Method for determining water jet pre-crack position in hard roof

Abstract

The application discloses a kind of hard roof in water jet prefabricated crack position determination method, comprising: step 1: interval construction N drill holes on the roof of mine;Step 2: the hole wall of each described drill hole is peeped using drill hole peep instrument, obtains the panoramic imaging graph of the drill hole at different depths;Step 3: according to the panoramic imaging graph obtained in step 2, the hardness degree grade of rock stratum at different depths of each drill hole is analyzed and is assigned f;Step 4: select n drill hole samples, according to the hardness degree assignment f of rock stratum at different depths in each drill hole obtained in step 3, the average hardness degree assignment of roof rock stratum at different depths is obtained.The hard roof in water jet prefabricated crack position determination method provided by the application is high in step science, strong in objectivity, compared with the traditional experience determination water jet prefabricated crack position mode, more reliable, also more universal, can provide more scientific and effective optimization scheme for prefabricated crack position determination.

Description

Technical Field

[0001] This invention relates to the field of coal mine safety technology, and in particular to a method for determining the location of pre-fabricated cracks in the roof. Background Technology

[0002] Hydraulic fracturing, employing water jet pre-fabrication in rigid roof slabs, is a crucial technique for preventing rockburst disasters. Water jet pre-fabrication involves first drilling a borehole to a certain depth (typically 30-80m) into the roof slab, then pre-fabricating multiple sections of cracks at various intervals within the borehole using water jets. High-pressure water is then injected to further fracturize the roof strata. The pre-fabricated cracks allow for controlled high-pressure water fracturing direction, altering the direction and location of roof collapse, ultimately reducing the dynamic load released by roof collapse and achieving source control of rockbursts.

[0003] A crucial step in modifying the lithology of the roof using waterjet pre-cast fractures is designing a waterjet pre-cast fracture construction plan based on the roof lithology. A key parameter in this plan is the location of the pre-cast fracture within the borehole. Currently, the location of the pre-cast fracture is often determined based on engineering experience or by referring to the construction conditions of surrounding mines, exhibiting significant arbitrariness and subjectivity, lacking sufficient scientific basis, and making it difficult to guarantee the construction effect. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for determining the location of water jet pre-fabricated cracks in a rigid roof slab.

[0005] The method for determining the location of water jet pre-fabricated cracks in a rigid roof slab according to an embodiment of the present invention is characterized by comprising:

[0006] Step 1: Drill N holes at intervals on the roof of the mine;

[0007] Step 2: Use a borehole inspection instrument to inspect the borehole wall of each borehole and obtain multiple panoramic images of the borehole at different depths;

[0008] Step 3: The hardness of the rock strata is graded based on the integrity of the borehole wall and the spacing of the threads on the borehole wall. The more intact the borehole wall and the smaller the spacing of the threads on the borehole wall, the higher the hardness grade of the rock strata. Hardness grades are assigned values ​​ranging from 0 to 10, with higher hardness grades receiving larger values. Based on the panoramic image obtained in Step 2, the hardness grade of the rock strata at different depths for each borehole is analyzed and assigned values. f ;

[0009] Step 4: Select n borehole samples and assign values ​​based on the rock hardness at different depths within each borehole obtained in Step 3. f The average hardness of the top strata at different depths is obtained using the following formula:

[0010]

[0011] A l Assign a value to the average hardness of the rock strata at depth l, where n is the number of selected borehole samples, and N ≥ n. f i The rock hardness value is assigned to the i-th borehole in the selected borehole sample at a depth of l.

[0012] like A l If the depth is ≥5, then the corresponding depth is determined to be the location of the precast crack; if A l If the value is less than 5, then the corresponding depth is determined to be where no precast cracks are needed.

[0013] The method for determining the location of water jet precast cracks in a rigid roof slab provided in this invention is highly scientific and objective. Compared with the traditional method of determining water jet precast cracks based on experience, it is more reliable and more universal, and can provide a more scientific and effective optimization scheme for determining the location of precast cracks.

[0014] In some embodiments, the rock hardness level in step 3 is greater than or equal to 4, and the assigned values ​​include at least 0, 3, 7, and 10.

[0015] In some embodiments, the borehole wall conditions at different depths are observed based on the panoramic imaging obtained in step 2:

[0016] If the borehole wall is broken and the thread gap is greater than 200mm, the hardness of the rock strata at that depth is assigned a value of 0.

[0017] If the borehole wall is intact and the thread clearance is 30mm-200mm, the hardness of the rock strata at this depth is assigned a value of 3.

[0018] If the borehole wall is intact and the thread clearance is 15mm-30mm, the hardness of the rock strata at this depth is assigned a value of 7.

[0019] If the borehole wall is intact and the thread clearance is 0-15mm, the hardness of the rock strata at that depth is assigned a value of 10.

[0020] In some embodiments, a tower drill bit is used to drill the hole in step 1, and the travel speed of the drill bit is 0.3m / min-1m / min.

[0021] In some embodiments, the rock hardness level in step 3 is 11 levels, and the difference between adjacent values ​​is 1.

[0022] In some embodiments, n adjacent boreholes among the N boreholes mentioned in step 1 are selected as borehole samples in step 4, where n is greater than or equal to 10.

[0023] In some embodiments, the diameter of the rock strata covered by the n borehole samples selected in step 4 is less than or equal to 500 meters.

[0024] In some embodiments, the N boreholes mentioned in step 1 are divided into several groups, each group including n boreholes, and step 4 further includes:

[0025] The average hardness value was calculated by selecting n boreholes from different borehole groups as borehole samples.

[0026] In some embodiments, N is greater than or equal to 50.

[0027] In some embodiments, the depth of the borehole is 30-80m. Attached Figure Description

[0028] Figure 1 This is a panoramic image of the borehole wall obtained in step 2 of this embodiment of the invention.

[0029] Figure 2 Yes Figure 1 A classification diagram of the hardness of rock strata at different depths in the borehole. Detailed Implementation

[0030] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0031] The purpose of this invention is to address the shortcomings of existing methods for determining the location of precast water jet cracks in related technologies, and to provide a method for optimizing the location of precast water jet cracks in rigid roof slabs. The determination process is scientific and objective, making the construction effect of precast water jet cracks more reliable.

[0032] The method for determining the location of water jet precast cracks in a rigid roof slab provided in this invention includes:

[0033] Step 1: Drill N holes at intervals on the roof of the mine;

[0034] Step 2: Use a borehole inspection instrument to insert into the borehole and inspect the borehole wall of each borehole mentioned in Step 1 to obtain multiple panoramic images of the borehole at different depths;

[0035] Step 3: The hardness of the rock strata is graded based on the integrity of the borehole wall and the spacing of the threads on the borehole wall. A more intact borehole wall and a smaller thread spacing indicate a higher level of rock hardness. Hardness grades are assigned values ​​ranging from 0 to 10, with higher hardness grades receiving larger values. Based on the panoramic image obtained in Step 2, the hardness grades of the rock strata at different depths for each borehole are analyzed and assigned values. f ;

[0036] Step 4: Select n boreholes from the N boreholes as borehole samples, and assign values ​​based on the rock hardness at different depths within each borehole obtained in Step 3. f The average hardness of the top strata at different depths is obtained using the following formula:

[0037]

[0038] A l Assign a value to the average hardness of the rock strata at depth l, where n is the number of selected borehole samples, and N ≥ n. f i The rock hardness value is assigned to the i-th borehole in the selected borehole sample at a depth of l.

[0039] After calculation, a judgment is made if... A l If the depth is ≥5, then the corresponding depth is determined to be the location of the precast crack; if A l If the value is less than 5, then the corresponding depth is determined to be where no precast cracks are needed.

[0040] The N boreholes drilled in Step 1 serve as the structural foundation for subsequent waterjet precast cracks. First, the lithology of the rock strata at different depths within the boreholes must be determined. Based on the 360° panoramic image of the borehole wall obtained in Step 2, the hardness level of the rock strata at different depths is analyzed, and the corresponding rock strata assignment value is further obtained. To shorten the precast crack construction time, Step 4 performs batch calculations on the N boreholes to obtain the average assignment value of the rock strata at different depths within a batch of borehole samples. A l If you want to determine a certain depth A l If the depth is ≥5, the rock strata are considered to be relatively hard, potentially accumulating high strain energy, necessitating waterjet pre-fracture. Therefore, in subsequent construction, waterjet pre-fracture was performed on all boreholes in this batch of borehole samples at this depth to effectively prevent rockburst accidents. However, if at a certain depth... A lIf the value is less than 5, it is considered that the rock strata at this location are relatively hard and the possibility of rockburst accidents is small, so there is no need to carry out precast crack construction.

[0041] The method for determining the location of water jet precast cracks in a rigid roof slab provided in this invention is highly scientific and objective. Compared with the traditional method of determining water jet precast cracks based on experience, it is more reliable and more universal, and can provide a more scientific and effective optimization scheme for determining the location of precast cracks.

[0042] In some embodiments, the rock strata hardness level in step 3 is greater than or equal to 4, and the assigned values ​​include at least 0, 3, 7, and 10. For example, the rock strata hardness level is divided into four levels: level 1, level 2, level 3, and level 4. The higher the level, the harder the rock strata. Level 1 is assigned a value of 0, level 2 is assigned a value of 3, level 3 is assigned a value of 7, and level 4 is assigned a value of 10. Making the rock strata hardness level greater than or equal to 4 allows for more precise strata classification, thereby enabling more accurate determination of the location of pre-existing cracks.

[0043] When classifying the hardness of rock strata, the classification indicators include the integrity of the borehole wall and the thread pitch on the borehole wall, and both factors need to be comprehensively evaluated. Generally speaking, the harder the rock strata, the more intact the borehole wall becomes, while the thread pitch on the borehole wall decreases as the rock strata harden. This is because the harder the rock strata, the lower the drilling speed.

[0044] In some specific embodiments, the borehole wall conditions at different depths are observed based on the panoramic imaging obtained in step 2:

[0045] If the borehole wall is broken and the thread gap is greater than 200mm, the hardness of the rock strata at that depth is assigned a value of 0.

[0046] If the borehole wall is intact and the thread clearance is 30mm-200mm, the hardness of the rock strata at this depth is assigned a value of 3.

[0047] If the borehole wall is intact and the thread clearance is 15mm-30mm, the hardness of the rock strata at this depth is assigned a value of 7.

[0048] If the borehole wall is intact and the thread clearance is 0-15mm, the hardness of the rock strata at that depth is assigned a value of 10.

[0049] "Broken borehole wall" refers to borehole walls with cracks, gaps, or unevenness due to breakage, indicating that the rock strata are relatively soft, the drill bit advances quickly, resulting in very sparse or even inconspicuous thread clearance. "Intact borehole wall" refers to borehole walls without cracks, gaps, or other similar features.

[0050] As an example, Figure 1A panoramic image of the borehole wall obtained by observing the borehole wall during drilling. Figure 2 Based on Figure 1 The panoramic imaging image divides the rock strata at different depths according to the morphology of the borehole wall. For example... Figure 2 As shown, the borehole wall is divided into four zones: A, D, and E. The borehole wall morphology, thread gaps, and lithological descriptions of different zones are shown in Figure 1.

[0051] Specifically, in area A, the borehole wall is intact but the threads are unclear, with thread gaps ranging from approximately 30mm to 200mm, indicating that the rock strata here are mostly hard rocks such as argillaceous sandstone, and the hardness of the rock strata at this depth is assigned a value of 3; in area B, the borehole wall is broken and uneven, with thread gaps greater than 200mm, indicating that the rock strata here are fracture zones such as mudstone and sandy mudstone, and the hardness of the rock strata at this depth is assigned a value of 0; in area C, the borehole wall is intact, the threads are clearly visible, the thread spacing is relatively sparse, and the thread gaps range from approximately 15mm to 30mm, indicating that the rock strata here are mostly hard rocks such as coarse-grained sandstone, and the hardness of the rock strata at this depth is assigned a value of 7; in area D, the borehole wall is intact, the threads are clearly visible, the thread spacing is dense, and the thread gaps are less than 15mm, indicating that the rock strata here are mostly hard rocks such as fine-grained sandstone, and the hardness of the rock strata at this depth is assigned a value of 10.

[0052] Table 1. Determination of Lithological Hardness

[0053]

[0054] Optionally, in step 1, a tower drill bit is used to construct the borehole, and the travel speed of the drill bit is 0.3m / min-1m / min.

[0055] It should be noted that the thread pitch on the hole wall is related to the drill bit's structural parameters and its rotation and travel speeds, which will be explained in detail below.

[0056] Drill bit structural parameters: The cutting edge length of the tower drill bit is 10mm. Generally speaking, the longer the cutting edge length of the drill bit, the sparser the thread on the hole wall. However, the drill bit rotates at extremely high speeds, which greatly weakens the correlation between the cutting edge length and the thread density on the hole wall. Therefore, the correlation between the cutting edge length and the density of the thread on the hole wall is negligible.

[0057] Drill bit rotation speed: During the drilling process, to ensure the stability of the drilling direction, the drill bit rotation speed is manually set to a low speed (around 20 rpm). After the drill bit has entered the hole for 3-4 meters, the drill bit rotation speed is manually increased to a certain speed (around 200 rpm) and maintained until drilling is completed. Therefore, the drill bit rotation speed remains basically constant throughout the drilling process and is not related to the density of the threads on the hole wall.

[0058] Drill bit travel speed: Throughout the drilling process, the operator will adjust the forward pressure and thus the forward speed in real time according to changes in the drill bit's forward speed. Generally speaking, when the borehole wall rock is hard, the applied pressure is high and the drill bit travel speed is slow (around 0.3 m / min), resulting in dense threads on the borehole wall; when the borehole wall rock is soft, the applied pressure is high and the drill bit travel speed is fast (around 1 m / min), resulting in sparse threads on the borehole wall.

[0059] In some alternative embodiments, the rock strata hardness level in step 3 is 11, and the difference between adjacent values ​​is 1. The more hardness levels the rock strata have, the more finely they can be classified, thus making the location of precast cracks more accurate.

[0060] In some preferred embodiments, n adjacent boreholes from the N boreholes mentioned in step 1 are selected as borehole samples in step 4, where n is greater than or equal to 10. That is, when selecting the n boreholes in step 4, 10 or more adjacent boreholes from all boreholes are selected as samples. This ensures that the determination result obtained in step 4 is valid within a certain range, making the determination of the precast crack location more accurate.

[0061] Optionally, the diameter of the rock strata covered by the n borehole samples selected in step 4 is less than or equal to 500 meters. This is because if the diameter of the rock strata covered by the selected borehole samples is greater than 500 meters, the hardness distribution of the rock strata may vary. Therefore, controlling the diameter of the rock strata covered by the n borehole samples selected in step 4 to within 500 meters can make the determination of the location of the precast cracks more accurate.

[0062] In some specific embodiments, the N boreholes mentioned in step 1 are divided into several groups, each group including n boreholes, and step 4 further includes:

[0063] The average hardness value was calculated by selecting n boreholes from different borehole groups as borehole samples.

[0064] Optionally, N is greater than or equal to 50, meaning the number of boreholes drilled on the mine roof is greater than or equal to 50, so that the subsequent waterjet precast cracks can completely cover the mine roof. Too few boreholes may result in excessively large borehole spacing, and the waterjet precast cracks may not be able to completely prevent the dynamic loads released by roof collapse.

[0065] For example, in step 1, a total of 50 boreholes are drilled. These 50 boreholes are divided into 5 groups according to different areas, and each group of boreholes includes 10 adjacent boreholes.

[0066] In step 4, the average hardness value is calculated for each of the 10 boreholes in each group to obtain the average hardness value of the five borehole groups, so as to guide the construction of precast cracks in boreholes in different areas.

[0067] Optionally, the depth of the borehole drilled in step 1 is 30m-80m.

[0068] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0069] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0070] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0071] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0072] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0073] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for determining the location of water jet pre-fabricated cracks in a rigid roof slab, characterized in that, include: Step 1: Drill N holes at intervals on the roof of the mine; Step 2: Use a borehole inspection instrument to inspect the borehole wall of each borehole and obtain multiple panoramic images of the borehole at different depths; Step 3: The hardness of the rock strata is graded based on the integrity of the borehole wall and the spacing of the threads on the borehole wall. The more intact the borehole wall and the smaller the spacing of the threads on the borehole wall, the higher the hardness grade of the rock strata. Hardness grades are assigned values ​​ranging from 0 to 10, with higher hardness grades receiving larger values. Based on the panoramic image obtained in Step 2, the hardness grade of the rock strata at different depths for each borehole is analyzed and assigned values. f ; Step 4: Select n borehole samples and assign values ​​based on the rock hardness at different depths within each borehole obtained in Step 3. f The average hardness of the top strata at different depths is obtained using the following formula: A l Assign a value to the average hardness of the rock strata at depth l, where n is the number of selected borehole samples, and N ≥ n. f i The rock hardness value is assigned to the i-th borehole in the selected borehole sample at a depth of l. like A l If the depth is ≥5, then the corresponding depth is determined to be the location of the precast crack; if A l If the value is less than 5, then the corresponding depth is determined to be a depth where no precast cracks are required. In step 3, the rock strata must be of hardness grade 4 or higher, and the assigned values ​​must include at least 0, 3, 7, and 10. Based on the panoramic image obtained in step 2, observe the borehole wall conditions at different depths: If the borehole wall is broken and the thread gap is greater than 200mm, the hardness of the rock layer at that depth is assigned a value of 0. If the borehole wall is intact and the thread clearance is 30mm-200mm, the hardness of the rock strata at this depth is assigned a value of 3. If the borehole wall is intact and the thread clearance is 15mm-30mm, the hardness of the rock strata at this depth is assigned a value of 7. If the borehole wall is intact and the thread clearance is 0-15mm, the hardness of the rock strata at that depth is assigned a value of 10.

2. The method for determining the location of water jet prefabricated cracks in a rigid roof slab according to claim 1, characterized in that, In step 1, a tower drill bit is used to drill the hole, and the drill bit travels at a speed of 0.3 m / min to 1 m / min.

3. The method for determining the location of water jet prefabricated cracks in a rigid roof slab according to claim 1, characterized in that, The rock strata in step 3 have a hardness level of 11 and a neighboring value difference of 1.

4. The method for determining the location of water jet prefabricated cracks in a rigid roof slab according to claim 1, characterized in that, Select the n nearest boreholes from the N boreholes mentioned in step 1 as the borehole sample mentioned in step 4, where n is greater than or equal to 10.

5. The method for determining the location of water jet pre-fabricated cracks in a rigid roof slab according to claim 1 or 4, characterized in that, The diameter of the rock strata covered by the n borehole samples selected in step 4 is less than or equal to 500 meters.

6. The method for determining the location of water jet pre-fabricated cracks in a rigid roof slab according to claim 1 or 4, characterized in that, The N boreholes mentioned in step 1 are divided into several groups, each group including n boreholes. Step 4 also includes: The average hardness value was calculated by selecting n boreholes from different borehole groups as borehole samples.

7. The method for determining the location of water jet prefabricated cracks in a rigid roof slab according to claim 1 or 4, characterized in that, N is greater than or equal to 50.

8. The method for determining the location of water jet prefabricated cracks in a rigid roof slab according to claim 1, characterized in that, The depth of the borehole is 30m-80m.

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