Simulation of mine water inflow and gas emission during longwall mining

Reliable prediction of rock mass deformation, mine stability, mine water inflow and mine gas emission is not only essential for improving mine safety and reduction of coal production costs, but also important for the assessment of environmental impact of mining. This prediction requires the accurate simulation of complex, highly non-linear and irreversible processes including the mechanics of rock deformation and failure due to coal mining and the consequent water flow and gas desorption and flow. This paper describes a three-dimensional numerical model, called COSFLOW. It uses a Cosserat continuum approach for the efficient description of mechanical stress changes and deformation in weak layered rock, typical of coal measures. This mechanical model is coupled with a two-phase dual porosity fluid flow model to describe flow of water and gas through porous rock, desorption/adsorption of gas from the matrix and subsequent flow of water and gas through the fracture network. The coupling includes simulation of permeability and porosity changes with rock deformation. The numerical model is used to simulate water inflow and gas emission in two Australian mines. The model is calibrated using existing extensive mine water inflow and gas emission measurements and used to make predictions for future longwall panels. Comparisons of numerical predictions with later mine measurements of water inflow and gas emission demonstrate the suitability of such a code in accurately predicting mine water inflow and gas emission into a coal mine.