Method for preventing regional rock burst in thick and hard key stratum

Abstract

The thick and hard key layer regional rock burst prevention method is characterized in that: the thick and hard key layer of a coal mining face is determined, the thick and hard key layer is tested by fracturing, the fracturing radius R of the roof hydraulic fracturing borehole is determined; a plurality of fracturing units are divided along the tendency of the panel face, a plurality of fracturing sections are divided in each fracturing unit along the strike of the panel face; the fracturing equipment is installed in each fracturing section in the first fracturing unit, the thick and hard key layer of the fracturing section is drilled and hydraulically fractured along the tendency of the face by the fracturing equipment; and finally, the fracturing operation is sequentially performed on the fracturing sections in the subsequent fracturing units along the mining direction of the panel face. The present application solves the problem that the fracturing operation and the mining operation are located in the same face roadway, which causes the mining period to be tight.

Description

Technical Field

[0001] This invention belongs to the field of coal mine safety mining technology, specifically relating to a method for preventing regional rockbursts in thick and hard key strata. Background Technology

[0002] Rockbursts, as one of the major hazards faced in deep coal mining, cause incalculable losses to mines and personnel. Statistics show that most rockburst accidents occur in roadways, with more than half of them occurring in the two leading roadways of the working face. In actual production, rockburst disasters are mostly roof-type, especially in mining areas with hard roofs. Due to the high strength and thickness of the roof, it is not easy to break during mining, resulting in energy accumulation that can easily induce rockbursts.

[0003] In recent years, rockburst-prone mines have gradually adopted both surface and underground hydraulic fracturing to address the thick, hard, critical strata above the working face. This typically involves surface directional hydraulic fracturing and underground roof hydraulic fracturing. Surface directional hydraulic fracturing has a wider fracturing range and is not limited by mining layout, but it is costly, and its effectiveness in preventing rockbursts remains unclear. Underground roof hydraulic fracturing, on the other hand, is relatively cheaper and is currently widely deployed in already excavated roadways within the working face awaiting mining, with fracturing boreholes oriented along the working face direction. However, when performing underground roof hydraulic fracturing, fracturing and mining often occur in the same working face roadway, which is often constrained by mining schedules, leading to tight mining timelines. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preventing regional rockburst in thick and hard key layers, which solves the problem of tight mining schedules caused by the fracturing operation and mining operation being located in the same working face roadway during existing underground hydraulic fracturing of the roof.

[0005] The technical solution adopted in this invention is a method for preventing regional rockbursts in thick and hard critical layers, comprising the following steps: Step 1: Identify the thick and hard key layer of the coal mining face, conduct fracturing tests on the thick and hard key layer, and determine the fracturing radius R of the hydraulic fracturing borehole in the roof. Step 2: Divide the working face of the panel into several fracturing units, and within each fracturing unit, divide the working face of the panel into several fracturing sections. Step 3: Install fracturing equipment in each fracturing section corresponding to the first fracturing unit. Install fracturing equipment in each fracturing section through the rubber transport roadway of the working face. The fracturing equipment drills and hydraulically fractures the thick and hard key layer of the fracturing section along the dip of the working face. After the thick and hard key layer of the fracturing section I of the first fracturing unit is hydraulically fracturing, the fracturing section I is recycled through the rubber transport roadway of the first production face and the return air roadway of the first production face. At the same time, the fracturing equipment performs fracturing operation in the fracturing section II of the first fracturing unit in the rubber transport roadway of the working face. Step 4: Perform fracturing operations on the fracturing sections in the subsequent fracturing units in sequence along the mining direction of the working face. Before the coal mining face is mined back, perform hydraulic fracturing on the fracturing sections in the advanced coal mining face to cause all rock strata below the thick and hard key layer of the coal mining face to collapse regularly.

[0006] The invention is further characterized in that, In step 2, the fracturing units and fracturing sections are divided at equal intervals. The interval LS between the fracturing sections is shown in the following formula: LS = 2RX; Where R is the fracturing radius and X is the number of boreholes drilled by the fracturing equipment in a single fracturing section.

[0007] In step 3, the fracturing equipment is set at equal intervals along the working face, with the distance between adjacent fracturing equipment being LS and the distance between the first fracturing equipment and the working face cut-off point being LS / 2.

[0008] Step 3, which involves drilling and hydraulic fracturing the thick, hard, critical layers along the working face in the fracturing zone, specifically includes the following steps: Step 3.1: Generate fracturing borehole trajectory lines based on the number of boreholes; Step 3.2: Drill the inclined and horizontal sections according to the fracturing borehole trajectory line, and withdraw the drill rod after drilling to the designated position; Step 3.3: Perform hydraulic fracturing on the horizontal section of the borehole until all horizontal sections of the borehole within the fracturing zone are fracturing.

[0009] In step 3.3, hydraulic fracturing is carried out by lowering packers or bridge plugs, injecting high-pressure water into the two-stage packers or bridge plugs for fracturing. The hydraulic fracturing is carried out in a backward manner, and fracture proppant is continuously injected during the fracturing process.

[0010] The length LA of the borehole in the first fracturing unit shall not be less than Y1 times the dip length of a single coal mining face, where Y1 is an integer not less than 2.

[0011] The distance between the roadway where the fracturing equipment is located in the Nth fracturing unit and the roadway where the fracturing equipment is located in the (N-1)th fracturing unit is Y2 times the dip length of a single coal mining face, where Y2 is either Y1 or Y1-1.

[0012] LA length of borehole in non-first fracturing unit * As shown in the following formula: LA * =Y2*LG+LN; Where LG is the dip length of a single coal mining face; LN is the lateral projection length of the inclined section of the borehole in the (N-1)th fracturing unit.

[0013] The beneficial effects of this invention are: The present invention provides a method for preventing regional rockburst in thick and hard key strata. By adjusting the direction of the fracturing borehole to the dip direction of the working face and using the working roadway for fracturing operations to be a non-mining working face, the fracturing efficiency of the working face and the mining efficiency of the working face to be mined are improved. At the same time, it is more conducive to controlling the pressure situation during the mining period and ensuring the personal safety of personnel during mining.

[0014] This invention can not only meet the fracturing needs of the entire working face, but also carry out fracturing operations in specific areas of the working face to prevent rockbursts, thereby reducing the cost of rockburst prevention and control while improving the safe and efficient production of the working face. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the working face of the panel area; Figure 2 This is a schematic diagram of the fracturing equipment layout in the regional rockburst prevention method for thick and hard key layers of the present invention; Figure 3 This is a schematic diagram of the operation and construction of the first fracturing unit in the method for preventing regional rockburst in thick and hard key layers of the present invention; Figure 4 This is a schematic diagram of the operation and construction of a non-first fracturing unit in the regional rockburst prevention method for thick and hard key layers of the present invention.

[0016] In the figure, 1. First mining face adhesive transport roadway, 2. First mining face return air roadway, 3. Free working face return air roadway, 4. Free working face adhesive transport roadway, 5. Cutting hole, 6. Fracturing equipment, 7. Fracturing borehole trajectory line, 8. Fracturing section of fracturing borehole. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] like Figure 1 As shown, the regional rockburst prevention method for thick and hard key strata of the present invention is applied to the working face of the panel. In the figure, I, II, ... represent the working faces to be mined. During mining operations, mining is carried out sequentially starting from working face I. Usually, before mining, the first mining face I will have the first mining face haulage roadway 1 and the first mining face return air roadway 2 excavated on both sides. On both sides of working face II and subsequent working faces, the free-face return air roadway 3 and the free-face haulage roadway 4 will often be excavated in advance. Before mining the corresponding working face, the free-face return air roadway 3 and the free-face haulage roadway 4 are in a closed state. The present invention uses the pre-excavated free-face return air roadway 3 and free-face haulage roadway 4 to hydraulically fracture the thick and hard key strata of the working face to be mined, which plays a very good role in preventing rockburst.

[0019] Example 1 The present invention provides a method for preventing regional rockbursts in thick, hard, critical strata, specifically comprising the following steps: Step 1: Identify the thick, hard, critical strata in the coal face and conduct fracturing tests on them. Fracturing testing is a commonly used testing method in existing fracturing operations. The fracturing radius R of the hydraulic fracturing borehole in the roof is determined through fracturing tests.

[0020] Step 2, as follows Figure 2 As shown, the working face of the panel is divided into several fracturing units, and within each fracturing unit, several fracturing sections are divided along the direction of the working face of the panel. The fracturing units and fracturing sections are divided at equal intervals, and the interval LS between the fracturing sections is shown in the following formula: LS = 2RX; Where R is the fracturing radius and X is the number of boreholes drilled by the fracturing equipment in a single fracturing section.

[0021] To ensure that the thick, hard, critical layers in each fracturing section can be covered by fracturing, the number of boreholes drilled by the fracturing equipment within the fracturing section depends on the farthest drilling distance of the drilling rig. In other words, the division spacing LS of the fracturing section is also determined by the farthest drilling performance of the drilling rig.

[0022] In this embodiment, the fracturing unit consists of two working faces.

[0023] Step 3: Install fracturing equipment 6 in each fracturing section within the first fracturing unit to form the drilling field required for hydraulic fracturing. The fracturing equipment 6 drills and hydraulically fractures the thick and hard key layer of the fracturing section along the working face. like Figure 3 As shown, fracturing equipment 6 is installed in each fracturing section via the free-face conveyor chute 4. The fracturing equipment 6 is set at equal intervals along the working face, with a spacing of LS between adjacent fracturing equipment 6. The purpose is to ensure that all thick and hard key layers in the fracturing section can be fracturing, thereby improving the prevention effect of rockburst. The distance between the first fracturing equipment and the cut-out 5 of the working face is LS / 2.

[0024] After hydraulic fracturing of the thick and hard key layer of fracturing section I, the operators can carry out the recovery of fracturing section I through the first production face rubber transport roadway 1 and the first production face return air roadway 2. At the same time, the operators of fracturing equipment 6 can carry out fracturing operations in fracturing section II in the free working face rubber transport roadway 4. The operators of both sides do not need to wait for each other, which greatly improves the efficiency of the operation and alleviates the pressure of the construction period.

[0025] In the current process of connecting coal seams in mines prone to rock bursts, small coal pillars or even no coal pillars are used. Before the first mining face I is mined, the excavation of the solid coal roadways of the subsequent mining faces II, III, IV, etc. must be completed, and the fracturing of the thick and hard key layer that causes the disaster must be carried out in advance in the mining face I area.

[0026] Step 4, as follows Figure 4 As shown, fracturing operations are carried out sequentially in the fracturing sections of the subsequent fracturing units along the mining direction of the panel. When the subsequent fracturing units are operated, the unfractured parts in the previous fracturing unit need to be fractured. At the same time, hydraulic fracturing is carried out on the fracturing sections of the advanced coal mining face before the coal mining face is mined back, so that all rock strata below the thick and hard key layer of the coal mining face collapse regularly.

[0027] If mining operations are required for working face II after the mining of working face I is completed, then the fracturing operations of the corresponding fracturing section in the second fracturing unit must be completed to ensure the personal safety of personnel during mining.

[0028] Example 2 Step 3 of the method for preventing regional rockburst in thick and hard key layers of the present invention specifically includes the following steps: drilling and hydraulic fracturing of the thick and hard key layers in the fracturing section along the working face: Step 3.1: Generate fracturing borehole trajectory line 7 based on the number of boreholes. Existing drilling equipment can generate the fracturing borehole trajectory line 7 automatically. Step 3.2: Drill the inclined and horizontal sections according to the fracturing borehole trajectory line 7, and withdraw the drill rod after drilling to the designated position; In this invention, when performing hydraulic fracturing operations, only the horizontal section is fracturing to form a fracturing section length LY. The thick and hard key layer corresponding to the inclined section area is not fracturing in this fracturing unit, and is the unfracturing section length LN. The unfracturing section is fracturing by the next fracturing unit.

[0029] Among them, the fracturing borehole trajectory line 7 requires that, based on the drilling capacity of the fracturing equipment and the fracturing layer, the length of the fracturing section LY is the largest and the length of the unfracturing section LN is the smallest.

[0030] Step 3.3: Perform hydraulic fracturing on the horizontal section of the borehole until all horizontal sections of the borehole within the fracturing zone are fracturing.

[0031] When performing hydraulic fracturing in the horizontal section, several fracturing sections 8 are evenly divided into fracturing boreholes. Then, packers or bridge plugs are lowered, and high-pressure water is injected into the two-stage packers or bridge plugs for fracturing. Hydraulic fracturing is carried out in a retreating manner, and fracture proppant is continuously injected during the fracturing process.

[0032] In this invention, the length LA of the borehole in the first fracturing unit is not less than Y1 times the dip length of a single coal mining face, where Y1 is an integer not less than 2. LA is the sum of the length LY of the fracturing section and the length LN of the unfracturing section.

[0033] That is, when the first fracturing unit operation is carried out, the fracturing equipment is installed in the coal mining roadway of working face II at least. If the drilling rig has excellent performance, the fracturing equipment can be installed in the coal mining roadway of working face III, provided that the fracturing operation can be completed on the thick and hard key side of the first mining face 1 of working face I.

[0034] Furthermore, the distance between the roadway where fracturing equipment 6 is arranged in the Nth fracturing unit and the roadway where fracturing equipment 6 is arranged in the N-1th fracturing unit is Y2 times the dip length of a single coal mining face. At the same time, the construction of the roadway where fracturing equipment is arranged in the Nth fracturing unit needs to be completed before the mining face where the roadway where fracturing equipment is arranged in the N-1th fracturing unit is located is mined.

[0035] This means that during the construction of a fracturing drilling site, the fracturing area corresponding to the previous fracturing drilling site in the dip direction must not be mined back, in order to ensure the stability of the fracturing rock layer during the construction of the fracturing drilling site.

[0036] Wherein, when the drilling rig has sufficient drilling capacity, Y2=Y1; otherwise, Y2=Y1-1. LA length of borehole in non-first fracturing unit * As shown in the following formula: LA * =Y2*LG+LN; Where Y2 is Y1 or Y1-1; LG is the dip length of a single coal mining face; LN is the lateral projection length of the inclined section of the borehole in the (N-1)th fracturing unit.

[0037] Example 3 Taking the conditions of a mine in the Inner Mongolia-Shaanxi region as an example, the layout of the working face within the coiled area is as follows: Figure 1 As shown, the first working face is located on one side of the panel, and the small coal pillar tunneling process is used sequentially. The working face is 300m long, the strike length is 3120m, the width of the two roadways is 5.6m, and the designed width of the small coal pillar is 6m. Based on the existing directional hydraulic fracturing survey of the roof in the area, it is known that the drilling rig's drilling capacity can reach 800-1000m. When the drilling depth exceeds 500-600m, the drilling difficulty gradually increases, and the removal of slag in the horizontal section becomes difficult. Therefore, this embodiment presents a method for preventing regional rockburst in thick, hard, and hazardous key strata. The specific operation steps are as follows: Step 1, refer to Figure 1 For rockburst mines with thick and hard critical layers, hydraulic fracturing tests of the thick and hard critical layers are carried out on the coiled working face to be implemented to determine the hydraulic fracturing radius R of the roof hydraulic fracturing borehole, taking 30m as an example.

[0038] Step 2: Drill 4 boreholes in a single drilling site. Based on the length of the working face within the panel, divide the working face into several fracturing sections with a spacing of LS=2RX=240m, namely fracturing section 1, fracturing section 2, fracturing section 3, ..., fracturing section Z.

[0039] Step 3: Install fracturing equipment 6 in each fracturing section within the first fracturing unit at intervals of 240m. Adjust the dimensions of the hydraulic fracturing equipment 6 according to its placement (taking a length of 13m and a width of 5m as an example) to form the drilling site required for hydraulic fracturing. In the first fracturing unit, the roadway where fracturing equipment 6 is installed is the haulage roadway 4 of the working face II. The total borehole length LA = Y1 * LG = 624m, where LG is the dip length of a single coal mining face, including the face length and the width of the two roadways, approximately 312m. During the excavation of the panel working face, the haulage roadway 1 of the first mining face, the return air roadway 2 of the first mining face, and the return air roadway 3 of the working face II are excavated simultaneously. Before the first mining face is mined, fracturing is carried out on the thick, hard, disaster-causing key strata in the mining area.

[0040] Design the fracturing borehole trajectory line 7 for the hydraulic fracturing drilling site on the downhole roof. The target azimuth of the boreholes in the drilling site is along the dip of the working face in the panel. The fracturing section is divided into LY and LN horizontally along the dip according to whether it is fracturing or not. LY is the length of the fracturing section, which is 450m, and LN is the length of the unfracturing section, which is 174m. The total length of the boreholes is LA.

[0041] Step 4: The roadway where fracturing equipment 6 is arranged in the second fracturing unit is located in the solid coal roadway of working face IV. At this time, the horizontal length of the borehole is LA*=Y2*LG+LN=797m. The number of working faces involved in the fracturing unit needs to be adjusted according to the actual capacity of the drilling rig. Fracturing operations are carried out on the fracturing sections in the subsequent fracturing units in sequence to complete the rockburst prevention work of the entire panel working face.

Claims

1. A method for preventing regional rockbursts in thick, hard, critical strata, characterized in that: Includes the following steps: Step 1: Identify the thick and hard key layer of the coal mining face, conduct fracturing tests on the thick and hard key layer, and determine the fracturing radius R of the hydraulic fracturing borehole in the roof. Step 2: Divide the working face of the panel into several fracturing units, and within each fracturing unit, divide the working face of the panel into several fracturing sections. Step 3: Install fracturing equipment (6) in each fracturing section corresponding to the first fracturing unit. Install fracturing equipment (6) in each fracturing section through the rubber transport roadway (4) of the working face. The fracturing equipment (6) drills and hydraulically fractures the thick and hard key layer of the fracturing section along the working face dip. After the thick and hard key layer of the fracturing section I of the first fracturing unit is hydraulically fractured, the fracturing section I is recycled through the rubber transport roadway (1) of the first production face and the return air roadway (2) of the first production face. At the same time, the fracturing equipment (6) performs fracturing operation on the fracturing section II of the first fracturing unit in the rubber transport roadway (4) of the working face. Step 4: Perform fracturing operations on the fracturing sections in the subsequent fracturing units in sequence along the mining direction of the working face. Before the coal mining face is mined back, perform hydraulic fracturing on the fracturing sections in the advanced coal mining face to cause all rock strata below the thick and hard key layer of the coal mining face to collapse regularly.

2. The method for preventing regional rockbursts in thick, hard key layers according to claim 1, characterized in that, In step 2, the fracturing units and fracturing sections are divided at equal intervals. The interval LS between the fracturing sections is shown in the following formula: LS = 2RX; Where R is the fracturing radius and X is the number of boreholes drilled by the fracturing equipment in a single fracturing section.

3. The method for preventing regional rockbursts in thick, hard key strata according to claim 2, characterized in that, The fracturing equipment (6) described in step 3 is set at equal intervals along the working face. The distance between adjacent fracturing equipment (6) is LS, and the distance between the first fracturing equipment (6) and the working face cut (5) is LS / 2.

4. The method for preventing regional rockbursts in thick, hard key strata according to claim 1, characterized in that, Step 3, which involves drilling and hydraulic fracturing the thick, hard, critical layers along the working face in the fracturing zone, specifically includes the following steps: Step 3.1: Generate fracturing borehole trajectory lines (7) based on the number of boreholes. Step 3.2: Drill the inclined and horizontal sections according to the fracturing borehole trajectory line (7), and withdraw the drill rod after drilling to the designated position; Step 3.3: Perform hydraulic fracturing on the horizontal section of the borehole until all horizontal sections of the borehole within the fracturing zone are fracturing.

5. The method for preventing regional rockbursts in thick, hard key strata according to claim 4, characterized in that, In step 3.3, hydraulic fracturing is carried out by lowering packers or bridge plugs, injecting high-pressure water into the two-stage packers or bridge plugs for fracturing. The hydraulic fracturing is carried out in a backward manner, and fracture proppant is continuously injected during the fracturing process.

6. The method for preventing regional rockbursts in thick, hard key strata according to claim 4, characterized in that, The length LA of the borehole in the first fracturing unit is not less than Y1 times the dip length of a single coal mining face, where Y1 is an integer not less than 2.

7. The method for preventing regional rockbursts in thick, hard key strata according to claim 6, characterized in that, The distance between the roadway in the Nth fracturing unit where the fracturing equipment (6) is arranged and the roadway in the (N-1)th fracturing unit where the fracturing equipment (6) is arranged is Y2 times the dip length of a single coal mining face, where Y2 is Y1 or Y1-1.

8. The method for preventing regional rockbursts in thick, hard key strata according to claim 7, characterized in that, The length LA of the borehole in the non-first fracturing unit * As shown in the following formula: LA * =Y2*LG+LN. Wherein, LG is the dip length of a single coal mining face; LN is the lateral projection length of the inclined section of the borehole in the (N-1)th fracturing unit.

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