The pore geometries of reservoir rocks

Abstract

A ternary pore geometry classification scheme for reservoir rocks places intergranular and intercrystalline porosity at a common pole. These porosity types tend to have well interconnected pores and usually are good reservoirs. Intragranular, moldic, and vuggy porosity are grouped at another pole of the classification triangle. Rocks with these porosity types usually have poorly interconnected pores and low permeability. Rocks with microporosity are grouped at the final pole of the triangle. These may be argillaceous sandstones, finely textured carbonates, diatomites,or tripolitic cherts. Water‐wet microporous rocks hold bound water. Rocks with significant amounts of microporosity and/or intragranular, moldic, and vuggy porosity need fractures, either natural or induced, to make an attractive reservoir. Fracture porosity may occur by itself or combined with any other porosity type. Reservoirs typically contain multiple pore types, although one type often predominates. Large scale cavernous features in carbonates occasionally contain oil.