Application of petrographic image analysis to the characterization of fluid-flow pathways in a highly-cemented reservoir: Kane Field, Pennsylvania, U.S.A.

The Kane Field reservoir is a well-cemented Upper Devonian sandstone with an average porosity of 11%. The bulk of the pore space occurs as microporosity in authigenic clays. Despite this apparently poor quality, the reservoir produces oil under waterflood at commercial rates of up to 17 bd per well. The purpose of this paper is to explain this behavior in terms of the nature of the porous microstructure of the reservoir. Statistical analysis of digital image data from thin sections of the Kane reservoir demonstrates the existence of five pore types, two of which (Pore Types 4 and 5) are a product of feldspar dissolution. Correlation of the image-analysis results with data from mercury injection of core plugs shows that Pore Type 4 has sufficiently large throats for it to be controlling the permeability of the reservoir. However, modelling Pore Type 4 as a system with conventional intergranular throats gives predicted permeabilities that are an order of magnitude lower than measured values. A much better match is obtained by considering the throats as slots that transmit fluid in a fracture-like manner. Such a configuration allows Pore Type 4 to provide highly efficient flow circuits that occupy only a small proportion of the total porosity. These circuits are a product of both depositional and diagenetic processes: concentration of local aggregates of feldspar grains, and subsequent dissolution of those grains by corrosive pore fluids.