Upper fracturing and lower drainage efficient permeability-increasing extraction method for high-watster thick coal seam

Abstract

The invention relates to the technical field of coal seam extraction, and relates to an upper fracturing and lower drainage efficient anti-reflection extraction method for a high-watster thick coal seam, which comprises the following steps of: dividing an extra-thick coal seam into an upper coal seam and a middle-lower coal seam, constructing a layer-penetrating guide drainage hole in the middle-lower coal seam, and constructing a layer-penetrating guide drainage hole in the upper coal seam of which the layer-penetrating guide drainage hole is not controlled, performing pressure relief and permeability increase by adopting segmented hydraulic fracturing drilling, and releasing gas of an upper coal seam; the vertical crack guiding effect of the layer-penetrating guiding drainage and mining holes is utilized, and fracturing cracks generated by segmented hydraulic fracturing drilling in the upper coal seam are communicated with the layer-penetrating guiding drainage and mining holes in the lower portion; pre-extracting gas around the crossing guide drainage holes in the lower coal seam through the crossing guide drainage holes, and performing pressure relief extraction on gas released after pressure relief and permeability increase of the staged hydraulic fracturing drill holes in the upper coal seam at the same time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coal seam extraction, and relates to an efficient permeability-increasing extraction method for upper fracturing and lower drainage in a high-gas thick coal seam. BACKGROUND

[0003] The existing gas control methods for high-gas coal seams include the conventional cross-seam drilling extraction method, the surface well extraction method, and the hydraulic permeability-increasing extraction method. The above-mentioned technologies have the following advantages and disadvantages: (1) The conventional cross-seam drilling extraction method has the advantage of simple construction process, but has the disadvantages of small influence range of single-hole extraction and low extraction efficiency, especially in the case of a thick coal seam, the length of the rock hole section plus the thickness of the thick coal seam leads to a drilling depth of more than 50 m, the thicker the coal seam, the greater the length of the drill pipe, and the gravity of the drill pipe will cause the drilling trajectory in the coal seam to be difficult to drill according to the design method, and the reliability of gas extraction is low. (2) The surface well extraction method includes surface vertical well extraction, surface L-shaped well extraction, and branch well extraction, and has the advantage of large extraction range, but has the disadvantages of long construction period and long extraction period, which will exacerbate the tension between mining and excavation, and is suitable for gas control in the planned area of a mine, but not suitable for the working face ready for mining. (3) The commonly used hydraulic permeability-increasing extraction method includes hydraulic fracturing and hydraulic slotting technology, and the specific advantages and disadvantages are as follows: ① The hydraulic fracturing technology has the advantage of wide permeability-increasing range, but the cracks generated by permeability-increasing mainly expand in the horizontal direction, and the vertical crack expansion is limited; ② The hydraulic slotting technology has good effect on local area pressure relief and permeability-increasing of a working face, generally 2-3 m of slotting is performed at a time, and as the thickness of the coal seam increases, the number of slotting also increases, which has the disadvantages of complex process and large slotting engineering quantity, and also has the problem of difficult drilling and slotting deslagging.

[0004] Based on the analysis of the advantages and disadvantages of the above-mentioned technologies, there is an urgent need for an efficient and effective permeability-increasing extraction method for high-gas thick coal seams. Therefore, the present application provides an efficient permeability-increasing extraction method for upper fracturing and lower drainage in a high-gas thick coal seam to improve the safe and efficient gas control of thick coal seams under similar conditions. SUMMARY

[0005] Therefore, the present application provides an efficient permeability-increasing extraction method for upper fracturing and lower drainage in a high-gas thick coal seam to improve the safe and efficient gas control of thick coal seams under similar conditions.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution:

[0007] An efficient permeability-increasing extraction method for upper fracturing and lower drainage in a high-gas thick coal seam is applied to a thick coal seam, and includes the following steps:

[0008] The upward through-seam guide drainage borehole is constructed in the floor roadway under the extra-thick coal seam, and the depth of the through-seam guide drainage borehole is controlled within 50 m; wherein, the coal seam through which the through-seam guide drainage borehole passes is the middle and lower coal seam, and the coal seam above the through-seam guide drainage borehole is the upper coal seam; and the pressure relief and permeability improvement by the staged hydraulic fracturing is carried out in the upper coal seam to release the gas in the upper coal seam;

[0009] The vertical crack guide effect of the through-seam guide drainage borehole is utilized to guide the fracturing fissures generated by the staged hydraulic fracturing borehole in the upper coal seam to the through-seam guide drainage borehole below;

[0010] The gas in the middle and lower coal seam around the through-seam guide drainage borehole is pre-drained through the through-seam guide drainage borehole, and the gas released after the pressure relief and permeability improvement by the staged hydraulic fracturing borehole in the upper coal seam is drained.

[0011] Further, the method specifically comprises the following steps:

[0012] S1, constructing upward through-seam guide drainage boreholes in the floor roadway under the extra-thick coal seam, the through-seam guide drainage borehole is constructed to the top of the middle and lower coal seam of the extra-thick coal seam, and the terminal hole spacing L1 of two adjacent through-seam guide drainage boreholes is 2 times of the drainage radius R1 of the through-seam guide drainage borehole;

[0013] S2, connecting all the through-seam guide drainage boreholes to the drainage pipeline in the floor roadway, and draining the original gas around the through-seam guide drainage borehole by using the negative pressure effect of the drainage;

[0014] S3, on the basis of step S2, constructing the staged hydraulic fracturing borehole in the fracturing drilling field, carrying out the retreating staged hydraulic fracturing, the staged fracturing spacing L2 is 2 times of the fracturing influence radius R2 of the single-stage fracturing in the radial direction of the borehole, according to the length L3 of the fracturing area and the staged fracturing spacing L2, the fracturing area is divided into n sections, wherein n=L3 / L2;

[0015] S4, taking the daily water accumulation amount in the drainage and discharging device connected to the drainage pipeline below each staged fracturing area as the evaluation standard, when the daily water accumulation amount Q during the fracturing is more than 2 times of Q0 before the fracturing, it is considered that the fracturing fissures generated by the staged hydraulic fracturing borehole are effectively connected to the guide drainage borehole, and it is regarded as the end of the staged fracturing; 压 is more than 2 times of Q0 before the fracturing, it is considered that the fracturing fissures generated by the staged hydraulic fracturing borehole are effectively connected to the guide drainage borehole, and it is regarded as the end of the staged fracturing;

[0016] S5, repeating step S4 until the staged hydraulic fracturing work of the fracturing area is completed.

[0017] Further, in step S5, it also includes observing the gas drainage amount growth of the through-seam guide drainage borehole after the fracturing work is completed as an auxiliary judgment index of the fracturing effectiveness.

[0018] Further, the observation of the gas extraction amount growth situation includes at least 7 consecutive days of comparison of the growth range of the single-hole extraction flow of the through-seam guided drainage hole before and after the fracturing as an auxiliary judgment basis of the fracturing effect, when the single-hole extraction flow is positively correlated with the extraction time, and the flow value of the 7th day is increased by at least 50% more than the average value before the fracturing, it is determined that the effective fracturing influence range.

[0019] Further, it also includes:

[0020] S6, controlling the drainage time based on the provisions of the Coal Mine Safety Regulations.

[0021] Further, step S6 specifically includes that when the original gas content of the coal seam is greater than or equal to 6m 3 / t, the drainage time of the through-seam guided drainage hole is stopped until the residual gas content of the coal seam is reduced to 6m 3 / t or less, and the extraction time is not less than 6 months;

[0022] When the original gas content of the coal seam is less than 6m 3 / t, the drainage time of the through-seam guided drainage hole is stopped until the gas extraction rate of the coal seam reaches 30% or more.

[0023] Further, in step S3, the segmented hydraulic fracturing borehole is constructed by using a directional long borehole, and it is ensured that the fracturing fissure extends along the vertical direction and communicates with the through-seam guided drainage hole below.

[0024] Further, the thickness of the middle and lower coal seam is 10-20m, and the thickness of the upper coal seam is 10-15m.

[0025] The beneficial effects of the present application are:

[0026] For the problem of gas extraction in a super-thick coal seam (thickness greater than 20m), the present application proposes a high-efficiency permeability-increasing extraction method, i.e., the "upper fracturing and lower drainage technology for high-gas super-thick coal seams". Traditional methods such as through-seam drilling or bedding drilling often have problems such as borehole deviation and low extraction efficiency, which are difficult to meet the needs of super-thick coal seams. However, the present application significantly improves the extraction effect by innovatively combining segmented hydraulic fracturing with through-seam guided drainage holes. The core is as follows: first, a through-seam guided drainage hole is constructed in the middle and lower part of the coal seam, with a hole depth controlled within 50m to reduce deviation; then, a directional long borehole is used to perform segmented hydraulic fracturing on the upper coal seam to release gas and achieve pressure relief and permeability increase; finally, the through-seam guided drainage hole is connected with the lower extraction hole to form an extraction crack network, realizing synchronous and efficient extraction of the middle and lower coal seams and the upper coal seam. The specific effects are as follows:

[0027] Improve permeability and extraction efficiency: The staged hydraulic fracturing technology can greatly reduce the stress of the upper coal seam, increase the coal body fracture, and improve the permeability, so that the gas is fully released. Combined with the extraction seam network formed by the through-layer guide drainage hole, the efficient extraction of gas is ensured, and the extraction time is significantly shortened.

[0028] Make up for the lack of vertical cracks: Although hydraulic fracturing can generate horizontal cracks, the development of vertical cracks is limited. The vertical cracks of the through-layer guide drainage hole guide the upper fracturing cracks and the lower drainage hole to effectively communicate, solving the problem of insufficient vertical cracks.

[0029] Reduce the problem of drilling deviation: The length of the through-layer drilling is shortened to within 50 meters, avoiding the deviation phenomenon that often occurs in traditional long drilling, improving the drilling accuracy and construction reliability.

[0030] Synchronous extraction saves time: Through the pressure relief and permeability improvement of the upper coal seam and the pre-extraction of the middle and lower coal seam, the double-layer synchronous extraction is realized, which not only improves the efficiency, but also relieves the tense situation of mine excavation replacement.

[0031] In general, the technical solution effectively solves the technical bottleneck of gas extraction in thick coal seams through the innovative combination of fracturing and extraction. Compared with traditional methods, it not only improves the efficiency and safety of gas extraction, but also reduces the construction difficulty and cost, and has significant economic and social benefits. In practical application, the scheme provides a reliable guarantee for mine safety production, and improves the efficiency of coal resource exploitation, providing a feasible reference for gas control under similar geological conditions.

[0032] Other advantages, objects and features of the present application will be set forth in part in the description which follows, and in part will be apparent from the examination of the following specification, or can be learned from the practice of the present application. The objects and other advantages of the present application can be realized and attained by the methods and instrumentalities set forth in the following description. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to make the purpose, technical scheme and advantages of the present application clearer, the preferred detailed description of the present application will be combined with the drawings as follows, in which:

[0034] Fig. 1 The extraction schematic diagram of the upper fracturing and lower drainage extraction along the strike direction of the coal seam in the embodiment;

[0035] Fig. 2 The change schematic diagram of the water amount in the drainage and slag extractor before and after fracturing;

[0036] Fig. 3 The comparison schematic diagram of the conventional through-layer drilling extraction and the upper fracturing and lower drainage extraction.

[0037] Signs: floor lane 1, through layer guide row mining hole 2, middle and lower coal seam 31, upper coal seam 32, fracturing drilling field 4, segmented hydraulic fracturing borehole 5, fracturing fissure 51, drainage pipeline 11, drainage pipeline 21, drainage slag discharger 22, water accumulation 23. DETAILED DESCRIPTION

[0038] The advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure of the specification. The present application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made to the details in the specification without departing from the spirit of the present application based on different views and applications. It should be noted that the drawings provided in the following examples only illustrate the basic concept of the present application in a schematic manner, and the features in the following examples and embodiments can be combined with each other without conflict.

[0039] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and cannot be understood as a limitation on the present application; in order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some known structures and their descriptions in the drawings may be omitted.

[0040] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and cannot be understood as a limitation on the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0041] First of all, it should be noted that the very thick coal seam referred to in the present application is a coal seam with a thickness greater than 20m. For such a coal seam, whether it is a through layer drilling or a bedding drilling, the drilling length is large, and the drilling deviation phenomenon will occur, and the drilling bottom area has low extraction negative pressure, poor extraction effect, and is prone to extraction blank area. For example, the length of a small inclination drilling can reach 70-80m, and field practice shows that the horizontal deviation of a drilling constructed by an ordinary drilling machine can reach more than 5m, and in this case, there may be an extraction blank area between the extraction drillings. Therefore, a single through layer drilling or bedding drilling is not suitable for very thick coal seams.

[0042] Extra-thick coal seams have well-developed bedding. While hydraulic fracturing can increase fracture development and relieve pressure, the resulting cracks tend to propagate horizontally along the bedding planes. This approach is more effective for medium-thick coal seams (2-3m thick). Vertical cracks, however, develop relatively less. If hydraulic fracturing is performed at different levels within an extra-thick coal seam, the fracturing cycle is long, and adjacent fracturing areas may lead to the development of localized fractures in the unfractured areas, potentially resulting in fracturing failure.

[0043] Example 1

[0044] like Figs. 1-2 As shown, this embodiment provides a highly efficient permeability-enhancing extraction method for fracturing and draining in high-waste, thick coal seams, applicable to extra-thick coal seams, including the following steps:

[0045] Depending on the gas extraction process of the extra-thick coal seam, the extra-thick coal seam is divided into an upper coal seam and a middle and lower coal seam. An upward-facing cross-seam guide drainage hole is constructed in the bottom roadway below the extra-thick coal seam, and the depth of the cross-seam guide drainage hole is controlled within 50m. The coal seam through which the cross-seam guide drainage hole passes is the middle and lower coal seam, and the coal seam above the cross-seam guide drainage hole is the upper coal seam. In the upper coal seam, segmented hydraulic fracturing is used to depressurize and enhance permeability, releasing the gas in the upper coal seam.

[0046] Specifically, the upper coal seam is depressurized and permeable by segmented hydraulic fracturing to release the gas in the upper coal seam. The height range of the fractures generated by the fracturing is the upper coal seam range, and the thickness of the upper coal seam is generally 10 to 15m. The middle and lower coal seams are mainly used for pre-drainage and drainage, and the thickness of the coal seam is generally 10 to 20m.

[0047] It should be noted that the depth of the cross-layer guide drainage hole is the thickness of the middle and lower coal seam plus the thickness of the bottom rock strata.

[0048] By utilizing the vertical crack guiding effect of the cross-layer guide drainage hole, the fracturing fractures generated by the segmented hydraulic fracturing boreholes in the upper coal seam are connected to the cross-layer guide drainage hole below.

[0049] The gas around the cross-layer guide drainage hole in the lower coal seam is pre-extracted through the cross-layer guide drainage hole, while the gas released from the upper coal seam after depressurization and permeability enhancement through the segmented hydraulic fracturing borehole is depressurized and extracted.

[0050] Specifically, the following steps are included:

[0051] (1) First, construct an upward cross-layer guide drainage hole 2 in the bottom roadway 1 below the extra-thick coal seam. The cross-layer guide drainage hole 2 is constructed to the top of the middle and lower coal body 31 of the extra-thick coal seam. The final hole spacing L1 between two adjacent cross-layer guide drainage holes is twice the extraction radius R1 of the cross-layer guide drainage hole 2.

[0052] (2) In the extraction pipeline 11 connected to all the cross-layer guide drainage holes 2 in the bottom roadway 1, the original gas around the cross-layer guide drainage holes 2 is extracted using the negative pressure of extraction. At the same time, the extraction pipeline 11 is connected to the drainage slag remover 22 through the drainage hose 21, and the change of the water accumulation 23 in the drainage slag remover 22 is observed. It should be noted that at this time, the upper coal seam 33 has not yet undergone hydraulic fracturing and extraction.

[0053] (3) Based on step (2), construct segmented hydraulic fracturing boreholes 5 in fracturing drilling site 4, and carry out retreating segmented hydraulic fracturing work in the upper coal body 32. The segmented fracturing spacing L2 is twice the fracturing influence radius R2 of single-segment fracturing along the radial direction of the borehole. According to the length L3 of the fracturing area and the segmented fracturing spacing L2, the fracturing area is divided into n segments, n=L3 / L2;

[0054] (4) The daily water volume 23 in the drainage and slag removal device 22 below each stage of hydraulic fracturing is used as the evaluation criterion. When the value of the daily water volume 23 during fracturing is Q 压 When the value is more than twice the value of Q0 before fracturing, it is considered that the fracturing fracture 51 generated by the segmented hydraulic fracturing borehole 5 is effectively connected with the cross-layer guide drainage hole 2, and this serves as a sign that the segmented fracturing has ended.

[0055] (5) Repeat step (4) until all the hydraulic fracturing work in the fracturing area is completed. At the same time, observe the increase in the pumping volume of the guide drainage hole 2 after the fracturing work is completed, as an auxiliary indicator for judging the effectiveness of fracturing;

[0056] (6) The Coal Mine Safety Regulations stipulate that the residual gas content in a fully mechanized top-coal caving coal seam is less than 6m³. 3 The requirement is / t, therefore, when the original gas content of the coal seam is greater than or equal to 6m 3 At / t, the drainage time of the cross-layer guide drainage hole 2 is until the residual gas content of the coal seam decreases to 6m 3 Stop extraction when the volume is below 6 tons, and the extraction period should not be less than 6 months; when the original gas content of the coal seam is less than 6 m³ / t. 3 When the gas extraction rate reaches 30% or higher, the extraction time of the upward cross-layer guide extraction hole shall continue until the gas extraction rate of the coal seam reaches 30% or higher.

[0057] Specifically, in step S1, the depth of the through-layer guide drainage hole is controlled within 50m.

[0058] Further, in step S3, the segmented hydraulic fracturing borehole is constructed by directional long borehole construction, and it is ensured that the fracturing fissures extend along the vertical direction and communicate with the lower layer-penetrating guide drainage borehole.

[0059] Further, in step S5, the gas extraction amount growth condition of the layer-penetrating guide drainage borehole after the fracturing work is completed is also observed, so as to serve as an auxiliary judgment index of the fracturing effect.

[0060] Further, the observation of the gas extraction amount growth condition includes at least a comparison of the growth amplitude of the single-hole extraction flow of the layer-penetrating guide drainage borehole before and after the fracturing for 7 consecutive days, which serves as an auxiliary judgment basis of the fracturing effect. When the single-hole extraction flow is positively correlated with the extraction time, and the flow value on the seventh day is increased by at least 50% or more than the average value before the fracturing, it is determined that the effective fracturing influence range is obtained.

[0061] Example 2: Comparison between the conventional layer-penetrating borehole extraction method and the method of the present application

[0062] Engineering background: For the problem of gas control in a super-thick coal seam, taking the intake airway and return airway pre-extraction area of a super-thick coal seam mining face in a mine in the northwest region as an example, the strike length of the two coal roadways is 500 m, the inclination control range is 20 m on both sides of the coal roadway, the longitudinal coal seam thickness is 30 m, the coal roadway width is 5 m, and the height is 4 m. The original gas content of the coal seam is 17 m 3 / t, and there is a serious risk of coal and gas outburst. In the past, upward layer-penetrating boreholes were mainly constructed in the floor roadway to pre-extract the full coal thickness gas in the coal roadway strip area. The floor roadway is located 25 m below the coal seam, and the upper coal seam extraction effect is poor and the residual gas content is high, which leads to high gas emission during the coal roadway excavation, seriously affecting the safety of the coal roadway excavation and the mining and excavation replacement production plan of the mine.

[0063] The coal seam thickness in the longitudinal direction of the super-thick coal seam is divided into a lower coal seam 31 and an upper coal seam 32, wherein the thickness of the lower coal seam 31 is 10-20 m, and the thickness of the upper coal seam 32 is 10-15 m.

[0064] Based on this engineering background, an industrial test of the upper fracturing and lower drainage of the super-thick coal seam in the present embodiment is carried out, and the treatment effects of the conventional layer-penetrating borehole full coal thickness extraction and the upper fracturing and lower drainage of the super-thick coal seam are compared and analyzed.

[0065] The intake airway is treated by using the conventional method, and the construction steps of the conventional method are as follows:

[0066] Drilling arrangement: Through site investigation, the single-hole extraction influence radius of the layer-penetrating borehole is 3 m.

[0067] The upward through-seam guide drainage boreholes are arranged in a net pattern in the floor roadway, 8 boreholes in each row, 57 rows in total, and the borehole length is 55-60 m, and the boreholes are drilled to the top of the coal seam.

[0068] Gas extraction: all the through-seam guide drainage boreholes are connected to the extraction pipeline in the floor roadway of the air intake roadway, and gas is extracted by using negative pressure, and the extraction time is 11 months.

[0069] Conventional method extraction effect

[0070] Single-hole extraction flow: 0.06-0.18 m 3 / min

[0071] Single-hole extraction concentration: 30-58%

[0072] Residual gas content: 7.72 m 3 / t in the upper coal seam, 5.56 m 3 / t in the middle coal seam, and 4.74 m 3 / t in the lower coal seam

[0073] Extraction standard time: 11 months

[0074] Problems: the extraction effect of the upper coal seam is poor, the residual gas content is high, the extraction time is long, and the safety production of the mine is affected.

[0075] In the return airway, a high-efficiency permeability-enhancing and extraction method for high-gas thick coal seams is constructed according to the present application, and the construction steps are as follows:

[0076] Through-seam guide drainage borehole construction: upward through-seam guide drainage boreholes are constructed in the floor roadway, drilled to the top of the middle and lower coal seams, and the borehole depth is controlled within 50 m.

[0077] The extraction radius R1 is 3 m, the final hole spacing L1 is 2xR1=6 m, the boreholes are arranged in a net pattern, 8 boreholes in each row, 57 rows in total, and the borehole length is 35-50 m.

[0078] Gas pre-extraction: the through-seam guide drainage boreholes are connected to the extraction pipeline, and the gas in the middle and lower coal seams is extracted by using negative pressure, and at the same time, the water drainage hose is connected to the water drainage and slag discharge device to observe the water accumulation change.

[0079] Segmented hydraulic fracturing borehole construction: directional long boreholes are constructed in the fracturing drilling field as segmented hydraulic fracturing boreholes, and the fracturing influence radius R2 is 25 m obtained by field investigation, and the segmented fracturing spacing L2 is 2xR2=50 m.

[0080] The fracturing region length L3 is 500 m, and is divided into n=L3 / L2=10 segments.

[0081] Retreating type segmented hydraulic fracturing:

[0082] Perform backward hydraulic fracturing in stages, and observe the daily water accumulation Q in the lower drainage and slag discharge device after each stage of fracturing. 压 When Q 压 When the volume of water accumulated before fracturing reaches ≥2×Q0 (Q0 is the volume of water accumulated before fracturing), the fracturing of this segment is terminated.

[0083] Repeated fracturing: Repeat the segmented hydraulic fracturing drilling steps until 10 segments of fracturing are completed, and observe the increase in gas extraction volume of the cross-layer guide drainage holes after fracturing.

[0084] Controlling drainage time: According to the "Coal Mine Safety Regulations", the initial gas content is 17m³. 3 6m 3 / t, extracted until the residual gas content is below 6m 3 / t, the actual sampling period is 8 months.

[0085] The sampling effect of the method of this invention:

[0086] Single-well pumping flow rate: 0.21~0.82m³ 3 / min

[0087] Single-well sampling concentration: 45-67%

[0088] Residual gas content: 5.81m in the upper coal seam 3 / t, middle coal seam 5.74m 3 / t, lower coal seam 5.06m 3 / t

[0089] Time to achieve sampling standards: 8 months

[0090] Table 1 Comparison of Gas Drainage Effectiveness

[0091]

[0092] Performance Comparison: Compared with conventional methods, the method of this invention increases the single-hole extraction flow rate by 3 to 5 times, and reduces the residual gas content in the upper coal seam from 7.72 m³. 3 / t decreased to 5.81m 3 / t, the time to reach the extraction standard was shortened by 27.3%, which significantly improved the extraction efficiency.

[0093] The above implementation results show that if only cross-layer drilling is used for pre-drainage, not only is the time required to reach the drainage standard long, but the pre-drainage effect is also poor, and the upper coal seam is a weak area for drainage. Compared with the conventional cross-layer drilling drainage method, the upper fracturing and lower drainage method of this invention can save 15 yuan per ton of coal, generating direct economic benefits of 13.4 million yuan. It can also shorten the drainage standard time and drainage pipeline maintenance time by 3 months, and while solving the tight situation of mine mining succession, it can also create nearly 200 million yuan in indirect economic benefits.

[0094] Finally, it is to be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the purpose and scope of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A high-efficiency permeability-increasing and extraction method for mining in a high-waste thick coal seam by fracturing the upper part and draining the lower part, applied to a super-thick coal seam, characterized in that, The method comprises the following steps: an upward through-seam guide drainage hole is constructed in a floor roadway under a super-thick coal seam, and the depth of the through-seam guide drainage hole is controlled within 50 m; the through-seam guide drainage hole penetrates a middle and lower coal seam, and an upper coal seam above the through-seam guide drainage hole; and pressure relief and permeability improvement are performed on the upper coal seam by using staged hydraulic fracturing, so as to release gas in the upper coal seam; the pressure relief fractures generated by the staged hydraulic fracturing boreholes in the upper coal seam are guided to the through-seam guide drainage hole below by using the vertical fracture guiding effect of the through-seam guide drainage hole; the gas in the middle and lower coal seam around the through-seam guide drainage hole is pre-drained through the through-seam guide drainage hole, and the gas released after the pressure relief and permeability improvement of the upper coal seam by using the staged hydraulic fracturing boreholes is relieved and drained.

2. The high-efficiency permeation-enhancing and extraction method for high-waste thick coal seam upper fracturing and lower drainage according to claim 1, characterized in that, The method comprises the following steps: S1, an upward through-seam guide drainage hole is constructed in a floor roadway under a super-thick coal seam, and the through-seam guide drainage hole is constructed to the top of a middle and lower coal seam of the super-thick coal seam, and the terminal hole spacing L1 of two adjacent through-seam guide drainage holes is 2 times of the drainage radius R1 of the through-seam guide drainage hole; S2, all the through-seam guide drainage holes are connected to a drainage pipeline in the floor roadway, and the original gas around the through-seam guide drainage hole is drained by using the negative pressure effect of the drainage; S3, on the basis of step S2, staged hydraulic fracturing boreholes are constructed in a fracturing drilling field, and a retreating staged hydraulic fracturing is performed, the staged fracturing spacing L2 is 2 times of the pressure relief influence radius R2 of a single-stage fracturing in the radial direction of the borehole, and the fracturing area is divided into n stages according to the length L3 of the fracturing area and the staged fracturing spacing L2, wherein n=L3 / L2; S4, taking the daily water accumulation amount in the drainage and slag discharger connected with the extraction pipeline under each staged fracturing area as the evaluation standard, when the daily water accumulation amount Q during fracturing is more than 2 times of Q0 before fracturing, it is considered that the fracturing fracture produced by the staged hydraulic fracturing borehole is effectively communicated with the guide drainage hole, and serves as the sign of the end of the staged fracturing. 压 is more than 2 times of Q0 before fracturing, it is considered that the fracturing fracture produced by the staged hydraulic fracturing borehole is effectively communicated with the guide drainage hole, and serves as the sign of the end of the staged fracturing. S5, step S4 is repeated until the staged hydraulic fracturing work of the fracturing area is completed.

3. The high-efficiency permeation-enhancing and extraction method for high-waste thick coal seam upper fracturing and lower drainage according to claim 2, characterized in that, In step S5, the growth of the gas drainage amount of the through-seam guide drainage hole after the fracturing work is completed is observed as an auxiliary judgment index of effective fracturing.

4. The high-efficient permeability-increasing and extraction method for high-waste thick coal seam upper fracturing and lower drainage according to claim 3, characterized in that: The observation of the growth of the gas drainage amount comprises comparing the growth amplitude of the single-hole drainage flow of the through-seam guide drainage hole before and after the fracturing for at least 7 consecutive days as an auxiliary judgment basis of the fracturing effect, when the single-hole drainage flow is positively correlated with the drainage time, and the flow value on the seventh day is increased by at least 50% more than the average value before the fracturing, it is determined that the effective fracturing influence range is determined.

5. The high-efficient permeability-increasing and extraction method for high-waste thick coal seam upper fracturing and lower drainage according to claim 2, characterized in that, Further comprising: S6, the drainage time is controlled according to the provisions of the Coal Mine Safety Regulations.

6. The high-efficient permeability-increasing and extraction method for high-waste thick coal seam upper fracturing and lower drainage according to claim 5, characterized in that, Step S6 specifically includes that when the original gas content of the coal seam is greater than or equal to 6m 3 / t, the drainage time of the cross-layer guide drainage hole is until the residual gas content of the coal seam is reduced to 6m 3 / t or less, and the drainage time is not less than 6 months. When the original gas content of the coal seam is less than 6m 3 / t, the drainage time of the cross-layer guide drainage hole is until the coal seam gas drainage rate reaches more than 30%.

7. The high-efficient permeability-increasing and extraction method for high-waste thick coal seam upper fracturing and lower drainage according to claim 2, characterized in that: In step S3, the staged hydraulic fracturing borehole is constructed by using a directional long borehole, and it is ensured that the pressure relief fractures extend vertically and are connected to the through-seam guide drainage hole below.

8. The high-efficient permeability-increasing and extraction method for high-waste thick coal seam upper fracturing and lower drainage according to claim 1, characterized in that: The thickness of the middle and lower coal seam is 10-20 m, and the thickness of the upper coal seam is 10-15 m.

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