Abstract
Coal seam gas is one of the most significant energy resources in unconventional gas fields. The identification of influenc- ing parameters and methane drainage assessment are, thus, a prime geotechnical focus for all potential methane drain- age projects. In methane drainage operations of coal seams, many factors, such as natural factors and operational factors affect the drainage efficiency. In this paper, a new coal seam methane drainageability index (CMDI) is introduced for pre-drainage techniques in a working mine. In this approach, seventeen parameters are considered as the main factors affecting the methane drainage form coal seam, and the interaction matrix based on the fuzzy rock engineering system (FRES), which analyzes the interrelationship between the parameters affecting methane drainage activities, are used to study coal seam methane drainageability. Since the value of interaction in the RES method is not unique, the fuzzy sys- tem is used to minimize subjectivity of the weights which are computed in the RES method. The Tabas coal mine (Iran) was selected as a case study and the proposed index was used to rank the C1 seam in this mine. It was observed that the methane drainageability index could suitably predict the potential of the methane drainage of coal seam. The newly proposed index can be used as a basis for decision-making when uncertainties about the evaluation of the parameters affect the methane drainage of a coal seam and reduce the risk of methane drainage projects.
Highlights
Coal seams may contain 60% to more than 95% methane that depend on the presence of other gases in the coal seam (Karacan et al, 2011; Darling, 2011; Wilson et al, 1995; Hamawand et al, 2013)
In the coal mine methane (CMM) method, gas is captured in working coal mines by underground or surface and underground methane drainage techniques to ensure the safety of a mine
In the enhanced coalbed methane (ECBM) method, the CO2 is injected into the coal bed and the methane gas is released by some chemical reactions and it is extracted by a drainage operation (Thakur, 2014; Gale & Freund., 2001; Wong et al, 2007; Karacan et al, 2011)
Summary
Methane drainage methods involve the removal of methane prior to mining activity on a virgin coal seam and during extraction. Dougherty and Karacan discussed methane control and prediction (MCP) software which was developed by NIOSH This software can determine the type of degasification system, predict the production performance of a gob gas venthole, predict ventilation emissions from longwall mines and predict the dynamic elastic properties of coal (Dougherty and Karacan, 2011). Black studied the relationship between gas production from underground inseam drainage boreholes, coal seam properties and operational factors. The results indicated that the weight of geological factors, engineering factors and drainage factors are 50%, 25% and 25%, respectively (Liu et al, 2014) In all those methods, the researchers did not consider all the parameters and their interactions completely. The development of a new index that can classify the coal seam capability drainage by considering the interactions of influencing parameters is important. Length of Boreholes (m) Orientation of Boreholes to the principal horizontal stress) (Degree) Boreholes and Wellbore Stability Boreholes Spacing (m) Panel Dimension (Width and Length) (m) Cut Depth (cm)
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