A numerical evaluation of using thin spray-on liners for coal mine gas management

Abstract

Gas drainage is the most commonly used and reliable technique for underground coal mine gas management. However, due to the suction pressure applied, air may migrate into the drainage boreholes through the fractures in the coal seam and dilute the drained gas. The low concentration gas may lead to risks such as spontaneous combustion and gas explosion. For these reasons, various types of sealants are used to prevent the interaction between the mine environment and the coal seam. As a surface support tool, thin spray-on liners (TSLs) offer promising potential in terms of a reduction of mining operating costs. In addition to ground support, there is potential for TSLs to be used for coal mine gas management, due to their relatively low permeability characteristics. This paper includes a numerical study to investigate TSL applications to improve the gas drainage efficiency in underground coal mines. A coupled simulation method was adopted in this study. The permeability variations due to mining disturbance were estimated by geomechanical modelling, while the gas flow within the coal seam was modelled with a commercial reservoir simulator. The model was first calibrated by history matching the gas production and gas concentration data in the study area to determine the unknown reservoir properties. Sensitivity analysis was then carried out on the calibrated model to predict the drainage borehole performance with different TSL application scenarios. Parameters studied in this study include TSL application length, application time, TSL permeability and coal permeability. The results from this study can be used to understand the effect of TSL applications on gas drainage efficiency and to assist the future operational capability of TSL applications in underground coal mines.