Modeling and simulation on heat-injection enhanced coal seam gas recovery with experimentally validated non-Darcy gas flow

摘要

Heat-injection into coal seam has gained great attention as a supplementary method for the improvement of unconventional gas recovery from deep reservoirs in recent years. However, it involves a lot of ambiguous interactions among the deformation of formation, the transport of gas and the diffusion of heat in the porous coal media, especially the property of gas. In this paper, the seepage behavior of coal seam gas (CSG) that obeys nonDarcy flow law was directly observed in a conducted laboratory experiments. Then, a general Forchheimer equation was confirmed and strictly validated by the experimental data to characterize the non-Darcy seepage phenomenon. Subsequently, a fully coupled thermo-hydro-mechanical model was mathematically established. Based on the finite element approach, a numerical simulation for heat-injection enhanced coal seam gas recovery was then implemented. The susceptibilities of coal permeability and gas production to the gas sorption, heatmass transfer, and the porosity-seepage characteristics of coal were quantified by a series of numerical scenarios. Final modeling and simulation results reveal that (1) coal seam gas flow obeys non-Darcy law when the gradient of gas pressure is higher, but trends to be laminar flow that obeys Darcy law when the gradient is lower, and (2) heat-injection to stimulate coal seam could improve the production efficiency, increasing the Langmuir volume sorption parameter, the temperature correction coefficient and the initial values of permeability can improve coal permeability and enhance gas production.