Two-way double-row water injection softening borehole arrangement method suitable for weakly cemented strata

Abstract

The present application relates to the technical field of coal mining, and relates to a two-way double-row water injection softening drilling arrangement method suitable for weakly cemented strata. The method comprises the following steps: (1) determining the position of the weakly cemented strata; (2) obtaining actual collection data of the weakly cemented strata, and determining the fracturing parameters of the hydraulic fracturing drilling according to the actual collection data; (3) according to the fracturing parameters, carrying out numerical simulation according to the position of the weakly cemented strata, and arranging the two-way double-row hydraulic fracturing drilling track; (4) arranging the two-way double-row water injection softening drilling according to the hydraulic fracturing drilling track, and sequentially performing water injection operation on the weakly cemented strata. The method provided by the present application arranges the two-way double-row water injection softening drilling according to the hydraulic fracturing drilling track, sequentially performs water injection operation on the weakly cemented strata, and uniformly injects water in the two-way double-row arrangement mode, which is beneficial to the softening and caving of the roof rock.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mining, specifically to a two-way double-row water injection softening drilling arrangement method suitable for weakly cemented strata. BACKGROUND

[0002] The Jurassic and Cretaceous strata have a late diagenetic age, and their properties exhibit some unique characteristics, such as weak cementation, easy weathering, and easy sanding when encountering water. Due to the relatively hard and complete structure of the overburden rock, it is difficult to grasp the mine pressure law during the initial mining stage of the working face, which is directly manifested in the excessively large initial pressure step distance and the difficulty in predicting the timing of the hard roof pressure, leading to strong mine pressure in the working face and significantly increasing the impact risk, which easily leads to impact-type dynamic disasters.

[0003] In the process of coal mining, roof control is a crucial link to ensure the safety of the working face. Traditional roof control methods often rely on blasting or mechanical cutting, which have certain limitations and shortcomings. In view of the characteristics of weakly cemented strata, water injection softening technology can effectively release the stress of the roof. For example, the patent "Method for controlling caving step distance by water softening cutting roof" (CN114483036A) proposes a new technical solution, which softens the rock layer by water injection to reduce the strength of the rock, so as to control the caving step distance of the roof. Although the above patent provides an effective roof control method, there are still the following technical problems in actual application: in some stratum conditions, one-way water injection may not uniformly soften the entire target layer, resulting in uneven softening effect and affecting the control accuracy of the caving step distance.

[0004] To improve the control accuracy of the caving step distance, drilling arrangement can be carried out accordingly. Traditional drilling arrangement methods, such as right-angle arrangement and parallel arrangement, can control the pressure of the hard roof overlying the coal seam in high stress areas to some extent, but they each have limitations. The right-angle arrangement method does not have an ideal effect on improving the stability of the coal seam due to insufficient drilling density, while the parallel arrangement method has low efficiency due to its high demand for manpower and material resources and long construction period. SUMMARY

[0005] To solve the above problems, in view of the above technical problems, the present application proposes a two-way double-row water injection softening drilling arrangement method suitable for weakly cemented strata. By arranging two-way double-row water injection holes in the target layer, the water injection efficiency and the uniformity of the softening effect are improved, thereby more accurately controlling the caving step distance. By optimizing the water injection parameters and drilling arrangement, the impact on the surrounding environment is reduced, such as controlling the water injection volume and water injection pressure to reduce the impact on the underground water level and ground subsidence. At the same time, the water injection parameters can be adjusted according to the characteristics of the strata, making them suitable for a wider range of stratum conditions.

[0006] To achieve the above object, the technical scheme adopted by the present application is:

[0007] The method is suitable for the layout of bidirectional double-row water injection softening boreholes in weakly cemented strata, and comprises the following steps:

[0008] (1) determining the location of the weakly cemented strata;

[0009] (2) obtaining actual collection data of the weakly cemented strata, and determining the fracturing parameters of the hydraulic fracturing borehole according to the actual collection data, wherein the fracturing parameters include the through-layer hydraulic fracturing radial cracking pressure, the fracturing liquid volume, and the water injection wetting radius;

[0010] (3) performing numerical simulation according to the location of the weakly cemented strata, and arranging the trajectory of the bidirectional double-row hydraulic fracturing borehole;

[0011] (4) arranging the bidirectional double-row water injection softening borehole according to the trajectory of the hydraulic fracturing borehole, and sequentially performing water injection operation on the weakly cemented strata.

[0012] Further, in step (2), the actual collection data includes geological related parameters and physical and mechanical parameters, and specifically includes: the vertical stress q0, the lateral stress coefficient λ c , the tensile strength of the layered coal R ti , the pipe radius γ g , the pipe length h g , the fracturing hole radius γ k , the coal seam volume v 体 within the fracturing influence range, the water absorption coefficient λ, the length l of the water permeable part of the borehole, the water injection time t, the rock bulk density γ, the rock water absorption rate n, the water injection flow rate Q, and the non-uniformity coefficient K.

[0013] Further, in step (2), the through-layer hydraulic fracturing radial cracking pressure is determined by the following formula:

[0014] p H =(1+λ c )q0+2(1-λ c )q0cos 2θ+min{R ti}

[0015] i=1,2;…,m

[0016] wherein p H represents the through-layer hydraulic fracturing radial cracking pressure, with the unit of MPa; q 0、 R ti respectively represent the vertical stress and the tensile strength of the i-th layered coal, with the unit of MPa; and λ crepresents lateral stress coefficient; θ represents the elevation angle between the bedding plane and the drilling axis, unit °; i represents the number of coal sub-layers through which the drilling passes; m represents the maximum number of coal sub-layers through which the drilling passes.

[0017] Further, in step (2), the fracturing liquid volume is determined by the following formula:

[0018] v c = v g + v k + v 水

[0019]

[0020] v 水 = 0.02v 体 λ2λ3

[0021] wherein v c , v g , v k respectively represent the total water volume, the water volume required for filling the pipeline and the water volume required for the fracturing hole, unit m 3 ; γ g , h g , γ k respectively represent the pipeline radius, the pipeline length, the fracturing hole radius, unit m; v 水 , v 体 respectively represent the fracturing liquid volume and the coal seam volume within the fracturing influence range, unit m 3 ; λ2 represents the water absorption coefficient of the floor rock; λ3 represents the water absorption coefficient when the coal seam is dense and hard.

[0022] Further, in step (2), the water injection wetting radius is determined by the following formula:

[0023]

[0024] wherein R represents the water injection wetting radius, unit m; l represents the length of the water-permeable part of the drilling, unit m; t represents the water injection time, unit min; γ represents the rock bulk density, unit t / m; n represents the water absorption rate of the rock, unit %; Q represents the water injection flow rate, unit t / min; K represents the uneven coefficient, taken as 0.08-0.2.

[0025] Further, in step (3), the software Flac 3D, COMSOL, XSite or ABAQUS is used for the numerical simulation design according to the location of the weakly cemented stratum.

[0026] Further, in step (3), the method for arranging the bi-directional double-row water pressure fracturing drilling trajectory specifically comprises:

[0027] According to the lithology column chart, high-position hydraulic fracturing boreholes and low-position hydraulic fracturing boreholes are designed on the side of the cut; the hole bottom of the high-position hydraulic fracturing borehole completely exceeds a basic roof rock layer of the rock in front of the fully-mechanized rock roadway on the side of the cut, the hole bottom of the low-position hydraulic fracturing borehole completely exceeds a direct roof rock layer of the rock in front of the fully-mechanized rock roadway on the side of the cut by more than 2-3 m, when there is no direct roof rock layer, the hole bottom of the low-position hydraulic fracturing borehole completely exceeds the coal seam by more than 2-3 m; and the angle between the bedding plane and the axis of the borehole is greater than the internal friction angle of the rock, the distance between the designed boreholes is greater than the water wetting radius, the high-position hydraulic fracturing borehole and the low-position hydraulic fracturing borehole cover the range of the hard rock layer above the direct roof rock layer, the basic roof rock layer, the direct roof rock layer and the basic roof rock layer.

[0028] Single-layer hydraulic fracturing boreholes are arranged on the side of the belt entry, i.e., belt entry boreholes are arranged; the diameters of the belt entry boreholes are all 75-80 mm, and the lengths of the belt entry boreholes exceed a basic roof rock layer in the rock in front of the fully-mechanized rock roadway by 2-5 m, and the angle between the bedding plane and the axis of the borehole is greater than the internal friction angle of the rock by 1-3°.

[0029] Further, in step (4), the water injection operation specifically includes: after the borehole construction, the borehole is sealed by using the AB glue sealing process, the sealing length is 3-3.5 m, a valve is installed at the borehole mouth after the sealing, and a high-pressure water pump is connected to the valve, the cracking pressure is greater than the water pressure of the hydraulic fracturing radial cracking, the liquid amount for fracturing is greater than the total water amount, the borehole is ensured to be filled with water and have a certain outward diffusion pressure, and the water injection operation time is 10-12 days.

[0030] Further, the method further includes step (5): according to the arrangement position of the bidirectional double-row water injection softening borehole, a roadway displacement monitoring station is arranged, and the fracturing pressure relief effect is analyzed and evaluated.

[0031] Further, step (5) specifically includes: according to the hydraulic fracturing borehole track, one group of roadway displacement monitoring stations is arranged every 30-35 m outward from the borehole position, and a total of 10-12 groups are arranged.

[0032] The present application has the following beneficial effects:

[0033] (1) The method provided by the present application determines key parameters such as the water injection wetting radius, the cracking pressure and the liquid amount for fracturing in the thick and hard coal seam above the mining coal seam, and the bidirectional double-row water injection softening boreholes of different heights are designed to perform collaborative fracturing, the hydraulic fracturing borehole track is arranged according to the fracturing parameters of the hydraulic fracturing borehole, the strength structure of the thick and hard rock layer of the weakly cemented stratum roof is effectively weakened, the initial pressure relief step distance of the working face and the pressure relief strength of the working face are reduced, and the purpose of controlling the pressure relief step distance of the hard roof and the pressure relief peak value of the working face is effectively achieved.

[0034] (2) The method provided by the application is suitable for pressure control of hard roof overlying coal seam in weakly cemented strata high stress area, and the actual collected data and numerical simulation software are used to determine the water injection wetting radius, cracking pressure, fracturing liquid volume and other hydraulic fracturing parameters, and the double-direction double-row water injection softening boreholes are arranged according to the hydraulic fracturing borehole track, and the weakly cemented strata are sequentially subjected to water injection operation, and the double-direction double-row arrangement mode is uniform, which is beneficial to the softening and caving of the roof rock.

[0035] (2) The method provided by the application is suitable for pressure control of hard roof overlying coal seam in weakly cemented strata high stress area, and the actual collected data and numerical simulation software are used to determine the water injection wetting radius, cracking pressure, fracturing liquid volume and other hydraulic fracturing parameters, and the double-direction double-row water injection softening boreholes are arranged according to the hydraulic fracturing borehole track, and the weakly cemented strata are sequentially subjected to water injection operation, and the double-direction double-row arrangement mode is uniform, which is beneficial to the softening and caving of the roof rock. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only show some embodiments of the application, and for those skilled in the art, other drawings can also be obtained from the structures shown in the drawings without creative labor.

[0037] Figure 1 A flow chart of a double-direction double-row water injection softening borehole arrangement method suitable for weakly cemented strata is shown according to one embodiment of the technical solutions of the application.

[0038] Figure 2 A water injection softening roof pore water pressure distribution contour map is shown according to one embodiment of the technical solutions of the application.

[0039] Figure 3 A double-direction double-row water injection borehole inclined section vertical stress influence area is shown according to one embodiment of the technical solutions of the application.

[0040] Figure 4 A borehole arrangement plan view is shown according to one embodiment of the technical solutions of the application.

[0041] Figure 5 A belt entry borehole arrangement section view is shown according to one embodiment of the technical solutions of the application.

[0042] Figure 6 A deformation data graph of a measuring point roadway.

[0043] The implementation of the application, functional features and advantages will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0044] The exemplary embodiments will be described in detail herein with reference to the attached drawings. The description of the exemplary embodiments is intended to apply to all alternative embodiments, as would be understood by one skilled in the art. In the following description, of the exemplary embodiments, identical numbers represent the same or similar elements throughout the several drawings. The exemplary embodiments described herein are not meant to represent all embodiments consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with some aspects of the present disclosure.

[0045] The terms "first", "second", and the like, as used herein do not imply a particular order, unless otherwise specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are capable of operation in other sequences than described or otherwise illustrated herein.

[0046] In addition, the terms "comprising" and "having", and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, product or apparatus that comprises a list of steps or units not necessarily limited to those explicitly listed, but can include other steps or units not expressly listed or inherent to such processes, methods, products or apparatuses.

[0047] Multiple, including two or more.

[0048] And / or, it should be understood that the term "and / or" used in the present disclosure is only a description of the association relationship of the associated objects, which means that there can be three relationships. For example, A and / or B can represent three cases: A exists alone, A and B exist together, and B exists alone.

[0049] Embodiment 1: A method for arranging bidirectional double-row water injection softening boreholes suitable for weakly cemented strata, especially for designing a bidirectional double-row water injection softening borehole pressure relief scheme in the field of coal seam roof pressure relief engineering when the working face length is greater than 100m. The uniform water injection is achieved by arranging the boreholes in two directions, which is beneficial to the softening and caving of the roof rock, thereby improving the regional pressure relief effect.

[0050] The method comprises:

[0051] (1) determining the location of the weakly cemented strata; specifically, determining the location of the weakly cemented strata according to geological exploration data and mining exposure data; the mining exposure data includes lithology columnar graph, density, porosity, water content, elastic modulus, compressive strength, tensile strength, cohesion, internal friction angle and Poisson's ratio of rock;

[0052] (2) obtaining actual collection data of the weakly cemented strata, and determining the fracturing parameters of the hydraulic fracturing borehole according to the actual collection data, the fracturing parameters including the fracturing radial cracking pressure, the fracturing liquid volume, and the water injection wetting radius;

[0053] (3) According to the location of the weakly cemented stratum, numerical simulation is carried out to arrange the bi-directional double-row hydraulic fracturing borehole track;

[0054] (4) According to the hydraulic fracturing borehole track, bi-directional double-row water injection softening boreholes are arranged, and water injection operation is sequentially carried out on the weakly cemented stratum.

[0055] In step (2) of the embodiment, the actual collected data includes geological parameters and physical and mechanical parameters, specifically including: vertical stress q0, lateral stress coefficient λ c , tensile strength of layered coal R ti , pipe radius γ g , pipe length h g , fracturing hole radius γ k , coal seam volume v 体 in the fracturing influence range, water absorption coefficient λ, length of the water permeable part of the borehole l, water injection time t, rock bulk density γ, rock water absorption rate n, water injection flow rate Q, and non-uniformity coefficient K.

[0056] In step (2) of the embodiment, the through-layer hydraulic fracturing radial cracking pressure is determined by the following formula:

[0057] p H =(1+λ c )q0+2(1-λ c )q0cos 2θ+min{R ti}

[0058] i=1,2;…,m

[0059] Wherein, p H represents the through-layer hydraulic fracturing radial cracking pressure, unit MPa; q0 and R ti represent the vertical stress and the tensile strength of the i-th layered coal, respectively, unit MPa; λ c represents the lateral stress coefficient; θ represents the angle, unit °; i represents the number of coal layers passed through by the borehole; and m represents the maximum number of coal layers passed through by the borehole.

[0060] In step (2) of the embodiment, the fracturing liquid volume is determined by the following formula:

[0061] v c =v g +v k +v 水

[0062]

[0063] v 水 =0.02v 体 λ2λ3

[0064] wherein, v c , v g , v k respectively represent total water consumption, water consumption required for filling pipeline and water consumption required for fracturing hole, unit m 3 ; γ g , h g , γ k respectively represent pipeline radius, pipeline length, fracturing hole radius, unit m; v 水 , v 体 respectively represent fracturing liquid volume and coal seam volume within fracturing influence range, unit m 3 ; λ2 represents water absorption coefficient of floor rock stratum; λ3 represents water absorption coefficient when coal seam is dense and hard.

[0065] In step (2) of the embodiment, the water injection wetting radius is determined by the following formula:

[0066]

[0067] wherein, R represents water injection wetting radius, unit m; l represents length of water penetration part of borehole, unit m; t represents water injection time, unit min; γ represents rock bulk density, unit t / m; n represents water absorption rate of rock, unit %; Q represents water injection flow rate, unit t / min; K represents non-uniformity coefficient, taken as 0.08-0.2.

[0068] In step (3) of the embodiment, numerical simulation design is performed according to the location of the weakly cemented stratum, and the numerical simulation software for pressure is Flac 3D, COMSOL, XSite or ABAQUS.

[0069] Single-hole water injection softening diffusion radius is simulated and analyzed by using pressure numerical software, water injection pressure is 1 MPa, initial roof pore water pressure is 0.1 MPa, and pore water pressure diffusion process is as shown in Figure 2 At this time, the roof water injection softening range is 1 m of water injection hole. According to the roof water injection softening range, the trajectory of hydraulic fracturing borehole is simulated and analyzed, as shown in Figure 3 .

[0070] In step (3), the method for arranging the trajectory of bi-directional double-row hydraulic fracturing borehole specifically includes:

[0071] Based on the lithological columnar section on the cut-off side, high-level hydraulic fracturing boreholes and low-level hydraulic fracturing boreholes are designed. The bottom of the high-level hydraulic fracturing boreholes completely extends beyond a basic roof stratum of the fully mechanized tunnel face on the cut-off side, and the bottom of the low-level hydraulic fracturing boreholes completely extends beyond a direct roof stratum of the fully mechanized tunnel face on the cut-off side by more than 2 to 3 meters. When there is no direct roof stratum, the bottom of the low-level hydraulic fracturing boreholes completely extends beyond the coal seam by more than 2 to 3 meters. The angle between the designed bedding plane and the borehole axis is greater than the internal friction angle of the rock, and the designed borehole diameter is greater than the water injection wetting radius. The high-level and low-level hydraulic fracturing boreholes cover the range of the direct roof stratum, the basic roof stratum, and the hard rock strata of the direct roof stratum and the basic roof stratum.

[0072] A single layer of hydraulic fracturing boreholes is set on the side of the conveyor belt roadway, i.e., conveyor belt roadway boreholes are set; the borehole diameter of the conveyor belt roadway boreholes is 75-80mm, the borehole length of the conveyor belt roadway boreholes exceeds the basic top rock layer in the rock face of the fully mechanized tunnel by 2-5m, and the elevation angle between the bedding plane and the borehole axis is greater than the internal friction angle of the rock by 1-3°.

[0073] Specifically, in this embodiment, the weakly cemented strata roof is softened by water injection in a two-way, double-row arrangement according to the roof softening range, such as... Figure 4 As shown. Twelve low-level boreholes and fifteen high-level boreholes are arranged in the working face cut and the conveyor belt roadway to weaken the roof within a horizontal distance of 30m in front of the cut and 48m above. Seven boreholes with a spacing of 7m are arranged on the roof of the conveyor belt roadway to soften the roof 45m above the coal seam and 12m away. The design of the high and low-level boreholes covers the immediate roof, the main roof and the hard rock strata above it. Low-level borehole I (01), low-level borehole II (02), low-level borehole III (03), low-level borehole IV (04), low-level borehole V (05), low-level borehole VI (06), low-level borehole VII (07), low-level borehole VIII (08), low-level borehole IX (09), low-level borehole X (10), low-level borehole

[0074] The borehole diameters of XI (11) and low-level borehole XII (12) are all 75-80 mm. The borehole length is designed to exceed the direct top rock layer by 2-5 m based on the hardness of the rock at the face of the comprehensive excavation tunnel. The elevation angle should be greater than the internal friction angle of the rock by 1-3°. The horizontal distance between low-level borehole I (01) and the track roadway (along the empty side) is 6-7 m. The spacing between the continuous boreholes from low-level borehole II (02) to low-level borehole XII (12) is determined according to the wetting range (wetting radius) of the water injection hole. The horizontal distance is 20-22 m.

[0075] High-level drilling I (13), High-level drilling II (14), High-level drilling III (15), High-level drilling

[0076] The borehole diameters of IV (16), V (17), VI (18), VII (19), VIII (20), IX (21), X (22), XI (23), XII (24), XIII (25), XIV (26), and XV (27) are all 75-80 mm. The borehole length is determined according to the hardness of the rock at the face of the fully mechanized tunnel. The length exceeds one of the basic top rock layers by 2 to 5 m, and the elevation angle should be greater than the internal friction angle of the rock by 1 to 3°. The high-level borehole I (1) is located in the track roadway (along the empty side). The continuous borehole spacing between high-level borehole II (14) and high-level borehole XIV (26) is determined according to the wetting range (wetting radius) of the water injection hole. The horizontal distance is 20 to 22 m. The horizontal distance between high-level borehole XV (27) and high-level borehole XIV (26) is 9 to 10 m.

[0077] like Figure 5 As shown, a single layer of hydraulic fracturing boreholes is set on the side of the conveyor belt chute. The diameter of the drilling holes I (28), II (29), III (30), IV (31), V (32), VI (33), and VII (34) of the conveyor belt trench are all 75-80 mm. The length of the drilling holes is designed to exceed the hardness of one of the basic top rock layers by 2-5 m according to the rock hardness of the face of the fully mechanized tunnel. The elevation angle should be greater than the internal friction angle of the rock by 1-3°. The spacing between the holes is determined according to the wetting range (wetting radius) of the water injection hole. The horizontal distance between the conveyor belt trench hole I (28) and the cut is 7-8 m. Six holes with a spacing of 7-8 m are arranged sequentially from the conveyor belt trench hole I (28), from the conveyor belt trench hole II (29) to the conveyor belt trench hole VII (34).

[0078] In step (4) of this embodiment, the water injection operation specifically includes: after drilling, the hole is sealed using AB glue sealing technology, with a sealing length of 3 to 3.5 m. After sealing, a valve is installed at the hole opening, followed by a high-pressure water pump. The design fracturing pressure is greater than the radial fracturing pressure of the hydraulic fracturing, and the fracturing fluid volume is greater than the total water volume, ensuring that the borehole is filled with water and has a certain outward diffusion pressure. The water injection operation time is 10 to 12 days.

[0079] In this embodiment, the method further includes step (5): according to the arrangement of the bidirectional double-row water injection softening boreholes, a roadway displacement monitoring station is set up to analyze and evaluate the fracturing and pressure relief effect.

[0080] The step (5) specifically comprises: arranging 10-12 groups of roadway displacement monitoring stations every 30-35 m outward from the drilling position according to the hydraulic fracturing drilling track. The roadway displacement change and the old mountain collapse are monitored. The effect of the pressure relief is analyzed by comparing the roadway floor heave, roof subsidence and two side displacement of the non-fracturing pressure relief section and the fracturing pressure relief section. The effect is shown in the figure Figure 6 The maximum value of the support pressure is 43.85 MPa, the minimum value is 18.9 MPa, and the average value is 31.9 MPa. When the working face is subjected to the initial pressure, no large-scale roof water outflow phenomenon occurs, which indicates that the roof water injection softening region is controllable, and the water injection does not produce leakage.

[0081] The provided bidirectional double-row water injection softening drilling arrangement method suitable for weakly cemented strata in the application arranges the drilling field in the adjacent roadway of the target treatment area to perform the hydraulic fracturing drilling track. The pressure relief of the roof surrounding rock is timely cut by the hydraulic fracturing, the cantilever length of the two sides of the working face is reduced, the transmission of the mining stress to the air intake lane direction is cut off, the roof of the goaf is timely and fully collapsed, the drilling utilization rate is improved, safety and efficiency are high, and the method has wide practicability.

[0082] In the specification provided herein, a large number of specific details are described. However, it can be understood that the embodiments of the application can be practiced without these specific details. In some examples, well-known methods, structures and techniques are not shown in detail in order not to obscure the understanding of the present specification.

[0083] In addition, those skilled in the art can understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features of different embodiments are also meant to be within the scope of the present application and form different embodiments. For example, in the above embodiments, those skilled in the art can use in a combined manner according to the known technical solutions and the technical problems to be solved by the present application.

[0084] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with the preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above-mentioned technical content without departing from the scope of the technical solution of the present application, and any simple modification, equivalent change and modification of the above-mentioned embodiments according to the technical essence of the present application are still within the scope of the present application.

Claims

1. A method for arranging a two-way double-row water injection softening borehole suitable for a weakly cemented formation, characterized in that, The method comprises: (1) determining the location of the weakly cemented stratum; (2) obtaining actual acquisition data of the weakly cemented stratum, determining the fracturing parameters of the hydraulic fracturing borehole according to the actual acquisition data, the fracturing parameters comprising the trans-layer hydraulic fracturing radial cracking pressure, the fracturing liquid volume, and the water injection wetting radius; (3) performing numerical simulation according to the location of the weakly cemented stratum, and arranging the trajectory of the bidirectional double-row hydraulic fracturing borehole; (4) arranging the bidirectional double-row water injection softening borehole according to the trajectory of the hydraulic fracturing borehole, and sequentially performing water injection operation on the weakly cemented stratum. In step (2), the actual collected data includes: vertical stress q0, lateral stress coefficient λ c , tensile strength of layered coal R ti , pipe radius γ g , pipe length h g , fracturing hole radius γ k , coal seam volume v within the fracturing influence range 体 , water absorption coefficient λ, length of water seepage part of the borehole l, water injection time t, rock bulk density γ, rock water absorption rate n, water injection flow rate Q, and uneven coefficient K; In step (2), the trans-layer hydraulic fracturing radial cracking pressure is determined by the following formula: p H = (1 + λ c )q0+ 2(1 - λ c )q0cos2θ+ min{R ti} i = 1, 2; …, m wherein p H represents the radial cracking pressure of water fracturing through layers, unit MPa; q0, R ti respectively represent the vertical stress, the tensile strength of the i-th coal layer, unit MPa; λ c represents the lateral stress coefficient; θ represents the elevation angle between the bedding plane and the borehole axis, unit °; i represents the number of coal layers through which the borehole passes; m represents the maximum number of coal layers through which the borehole passes; In step (2), the fracturing liquid volume is determined by the following formula: v c = v g + v k + v 水 v 水 = 0.02v 体 λ2λ3 Wherein, v c , v g , v k respectively represent total water consumption, water required for filling pipeline and water required for fracturing hole, unit m 3 ; v 水 , v 体 respectively represent fracturing fluid volume and coal seam volume within fracturing influence range, unit m 3 ; γ g , h g , γ k respectively represent pipeline radius, pipeline length, fracturing hole radius, unit m; λ2 represents water absorption coefficient of floor rock stratum; λ3 represents water absorption coefficient when coal seam is dense and hard. In step (2), the water injection wetting radius is determined by the following formula: wherein R represents the water injection wetting radius, the unit being m; l represents the length of the water-permeable part of the borehole, the unit being m; t represents the water injection time, the unit being min; γ represents the rock bulk density, the unit being t / m; n represents the rock water absorption rate, the unit being %; Q represents the water injection flow rate, the unit being t / min; and K represents the non-uniformity coefficient, being 0.08-0.

2.

2. The method for bi-directional dual packer injection softening borehole arrangement suitable for weakly cemented formation as claimed in claim 1 wherein, In step (3), numerical simulation design is performed according to the location of the weakly cemented stratum, and the software used is Flac3D, COMSOL, XSite or ABAQUS.

3. The method for bi-directional dual packer injection softening borehole arrangement suitable for weakly cemented formation as claimed in claim 1 wherein, In step (3), the method of arranging the trajectory of the bidirectional double-row hydraulic fracturing borehole specifically comprises: According to the lithology columnar chart, a high-position hydraulic fracturing borehole and a low-position hydraulic fracturing borehole are designed on the side of the cut; the hole bottom of the high-position hydraulic fracturing borehole completely exceeds the basic roof rock layer of the rock heading face on the side of the cut, and the hole bottom of the low-position hydraulic fracturing borehole completely exceeds the immediate roof rock layer on the side of the cut by more than 2-3 m; when there is no immediate roof rock layer, the hole bottom of the low-position hydraulic fracturing borehole completely exceeds the coal seam by more than 2-3 m, the designed angle between the bedding plane and the borehole axis is greater than the internal friction angle of the rock, the designed borehole spacing is greater than the water injection wetting radius, and the high-position hydraulic fracturing borehole and the low-position hydraulic fracturing borehole cover the range of the immediate roof rock layer, the basic roof rock layer, the immediate roof rock layer and the hard rock layer above the basic roof rock layer; A belt entry borehole is arranged on the side of the belt entry; the borehole diameter of the belt entry borehole is 75-80 mm, and the borehole length of the belt entry borehole exceeds the basic roof rock layer in the rock heading face by 2-5 m, and the angle between the bedding plane and the borehole axis is greater than the internal friction angle of the rock by 1-3°.

4. The method for bi-directional dual packer softening borehole placement suitable for weakly consolidated formations of claim 1, wherein, In step (4), the water injection operation specifically comprises: after the borehole construction, hole sealing is performed by using AB glue sealing technology, the hole sealing length is 3-3.5 m, a valve is installed at the borehole mouth after the hole sealing, a high-pressure water pump is connected, the cracking pressure is greater than the trans-layer hydraulic fracturing radial cracking pressure, the fracturing liquid volume is greater than the total water volume, and the water injection operation time is 10-12 days.

5. The method for installing a bi-directional dual packer softening borehole arrangement in a weakly cemented formation of claim 1, wherein, The method further comprises step (5): according to the arrangement position of the bidirectional double-row water injection softening borehole, a roadway displacement monitoring station is arranged, and the fracturing pressure relief effect is analyzed and evaluated.

6. The method for installing a bi-directional dual packer softening borehole arrangement in a weakly cemented formation of claim 5, wherein, The step (5) specifically comprises: arranging 10-12 groups of roadway displacement monitoring stations every 30-35 m outward from the drilling position according to the drilling trajectory of hydraulic fracturing.

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