ABSTRACT:

Coal mining is extending to deeper and deeper levels, facing ever increasing coal seam methane contents and much higher methane emissions at production districts. The low permeability nature of coal seams exacerbates with the stress increase at deeper levels. This growing challenge is often not addressed effectively by the current gas drainage methods applied in coal mines. In recent years, slotting via hydraulic or mechanical force along underground gas drainage boreholes, as a general solution to stimulate low permeability coal reservoirs, has attracted increasingly attention. However, the role of prevailing stress state, coal properties, and slot geometry are the critical parameters to be considered in slotting operations. There has been no systematic research on assessing these key parameters and understanding the sensitivity of individual parameters in affecting slotting performance. By quantitatively assessing a series of numerical modelling scenarios, this paper aims at identifying the key parameters controlling slotting operation, analysing the sensitivity of individual parameters, and optimising slotting operation. Internal friction angle, slot diameter and the ratio of the maximum principal stress to minimum principal stress have been identified as the top three parameters affecting slotting performance.

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