A control method for roof fall of a roadway in a jointed coal seam under deep high stress

Abstract

The application provides a control method for spalling of a jointed coal seam roadway under deep high stress, which comprises the following steps: before roadway excavation, a drilling site chamber is arranged at the side of a coal roadway, drilling is performed in the axial direction of the coal roadway towards the inside of the surrounding rock of the roadway in the drilling site chamber, a plurality of fracturing water injection sections are divided in the extension direction of the drilling, fracturing equipment is pushed to the fracturing water injection sections, and the fracturing equipment is used to perform fracturing water injection in a retreating type sectional fracturing water injection mode, so as to form a water injection bonding layer in the circumferential coal body of the drilling, after the coal roadway is excavated, the water injection bonding layer can prevent spalling, in the extension direction of the drilling, the drilling is broken and collapsed under the action of high stress of the surrounding rock of the roadway, and a collapsed section is gradually formed, and the collapsed section is used to realize pressure relief. The control method for spalling of a jointed coal seam roadway under deep high stress can improve the stability of the coal wall of the roadway, reduces the construction cost, and improves the roadway excavation speed.

Description

Technical Field

[0001] This invention belongs to the field of coal mine roadway surrounding rock safety control technology, specifically, it relates to a method for controlling spalling in deep, high-stress jointed coal seam roadways. Background Technology

[0002] As mining depths increase, controlling the surrounding rock stability of jointed coal seam roadways remains a significant challenge for underground safety. Deep coal seams are susceptible to accidents such as sidewall collapse and spalling due to high stress, geological fracture zones, joint structures, and the impact of the advancing mining face. Especially in mining seams with well-developed longitudinal joints and fractures, even with high compressive strength, the complex dynamic and static stress caused by frequent impact energy disturbances during roadway excavation and the pressure from the advanced support of the mining face leads to the fracturing of shallow coal seams, resulting in spalling. This results in uneven roadways after excavation, making them difficult to shape, causing loss of pre-tension force in the sidewall support anchors (cables), deformation of the anchor mesh blocks, significantly reduced support effectiveness, frequent roadway repairs, and greatly increased support and maintenance costs.

[0003] In related technologies, drilling pressure-relief boreholes deep into the sides of roadways can effectively alleviate the high-stress environment of the surrounding rock. Simultaneously, combined with hydraulic fracturing and proper coal seam water injection, it can improve the coal's cohesion and shear strength, reduce compressive strength and brittleness, and thus help alleviate coal wall pressure and improve coal wall stability. However, in coal seams with obvious joints and fractures, blindly drilling pressure-relief boreholes and hydraulic fracturing, under high stress, can actually exacerbate the damage to the shallow coal seam in the sidewalls. In practice, the sidewall spalling phenomenon has not been improved, and the control effect is counterproductive. Furthermore, the large number of boreholes designed leads to long drilling and hydraulic fracturing construction cycles and frequent equipment relocations. These factors severely restrict the roadway excavation speed and affect underground safety and production efficiency. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a method for controlling spalling in deep, high-stress jointed coal seam roadways. This method can improve the stability of the coal wall in the roadway, reduce construction costs, and increase the roadway excavation speed.

[0006] A method for controlling spalling in deep, high-stress jointed coal seam roadways according to an embodiment of the present invention includes the following steps:

[0007] S1. Before tunnel excavation, a drilling chamber is set up on the side of the coal roadway, and drilling is carried out in the drilling chamber along the axial direction of the coal roadway toward the interior of the surrounding rock.

[0008] S2. Divide the borehole into multiple fracturing and water injection sections along its extension direction;

[0009] S3. Push the fracturing equipment into the fracturing and water injection section, and carry out fracturing and water injection in a backward segmented fracturing and water injection manner to form a water injection bonding layer in the circumferential coal body of the borehole.

[0010] S4. In the extension direction of the borehole, the borehole is broken and collapsed under the high stress of the surrounding rock of the roadway, and gradually forms a collapsed section, which is used to achieve the pressure relief function.

[0011] The method for controlling coal wall spalling in deep, high-stress jointed coal seam roadways according to embodiments of the present invention involves segmented hydraulic fracturing and water injection within boreholes along the roadway's strike. This allows for the creation of fissures around the boreholes, diffusing water into the jointed coal seam, increasing coal body cohesion and shear strength, enhancing coal body plasticity, and improving roadway coal wall stability, thereby controlling coal wall spalling. Furthermore, strike-oriented boreholes drilled in the deep coal seam of the roadway sidewalls can, without damaging the shallow surrounding rock, transfer the high stress concentration in the shallow surrounding rock to the deeper layers after borehole collapse, achieving the purpose of relieving pressure on the surrounding rock in deep coal roadways. Compared to traditional vertical coal wall drilling, by arranging drilling rigs and other equipment in the initial drilling chamber of the roadway, strike-oriented borehole drilling and hydraulic fracturing can be carried out ahead of or parallel to roadway excavation. This significantly reduces the number of construction and equipment relocations, minimizes the impact on roadway excavation and support construction, lowers construction costs, and increases roadway excavation speed.

[0012] In some embodiments, in step S1, there are multiple drilling chambers, which are spaced apart and arranged on both sides of the coal roadway, and each drilling chamber corresponds to at least one borehole.

[0013] In some embodiments, the borehole diameter is greater than or equal to 120 mm, and the length of the borehole is adapted to the length of the coal roadway.

[0014] In some embodiments, in step S2, the distance between two adjacent fracturing water injection sections is equal.

[0015] In some embodiments, the distance between the borehole and the sidewall of the coal roadway is greater than or equal to 4 meters.

[0016] In some embodiments, the distance between the fracturing water injection sections is greater than or equal to 10 meters, and the distance between two adjacent fracturing water injection sections is greater than or equal to 30 meters and less than or equal to 35 meters.

[0017] In some embodiments, in step S3, the fracturing equipment includes a dual-seal fracturing water injection device, wherein the fracturing water injection device uses a permeability enhancer.

[0018] In some embodiments, the dual-seal fracturing water injection device has a balanced pressure relief channel that connects the sealing cavity of the upper packer and the sealing cavity of the lower packer of the dual-seal fracturing water injection device.

[0019] In some embodiments, the fracturing equipment further includes a water supply component and a water injection hose, with a first end of the water injection hose connected to the water supply component and a second end of the water injection hose connected to the inlet of the double-sealed fracturing water injector.

[0020] In some embodiments, step S3 further includes, during a single fracturing water injection, the fracturing initiation pressure is greater than or equal to 18 MPa, and the drainage volume is greater than or equal to 40 m³ / h. 3 / h. Attached Figure Description

[0021] Figure 1 This is a horizontal plane schematic diagram of the implementation of the control method for jointed coal seam roadway under deep high stress according to an embodiment of the present invention.

[0022] Figure 2 This is the first construction drawing for implementing retreating segmented fracturing and water injection in the control method for jointed coal seam roadways under deep high stress according to an embodiment of the present invention.

[0023] Figure 3 This is the second construction drawing for implementing retreating segmented fracturing and water injection in the control method for jointed coal seam roadways under deep high stress according to an embodiment of the present invention.

[0024] Figure 4 This is a diagram showing the division of the water-injected bonding layer and the collapsed section in the control method for jointed coal seam roadways under deep high stress according to an embodiment of the present invention.

[0025] Figure label:

[0026] 1. Coal roadway,

[0027] 2. Drilling chamber, 21. Borehole,

[0028] 3. Fracturing and water injection section,

[0029] 4. Water-injected bonding layer,

[0030] 5. Collapsed section,

[0031] 6. Fracturing equipment; 61. Water injection hose. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0033] like Figures 1-4 As shown, the method for controlling spalling in deep, high-stress jointed coal seam roadways according to an embodiment of the present invention includes the following steps:

[0034] S1. Before tunnel excavation, a drilling chamber 2 is installed on the sidewall of coal roadway 1. Inside the drilling chamber 2, along the axial direction of coal roadway 1 (e.g., ... Figure 1 Drilling is performed in the direction of left and right towards the interior of the surrounding rock of the roadway. Understandably, when selecting a suitable location on the side of coal roadway 1 to set up the drilling chamber 2, a location with relatively stable surrounding rock is usually chosen. Drilling rigs are used to drill holes 21 along the axial direction of coal roadway 1. The depth and diameter of the holes 21 are determined based on the specific conditions of the coal seam and the design requirements of the roadway.

[0035] In other words, by setting up a drilling chamber 2 in the rib area, fracturing and water injection operations can be effectively carried out inside the coal seam without affecting the normal use of the roadway. The drilling operation of borehole 21 can be adjusted according to the joint and fracture conditions of the coal seam to improve the fracturing and water injection effect. S2, Divide the borehole 21 into multiple fracturing and water injection sections 3 along its extension direction. For example... Figures 1-4 As shown, it can be understood that, based on the internal conditions of borehole 21 and the requirements for fracturing and water injection, borehole 21 is divided into multiple water injection sections. Different fracturing parameters can be set for each water injection section to adapt to the coal body characteristics of different areas.

[0036] Furthermore, staged fracturing and water injection allows for more precise control of water volume and pressure, avoiding coal seam damage caused by blindly drilling pressure relief boreholes 21. Of course, fracturing parameters can also be adjusted according to the coal seam characteristics of different areas to improve fracturing effectiveness.

[0037] S3. Push the fracturing equipment 6 into the fracturing and water injection section 3, and perform fracturing and water injection using a retreating segmented fracturing and water injection method to form a water-injected bonding layer 4 in the circumferential coal body of borehole 21. Figure 2 and Figure 3 As shown, it can be understood that the retreating segmented fracturing and water injection construction method involves first sending the fracturing equipment 6 to the end of borehole 21 for the first stage of fracturing and water injection. After the first stage of fracturing and water injection is completed, the fracturing equipment 6 is moved to the second stage of fracturing and water injection. This process is repeated until all segmented fracturing and water injection are completed.

[0038] In other words, the retreating segmented fracturing water injection can effectively form a water-injected bonding layer 4, enhance the shear strength and cohesion of the coal body, reduce the brittle fracture of the coal body, and help improve the stability of the coal wall.

[0039] S4. In the extension direction of borehole 21, the borehole breaks and collapses under the high stress of the surrounding rock in the roadway, gradually forming a collapsed section 5, which is used to achieve pressure relief. Figures 2-4As shown, it is understandable that after the fracturing and water injection construction is completed, borehole 21 can undertake the task of relieving pressure on the coal wall of the roadway. As the roadway is excavated, the stress of the surrounding rock is redistributed, and the pressure of the advance support of the mining face is applied. Under the action of high stress, borehole 21 breaks to form a collapsed section 5, thereby transferring the high stress of the coal wall to the depth. The bonding layer formed around the borehole (collapsed section) can prevent the surrounding rock of the roadway from spalling.

[0040] It should be noted that in the method for controlling spalling in deep, high-stress jointed coal seam roadways according to the embodiments of the present invention, drilling, water injection, and crushing and decompression are carried out in advance, and the drilling is arranged parallel to the roadway excavation direction. This ensures stress transfer in the surrounding rock and prevents coal wall adhesion and spalling, while not affecting the roadway excavation speed.

[0041] In other words, the method for controlling spalling in deep, high-stress jointed coal seam roadways according to this invention involves segmented fracturing and water injection within borehole 21 along the roadway's strike. This allows for the generation of fissures around the borehole 21, which then diffuse into the coal seam and direct water towards the jointed coal seam. This increases the coal's cohesion and shear strength, enhances its plasticity, and improves the stability of the roadway's coal wall, thereby controlling spalling. Furthermore, the strike borehole 21 drilled in the deep coal seam of the roadway's sidewalls can, without damaging the shallow surrounding rock, transfer the high stress concentration in the shallow surrounding rock to the deeper layers after borehole collapse, achieving the purpose of relieving pressure on the surrounding rock of the deep coal roadway. Compared to traditional vertical coal face drilling 21, by arranging drilling rigs and other equipment in the drilling chamber 2 of the initial section of the roadway, the drilling of the strike borehole 21 and hydraulic fracturing can be carried out in advance or in parallel with the roadway excavation. Therefore, it can greatly reduce the number of construction and equipment relocations, reduce the impact on roadway excavation and support construction, reduce construction costs, and increase the speed of roadway excavation.

[0042] In some embodiments, in step S1, there are multiple drilling chambers 2, which are spaced apart and arranged on both sides of the coal roadway 1, and each drilling chamber 2 is provided with at least one borehole 21.

[0043] It is understandable that, such as Figure 1 As shown, the drilling chamber 2 is located at the end of the coal roadway 1, and the area of ​​the drilling chamber 2 needs to meet the usage space of the drilling equipment 21 to ensure the normal construction of the deep hole drilling rig. In addition, each drilling chamber 2 can be drilled with one or more boreholes 21 to more effectively adapt to different situations in the coal roadway 1.

[0044] In some embodiments, the borehole 21 has a diameter greater than or equal to 120 mm, and its length is adapted to the length of the coal roadway 1. It is understood that a larger borehole 21 diameter allows for easier accommodation of the fracturing equipment 6 and materials, thereby enabling more effective fracturing and water injection, forming a thicker water-injected bonding layer 4 to improve coal body stability and roadway support. A larger borehole 21 diameter and a longer borehole 21 length can also increase the pressure relief area, more effectively alleviating the high stress in the surrounding rock of the coal roadway 1, further reducing coal body damage, and improving coal wall stability. Furthermore, the borehole diameter and length can be determined based on the actual geological conditions and design requirements of the coal roadway 1.

[0045] In some embodiments, in step S2, the distance between two adjacent fracturing and water injection sections 3 is equal. It is understood that equally spaced segmented fracturing and water injection can more uniformly control the decompression of the surrounding rock in the coal roadway 1, avoiding localized stress concentration. The equal distance between adjacent fracturing and water injection sections 3 also ensures that each section can effectively reinforce the coal body, forming a uniform water-injected bonding layer 4, improving the stability of the coal body and the support effect of the roadway. Equally spaced segmented fracturing and water injection also simplifies the construction process and improves construction efficiency. Construction personnel can drill holes 21 and perform fracturing and water injection according to predetermined distances without the need for complex measurements and calculations.

[0046] In some embodiments, the distance between borehole 21 and the sidewall of coal roadway 1 is greater than or equal to 4 meters. It is understood that a larger distance between borehole 21 and the sidewall of coal roadway 1 can more effectively relieve pressure on the surrounding rock of coal roadway 1. That is, because the borehole 21 is farther from the sidewall of coal roadway 1, the stress generated during fracturing and water injection can be released more fully, thereby more effectively reducing the stress level of the surrounding rock of coal roadway 1. It can also reduce the direct impact and damage to the sidewall of coal roadway 1 during fracturing and water injection, thus better protecting the integrity of the sidewall of coal roadway 1 and preventing accidents such as sidewall collapse and spalling.

[0047] In some embodiments, the distance between the fracturing water injection sections 3 is greater than or equal to 10 meters, and the distance between two adjacent fracturing water injection sections 3 is greater than or equal to 30 meters and less than or equal to 35 meters.

[0048] Understandably, a distance of 10 meters or more between fracturing and water injection sections 3 ensures that the fracturing and water injection can penetrate deep into the coal seam, forming an effective water-injection bonding layer 4, thereby improving the stability and shear strength of the coal body. A distance of 30 meters or more and 35 meters or less between adjacent fracturing and water injection sections 3 achieves a uniform pressure relief effect. This spacing avoids localized stress concentration and effectively releases the high stress in the surrounding rock of coal roadway 1.

[0049] In other words, the distance between adjacent fracturing and water injection sections 3 is moderate, which ensures both construction flexibility and efficiency. Construction personnel can drill boreholes 21 and perform fracturing and water injection according to the predetermined distance without the need for complex measurements and calculations.

[0050] In some embodiments, in step S3, the fracturing equipment 6 includes a double-sealed fracturing water injector, wherein the fracturing water injected by the double-sealed fracturing water injector contains a permeability enhancer.

[0051] Understandably, the dual-sealing fracturing water injection device can effectively seal the fracturing water injection section 3, ensuring that the fracturing fluid can fully diffuse inside the coal seam, forming a more uniform and effective water injection bonding layer 4. Adding a permeability enhancer to the fracturing water injection can reduce the permeability resistance of the coal body and improve its permeability, allowing the fracturing fluid to more easily enter the coal seam and form a more effective water injection bonding layer 4.

[0052] Furthermore, adding permeability enhancers to fracturing water can strengthen the cohesion and shear strength of the coal seam while reducing its compressive strength and brittleness, thereby improving the stability of the coal seam and preventing accidents such as side collapse and spalling. These permeability enhancers can be polymeric, such as polysiloxane-based, organosilicon-based, epoxy-based, and polyurethane-based permeability enhancers.

[0053] In some embodiments, the dual-seal fracturing water injector has a balanced pressure relief channel that connects the sealing cavity of the upper packer and the sealing cavity of the lower packer of the dual-seal fracturing water injector.

[0054] Understandably, the pressure relief channel ensures that the pressure between the sealing chambers of the upper and lower packers can be transmitted and balanced during water injection fracturing. This prevents packer failure or damage due to pressure imbalance. Achieving pressure balance through the pressure relief channel during water injection fracturing reduces potential hazards such as packer rupture or leakage under high pressure, thereby improving operational safety.

[0055] In other words, the pressure balance between the separator and the water can be achieved by using the pressure relief channel, which can achieve "immediate sealing upon pressure release and unsealing upon pressure relief".

[0056] In some embodiments, the fracturing device 6 further includes a water supply component and a water injection hose 61, with a first end of the water injection hose 61 connected to the water supply component and a second end of the water injection hose 61 connected to the inlet of the double-sealed fracturing water injector.

[0057] Understandably, the water supply unit provides stable pressure and flow rate for fracturing water injection, ensuring that the fracturing fluid is injected evenly into the coal seam. The water injection hose 61 connects the water supply unit to the dual-seal fracturing water injector, facilitating movement and easy delivery of the fracturing fluid. The water injection hose 61 can be selected in different lengths and diameters to adapt to various construction environments. It should be noted that the water injection hose 61 is made of high-strength, high-pressure-resistant materials to withstand the high-pressure environment during fracturing water injection, ensuring construction safety.

[0058] In some embodiments, step S3 further includes, during a single fracturing water injection, the fracturing initiation pressure is greater than or equal to 18 MPa, and the drainage volume is greater than or equal to 40 m³ / h. 3 / h.

[0059] Understandably, fracturing pressure refers to the pressure at which fracturing fluid begins to form fractures in a coal seam. The selection of fracturing pressure needs to consider the strength and brittleness of the coal seam. Too low a fracturing pressure may prevent the fracturing fluid from forming effective fractures, while too high a pressure may lead to excessive damage to the coal seam, even causing safety accidents. An appropriate fracturing pressure ensures that the fracturing fluid can form effective fractures in the coal seam, improving the permeability of the coal body, thereby increasing gas extraction efficiency and the stability of the surrounding rock in the coal roadway.

[0060] Discharge rate refers to the amount of fracturing fluid injected into the coal seam per unit time. The selection of the discharge rate needs to consider both the permeability of the coal seam and the properties of the fracturing fluid. Too low a discharge rate may result in insufficient fracturing fluid penetration into the coal seam, while too high a discharge rate may lead to excessive damage to the coal seam, even causing safety accidents. An appropriate discharge rate ensures that the fracturing fluid can fully penetrate the coal seam, forming an effective fracture network, thereby improving the permeability of the coal body, increasing gas extraction efficiency, and enhancing the stability of the surrounding rock in the coal roadway.

[0061] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0063] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0064] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0065] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0066] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for controlling spalling in deep, high-stress jointed coal seam roadways, characterized in that, Includes the following steps: S1. Before tunnel excavation, drilling chambers are set up on the sidewalls of the coal roadway. Drilling is carried out in the drilling chambers along the axial direction of the coal roadway toward the interior of the surrounding rock. There are multiple drilling chambers, which are spaced apart and arranged on both sides of the coal roadway. At least one borehole is arranged in each drilling chamber. The distance between the borehole and the sidewall of the coal roadway is greater than or equal to 4 meters. S2. Divide the borehole into multiple fracturing and water injection sections along its extension direction; S3. Push the fracturing equipment into the fracturing and water injection section, and perform fracturing and water injection using a retreating segmented fracturing and water injection method to form a water-injected bonding layer in the circumferential coal body of the borehole. The fracturing equipment includes a dual-seal fracturing water injection device. The fracturing water injected by the dual-seal fracturing water injection device contains a penetration enhancer. The dual-seal fracturing water injection device has a balanced pressure relief channel, which connects the sealing chamber of the upper packer and the sealing chamber of the lower packer of the dual-seal fracturing water injection device. The fracturing equipment also includes a water supply component and a water injection hose. The first end of the water injection hose is connected to the water supply component, and the second end of the water injection hose is connected to the inlet of the double-sealed fracturing water injector. S4. In the extension direction of the borehole, the borehole is broken and collapsed under the high stress of the surrounding rock of the roadway, and gradually forms a collapsed section, which is used to achieve the pressure relief function.

2. The method for controlling spalling in deep, high-stress jointed coal seam roadways according to claim 1, characterized in that, The borehole diameter is greater than or equal to 120 mm, and the length of the borehole is adapted to the length of the coal roadway.

3. The method for controlling spalling in deep, high-stress jointed coal seam roadways according to claim 2, characterized in that, In step S2, the distance between two adjacent fracturing water injection sections is equal.

4. The method for controlling spalling in deep, high-stress jointed coal seam roadways according to claim 1, characterized in that, The length of the fracturing water injection section is greater than or equal to 10 meters, and the distance between two adjacent fracturing water injection sections is greater than or equal to 30 meters and less than or equal to 35 meters.

5. The method for controlling spalling in deep, high-stress jointed coal seam roadways according to claim 1, characterized in that, Step S3 further includes, during a single fracturing water injection, the fracturing initiation pressure being greater than or equal to Discharge volume greater than or equal to .

Images