Ground-underground cooperative area weakening based rockburst prevention and control method for thick and hard roof

Abstract

A ground-underground cooperative area weakening based rockburst prevention and control method for a thick and hard roof. The method comprises: first obtaining spatial distribution characteristics of a hard roof; then on the basis of the spatial distribution characteristics of the hard roof, obtaining different types of fracturing prevention and control target horizons and five fracturing prevention and control patterns corresponding thereto, wherein the five fracturing prevention and control patterns comprise: a low-position single thick and hard roof horizon, a low-position composite hard roof horizon, a high-low position composite thick and hard roof horizon, a high-position composite thick and hard roof horizon, and a high-position single thick and hard roof horizon. The method can fundamentally and comprehensively solve the problem of rockburst hazards induced by a thick and hard roof.

Description

A method for preventing erosion by coordinated regional weakening between the surface and underground of thick hard roof Technical Field

[0001] The present invention belongs to the technical field of underground coal mine safety, relates to a weakening and anti-collision method, and specifically relates to a weakening and anti-collision method for a coordinated area between a thick hard roof surface and an underground mine. Background Art

[0002] Coal in my country will remain the dominant energy source for a considerable period of time in the future, playing the role of "ballast and stabilizer" of energy. According to statistics, the number of deaths and the number of roof accidents in coal mine safety accidents in the past 10 years accounted for 27% and 35% of the national coal mine safety accidents respectively, ranking first among all types of accidents. The prevention and control of roof-type strong mine pressure dynamic disasters has become a key problem for safe and efficient mining of coal mines. One-third of my country's coal seams have thick and hard roofs (i.e. thick and hard roofs). Taking the Jurassic coalfields in the western mining areas as an example, under the lateral migration and ferrying of terrestrial sedimentary diversion channels, thick layers of hard sandstones have been formed. It is very easy to have strong mine pressure (rock burst) dynamic disasters caused by the sudden collapse of a single thick and hard large-scale hanging roof and the simultaneous or interactive breakage and migration of composite hard roofs.

[0003] At present, it is difficult to achieve accurate and efficient control of the thick and hard roof of coal mines, and thus it is impossible to effectively control the mine pressure in the mining area. As a result, mine pressure disasters are prone to occur frequently, which poses a huge hidden danger to production safety and causes serious economic losses.

[0004] Summary of the Invention

[0005] In view of the defects and shortcomings of the existing technology, the purpose of the present invention is to provide a method for weakening and preventing impact in the coordinated area of ​​the ground and underground thick hard roof, so as to solve the technical problem in the existing technology that the thick hard roof of coal mines is prone to induce impact ground pressure disasters.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for weakening and preventing erosion of a thick hard roof in a coordinated manner between the ground and underground areas, the method specifically comprising the following steps:

[0008] Step 1: Obtain the spatial distribution characteristics of the hard roof.

[0009] Step 2: Based on the spatial distribution characteristics of the hard roof obtained in step 1, a single thick roof layer and a composite hard roof layer are obtained; then, based on the formula for determining the position of the hard rock layer, the single thick roof layer and the composite hard roof layer are identified as hard rock layers to obtain the hard rock layer in the overburden and the soft rock layer group it controls.

[0010] The formula for determining the position of the hard rock layer is as follows:

[0011] Where:

[0012] E m+1 represents the elastic modulus of the m+1th rock layer.

[0013] h m+1 Represents the thickness of the m+1th rock layer.

[0014] γ m+1 Represents the bulk density of the m+1th rock layer.

[0015] h i Represents the thickness of the i-th rock layer, i = 1, 2,…, m.

[0016] γ i Represents the bulk density of the i-th rock layer, i = 1, 2,…, m.

[0017] E i Represents the elastic modulus of the i-th rock layer, i = 1, 2,…, m.

[0018] Step three: Based on the geological information of the hard rock layer and the soft rock layer group it controls obtained in step two, a hard rock layer with high static load energy density is obtained.

[0019] Step four, based on the hard rock formation with high static load energy density obtained in step three, obtain the dynamic load energy data of the hard rock formation with high static load energy density, and then determine the target layer for fracturing prevention and control according to the dynamic load energy data; the target layer for fracturing prevention and control belongs to one of the following five fracturing prevention and control modes, and the five fracturing prevention and control modes are: low-level single thick hard roof layer, low-level composite hard roof layer, high-low-level composite thick hard roof layer, high-level composite thick hard roof layer and high-level single thick hard roof layer.

[0020] Step 5: According to the different types of fracturing prevention and control target layers divided in step 4, different methods are used for weakening prevention and control. The specific steps include the following:

[0021] In step 5.1, when the target stratum for fracturing prevention and control is a low-lying single thick hard roof stratum, the weakening prevention and control method is as follows: construct a single-hole vertical well on the surface for large-volume fluid supply, and construct ultra-deep directional control borehole I on the thick hard roof downhole; use the single-hole vertical well on the surface as a fracturing fluid delivery channel, and drill multiple ultra-deep directional control boreholes I on the thick hard roof in the low-lying single thick hard roof stratum downhole as fracturing zone decompression drilling, and then carry out point-by-point and stage-by-stage fracturing stimulation.

[0022] In step 5.2, when the target stratum for fracturing prevention and control belongs to the low-level composite hard roof stratum, the weakening prevention and control method is as follows: construct a single-hole vertical well on the surface for large-volume fluid supply, and construct ultra-deep directional drilling II with thick hard roof in the well; use the single-hole vertical well on the surface as a fracturing fluid delivery channel, and drill multiple ultra-deep directional drilling II with thick hard roof in the low-level composite hard roof stratum in the well as the fracturing area for pressure relief. Then, fracturing stimulation is carried out using the low-level upper and lower two-layer method or the multi-layer staggered fracturing method.

[0023] In step 5.3, when the target stratum for fracturing prevention and control belongs to a high-low composite thick hard roof stratum, the weakening prevention and control method is as follows: construct a surface single-hole vertical well for large-volume fluid supply on the surface, and construct ultra-deep directional drilling hole III for the thick hard roof downhole; construct horizontal branch drilling holes in the surface horizontal well corresponding to the high-level thick hard roof rock layer to relieve pressure in the fracturing area; based on the surface single-hole vertical well to deliver fracturing fluid, use the ultra-deep directional drilling hole III for the thick hard roof to relieve pressure in the low-level thick hard roof area.

[0024] In step 5.4, when the target stratum for fracturing prevention and control belongs to the high-level composite hard roof stratum, the weakening prevention and control method is as follows: construct a single-hole vertical well and a surface ultra-long multi-horizontal branch borehole for large-volume fluid supply on the ground. Based on the surface single-hole vertical well to deliver fracturing fluid, the composite high-level thick hard roof is subjected to layered, dense and regional fracturing through the surface ultra-long multi-horizontal branch boreholes.

[0025] In step 5.5, when the target stratum for fracturing prevention and control is a high-level single thick hard roof stratum, the weakening prevention and control method is as follows: construct a single-hole vertical well and an extra-long surface borehole on the ground for large-volume fluid supply. Based on the single-hole vertical well, the fracturing fluid is delivered, and the high-level thick hard roof is subjected to intensive regional fracturing through the extra-long surface borehole.

[0026] The present invention also has the following technical features:

[0027] Specifically, in step 2, the hard rock layer identification includes the following steps:

[0028] Step 2.1, start calculating from the first rock layer above the coal seam and go up layer by layer. When the formula for determining the position of the hard rock layer is satisfied, the calculation will stop. At this time, starting from the first rock layer, the m+1th rock layer is the first hard rock layer.

[0029] Step 2.2, starting from the first hard rock layer, determine the position of the second hard rock layer according to the process of step 2.1, and so on, until the top hard rock layer is determined, which is set as the nth hard rock layer.

[0030] In step 2.3, after all hard rock layers are identified, the hard rock layers in the overburden and the soft rock layers they control are obtained.

[0031] Specifically, the process of step three is: input the geological information of the hard rock layer and the soft rock layer group it controls into the FLAC3D software, use the FISH language editing program built into the FLAC3D software to extract the stress state, elastic modulus and Poisson's ratio related parameters of each unit, generate an energy density cloud map based on the above parameters, and obtain a hard rock layer with high static load energy density.

[0032] Specifically, the process of step 4 is: using the microseismic joint monitoring system above and below the well to conduct online dynamic monitoring of the hard rock formation with high static energy density obtained in step 3, and obtain the dynamic load energy data of the hard rock formation with high static energy density; then screen 10 4 The above large energy events are analyzed, and the microseismic energy distribution law of the profile layer of hard rock formation with high static load energy density is analyzed to screen the key layers for breaking dynamic load energy release, and the comprehensive study of the overburden structure characteristics is carried out to determine the target layers for fracturing prevention and control in the thick hard roof impact.

[0033] Specifically, in step four, if there is one layer of hard roof within 60m of the coal seam roof, it belongs to a low-level single thick hard roof layer; if there are two layers of hard roof within 60m of the coal seam roof, it belongs to a low-level composite hard roof layer; if there is one layer of hard roof within 60m of the coal seam roof and one layer of hard roof above 60m, it belongs to a high-low-level composite thick hard roof layer; if there are two layers of hard roof above 60m of the coal seam roof, it belongs to a high-level composite thick hard roof layer; if there is a single hard roof above 60m of the coal seam roof, it belongs to a high-level single thick hard roof layer.

[0034] Specifically, in step 5.1, the distance between two adjacent ultra-deep directional control boreholes I in thick hard roof must satisfy the following formula: L1≤2D1; where L1 represents the distance between two adjacent ultra-deep directional control boreholes I in thick hard roof, and D1 represents the horizontal fracturing influence range of a single borehole.

[0035] Optional and specific, in step 5.2, when fracturing stimulation is performed using a low-level upper and lower two-layer method, the distance between the upper and lower layers of boreholes must satisfy the following formula: h1≤2d1; where h1 represents the distance between the upper and lower layers of boreholes, and d1 is the vertical fracturing influence range of a single hole.

[0036] Optional and specific, in step 5.2, when multi-layer staggered fracturing is used for fracturing transformation, the vertical distance between two adjacent layers needs to satisfy the following formula: h2≤2d2, where h2 represents the vertical distance between the two adjacent layers, and d2 represents the vertical fracturing influence range of a single hole; the horizontal distance between two adjacent layers needs to satisfy the following formula: L2≤2D2, where L2 represents the horizontal distance between the two adjacent layers, and D2 represents the horizontal fracturing influence range of a single borehole.

[0037] Specifically, in step 5.3, the distance between any two horizontal branch boreholes satisfies the following formula: d3≤r1; where d3 represents the distance between any two horizontal branch boreholes, and r1 represents the extension radius of the fracturing crack along the direction of the horizontal branch borehole.

[0038] Specifically, in step 5.4, the number of ultra-long multi-horizontal branch boreholes on the ground is calculated according to the following formula: N = (L3 / 2r2) + 1; where N represents the number of ultra-long multi-horizontal branch boreholes on the ground, L3 represents the length of the ultra-long multi-horizontal branch borehole on the ground, and r2 represents the extension radius of the fracturing crack along the direction of the ultra-long multi-horizontal branch borehole on the ground.

[0039] The beneficial technical effects of the present invention compared with the prior art are as follows:

[0040] (I) The method for coordinating the weakening and anti-bumping of the thick hard roof on the ground and underground of the present invention determines, after obtaining the spatial distribution characteristics of the hard roof, a low-level single thick hard roof layer, a low-level composite hard roof layer, a high-low-level composite thick hard roof layer, a high-level composite thick hard roof layer and a high-level single thick hard roof layer according to the spatial distribution characteristics of the hard roof.

[0041] For low-level single thick hard roof layers, the system uses large-volume, high-pressure delivery channels from surface wells, combined with precise downhole directional long drilling technology and staged fracturing technology based on open-hole directional aggregate fracturing to achieve effective regional pressure relief, weakening, and shock prevention for single low-level thick hard roof layers. For high-level single thick hard roof layers, the system directly utilizes staged fracturing with horizontal long boreholes on the ground to achieve regional pressure relief and shock prevention. For conditions where both high- and low-level thick hard roof layers exist (i.e., low-level composite hard roof layers, high- and low-level composite thick hard roof layers, and high-level composite thick hard roof layers), the high-level thick hard roof is controlled by staged fracturing with long surface directional drilling, and the entire panel is controlled by downhole open-hole directional long drilling with aggregate control and fracturing to weaken the low-level thick hard roof, thereby achieving effective regional pressure relief and shock prevention with full coverage of multiple working faces or panels.

[0042] Based on the above analysis, it can be seen that the present invention implements different prevention and control measures based on different strata, realizes the pressure relief and anti-impact technical mode of the fracturing area in the above five scenarios, and fundamentally and comprehensively solves the impact ground pressure disasters induced by thick and hard roof.

[0043] (II) The present invention's method for weakening and preventing impacts in the area of ​​thick hard roofs by coordinating ground and underground areas uses a vertical well on the ground as a large-volume liquid output channel, takes advantage of the precise opening of horizontal branches on the ground and the ultra-long horizontal drilling of underground holes, and carries out pressure relief technology for the artificial fractured areas of thick hard roofs by segmented fracturing, shortens the pressure step distance, reduces the rotational load energy, and reduces the static load storage energy by fracturing into blocks, thus achieving full-mode, precise, and effective prevention and control of impact ground pressure disasters in thick hard roofs. This method integrates the advantages of large displacement, high pressure, and spatial freedom of ground fracturing, as well as the advantages of underground directional long drilling, which is not affected by the terrain during the winter rainy season, is low-cost, is directly disaster-preventing, has a controllable construction period, and is low-priced.

[0044] (III) This method for coordinated regional weakening and anti-blowout of thick hard roofs, both on the surface and underground, uses sedimentary environmental analysis of the study area, combined with multi-scale, small-cycle sedimentary facies and detailed tracking analysis of single sand bodies, to transparently, meticulously, and accurately reveal the overburden characteristics of thick hard roofs on coal seams. Real-time trajectory control and precise drilling technology for ultra-long horizontal boreholes, both on the surface and underground, allows for precise control and management of the target anti-blowout strata.

[0045] (IV) The method for collaboratively weakening and preventing impact of thick hard roof on the ground and underground, through the static load energy calculation of FLAC3D and the real-time monitoring and analysis of the dynamic load energy of the microseismic online system, combined with the distribution characteristics of the coal seam roof overburden structure revealed by sedimentary microfacies, quantitatively screened the key strata for preventing and controlling impact ground pressure disasters in thick hard roof.

[0046] (V) The method for weakening and preventing impact of the thick hard roof on the ground and in the underground coordinated areas of the present invention can effectively prevent and control the impact ground pressure of the thick hard roof on multiple working faces or the entire panel area at one time, realize the safe and efficient recovery of the mine and the orderly mining and excavation connection, and provide effective support for the supply of coal energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a flow chart of the method for coordinated regional weakening and anti-blowout of thick hard roof on the ground and underground.

[0048] Figure 2 is a schematic diagram of the weakened anti-collision of a low-lying single thick hard roof layer.

[0049] Figure 3 is a schematic diagram of the weakened anti-collision of the low-level composite hard roof layer.

[0050] Figure 4 is a schematic diagram of the weakened anti-collision of the high-low composite thick hard roof layer.

[0051] Figure 5 is a schematic diagram of the weakened anti-collision of the high-level composite thick hard roof layer.

[0052] Figure 6 is a schematic diagram of the weakened anti-collision of a high-level single thick hard roof layer.

[0053] Figure 7 is a schematic diagram of the prevention and control effect of a low-lying single thick hard roof layer.

[0054] Figure 8 is a schematic diagram of the prevention and control effect of the low-level composite hard roof layer.

[0055] Figure 9 is a schematic diagram of the prevention and control effect of the high-low composite thick hard roof layer.

[0056] Figure 10 is a schematic diagram of the prevention and control effect of the high-level composite thick hard roof layer.

[0057] Figure 11 is a schematic diagram of the prevention and control effect of a high-level single thick hard roof layer.

[0058] The meanings of the numbers in the figure are: 1-single-hole vertical well on the ground, 2-ultra-deep directional control drilling hole I in thick hard roof, 3-ultra-deep directional control drilling hole II in thick hard roof, 4-horizontal branch drilling hole, 5-ultra-long multi-horizontal branch drilling hole on the ground, 6-ultra-long drilling hole on the ground.

[0059] The technical solution of the present invention is further described below in conjunction with embodiments. DETAILED DESCRIPTION

[0060] It should be noted that all software and systems used in the present invention, unless otherwise specified, are those known in the art. For example, the combined uphole and downhole microseismic monitoring system is a monitoring system known in the art. FLAC3D software is a three-dimensional numerical analysis software known in the art, developed by Itasca.

[0061] It should be noted that the "hard rock layer" in the present invention is not a hard rock layer in the general sense. It refers to rock layers whose deflection during deformation is smaller than that of the underlying rock layers and which do not deform in coordination with the underlying rock layers.

[0062] It should be noted that the data involved in the present invention all adopt conventional units known in the prior art, and the calculation process is all dimensionless operations.

[0063] In accordance with the above technical solution, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0064] Example:

[0065] This embodiment provides a method for weakening and preventing impacts in the coordinated areas of the thick hard roof on the ground and underground, as shown in FIG1 . The method specifically includes the following steps:

[0066] Step 1: Obtain the spatial distribution characteristics of the hard roof:

[0067] Through the fine tracking analysis of the trinity of "single well phase-profile phase-plane sedimentary phase" small cyclic sedimentary phases and single sand bodies, combined with the overburden structure of the hard roof, the spatial distribution characteristics of the hard roof were mapped out.

[0068] Step 2: Based on the spatial distribution characteristics of the hard roof obtained in step 1, single-layer tracking and detailed temporal and spatial distribution of single thick roof layers and composite hard roof layers at the mine and working face scales are performed to obtain single thick roof layers and composite hard roof layers; then, hard rock strata are identified for the single thick roof layers and composite hard roof layers to obtain the hard rock layers in the overburden and the soft rock layer groups they control. In step 2, the specific steps for hard rock strata identification include the following:

[0069] Step 2.1: Calculate from the first rock layer above the coal seam upwards. When the formula for determining the position of the hard rock layer is satisfied, the calculation stops. At this time, starting from the first rock layer, the m+1th rock layer is the first hard rock layer. The formula for determining the position of the hard rock layer is obtained according to the following steps:

[0070] In step 2.1.1, assume that the first rock layer is a hard rock layer, and the rock layers above it up to the mth layer deform in coordination with it, while the m+1th rock layer does not deform in coordination with it. In this case, the m+1th rock layer is the second hard rock layer. Since the first to mth rock layers deform in coordination, the curvatures of the rock layers are the same, and each rock layer forms a composite beam. The load exerted by the mth rock layer on the first hard rock layer can be deduced from the composite beam principle, as shown in the following formula I:

[0071] Where:

[0072] q1(x)| m It represents the load exerted by the mth rock layer on the first hard rock layer;

[0073] E1 represents the elastic modulus of the first hard rock layer;

[0074] h1 represents the thickness of the first hard rock layer;

[0075] h i represents the thickness of the i-th rock layer, i = 1, 2, ..., m;

[0076] γ i represents the bulk density of the i-th rock layer, i = 1, 2, ..., m;

[0077] E i Represents the elastic modulus of the i-th rock layer, i = 1, 2,…, m.

[0078] Step 2.1.2, the load generated by the m+1th layer on the first hard rock layer can be expressed as follows:

[0079] Where:

[0080] q1(x)| m+1 It represents the load exerted by the m+1th rock layer on the first hard rock layer.

[0081] Step 2.1.3: Since the m+1th layer is a hard rock layer, its deflection is smaller than that of the lower rock layer. The rock layers above the m+1th layer no longer need the lower rock layer to bear the load it bears. The following formula III can be obtained: q1(x)| m+1 <q1(x)| m Formula III;

[0082] In step 2.1.4, substitute Formula I and Formula II into Formula III. After simplification, we obtain Formula IV for determining the location of hard rock formations, which is:

[0083] Where:

[0084] E m+1 represents the elastic modulus of the m+1th rock layer;

[0085] h m+1 represents the thickness of the m+1th rock layer;

[0086] γ m+1 Represents the bulk density of the m+1th rock layer.

[0087] Step 2.2, starting from the first hard rock layer, determine the position of the second hard rock layer according to the process of step 2.1, and so on, until the top hard rock layer is determined, which is set as the nth hard rock layer.

[0088] In step 2.3, after all hard rock layers are identified, the hard rock layers in the overburden and the soft rock layer groups they control are obtained. The soft rock layer group controlled by a particular hard rock layer means that the soft rock between any two hard rock layers belongs to the soft rock layer group controlled by the next hard rock layer. For example, the soft rock between the first and second hard rock layers belongs to the soft rock layer group controlled by the second hard rock layer.

[0089] Step three, based on the geological information of the hard rock layer and the soft rock layer group it controls obtained in step two, obtain a hard rock layer with high static load energy density; the specific process is: input the geological information of the hard rock layer and the soft rock layer group it controls into FLAC3D software, use the built-in FISH language editing program of FLAC3D software to extract the stress state, elastic modulus and Poisson's ratio related parameters of each unit, generate an energy density cloud map according to the above parameters, and obtain a hard rock layer with high static load energy density.

[0090] Step 4: Based on the high static energy density hard rock formation obtained in step 3, dynamic energy data of the high static energy density hard rock formation is obtained, and then the target layer for fracturing prevention and control is determined according to the dynamic energy data. The specific process is as follows:

[0091] Using the microseismic joint monitoring system above and below the well, the high static load energy density hard rock formation obtained in step 3 is monitored online dynamically to obtain the dynamic load energy data of the high static load energy density hard rock formation; then 10 4 The above large energy events were analyzed, and the microseismic energy distribution law of the profile layer of hard rock formation with high static load energy density was analyzed. The key layers for the release of fracture dynamic load energy were screened. The structural characteristics of the overburden were comprehensively studied to determine the five fracturing prevention and control modes corresponding to the target layers of fracturing prevention and control in the thick hard roof impact, namely: low-level single thick hard roof layer (mode 1), low-level composite hard roof layer (mode 2), high-low-level composite thick hard roof layer (mode 3), high-level composite thick hard roof layer (mode 4) and high-level single thick hard roof layer (mode 5).

[0092] In this embodiment, the treatment mode is identified based on the number and distribution position of the screened hard roofs, where a single hard roof within 60m of the coal seam roof belongs to mode 1, two layers of hard roof within 60m of the coal seam roof belong to mode 2, one layer of hard roof within 60m of the coal seam roof and one layer of hard roof above 60m (especially above 100m) belong to mode 3, two layers of hard roof above 60m of the coal seam roof belong to mode 4, and a single hard roof above 60m of the coal seam roof belongs to mode 5.

[0093] Step 5: Based on the different types of fracturing prevention and control target layers divided in step 4, different methods are used for weakening prevention and control; the details are as follows:

[0094] Step 5.1, as shown in FIG2, when the target layer for fracturing prevention and control belongs to a low-level single thick hard roof layer, the weakening prevention and control method (i.e., mode 1) is as follows: constructing a single-hole vertical well (1) on the ground for large-volume fluid supply, and constructing a thick hard roof ultra-deep directional drilling hole I (2) underground; using the single-hole vertical well (1) on the ground as a fracturing fluid delivery channel, in the low-level single thick hard roof layer underground, using multiple thick hard roof ultra-deep directional drilling holes I (2) as fracturing area decompression drilling, and then performing point-by-point and section-by-section fracturing transformation.

[0095] In this embodiment, each thick hard roof ultra-deep directional control drill hole I (2) is horizontal, and the depth of each thick hard roof ultra-deep directional control drill hole I (2) is greater than 800m. The distance between two adjacent thick hard roof ultra-deep directional control drill holes I (2) must satisfy the following formula: L1≤2D1; where L1 represents the distance between two adjacent thick hard roof ultra-deep directional control drill holes I, and D1 represents the horizontal fracturing influence range of a single drill hole.

[0096] Step 5.2, as shown in FIG3, when the target layer for fracturing prevention and control belongs to the low-level composite hard roof layer, the weakening prevention and control method (i.e., mode 2) is as follows: constructing a single-hole vertical well (1) on the ground for large-volume fluid supply, and constructing a thick hard roof ultra-deep controlled drilling hole II (3) underground; using the single-hole vertical well (1) on the ground as a fracturing liquid delivery channel, in the low-level composite hard roof layer underground, using multiple thick hard roof ultra-deep controlled drilling holes II (3) as fracturing area decompression drilling, and then adopting a low-level upper and lower two-layer method or a multi-layer staggered fracturing method to carry out fracturing transformation. FIG3 takes the low-level upper and lower two-layer method as an example.

[0097] In this embodiment, each of the ultra-deep directional control drilling holes II (3) in the thick hard roof is in a horizontal direction, and the depth of each of the ultra-deep directional control drilling holes II (3) in the thick hard roof is greater than 800m.

[0098] When fracturing stimulation is performed using a low-level upper and lower two-layer method, the distance between the upper and lower layers of boreholes must satisfy the following formula: h1≤2d1; where h1 represents the distance between the upper and lower layers of boreholes, and d1 is the vertical fracturing influence range of a single hole.

[0099] When multi-layer staggered fracturing is used for fracturing stimulation, the number of layers needs to be determined based on the selection results of the thick hard roof impact fracturing prevention and control layers. The vertical distance between two adjacent layers needs to satisfy the following formula: h2≤2d2; where h2 represents the vertical distance between two adjacent layers, and d2 represents the vertical fracturing influence range of a single hole. The horizontal distance between two adjacent layers needs to satisfy the following formula: L2≤2D2; where L2 represents the horizontal distance between two adjacent layers, and D2 represents the horizontal fracturing influence range of a single borehole.

[0100] Step 5.3, as shown in Figures 3 and 4, when the target layer for fracturing prevention and control belongs to the high-low composite thick hard roof layer, the weakening prevention method (i.e., mode 3) is as follows: construct a single-hole vertical well (1) on the ground for large-volume fluid supply, and construct a thick hard roof ultra-deep directional drilling hole II (3) underground; construct a horizontal branch drilling hole (4) at the position of the high-level thick hard roof rock layer in the ground horizontal well to decompress the fracturing area; based on the single-hole vertical well (1) on the ground, the fracturing fluid is transported, and the thick hard roof ultra-deep directional drilling hole II (3) is used to decompress the low-level thick hard roof area.

[0101] In this embodiment, the distance between any two horizontal branch boreholes (4) must satisfy the following formula: d3≤r1; wherein d3 represents the distance between any two horizontal branch boreholes, and r1 represents the extension radius of the fracturing crack along the horizontal branch borehole.

[0102] Step 5.4, as shown in FIG5 , when the target layer for fracturing prevention and control belongs to the high-position composite hard roof layer, the weakening prevention and control method (i.e., mode 4) is: constructing a ground single-hole vertical well (1) and a ground ultra-long multi-horizontal branch borehole (5) for large-volume fluid supply on the ground, based on the ground single-hole vertical well (1) to transport fracturing fluid, and through the ground ultra-long multi-horizontal branch borehole (5) to carry out layered, dense and regional fracturing transformation on the composite high-position thick hard roof.

[0103] In this embodiment, the length of the ground super-long multi-horizontal branch borehole (5) is greater than 800m, and the number of the ground super-long multi-horizontal branch borehole (5) is calculated according to the following formula: N = (L3 / 2r2) + 1; wherein N represents the number of the ground super-long multi-horizontal branch boreholes, L3 represents the length of the ground super-long multi-horizontal branch borehole, and r2 represents the extension radius of the fracturing crack along the direction of the ground super-long multi-horizontal branch borehole.

[0104] Step 5.5, as shown in FIG6 , when the target stratum for fracturing prevention and control belongs to a high-position single thick hard roof stratum, the weakening prevention and control method (i.e., mode 5) is as follows: constructing a ground single-hole vertical well (1) and a ground super-long borehole (6) for large-volume fluid supply on the ground, based on the ground single-hole vertical well (1) to transport fracturing fluid, and through the ground super-long borehole (6) to carry out intensive regional fracturing transformation on the high-position thick hard roof.

[0105] In this embodiment, the length of the ground super-long borehole (6) is greater than 800m. The number of the ground super-long borehole (6) is obtained in the same manner as the above-mentioned ground super-long multi-horizontal branch borehole (5).

[0106] Effect verification:

[0107] (A) When the target stratum for fracturing prevention and control is a low-lying, single, thick, hard roof, the prevention and control effect is shown in Figure 7. As shown in Figure 7, by weakening and transforming the rock properties of the hard rock stratum, the collapse morphology can be changed, the pressure step distance can be shortened, and the concentration of stress transfer can be reduced in layers and sections. By controlling the movement state of the low-lying hard rock stratum, the intensity of the mine pressure in the single hard rock stratum can be effectively controlled.

[0108] (B) When the target stratum for fracturing prevention and control is a low-lying composite hard roof stratum, the prevention and control effect is shown in Figure 8. As shown in Figure 8, by staggering the fracturing stages, the upper and lower layers of the low-lying composite hard rock stratum can be forced to adopt asynchronous fracturing as the primary motion state, preventing the strong impact dynamic disasters caused by synchronous fracturing of the composite rock stratum. At the same time, the stress transmission path after asynchronous fracturing is destroyed, and the load and stress directly transmitted to the working face are dispersed. Through the comprehensive control of the fracture structure and stress transmission, comprehensive control of dynamic disasters in the low-lying composite hard rock stratum is achieved.

[0109] (C) When the target stratum for fracturing prevention and control is a high-low composite thick hard roof stratum, the prevention and control effect is shown in Figure 9. As shown in Figure 9, after adopting the combined high-low level control, the low-level weakening can change the collapse morphology, shorten the pressure step distance, and reduce the concentration of stress transfer; the high-level weakening can control the scale of the hard roof collapse, promote the timely fracture of the high-level rock layer, reduce the energy reduction and increase the frequency, and reduce the range and degree of damage of the single fracture of the high-level rock layer; the combination of the two can control and avoid the dynamic disasters of the working face caused by the synchronous movement of the high and low levels.

[0110] (D) When the target stratum for fracturing prevention and control is the high-level composite thick hard roof, the prevention and control effect is shown in Figure 10. As shown in Figure 10, by promoting asynchronous fracturing of the upper and lower layers of the high-level composite hard rock stratum and simultaneously breaking the concentrated stress transmission path, the high-level composite hard roof under control experienced a large-scale single fracture, resulting in high energy release. By comprehensively controlling the fracture range and stress transmission, comprehensive control of dynamic hazards in the high-level composite hard rock stratum is achieved.

[0111] (E) When the target stratum for fracturing prevention and control is a high, single, thick, hard roof stratum, the prevention and control effect is shown in Figure 11. As shown in Figure 11, by weakening and transforming the rock properties of the high, hard rock stratum, the range of the hanging roof can be reduced, the concentration of stress transfer can be reduced, and by controlling the movement of the high, hard rock stratum, the risk of a single high-energy release in the high-level rock stratum can be avoided, ultimately achieving effective control of the mine pressure manifestation at the working face.

Claims

1. A method for weakening and preventing impacts in the coordinated area between the ground and underground of a thick hard roof, characterized in that: The method specifically comprises the following steps: Step 1, obtaining the spatial distribution characteristics of the hard roof; Step 2: According to the spatial distribution characteristics of the hard roof obtained in step 1, a single thick roof and a composite hard roof layer are obtained; then, according to the formula for determining the position of the hard rock layer, the single thick roof and the composite hard roof layer are identified as hard rock layers, and the hard rock layer in the overburden and the soft rock layer group controlled by it are obtained; The formula for determining the position of the hard rock layer is as follows: Where: E m+1 represents the elastic modulus of the m+1th rock layer; h m+1 represents the thickness of the m+1th rock layer; γ m+1 represents the bulk density of the m+1th rock layer; h i represents the thickness of the i-th rock layer, i = 1, 2, ..., m; γ i represents the bulk density of the i-th rock layer, i = 1, 2, ..., m; E i represents the elastic modulus of the i-th rock layer, i = 1, 2, ..., m; Step 3, based on the geological information of the hard rock layer and the soft rock layer group controlled by it obtained in step 2, a hard rock layer with high static load energy density is obtained; Step 4, based on the hard rock formation with high static energy density obtained in step 3, dynamic load energy data of the hard rock formation with high static energy density is obtained, and then the target layer for fracturing prevention and control is determined according to the dynamic load energy data; the target layer for fracturing prevention and control belongs to one of the following five fracturing prevention and control modes, and the five fracturing prevention and control modes are: a low-level single thick hard roof layer, a low-level composite hard roof layer, a high-low-level composite thick hard roof layer, a high-level composite thick hard roof layer and a high-level single thick hard roof layer; Step 5: According to the different types of fracturing prevention and control target layers divided in step 4, different methods are used for weakening prevention and control; specifically, the following steps are included: Step 5.1, when the target stratum for fracturing prevention and control belongs to a low-level single thick hard roof stratum, the weakening prevention and control method is as follows: construct a single-hole vertical well (1) on the ground for large-volume fluid supply, and construct a thick hard roof ultra-deep directional drilling hole I (2) underground; use the single-hole vertical well (1) on the ground as a fracturing fluid delivery channel, and use multiple thick hard roof ultra-deep directional drilling holes I (2) in the low-level single thick hard roof stratum underground as fracturing area decompression drilling, and then perform point-by-point and section-by-section fracturing transformation; Step 5.2, when the target stratum for fracturing prevention and control belongs to a low-level composite hard roof stratum, the weakening prevention and control method is as follows: construct a single-hole vertical well (1) on the ground for large-volume fluid supply, and construct a thick hard roof ultra-deep controlled drilling hole II (3) underground; use the single-hole vertical well (1) on the ground as a fracturing fluid delivery channel, and use multiple thick hard roof ultra-deep controlled drilling holes II (3) as fracturing area decompression drilling in the low-level composite hard roof stratum underground, and then use a low-level upper and lower two-layer method or a multi-layer staggered fracturing method to carry out fracturing transformation; Step 5.3, when the target stratum for fracturing prevention and control belongs to the high-low composite thick hard roof stratum, the weakening prevention and control method is as follows: construct a single-hole vertical well (1) on the ground for large-volume fluid supply, and construct a thick hard roof ultra-deep directional drilling hole II (3) underground; construct a horizontal branch drilling hole (4) at the position of the high-level thick hard roof stratum in the ground horizontal well to depressurize the fracturing area; based on the single-hole vertical well (1) on the ground to transport fracturing fluid, use the thick hard roof ultra-deep directional drilling hole II (3) to depressurize the low-level thick hard roof area; Step 5.4, when the target stratum for fracturing prevention and control belongs to the high-position composite hard roof stratum, the weakening prevention and control method is: constructing a ground single-hole vertical well (1) and a ground super-long multi-horizontal branch borehole (5) for large-volume fluid supply on the ground, based on the ground single-hole vertical well (1) to transport fracturing fluid, and through the ground super-long multi-horizontal branch borehole (5) to perform layered, dense and regional fracturing transformation on the composite high-position thick hard roof; Step 5.5, when the target stratum for fracturing prevention and control belongs to a high-position single thick hard roof stratum, the weakening prevention and control method is: constructing a ground single-hole vertical well (1) and a ground super-long borehole (6) for large-volume fluid supply on the ground, based on the ground single-hole vertical well (1) to transport fracturing fluid, and through the ground super-long borehole (6) to carry out intensive regional fracturing transformation on the high-position thick hard roof.

2. The method for preventing the thick hard roof from being damaged by coordinated regional weakening on the ground and underground as claimed in claim 1, characterized in that: In step 2, the identification of hard rock formations specifically includes the following steps: Step 2.1, starting from the first rock layer above the coal seam, calculate upwards layer by layer. When the formula for determining the position of the hard rock layer is satisfied, the calculation will no longer be continued upwards. At this time, starting from the first rock layer, the m+1th rock layer is the first hard rock layer; Step 2.2, starting from the first hard rock layer, determine the position of the second hard rock layer according to the process of step 2.1, and so on, until the top hard rock layer is determined, which is set as the nth hard rock layer; Step 2.3, after all the hard rock layers are identified, the hard rock layers in the overburden and the soft rock layers they control are obtained.

3. The method for preventing the thick hard roof from being damaged by coordinated regional weakening on the ground and underground as claimed in claim 1, characterized in that: The specific process of step three is: input the geological information of the hard rock layer and the soft rock layer group it controls into the FLAC3D software, use the built-in FISH language editing program of the FLAC3D software to extract the stress state, elastic modulus and Poisson's ratio related parameters of each unit, generate an energy density cloud map based on the above parameters, and obtain a hard rock layer with high static load energy density.

4. The method for preventing the thick hard roof from being damaged by coordinated regional weakening on the ground and underground as claimed in claim 1, characterized in that: The specific process of step 4 is: using the microseismic joint monitoring system above and below the well to conduct online dynamic monitoring of the hard rock formation with high static energy density obtained in step 3, and obtain the dynamic load energy data of the hard rock formation with high static energy density; then select 10 4 For the above large energy events, we analyze the distribution law of microseismic energy in the profile layer of hard rock strata with high static load energy density, screen the key layers for breaking dynamic load energy release, comprehensively study the characteristics of overburden structure, and determine the target layers for fracturing prevention and control in the thick hard roof impact.

5. The method for preventing the thick hard roof from being weakened and eroded by coordinated areas on the ground and underground as claimed in claim 1, characterized in that: In step four, if there is one layer of hard roof within 60m of the coal seam roof, it belongs to a low-level single thick hard roof layer; if there are two layers of hard roof within 60m of the coal seam roof, it belongs to a low-level composite hard roof layer; if there is one layer of hard roof within 60m of the coal seam roof and one layer of hard roof above 60m, it belongs to a high-low-level composite thick hard roof layer; if there are two layers of hard roof above 60m of the coal seam roof, it belongs to a high-level composite thick hard roof layer; if there is a single hard roof above 60m of the coal seam roof, it belongs to a high-level single thick hard roof layer.

6. The method for preventing the thick hard roof from being damaged by coordinated regional weakening on the ground and underground as claimed in claim 1, characterized in that: In step 5.1, the distance between two adjacent thick hard roof ultra-deep directional control boreholes Ⅰ(2) must satisfy the following formula: L1≤2D1; where L1 represents the distance between two adjacent thick hard roof ultra-deep directional control boreholes Ⅰ, and D1 represents the horizontal fracturing influence range of a single borehole.

7. The method for preventing the thick hard roof from being weakened and eroded by coordinated areas on the ground and underground as claimed in claim 1, characterized in that: In step 5.2, when the low-level upper and lower layers are used for fracturing, the distance between the upper and lower layers of boreholes must satisfy the following formula: h1≤2d1; where h1 represents the distance between the upper and lower layers of boreholes, and d1 is the vertical fracturing influence range of a single hole.

8. The method for preventing the thick hard roof from being weakened and eroded by coordinated areas on the ground and underground as claimed in claim 1, characterized in that: In step 5.2, when multi-layer staggered fracturing is used for fracturing transformation, the vertical distance between two adjacent layers needs to satisfy the following formula: h2≤2d2, where h2 represents the vertical distance between two adjacent layers, and d2 represents the vertical fracturing influence range of a single hole; the horizontal distance between two adjacent layers needs to satisfy the following formula: L2≤2D2, where L2 represents the horizontal distance between two adjacent layers, and D2 represents the horizontal fracturing influence range of a single borehole.

9. The method for preventing the thick hard roof from being weakened and eroded by coordinated areas on the ground and underground as claimed in claim 1, characterized in that: In step 5.3, the distance between any two horizontal branch boreholes satisfies the following formula: d3≤r1; where d3 represents the distance between any two horizontal branch boreholes, and r1 represents the extension radius of the fracturing crack along the horizontal branch borehole.

10. The method for preventing the thick hard roof from being damaged by coordinated regional weakening on the ground and underground as claimed in claim 1, characterized in that: In step 5.4, the number of the ground super-long multi-horizontal branch boreholes (5) is calculated according to the following formula: N = (L3 / 2r2) + 1; wherein N represents the number of the ground super-long multi-horizontal branch boreholes, L3 represents the length of the ground super-long multi-horizontal branch boreholes, and r2 represents the extension radius of the fracturing cracks along the direction of the ground super-long multi-horizontal branch boreholes.

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