Estimating permeability from wireline logs has been difficult historically because of the large petrophysical heterogeneity typical of carbonate rocks. A simple relationship between porosity and permeability has not been observed, only between porosity, permeability, and pore size. In Clear Fork carbonates at Fullerton field, pore size is related to rock fabrics. Permeability was calculated for each well using porosity from wireline logs and rock-fabric information from stratigraphic relationships. Permeability profiles, calculated using a global transform, compare well with core permeability values. An exception is in the lower section of the reservoir (Wichita Formation), where karst fabrics are present, suggesting a touching-vug pore system.

Initial water saturation is required for estimating original oil in place and for flow simulation studies. Because most of the original wells in this field had very old log suites and the new wells were drilled after the advent of waterflooding, calculation of initial water saturation from wireline logs for most of these wells was not feasible. In this study, initial water saturations were calculated using capillary-pressure models generated for each petrophysical rock-fabric class. A generic rock-fabric model for class 1 fabrics was used, and new rock-fabric models were developed for class 2 and class 3 fabrics using the Thomeer approach. Water saturations calculated from capillary-pressure models show good agreement to saturations calculated using the Archie equation from wireline logs in intervals thought to be unflooded. The success of the rock-fabric-based method in calculating permeability and saturation in the Fullerton Clear Fork reservoir illustrates how valuable this technique can be in defining the petrophysical properties in carbonate reservoirs.