Harold Hedburg & Dale May, Schlumberger Well Services
The younger Permian carbonates have been prolific producers over the years. The San Andres and Grayburg dolomites, which are productive in nearly all areas of West, Texas, are of particular note. Although traditional log analysis has been generally successful in these reservoirs, the presence of gypsum in many has created difficulties. Gypsum tends to result in overly optimistic porosity calculations and also tends to restrict permeability by plugging the pore throats. This paper explains some of the difficulties encountered when using traditional log analysis techniques in gypsiferous reservoirs and shows how Schlumberger's ELAN log interpretation program has been used to give superior results.