A method for pre-extracting coal seam gas from a soft and hard composite coal seam

Abstract

The present application belongs to the technical field of underground gas extraction of coal mine, and relates to a coal seam gas pre-extraction method for soft and hard composite coal seam. The method comprises the following steps: 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 the structure parameters of the composite coal seam; step S3, matching the corresponding drilling strategy according to the type of the composite coal seam, and each of the upper soft layer type, the lower soft layer type, the middle soft layer type and the upper and lower soft layer type has its own drilling arrangement strategy; step S4, performing hydraulic fracturing drilling on the hard layer according to the drilling strategy, and performing gas extraction on the hard layer; and step S5, performing ordinary extraction drilling in the soft layer, and performing gas extraction on the soft layer. The present application solves the problem of low gas extraction efficiency of the soft layer drilling by performing hydraulic fracturing drilling in the hard layer to generate cracks and make them penetrate to the soft layer, thereby indirectly extracting the gas in the soft layer.

Description

TECHNICAL FIELD

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

[0002] In the technical field of underground coal mine gas extraction, 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 safety of miners. As a coal power, China has a large number of gas mines, and the gas content of coal seams directly affects the mining deployment and the safety production of coal mines. Therefore, gas extraction is particularly important.

[0003] Gas extraction usually requires a large number of extraction boreholes to be drilled in the coal seam, and the gas content in the coal seam is reduced to a certain extent through negative pressure extraction before mining activities can be carried out. However, in the process of gas extraction in soft layer-containing coal seams, due to the particularity of the structure of the coal seam, it brings great challenges to the extraction work. The soft layer-containing coal seam contains one or more layers of soft coal in the vertical direction. These soft layers have soft coal, high gas content, low permeability, and high cost and difficulty in drilling gas extraction boreholes. The traditional gas extraction method can only drill extraction boreholes in the hard layer, and cannot form effective boreholes in the soft layer. The borehole cannot penetrate the hard layer and the soft layer, and it is difficult to extract the gas in the soft layer. At the same time, due to the low permeability of the soft layer, the overall construction period and extraction time of the coal seam are significantly prolonged, which seriously affects the mining replacement efficiency of the coal mine.

[0004] For composite coal seams containing soft layers, if the gas in the soft layer is not effectively extracted, it will not only increase the gas emission during coal mining, but also may cause serious safety accidents such as gas explosion. Therefore, how to effectively extract the gas in the soft layer-containing coal seam has become a technical problem to be solved in coal mine safety production. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a coal seam gas pre-extraction method for soft and hard composite coal seams, which indirectly extracts the gas in the soft layer by drilling a hydraulic fracturing borehole in the hard layer to generate cracks and penetrate the soft layer, thereby solving the problem of low gas extraction efficiency in the soft layer.

[0006] To achieve the above purpose, the present application provides a coal seam gas pre-extraction method for soft and hard composite coal seams, 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 the structural parameters of the composite coal seam;

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

[0010] Step S4, performing hydraulic fracturing drilling on the hard layer according to the drilling strategy, and performing gas extraction on the hard layer;

[0011] Step S5, performing ordinary extraction drilling in the soft layer, and performing gas extraction on the soft layer.

[0012] Optionally, the type of the composite coal seam comprises:

[0013] an upper-soft-layer type coal seam, which has a soft layer above and a hard layer below;

[0014] a lower-soft-layer type coal seam, which has a hard layer above and a soft layer below.

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

[0016] Optionally, the drilling strategy comprises:

[0017] for the upper-soft-layer type coal seam, a plurality of hydraulic fracturing drillings are arranged in a horizontal line in the lower hard layer, the distance between the hydraulic fracturing drillings and the upper soft layer is b, the length of the hydraulic fracturing drilling is n, and the interval of the hydraulic fracturing drillings is a;

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

[0019] Optionally, the drilling strategy comprises:

[0020] for the lower-soft-layer type coal seam, a plurality of hydraulic fracturing drillings are arranged in a horizontal line in the upper hard layer, the distance between the hydraulic fracturing drillings and the lower soft layer is b, the length of the hydraulic fracturing drilling is n, and the interval of the hydraulic fracturing drillings is a;

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

[0022] Optionally, the type of the composite coal seam further comprises:

[0023] a middle-soft-layer type coal seam, which has a soft layer in the middle and hard layers above and below;

[0024] an upper-lower-soft-layer type coal seam, which has a hard layer in the middle and soft layers above and below.

[0025] Optionally, the drilling strategy further comprises:

[0026] For the middle soft layer type coal seam, multiple hydraulic fracturing boreholes are arranged in a horizontal line in the upper hard layer and the lower hard layer, and the hydraulic fracturing boreholes in the upper hard layer and the lower hard layer are arranged in a staggered manner;

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

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

[0029] Optionally, the interval of the hydraulic fracturing borehole in the lower hard layer and the hydraulic fracturing borehole in the upper hard layer in the horizontal direction is a / 2.

[0030] Optionally, the drilling strategy further comprises:

[0031] For the upper and lower soft layer type coal seam, multiple hydraulic fracturing boreholes are arranged in a horizontal line at the center position in 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 interval of the hydraulic fracturing borehole is a.

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

[0033] Optionally, step S4 comprises:

[0034] Step S41: constructing the hydraulic fracturing borehole in the hard layer according to the drilling strategy, and implementing the open hole staged hydraulic fracturing in the hydraulic fracturing borehole, the staged length Y 段长 is a, and the staged interval Y 间距 is 5-10 m.

[0035] Step S42: connecting the hydraulic fracturing borehole to the extraction system, and extracting the gas in the hard layer.

[0036] Optionally, step S5 comprises:

[0037] Step S51: constructing the ordinary extraction borehole with a certain interval in the soft layer, and the interval of the ordinary extraction borehole is determined according to the residual gas content and the extraction standard time requirement.

[0038] Step S52: connecting the ordinary extraction borehole to the extraction system, and extracting the gas in the soft layer.

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

[0040] The present application provides a method for pre-draining coal seam gas in soft and hard composite coal seams through hydraulic fracturing, effectively solving the problems faced by traditional gas extraction technology in soft and hard composite coal seams.

[0041] Firstly, by adopting hard layer drilling and combining with hydraulic fracturing technology, the present application successfully avoids the problem of difficult drilling in soft layers. Traditional methods directly drill in soft layers, which results in low drilling success rate and high cost due to the softness of the coal, high gas content and low permeability of the soft layers. However, the present application drills in hard layers and uses the fractures generated by hydraulic fracturing to penetrate the soft layers, thereby achieving the purpose of indirect extraction of soft layer gas and greatly improving the drilling success rate and construction efficiency.

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

[0043] In addition, the present application also has the advantages of simple operation and low cost. Through reasonable drilling design and fracturing parameter selection, the present application 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, by avoiding direct drilling in soft layers, the present application greatly reduces the construction difficulty and cost, bringing significant economic benefits to coal mining enterprises.

[0044] In summary, the method for pre-draining coal seam gas in soft and hard composite coal seams through hydraulic fracturing of the present application not only effectively solves the problems faced by traditional gas extraction technology in soft and hard composite coal seams, but also improves the gas extraction efficiency, reduces the construction difficulty and cost, and provides a strong guarantee for coal mine safety production and efficient mining.

[0045] Other advantages, objects and features of the present application will be described in the following specification to some extent, and will be apparent to those skilled in the art based on the study of the following, or can be taught from the practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred detailed description of the present application will be made below in combination with the drawings, in which:

[0047] Figure 1 A flowchart of a coal seam gas pre-draining method for soft and hard composite coal seams provided by the present application;

[0048] Figure 2 A working face drilling arrangement plan view of a coal seam gas pre-extraction method of a soft and hard composite coal seam provided by the present application;

[0049] Figure 3 An upper soft layer type drilling arrangement section view of a coal seam gas pre-extraction method of a soft and hard composite coal seam provided by the present application;

[0050] Figure 4 A lower soft layer type drilling arrangement section view of a coal seam gas pre-extraction method of a soft and hard composite coal seam provided by the present application;

[0051] Figure 5 An intermediate soft layer type drilling arrangement section view of a coal seam gas pre-extraction method of a soft and hard composite coal seam provided by the present application;

[0052] Figure 6 An upper and lower soft layer type drilling arrangement section view of a coal seam gas pre-extraction method of a soft and hard composite coal seam provided by the present application. DETAILED DESCRIPTION

[0053] The present application will be described in more detail below with reference to specific embodiments. The advantages and effects of the present application can be easily understood by those skilled in the art from the content disclosed in the specification. The present application can also be implemented or applied in other different embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0054] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and should not be understood as a limitation of 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. It can be understood by those skilled in the art that some known structures and their descriptions in the drawings may be omitted.

[0055] 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 is understood that if the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "back" and the like are based on the orientations or positional relationships 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 meanings of the above terms can be understood according to the specific circumstances.

[0056] As shown in the figure, Figure 1 The coal seam gas pre-extraction method of the soft and hard composite coal seam of the present application specifically comprises the following steps:

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

[0058] Step S2, obtaining the 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, performing hydraulic fracturing drilling on the hard layers according to the drilling strategy, and performing gas extraction on the hard layers;

[0061] Step S5, constructing ordinary extraction drilling in the soft layers, and performing gas extraction on the soft layers.

[0062] Further, as shown in the figure, Figures 3 to 6 The type of the composite coal seam in step S1 includes: an upper soft layer type with soft layers above and hard layers below, a lower soft layer type with hard layers above and soft layers below, a middle soft layer type with soft layers in the middle and hard layers above and below, and an upper and lower soft layer type with hard layers in the middle and soft layers above and below.

[0063] Further, as shown in the figure, Figure 2 The structural parameters of the composite coal seam include the working face width L and the thicknesses of each hard layer and soft layer.

[0064] Specifically, as shown in the figure, Figure 3 For the upper soft layer type coal seam, the thickness of the upper soft layer is H 软上 , and the thickness of the lower hard layer is H 硬下 .

[0065] Specifically, as shown in the figure, Figure 4 For the lower soft layer type coal seam, the thickness of the upper hard layer is H 硬上 , and the thickness of the lower soft layer is H 软下 .

[0066] Specifically, as shown in Figure 5 , for the middle soft layer type 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, as shown in Figure 6 , for the upper and lower soft layer type coal seam, 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 layer type coal seam, a plurality of hydraulic fracturing drill holes are arranged in a horizontal line in the lower hard layer, the distance between the hydraulic fracturing drill hole and the upper soft layer is b, b is 0.5-1m according to the construction hole effect. The length of the hydraulic fracturing drill hole is n, n=L-30m, and the spacing of the hydraulic fracturing drill hole is a, a is optimized within 5-15m according to the fracturing range;

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

[0071] For the middle soft layer type coal seam, a plurality of hydraulic fracturing drill holes are arranged in a horizontal line in the upper and lower hard layers respectively, the hydraulic fracturing drill holes are arranged in an upper and lower staggered manner, that is, the spacing between the hydraulic fracturing drill hole in the lower hard layer and the hydraulic fracturing drill hole in the upper hard layer in the horizontal direction is a / 2. The distance between the hydraulic fracturing drill hole and the middle soft layer is b, b is 0.5-1m according to the construction hole effect. The length of the hydraulic fracturing drill hole is n, n=L-30m, and the spacing of the hydraulic fracturing drill hole is a, a is optimized within 5-15m according to the fracturing range.

[0072] For the upper and lower soft layer type coal seam, a plurality of hydraulic fracturing drill holes are arranged in a horizontal line at the center position of the middle hard layer, the distance between the hydraulic fracturing drill hole and the upper soft layer and the lower soft layer is b, b=0.5H 硬中 . The length of the hydraulic fracturing drill hole is n, n=L-30m, and the spacing of the hydraulic fracturing drill hole is a, a is optimized within 5-15m according to the fracturing range.

[0073] Further, step S4 includes:

[0074] Step S41: constructing a hydraulic fracturing borehole in the hard layer according to the above drilling strategy, and implementing open-hole staged hydraulic fracturing in the hydraulic fracturing borehole, the staged length Y 段长 = a, the staged interval Y 间距 According to the hole sealing effect, 5-10 m;

[0075] Step S42: connecting 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 extracted for a period of time, the cracks generated due to the hydraulic fracturing and the gas pressure of the hard layer are reduced, the stress of the soft layer is relieved, so that the strength of the soft layer is increased, at this time, the ordinary borehole can be directly constructed in the soft layer.

[0077] Further, step S5 includes:

[0078] Step S51: constructing ordinary extraction boreholes with a certain interval in the soft layer, the interval of the ordinary extraction boreholes being determined according to the residual gas content and the extraction standard time requirement;

[0079] Step S52: connecting the ordinary extraction boreholes to the extraction system to extract the gas in the soft layer.

[0080] The present application proposes a coal seam gas pre-extraction method for soft and hard composite coal seams, which successfully avoids the problem of difficult borehole forming in the soft layer by constructing a hydraulic fracturing borehole in the hard layer, and expands the borehole coverage range, solving the problem of low extraction efficiency of the soft layer borehole. The method is simple and low in cost, significantly improves the gas extraction efficiency, and provides a powerful guarantee for coal mine safety production and efficient mining.

[0081] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. 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 replaced by equivalents without departing from the purpose and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A coal seam gas pre-extraction method for a soft and hard composite coal seam, characterized in that, The method comprises the following steps: 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 the structural parameters of the composite coal seam; Step S3, matching the 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, performing ordinary extraction drilling in the soft layer, and performing gas extraction on the soft layer; The type of the composite coal seam comprises: The upper soft layer type coal seam, which has a soft layer above and a hard layer below; The lower soft layer type coal seam, which 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 hard layer and soft layer; In the step S3, the drilling strategy comprises: For the upper soft layer type coal seam, a plurality of hydraulic fracturing drillings are arranged in a one-dimensional manner in the lower hard layer, the distance between the hydraulic fracturing drillings and the upper soft layer is b, the length of the hydraulic fracturing drilling is n, and the interval of the hydraulic fracturing drillings is a; Wherein, b is 0.5-1m, n=L-30m, and a is 5-15m; For the lower soft layer type coal seam, a plurality of hydraulic fracturing drillings are arranged in a one-dimensional manner in the upper hard layer, the distance between the hydraulic fracturing drillings and the lower soft layer is b, the length of the hydraulic fracturing drilling is n, and the interval of the hydraulic fracturing drillings is a; Wherein, b is 0.5-1m, n=L-30m, and a is 5-15m; The type of the composite coal seam further comprises: The middle soft layer type coal seam, which has a soft layer in the middle and hard layers above and below; The upper and lower soft layer type coal seam, which has a hard layer in the middle and soft layers above and below; The drilling strategy further comprises: For the middle soft layer type coal seam, a plurality of hydraulic fracturing drillings are arranged in a one-dimensional manner in the upper hard layer and the lower hard layer respectively, and the hydraulic fracturing drillings in the upper hard layer and the lower hard layer are arranged in a staggered manner; The distance between the hydraulic fracturing drillings and the middle soft layer is b, the length of the hydraulic fracturing drilling is n, and the interval of the hydraulic fracturing drillings is a; b is 0.5-1m, n=L-30m, and a is 5-15m; The drilling strategy further comprises: For the upper and lower soft layer type coal seam, a plurality of hydraulic fracturing drillings are arranged in a one-dimensional manner at the center position in the middle hard layer, the distance between the hydraulic fracturing drillings and the upper soft layer and the lower soft layer is b, the length of the hydraulic fracturing drilling is n, and the interval of the hydraulic fracturing drillings is a; where b = 0.5H 硬中 , H 硬中 is the thickness of the intermediate hard layer; n = L - 30m, a is 5-15m; The step S4 comprises: Step S41: constructing a hydraulic fracturing borehole in the hard layer according to the drilling strategy, implementing open-hole staged hydraulic fracturing in the hydraulic fracturing borehole, the staged length Y 段长 = a, the staged interval Y 间距 is 5-10 m; Step S42, connecting the hydraulic fracturing drillings to the extraction system to extract the gas in the hard layer; The step S5 comprises: Step S51, constructing ordinary extraction drillings with a certain interval in the soft layer, the interval of the ordinary extraction drillings is determined according to the residual gas content and the extraction standard time requirement; Step S52, connecting the ordinary extraction drillings to the extraction system to extract the gas in the soft layer.

2. The coal seam gas pre-extraction method according to claim 1, characterized by: The hydraulic fracture bore located within the lower hard layer is spaced horizontally from the hydraulic fracture bore located within the upper hard layer by a / 2.

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