Transformation of neutron, density, and sonic logs to estimations of calcite, dolomite, chert, and pore volume. Facies patterns related to depositional, diagenetic, and erosional trends. Controlled by depositional-shelf geography modified by subsequent uplift and erosion. The log analysis map shows a pronounced geographic grain whose directional features can be related directly to basement lineaments and their active role in tectonic uplift and erosion. A useful exploration aid, because Viola oil fields located in both structural and combination traps.--Modified journal abstract.