A method for improving top coal recovery rate by roof top coal synchronous and coordinated pre-splitting

Abstract

The application provides a roof and top coal synchronous and cooperative pre-splitting method for improving top coal recovery rate, the periodic breaking step distance of a key layer is obtained through calculation, the roof and top coal are synchronously fractured by using a hydraulic fracturing method, timely breaking and caving of the roof rock stratum is ensured, the lateral constraint force of the roof on the top coal recovery process is improved, and the top coal recovery rate in the caving process is improved, the method has strong operability and remarkable economic benefits.

Description

Technical Field

[0001] This invention relates to the field of fully mechanized top coal caving technology, and in particular to a method for improving top coal recovery rate through synchronous and coordinated pre-splitting of the roof and top coal. Background Technology

[0002] Fully mechanized top-coal caving mining technology is a new coal mining method developed on the basis of fully mechanized coal mining technology. Its characteristic is that it extracts all the coal mined in multiple layers at once, offering advantages such as high yield, high efficiency, safety, and low consumption. After years of production practice, the technology and processes of fully mechanized top-coal caving mining have become increasingly mature and perfected. However, there are still unresolved technical challenges in the application of fully mechanized top-coal caving technology, such as low top-coal recovery rate and serious resource waste.

[0003] In the process of top coal caving, the strength of the roof and the coupling effect between the roof and top coal are important factors affecting the recovery rate of top coal caving. When the roof strength is high, the rock strata are not easy to collapse, the overhang step distance is large, resulting in poor top coal crushing effect and low recovery rate. Under these conditions, how to improve the coupling effect between the roof and top coal and improve the top coal recovery rate has become an urgent problem to be solved. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for improving the top coal recovery rate by synchronous and coordinated pre-splitting of the top coal.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A method for improving top coal recovery rate through synchronous and coordinated pre-fracturing of top coal in the roof includes:

[0007] Determine the length of the coal face in the target area, and conduct core sampling tests on the top coal and overlying rock strata to obtain the geological parameters of each rock layer;

[0008] Based on the key layer theory, the vertical distance d between the nearest key layer and the coal seam is calculated according to the geological parameters.

[0009] The periodic fracture step L of the key layer and the horizontal distance from the boundary fracture line of the key layer to the roadway are calculated based on the geological parameters and the vertical distance.

[0010] Hydraulic fracturing is used to simultaneously fracturing the key layer and the top coal. Hydraulic fracturing holes are designed along the working face advance direction, with the starting point at the working face cut-off point, the hole spacing is L / 2, and the depth reaches the top boundary of the fracturing key layer. The angle of the designed hole toward the coal body side of the working face is θ.

[0011] Based on the thickness h of the key layer, fracturing is performed once within the key layer at intervals of 1 / 4 to 1 / 3 h, and fracturing is performed once at intervals of 1 / 3 to 1 / 2 dh within the range from the bottom boundary of the key layer to the top boundary of the top coal seam.

[0012] The fracturing parameters within the top coal are designed based on the strength f and thickness h1 of the top coal.

[0013] Based on the thickness of the top coal and the actual amount of coal mined, calculate the actual recovery rate of the top coal and monitor the lump coal rate of the coal being discharged on site.

[0014] The fracturing parameters in the key layer and top coal are adjusted based on the actual recovery rate and the lump coal rate, respectively.

[0015] Preferably, the fracturing parameters within the top coal seam include:

[0016] When the top coal strength f>1, the fracturing interval distance is 1 / 5 to 1 / 3 times h1; when the top coal strength f≤1, the fracturing interval distance is 1 / 4 to 1 / 2 times h1.

[0017] Preferably, the formula for calculating θ is: θ = arctan(d / n).

[0018] Preferably, the fracturing parameters in the key layer and top coal are adjusted according to the actual recovery rate and the lump coal rate, respectively, including:

[0019] If the actual recovery rate of top coal is less than 80% and the lump coal rate is greater than 60%, then fracturing should be performed once at intervals of 1 / 6 to 1 / 5 h within the key layer, and once at intervals of 1 / 5 to 1 / 4 dh within the range from the bottom boundary of the key layer to the top boundary of the coal seam; if the top coal strength f>1, the fracturing interval should be 1 / 7 to 1 / 5 h1; if the top coal strength f≤1, the fracturing interval should be 1 / 6 to 1 / 3 h1.

[0020] If the actual recovery rate of top coal is greater than 80% and the lump coal rate is less than 60%, no improvement will be made.

[0021] If the actual recovery rate of top coal is greater than 80% and the lump coal rate is greater than 60%, then fracturing should be performed once at intervals of 1 / 4 to 1 / 3 h within the key layer, and once at intervals of 1 / 3 to 1 / 2 dh within the range from the bottom boundary of the key layer to the top boundary of the coal seam; if the top coal strength f>1, the fracturing interval should be 1 / 7 to 1 / 5 h1; if the top coal strength f≤1, the fracturing interval should be 1 / 6 to 1 / 3 h1.

[0022] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0023] This invention provides a method for improving top coal recovery through synchronous and coordinated pre-fracture of the top coal face, comprising: determining the length of the coal face in the target area and performing core sampling tests on the top coal and overlying strata to obtain the geological parameters of each stratum; based on the key layer theory, calculating the vertical distance d between the nearest key layer and the coal seam according to the geological parameters; calculating the periodic fracturing step L of the key layer and the horizontal distance from the key layer boundary fracture line to the roadway according to the geological parameters and the vertical distance; synchronously fracturing the key layer and the top coal using hydraulic fracturing, designing hydraulic fracturing holes along the face advance direction, with the fracturing holes located at the face cut-off point. Starting from the critical layer, the borehole spacing is L / 2, and the depth extends to the top boundary of the critical layer. The borehole angle towards the coal face is designed as θ. Based on the thickness h of the critical layer, fracturing is performed once at intervals of 1 / 4 to 1 / 3 h within the critical layer. Within the range from the bottom boundary of the critical layer to the top boundary of the top coal, fracturing is performed once at intervals of 1 / 3 to 1 / 2 dh. The fracturing parameters within the top coal are designed based on the strength f and thickness h1 of the top coal. The actual recovery rate of the top coal is calculated based on the thickness of the top coal and the actual amount of coal extracted, and the lump coal rate is monitored on-site. The fracturing parameters within the critical layer and the top coal are adjusted according to the actual recovery rate and the lump coal rate, respectively. This invention designs reasonable hydraulic fracturing technical parameters by calculating the critical layer fracture step distance and its fracture characteristics. The borehole angle is designed based on the fracture characteristics of the rock strata, and the fracturing interval distance is designed based on the physical and mechanical properties of the coal and rock mass. Through reasonable fracturing arrangement, the fracture step distance of the hard roof is reduced, and the coupling relationship between the roof and the top coal is improved, thereby increasing the top coal recovery rate. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A flowchart of the method provided in an embodiment of the present invention;

[0026] Figure 2 A flowchart of simultaneous fracturing provided for embodiments of the present invention;

[0027] Figure 3 This is a diagram showing the arrangement of boreholes in the roof coal seam according to an embodiment of the present invention.

[0028] Figure 4 This is a cross-sectional view of the roof coal borehole provided in an embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures:

[0030] 1-Top coal, 2-Key seam KS1, 3-Working face, 4-Borehole, 5-Roadway. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The purpose of this invention is to provide a method for improving the top coal recovery rate through synchronous and coordinated pre-splitting of the top coal in the roof.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] Figure 1 The method flowchart provided in the embodiments of the present invention is as follows: Figure 1 As shown, the present invention provides a method for improving top coal recovery rate through synchronous and coordinated pre-fracturing of top coal in the roof, comprising:

[0035] Step 100: Determine the length of the coal face in the target area and conduct core sampling tests on the top coal and overlying rock strata to obtain the geological parameters of each rock layer;

[0036] Step 200: Based on the key layer theory, calculate the vertical distance d between the nearest key layer and the coal seam according to the geological parameters;

[0037] Step 300: Calculate the periodic fracture step L of the key layer and the horizontal distance from the boundary fracture line of the key layer to the roadway based on the geological parameters and the vertical distance;

[0038] Step 400: Hydraulic fracturing is used to simultaneously fracture the key layer and the top coal. Hydraulic fracturing holes are designed along the working face advance direction, with the starting point at the working face cut-off point, the hole spacing is L / 2, and the depth reaches the top boundary of the fracturing key layer. The angle of the designed hole toward the coal body side of the working face is θ.

[0039] Step 500: Based on the thickness h of the key layer, perform fracturing once within the key layer at intervals of 1 / 4 to 1 / 3 h, and perform fracturing once at intervals of 1 / 3 to 1 / 2 dh within the range from the bottom boundary of the key layer to the top boundary of the top coal seam.

[0040] Step 600: Design the fracturing parameters within the top coal based on the strength f and thickness h1 of the top coal;

[0041] Step 700: Calculate the actual recovery rate of the top coal based on the thickness of the top coal and the actual amount of coal mined, and monitor the lump coal rate of the coal being discharged on site.

[0042] Step 800: Adjust the fracturing parameters in the key layer and top coal according to the actual recovery rate and the lump coal rate, respectively.

[0043] like Figure 2 As shown, the process in this embodiment is as follows:

[0044] a. Determine the length X of the coal mining face, and conduct core sampling tests on the top coal 1 and the overlying rock strata to obtain parameters such as the thickness, compressive strength, and tensile strength of each rock layer;

[0045] b. Based on the key layer theory, the vertical distance d between the closest key layer KS12 and the coal seam is calculated.

[0046] c. The periodic fracture step L of the key layer KS12 is obtained by theoretical calculation, and the horizontal distance n from the boundary fracture line of the key layer KS12 to the roadway is 5.

[0047] d. Hydraulic fracturing is used to simultaneously fracture KS12 and top coal 1. Hydraulic fracturing holes are designed along the advancing direction of working face 3. Starting from the cut-off point of the working face, the spacing of the boreholes 4 is L / 2, and the depth reaches the top boundary of the key fracturing layer KS12. The angle of the boreholes 4 toward the coal body side of the working face is designed to be θ.

[0048] e. Based on the thickness h of the key layer KS12, fracturing is performed once within the key layer KS12 at intervals of (1 / 4 to 1 / 3)h. Within the range from the bottom boundary of the key layer KS12 to the top boundary of the top coal, fracturing is performed once at intervals of (1 / 3 to 1 / 2)(dh).

[0049] f. Design the fracturing parameters within the top coal seam based on the strength f and thickness h1 of the top coal seam 1. If the strength f of the top coal seam 1 is greater than 1, the fracturing interval distance is (1 / 5 to 1 / 3)h1; if the strength f of the top coal seam 1 is less than or equal to 1, the fracturing interval distance is (1 / 4 to 1 / 2)h1.

[0050] g. Calculate the actual recovery rate of top coal 1 based on the thickness of top coal 1 and the actual amount of coal mined, and monitor the lump coal rate of the coal being discharged on site.

[0051] If the recovery rate of top coal 1 is less than 80% and the lump coal rate is greater than 60%, then the fracturing design parameters should be improved. Within the key stratum KS12, fracturing should be performed once at intervals of (1 / 6 to 1 / 5)h. Within the range from the bottom boundary of the key stratum KS12 to the top boundary of the coal seam, fracturing should be performed once at intervals of (1 / 5 to 1 / 4)(dh). If the strength of top coal 1 is f>1, the fracturing interval should be (1 / 7 to 1 / 5)h1. If the strength of top coal 1 is f≤1, the fracturing interval should be (1 / 6 to 1 / 3)h1.

[0052] i. If the recovery rate of top coal 1 is greater than 80% and the lump coal rate is less than 60%, then no improvement is needed;

[0053] j. If the recovery rate of top coal 1 is greater than 80% and the lump coal rate is greater than 60%, then the fracturing design parameters should be improved. Within the key stratum KS12, fracturing should be performed once every (1 / 4 to 1 / 3) h intervals. Within the range from the bottom boundary of the key stratum KS12 to the top boundary of the coal seam, fracturing should be performed once every (1 / 3 to 1 / 2)(dh). If the strength of top coal 1 f>1, the fracturing interval is (1 / 7 to 1 / 5) h1; if the strength of top coal 1 f≤1, the fracturing interval is (1 / 6 to 1 / 3) h1.

[0054] In step d, θ is obtained by tanθ = d / n and θ = arctan(d / n).

[0055] The following is a specific example using a coal mine in Shanxi Province:

[0056] a. The length of the coal face was determined to be 200m. Core sampling was conducted on the top coal seam 1 and the overlying rock strata to obtain parameters such as thickness, compressive and tensile strength of each rock layer: average coal seam thickness 7.0m, thickness of the nearest critical layer 9.0m, tensile strength 3.0MPa, maximum load that the rock strata can withstand 12MPa; immediate roof thickness 5.5m, tensile failure strength 2.5MPa, rock strata subjected to uniformly distributed load 6MPa;

[0057] b. Based on the key layer theory, the closest key layer to the coal seam, KS12, is calculated. The distance between this key layer KS12 and the coal seam is 15m.

[0058] c. Theoretical calculations show that the periodic fracture step of the key layer KS12 is 15m, and the distance n = 7.8m from the boundary fracture line of the key layer KS12 to the roadway 5.

[0059] d. For example Figure 3 and Figure 4 As shown, hydraulic fracturing was used to simultaneously fracture KS12 and top coal 1. Starting from 0m along the advancing direction of working face 3, the spacing of boreholes 4 was 7.5m, and the depth reached the top boundary of the key fracturing layer KS12. The angle θ of boreholes 4 toward the coal body side of the working face was θ = arctan(15 / 7.8) = 63°.

[0060] e. The thickness of the key layer KS12 is 9m. Within the key layer KS12, fracturing is performed once at intervals of 2.25m. Within the range from the bottom boundary of the key layer KS12 to the top boundary of the coal seam, fracturing is performed once at intervals of 2m.

[0061] f, the strength of top coal 1 is f≤1, the thickness is 7m, and the fracturing interval is 1.75m;

[0062] g. Based on the thickness of top coal 1 and the actual amount of coal mined, the actual recovery rate of top coal 1 is 83.2%, and the on-site lump coal rate is 57.4%. Therefore, there is no need to improve the fracturing parameters.

[0063] The beneficial effects of this invention are as follows:

[0064] This invention calculates the periodic fracturing step L of the key layer and uses hydraulic fracturing to simultaneously fracture the top coal in the roof, ensuring timely fracturing and collapse of the roof strata, improving the lateral constraint force of the roof on the top coal recovery process, and thus increasing the top coal recovery rate during the caving process. It is highly operable and has significant economic benefits.

[0065] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0066] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for improving top coal recovery rate through synchronous and coordinated pre-splitting of top coal in the roof, characterized in that, include: Determine the length of the coal mining face in the target area, and conduct core sampling tests on the top coal and overlying strata to obtain the geological parameters of the top coal and overlying strata. Based on the key layer theory, the vertical distance d between the nearest key layer and the coal seam is calculated according to the geological parameters. Based on the geological parameters and the vertical distance d, the periodic fracture step L of the key layer and the horizontal distance from the boundary fracture line of the key layer to the roadway are calculated. Hydraulic fracturing is used to simultaneously fracturing the key layer and the top coal. Hydraulic fracturing holes are designed along the working face advance direction, with the starting point at the working face cut-off point, the hole spacing is L / 2, and the depth reaches the top boundary of the fracturing key layer. The angle of the designed hole toward the coal body side of the working face is θ. Based on the thickness h of the key layer, fracturing is performed once within the key layer at intervals of 1 / 4 to 1 / 3 h, and fracturing is performed once within the range from the bottom boundary of the key layer to the top boundary of the top coal seam at intervals of 1 / 3 to 1 / 2 dh. The fracturing parameters within the top coal are designed based on the strength f and thickness h1 of the top coal. Based on the thickness of the top coal and the actual amount of coal mined, calculate the actual recovery rate of the top coal and monitor the lump coal rate of the coal being discharged on site. The fracturing parameters in the key layer and top coal are adjusted according to the actual recovery rate and the lump coal rate, respectively. The fracturing parameters within the top coal seam include: When the top coal strength f>1, the fracturing interval distance is 1 / 5 to 1 / 3 times h1; when the top coal strength f≤1, the fracturing interval distance is 1 / 4 to 1 / 2 times h1. The fracturing parameters in the key strata and top coal are adjusted based on the actual recovery rate and the lump coal rate, respectively, including: If the actual recovery rate of top coal is less than 80% and the lump coal rate is greater than 60%, then fracturing should be performed once at intervals of 1 / 6 to 1 / 5 h within the key layer, and once at intervals of 1 / 5 to 1 / 4 dh within the range from the bottom boundary of the key layer to the top boundary of the coal seam; if the top coal strength f>1, the fracturing interval should be 1 / 7 to 1 / 5 h1; if the top coal strength f≤1, the fracturing interval should be 1 / 6 to 1 / 3 h1. If the actual recovery rate of top coal is greater than 80% and the lump coal rate is less than 60%, no improvement will be made. If the actual recovery rate of top coal is greater than 80% and the lump coal rate is greater than 60%, then fracturing should be performed once at intervals of 1 / 4 to 1 / 3 times h within the key layer, and once at intervals of 1 / 3 to 1 / 2 times dh within the range from the bottom boundary of the key layer to the top boundary of the coal seam; if the top coal strength f > 1, the fracturing interval should be 1 / 7 to 1 / 5 times h1; if the top coal strength f ≤ 1, the fracturing interval should be 1 / 6 to 1 / 3 times h1.

2. The method for improving top coal recovery rate through synchronous and coordinated pre-fracturing of top coal as described in claim 1, characterized in that, The formula for calculating θ is: θ = arctan(d / n), where n is the distance from the critical layer boundary fracture line to the roadway.

Images