| As a typical coal and gas outburst mine in China,Shihe mine needs to solve the problems such as gas outburst during coal mining by means of gas pre-pumping before coal mining.In order to accomplish the coordinated development with coal,the best selection of CBM(coalbed methane)extraction blocks and the reasonable development service of well locations are extremely important.The main mining of the Sihe mine is the No.3 coal seam of the upper group coal.With the large area of the No.3 coal seam retrieved,the gas management work of mining the under-group coal seam needs to be carried out in advance.Due to the influence of overlying rock collapse and fracture development caused by coal mining of upper group coal,the CBM development of under-group coal seam has become harder in terms of well deployment service and development technology.Based on this,this paper adopts various research means such as theoretical analysis,numerical simulation and engineering test to study the stress change,mobile deformation and spatial and temporal evolution law of the distribution of plastic zone in the subducting coal rock body after mining the upper group coal,constructs the evaluation index system of coalbed methane development potential of No.15 coal in the mining area,evaluates the favorable blocks for coalbed methane development,determines the principles of coalbed methane extraction well deployment in horizontal wells through coal pillars,studies the horizontal well The key elements and contents of the design of horizontal wells are studied,and the CBM extraction test is carried out in the horizontal wells of the lower group coal penetration column.This paper takes the Temple River coal mine as a research example,and the conclusions of the paper are as follows:(1)Using The slip-line field and Stress equilibrium theory of loose media to study the deformation and damage characteristics of the overlying coal mining on the underlying coal rock body,the maximum depth of the bottom drum fissure zone is calculated to be 37.06 m according to the geological mining parameters of the Sihe mine.(2)Combined with the coal mine deployment,on the basis of the completed drilling data,the geological model of coal seam floor mining effect was established by using FLAC3D software simulation,analyzing the stress change,rock movement deformation and spatial and temporal evolution law of the distribution of plastic zone of the underlying surrounding rock during the mining of the No.3 coal seam of the upper group coal.The results show that both No.9 coal seam and No.15 coal seam are within the mining pressure relief range of No.3 coal seam,and the gas conductivity of the subordinate coal rock layer of No.3 coal seam has changed significantly by the mining pressure of the overlying coal seam,and the permeability of the coal rock layer has been enhanced.(3)Study and select the main control factors for the development of the horizontal CBM wells of No.15 coal of the under-group coal seam,and use them as evaluation indexes to establish the evaluation index system for the development potential of No.15 CBM in the mining area,and use a combination of hierarchical analysis and fuzzy comprehensive evaluation method to evaluate the favorable blocks for CBM development as the Dongwupan of Sihe mine.Based on the premise of coordinated development of CBM and coal,according to the requirements of CBM development engineering,the key elements and contents of horizontal well design are studied following the method of comprehensive analysis of ground wells,and optimizes the deployment of horizontal wells through the coal pillar of under-group coal seam in the Dongwupan of Sihe mine.(4)The maximum daily gas production reached 9,522 m~3and the cumulative gas production was 2.2 million cubic metre in 14 months,which proved the technical feasibility of extracting CBM from the under-group coal seam of the Shihe mine through the horizontal wells of the coal pillar. |
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