Method for preventing and controlling rock burst when coal mine working face stoped over overlying goaf

Abstract

The rock burst prevention and control method for the overlying goaf stoped through the coal mine working face comprises the following steps that S1, according to the position of the overlying goaf of the coal mine working face, a rock stratum located above the coal mine working face and adjacent to the overlying goaf is divided into a fracturing target area; s2, a drill hole is formed in the fracturing target area; and S3, before stoping is carried out on the stoping working face, liquid is injected into the drill holes in the fracturing target area so that hydraulic fracturing can be carried out on the fracturing target area. Therefore, the method for preventing and controlling the rock burst through the overlying goaf stoped on the coal mine working face has the advantage that the rock burst can be conveniently prevented from appearing.

Description

Technical Field

[0001] The invention relates to the technical field of mining, and in particular to a method for preventing and controlling rock burst during mining of a coal mine working face through an overlying goaf area. Background Art

[0002] When the mining face passes through the overlying goaf, on the one hand, the concentrated stress formed by the working face is superimposed on the concentrated stress of the overlying goaf, thereby forming a high concentrated stress, which makes the surrounding rock under a higher concentrated static load level; on the other hand, the mining of the working face will continuously disturb the overlying goaf, and the movement of the surrounding rock will form a concentrated dynamic load. The superposition of dynamic and static loads will induce impact ground pressure when the bearing limit of the surrounding rock is exceeded, making the mining of the working face below more dangerous. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides a method for preventing and controlling rock burst during mining of a coal mine working face through an overlying goaf.

[0004] The method for preventing and controlling rock burst in a coal mine working face through an overlying goaf area according to an embodiment of the present invention comprises the following steps:

[0005] S1. According to the position of the overlying goaf area of ​​the mining working face, the rock strata located above the mining working face and adjacent to the overlying goaf area are divided into the fracturing target area;

[0006] S2, drilling a hole in the target fracturing area;

[0007] S3. Before mining the mining working face, inject liquid into the borehole in the fracturing target area to hydraulically fracture the fracturing target area.

[0008] Therefore, the method for preventing and controlling rock burst during mining of a coal mine working face through an overlying goaf according to an embodiment of the present invention has the advantage of being able to prevent rock burst from occurring.

[0009] In some embodiments, in the step S1, the rock formation located above the mining working face and adjacent to the overlying goaf in the horizontal direction is divided into the fracturing target area.

[0010] In some embodiments, in the step S1, the rock layer divided into the fracturing target area is a thick hard sandstone layer with a thickness greater than or equal to 10 meters and a uniaxial compressive strength greater than or equal to 60 MPa.

[0011] In some embodiments, in step S1, the vertical distance between the fracturing target area and the mining working face is greater than or equal to 10 meters and less than or equal to 60 meters.

[0012] In some embodiments, in step S1,

[0013] The horizontal distance between any point in the fracturing target area and the overlying goaf area is less than or equal to 600 meters;

[0014] The length of the fracturing target zone is less than or equal to the length of the mining working surface, and the width of the fracturing target zone is less than or equal to the width of the mining working surface.

[0015] In some embodiments, in step S2, a plurality of the boreholes are opened in the fracturing target area so that the plurality of the boreholes are located around the overlying goaf area.

[0016] In some embodiments, in step S2, the length direction of the main body of the drilled hole is the first direction, and the main bodies of the multiple drilled holes are spaced apart in the second direction, and any two of the first direction, the second direction and the up and down directions are perpendicular to each other.

[0017] In some embodiments, in step S2,

[0018] The distance between the bodies of two adjacent boreholes in the second direction is greater than or equal to 60 meters and less than or equal to 80 meters;

[0019] The fracturing target area is provided with at least one drilling layer in the up-down direction, and the distance between two adjacent drilling holes in each drilling layer in the second direction in the up-down direction is greater than or equal to 3 meters and less than or equal to 8 meters.

[0020] In some embodiments, in step S2,

[0021] The first direction is the direction of the mining face, and the mining face is provided with a transport tunnel and a return air tunnel on both sides of the second direction;

[0022] The plurality of boreholes are located between the transport tunnel and the return air tunnel of the mining working face in the second direction;

[0023] The size of the fracturing target area in the second direction is consistent with that of the mining working face, the distance between the borehole closest to the transport roadway in the second direction and the transport roadway is greater than or equal to 10 meters and less than or equal to 20 meters, and the distance between the borehole closest to the return air roadway in the second direction and the return air roadway is greater than or equal to 10 meters and less than or equal to 20 meters;

[0024] The fracturing target area is consistent with the size of the mining working face in the second direction, and when the transport roadway is adjacent to the goaf of the working face at the same height, the distance between the drill hole closest to the transport roadway in the second direction and the transport roadway is greater than or equal to 20 meters and less than or equal to 30 meters;

[0025] The fracturing target area is consistent with the size of the mining working face in the second direction, and when the return air roadway is adjacent to the goaf of the working face at the same height, the distance between the drill hole closest to the return air roadway in the second direction and the return air roadway is greater than or equal to 20 meters and less than or equal to 30 meters.

[0026] In some embodiments, in step S2,

[0027] The plurality of boreholes in each of the borehole layers include a first borehole group and a second borehole group, the plurality of boreholes in the first borehole group and the plurality of boreholes in the second borehole group are alternately arranged in sequence in the second direction, and the distance between the plurality of boreholes in the first borehole group and the plurality of boreholes in the second borehole group in the vertical direction is greater than or equal to 3 meters and less than or equal to 8 meters;

[0028] A plurality of drilling sites are opened around the target fracturing zone, and at least one borehole is opened from each of the drilling sites toward the target fracturing zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 3 is a top view of the overlying goaf and the fracturing target layer according to an embodiment of the present invention.

[0030] Figure 2 yes Figure 1 Cross-sectional view at AA.

[0031] Figure 3 yes Figure 1 Cross-sectional view at BB.

[0032] Figure 4 yes Figure 1 Cross-sectional view at CC.

[0033] Figure numerals: 1. mining working face, 2. overlying goaf, 3. fracturing target area, 4. borehole, 5. drilling site, 6. transportation tunnel, 7. return air tunnel, 8. working face goaf. DETAILED DESCRIPTION

[0034] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0035] The following describes the method for preventing and controlling rock burst in the coal mine working face through the overlying goaf area according to the embodiment of the present invention with reference to the accompanying drawings. Figures 1 to 4 As shown, the method for preventing and controlling rock burst in a coal mine working face through an overlying goaf according to an embodiment of the present invention comprises the following steps:

[0036] S1. According to the position of the overlying goaf 2 of the mining face 1, the rock strata located above the mining face 1 and adjacent to the overlying goaf 2 are divided into the fracturing target area 3. Specifically, the overlying goaf 2 is the goaf located directly above the mining face 1. In step S1, the rock strata located above the mining face 1 and adjacent to the overlying goaf 2 in the horizontal direction are divided into the fracturing target area 3. That is, the rock strata adjacent to the surrounding side of the overlying goaf 2 are divided into the fracturing target area 3.

[0037] In some embodiments, in step S1, the rock layer divided into the target area 3 for fracturing is a thick hard sandstone layer with a thickness of 10 meters or more and a uniaxial compressive strength of 60 MPa or more. That is, the thick hard sandstone layer with a thickness of 10 meters or more and a uniaxial compressive strength of 60 MPa or more located above the mining face 1 and adjacent to the overlying goaf 2 in the horizontal direction is divided into the target area 3 for fracturing. For example, according to the column chart of the boreholes around the working face, a thick hard sandstone layer with a thickness of 10 meters or more and a uniaxial compressive strength of 60 MPa or more is selected.

[0038] In some embodiments, in step S1, the vertical distance (in the up-down direction) between the fracturing target area 3 and the mining face 1 is greater than or equal to 10 meters and less than or equal to 60 meters. That is, if at least part of the rock formation adjacent to the overlying goaf 2 in the horizontal direction is located in the area 10 meters to 60 meters above the mining face 1, the rock formation is divided into the fracturing target area 3.

[0039] In some embodiments, the maximum distance between the fracturing target area 3 and the mining working face 1 in the vertical direction is less than 100 meters.

[0040] In some embodiments, in step S1, the horizontal distance between any point in the fracturing target area 3 and the overlying goaf area 2 is less than or equal to 600 meters. That is, the rock layer located above the mining working face 1 and the horizontal distance between any point in the fracturing target area 3 and the overlying goaf area 2 is less than or equal to 600 meters is divided into the fracturing target area 3.

[0041] In some embodiments, the length of the fracturing target area 3 is less than or equal to the length of the mining face 1, and the width of the fracturing target area 3 is less than or equal to the width of the mining face 1. Specifically, the area of ​​the rock formation directly above the mining face 1 is divided into the fracturing target area 3. For example, the length of the fracturing target area 3 is equal to the length of the mining face 1, and the width of the fracturing target area 3 is equal to the width of the mining face 1.

[0042] S2. Drilling holes 4 are opened in the target fracturing area 3. Specifically, in step S2, multiple drill holes 4 are opened in the target fracturing area 3, so that the multiple drill holes 4 are located around the overlying goaf area 2, so as to evenly fractur the target fracturing area 3. Multiple drilling sites 5 are opened around the target fracturing area 3, and at least one drill hole 4 is opened from each drilling site 5 to the target fracturing area 3, so as to improve efficiency.

[0043] In some embodiments, in step S2, the length direction of the main body of the borehole 4 is the first direction, the main bodies of the plurality of boreholes 4 are spaced apart in the second direction, and any two of the first direction, the second direction and the up-down direction are perpendicular to each other. Specifically, the main body of the borehole 4 is the portion of the borehole 4 extending in a straight line. The first direction is the direction of the mining face, that is, the direction of the mining face in the length direction of the main body of the borehole 4. For example, the direction of the mining face is the left-right direction, the length direction of the main body of the borehole 4 is the left-right direction, and the main bodies of the plurality of boreholes 4 are spaced apart in the front-back direction.

[0044] In some embodiments, in step S2, the distance between the main bodies of two adjacent boreholes 4 in the second direction is greater than or equal to 60 meters and less than or equal to 80 meters. Specifically, the hydraulic fracturing range of each borehole 4 is greater than 30 meters and less than 40 meters. The distance between the main bodies of two adjacent boreholes 4 in the second direction is greater than or equal to 60 meters and less than or equal to 80 meters, which can reduce the portion of the fracturing target area 3 that is not hydraulically fractured. For example, the distance between the main bodies of two adjacent boreholes 4 in the front-to-back direction is 70 meters.

[0045] In some embodiments, at least one drilling layer is provided in the vertical direction of the fracturing target area 3. Specifically, when the fracturing target area 3 is large, multiple drilling layers can be provided, each of which is provided with multiple boreholes 4, so as to perform hydraulic fracturing on the layer.

[0046] The vertical distance between two adjacent boreholes 4 in the second direction of each borehole layer is greater than or equal to 3 meters and less than or equal to 8 meters. In other words, the vertical distance between two adjacent boreholes 4 in the second direction of each borehole layer is a certain distance to prevent the cracks formed by the previous borehole fracturing from affecting the expansion of the cracks in the next borehole fracturing. For example, Figure 4 As shown, the distance between two adjacent boreholes 4 in the second direction in each borehole layer in the vertical direction is 5 meters.

[0047] like Figure 2As shown, in some embodiments, the multiple boreholes 4 of each drilling layer include a first borehole group and a second borehole group, the multiple boreholes 4 of the first borehole group and the multiple boreholes 4 of the second borehole group are alternately arranged in sequence in the second direction, and the distance between the multiple boreholes 4 of the first borehole group and the multiple boreholes 4 of the second borehole group in the vertical direction is greater than or equal to 3 meters and less than or equal to 8 meters. For example, the distance between the multiple boreholes 4 of the first borehole group and the multiple boreholes 4 of the second borehole group in the vertical direction is 5 meters.

[0048] like Figures 2 to 4 As shown, in some embodiments, the mining face 1 is provided with a transport tunnel 6 and a return air tunnel 7 on both sides in the second direction, and a plurality of boreholes 4 are located between the transport tunnel 6 and the return air tunnel 7 of the mining face 1 in the second direction. For example, the mining face 1 is provided with a transport tunnel 6 and a return air tunnel 7 on both sides in the front-to-back direction, and a plurality of boreholes 4 are located between the transport tunnel 6 and the return air tunnel 7 of the mining face 1 in the front-to-back direction.

[0049] The size of the fracturing target area 3 and the mining face 1 in the second direction is consistent, and the distance between the drill hole 4 closest to the transport tunnel 6 in the second direction and the transport tunnel 6 is greater than or equal to 10 meters and less than or equal to 20 meters. The distance between the drill hole 4 closest to the return air tunnel 7 in the second direction and the return air tunnel 7 is greater than or equal to 10 meters and less than or equal to 20 meters. Thus, the transport tunnel 6 and the return air tunnel 7 can be protected. For example, the distance between the drill hole 4 closest to the transport tunnel 6 in the second direction and the transport tunnel 6 is 15 meters. The distance between the drill hole 4 closest to the return air tunnel 7 in the second direction and the return air tunnel 7 is 15 meters.

[0050] When the size of the fracturing target area 3 and the mining working face 1 in the second direction is consistent, and the transport tunnel 6 is adjacent to the working face goaf 8 at the same height, the distance between the drill hole 4 closest to the transport tunnel 6 in the second direction and the transport tunnel 6 is greater than or equal to 20 meters and less than or equal to 30 meters. In this way, the transport tunnel 6 can be protected. For example, the distance between the drill hole 4 closest to the transport tunnel 6 in the second direction and the transport tunnel 6 is 25 meters.

[0051] When the size of the fracturing target area 3 and the mining working face 1 in the second direction is consistent, and the return air roadway 7 is adjacent to the working face goaf 8 at the same height, the distance between the drill hole 4 closest to the return air roadway 7 in the second direction and the return air roadway 7 is greater than or equal to 20 meters and less than or equal to 30 meters. In this way, the return air roadway 7 can be protected. For example, the distance between the drill hole 4 closest to the return air roadway 7 in the second direction and the return air roadway 7 is 25 meters.

[0052] S3. Before mining the mining face 1, inject liquid into the borehole 4 in the fracturing target area 3 to hydraulically fracture the fracturing target area 3. Specifically, before mining the mining face 1, perform regional hydraulic fracturing on the thick hard rock layer in the goaf area 2 overlying the mining face 1 in advance to avoid the pre-fracture blind area and ensure that the fracturing cracks are fully extended in the overlying goaf influence area. Then, the mining face 1 located below the fracturing target area 3 after fracturing and with reduced stress is safely mined.

[0053] like Figures 1 to 4 As shown, in a specific embodiment, the mining face 1 of the lower layer mines the 3-1 coal seam with a thickness of 5m, and there is an overlying goaf 2 on the upper layer. The mining face 1 at the lower layer 3-1 coal seam is affected by the overlying goaf 2 during mining. When the mining face 1 gradually approaches the overlying goaf affected area (overlying goaf 2), the supporting pressures are superimposed on each other, thereby greatly increasing the supporting pressure of the surrounding rock in this area. Under the action of mining disturbance, the roof of the overlying goaf (overlying goaf 2) moves, forming a certain scale of dynamic load, which is easy to induce rock burst.

[0054] The rock layer located above the mining face 1 and adjacent to the overlying goaf 2 in the horizontal direction is divided into the fracturing target area 3, and the length and width of the fracturing target area 3 are consistent with those of the mining face 1. According to the layout of the underground tunnels in the coal mine, a total of 4 drilling sites 5 are set up, namely, 1# drilling site, 2# drilling site, 3# drilling site and 4# drilling site, among which 1# drilling site constructs 5 directional long boreholes 4, 2# drilling site constructs 2 directional long boreholes 4, 3# drilling site constructs 3 directional long boreholes 4, 4# drilling site constructs 2 directional long boreholes 4, and the spacing between boreholes 4 is 70m.

[0055] In order to prevent hydraulic fracturing from affecting the lower tunnel, a 16-meter protection distance is reserved between the borehole 4 closest to the transport tunnel 6 in the second direction and the transport tunnel 6. A 24-30-meter protection distance is reserved between the borehole 4 closest to the return air tunnel 7 in the second direction and the return air tunnel 7.

[0056] In view of the sources of dynamic and static loads that induce rock burst, the rock burst prevention and control method for coal mine working face mining through the overlying goaf according to an embodiment of the present invention performs regional hydraulic fracturing on the overlying goaf 2 in advance to release the accumulated energy of the thick hard rock layer (fracturing target area 3) in advance. The stress level of the mining area above the mining face 1 to be mined is reduced, so that the mining face 1 forms a low stress area through the overlying goaf 2 and is in a protected state, thereby significantly reducing the impact hazard, reducing the concentration of dynamic and static loads and the impact risk that induces impact. Through the rock burst prevention and control method for coal mine working face mining through the overlying goaf, the coal mine mining face 1 can meet safety requirements during the mining of the overlying goaf 2, hydraulic fracturing weakens the thick hard rock layer of the roof to effectively reduce the stress concentration, and the surrounding rock of the tunnel is in a low stress state, which significantly prevents the possibility of rock burst.

[0057] Therefore, the method for preventing and controlling rock burst during mining of a coal mine working face through an overlying goaf according to an embodiment of the present invention has the advantage of being able to prevent rock burst from occurring.

[0058] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0059] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0060] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0061] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0062] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0063] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face, characterized in that: Includes the following steps: S1. According to the position of the overlying goaf area of ​​the mining working face, the rock strata located above the mining working face and adjacent to the overlying goaf area are divided into the fracturing target area; S2, drilling a hole in the target fracturing area; S3. Before mining the mining working face, inject liquid into the borehole in the fracturing target area to hydraulically fracture the fracturing target area.

2. The method for preventing and controlling rock burst in coal mine working face mining through overlying goaf according to claim 1, characterized in that: In the step S1, the rock strata located above the mining working face and adjacent to the overlying goaf in the horizontal direction are divided into the fracturing target area.

3. The method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face according to claim 2, characterized in that: In the step S1, the rock layer divided into the target fracturing area is a thick hard sandstone layer with a thickness greater than or equal to 10 meters and a uniaxial compressive strength greater than or equal to 60 MPa.

4. The method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face according to claim 2, characterized in that: In the step S1, the vertical distance between the fracturing target area and the mining working face is greater than or equal to 10 meters and less than or equal to 60 meters.

5. The method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face according to claim 2, characterized in that: In step S1, The horizontal distance between any point in the fracturing target area and the overlying goaf area is less than or equal to 600 meters; The length of the fracturing target zone is less than or equal to the length of the mining working surface, and the width of the fracturing target zone is less than or equal to the width of the mining working surface.

6. The method for preventing and controlling rock burst in a coal mine working face through an overlying goaf according to any one of claims 1 to 5, characterized in that: In the step S2, a plurality of the boreholes are opened in the fracturing target area so that the plurality of the boreholes are located around the overlying goaf area.

7. The method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face according to claim 6, characterized in that: In step S2, the length direction of the main body of the drill hole is the first direction, and the main bodies of the plurality of drill holes are spaced apart in the second direction, and any two of the first direction, the second direction and the up-down direction are perpendicular to each other.

8. The method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face according to claim 7, characterized in that: In step S2, The distance between the bodies of two adjacent boreholes in the second direction is greater than or equal to 60 meters and less than or equal to 80 meters; The fracturing target area is provided with at least one drilling layer in the up-down direction, and the distance between two adjacent drilling holes in each drilling layer in the second direction in the up-down direction is greater than or equal to 3 meters and less than or equal to 8 meters.

9. The method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face according to claim 7, characterized in that: In step S2, The first direction is the direction of the mining face, and the mining face is provided with a transport tunnel and a return air tunnel on both sides of the second direction; The plurality of boreholes are located between the transport tunnel and the return air tunnel of the mining working face in the second direction; The size of the fracturing target area in the second direction is consistent with that of the mining working face, the distance between the borehole closest to the transport roadway in the second direction and the transport roadway is greater than or equal to 10 meters and less than or equal to 20 meters, and the distance between the borehole closest to the return air roadway in the second direction and the return air roadway is greater than or equal to 10 meters and less than or equal to 20 meters; The fracturing target area is consistent with the size of the mining working face in the second direction, and when the transport roadway is adjacent to the goaf of the working face at the same height, the distance between the drill hole closest to the transport roadway in the second direction and the transport roadway is greater than or equal to 20 meters and less than or equal to 30 meters; The fracturing target area is consistent with the size of the mining working face in the second direction, and when the return air roadway is adjacent to the goaf of the working face at the same height, the distance between the drill hole closest to the return air roadway in the second direction and the return air roadway is greater than or equal to 20 meters and less than or equal to 30 meters.

10. The method for preventing and controlling rock burst during mining of overlying goaf in a coal mine working face according to claim 8, characterized in that: In step S2, The plurality of boreholes in each of the borehole layers include a first borehole group and a second borehole group, the plurality of boreholes in the first borehole group and the plurality of boreholes in the second borehole group are alternately arranged in sequence in the second direction, and the distance between the plurality of boreholes in the first borehole group and the plurality of boreholes in the second borehole group in the vertical direction is greater than or equal to 3 meters and less than or equal to 8 meters; A plurality of drilling sites are opened around the target fracturing zone, and at least one borehole is opened from each of the drilling sites toward the target fracturing zone.

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