Abstract

The Permian Basin is a highly developed petroleum province, but remains highly prospective for additional conventional and unconventional oil and gas opportunities. The magnitude of its conventional resource is matched by its potential for unconventional resources including shale-gas, shale-oil, and tight gas sands. No complete study of conventional petroleum systems has been published and understanding these systems is important to evaluation of the total basin resource potential. Our study of over 500 oils from across the basin suggests at least eleven different petroleum systems including multiple Ordovician, Devonian, Mississippian, Pennsylvanian, and Permian source and reservoir rocks.

Unconventional resource potential exists in many source rock units. While recent focus has been on shale-gas and tight gas sands, there is also shale-oil potential. Shale-gas potential has been limited primarily by depth to mature source-reservoir rocks as thermal maturities above 1.0 to 1.2% vitrinite reflectance occur only at depths exceeding 9-10,000 feet depending on age. However, shale-oil potential exists at much shallower depths in all ages of source rocks across the entire basin. The key is identifying areas of high residual oil contents containing high quality oils. Because most of the sources in the Paleozoic are marine shales that are low in sulfur, the oils are very high quality in terms of API gravity and viscosity even at low thermal maturation levels. Oil saturations are affected by generation and expulsion processes including both hydrocarbons and non-hydrocarbons such as organic acids that can leach conduits for expulsion-migration and create secondary porosity for oil storage.