Coal seam gas pre-extraction method for soft and hard composite coal seam

Abstract

The invention belongs to the technical field of coal mine underground gas extraction, and relates to a coal seam gas pre-extraction method for a soft and hard composite coal seam. Comprising the following steps that S1, the type of the composite coal seam is determined according to the positions of a hard layer and a soft layer; s2, obtaining structural parameters of the composite coal seam; s3, corresponding drilling strategies are matched according to the type of the composite coal seam, and the upper soft layer type, the lower soft layer type, the middle soft layer type and the upper and lower soft layer type all have respective drilling arrangement strategies; s4, hydraulic fracturing drilling is conducted on the hard layer according to the drilling strategy, and gas extraction is conducted on the hard layer; and S5, common extraction drill holes are constructed in the soft layer, and gas extraction is conducted on the soft layer. According to the method, the hydraulic fracturing drill hole is constructed in the hard layer, so that the crack is generated and penetrates through the soft layer, the gas of the soft layer is indirectly extracted, and the problem that the gas extraction efficiency of soft layer drill holes is low is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of underground coal mine gas extraction, and relates to a coal seam gas pre-extraction method for a soft and hard composite coal seam. Background Art

[0002] In the field of underground gas extraction technology in coal mines, gas extraction is not only an important part of coal mine safety production, but also a necessary measure to improve coal mining efficiency and protect the lives of miners. As a major coal-producing country, my country has a large number of gas mines, and the gas content in coal seams directly affects mining deployment and coal mine safety production. Therefore, gas extraction work is particularly important.

[0003] Gas extraction usually requires the construction of a large number of extraction boreholes in the coal seam. Mining activities can only be carried out after the gas content in the coal seam is reduced to a certain level through negative pressure extraction. However, in the process of gas extraction in coal seams containing soft layers, the particularity of the coal seam structure poses great challenges to the extraction work. Coal seams containing soft layers contain one or more layers of softer coal in the vertical direction. These soft layers are soft, have high gas content, and low permeability. In addition, it is difficult and costly to construct gas extraction boreholes. Traditional gas extraction methods can only construct extraction boreholes in hard layers, but cannot form effective boreholes in soft layers. The boreholes cannot penetrate the hard and soft layers, making it difficult to extract gas from the soft layers. At the same time, due to the low permeability of the soft layers, the overall construction period and extraction time of the coal seam are significantly extended, which seriously affects the efficiency of mining and succession in coal mines.

[0004] For composite coal seams containing soft layers, if the gas in the soft layers cannot be effectively extracted, it will not only increase the gas outflow during coal mining, but may also cause serious safety accidents such as gas explosions. Therefore, how to effectively extract gas from coal seams containing soft layers has become a technical problem that needs to be solved urgently for coal mine safety production. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a coal seam gas pre-extraction method for soft and hard composite coal seams, which solves the problem of low gas extraction efficiency of soft layer drilling holes by constructing hydraulic fracturing holes in the hard layer to generate cracks and penetrate them to the soft layer, thereby indirectly extracting gas from the soft layer.

[0006] To achieve the above object, the present invention provides a method for pre-extraction of coal seam gas in a soft-hard composite coal seam, comprising the following steps:

[0007] Step S1, determining the type of the composite coal seam according to the positions of the hard layer and the soft layer;

[0008] Step S2, obtaining structural parameters of the composite coal seam;

[0009] Step S3, matching the corresponding drilling strategy according to the type of the composite coal seam;

[0010] Step S4, hydraulically fracturing the hard layer according to the drilling strategy, and extracting gas from the hard layer;

[0011] Step S5: construct a common extraction borehole in the soft layer and extract gas from the soft layer.

[0012] Optional, composite coal seam types include:

[0013] Upper soft layered coal seam, with soft layers above and hard layers below;

[0014] The lower soft stratified coal seam has a hard stratification above and a soft stratification below.

[0015] Optionally, the structural parameters of the composite coal seam include the working face width L and the thickness of each hard layer and soft layer.

[0016] Optional drilling strategies include:

[0017] For the upper soft layered coal seam, multiple hydraulic fracturing boreholes are arranged in a straight line in the lower hard layer, the distance between the hydraulic fracturing borehole and the upper soft layer is b, the length of the hydraulic fracturing borehole is n, and the spacing between the hydraulic fracturing boreholes is a;

[0018] Among them, b is 0.5~1m, n=L-30m, and a is 5~15m.

[0019] Optional drilling strategies include:

[0020] For the lower soft layer type coal seam, multiple hydraulic fracturing boreholes are arranged in a straight line in the upper hard layer, the distance between the hydraulic fracturing borehole and the lower soft layer is b, the length of the hydraulic fracturing borehole is n, and the spacing between the hydraulic fracturing boreholes is a;

[0021] Among them, b is 0.5~1m, n=L-30m, and a is 5~15m.

[0022] Optionally, the types of composite coal seams also include:

[0023] Intermediate soft layered coal seam, with the middle layer being soft and the upper and lower layers being hard;

[0024] The upper and lower soft stratified coal seam has a hard layer in the middle and soft layers above and below.

[0025] Optionally, the drilling strategy also includes:

[0026] For the intermediate soft layered coal seam, multiple hydraulic fracturing drill holes are arranged in a straight line in the upper hard layer and the lower hard layer, and the hydraulic fracturing drill holes in the upper hard layer and the lower hard layer are arranged in a staggered manner;

[0027] The distance between the hydraulic fracturing borehole and the middle soft layer is b, the length of the hydraulic fracturing borehole is n, and the spacing between the hydraulic fracturing boreholes is a;

[0028] b is 0.5~1m, n=L-30m, and a is 5~15m.

[0029] Optionally, the hydraulic fracturing borehole located in the lower hard layer and the hydraulic fracturing borehole located in the upper hard layer are spaced apart in the horizontal direction by a / 2.

[0030] Optionally, the drilling strategy also includes:

[0031] For the upper and lower soft layered coal seam, multiple hydraulic fracturing boreholes are arranged in a straight line at the center of the middle hard layer. The distance between the hydraulic fracturing borehole and the upper soft layer and the lower soft layer is b. The length of the hydraulic fracturing borehole is n, and the spacing between the hydraulic fracturing boreholes is a.

[0032] Where b = 0.5H 硬中 , H 硬中 is the thickness of the middle hard layer; n=L-30m, a is 5~15m.

[0033] Optionally, step S4 includes:

[0034] Step S41: construct hydraulic fracturing boreholes in the hard layer according to the drilling strategy, and perform open hole segmented hydraulic fracturing in the hydraulic fracturing boreholes, with segment length Y 段长 =a, segment spacing Y 间距 5 to 10 m;

[0035] Step S42: Connect the hydraulic fracturing borehole to the extraction system to extract the gas in the hard layer.

[0036] Optionally, step S5 includes:

[0037] Step S51: constructing common drainage boreholes at a certain interval in the soft layer, and the interval of the common drainage boreholes is determined according to the residual gas content and the drainage reaching standard time requirement;

[0038] Step S52: Connect the common drainage borehole to the drainage system to drain the gas in the soft layer.

[0039] The beneficial effects of the present invention are:

[0040] The present invention proposes a method for pre-extracting coal seam gas by hydraulic fracturing in a soft-hard composite coal seam, which effectively solves the difficulties faced by traditional gas extraction technology in soft-layered coal seams.

[0041] First, by using hard layer drilling and combining hydraulic fracturing technology, the present invention successfully avoids the problem of difficult drilling in soft layers. The traditional method directly drills holes in the soft layer. Due to the soft coal quality, high gas content and low permeability in the soft layer, the drilling porosity is low and the cost is high. However, the present invention drills holes in the hard layer and uses the cracks generated by hydraulic fracturing to penetrate to the soft layer, thereby achieving the purpose of indirect extraction of gas in the soft layer, greatly improving the porosity and construction efficiency of the drilling.

[0042] Secondly, the present invention expands the coverage of the borehole through hydraulic fracturing technology, solving the problem of low extraction efficiency of soft layer drilling. Since the length of the construction borehole in the soft layer is short, it is difficult to cover a large area, resulting in poor extraction effect. However, the fracture network generated by hydraulic fracturing in the present invention can penetrate the soft layer, allowing the gas to smoothly gush out of the soft layer and be extracted to the ground, thereby significantly improving the gas extraction efficiency.

[0043] In addition, the present invention has the advantages of simple operation and low cost. Through reasonable drilling design and fracturing parameter selection, the present invention realizes the coordinated design of hydraulic fracturing drilling and extraction drilling, ensuring the maximization of fracturing effect and the improvement of extraction efficiency. At the same time, since direct drilling in the soft layer is avoided, the present invention greatly reduces the construction difficulty and cost, bringing significant economic benefits to coal mining enterprises.

[0044] To sum up, the method for pre-extraction of coal seam gas by hydraulic fracturing in soft and hard composite coal seams of the present invention not only effectively solves the problems faced by traditional gas extraction technology in soft stratified coal seams, but also improves the gas extraction efficiency, reduces construction difficulty and cost, and provides a strong guarantee for safe production and efficient mining of coal mines.

[0045] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0047] Figure 1 A flow chart of a coal seam gas pre-extraction method for a soft and hard composite coal seam provided by the present invention;

[0048] Figure 2 A plan view schematic diagram of the arrangement of drilling holes on the working face of a coal seam gas pre-extraction method for a soft-hard composite coal seam provided by the present invention;

[0049] Figure 3 A schematic cross-sectional view of an upper soft layered drilling arrangement of a coal seam gas pre-extraction method for a soft-hard composite coal seam provided by the present invention;

[0050] Figure 4 A cross-sectional schematic diagram of a lower soft layered drilling arrangement of a coal seam gas pre-extraction method for a soft-hard composite coal seam provided by the present invention;

[0051] Figure 5 A schematic cross-sectional view of an intermediate soft layered drilling arrangement of a coal seam gas pre-extraction method for a soft-hard composite coal seam provided by the present invention;

[0052] Figure 6 A schematic cross-sectional diagram of an arrangement of upper and lower soft layered drilling holes for a coal seam gas pre-extraction method for a soft-hard composite coal seam provided by the present invention. DETAILED DESCRIPTION

[0053] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0054] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0055] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0056] like Figure 1 As shown, a coal bed gas pre-extraction method for a soft and hard composite coal seam of the present invention specifically comprises the following steps:

[0057] Step S1, determining the type of the composite coal seam according to the positions of the hard layer and the soft layer;

[0058] Step S2, obtaining structural parameters of the composite coal seam;

[0059] Step S3, matching the corresponding drilling strategy according to the type of the composite coal seam;

[0060] Step S4, hydraulically fracturing the hard layer according to the drilling strategy, and extracting gas from the hard layer;

[0061] Step S5: construct a common extraction borehole in the soft layer and extract gas from the soft layer.

[0062] Furthermore, if Figures 3 to 6 As shown, the types of composite coal seams in step S1 include: an upper soft layer type with a soft layer on the top and a hard layer on the bottom, a lower soft layer type with a hard layer on the top and a soft layer on the bottom, a middle soft layer type with a soft layer in the middle and hard layers on both the top and bottom, and an upper and lower soft layer type with a hard layer in the middle and soft layers on both the top and bottom.

[0063] Furthermore, if Figure 2 As shown, the structural parameters of the composite coal seam include the working face width L and the thickness of each hard layer and soft layer.

[0064] Specifically, Figure 3 As shown, for the upper soft layered coal seam, the thickness of the upper soft layer is H 软上 , the thickness of the hard layer below is H 硬下 ;

[0065] Specifically, Figure 4 As shown, for the lower soft layered coal seam, the thickness of the upper hard layer is H 硬上 , the thickness of the soft layer below is H 软下 ;

[0066] Specifically, Figure 5 As shown, for the middle soft layered coal seam, the thickness of the middle soft layer is H 软中 , the thickness of the upper hard layer is H 硬上 ', the thickness of the lower hard layer is H 硬下 '.

[0067] Specifically, Figure 6 As shown, for the upper and lower soft layered coal seams, the thickness of the middle hard layer is H 硬中 , the thickness of the upper soft layer is H 软上 ', the thickness of the lower soft layer is H 软下 '.

[0068] Specifically, in step S3, the drilling strategy includes:

[0069] For the upper soft layered coal seam, multiple hydraulic fracturing boreholes are arranged in a straight line in the lower hard layer. The distance between the hydraulic fracturing borehole and the upper soft layer is b, which is 0.5 to 1 m according to the construction hole effect. The length of the hydraulic fracturing borehole is n, n = L-30m, and the spacing of the hydraulic fracturing boreholes is a, which is optimized within 5 to 15m according to the fracturing range;

[0070] For the lower soft layered coal seam, multiple hydraulic fracturing boreholes are arranged in a straight line in the upper hard layer. The distance between the hydraulic fracturing borehole and the lower soft layer is b, which is 0.5 to 1 m according to the construction hole effect. The length of the hydraulic fracturing borehole is n, n = L-30m, and the spacing of the hydraulic fracturing boreholes is a, which is optimized within 5 to 15m according to the fracturing range;

[0071] For the middle soft layered coal seam, multiple hydraulic fracturing boreholes are arranged in a straight line in the upper hard layer and the lower hard layer, and the hydraulic fracturing boreholes are arranged in an up-down staggered manner, that is, the horizontal spacing between the hydraulic fracturing boreholes in the lower hard layer and the hydraulic fracturing boreholes in the upper hard layer is a / 2. The distance between the hydraulic fracturing boreholes and the middle soft layer is b, and b is 0.5 to 1m according to the construction hole effect. The length of the hydraulic fracturing borehole is n, n = L-30m, and the spacing of the hydraulic fracturing boreholes is a, which is optimized within 5 to 15m according to the fracturing range.

[0072] For upper and lower soft layered coal seams, multiple hydraulic fracturing boreholes are arranged in a straight line at the center of the middle hard layer. The distance between the hydraulic fracturing boreholes and the upper soft layer and the lower soft layer is b, b = 0.5H 硬中 The length of the hydraulic fracturing borehole is n, n = L-30m, and the spacing of the hydraulic fracturing boreholes is a, which is optimized within 5 to 15m according to the fracturing range.

[0073] Further, step S4 includes:

[0074] Step S41: construct hydraulic fracturing boreholes in the hard layer according to the above drilling strategy, and perform open hole segmented hydraulic fracturing in the hydraulic fracturing boreholes, with segment length Y 段长 =a, segment spacing Y 间距 5 to 10 m is required according to the sealing effect;

[0075] Step S42: Connect the hydraulic fracturing borehole to the extraction system to extract the gas in the hard layer.

[0076] Specifically, in step S5, after the hard layer is pumped for a period of time, the gas pressure of the fissures and hard layer caused by hydraulic fracturing is reduced, and the stress of the soft layer is relieved, thereby increasing the strength of the soft layer. At this time, ordinary drilling can be directly constructed in the soft layer.

[0077] Further, step S5 includes:

[0078] Step S51: constructing common drainage boreholes at a certain interval in the soft layer, and the interval of the common drainage boreholes is determined according to the residual gas content and the drainage reaching standard time requirement;

[0079] Step S52: Connect the common drainage borehole to the drainage system to drain the gas in the soft layer.

[0080] The present invention proposes a coal seam gas pre-extraction method for soft and hard composite coal seams. By constructing hydraulic fracturing drilling holes in hard layers, the problem of difficult drilling holes in soft layers is successfully avoided, and the drilling coverage is expanded, solving the problem of low extraction efficiency of drilling holes in soft layers. The method is easy to operate, low in cost, and significantly improves the gas extraction efficiency, providing a strong guarantee for safe production and efficient mining in coal mines.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for pre-extraction of coal seam gas from a soft and hard composite coal seam, characterized in that: The following steps are involved: Step S1, determining the type of the composite coal seam according to the positions of the hard layer and the soft layer; Step S2, obtaining structural parameters of the composite coal seam; Step S3, matching a corresponding drilling strategy according to the type of the composite coal seam; Step S4, performing hydraulic fracturing drilling on the hard layer according to the drilling strategy, and performing gas extraction on the hard layer; Step S5, constructing a common extraction borehole in the soft layer, and extracting gas from the soft layer; Among them, the types of composite coal seams include: Upper soft layered coal seam, with soft layers above and hard layers below; The lower soft layered coal seam has a hard layer above and a soft layer below; The structural parameters of the composite coal seam include the working face width L and the thickness of each of the hard layer and the soft layer; In step S3, the drilling strategy includes: For the upper soft layered coal seam, a plurality of hydraulic fracturing boreholes are arranged in a straight line in the lower hard layer, the distance between the hydraulic fracturing borehole and the upper soft layer is b, the length of the hydraulic fracturing borehole is n, and the spacing between the hydraulic fracturing boreholes is a; Wherein, b is 0.5 to 1 m, n = L-30 m, and a is 5 to 15 m; For the lower soft layered coal seam, a plurality of hydraulic fracturing boreholes are arranged in a straight line in the upper hard layer, the distance between the hydraulic fracturing borehole and the lower soft layer is b, the length of the hydraulic fracturing borehole is n, and the spacing between the hydraulic fracturing boreholes is a; Among them, b is 0.5~1m, n=L-30m, and a is 5~15m.

2. The coal bed gas pre-extraction method according to claim 1, characterized in that: The types of composite coal seams also include: Intermediate soft layered coal seam, with the middle layer being soft and the upper and lower layers being hard; The upper and lower soft stratified coal seam has a hard layer in the middle and soft layers above and below.

3. The coal bed gas pre-extraction method according to claim 2, characterized in that: The drilling strategy also includes: For the intermediate soft layered coal seam, a plurality of hydraulic fracturing drill holes are arranged in a straight line in the upper hard layer and the lower hard layer, and the hydraulic fracturing drill holes in the upper hard layer and the lower hard layer are arranged in a staggered manner; The distance between the hydraulic fracturing borehole and the middle soft layer is b, the length of the hydraulic fracturing borehole is n, and the spacing between the hydraulic fracturing boreholes is a; b is 0.5~1m, n=L-30m, and a is 5~15m.

4. The coal bed gas pre-extraction method according to claim 3, characterized in that: The distance in the horizontal direction between the hydraulic fracturing borehole located in the lower hard layer and the hydraulic fracturing borehole located in the upper hard layer is a / 2.

5. The coal bed gas pre-extraction method according to claim 2, characterized in that: The drilling strategy also includes: For the upper and lower soft layered coal seam, multiple hydraulic fracturing boreholes are arranged in a straight line at the center of the middle hard layer. The distance between the hydraulic fracturing boreholes and the upper soft layer and the lower soft layer is b. The length of the hydraulic fracturing borehole is n. The spacing between the hydraulic fracturing boreholes is a. Where b = 0.5H 硬中 , H 硬中 is the thickness of the middle hard layer; n=L-30m, a is 5~15m.

6. The coal bed gas pre-extraction method according to any one of claims 1 to 5, characterized in that: The step S4 comprises: Step S41: construct hydraulic fracturing boreholes in the hard layer according to the drilling strategy, and perform open hole segmented hydraulic fracturing in the hydraulic fracturing boreholes, with segment length Y 段长 =a, segment spacing Y 间距 5 to 10 m; Step S42: Connect the hydraulic fracturing borehole to a drainage system to drain the gas in the hard layer.

7. The coal bed gas pre-extraction method according to claim 6, characterized in that: The step S5 comprises: Step S51: constructing common extraction boreholes at a certain interval in the soft layer, wherein the interval of the common extraction boreholes is determined according to the residual gas content and the extraction reaching standard time requirement; Step S52: Connect the common extraction borehole to the extraction system to extract the gas in the soft layer.

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