Porosity and permeability within the middle member are generally very low. Porosity averages 5%, while permeability averages 0.04 millidarcies (MD). Porosity is influenced by burial depth, cement dissolution, and oil emplacement. However, the highest values are associated with naturally occurring hydraulic fractures. Higher values of permeability are also associated with natural fractures and contain higher volumes of residual oil.
Although total organic carbon levels may reach 7% in some of the shale interbeds, the organic content of the middle member is generally very low; it serves as a trap for oil derived from the upper and lower members, generally resulting in overpressurized conditions. 2