阅读说明：本技术 近距离薄煤层群上保护层开采邻近层卸压瓦斯抽采方法 (Method for extracting pressure-relief gas from adjacent layer mined by upper protection layer of close-distance thin coal seam group ) 是由 胡杰 吕贵春 冯康武 孙臣 张睿 刘志伟 邓华易 蒋昱行 肖乔 韩恩光 李思乾 于 2021-09-08 设计创作，主要内容包括：本发明属于煤层瓦斯抽采技术领域。涉及一种近距离薄煤层群上保护层开采邻近层卸压瓦斯抽采方法,根据煤岩体破碎前的应力、裂隙、渗透率之间的关系,建立卸压瓦斯三维渗流模型,并根据煤体渗透率的大小,利用卸压瓦斯三维渗流模型将被保护层下的煤层划分为近场、远场及其它区域,针对不同区域采用不同的瓦斯抽采方式,以减少煤层中瓦斯涌出到上保护层工作面。本发明对近场内的煤层采用大直径顺层定向钻孔全覆盖抽采卸压瓦斯,远场内的煤层采用穿层钻孔层间卸压抽采卸压瓦斯,其它区域的煤层不进行瓦斯抽采；实现了近距离薄煤层群上保护层开采过程中邻近层瓦斯有效抽采与截流,有效控制上保护层开采过程中工作面瓦斯涌出,实现安全回采。(The invention belongs to the technical field of coal seam gas extraction. The method comprises the steps of establishing a pressure relief gas three-dimensional seepage model according to the relation among stress, cracks and permeability before a coal rock body is broken, dividing a coal bed under a protected layer into a near field, a far field and other areas by using the pressure relief gas three-dimensional seepage model according to the permeability of the coal body, and adopting different gas extraction modes aiming at different areas so as to reduce gas in the coal bed from flowing out to the working face of an upper protection layer. The method adopts large-diameter bedding directional drilling holes to fully cover and extract the pressure relief gas for the coal seams in the near field, adopts bedding drilling hole interlayer pressure relief and extracts the pressure relief gas for the coal seams in the far field, and does not extract the gas for the coal seams in other areas; the gas of the adjacent layer is effectively extracted and intercepted in the process of mining the upper protective layer of the short-distance thin coal seam group, the gas emission of the working face in the process of mining the upper protective layer is effectively controlled, and the safe extraction is realized.)

1. The extraction method of the pressure relief gas of the adjacent layer mined by the upper protection layer of the close-distance thin coal seam group is characterized by comprising the following steps: the method comprises the steps of establishing a pressure relief gas three-dimensional seepage model according to the relation among stress, cracks and permeability before a coal rock body is broken, carrying out regional division on a coal bed under a protected layer by using the pressure relief gas three-dimensional seepage model according to the permeability of the coal body, and adopting different gas extraction modes aiming at different regions so as to reduce gas in the coal bed from flowing out to a working surface of an upper protection layer.

2. The method for extracting pressure-relief gas from the mining adjacent layer of the protective layer on the close-distance thin coal seam group according to claim 1, characterized by comprising the following steps: assigning the monitored or calculated coal and rock body parameters to a pressure relief gas three-dimensional seepage model, establishing a model diagram of coal body permeability distribution of a stope, and dividing the ranges of a three-dimensional permeability increasing area, a horizontal permeability increasing area and an original permeability area along the coal seam burial depth direction according to the coal body permeability value distribution condition in the model diagram;

the three-dimensional permeation increasing area is a near field of a permeation section of the protected layer, the horizontal permeation increasing area is a far field of the permeation section of the protected layer, and coal beds in the near field and the far field are determined according to the relation between the layer position and the buried depth of the protected layer;

gas extraction is not carried out on the coal seam in the original permeable area, and the coal seam in the near field adopts large-diameter bedding directional drilling to fully extract pressure-relief gas; and the coal seam in the far field adopts cross-layer drilling interlayer pressure relief to extract pressure relief gas.

3. The extraction method of the pressure-relief gas in the adjacent layer mined by the upper protective layer of the close-distance thin coal seam group according to claim 2, characterized in that the establishment process of the pressure-relief gas three-dimensional seepage model is as follows:

the closing or expansion of the crack is influenced by the positive stress, and the relation between the crack pressure-bearing closing size and the positive stress is as follows:

wherein σ is the forward stress; k is a radical of₀Initial stiffness for the fracture; delta is the fracture closure size; delta_mThe ultimate width of the fracture before fracture failure;

b is defined as the width of the crack, then b is δ_mδ, proportional to the square of the permeability k of an individual fracture and its fracture width, i.e.Substituting σ to obtain:

wherein σ₀＝k₀δ_mInitial positive stress;

due to the fact thatIs constant, defines a non-dimensional permeabilityTo obtain:

in the initial stress state, σ ═ σ₀，k_fThe value is 0.25, when 0 is more than k_fLess than 0.25, the positive stress is greater than the initial positive stress, and the permeability of the coal body is reduced; k is a radical of_fWhen the stress is more than 0.25, the forward stress is less than the initial forward stress, and the permeability of the coal body is increased; therefore, the three-dimensional seepage model under the three-dimensional stress state is established as follows:

wherein the x direction is the working face trend direction, the y direction is the working face trend direction, and the z direction is the coal seam burial depth direction; k is a radical of_xoy，k_xoz，k_yozDimensionless permeability along xoy, xoz, yoz plane, respectively; sigma_x，σ_y，σ_zThe ground stress along the x, y and z directions respectively; sigma_xo，σ_yo，σ_zoInitial stresses in the x, y, z directions, respectively.

4. The method for extracting pressure-relief gas from the mining adjacent layer of the protective layer on the close-distance thin coal seam group as claimed in claim 3, wherein the method comprises the following steps: the method for dividing the three-dimensional permeation-increasing area, the horizontal permeation-increasing area and the original permeation area comprises the following steps: in model diagram k_xoy、k_xoz、k_yozThe regions with values greater than 0.25 are three-dimensional permeation-increasing regions, k_xoz、k_yozEqual to the original value 0.25, k_xoyThe region with the value still larger than 0.25 is a horizontal permeation-increasing region, and the rest regions are original permeation regions.

5. The method for extracting pressure-relief gas from the mining adjacent layer of the protective layer on the close-distance thin coal seam group as claimed in claim 2, wherein the method comprises the following steps: the large-diameter bedding directional drilling hole full-coverage extraction pressure relief gas is to adopt the coal seam gas extraction mode to extract gas, a directional drilling machine is used for performing driller construction from a transportation roadway to a return air roadway, the construction drilling hole is a full coal section drilling hole, the drilling holes are penetrated in two roadways of the coal seam in a pair mode, and pressure relief extraction is performed on the coal seam;

and in the step of pressure relief gas drainage between the cross-layer drilling layers, a directional drilling machine is used for drilling, long drilling and cross-layer drainage are carried out on multiple coal layers in the far field section in the lowest coal seam floor roadway, and pressure relief drainage is carried out on the multiple coal layers at the same time.

6. The method for extracting pressure-relief gas from the mining adjacent layer of the protective layer on the close-distance thin coal seam group as claimed in claim 5, wherein the method comprises the following steps: and after the drilling construction of the coal seam in the near field is finished, simultaneously connecting extraction metering devices to the orifices at two ends of the drilled hole to perform bidirectional gas extraction on the coal seam in the near field.

Technical Field

The invention belongs to the technical field of coal seam gas extraction, and relates to a method for extracting pressure relief gas of an adjacent layer mined by an upper protection layer of a close-distance thin coal seam group.

Background

The combination of protective layer mining and protected layer pressure relief gas extraction becomes a regional gas disaster control technology preferentially popularized in coal mines in China, but for short-distance serious outburst coal seam group mining, the problems of long extraction standard reaching time, large gas emission quantity of adjacent layers, short mining succession and the like are faced in the first mining layer mining process. For a short-distance thin coal seam group mined by an upper protective layer, because the short-distance thin coal seam group is fully decompressed by the protective layer, the decompressed gas migrates and flows into the protective layer working face space along the cracks in the coal rock mass, and meanwhile, because the first-mined thin coal seam has small ventilation space and limited ventilation capacity, the gas on the protective layer working face is easily over-limited, and a great potential safety hazard is formed; in addition, the pressure relief effect gradually deteriorates along with the increase of the distance, and how the pressure relief gas of the coal seam at a longer distance influences the gas emission of the working face is not clear. Therefore, the more targeted treatment of the pressure relief gas of the adjacent coal seam group is an urgent problem to be solved in the process of mining the protective layer of the thin coal seam group.

Disclosure of Invention

In view of the above, the invention aims to reduce the influence of pressure relief gas of a coal seam on gas emission of a working face, and provides a method for extracting pressure relief gas of an adjacent layer mined by a protective layer on a short-distance thin coal seam group.

In order to achieve the purpose, the invention provides the following technical scheme:

the method for extracting the pressure relief gas of the adjacent layer mined by the upper protection layer of the close-distance thin coal seam group comprises the steps of establishing a pressure relief gas three-dimensional seepage model according to the relation among stress, cracks and permeability before a coal rock body is crushed, carrying out regional division on the coal seam below the protected layer by using the pressure relief gas three-dimensional seepage model according to the permeability of the coal body, and adopting different gas extraction modes aiming at different regions so as to reduce the gas in the coal seam from gushing out to the working surface of the upper protection layer.

Further, assigning the monitored or calculated coal and rock body parameters to a pressure relief gas three-dimensional seepage model, establishing a model diagram of coal body permeability distribution of a stope, and dividing ranges of a three-dimensional permeability-increasing area, a horizontal permeability-increasing area and an original permeability area along the coal seam burial depth direction according to the coal body permeability value distribution condition in the model diagram;

the three-dimensional permeation increasing area is a near field of a permeation section of the protected layer, the horizontal permeation increasing area is a far field of the permeation section of the protected layer, and coal beds in the near field and the far field are determined according to the relation between the layer position and the buried depth of the protected layer;

gas extraction is not carried out on the coal seam in the original permeable area, and the coal seam in the near field adopts large-diameter bedding directional drilling to fully extract pressure-relief gas; and the coal seam in the far field adopts cross-layer drilling interlayer pressure relief to extract pressure relief gas.

Further, the establishment process of the pressure relief gas three-dimensional seepage model is as follows:

the closing or expansion of the crack is influenced by the positive stress, and the relation between the crack pressure-bearing closing size and the positive stress is as follows:

wherein σ is the forward stress; k is a radical of₀Initial stiffness for the fracture; delta is the fracture closure size; delta_mThe ultimate width of the fracture before fracture failure;

b is defined as the width of the crack, then b is δ_mδ, proportional to the square of the permeability k of an individual fracture and its fracture width, i.e.Substituting σ to obtain:

wherein σ₀＝k₀δ_mInitial positive stress;

due to the fact thatIs constant, defines a non-dimensional permeabilityTo obtain:

in the initial stress state, σ ═ σ₀，k_fThe value is 0.25, when 0<k_f<0.25, the forward stress is greater than the initial forward stress, and the permeability of the coal body is reduced; k is a radical of_f>When the stress is 0.25, the forward stress is smaller than the initial forward stress, and the permeability of the coal body is increased; therefore, the three-dimensional seepage model under the three-dimensional stress state is established as follows:

wherein the x direction is the working face direction, and the y direction is the working face inclinationThe direction is towards the direction, and the direction z is the coal seam burial depth direction; k is a radical of_xoy，k_xoz，k_yozDimensionless permeability along xoy, xoz, yoz plane, respectively; sigma_x，σ_y，σ_zThe ground stress along the x, y and z directions respectively; sigma_xo，σ_yo，σ_zoInitial stresses in the x, y, z directions, respectively.

Further, the dividing method of the three-dimensional permeation-increasing area, the horizontal permeation-increasing area and the original permeation area comprises the following steps: in model diagram k_xoy、k_xoz、k_yozThe regions with values greater than 0.25 are three-dimensional permeation-increasing regions, k_xoz、k_yozEqual to the original value 0.25, k_xoyThe region with the value still larger than 0.25 is a horizontal permeation-increasing region, and the rest regions are original permeation regions.

Further, the full-coverage extraction of the large-diameter bedding directional drill hole is to adopt the coal seam gas extraction mode to extract gas, a directional drilling machine is used for performing driller construction from a transportation roadway to a return air roadway, the construction drill hole is a full-coal-section drill hole, the drill holes are penetrated in two roadways of the coal seam in a pair mode, and the pressure-relief extraction is performed on the coal seam;

and in the step of pressure relief gas drainage between the cross-layer drilling layers, a directional drilling machine is used for drilling, long drilling and cross-layer drainage are carried out on multiple coal layers in the far field section in the lowest coal seam floor roadway, and pressure relief drainage is carried out on the multiple coal layers at the same time.

And further, after the drilling construction of the coal seam in the near field is finished, simultaneously connecting extraction metering devices to the orifices at two ends of the drilled hole to perform bidirectional gas extraction on the coal seam in the near field.

The invention has the beneficial effects that:

according to the method, a pressure relief gas three-dimensional seepage model is established, coal and rock body parameters obtained through monitoring or calculation are assigned to the pressure relief gas three-dimensional seepage model to obtain a coal body permeability distribution model map of a stope, a three-dimensional permeability increasing area, a horizontal permeability increasing area and an original permeability area are divided according to the permeability of the coal body, gas extraction is not carried out on a coal seam of the original permeability area, and the coal seam in a near field adopts a large-diameter bedding directional drilling hole to extract pressure relief gas in a full-coverage mode; the coal seam in the far field adopts cross-layer drilling interlayer pressure relief to extract pressure relief gas; the gas of the adjacent layer is effectively extracted and intercepted in the process of mining the upper protective layer of the short-distance thin coal seam group, the gas emission of the working face in the process of mining the upper protective layer is effectively controlled, and the safe extraction is realized.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.

Drawings

For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic flow diagram of a process of the present invention;

FIG. 2 is a schematic diagram of an embodiment of the present invention;

fig. 3 is a sectional view taken along line a-a of fig. 2.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.

Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; 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 an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.

Referring to fig. 1, an implementation flow of a method for extracting pressure-relief gas from adjacent layers of a protective layer on a short-distance thin coal seam group is shown, a three-dimensional pressure-relief gas seepage model is established according to a relation among stress, cracks and permeability before a coal rock mass is broken, the coal seam under the protected layer is divided into regions according to the permeability of the coal mass by using the three-dimensional pressure-relief gas seepage model, and different gas extraction modes are adopted for different regions to reduce gas emission from the coal seam to a working surface of an upper protective layer.

Assigning the monitored or calculated coal and rock body parameters to a pressure relief gas three-dimensional seepage model, establishing a model diagram of coal body permeability distribution of a stope, and dividing the ranges of a three-dimensional permeability increasing area, a horizontal permeability increasing area and an original permeability area along the coal seam burial depth direction according to the coal body permeability value distribution condition in the model diagram; the three-dimensional permeation-increasing area is a near field of a permeation section of the protected layer, the horizontal permeation-increasing area is a far field of the permeation section of the protected layer, and coal beds in the near field and the far field are determined according to the position relation and the buried depth position relation of the protected layer.

Gas extraction is not carried out on the coal seam in the original permeable area, and pressure relief gas is extracted from the coal seam in the near field in a full-coverage mode by adopting large-diameter bedding directional drilling; and the coal seam in the far field adopts cross-layer drilling interlayer pressure relief to extract pressure relief gas.

In this embodiment, the process of establishing the three-dimensional pressure relief gas seepage model is as follows:

the closing or expansion of the crack is influenced by the positive stress, and the relation between the crack pressure-bearing closing size and the positive stress is as follows:

wherein σ is the forward stress; k is a radical of₀Initial stiffness for the fracture; delta is the fracture closure size; delta_mThe ultimate width of the fracture before fracture failure;

b is defined as the width of the crack, then b is δ_mδ, proportional to the square of the permeability k of an individual fracture and its fracture width, i.e.Substituting σ to obtain:

wherein σ₀＝k₀δ_mInitial positive stress;

due to the fact thatIs constant, defines a non-dimensional permeabilityTo obtain:

in the initial stress state, σ ═ σ₀，k_fThe value is 0.25, when 0<k_f<0.25, the forward stress is greater than the initial forward stress, and the permeability of the coal body is reduced; k is a radical of_f>At 0.25, the forward stress is less than the initial normal stress, and the permeability of the coal bodyIncreasing; therefore, the three-dimensional seepage model under the three-dimensional stress state is established as follows:

wherein the x direction is the working face trend direction, the y direction is the working face trend direction, and the z direction is the coal seam burial depth direction; k is a radical of_xoy，k_xoz，k_yozDimensionless permeability along xoy, xoz, yoz plane, respectively; sigma_x，σ_y，σ_zThe ground stress along the x, y and z directions respectively; sigma_xo，σ_yo，σ_zoInitial stresses in the x, y, z directions, respectively.

In this embodiment, the method for dividing the three-dimensional permeation-increasing zone, the horizontal permeation-increasing zone and the original permeation zone is as follows: in model diagram k_xoy、k_xoz、k_yozThe regions with values greater than 0.25 are three-dimensional permeation-increasing regions, k_xoz、k_yozEqual to the original value 0.25, k_xoyThe region with the value still larger than 0.25 is a horizontal permeation-increasing region, and the rest regions are original permeation regions.

Referring to fig. 3, the large-diameter bedding directional drilling hole full-coverage extraction of pressure relief gas is to adopt the coal seam gas extraction mode to perform gas extraction, a directional drilling machine is used for performing driller construction from a transportation roadway to a return air roadway, the construction drilling hole is a full-coal-section drilling hole, the drilling holes are penetrated in two roadways of the coal seam in a pair mode, and pressure relief extraction is performed on the coal seam;

referring to fig. 2, for pressure relief gas drainage between cross-layer drill hole layers, a directional drilling machine is used for drilling, long drill hole cross-layer is conducted on multiple coal seams in a far field section in a bottom roadway of the lowest coal seam, and pressure relief drainage is conducted on the multiple coal seams at the same time.

After the drilling construction of the coal seam in the near field is finished, the orifices at the two ends of the drill hole are simultaneously connected with an extraction metering device for bidirectional gas extraction of the coal seam in the near field.

Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.