Storage and Transport of Hydrocarbons in Organic-Rich Mudstones

Abstract:

Organic-rich mudstones – also called source rocks - are capable of economically producing significant quantities of oil and natural gas. Although the static physical and chemical properties of these rocks are generally well understood, the dynamics of hydrocarbon fluids in them is still a matter of conjecture and debate. In conventional porous petroleum reservoirs, the solid matrix is composed of inorganic minerals such as quartz or calcite, pore sizes are in the range of micrometers, and the following assumptions generally hold to a high degree of approximation: (1) thermodynamic and transport properties of the pore fluids are identical to their bulk values; (2) matrix solids are inert; (3) fluid-solid interactions are fully described by simple notions of wettability. In contrast, in source rock, oil and gas are in intimate contact with an organic solid called kerogen, the pore spaces of which are comparable to molecular dimensions. Therefore the dynamics of hydrocarbons in organic-rich mudstones must take into account significant departures from bulk thermodynamics and hydrodynamics, and fluid-solid interactions are molecular-species specific. We present a multi-scale model of organic-rich mudstone that is consistent with a variety of molecular-level computations and physical property measurements, and that may serve as a basis for understanding the oil and gas production mechanisms of these rocks.