Modeling Multicomponent Diffusion and Convection in Porous Media

Abstract

Summary Numerical investigations of diffusion and convection in multicomponent hydrocarbon mixtures in two-dimensional (2D) crosssectional (x,z) porous media are performed using the finite-volume method. Spatial discretization is performed by a second-order centered scheme. It is shown that methane, unlike in binary hydrocarbons where it often segregates towards the bottom-hot side of the porous media, may be at higher concentration at the cold-top side in ternary mixtures and in multicomponent reservoir fluids. This behavior, which is consistent with oilfield data, is due to competing diffusion mechanisms which have not been properly accounted for in the past. It is also demonstrated that convection may significantly affect the compositional variation in some hydrocarbon reservoirs. Depending on fluid mixtures, a weak convection may drastically change compositional variation.