Pressure relief gas extraction method for dry type dense fracturing area of broken and soft coal seam roof

Abstract

The invention discloses a broken soft coal seam roof dry type dense fracturing area pressure relief gas extraction method, which comprises the following steps of: intensively arranging drill holes in a broken soft coal seam roof, and controlling a drill hole track to be close to a coal seam by utilizing pneumatic directional drilling; dense packing and dry fracturing are carried out in the drill hole through a packer, and a dense seam net for conducting the coal seam is manufactured; the whole layer of the regional roof is broken and weakened through the centrally-arranged drill holes and dense fracturing in the holes, so that pressure relief is conducted on the coal seam, finally, a three-stage efficient seepage gas extraction channel of the pressure relief coal seam, a roof dense seam net and the roof drill holes is formed, and efficient gas extraction of the coal seam is achieved. According to the method, the drilling track is controlled to be close to the coal seam through pneumatic directional drilling, the hole shrinkage and hole collapse problems of hydraulic drilling of the muddy coal seam roof are avoided, and the drilling track is close to the coal seam to create conditions for dense packing dry fracturing; in the dense packing dry fracturing, a packer is adopted to pack drill holes section by section to implement low-energy dry fracturing, so that the influence of muddy rock strata on fracturing is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine safety, and relates to a method for enhanced gas extraction from a dry-type densely fractured area of ​​a broken soft coal seam roof. Background Art

[0002] Broken and soft coal seams have poor permeability and are difficult to drill. Conventional gas extraction technology is not ideal. Roof hydraulic fracturing and permeability enhancement and extraction technology is restricted by the rock properties of the roof. Generally, coal seams have muddy roofs, which not only make hydraulic drilling construction difficult, but also fail to achieve the expected results with hydraulic fracturing and permeability enhancement. Summary of the invention

[0003] In view of the shortcomings in the prior art, the purpose of the present invention is to provide a method for decompression gas extraction in a dry dense fracturing area of ​​a broken and soft coal seam roof, so as to solve the problems of difficult hydraulic fracturing construction of muddy roof, dependence of decompression coal seam gas extraction on adjacent mining layers, and unsatisfactory gas extraction effect in broken and soft coal seams, thereby realizing dense fracturing decompression gas extraction in the muddy roof of a broken and soft coal seam.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve the above problems:

[0005] A method for decompressing gas extraction in a broken soft coal seam roof by dry dense fracturing. The method comprises the following steps: arranging boreholes in a concentrated manner on the broken soft coal seam roof, using pneumatic directional drilling to control the borehole trajectory to be close to the coal seam; using packers in the boreholes to implement dense isolation and dry fracturing to manufacture a dense seam network that conducts through the coal seam; and using concentrated boreholes and dense fracturing in the holes to fracture and weaken the entire regional roof layer, thereby decompressing the coal seam, and finally forming a three-level high-efficiency seepage extraction gas channel of a decompressed coal seam, a dense seam network on the roof, and boreholes on the roof, thereby achieving efficient extraction of coal seam gas.

[0006] The present invention also includes the following technical features:

[0007] Specifically, the following steps are included:

[0008] s1, using pneumatic directional drilling technology to drill holes in the top plate of the soft coal seam close to the coal seam, and controlling the drilling trajectory close to the coal seam;

[0009] s2, using a drilling fracturing packer to isolate the borehole section by section to implement dense isolation in the top plate borehole;

[0010] s3, using gas fracturing or low-intensity safety explosives and controlled shock wave fracturing to achieve dense isolation and low-energy dry fracturing in the top plate borehole;

[0011] s4, through the dense dry fracturing of roof drilling, a dense fracture network that conducts the coal seam is formed in the roof, and the coal seam is depressurized by weakening the roof area; by using the roof drilling and the dense fracture network of the roof, the regional depressurization of the coal seam is increased, and gas is extracted from the depressurized coal seam to improve the gas extraction effect of the broken soft coal seam.

[0012] Specifically, the method adopts grouped drilling areas to progressively fracture and weaken the roof to extract and decompress coal seam gas: according to the formation stress, roof lithology and the influence range of intensive fracture, multiple groups of roof drilling holes are divided, including the first group of drilling holes,..., the nth group of drilling holes; the first group of drilling holes is subjected to intensive isolation dry fracture weakening, and then the coal seam gas in the decompression area of ​​the first group of drilling holes is preferentially extracted. After the expected effect is achieved, the second group of drilling holes is subjected to intensive isolation dry fracture weakening, and then the coal seam gas in the decompression area of ​​the second group of drilling holes is extracted, and so on; when the current group of drilling holes is decompressing the coal seam gas and extracting it, the extraction of the previous multiple groups of drilling holes is maintained at the same time.

[0013] Specifically, the method for determining the radius R of the fracture network caused by dry fracturing in the borehole is as follows: drill holes from the coal seam upward and gradually away from the roof of the coal seam, and after reaching a distance of more than 5-10m from the coal seam, control the drilling trajectory downward, gradually approach or expose the coal seam, and if the coal seam is exposed, grouting is performed on the coal seam, and then, starting from the maximum distance from the coal seam, a double-seal single-card packer tool combination is used to perform fracturing in stages in a backward manner with a card distance of 1 to 2m, and after each fracturing stage is completed, monitor the orifice gas until the orifice gas gas obviously gushes out, and the distance between the fracturing stage and the coal seam at this time is determined as R.

[0014] Specifically, the length of the borehole covers the mining working face, the distance between the borehole trajectory and the coal seam is not greater than R, and the distance between the boreholes is not greater than R.

[0015] Specifically, the packer spacing is no greater than R.

[0016] Specifically, among the multiple groups of roof boreholes, the method for determining the number of boreholes in each group includes: determining the number of boreholes in each fracturing group by R value and the scope of artificial regional fracturing weakened and unloaded coal seam based on numerical simulation of overlying strata; or determining by monitoring data analysis of intensive fracturing drilling continuous extraction experiment, after completing the intensive fracturing of the first borehole, the extraction monitoring of the borehole is carried out, and the first borehole is continuously monitored during the subsequent intensive fracturing of the boreholes until the extraction volume of the first borehole rapidly decreases, and the first borehole to the first borehole where intensive fracturing drilling is being implemented is used as a fracturing group.

[0017] Compared with the prior art, the present invention has the following technical effects:

[0018] The present invention fundamentally avoids a series of problems in hydraulic drilling and hydraulic fracturing construction in muddy roof. It controls the drilling trajectory close to the coal seam through pneumatic directional drilling technology, densely isolates dry fracturing technology, and artificially creates a large-scale fracture network, which makes up for the defect of small influence range of dry fracturing. At the same time, it forms regional coal seam pressure relief, greatly improving the extraction effect of coal seam gas.

[0019] The present invention adopts pneumatic directional drilling to not only control the drilling trajectory close to the coal seam, but also avoids the shrinkage and collapse problem of hydraulic drilling on the top of the muddy coal seam. The drilling trajectory close to the coal seam creates conditions for dense isolation and dry fracturing.

[0020] The dense isolation dry fracturing of the present invention uses a packer to isolate the borehole section by section to implement low-energy dry fracturing. Dry fracturing can be implemented using technologies such as gas fracturing, low-intensity explosives, and controlled shock wave fracturing, which fundamentally avoids the influence of mudstone formations on fracturing. At the same time, the use of dense isolation greatly adapts to the characteristics of low energy or small impact range of instantaneous fracturing of dry fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of dry fracturing with dense drilling and isolation adjacent to the coal seam in the regional roof.

[0022] Figure 2 Schematic diagram of the drilling trajectory for the pilot experiment of roof drilling gas fracturing.

[0023] Figure 3 This is a cross-sectional view of the dry fracturing trend of the densely drilled holes adjacent to the coal seam on the roof.

[0024] Figure 4 This is a cross-sectional diagram of the dry intensive fracturing caused by roof drilling and the coal seam pressure relief trend.

[0025] Figure 5 It is a radial cross-section diagram of progressive fracturing weakening and coal seam pressure relief in the grouped drilling area. DETAILED DESCRIPTION

[0026] The present invention proposes a technology for enhanced gas extraction by dry dense fracturing in the roof of a broken and soft coal seam. The drill holes are centrally arranged on the roof, and the pneumatic directional drilling technology is used to control the trajectory of the drill holes to be close to the coal seam. Dense isolation is used in the drill holes for dry fracturing to create a dense seam network that conducts the coal seam. The centralized arrangement of the drill holes and the dense fracturing in the holes cause the entire roof layer in the region to be broken and weakened, thereby unloading the coal seam, and finally forming a three-level efficient seepage extraction gas channel system of unloaded coal seam, dense seam network in the roof, and drill holes in the roof, to achieve efficient extraction of coal seam gas. The use of pneumatic directional drilling not only realizes the control of the trajectory of the drill holes to be close to the coal seam, but also avoids the problem of shrinkage and collapse of the hole in the hydraulic drilling of the roof of the muddy coal seam. The trajectory of the drill holes to be close to the coal seam creates conditions for dense isolation and dry fracturing. Dense isolation dry fracturing uses packers to isolate the borehole section by section to implement low-energy dry fracturing. Dry fracturing can be implemented using technologies such as gas fracturing, low-intensity explosives, and controlled shock wave fracturing, which fundamentally avoids the impact of mudstone formations on fracturing. At the same time, the use of dense isolation greatly adapts to the low energy or small impact range of instantaneous fracturing of dry fracturing.

[0027] The specific steps include:

[0028] s1, using pneumatic directional drilling technology to drill holes in the top plate of the soft coal seam adjacent to the coal seam, and using directional drilling technology to control the drilling trajectory adjacent to the coal seam;

[0029] s2, using a drilling fracturing packer to implement dense isolation in the roof borehole, and determining the isolation spacing and fracturing segment spacing based on the effective fracturing range of the roof dry fracturing;

[0030] s3, using gas fracturing or low-intensity safety explosives, controlled shock waves and other fracturing methods without water to achieve dense isolation dry fracturing in the top plate borehole; specifically, using liquid carbon dioxide phase change gas to perform dense staged fracturing in the borehole, or other non-water (such as liquid nitrogen, low-intensity safety explosives, etc.) rock formation fracturing methods to perform dense staged fracturing in the borehole;

[0031] s4, through intensive dry fracturing by drilling holes in the roof, artificial regional roof weakening is implemented, and stress redistribution of the overlying strata is artificially induced. The core is to form a dense fracture network in the roof that conducts the coal seam and decompress the coal seam through regional weakening of the roof; by drilling holes in the roof and forming a dense fracture network in the roof, the regional decompression of the coal seam is increased in permeability, and gas is extracted from the decompression coal seam to improve the gas extraction effect of the broken soft coal seam.

[0032] like Figure 1 This is a schematic diagram of the densely sealed dry fracturing of the regional roof adjacent to the coal seam. From top to bottom, there are the roof, coal seam and floor. There are multiple holes drilled in the roof, and each hole has dense fracturing cracks. Figure 3 The profile diagram of the densely packed dry fracturing in the boreholes close to the coal seam at the top plate is shown. Fracturing and dense packers are arranged in the boreholes to carry out dense dry fracturing in the boreholes. Figure 4 This is a cross-sectional diagram of the dry dense fracturing caused by roof drilling and coal seam pressure relief. The overlying rock strata on the roof are under stress, and the roof drilling holes form a dense fracture network.

[0033] The core of the method of gas extraction by dry intensive fracturing in the area of ​​pressure relief of the broken soft coal seam roof is to artificially weaken the regional roof through intensive dry fracturing of the roof drilling holes, and artificially induce stress redistribution of the overlying rock strata. Through the dense arrangement of directional drilling holes and intensive dry fracturing in the boreholes, the thin layer of the coal seam roof in the area covered by the drilling holes is broken and fractured in the entire area, so that the original rock stress of the coal seam roof is transferred to the deep and redistributed, thereby artificially creating a low stress area in the coal seam in the area, and coal seam gas extraction in this area can achieve the effect of extracting and unloading coal seam gas. After the coal seam gas in this area achieves the expected effect, the intensive dry fracturing and pressure relief extraction in the succession area will continue, and so on, the coal seam gas extraction will be controlled in the pressure relief area until the entire mining coal seam area is fully covered. The optimal range of the coal seam roof pressure relief area is controlled by the regional geological conditions (formation stress, roof lithology, etc.) and the arrangement of dense fracturing directional drilling, and can be obtained through field experiments.

[0034] This method uses grouped drilling areas to progressively fracture and weaken the roof to extract and decompress coal seam gas: according to the formation stress, roof lithology and the range of intensive fracture influence, multiple groups of roof holes are drilled, such as Figure 5 , including the first group of boreholes, ..., the nth group of boreholes; the first group of boreholes are subjected to intensive isolation dry fracturing and weakening, and then the coal seam gas in the pressure relief area of ​​the first group of boreholes is preferentially extracted. After the expected results are achieved, the second group of boreholes are subjected to intensive isolation dry fracturing and weakening, and then the coal seam gas in the pressure relief area of ​​the second group of boreholes is extracted, and so on; when the current group of boreholes is decompressing and extracting coal seam gas, the extraction of the previous multiple groups of boreholes is maintained at the same time.

[0035] The method for determining the radius R of the crack network caused by dry fracturing in the borehole is as follows: Figure 2 , drill holes gradually away from the roof of the coal seam from the coal seam upward, and control the drilling trajectory downward after reaching more than 5-10m away from the coal seam, gradually approaching or exposing the coal seam. If the coal seam is exposed, grouting is carried out to seal the coal seam (if the occurrence of the coal seam is fully understood, the distance between the borehole and the coal seam is completely controllable, and the drilling of the downward section may not be constructed). Then, starting from the maximum distance from the coal seam, a "double-seal single-card" packer tool combination is used to perform fracturing in a backward manner with a card distance of 1 to 2m. After each fracturing section is completed, monitor the orifice gas until the orifice gas gas gushes out significantly. The distance between the fracturing section and the coal seam at this time is determined as R.

[0036] The length of the borehole covers the mining face, the distance between the borehole trajectory and the coal seam is not greater than R, and the distance between the boreholes is not greater than R.

[0037] The spacing between packers is not greater than R.

[0038] Among multiple groups of roof boreholes, methods for determining the number of boreholes in each group include: determining the number of boreholes in each fracturing group through the R value and the scope of the artificial regional fracturing weakened and unloaded coal seam based on numerical simulation of the overlying strata; or determining through monitoring data analysis of a dense fracturing drilling and continuous extraction experiment, conducting extraction monitoring of the boreholes after completing the dense fracturing of the first borehole, and continuously monitoring the first borehole during the subsequent dense fracturing of the boreholes until the extraction volume of the first borehole rapidly decreases, and then the first borehole to the first borehole where the dense fracturing drilling is being implemented is regarded as a fracturing group.

[0039] 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.

[0040] Example:

[0041] The steps of this embodiment are described by taking the dry fracturing method of gas fracturing as an example:

[0042] 1) According to the pilot experiment of gas fracturing in roof drilling (experimental operation attached) or the practice of gas fracturing engineering under similar conditions, determine the radius R of the fracture network caused by gas fracturing in the roof drilling of coal seams in the construction area; combined with previous practical experience, the value of the fracture network radius R is generally not more than 2m for liquid nitrogen fracturing, not more than 5m for liquid carbon dioxide, and not more than 10m for low-intensity safety explosives.

[0043] Pilot experiment of gas fracturing in roof drilling: construct roof drilling holes gradually away from the coal seam from the coal seam upwards, and control the drilling trajectory downward after reaching more than 5m away from the coal seam, gradually approaching or even exposing the coal seam. If the coal seam is exposed, grouting is carried out to seal the coal seam section (if the occurrence of the coal seam is fully understood, the distance between the borehole and the coal seam is completely controllable, and the drilling of the downward section can be omitted). Then, starting from the maximum distance from the coal seam, a "double-seal single-card" packer tool combination is used to perform gas fracturing in sections with a 1-2m card distance and retreat. After each section of fracturing is completed, monitor the gas at the orifice until the gas at the orifice visibly gushes out. The distance between the fracturing section and the coal seam at this time is determined as R.

[0044] Design the roof drilling holes close to the broken soft coal seam, the drilling length covers the mining working face, the distance between the drilling trajectory and the coal seam is not greater than R, controlled between 1 and 5m, and the drilling spacing is not greater than R;

[0045] Use pneumatic directional drilling technology to drill holes in the roof, strictly control the drilling trajectory, and explore the coal seam before constructing branch holes when necessary, so that the drilling trajectory is close to the coal seam.

[0046] 2) Insert a "double-seal single-card" packer tool assembly into the top plate borehole, with the distance between the two packers no greater than R. After inserting them into the bottom of the hole, perform gas setting and gas fracturing operations;

[0047] 3) After the inner section fracturing is completed, the packer is unsealed and retreated by no more than the R spacing, and the packer gas setting and gas fracturing operations are performed again; step 3) is repeated until all dense packing gas fracturing operations of the borehole are completed;

[0048] 4) Connect the borehole that has completed gas fracturing to the mine gas extraction system to extract gas from the depressurized coal seam;

[0049] Continue to carry out dry dense packer gas fracturing of subsequent roof boreholes, and after fracturing is completed, carry out joint pumping of the boreholes;

[0050] After completing the gas fracturing and joint extraction of one group of boreholes with dry dense isolation, gas extraction of the depressurized coal seam in this group shall be implemented first. After achieving the expected effect, the drilling fracturing and joint extraction of the next group shall be repeated;

[0051] The fracturing grouping of the roof boreholes can be determined by numerical simulation or experimental monitoring to determine the number of boreholes in each group. The number of boreholes in each fracturing group can be optimized by the R value and the range of the artificial regional fracturing weakened and unloaded coal seam based on the numerical simulation of the overlying strata; it can also be determined by the monitoring data analysis of the intensive fracturing drilling continuous extraction experiment. After the intensive fracturing of the first borehole is completed, the extraction monitoring of the boreholes is carried out, and the first borehole is continuously monitored during the subsequent intensive fracturing of the boreholes until the extraction volume of the first borehole rapidly decreases. Then, the first borehole to the first borehole where the intensive fracturing drilling is being implemented is regarded as a fracturing group. The dry fracturing drilling is advanced in batches, the roof area decompression is dynamically advanced, and the decompression extraction is continuously followed up.

[0052] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0053] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0054] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for extracting gas from a dry dense fractured area of ​​a broken soft coal seam roof, characterized in that: This method involves arranging boreholes in a concentrated manner on the roof of a broken and soft coal seam, and using pneumatic directional drilling to control the borehole trajectory to be close to the coal seam; using packers in the boreholes to implement dense isolation and perform dry fracturing to create a dense seam network that conducts through the coal seam; through the concentrated arrangement of boreholes and dense fracturing in the holes, the entire roof layer of the region is broken and weakened, thereby depressurizing the coal seam, and ultimately forming a three-level high-efficiency seepage gas extraction channel consisting of a depressurized coal seam, a dense seam network on the roof, and boreholes on the roof, thereby achieving efficient extraction of coal seam gas.

2. The method for extracting gas from the dry dense fracturing area of ​​the broken soft coal seam roof according to claim 1, characterized in that: The following steps are involved: s1, using pneumatic directional drilling technology to drill holes in the top plate of the soft coal seam close to the coal seam, and controlling the drilling trajectory close to the coal seam; s2, using a drilling fracturing packer to isolate the borehole section by section to implement dense isolation in the top plate borehole; s3, using gas fracturing or low-intensity safety explosives and controlled shock wave fracturing to achieve dense isolation and low-energy dry fracturing in the top plate borehole; s4, through the dense dry fracturing of roof drilling, a dense fracture network that conducts the coal seam is formed in the roof, and the coal seam is depressurized by weakening the roof area; by using the roof drilling and the dense fracture network of the roof, the regional depressurization of the coal seam is increased, and gas is extracted from the depressurized coal seam to improve the gas extraction effect of the broken soft coal seam.

3. The method for extracting gas from the dry dense fracturing area of ​​the broken soft coal seam roof as claimed in claim 2, characterized in that: The method adopts grouped drilling areas to progressively fracture and weaken the roof to extract and decompress coal seam gas: according to the formation stress, roof lithology and the influence range of intensive fracture, multiple groups of roof drilling holes are divided, including the first group of drilling holes, ..., the nth group of drilling holes; the first group of drilling holes is subjected to intensive isolation dry fracture weakening, and then the coal seam gas in the decompression area of ​​the first group of drilling holes is preferentially extracted. After the expected effect is achieved, the second group of drilling holes is subjected to intensive isolation dry fracture weakening, and then the coal seam gas in the decompression area of ​​the second group of drilling holes is extracted, and so on; when the current group of drilling holes is decompressing the coal seam gas, the extraction of the previous multiple groups of drilling holes is maintained at the same time.

4. The method for extracting gas from the dry dense fracturing area of ​​the broken soft coal seam roof as claimed in claim 3, characterized in that: The method for determining the radius R of the fracture network caused by dry fracturing in the borehole is as follows: drill holes from the coal seam upward and gradually away from the roof of the coal seam, and after reaching a distance of more than 5-10m from the coal seam, control the drilling trajectory downward, gradually approach or expose the coal seam, and if the coal seam is exposed, grouting is performed on the coal seam, and then, starting from the maximum distance from the coal seam, a double-seal single-card packer tool combination is used to perform fracturing in a backward manner with a card distance of 1-2m, and after each fracturing section is completed, the orifice gas is monitored until the orifice gas gas obviously gushes out, and the distance between the fracturing section and the coal seam at this time is determined as R.

5. The method for extracting gas from the dry dense fracturing area of ​​the broken soft coal seam roof as claimed in claim 4, characterized in that: The drilling length covers the mining working face, the distance between the drilling trajectory and the coal seam is not greater than R, and the drilling distance is not greater than R.

6. The method for extracting gas from a dry dense fracturing area in a broken soft coal seam roof as claimed in claim 4, characterized in that: The packer spacing is no greater than R.

7. The method for extracting gas from a dry dense fracturing area in a broken soft coal seam roof as claimed in claim 4, characterized in that: Among the multiple groups of roof boreholes, the method for determining the number of boreholes in each group includes: determining the number of boreholes in each fracturing group by R value and the scope of artificial regional fracturing weakened and unloaded coal seam based on numerical simulation of overlying strata; or determining by monitoring data analysis of intensive fracturing drilling continuous extraction experiment, after completing the intensive fracturing of the first borehole, the extraction monitoring of the borehole is carried out, and the first borehole is continuously monitored during the subsequent intensive fracturing of the boreholes until the extraction volume of the first borehole rapidly decreases, and the first borehole to the first borehole where the intensive fracturing drilling is being carried out is regarded as a fracturing group.

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