Method for preventing and treating artificial fracturing rock burst of key layer of far and near fields of extra-thick coal seam

Abstract

The invention relates to the field of coal mining rock burst prevention and control, in particular to an extra-thick coal seam far and near field key layer artificial fracturing rock burst prevention and control method. In order to solve the problem of chain type instability of a near-field overlying strata structure during mining of an extra-thick coal seam, a first sub-key layer of the near field is not intervened, the extra-thick coal seam stope is protected by utilizing the cantilever supporting effect of the first sub-key layer, and the fracture position of a second sub-key layer of the near field is intervened; the second subkey layer and the first subkey layer are prevented from being broken at the same time or nearly at the same time, and large disturbance to the stope caused by superposition of generated breaking energy is avoided. For a far-field sub-key layer, the sub-key layer with large mine pressure impact on the stope is selected, manual fracturing is carried out to release energy in advance, and a lower crushing and fracturing cushion layer is additionally arranged to reduce rotary support and carry out energy absorption and buffering; for a sub-key layer at the upper part of a top interface of a far-field water flowing fractured zone, a separation layer at the lower part of the sub-key layer is filled during stoping, so that the stress transmitted to a front stope due to suspension of the sub-key layer is reduced.

Description

Technical Field

[0001] This invention relates to the field of rockburst prevention in coal mining, and more particularly to a method for preventing rockburst through artificial fracturing of key layers in the near and far fields of extra-thick coal seams. Background Technology

[0002] Extra-thick coal seams generally refer to coal seams with a thickness greater than 8 meters. Compared to thin and medium-thick coal seams, extra-thick coal seam working faces are characterized by a large mining area, severe impact and extensive damage from overburden mining, and a large space for overburden strata movement, deformation, and fracturing on the working face. During the mining of extra-thick coal seams, large-space near-field and far-field overburden structures exist within the mined overburden. Compared to thin and medium-thick coal seams, the far-field overburden structure has a significant impact on the mining of extra-thick coal seams.

[0003] During the mining of extra-thick coal seams, the near-field and far-field overburden structures are in a bearing and energy-storing stage before fracturing. While accumulating elastic energy, these structures transfer energy from the far-field load layer to the surrounding areas of the working face through the load transfer layer. With the instantaneous fracturing and rotation of the near-field and far-field overburden structures, the accumulated energy is released instantaneously, causing abrupt changes in the energy and stress fields of the mining-induced overburden. Simultaneously, the rotation of the far-field overburden structure applies loads from the far-field load layer to the near-field overburden structure, causing large-area rotational movement and potentially even chain-like instability. This chain-like instability of the near-field and far-field overburden structures during extra-thick coal seam mining has a synergistic effect on the evolution of the mining-induced overburden stress field, energy accumulation and release, and the movement of the overburden strata over a large space, ultimately leading to powerful mine pressure shocks. Therefore, preventing chain-like instability of the near-field and far-field overburden structures during extra-thick coal seam mining is crucial for preventing rockbursts. Summary of the Invention

[0004] To address the chain-like instability problem of the overburden structure in the near and far fields of extra-thick coal seams, this invention proposes a method for preventing rockbursts by artificial fracturing of key strata in the near and far fields of extra-thick coal seams, comprising the following steps:

[0005] Step 1: Based on the critical layer theory, determine the location of each subcritical layer within the water-conducting fracture zone and its corresponding natural fracture location during the mining of extra-thick coal seams; the locations of each subcritical layer are numbered sequentially from bottom to top;

[0006] Step 2: Do not intervene in subcritical layer 1 and maintain its natural fracture position; intervene in the fracture position of subcritical layer 2 to avoid subcritical layer 2 and subcritical layer 1 from fractured at the same time or close to the same time.

[0007] Step 3: For the remaining subcritical layers in the water-conducting fracture zone, select the subcritical layer that has the greatest impact on the mining pressure, and artificially fracture all the expected natural fracture locations to form artificial fracture locations; and perform fracturing artificial fracturing on the soft rock layer below the selected subcritical layer to make the fracturing soft rock layer extremely broken to form a fracturing cushion layer.

[0008] Step 4: Mining the extra-thick coal seam. When the space generated by the mining is transferred to the subcritical layer above the top interface of the water-conducting fracture zone, drilling is carried out on the construction surface to the lower separation space of the subcritical layer, and only gravel is injected into it for filling.

[0009] As a further optimization of the above scheme, in the second step, along the working face advancement direction, when the first occurrence of the natural fracture position of subcritical layer two is determined to be simultaneous with or close to the natural fracture position of subcritical layer one, artificial fracturing is used to change the natural fracture position of subcritical layer two, forming the first artificial fracturing fracture position, so as to avoid simultaneous or near-simultaneous fracture with subcritical layer one; then, subcritical layer two fractures from the first artificial fracturing fracture position according to the original fracture step distance. When the next occurrence of the natural fracture position of subcritical layer two being simultaneous with or close to the natural fracture position of subcritical layer one, artificial fracturing is used to change the natural fracture position of subcritical layer two, forming the second artificial fracturing fracture position, so as to avoid simultaneous or near-simultaneous fracture with subcritical layer one; this cycle continues until the end of the entire working face advancement length.

[0010] As a further optimization of the above scheme, in the fourth step, the diameter of the gravel is 8-12mm.

[0011] Invention Points and Beneficial Effects: Addressing the chain-like instability problem of the overburden structure in the near and far fields of extra-thick coal seam mining, this invention does not intervene in the first subcritical layer in the near field, maintaining its natural fracture position and utilizing its cantilever support to protect the extra-thick coal seam mining area. For the second subcritical layer in the near field, intervention is made at its fracture position to prevent simultaneous or near-simultaneous fracture of the first and second subcritical layers, thus avoiding the superposition of fracture energy and significant disturbance to the mining area. For the subcritical layers in the far field, the layer with the greatest impact on the mining area's mining pressure is selected, and artificial fracturing is performed to release energy in advance. A lower fracturing pad is added to reduce rotational support and provide energy absorption buffering. For the subcritical layer above the top interface of the water-conducting fracture zone in the far field, the lower delamination is filled during mining to reduce stress transmitted to the preceding mining area due to its suspension.

[0012] 2. This invention creatively proposes to fill the delamination at the top interface of the water-conducting fracture zone with large-diameter rounded gravel (8-12mm in diameter). The filling material will not flow downward along the fracture in the water-conducting fracture zone, but will remain basically in the delamination at the top interface of the water-conducting fracture zone. Moreover, it does not need to be carried by water, but can play a supporting role by its own weight and rolling. It does not need to be filled densely, and it takes effect quickly, requires a small filling amount, and has low cost. Attached Figure Description

[0013] When considered in conjunction with the accompanying drawings, the invention will be more fully and better understood, and many of its accompanying beneficial effects will become readily apparent, through the following detailed description. However, the accompanying drawings, which are provided to further illustrate the invention and form part of this invention, and the illustrative embodiments thereof, together with their descriptions, are used to explain the invention and do not constitute an undue limitation thereof, wherein:

[0014] Figure 1 —Schematic diagram of the key layer structure of the near and far fields of the extra-thick coal seam in this invention;

[0015] Figure 2 —A schematic diagram of the method for preventing rockburst by artificial fracturing in the key layer of this invention;

[0016] Figure 3 —A schematic diagram illustrating the mechanism of artificial fracturing for preventing rockburst in the key layer of this invention;

[0017] Figure descriptions: 1-Extra-thick coal seam; 2-Subcritical layer one; 3-Subcritical layer two; 4-Subcritical layer three; 5-Subcritical layer four; 6-Bending subsidence zone; 7-Natural fracture location; 8-Artificial fracturing fracture location; 9-Fracturing cushion layer; 10-Collapse zone; 11-Gravel filling layer. Detailed Implementation

[0018] To better understand the technical content of this invention, specific embodiments are described below in conjunction with the accompanying drawings. Various aspects of this invention are described with reference to the accompanying drawings, which illustrate numerous illustrative embodiments. The embodiments of this invention are not limited to those shown in the drawings. It should be understood that this invention is implemented through any of the various concepts and embodiments described above, as well as the concepts and embodiments described in detail below, because the concepts and embodiments disclosed in this invention are not limited to any particular implementation. Furthermore, some aspects of this invention can be used alone or in any suitable combination with other aspects disclosed in this invention.

[0019] like Figure 1-3 As shown, this invention proposes a method for preventing rockbursts by artificial fracturing in key strata near and far of extra-thick coal seams, comprising the following steps:

[0020] Step 1: As Figure 1As shown, based on the key layer theory, the locations of each sub-key layer and its corresponding fracture locations within the water-conducting fracture zone during the mining of the extra-thick coal seam 1 are determined. In this embodiment, there are a total of 3 key layers within the water-conducting fracture zone during the mining of the extra-thick coal seam 1. Based on the naming rules of key layers, they are named sub-key layer 1, sub-key layer 2, sub-key layer 2, and sub-key layer 3 from bottom to top. The sub-key layer at the top interface of the water-conducting fracture zone is sub-key layer 4, and the strata below sub-key layer 4 to the extra-thick coal seam 1 (excluding sub-key layer 4) constitute the water-conducting fracture zone. The strata above sub-key layer 4 (including sub-key layer 4) constitute the bending subsidence zone 6, in which no water-conducting fractures are generated. At the same time, based on the key layer theory, the fracture locations of each sub-key layer within the water-conducting fracture zone can be determined, that is, the natural fracture locations 7 of the key layers of each sub-key layer without human intervention.

[0021] Step 2: As Figure 2 As shown, no intervention is made for the subcritical layer 2, and its natural fracture position 7 is maintained. The cantilever support of the subcritical layer 2 is used to form protection for the extra-thick coal seam 1 mining area.

[0022] For subcritical layer 23, since it is the closest subcritical layer to subcritical layer 12 and the mining area, its failure will disturb the extra-thick coal seam 1 mining area. Especially when it fails simultaneously or nearly simultaneously with subcritical layer 12, the failure energy will be superimposed. Therefore, simultaneous or near-simultaneous failure of subcritical layer 23 and subcritical layer 12 should be avoided. Specifically, along the working face advance direction, determine the first occurrence of a natural failure location 7 in subcritical layer 23 that is simultaneously or nearly simultaneous with the natural failure location 7 in subcritical layer 12. Then, artificial fracturing should be used to change the natural failure location 7 in subcritical layer 23, forming an artificially fracturing failure location 8. Figure 2 The first artificial fracturing fracture position 8 in the second critical layer 3 of Central Asia is used to prevent it from fracturing simultaneously or nearly simultaneously with the first subcritical layer 2. Subcritical layer 3 will then fracture according to the original fracture step distance, starting from the first artificial fracturing fracture position 8. When the next natural fracture position 7 of subcritical layer 3 occurs simultaneously or nearly simultaneously with the natural fracture position 7 of subcritical layer 2, artificial fracturing is used to change the natural fracture position 7 in subcritical layer 3, forming the artificial fracturing fracture position 8. Figure 2 The second artificial fracturing fracture location (8) in the second critical layer 2 of Central Asia is used to prevent it from fracturing simultaneously or nearly simultaneously with the first critical layer 2; this process is repeated until the end of the entire working face advance length (stop line);

[0023] Step 3: As Figure 2As shown, for the remaining subcritical layers in the water-conducting fracture zone, the subcritical layer with the greatest impact from the mining pressure (generally the subcritical layer with greater thickness and hardness) is selected, and artificial fracturing is performed on all the expected natural fracture locations 7 to form artificial fracturing fracture locations 8; a large amount of fracture energy at the natural fracture location 7 is released in advance through artificial fracturing to avoid a large and sudden release of energy, especially when the sudden release is superimposed with the energy release when the other subcritical layers are fractured;

[0024] Since the other subcritical layers in the water-conducting fracture zone (subcritical layer 1, subcritical layer 2, and critical layers other than the subcritical layers selected in the third step) have a relatively small impact on the mining impact and are not the focus of this invention, the given embodiment only illustrates the subcritical layer with a large mining pressure impact, namely subcritical layer 3, 4 in this embodiment.

[0025] Due to the large thickness and hardness of the subcritical layer 3 4, even if artificial fracturing is carried out in advance, when mining reaches the artificially fracturing fracture position 8, a large amount of deformation energy may still be released due to the interlocking and rotational action between adjacent fractured blocks. Therefore, this invention further proposes to carry out fracturing-type artificial fracturing on the soft rock layer (such as mudstone and shale) below the subcritical layer 3 4. Even if the soft rock layer is greatly broken after fracturing, forming a fracturing cushion layer 9, when the space is transferred to this location during the mining of the extra-thick coal seam 1, the fracturing cushion layer 9 has certain fragmentation and swelling characteristics to reduce the deformation of the subcritical layer 3 4, and in another direction, it has an energy absorption effect as a soft cushion layer.

[0026] Step 4: When mining the extra-thick coal seam 1, if the space created by the mining extends to the sub-critical layer 4.5 above the top interface of the water-conducting fracture zone, to reduce the stress transmitted to the preceding mining area due to its suspension, boreholes can be drilled through the construction surface to the lower separation space of sub-critical layer 4.5. Only gravel with a diameter of 8-12mm can be injected into this space for filling. One reason for using only gravel is that the purpose is not to completely fill the separation space, but to reduce the degree of suspension of sub-critical layer 4.5 above the top interface of the water-conducting fracture zone, thus creating support in the previously suspended area and preventing… This could reduce the stress transmitted to the front stope due to its suspension. The second reason is that fine-grained filling materials will flow downwards along the fractures in the water-conducting fracture zone in large quantities. Moreover, fine-grained filling materials mostly need to be carried by water for transport, and they can only play a supporting role if they are filled densely. They are slow to take effect, require a large amount of filling, and are costly. On the other hand, gravel has a large particle size and will not flow downwards along the fractures in the water-conducting fracture zone. It basically stays in the delamination at the top interface of the water-conducting fracture zone and does not need to be carried by water. It can play a supporting role by its own weight and rolling movement, without the need for dense filling. It takes effect quickly, requires a small amount of filling, and is low in cost.

[0027] Of course, the above description is only a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A method for preventing rockbursts by artificial fracturing in key strata near and far of extra-thick coal seams, characterized in that: Includes the following steps: Step 1: Based on the critical layer theory, determine the location of each subcritical layer within the water-conducting fracture zone during the mining of extra-thick coal seams and its corresponding natural fracture location; the locations of each subcritical layer are numbered sequentially from bottom to top; Step 2: Do not intervene in subcritical layer 1 and maintain its natural fracture position; intervene in the fracture position of subcritical layer 2 to avoid subcritical layer 2 and subcritical layer 1 from fractured at the same time or close to the same time. Step 3: For the remaining subcritical layers in the water-conducting fracture zone, select the subcritical layer that has the greatest impact on the mining pressure, and artificially fracture all the expected natural fracture locations to form artificial fracture locations; and perform fracturing artificial fracturing on the soft rock layer below the selected subcritical layer to make the fracturing soft rock layer extremely broken to form a fracturing cushion layer. Step 4: Mining the extra-thick coal seam. When the space generated by the mining is transferred to the subcritical layer above the top interface of the water-conducting fracture zone, drilling is carried out on the construction surface to the lower separation space of the subcritical layer, and only gravel is injected into it for filling.

2. The method for preventing rockburst from artificially fractured key strata in ultra-thick coal seams according to claim 1, characterized in that, In the second step, along the working face advancement direction, when the first occurrence of the natural fracture location of subcritical layer two is determined to be simultaneous with or close to the natural fracture location of subcritical layer one, artificial fracturing is used to change the natural fracture location of subcritical layer two, forming the first artificial fracturing fracture location, so as to avoid simultaneous or near-simultaneous fracture with subcritical layer one. Then, subcritical layer two fractures from the first artificial fracturing fracture location according to the original fracture step distance. When the next occurrence of the natural fracture location of subcritical layer two being simultaneous with or close to the natural fracture location of subcritical layer one is seen, artificial fracturing is used to change the natural fracture location of subcritical layer two, forming the second artificial fracturing fracture location, so as to avoid simultaneous or near-simultaneous fracture with subcritical layer one. This cycle continues until the end of the entire working face advancement length.

3. The method for preventing rockburst from extra-thick coal seams by artificial fracturing in key strata near and far fields according to claim 1, characterized in that, In the fourth step, the diameter of the gravel is 8-12 mm.

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