Methane Emissions in Porous Media under different Atmospheric Conditions: A Bench-Scale Computational and Experimental Study

Abstract

Fugitive atmospheric emission of methane, a potent greenhouse gas with a 25-fold global warming potential compared to CO2, from the natural gas industry has raised significant environmental and health concerns during last few years. Migration of gases in soil is controlled by subsurface conditions (e.g., heterogeneity) and their emission across the soil-atmosphere continuum is affected by atmospheric boundary conditions (e.g., wind, temperature). A bench-scale experiment was conducted in a wind tunnel coupled with porous media facility to investigate the effects of two nearsurface (above ground) controls, wind (0.5 and 2.0 ms1) and temperature (24°C and 38°C), on atmospheric concentration profiles of methane migrated from a point source. We used COMSOL Multiphysics to simulate methane dynamics under the coupled temperature, pressure (wind) and concentration-driven flow conditions, taking also into account the density-dependent flow. The results show marked differences in atmospheric concentration boundary layer development under different wind velocity conditions. A good agreement was observed between the measured and simulated concentration profiles. Based on the permissible occupational exposure limits for methane, we further discussed the potential effects of wind and temperature on controlling safe workplace atmospheric conditions.