Impact of Reservoir Heterogeneity on Initial Distributions of Hydrocarbons

Abstract

Abstract The objective of this study was to demonstrate the effects of heterogeneity on the initial distributions of oil, water and gas in sandstone reservoirs and to provide a preliminary assessment of the effects of this structure on primary recovery. This is achieved by generating realistic capillary pressure and relative permeability relations parameterized by absolute permeability. These were then employed to compute initial fluid saturation distributions in composite blocks based on capillary-gravity equilibrium. The method is also illustrated in a real geological setting by employing the spatial distribution of permeability measured in an outcrop of Page Eolian sandstone. Severe discontinuities in saturation and effective permeability are demonstrated. These effects are most dramatic in water-wet systems; the higher capillary pressures in the low permeability laminae of a cross-bedded system cause high water retention, with correspondingly low hydrocarbon permeabilities, over the entire range of average saturations. Thus such "tight streaks" literally become permeability barriers to hydrocarbon flow and create very non-uniform reservoir drainage patterns; extensive pockets of trapped hydrocarbons result.