A numerical simulation on coal seam gas recovery from high temperature reservoir

Abstract

The coal seam gas recovery in deep reservoirs often meets high temperature. The change of temperature can greatly influence gas sorption, and couples heat transfer with coal deformation and gas-flow. This paper modifies the conventional Langmuir adsorption equation into a non-isothermal adsorption equation with a set of experimental data. After then, a fully coupled thermo-hydro-mechanical model of coal deformation, gas-flow and heat transfer is established. By using a finite element approach of COMSOL multi-physics, a numerical simulation of coal seam gas recovery from high temperature reservoir is subsequently implemented. The results show that the gas pressure and temperature decrease with production time and increase with the distance from production well, the reservoir permeability decreases with production time due to the compaction of increasing effective stress to coal fracture network, the cumulative gas production increases with production time exponentially whereas the production efficiency decreases negative exponentially, that the gas production in earlier 10 years accounts for 80% of the total production in 30 years. Our fully coupled thermo-hydro-mechanical model can improve the current understanding of coal seam gas recovery from high temperature reservoirs.