5. Water and Methane in Shale Rocks: Flow Pattern Effects on Fluid Transport and Pore Structure

In the last decade, because of the shale gas revolution in the USA the fluid flow in shale nanopores have attracted great attention of scientists worldwide. In shale formation water and natural gas can co-exist within the narrow pores, leading to the possibility of two-phase flow. In this work, I designed the molecular simulation system, that include water and methane confined in slit-shape muscovite nanopore, to investigate the effect of the two-phase flow patterns on the fluids transport and on the pore structure. The results indicate that when the driving force, i.e., the pressure drop, increases above a pore-size dependent threshold the two-phase flow pattern is altered. As a result, the velocity of methane with respect to that of water changes. My results also illustrate the importance of the capillary force, due to the formation of water bridges across the clay pores, not only on the fluid flow, but also on the pore structure, in particular its width. When the water bridges are broken, perhaps because of fast fluid flow, the capillary force vanishes leading to significant pore expansion. Because muscovite is a model for illite, a clay mineral often found in shale rocks, these results advance our understanding regarding the mechanism of water and gas transport in tight shale gas formations.