Abstract

Exploration for new Silurian and Devonian hydrocarbon reservoirs in the Permian Basin is hampered by the variable stratigraphic and structural styles in sub-Woodford strata. These different styles in turn affect the seismic expression at major seismic marker horizons, such as the base of the Woodford Shale, which is commonly used to explore for those reservoirs. Four field examples are presented which illustrate the importance of these geologic changes and the need for more detailed stratigraphic exploration techniques on the search for new Silurian and Devonian prospects.

Topographic relief at the top of the Fusselman Formation at Patricia Field is largely responsible for the trap development of Fusselman reservoirs there, and this relief contrasts sharply with lower magnitude structural relief at the base of the Woodford. Brahaney Northwest Field produces from reverse structure sub-unconformity traps in Devonian dolomites that are immediately below the base of the gently folded Woodford Shale. Seminole Devonian Field pays from a series of discrete dolomite reservoirs which form part of a low-angle paleo-hogback feature beneath a cover of more intensely folded Woodford Shale. West Garrett Field is an example of a Devonian reservoir which has been modified through several episodes of tectonic reactivation.