealing hose.

The fracturing hose is provided with a fracturing stop valve, a fracturing drain valve, a pressure sensor and a flow sensor in sequence along the water flow direction; the sealing hose is provided with a one-way valve, a pressure gauge and a sealing drain valve in sequence along the water flow direction;

A hydraulic fracturing monitoring and control instrument, connected to the pressure sensor and flow sensor signals, for monitoring and recording the pulse water pressure and flow during the fracturing process;

The automatic packer comprises two expansion capsule hole sealers, which are connected through a first dual-way water injection steel pipe with an outer pipe channel, and the interior of the expansion capsule hole sealer is a second dual-way water injection steel pipe with an inner pipe channel, and the outer side of the second dual-way water injection steel pipe with an inner pipe channel is wrapped with a steel wire rubber sleeve, one end of the steel wire rubber sleeve is fixed to one end of the second dual-way water injection steel pipe with an inner pipe channel, and the other end of the steel wire rubber sleeve can slide on the second dual-way water injection steel pipe with an inner pipe channel, and the connection is high-pressure sealed;

A mechanical rod delivery machine, used to deliver the automatic packer to the drilling and fracturing area, comprising:

cylinder;

A tray is sleeved on the cylinder wall and can slide on the cylinder wall;

A leg connecting piece is fixedly connected to the top of the cylinder wall of the cylinder, the leg connecting piece is connected to the leg via a latch, and the leg can rotate around the latch on the side of the leg connecting piece;

A connecting rod, one end of which is connected to the tray, and the other end of which passes through the leg connecting piece and is connected to a connecting plate, wherein the connecting plate is fixedly connected to the end of the cylinder piston rod;

A third dual-circuit water injection steel pipe has one end fixedly connected to the support leg connector and the other end provided with a connection to the second dual-circuit water injection steel pipe on the automatic packer.

The third dual-way water injection steel pipe is fixedly connected to the support leg connector through a limit clamp, and the dual-way water injection steel pipe includes an external pulse steel pipe and an internal high-pressure steel pipe of equal length and coaxial sleeve connection, and the external pulse steel pipe and the internal high-pressure steel pipe are connected by a connecting rod, and the external pulse steel pipe has internal and external threads on both sides, and the internal high-pressure steel pipe has male and female threads on both sides. Quick plug;

A sealing ring is placed in the inner thread of the external pulse steel pipe to provide high pressure sealing at the connection between the two dual-path water injection steel pipes;

The outer pulse steel pipe has a limit ring on one side close to the internal thread, which is used to cooperate with the limit clamp to fix the dual-path water injection steel pipe;

A two-way conversion joint, the outside of which is threadedly connected to one end of the external pulse steel pipe, and the inside of which is quickly connected to one end of the internal high-pressure steel pipe.

The supporting legs are retractable supporting legs.

The operating method of the rock formation variable frequency pulse network fracturing equipment comprises the following steps:

Step 1: Place the mechanical rod feeder directly below the borehole to be fracturing, and adjust the angle of the mechanical rod feeder by adjusting the legs so that it is in a straight line with the borehole; connect the two expansion capsule sealers of the automatic packer with an outer pipe with a channel double-way water injection steel pipe, and send them into the hole position;

First, one end of the first third dual-way water injection steel pipe is installed on the support leg connector of the mechanical rod feeder, and the other end is connected to the lower end of the second dual-way water injection steel pipe on the automatic packer. By injecting high-pressure gas into the cylinder of the mechanical rod feeder, the tray is driven to slide upward on the outer wall of the cylinder, and then the automatic packer and the first third dual-way water injection steel pipe are lifted upward for a distance S1 and then the gas injection is stopped; the automatic packer and the first third dual-way water injection steel pipe are fixed to the support leg connector of the mechanical rod feeder by a limit clamp to prevent the automatic packer and the first third dual-way water injection steel pipe from sliding down under the action of their own weight; the cylinder gas is discharged, and the tray returns to the bottom of the cylinder under the action of gravity. end, then take the second third dual-way water injection steel pipe and connect it to the third dual-way water injection steel pipe at the limit clamp, inflate the cylinder again, and when the tray contacts the lower end of the second third dual-way water injection steel pipe, open the limit clamp, and lift the second third dual-way water injection steel pipe, the first third dual-way water injection steel pipe and the automatic packer again by a distance S1, and repeat this process until the automatic packer is delivered to the drilling and fracturing area; finally, close the limit clamp, fix the last third dual-way water injection steel pipe on the leg connector of the mechanical rod delivery machine, exhaust the gas in the cylinder, return the tray to the bottom end of the cylinder, and connect the dual-way conversion joint to the end of the third dual-way water injection steel pipe at the limit clamp;

Step 2: sequentially install the variable pumping mode and frequency fracturing pump and the matching water tank, hydraulic fracturing monitoring and control instrument, and connect them to each other, and connect the ends of the fracturing hose and the sealing hose to the third two-way water injection steel pipe at the limit clamp through a two-way conversion joint;

Step 3: Close the fracturing stop valve, open the hydraulic fracturing control instrument, open the inlet stop valve and the discharge stop valve of the pumping mode and variable frequency fracturing pump, close the water stop valve of the pumping mode and variable frequency fracturing pump, open the pumping mode and variable frequency fracturing pump, so that its three pistons can work normally, input constant displacement water into the automatic packer to seal the hole, and close the pumping mode and variable frequency fracturing pump when the water pressure of the pressure gauge on the sealing hose rises to 35MPa. Since a one-way valve is provided on the sealing hose, the water in the automatic sealer will not flow back after the pumping mode and variable frequency fracturing pump are closed, and the sealing is completed;

Step 4: Open the water shut-off valve of the pumping mode and variable frequency fracturing pump, close the liquid inlet shut-off valve and the liquid discharge shut-off valve of the pumping mode and variable frequency fracturing pump, open the fracturing shut-off valve, start the pumping mode and variable frequency fracturing pump, make its two pistons work normally, and one piston idle, the liquid inlet channel and the liquid discharge channel of the working chamber corresponding to the idle piston are closed, and the working chamber corresponding to the idle piston cannot supply liquid to the fracturing hose, and the working chamber corresponding to the idle piston is directly connected to the water tank through the water hose, which ensures normal water absorption and drainage of this piston when idling, thereby ensuring lubrication, and input pulse water into the borehole in this mode.

Compared with the existing method of forming cracks in rock formations, the present invention has the following beneficial effects:

First: The present invention proposes a variable frequency pulse fracture network fracturing method for rock formations. During the constant displacement pump fracturing process, when the water pressure reaches the critical value of the water pressure for the formation of the dominant fracture surface, a single main crack will appear inside the rock formation under the control of the ground stress, and the direction is controlled by the ground stress. It is difficult to penetrate the surface and the interlayer of gangue, the mechanical properties of the layers are greatly different, and the transformation volume is limited. During the pulse hydraulic fracturing process, the pumping displacement is a high-frequency periodic fluctuation in the form of pulse waves, resulting in periodic changes in water pressure. A large number of randomly distributed micro cracks in the rock formation near the borehole do not form main cracks under the action of low cyclic loads, but instead suffer random fatigue damage. In addition, compared with slow quasi-static cyclic loading, the pulse fracturing cycle loading period is shorter (higher frequency), and pulse fracturing is a dynamic loading with collision energy input, resulting in the collision force during the collision between the fracturing fluid and the rock formation near the borehole further increasing the degree of random fatigue damage to the rock formation near the borehole. Combining the above two factors, when the fracture pressure of traditional constant-displacement fracturing statics is far from being reached, the fatigue impact of pulse fracturing gradually stimulates the micro cracks and micro voids inside the rock formation and then expands forward and penetrates each other. At the same time, the fracture network formed by pulse fracturing changes the local stress field, the interference between the fractures turns slowly, and the far-field stress is slowed down to control the fracture turning, forming a larger fracture network, thereby forming a dense fracture network near the borehole, overcoming the influence of the principal stress difference of the surrounding rock. Secondly, pulse pumping produces compressive shear fatigue, tensile fatigue and impact effects on the layer, breaking the layer and the gangue, and the crack network penetrates the layer, opening up a new way to solve the problem of "the gangue fracture energy is much higher than the layer" to inhibit crack penetration. Based on the above-mentioned characteristics of pulse fracturing, the rock formation variable frequency pulse crack network fracturing method proposed by the present invention is to change the initial pulse pressure peak and pulse frequency to adapt to different strength rock formations. During the fracturing of each rock formation, the pulse pressure peak is gradually increased to form multiple annular crack network structures from near to far near the borehole, and finally superimposed into a large-scale crack network in sequence, thereby fully crushing a large range of rock mass.

In addition to fracturing coal seams and rock strata by step-by-step pressurization, constant-displacement fracturing can also be performed on the basis of pulse fracturing networks. The tips of dense fracture networks are reopened to form dense and multi-fracture expansion. The characteristics of pulse fracturing are that there are many but not long fractures, while the characteristics of constant-displacement fracturing are that there are long but not many fractures. Combining the advantages of the two, a "variable frequency pulse + constant displacement" fracture network fracturing method was proposed, which breaks through the difficulties of principal stress difference, layer level, and interlayer performance differences, and produces a long-distance fracture network.

Second: The present invention proposes a complete set of rock formation variable frequency pulse fracture network fracturing equipment, including a pumping mode and variable frequency fracturing pump and a matching water tank, a hydraulic fracturing measurement and control instrument, a mechanical rod feeder and its matching dual-way water injection steel pipe, and an automatic packer. The variable mode and frequency fracturing pump is used to output pulse water to fracture the rock formation and provide constant displacement water to the packer for sealing the hole; the hydraulic fracturing monitoring and control instrument is used to monitor and record the pulse water pressure and flow rate during the fracturing process; the mechanical rod delivery machine is used to deliver the automatic packer to the drilling fracturing area; the automatic packer is used to seal the hole.

The motor connected to the power end of the variable frequency fracturing pump is a variable frequency motor, and the variable frequency pulse adapts to the difference in mechanical properties between layers; the hydraulic end of the variable frequency fracturing pump consists of three plungers, one of which corresponds to the discharge channel and the inlet channel at the pump head, and a discharge stop valve and an inlet stop valve are respectively set, and the working chamber corresponding to this plunger is provided with a channel connected to the outside world, and a water stop valve is set at this channel, and the water stop valve is connected to the water tank through a water hose. By opening and closing the discharge stop valve, the inlet stop valve, and the water stop valve, one of the pistons can be made to work normally or idle, thereby realizing the free switching of the three-plunger pump and the two-plunger pump, and finally outputting constant displacement water for sealing the hole and outputting pulse water for fracturing the rock formation. Furthermore, a one-way valve is provided on the sealing hose. After the sealing is completed, when the pumping mode and the frequency-variable fracturing pump are closed to switch between constant displacement and pulse, the one-way valve prevents the water in the automatic sealer from flowing back, thereby ensuring the stability of the sealing at the beginning of fracturing. In the normal fracturing stage, since the rock formation in the sealing section is compressed for a long time, the pore size may be enlarged and the water pressure in the automatic sealer may decrease. Once the pressure in the automatic sealer is lower than the pressure in the hole, the one-way valve on the sealing hose will open in time, so that the water pressure in the automatic sealer is always greater than or equal to the pressure in the hole, thereby ensuring the stability of the sealing in the normal stage of fracturing. Compared with the use of pulse water for sealing, the use of constant displacement water for initial sealing allows the automatic sealer to be subjected to constant water pressure for most of the time, thereby reducing fatigue damage to the automatic sealer and extending the service life of the automatic sealer.

The mechanical rod feeder consists of a cylinder, a tray, a leg connector, a leg, and a limit clamp. The tray is mounted on the cylinder wall and can slide on the cylinder wall. It is connected to the piston rod of the cylinder through a connecting rod and a connecting plate. The connecting rod can slide in the leg connector. The leg connector is connected to the four legs through a latch, and the legs can rotate around the latch on the side of the leg connector. The four legs are retractable. The limit clamp is located on the front of the leg connector and is used to fix the dual-way water injection steel pipe. The mechanical rod feeder is small, light, and easy to carry. At the same time, it can realize mechanical rod feeding at multiple angles; it solves the problem of manual rod feeding in the transmission fracturing process, greatly saving manpower.

The dual-way water injection steel pipe includes an external pulse steel pipe and an internal high-pressure steel pipe of equal length and coaxial sleeve. The external pulse steel pipe and the internal high-pressure steel pipe are connected by a connecting rod. The external pulse steel pipe has internal and external threads on both sides, and the internal high-pressure steel pipe has male and female quick plugs on both sides. A sealing ring is placed in the internal thread of the external pulse steel pipe to seal the high pressure connection of the two dual-way water injection steel pipes. The external pulse steel pipe has a limit ring on the side close to the internal thread to cooperate with the limit clamp on the mechanical rod feeder to fix the dual-way water injection steel pipe. The dual-way water injection steel pipe combines the pulse fracturing fluid channel and the automatic sealer high-pressure water channel into one, which saves space in the hole and installation time compared with the water injection steel pipe and sealing hose required for conventional dual-way hole sealers. At the same time, the water injection steel pipe and sealing hose required for conventional dual-way hole sealers are often entangled with the water injection steel pipe during the removal process after fracturing, making it impossible to remove them, resulting in the loss of a large number of conventional dual-way hole sealers and water injection steel pipes. The double-way water injection steel pipe avoids the occurrence of such problems by using materials such as pipes and sealing thin hoses.

The automatic packer includes two expansion capsule hole sealers. The two expansion capsule hole sealers are connected through an outer pipe with a channel and a dual-way water injection steel pipe with different number of sections. The inside of the expansion capsule hole sealer is an inner pipe with a channel and a dual-way water injection steel pipe. The outer side of the inner pipe with a channel and the dual-way water injection steel pipe is wrapped with a steel wire rubber sleeve. One end of the steel wire rubber sleeve is fixed to one end of the water injection steel pipe, and the other end of the steel wire rubber sleeve can slide on the water injection steel pipe (high pressure seal at the connection). The automatic packer overcomes the shortcomings of conventional single-way hole sealers, such as unstable sealing and easy punching.

Third, in terms of technology application:

① Pulse fracturing to assist rock breaking in hard rock tunnel (tunnel) excavation: The rock strata exposed during hard rock tunnel (tunnel) excavation are relatively hard, which seriously affects the tunneling speed of the tunnel (tunnel). Long drilling and pulse fracturing are carried out in the tunneling head to form a dense crack network in the hard rock strata to be exposed in front of the tunneling head, which fully breaks the rock strata and allows them to fall smoothly under the cutting of the subsequent tunneling machine or blasting, thereby increasing the excavation speed.

② Pulse fracturing control of the first roof caving of the coal mining face: The roof can be simplified as a cantilever beam during the periodic pressure of the coal mining face, and can be simplified as a beam with fixed support at both ends during the first pressure, which causes the first pressure step to be larger than the periodic pressure step. If the first collapse step of the coal mining face is too large, the sudden collapse of the roof is likely to form a hurricane, and a large amount of harmful gases such as gas in the goaf will be pushed into the working face, posing a serious safety hazard. A dense crack network is formed in the hard roof above the opening and two drifts, overcoming the shortcomings of conventional fracturing with a single crack and crack expansion controlled by ground stress, fully breaking the rock formation in this area, and changing the roof from a fixed support state at both ends to a cantilever beam state during the period from the start of mining to the first pressure, which can significantly shorten the first roof caving step.

③ Pulse fracturing control of the suspended roof at the end of the coal mining face: During normal mining, the roof in the middle of the working face is generally easy to collapse, but due to the support of the coal pillar, the roof at the end is not easy to collapse. The pulse fracturing technology is used to form a dense crack network in the hard roof above the end of the drift, overcoming the shortcomings of conventional fracturing with a single crack and crack expansion controlled by ground stress, and fully breaking the rock formation in this area. As the working face advances, the fractured roof above the end enters the goaf, and under the action of the mine pressure, the end roof can collapse in time.

④ Pulse fracturing to assist rock breaking when the coal mining face is too thick and hard interlayers and bottom pulling: There is often one or more layers of interlayers in the coal seam. When the thickness of the interlayers is too large, the drum of the coal mining machine will not be able to cut it off. Generally, drilling and blasting are carried out in the working face to loosen the gangue, which seriously affects the efficiency of coal cutting. When the coal seam suddenly becomes thinner and the thickness of the coal seam is less than the minimum mining height of the coal mining machine, the bottom pulling method is generally adopted to continue advancing, that is, drilling and blasting are carried out in the working face to pre-crack the bottom plate. Pulse fracturing technology is used to construct long boreholes and fracturing in the drift, forming a dense crack network in the interlayers or bottom plate, fully crushing the gangue or bottom plate, so that it can fall smoothly under the subsequent cutting of the coal mining machine. It overcomes the shortcomings of explosive blasting that drilling and blasting in the working face affect normal mining.

⑤ Pulse fracturing to assist rock breaking in coal mining face across faults: When encountering faults during mining, the coal mining face is often handled by blasting in the face, which seriously affects the efficiency of coal cutting. Pulse fracturing technology is used to construct long boreholes and fracturing in the drift, forming a dense crack network in the fault, fully breaking the fault rock layer so that it can fall smoothly under the cutting of the subsequent coal mining machine. It overcomes the deficiency of explosive blasting that requires drilling and blasting in the face, which affects normal mining.

⑥ Pulse fracturing of the surrounding rock of the coal mining face chute to prevent and control rock burst: During the mining period of the coal mining face, the mining dynamic pressure will be transmitted to the advance support sections of the two chute sections, which is easy to form rock burst. The pulse fracturing technology can be used to fully crush the outer rock of the chute support structure. The crushed surrounding rock can prevent the mining dynamic pressure of the working face from being transmitted to the chute of the working face, thereby reducing the impact tendency of the advance support section of the chute of the working face.

⑦ Pulse fracturing of the roof of the coal mining face controls large deformation of adjacent drifts: When the working face is designed to be long, ventilation is often difficult during drift excavation. Therefore, many mines use double tunnel excavation, which results in one drift being affected by the dynamic pressure of two working face mining operations. The pulse fracturing technology is used to first perform multi-hole pulse fracturing on the old roof above the coal pillar in the drift, forming a resonance effect between the surrounding rocks near the holes, and the rock layers between the holes are preferentially broken, and finally a broken zone is formed along the direction of the drilling line, preventing the dynamic pressure of mining from being transmitted to the adjacent drift; then the suspended roof at the end of the working face is treated, and the rotation and sinking of the roof of the goaf is accelerated to avoid the formation of a suspended roof, and reduce the transmission of stress in the goaf to the adjacent drift. The above two aspects can reduce the degree of influence of dynamic pressure and static pressure on adjacent drifts, and effectively control the deformation of adjacent drifts.

⑧ Pulse fracturing stress transfer of coal mining face roof to protect mining tunnels: At the end of mining of the working face, the mining area tunnels are often affected by mining and deformed. When the tunnels are deformed greatly, it will seriously affect the later use of the tunnels. The pulse fracturing technology is used. First, before the working face advances to the stop mining line, multiple holes are simultaneously pulsed in the mining area tunnels to form a resonance effect between the holes and the surrounding rocks near the holes. The rock layers between the holes are broken first, and finally a broken zone is formed along the direction of the drilling line, blocking the propagation path of mining stress to the disk area tunnels; then, when the working face is mined to the stop mining line, the hard roof above the coal seam is fractured at the stop mining line of the working face to avoid the formation of a cantilever beam structure on the side of the goaf of the stop mining line, thereby blocking the high stress in the goaf from propagating to the system tunnels, and further reducing the deformation and damage of the mining area tunnels.

⑨ Pulse fracturing weakening of hard ore in the working face of metal mine stage natural caving method: In the process of metal mining, when the stage natural caving method is used to recover metal ore, it is required that the ore is easy to collapse naturally. When the ore is relatively hard and not easy to collapse, long drill holes can be constructed in the weakening tunnel and pulse fracturing can be performed to form a dense crack network inside the ore, fully crush the ore, and enable the ore to fall smoothly in the subsequent ore discharge process. Improve the ore discharge efficiency.

⑩ Control of initial pressure and periodic pressure pulse fracturing of the single-layer caving method for metal mines: In the process of metal mining, when the metal ore body is a gently inclined ore layer less than 3m, the single-layer caving method is often used for mining. When the old roof is relatively hard, the excessive collapse step of the old roof will not only threaten production safety, but also greatly affect labor productivity, pillar consumption and mining costs. Fan-shaped drill holes can be drilled in the vein transportation tunnel just below the working face when cutting up the mountain. Pulse fracturing is carried out to weaken the hard old roof above the mining surface, thereby effectively shortening the collapse step distance of the old roof and reducing the impact risk caused by the collapse of the old roof.

Permeability enhancement of low permeability sandstone uranium deposits by pulse fracturing

In-situ uranium leaching is an advanced process technology for efficient mining of sandstone uranium mines. The basic principle of in-situ uranium leaching is to inject in-situ leaching liquid through the injection hole through the drilling hole (well) to fully react with uranium, and then extract it from the ground through the extraction hole to extract uranium on the surface. Based on the technical characteristics of in-situ uranium leaching, the permeability of the uranium-bearing aquifer is a key factor affecting in-situ uranium leaching. When the hypopermeability of the ore-bearing aquifer is low, it will lead to a small amount of liquid injection per well, low production capacity and a small ore-control area per well during in-situ leaching development of the deposit. Under the existing technical conditions, it is necessary to increase the well network for mining, resulting in high cost and low efficiency of uranium mining. To solve this problem, pulse fracturing can be performed in the injection hole to form a dense fracture network near the injection hole, thereby increasing the permeability of the uranium-bearing aquifer, thereby improving the mining efficiency of uranium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a diagram showing the formation mechanism of constant displacement hydraulic fracturing cracks according to the present invention;

FIG2 is a diagram showing the fracture network formation mechanism of the rock formation variable frequency pulse fracture network fracturing of the present invention;

FIG3 is a rock formation variable frequency pulse network fracturing method according to the present invention;

FIG4 is a rock formation "variable frequency pulse + constant displacement" fracture network fracturing method of the present invention;

FIG5 is a schematic diagram of the overall structure of the rock formation pulse fracture network fracturing device of the present invention;

FIG6 is a schematic diagram of the pumping mode and the structure of the variable frequency fracturing pump of the present invention;

FIG. 7( a ) is a schematic structural diagram of a mechanical rod feeder of the present invention;

FIG7( b ) is a schematic structural diagram of a two-way conversion joint and a third two-way water injection steel pipe according to the present invention;

Fig. 7(c) is a cross-sectional view taken along line A-A of Fig. 7(b);

FIG8 is a schematic diagram of the structure of an automatic packer;

FIG9 is a three-dimensional diagram of pulse fracturing assisted rock breaking in hard rock roadway (tunnel) excavation;

FIG10 is a cross-sectional view of pulse fracturing assisted rock breaking in hard rock roadway (tunnel) excavation;

Figure 11 is a plan view of the initial pulse fracturing control of the coal mining face;

FIG12 is a cross-sectional view taken along line A-A of FIG11;

FIG13 is a cross-sectional view taken along line B-B of FIG11;

Figure 14 is a plan view of pulse fracturing control at the top of the coal mining face;

Fig. 15 is a cross-sectional view taken along line A-A of Fig. 14;

Figure 16 is a plan view of the coal mining face with too thick hard gangue and bottom pulse fracturing assisted rock breaking;

FIG17 is a cross-sectional view taken along line AA of FIG16 ;

Fig. 18 is a cross-sectional view taken along line B-B of Fig. 16;

Figure 19 is a plan view of pulse fracturing assisted rock breaking across faults in a coal mining face;

Fig. 20 is a cross-sectional view taken along line A-A of Fig. 19;

Figure 21 is a plan view of pulse fracturing of surrounding rocks of coal mining face for preventing and controlling rock burst;

Fig. 22 is a cross-sectional view taken along line A-A of Fig. 21;

Figure 23 is a plan view of the large deformation of the adjacent drift under the control of pulse fracturing on the roof of the coal mining face;

Fig. 24 is a cross-sectional view taken along line A-A of Fig. 23;

Fig. 25 is a cross-sectional view taken along line B-B of Fig. 23;

Figure 26 is a plan view of the main mining tunnel for pulse fracturing stress transfer protection of the coal mining face roof;

Fig. 27 is a cross-sectional view taken along line A-A of Fig. 26;

FIG28 is a schematic diagram of pulse fracturing weakening of hard ore in the natural caving working face at the metal mine stage;

FIG29 is a plan view of the initial pressure and periodic pressure pulse fracturing control structure of a single-layer caving mining face in a metal mine;

Fig. 30 is a cross-sectional view taken along line A-A of Fig. 29;

Figure 31 is a schematic diagram of pulse fracturing to increase permeability in low permeability sandstone uranium ore layers.

In the figure, 1-1, fracturing borehole, 1-2, observation borehole, 2, constant displacement hydraulic fracture, 3, pulse hydraulic fracture network, 3-1, first order pulse fracture network, 3-2, second order pulse fracture network, 3-3, third order pulse fracture network, 4, pumping mode and variable frequency fracturing pump, 4-1, crankshaft, 4-2, crosshead, 4-3, connecting rod, 4-4, plunger, 4-5, pump head, 4-5-1, discharge valve cover, 4-5-2, inlet valve cover, 4-5-3, working chamber, 4-5-4, discharge stop valve, 4-5-5, inlet stop valve, 4-5-6, Water stop valve, 5, liquid inlet hose, 6, water hose, 7, countercurrent hose, 8, water tank, 9, tee, 10, fracturing stop valve, 11, fracturing drain valve, 12, sensor, 13, hydraulic fracturing monitoring and control instrument, 14, one-way valve, 14-1, water flow, 14-2, iron ball, 14-3, spring, 15, pressure gauge, 16, sealing drain valve, 17, sealing hose, 18, fracturing hose, 19, mechanical rod feeder, 19-1, cylinder, 19-2, support leg, 19-3, connecting rod, 19-4, tray, 19-5, slide, 19-6, piston rod, 19- 7. Connecting plate, 19-8, limit card, 20, dual-way water injection steel pipe, 20-1, external pulse steel pipe, 20-2, internal high-pressure steel pipe, 20-3, internal thread, 20-4, limit ring, 20-5, sealing ring, 20-6, connecting rod Ⅰ, 20-7, quick plug male head Ⅰ, 20-8, external thread Ⅰ, 20-9, quick plug female head Ⅰ, 21, automatic packer, 21-1, expansion capsule sealer, 21-1-1, fixed end, 21-1-2, sliding end, 21-1-3, steel wire rubber sleeve, 21-1-4, dual-way water injection steel pipe with inner pipe channel, 21 -1-4-1, channel Ⅰ, 21-2, outer pipe with channel double-way water injection steel pipe, 21-2-1, channel Ⅱ, 21-3, nut, 22, two-way conversion joint, 22-1, quick plug female head Ⅱ, 22-2, quick plug male head Ⅱ, 22-3, external thread Ⅱ, 22-4, connecting rod Ⅱ, 23, tunnel, 23-1, chute, 23-1-1, transport chute, 23-1-2, return air chute, 23-2, main tunnel, 23-3, weakening tunnel, 23-4, transport tunnel along the vein, 24, roof, 25, bottom plate, 26, working face, 27, coal seam, 28, Hard-interposed gangue, 29. Fault, 30. Dynamic pressure caused by roof fracture, 31. Coal pillar, 32. Stop mining line, 33. Ore discharge funnel, 34. Ground, 35. Aquifer, 36. Ore-bearing aquifer, 37. Sealing section.

Detailed ways

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

During the constant-displacement pump fracturing process, when the water pressure reaches the critical value of the water pressure for the formation of a dominant fracture surface, a single main crack will appear inside the rock formation under the control of the ground stress, and its direction is controlled by the ground stress. It is difficult to penetrate the layers and interlayers, the mechanical properties between layers vary greatly, and the transformation volume is limited. During the pulse hydraulic fracturing process, the pumping displacement is a high-frequency periodic fluctuation in the form of pulse waves, resulting in periodic changes in water pressure. A large number of randomly distributed micro cracks in the rock formation near the borehole do not form main cracks under the action of low cyclic loads, but instead suffer random fatigue damage. In addition, compared with slow quasi-static cyclic loading, the pulse fracturing cycle loading period is shorter (higher frequency), and pulse fracturing is a dynamic loading with collision energy input, resulting in the collision force during the collision between the fracturing fluid and the rock formation near the borehole further increasing the degree of random fatigue damage to the rock formation near the borehole. Combining the above two factors, when the fracture pressure of traditional constant-displacement fracturing statics is far from being reached, the fatigue impact of pulse fracturing gradually stimulates the micro cracks and micro voids inside the rock formation and then expands forward and penetrates each other. At the same time, the fracture network formed by pulse fracturing changes the local stress field, the interference between the fractures turns slowly, and the far-field stress is slowed down to control the fracture turning, forming a larger fracture network, thereby forming a dense fracture network near the borehole, overcoming the influence of the principal stress difference of the surrounding rock. Secondly, pulse pumping produces compressive shear fatigue, tensile fatigue and impact effects on the layer, breaking the layer and the gangue, and the crack network penetrates the layer, opening up a new way to solve the problem of "the gangue fracture energy is much higher than the layer" to inhibit crack penetration. Based on the above-mentioned characteristics of pulse fracturing, the present invention proposes a rock formation variable frequency pulse crack network fracturing method by changing the initial pulse pressure peak and pulse frequency to adapt to different strength rock layers. During the fracturing of each rock layer, the pulse pressure peak is gradually increased to form multiple annular crack network structures from near to far near the borehole, and finally superimposed into a large-scale crack network in sequence, thereby fully crushing a large range of rock mass. The specific technical means are as follows:

As shown in Figure 1, the rock formation is a non-homogeneous anisotropic material with a large number of micro cracks, micro holes and layers randomly distributed inside it; a large number of micro cracks will also be formed on the hole wall during the drilling process into the rock formation.

During the constant-displacement pump fracturing process, when the water pressure reaches the critical value of the water pressure for the formation of a dominant fracture surface, a single main crack will appear inside the rock formation under the control of the ground stress, and its direction is controlled by the ground stress. It is difficult to penetrate the layers and interlayers, the mechanical properties between layers vary greatly, and the transformation volume is limited.

As shown in Figure 2, during the pulse hydraulic fracturing process, the pumping rate is in the form of a pulse wave with a high frequency cycle. The fluctuation of the water pressure leads to periodic changes. A large number of randomly distributed micro cracks in the rock formation near the borehole do not form main cracks under the action of low cyclic loads, but suffer random fatigue damage. In addition, compared with slow quasi-static cyclic loading, pulse fracturing has a shorter cyclic loading period (higher frequency). Pulse fracturing is a dynamic loading with collision energy input, which leads to the collision force during the collision between the fracturing fluid and the rock formation near the borehole, which further increases the degree of random fatigue damage of the rock formation near the borehole. Combining the above two factors, when the fracture pressure of traditional constant-displacement fracturing statics is far from being reached, the fatigue impact of pulse fracturing gradually stimulates the micro cracks and micro voids inside the rock formation, which then expand forward and penetrate each other. At the same time, the fracture network formed by pulse fracturing changes the local stress field, the interference between the fractures turns slowly, and the far-field stress is slowed down to control the fracture turning, forming a larger fracture network, thereby forming a dense fracture network near the borehole, overcoming the influence of the principal stress difference of the surrounding rock. Secondly, pulse pumping produces compressive shear fatigue, tensile fatigue and impact effects on the layer, breaking the layer and penetrating the layer through the seam network, thus finding a new way to solve the problem of "the fracture energy of gangue is much higher than that of the layer" to inhibit crack penetration.

As shown in Figure 3, when the pulse pressure remains unchanged, after the pulse fracture network expands to a certain range, due to the loss of pressure along the fracture network, the fracture tip stress at the front of the fracture network cannot meet the damage condition of the rock formation, and the fracture network stops expanding. If the pulse pressure remains unchanged after the fracture network stops expanding, since the pressure at the hole wall is the highest, several new cracks will start to expand from the hole wall again, and the density of the fracture network will increase in sequence. In order to expand the fracture network radius, when the fracture network stops expanding, the peak value of the pulse pressure can be increased step by step so that the fracture tip stress at the front of the fracture network gradually meets the damage condition of the rock formation, thereby gradually expanding the fracture network radius until it meets the design requirements.

As shown in Figure 4, in addition to pulse fracturing each rock layer by step-by-step pressurization, constant displacement fracturing can also be performed on the basis of the pulse fracturing network. The tips of the dense fracture network will be reopened to form dense and multi-fracture expansion. The characteristics of pulse fracturing are that the fractures are numerous but not long, and the characteristics of constant displacement fracturing are that the fractures are long but not numerous. Combining the advantages of the two, a "pulse + constant displacement" fracture network fracturing method for composite coal seams is proposed, which breaks through the difficulties of principal stress difference, layer level, and interlayer performance difference, and produces a long-distance fracture network.

In order to solve the problem of single cracks and difficulty in penetrating layers formed by conventional fracturing, based on the above-mentioned pulse fracturing rock breaking principle, the present invention specifically proposes a variable frequency pulse fracture network fracturing method for rock formations. First, the initial pulse pressure of each rock layer is determined according to the physical and mechanical properties of each rock layer, and the pulse frequency of each rock layer is determined according to the collision force measurement experiment. Then, a fracturing hole is drilled on the rock layer to be fractured, and an observation hole is drilled at the edge of the designed fracture network expansion area. Finally, after fracturing for 5 minutes with the initial pulse pressure and pulse frequency of each rock layer, the pulse pressure is increased by 2MPa, and the pulse pressure is increased by 2MPa again after 5 minutes of fracturing, and so on until the fracturing fluid flows out of the observation hole and then stops fracturing; then, after fracturing for 5 to 10 minutes with the initial pulse pressure peak and pulse frequency corresponding to the second rock layer, the pulse pressure peak is increased by 2 to 5MPa, and the pulse pressure peak is increased by 2 to 5MPa after 5 to 10 minutes of fracturing, and so on until the fracturing of the second rock layer is completed; the same method is used until the fracturing of all rock layers is completed.

The determination method of pulse pressure and pulse amplitude: When the pulse pressure is less than the fatigue damage condition of the rock formation (tensile yield point When the pulse pressure is slightly greater than the fatigue damage condition of the rock formation, the rock formation undergoes a small plastic deformation, resulting in multiple random damages, which is conducive to the formation of a fracture network in the later stage. When the pulse pressure is much greater than the fatigue damage condition of the rock formation, the rock formation undergoes a large plastic deformation, forming a main crack, which is not conducive to the formation of a fracture network in the later stage. Therefore, before determining the initial pulse pressure, the physical and mechanical parameters of the rock formation should be tested by taking rock samples on site to obtain the tensile yield strength of the rock formation. The initial pulse pressure can be made slightly greater than the tensile yield strength. A small stress amplitude represents the development of microcracks, and a large stress amplitude represents the development of main cracks. Therefore, we control the initial pulse pressure to be slightly greater than the tensile yield strength to obtain a smaller stress amplitude.

Method for determining pulse frequency: Different pulse frequencies represent different speeds at which a certain mass of water is pumped into the sealing section rock formation in each cycle, resulting in different collision forces. In order to produce more cracks, the collision force should be slightly greater than the tensile yield strength of the rock formation. In the laboratory, the different collision forces generated by a certain mass of water pumped by a fracturing pump in one cycle colliding with the on-site rock samples at different frequencies are measured. The frequency corresponding to the collision force slightly higher than the tensile yield strength is selected as the pulse frequency.

As shown in Figures 5 to 8, in order to implement the rock formation pulse seam network fracturing method on site, the present invention proposes a rock formation pulse seam network fracturing equipment set, which includes a pumping mode and variable frequency fracturing pump and a matching water tank, a hydraulic fracturing measuring and controlling instrument, a mechanical rod delivery machine and its matching dual-way water injection steel pipe, and an automatic packer. The pumping mode and variable frequency fracturing pump are used to output pulse water to fractur e the rock formation, and provide a constant displacement water for the automatic packer to seal the hole; the hydraulic fracturing measuring and controlling instrument is used to monitor and record the pulse water pressure and flow rate during the fracturing process; the mechanical rod delivery machine is used to deliver the automatic packer to the drilling and fracturing area; and the automatic packer is used to seal the hole.

(1) Variable injection mode and frequency fracturing pump and supporting water tank

It includes a pumping mode and variable frequency fracturing pump and a matching water tank. The motor connected to the power end of the pumping mode and variable frequency fracturing pump is a variable frequency motor. The hydraulic end of the pumping mode and variable frequency fracturing pump consists of three plungers, one of which corresponds to the discharge channel and the inlet channel at the pump head, respectively, and a discharge stop valve and an inlet stop valve are set, and the working chamber corresponding to the plunger is provided with a channel connected to the outside world, and a water stop valve is set at this channel, and the water stop valve is connected to the water tank through a water hose. The high-pressure hose output by the pumping mode and variable frequency fracturing pump is divided into two ways by a three-way, one is used to input pulse water into the borehole to fractur the rock formation, which is called a fracturing hose, and the other is used to provide a constant displacement water for the automatic packer to seal the hole, which is called a sealing hose. The fracturing hose is sequentially pressed with a fracturing stop valve, a fracturing drain valve, and sensors (pressure sensor and flow sensor) of the measuring and control instrument. The sealing hose is sequentially pressed with a one-way valve, a pressure gauge, and a sealing drain valve.

(2) Hydraulic fracturing monitoring and control instrument

It includes the measuring and controlling instrument host and sensors (pressure sensor and flow sensor).

(3) Mechanical rod feeder and its matching dual-channel water injection steel pipe

It includes a mechanical rod feeder, a matching dual-way water injection steel pipe, and a dual-way conversion joint. The mechanical rod feeder consists of a cylinder, a tray, a leg connector, a leg, and a limit clamp. The tray is sleeved on the cylinder wall and can slide on the cylinder wall and is connected to the cylinder through a connecting rod and a connecting plate. The connecting rod can slide in the leg connector. The leg connector is connected to the four legs by a pin, and the legs can rotate around the pin on the side of the leg connector. The four legs are retractable legs. The limit clamp is located on the front of the leg connector and is used to fix the dual-way water injection steel pipe. The matching dual-way water injection steel pipe includes an external pulse steel pipe and an internal high-pressure steel pipe of equal length and coaxial sleeve. The external pulse steel pipe and the internal high-pressure steel pipe are connected by a connecting rod. The external pulse steel pipe has internal and external threads on both sides, and the internal high-pressure steel pipe has male and female quick plugs on both sides. A sealing ring is placed in the internal thread of the external pulse steel pipe to seal the high pressure at the connection of the two dual-way water injection steel pipes. The external pulse steel pipe has a limit ring on the side close to the internal thread to cooperate with the limit clamp on the mechanical rod feeder to fix the dual-way water injection steel pipe.

(4) Automatic Packer

It includes two expansion capsule hole sealers. The two expansion capsule hole sealers are connected by an outer tube with a channel double-way water injection steel pipe. The inside of the expansion capsule hole sealer is an inner tube with a channel double-way water injection steel pipe, and the outer side of the inner tube with a channel double-way water injection steel pipe is wrapped with a steel wire rubber sleeve, one end of the steel wire rubber sleeve is fixed to one end of the water injection steel pipe, and the other end of the steel wire rubber sleeve can slide on the water injection steel pipe (high pressure seal at the connection).

The operation method of rock formation variable frequency pulse network fracturing equipment is as follows:

Step 1: Place the mechanical rod feeder directly below the borehole to be fractured, and adjust the angle of the mechanical rod feeder by adjusting the four legs so that it is in a straight line with the borehole. Connect the two expansion capsule hole sealers of the automatic packer with a double-way water injection steel pipe with different number of outer pipes and channels, and send them into the hole position. Connect the lower end of the automatic packer to the double-way water injection steel pipe. By injecting high-pressure gas into the cylinder of the mechanical rod delivery machine, the tray is driven to slide upward on the outer wall of the cylinder, and then the automatic packer and the dual-way water injection steel pipe are lifted up 1m and then the gas injection is stopped; the automatic packer and the dual-way water injection steel pipe are fixed to the leg connector of the mechanical rod delivery machine through the limit clamp and the limit ring on the dual-way water injection steel pipe; the gas in the cylinder is discharged, so that the tray returns to the bottom of the cylinder under the action of gravity, and then a dual-way water injection steel pipe is connected to the dual-way water injection steel pipe at the limit clamp, and the cylinder is inflated again. When the tray contacts the lower end of the dual-way water injection steel pipe, the limit clamp is opened, and the automatic packer and the dual-way water injection steel pipe are lifted up 1m again. This process is repeated until the automatic packer is delivered to the drilling and fracturing area. Finally, the limit clamp is closed to fix the dual-way water injection steel pipe on the leg connector of the mechanical rod delivery machine, and the gas in the cylinder is discharged to return the tray to the bottom of the cylinder, and the dual-way conversion joint is connected to the end of the dual-way water injection steel pipe at the limit clamp.

Step 2: Install the variable pumping mode and frequency fracturing pump and the matching water tank, hydraulic fracturing monitoring instrument in sequence, and connect them to each other. Connect the ends of the fracturing hose and the sealing hose to the dual-way water injection steel pipe through a dual-way conversion joint.

Step 3: Close the fracturing stop valve, open the hydraulic fracturing control instrument, open the pumping mode and the variable frequency fracturing pump's inlet stop valve and discharge stop valve, close the pumping mode and the variable frequency fracturing pump's water stop valve, open the pumping mode and the variable frequency fracturing pump, so that its three pistons can work normally, input constant displacement water into the automatic packer to seal the hole, and close the pumping mode and the variable frequency fracturing pump when the water pressure on the pressure gauge on the sealing hose rises to 35MPa. A one-way valve is provided on the hose. After the pumping mode and the variable frequency fracturing pump are turned off, the water in the automatic hole sealer will not flow back, and the hole sealing is completed.

Step 4: Open the water shut-off valve of the pumping mode and variable frequency fracturing pump, close the liquid inlet shut-off valve and the liquid discharge shut-off valve of the pumping mode and variable frequency fracturing pump, open the fracturing shut-off valve, adjust the frequency of the variable frequency motor, start the pumping mode and the variable frequency fracturing pump, so that its two pistons work normally and one piston runs idle (the liquid inlet channel and liquid discharge channel of the working chamber corresponding to this piston are closed, so that this working chamber cannot supply liquid to the fracturing hose. This working chamber is directly connected to the water tank through the water hose, which ensures normal water absorption and drainage of this piston when it is idling, thereby ensuring lubrication), and input pulse water into the borehole in this mode.

The specific application of the present invention is as follows:

Example 1: Pulse fracturing to assist rock breaking in hard rock tunnel (tunnel) excavation

As shown in Figures 9 and 10, a coal mine has a full-rock tunnel with a design length of 1373.437m. The cross-section shape is a straight wall semicircular arch, and the support form is anchor mesh cable spraying. The tunnel is located in the fine sandstone layer with a hard texture, which seriously affects the tunneling speed.

As shown in Figures 9 and 10, in order to solve this problem, a long borehole can be constructed in the central position of the tunneling head along the tunneling direction and pulse fracturing can be performed. A dense crack network is pre-formed in the hard rock layer to be exposed in front of the tunneling head, and the rock layer is fully broken so that it can fall smoothly under the cutting or blasting of the subsequent tunneling machine, thereby increasing the tunneling speed. In order to ensure that the pulse cracks will not damage the top plate of the pre-excavated tunnel, it is necessary to strictly control the expansion range of the pulse crack network; the expansion range of the pulse crack network can be controlled by controlling the fracturing time. The fracturing time can be determined by field tests. Before the formal fracturing construction, a borehole is first drilled in the center of the tunneling head along the excavation direction, and an observation borehole parallel to and equal in length to the central borehole is drilled on the top plate, two sides and bottom plate of the tunnel, and a humidity sensor is arranged. The central long borehole is fractured and the change of humidity in each observation borehole with the fracturing time is recorded, so as to infer the time when the cracks extend to the surrounding rock of the pre-excavated tunnel; this time is used as the subsequent pulse fracturing time.

Example 2: Pulse fracturing control of the first caving of coal mining face

As shown in Figures 11 to 13, the average thickness of the coal seam mined in a coal mine is 10.5m; above the coal seam there are 4.6m thick mudstone layer, 8m thick siltstone layer, and 21m thick fine sandstone layer. The cross-sections of the two drifts of the working face are both rectangular cross-sections, and the support method is a combination of anchor rods, anchor cables, and metal mesh support. Both drifts are excavated along the bottom plate; the specifications of the air intake lane are: width × height = 5.6 × 4.2m ² , and the specifications of the return air lane are: width × height = 5.6 × 4.2m ^2. The roof of the wall-type coal mining working face during the periodic pressure can be simplified as a cantilever beam, and the roof during the initial pressure can be simplified as a beam with fixed supports at both ends, which causes the initial pressure step distance to be greater than the periodic pressure step distance. In addition, there are thick siltstone and fine sandstone layers above the coal seams. The sudden collapse of the roof can easily form a hurricane, causing the initial collapse step of the coal mining face to be too large, and will push a large amount of harmful gases such as gas in the goaf into the working face, posing a serious safety hazard.

As shown in Figures 11 to 13, in order to solve this problem, drill holes can be drilled into the hard top plate above the cut eye and the two slots. The holes are drilled and pulse fracturing is performed to form a dense network of fractures in the roof, which overcomes the shortcomings of conventional fracturing, that is, single fractures and fracture expansion is controlled by ground stress. The rock formation in this area is fully broken, and the roof is changed from a fixed support state at both ends to a cantilever beam state during the period from the start of mining to the first pressure, which can significantly shorten the initial roof release step. Because the fracture network density required for the initial roof release pulse fracturing control of the coal mining working face is relatively small, in addition to the method of using pulse fracturing throughout the process, the method of switching to a constant displacement pumping method for continued fracturing after fracturing for 5 minutes with the initial pulse pressure and pulse frequency can also be used. In order to minimize the initial roof release step, the opening position of the cut-eye drilling hole should be as close to the rear coal wall as possible; in order to fully weaken the end roof and anchor body, the opening position of the transportation chute drilling hole and the opening position of the return air chute drilling hole are at the center line of the chute roof.

Example 3: Pulse fracturing control at the top of the coal mining face

As shown in Figures 14 and 15, the average thickness of the coal seam mined in a coal mine is 10.5m; above the coal seam there are 4.6m thick mudstone layer, 8m thick siltstone layer, and 21m thick sandstone layer. The cross-sections of the two drifts of the working face are both rectangular, and the support method is a combination of anchor rods, anchor cables, and metal mesh support. Both drifts are excavated along the bottom plate; the specifications of the air intake lane are: width × height = 5.6 × 4.2m ² , and the specifications of the return air lane are: width × height = 5.6 × 4.2m ^2. During the mining process of the working face, a suspended roof with a strike of 15m and a dip of 7m appeared at the end of the run. During normal mining, the roof in the middle of the working face is generally easy to collapse, but due to the support of the coal pillar, the roof at the end is not easy to collapse.

As shown in Figures 14 and 15, in order to solve this problem, a borehole can be drilled at the end of the working face and pulse fracturing can be performed to form a dense crack network in the hard roof above the end of the working face, overcoming the shortcomings of conventional fracturing, where crack expansion is controlled by ground stress, and the rock formation in this area is fully broken. As the working face advances, the fractured roof above the end enters the goaf, and under the action of the mine pressure, the end roof can collapse in time. In order to fully weaken the end roof and anchor body, the opening position of the drill hole is at the center line of the slot roof. In order to make the end hanging roof collapse as soon as possible, the drill hole is tilted 70° toward the goaf.

Example 4: Pulse fracturing to assist rock breaking in coal mining face with too thick hard gangue and bottom pulling

As shown in Figures 16 to 18, the average thickness of the coal seam mined in a coal mine is 3.5m; the lower middle part of the coal seam contains 1.2m thick sandstone intercalated with gangue, which is relatively hard; at the end of mining, the coal seam below the gangue gradually becomes thinner and disappears, leaving only the coal seam above the gangue available for mining. The cross-sections of the two drifts of the working face are both rectangular, and the support method is a combination of anchor rods, anchor cables, and metal mesh support. Both drifts are excavated along the bottom plate; the specifications of the air intake lane are: width × height = 5.6 × 4.2m ² , and the specifications of the return air lane are: width × height = 5.6 × 4.2m ² . There is often one or more layers of interlayered gangue in the coal seam. When the thickness of the interlayered gangue is too large, the coal mining machine drum will not be able to cut it off. Generally, drilling and blasting are carried out in the working face to loosen the gangue, which seriously affects the efficiency of coal cutting. When the coal seam suddenly becomes thinner and the thickness of the coal seam is less than the minimum mining height of the coal mining machine, the method of pulling the bottom is generally adopted to continue advancing, that is, drilling and blasting are carried out in the working face to pre-crack the bottom plate.

As shown in Figures 16 to 18, to solve this problem, long boreholes can be constructed in the drift and pulse fracturing can be performed to form a dense crack network in the gangue or floor, fully crushing the gangue or floor so that it can be smoothly cut off by the subsequent coal mining machine. It overcomes the shortcoming that explosive blasting needs to be drilled and blasted in the working face, which affects normal mining. In order to crush the gangue and the bottom plate as much as possible, the drilling hole is located at the center line of the gangue or pre-cut bottom plate on the side wall of the chute working face, and the construction is carried out along the inclined direction of the gangue or bottom plate. The drilling hole is located on the side wall of the other chute working face of the working face, and the drilling spacing is controlled at about 5m.

Example 5: Pulse fracturing to assist rock breaking across faults in coal mining face

As shown in Figures 19 and 20, the average thickness of the coal seam mined in a coal mine is 3.5m; the direct bottom of the coal seam is a 7m thick siltstone layer with a relatively hard texture. There is a normal fault 115m away from the cutting eye, with a drop of 3 to 5m. The cross-sections of the two drifts of the working face are both rectangular, and the support method is a combination of anchor rods, anchor cables, and metal mesh support. Both drifts are excavated along the bottom plate; the specifications of the air intake lane are: width × height = 5.6 × 4.2m ² , and the specifications of the return air lane are: width × height = 5.6 × 4.2m ^2. When encountering faults during the mining of the coal mining face, blasting is often used to deal with them, which seriously affects the efficiency of coal cutting.

As shown in Figures 19 and 20, to solve this problem, long boreholes can be constructed in the drift and pulse fracturing can be performed to form a dense crack network in the fault, fully crushing the fault rock layer so that it can fall smoothly under the cutting of the subsequent coal mining machine. This overcomes the disadvantage that explosive blasting requires drilling and blasting in the working face, which affects normal mining. In order to crush the rock layer near the fault as much as possible, the drilling hole is located in the middle of the side wall of the drift working face, and is constructed along the inclined direction of the cutting eye. The location of the drilling hole is where the coal is seen through the fault, and the drilling hole spacing is controlled at about 5m.

Example 6: Pulse fracturing of surrounding rock in coal mining face to prevent rock burst

As shown in Figures 21 and 22, the average thickness of the coal seam mined in a certain mine is 6.5m; the average burial depth is 810m. At 56.2m above the coal seam, there is a 30.2m thick hard siltstone layer; below the coal seam, there is a 25.2m thick hard siltstone layer. The sections of the two drifts of the working face are both rectangular sections, and the support method is a combination of anchor rods, anchor cables, and metal mesh support. Both drifts are excavated along the bottom plate; the specifications of the air intake lane are: width × height = 5.6 × 4.2m ² , and the specifications of the return air lane are: width × height = 5.6 × 4.2m ^2. During the mining of the coal mining face, due to the large burial depth of the coal seam and the presence of thick hard rock layers on the top and bottom plates of the coal seam, the mining dynamic pressure will be transferred to the advance support section of the two drifts, which is easy to form rock burst.

As shown in Figures 21 and 22, to solve this problem, long boreholes can be constructed on the roof and side walls of the two drifts and pulse fracturing can be performed to fully break the surrounding rock of the drift support structure. The broken surrounding rock can prevent the dynamic pressure of the working face from being transmitted to the drift of this working face, reducing the impact risk of the advanced support section of the drift of this working face. In order to ensure the stability of the surrounding rock and support body of the weak structure internal tunnel, the borehole length is determined to be 40m, of which the range of 20m to 40m is set as the fracturing section.

Example 7: Pulse fracturing of the roof of the coal mining face to control large deformation of adjacent drifts

As shown in Figures 23 to 25, the average thickness of the coal seam mined in a certain mine is 2.7m, and there is a 14m thick fine sandstone layer 10m above the coal seam, which is relatively hard. The working face is designed to have a strike length of 3200m. When excavating the drift, ventilation is often difficult, so double tunnel excavation is adopted, resulting in one drift being affected by the dynamic pressure of two working face mining operations.

As shown in Figures 23 to 25, to solve this problem, the old roof above the coal pillar can be first subjected to multi-hole simultaneous pulse fracturing in the drift, forming a resonance effect in the surrounding rock near the holes, and the rock layer between the holes is broken first, and finally a broken zone is formed along the direction of the borehole connection, preventing the dynamic pressure of mining from being transmitted to the adjacent drift; then the suspended roof at the end of the working face is treated, and the rotation and sinking of the roof of the goaf is accelerated to avoid the formation of a suspended roof and reduce the transmission of stress in the goaf to the adjacent drift. The above two aspects can reduce the degree of influence of dynamic pressure and static pressure on the adjacent drift, and effectively control the deformation of the adjacent drift. In order to ensure the stability of the surrounding rock of the drift of this working face and the adjacent working face after fracturing, the opening position of the drill hole is at the top of the drift near the side wall of the coal pillar 0.2m, the position of the comprehensive drilling hole is the upper surface of the old roof just above 1/3 of the width of the coal pillar, and the drilling spacing is controlled at about 5m.

Example 8: Pulse fracturing stress transfer to protect the main mining tunnel in the coal mining face roof

As shown in Figures 26 and 27, the average thickness of the coal seam mined in a working face of a coal mine is 7.9m; the overlying roof of the coal seam is 13.5m of fine sandstone, 2.8m of mudstone, 3.5m of mudstone, and 10.2m of fine sandstone; the direct bottom of the coal seam is 25m of siltstone; the strike length of the working face is 1388m and the inclined width is 207m. At the end of the mining of the working face, the main roadway in the mining area was affected by mining and had a large deformation, which seriously affected the later use of the roadway.

As shown in Figures 26 and 27, to solve this problem, before the working face advances to the stop mining line, multiple holes can be simultaneously pulsed in the main tunnel of the mining area to form a resonance effect in the surrounding rock near the holes, and the rock layer between the holes is broken first, and finally a broken zone is formed along the direction of the borehole connection line, blocking the propagation path of the mining stress to the main tunnel of the disk area; then, when the working face is mined to the stop mining line, the hard roof above the coal seam is fractured at the stop mining line of the working face to avoid the formation of a cantilever beam structure on the side of the goaf of the stop mining line, thereby blocking the high stress in the goaf from propagating to the main tunnel of the system, and further reducing the deformation and damage degree of the main tunnel of the mining area. In order to ensure that the pulse cracks after fracturing will not destroy the stability of the surrounding rock of the main tunnel, the position of the drill hole that cuts off the dynamic pressure should be more than 30m away from each main tunnel in the horizontal direction, but cannot exceed the stop mining line.

Example 9: Pulse fracturing weakening of hard ore in natural caving working face at metal mine stage

As shown in Figure 28, a copper mine uses a staged natural caving method to recover ore, with a stage height of 70m and an ore body thickness of 30m. The ore is relatively hard and not easy to collapse, which seriously affects the ore recovery rate.

As shown in Figure 28, to solve this problem, long boreholes can be constructed in the weakened tunnel and pulse fracturing can be performed to form a dense crack network inside the ore, fully crushing the ore so that the ore can fall smoothly in the subsequent ore-feeding process. The ore-feeding efficiency is improved. In order to fully crush the ore, the drilling spacing is controlled within the range of 4-8m.

Example 10: Initial and periodic pulse fracturing control of a metal mine single-layer caving mining face

As shown in Figures 29 and 30, a certain iron ore seam has a strike length of 8600m, a thickness of 1.5m, and a dip angle of 25° to 35°. The long-arm caving method is used to recover ore. The old top of the ore seam is relatively hard, resulting in a large step distance of the old top collapse, which not only threatens safe production, but also greatly affects labor productivity, pillar consumption and recovery costs.

As shown in Figures 29 and 30, in order to solve this problem, a transport tunnel along the vein can be cut at the stage just below the uphill section of the working face. Fan-shaped holes are drilled inside and pulse fracturing is performed to weaken the hard old roof above the mining face, which can effectively shorten the collapse step of the old roof and reduce the impact risk caused by the collapse of the old roof. In order to fully break the old roof, the fan-shaped end hole spacing is 5m and covers the entire upper roof of the working face.

Example 11: Pulse fracturing to increase permeability of low permeability sandstone uranium deposits

As shown in Figure 31, the thickness of a uranium mine is 6m, the inclination is 1° to 5°, and it is mined by in situ leaching uranium technology. In situ leaching uranium is an advanced process technology for efficient mining of sandstone uranium mines. The basic principle of in situ leaching uranium is to inject in situ leaching liquid through the injection hole through the drilling hole (well) to fully react with uranium, and then extract it from the ground through the extraction hole, and extract uranium on the surface. Based on the technical characteristics of in situ leaching uranium, the permeability of the uranium-bearing aquifer is a key factor affecting in situ leaching uranium. The low permeability of the ore-bearing aquifer of this mine leads to a small injection volume, low production capacity and small ore control area of a single well during in situ leaching development of the ore deposit. Under the existing technical conditions, it is necessary to increase the well network for mining, resulting in high cost and low efficiency of uranium mining.

As shown in Figure 31, to solve this problem, pulse fracturing can be performed in the injection hole to form a dense fracture network near the injection hole, thereby increasing the permeability of the uranium-bearing aquifer, thereby improving the mining efficiency of the uranium mine. In-situ leaching of uranium mines, the integrity of the upper and lower roof and floor plates of the ore-bearing aquifer must be ensured, otherwise the water level of the ore-bearing aquifer will continue to drop, making it impossible to mine the uranium mine. In order to ensure that the pulse cracks do not damage the top and bottom plates of the ore-bearing aquifer, it is necessary to strictly control the expansion range of the pulse fracture network. To this end, when designing fracturing drilling holes, the hole spacing of the fracturing drilling holes should be slightly less than 2 times the distance from the sealing section to the upper and lower roof and floor plates, so that when the cracks in the two boreholes are connected, the cracks have not yet expanded to the roof and floor plates. In addition, the fracturing time needs to be accurately controlled. The fracturing time can be determined through field tests. Before the formal fracturing construction, an observation borehole parallel to and of the same length as the fracturing borehole is drilled between the two fracturing boreholes and a humidity sensor is arranged. One of the fracturing boreholes on both sides of the fracturing observation hole observes and records the change of borehole humidity with fracturing time, so as to infer the time when the crack extends to the observation borehole; this time is used as the subsequent pulse fracturing time.

Claims

A rock formation variable frequency pulse fracture network fracturing method, characterized in that it comprises the following steps:

S1. Adapt to different strength rock layers by changing the initial pulse pressure peak and pulse frequency; determine the initial pulse pressure peak of each rock layer according to the physical and mechanical properties and confining pressure of each rock layer, and the initial pulse pressure peak is less than the fracture pressure of the rock during constant displacement fracturing; determine the pulse frequency of each rock layer according to the collision force measurement experiment of each rock layer;

S2. Design a variable frequency pulse fracture network fracturing pumping scheme. After fracturing for 5 to 10 minutes with the initial pulse pressure peak and pulse frequency corresponding to the first rock layer, the pulse pressure peak is increased by 2 to 5 MPa. After fracturing for 5 to 10 minutes, the pulse pressure peak is increased by 2 to 5 MPa again, and so on until the fracturing of the first rock layer is completed; then, after fracturing for 5 to 10 minutes with the initial pulse pressure peak and pulse frequency corresponding to the second rock layer, the pulse pressure peak is increased by 2 to 5 MPa. After fracturing for 5 to 10 minutes, the pulse pressure peak is increased by 2 to 5 MPa again, and so on until the fracturing of the second rock layer is completed; the same method is used until the fracturing of all rock layers is completed; during the fracturing of each rock layer, the pulse pressure peak is gradually increased to form multiple annular fracture network structures from near to far near the borehole, and finally superimposed into a large-scale fracture network in sequence, thereby fully crushing a large range of rock mass;

S3. Design the rock formation variable frequency pulse network fracturing drilling arrangement plan according to different working conditions;

S4. According to the rock formation variable frequency pulse fracture network fracturing drilling arrangement plan, fracturing holes are drilled in the rock formation to be fractured, and observation holes are drilled at the edge of the designed fracture network expansion area;

S5. Fracturing is performed according to the rock formation variable frequency pulse fracture network fracturing pumping scheme, and the pumping displacement is controlled to perform high-frequency periodic fluctuations in the form of pulse waves, resulting in periodic changes in water pressure. A large number of randomly distributed micro cracks in the rock formation near the borehole undergo random fatigue damage under the action of a lower pulse cycle load, overcoming the influence of the principal stress difference of the surrounding rock and forming a dense fracture network near the borehole;

S6. Stop fracturing after fracturing fluid flows out of the observation hole;

The method for determining the peak value of the initial pulse pressure is as follows: by taking rock samples on site and testing the confining pressure, the physical and mechanical parameters of the rock formation are tested, thereby obtaining the triaxial tensile yield strength of the rock formation. The peak value of the initial pulse pressure is the triaxial tensile yield strength of the rock. The method for determining the pulse frequency is as follows: in the laboratory, different collision forces generated by a certain mass of water pumped by a fracturing pump in one cycle colliding with the on-site rock samples at different frequencies are measured, and the frequency corresponding to the tensile yield strength is selected as the pulse frequency.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that step S2 adopts a variable frequency pulse + constant displacement network fracturing method, and after fracturing for a period of time with an initial pulse pressure and pulse frequency to form a pulse fracture network, a constant displacement pumping method is used to continue fracturing, so that the tips of the dense pulse fracture network are reopened to form dense multiple fracture extensions; at the same time, the fracture network formed by pulse fracturing changes the local stress field, the interference between the fractures turns slowly, and the far field stress is slowed down to control the fracture turning, forming a larger fracture network.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that the fracturing The fractured rock layer is the hard rock layer that is about to be exposed in front of the tunneling head. During the excavation of the hard rock tunnel, a central long borehole is constructed at the central position of the tunneling head along the excavation direction and pulse fracturing is carried out. A dense crack network is pre-formed in the hard rock layer that is about to be exposed in front of the tunneling head, and the rock layer is fully broken so that it can fall smoothly under the cutting of the subsequent tunneling machine or under the action of blasting, thereby increasing the excavation speed; before the formal fracturing construction, a central long borehole is firstly drilled in the center of the tunneling head along the excavation direction, and an observation borehole parallel to and of the same length as the central long borehole is drilled on the top plate, two sides and bottom plate of the tunnel, and humidity sensors are arranged. The central long borehole is fractured and the changes in humidity of each observation borehole with fracturing time are recorded, so as to infer the time when the cracks extend to the surrounding rock of the pre-excavated tunnel, and this time is used as the subsequent pulse fracturing time.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that the rock formation to be fractured in step S4 is the hard roof above the coal seam during the initial roof caving of the coal mining face. During the initial roof caving of the coal mining face, holes are drilled in the hard roof above the cutting eye and the two chute and pulse fracturing is performed to form a dense crack network in the roof. The opening position of the cutting eye drilling hole is close to the rear coal wall; the opening position of the transport chute drilling hole and the return air chute drilling hole are at the centerline position of the chute roof.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that the rock formation to be fractured in step S4 is the hard roof above the two ends of the coal mining working face during the period when the end of the coal mining working face is suspended. During the period when the end of the coal mining working face is suspended, a borehole is drilled at the end of the working face and pulse fracturing is performed to form a dense crack network in the hard roof above the end of the working face, fully breaking the rock formation in this area, and the opening position of the borehole drilled at the end of the working face is at the center line position of the longitudinal groove roof, the borehole inclination angle is 70°, and the drilling direction is inclined toward the goaf.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that the rock formation to be fractured in step S4 is thick and hard interlayer gangue and thick and hard bottom plate within the mining height range during the period of excessively thick and hard interlayer gangue and bottom pulling of the coal mining working face. During the period of excessively thick and hard interlayer gangue and bottom pulling of the coal mining working face, long boreholes are constructed in the drift and pulse fracturing is performed to form a dense crack network in the interlayer gangue or bottom plate, and the gangue or bottom plate is fully broken so that the gangue or bottom plate can fall smoothly under the subsequent cutting of the coal mining machine; the opening position of the long borehole constructed in the drift is at the midline position of the interlayer gangue of the side wall of the drift working face or the pre-cut bottom plate, and the drilling is carried out along the inclined direction of the interlayer gangue or bottom plate, and the position of the drill hole falls on the side wall of the other drift working face of the working face, and the drilling hole spacing is controlled to be 4m to 5m.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that the rock formation to be fractured in step S4 is a hard rock formation near the fault during the period when the coal mining working face passes the fault, and during the period when the coal mining working face passes the fault, a long borehole is constructed in the drift and pulse fracturing is performed to form a dense crack network in the fault, fully crush the fault rock formation, so that the fault rock formation can fall smoothly under the subsequent cutting of the coal mining machine; the opening position of the long borehole constructed in the drift is in the middle position of the side wall of the drift working face, and is constructed along the inclined direction of the cutting eye. The position of the drilling hole passes through the fault where the coal is seen, and the drilling hole spacing is controlled at 4m to 5m.
The rock formation variable frequency pulse seam fracturing method according to claim 1 is characterized in that the rock formation to be fractured described in step S4 is a hard rock formation above the coal seam mined by the coal mining face during the prevention and control of rock burst by the coal mining face, and long boreholes are constructed on the roofs and side walls of the two chute of the coal mining face and pulse fracturing is performed to fully crush the peripheral rock of the chute support structure, and the crushed surrounding rock is used to prevent the dynamic pressure of the working face from being transmitted to the chute of the working face, thereby reducing the impact risk of the advance support section of the chute of the working face; the length of the long borehole constructed on the roofs and side walls of the two chute of the coal mining face is 40m, of which the range of 20m to 40m is defined as the fracturing section.
The rock formation variable frequency pulse seam network fracturing method according to claim 1 is characterized in that the rock formation to be fractured described in step S4 is a hard rock formation above the tunnel during double tunnel excavation, and in the drift of double tunnel excavation, the old roof above the coal pillar is first subjected to multi-hole simultaneous pulse fracturing, a resonance effect is formed in the surrounding rock near the holes, the rock formation between the holes is preferentially broken, and finally a broken zone is formed along the direction of the borehole connection line, preventing the dynamic pressure of mining from being transmitted to the adjacent drift; then the hanging roof at the end of the working face is processed, the rotation and sinking of the roof of the goaf is accelerated, the formation of a hanging roof is avoided, and the stress of the goaf is reduced. The transmission to the adjacent drift; the opening position of the old roof drill hole above the coal pillar is at the roof of the drift close to the side wall of the coal pillar 0.2m, the position of the comprehensive drilling hole is the upper surface of the old roof just above 1/3 of the width of the coal pillar, and the drilling spacing is controlled at 4m to 5m.
The rock formation variable frequency pulse seam network fracturing method according to claim 1 is characterized in that the rock formation to be fractured in step S4 is a hard rock formation above the protective coal pillar in the main lane at the end of the mining face recovery. At the end of the mining face recovery, first, before the working face advances to the stop mining line, multi-hole simultaneous pulse fracturing is performed in the main lane of the mining area to form a resonance effect in the surrounding rock near the holes, and the rock formation between the holes is preferentially broken, and finally a broken zone is formed along the direction of the borehole connection line, thereby blocking the propagation path of the mining stress to the main lane of the disk area; then, when the working face is recovered to the stop mining line, the hard roof above the coal seam is fractured at the stop mining line of the working face to avoid the formation of a cantilever beam structure on the goaf side of the stop mining line, thereby blocking the high stress in the goaf from propagating to the main lane of the system, and further reducing the deformation and damage degree of the main lane of the mining area; the position of the drill hole for cutting off the dynamic pressure should be more than 30m away from each main lane in the horizontal direction and not exceed the stop mining line.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that the rock formation to be fractured in step S4 is a metal ore mined by the staged natural caving method. In the project of mining metal ore by the staged natural caving method, a long borehole is constructed in the weakened tunnel and pulse fracturing is performed to form a dense crack network inside the ore, fully crush the ore, and enable the ore to fall smoothly in the subsequent mining process; the borehole spacing is controlled within the range of 4-8m.
The rock formation variable frequency pulse network fracturing method according to claim 1 is characterized in that the rock formation to be fractured in step S4 is a metal ore mined by a single-layer caving method. In the project of mining metal ore by a single-layer caving method, fan-shaped drill holes are drilled in the vein transport tunnel just below the working face when cutting up the mountain, and pulse fracturing is performed to weaken the hard old roof above the mining face. The fan-shaped terminal hole spacing is 5m, and covers the entire upper roof of the working face.
The rock formation variable frequency pulse network fracturing method according to claim 1, characterized in that the desired The rock formation to be fractured is a low-permeability uranium-bearing aquifer. When the low permeability of the aquifer leads to high cost and low efficiency in uranium mining, pulse fracturing is performed in the injection hole to form a dense fracture network near the injection hole, thereby increasing the permeability of the uranium-bearing aquifer and improving the mining efficiency of the uranium ore. When designing the fracturing boreholes, the hole spacing of the fracturing boreholes is equal to twice the distance from the sealing section to the upper and lower top and bottom plates, so that when the cracks in the two boreholes are connected, the cracks have not yet expanded to the top and bottom plates. In addition, the fracturing time needs to be accurately controlled, and the fracturing time is determined through field tests. Before the formal fracturing construction, an observation borehole parallel to and of the same length as the fracturing borehole is drilled in the middle of the two fracturing boreholes and a humidity sensor is arranged. One of the fracturing boreholes on both sides of the fracturing observation hole observes and records the changes in the borehole humidity with the fracturing time, thereby inferring the time when the cracks extend to the observation borehole; this time is used as the subsequent pulse fracturing time.
A rock formation variable frequency pulse network fracturing equipment, characterized by comprising:

A pumping mode and variable frequency fracturing pump is used to output pulse water to fractur e rock formations and provide a constant displacement water for an automatic packer to seal holes. The motor connected to the power end of the pumping mode and variable frequency fracturing pump is a variable frequency motor. The hydraulic end of the pumping mode and variable frequency fracturing pump consists of three plungers, one of which corresponds to a discharge channel and a liquid inlet channel at a pump head, respectively, and a discharge stop valve and a liquid inlet stop valve are arranged. The working chamber corresponding to the plunger is provided with a channel connected to the outside world, and a water stop valve is arranged at the channel, and the water stop valve is connected to the water tank through a water hose.

The high-pressure hose output by the variable-frequency fracturing pump is divided into two paths by a tee. One path is used to input pulse water into the borehole to fractur e the rock formation, which is called the fracturing hose. The other path provides constant-displacement water for the automatic packer to seal the hole, which is called the sealing hose.

The fracturing hose is provided with a fracturing stop valve, a fracturing drain valve, a pressure sensor and a flow sensor in sequence along the water flow direction; the sealing hose is provided with a one-way valve, a pressure gauge and a sealing drain valve in sequence along the water flow direction;

A hydraulic fracturing monitoring and control instrument, connected to the pressure sensor and flow sensor signals, for monitoring and recording the pulse water pressure and flow during the fracturing process;

The automatic packer comprises two expansion capsule hole sealers, which are connected through a first dual-way water injection steel pipe with an outer pipe channel, and the interior of the expansion capsule hole sealer is a second dual-way water injection steel pipe with an inner pipe channel, and the outer side of the second dual-way water injection steel pipe with an inner pipe channel is wrapped with a steel wire rubber sleeve, one end of the steel wire rubber sleeve is fixed to one end of the second dual-way water injection steel pipe with an inner pipe channel, and the other end of the steel wire rubber sleeve can slide on the second dual-way water injection steel pipe with an inner pipe channel, and the connection is high-pressure sealed;

A mechanical rod delivery machine, used to deliver the automatic packer to the drilling and fracturing area, comprising:

cylinder;

A tray is sleeved on the cylinder wall and can slide on the cylinder wall;

A leg connecting piece is fixedly connected to the top of the cylinder wall of the cylinder, the leg connecting piece is connected to the leg via a latch, and the leg can rotate around the latch on the side of the leg connecting piece;

A connecting rod, one end of which is connected to the tray, and the other end of which passes through the leg connecting piece and is connected to a connecting plate, wherein the connecting plate is fixedly connected to the end of the cylinder piston rod;

A third dual-way water injection steel pipe has one end fixedly connected to the support leg connector and the other end provided with a connection to the second dual-way water injection steel pipe on the automatic packer.
The rock formation variable frequency pulse network fracturing equipment according to claim 14 is characterized in that:

The third dual-way water injection steel pipe is fixedly connected to the support leg connector through a limit clamp, and the dual-way water injection steel pipe includes an external pulse steel pipe and an internal high-pressure steel pipe of equal length and coaxial sleeve connection, and the external pulse steel pipe and the internal high-pressure steel pipe are connected by a connecting rod, and the external pulse steel pipe has internal and external threads on both sides, and the internal high-pressure steel pipe has male and female quick plugs on both sides;

A sealing ring is placed in the inner thread of the external pulse steel pipe to provide high pressure sealing at the connection between the two dual-path water injection steel pipes;

The outer pulse steel pipe has a limit ring on one side close to the internal thread, which is used to cooperate with the limit clamp to fix the dual-path water injection steel pipe;

A two-way conversion joint, the outside of which is threadedly connected to one end of the external pulse steel pipe, and the inside of which is quickly connected to one end of the internal high-pressure steel pipe.
The rock formation variable frequency pulse network fracturing equipment according to claim 14 is characterized in that:

The supporting legs are retractable supporting legs.
The method for operating the rock formation variable frequency pulse network fracturing equipment according to any one of claims 14 to 16 is characterized in that it comprises the following steps:

Step 1: Place the mechanical rod feeder directly below the borehole to be fracturing, and adjust the angle of the mechanical rod feeder by adjusting the legs so that it is in a straight line with the borehole; connect the two expansion capsule sealers of the automatic packer with an outer pipe with a channel double-way water injection steel pipe, and send them into the hole position;

First, one end of the first third dual-way water injection steel pipe is installed on the leg connector of the mechanical rod feeder, and the other end is connected to the lower end of the second dual-way water injection steel pipe on the automatic packer. By injecting high-pressure gas into the cylinder of the mechanical rod feeder, the tray is driven to slide upward on the outer wall of the cylinder, and then the automatic packer and the first third dual-way water injection steel pipe are lifted upward for a distance S1 and then the gas injection is stopped; the automatic packer and the first third dual-way water injection steel pipe are fixed to the leg connector of the mechanical rod feeder by a limit clamp to prevent the automatic packer and the first third dual-way water injection steel pipe from sliding down under the action of their own weight The gas in the cylinder is discharged, and the tray returns to the bottom of the cylinder under the action of gravity. Then the second third dual-way water injection steel pipe is connected to the third dual-way water injection steel pipe at the limit clamp, and the cylinder is inflated again. When the tray contacts the lower end of the second third dual-way water injection steel pipe, the limit clamp is opened, and the second third dual-way water injection steel pipe, the first third dual-way water injection steel pipe and the automatic packer are lifted up again by a distance S1, and this process is repeated until the automatic packer is delivered to the drilling and fracturing area; finally, the limit clamp is closed, and the last third dual-way water injection steel pipe is fixed on the leg connector of the mechanical rod feeder, and the tray is discharged. Expel the gas in the cylinder to return the tray to the bottom of the cylinder, and connect the two-way conversion joint to the end of the third two-way water injection steel pipe at the limit clamp;

The second step: install the pumping mode and variable frequency fracturing pump and the supporting water tank, hydraulic fracturing monitoring and control instrument in sequence, and connect them to each other, connect the ends of the fracturing hose and the sealing hose to the third two-way water injection steel pipe at the limit clamp through a two-way conversion joint; the third step: close the fracturing stop valve, open the hydraulic fracturing monitoring and control instrument, open the liquid inlet stop valve and the liquid discharge stop valve of the pumping mode and variable frequency fracturing pump, close the water through stop valve of the pumping mode and variable frequency fracturing pump, open the pumping mode and variable frequency fracturing pump, so that its three pistons can work normally, input constant displacement water into the automatic packer for sealing, and close the pumping mode and variable frequency fracturing pump when the water pressure of the pressure gauge on the sealing hose rises to 35MPa. Since a one-way valve is provided on the sealing hose, the water in the automatic sealer will not flow back after the pumping mode and variable frequency fracturing pump are closed, and the sealing is completed;

Step 4: Open the water shut-off valve of the pumping mode and variable frequency fracturing pump, close the liquid inlet shut-off valve and the liquid discharge shut-off valve of the pumping mode and variable frequency fracturing pump, open the fracturing shut-off valve, start the pumping mode and variable frequency fracturing pump, make its two pistons work normally, and one piston idle, the liquid inlet channel and the liquid discharge channel of the working chamber corresponding to the idle piston are closed, and the working chamber corresponding to the idle piston cannot supply liquid to the fracturing hose, and the working chamber corresponding to the idle piston is directly connected to the water tank through the water hose, which ensures normal water absorption and drainage of this piston when idling, thereby ensuring lubrication, and input pulse water into the borehole in this mode.