Steady-state migration and diffusion of hydrocarbons in complex stratigraphic sequences

A mean-field method is used to describe both average and fluctuating flow properties of water and oil in sedimentary basins. Comparison of oil and water flow shows the relative strengths of capillarity and buoyancy in controlling the mean and fluctuating components of flow. Effects of sandiness and water-wetness are studied as is the effect of decreasing porosity with increasing subsurface burial. Numerical estimates suggest that sandiness percentages between about 20 to 80% influence mean and fluctuating components of flow. Outside of this regime the end-member situations of shale or sand prevail.The extra effects of vertical buoyancy and capillarity generally make lateral diffusion less important for oil flow than for water flow.