Abstract: Sans Spring Field Exploration Model, Nye County, Nevada

Michael H. Mitchell

The existing model for Oligocene volcanic reservoir production in Railroad Valley was expanded with the discovery of oil at Sans Spring field by CENEX, et. al in March, 1993. Prior to drilling the CENEX #5-14 Federal (SWNW, section 14, T7N-R56E), economic production had only been established along the east and west borders of the valley, in structures associated with large offset normal faults.

The location of Sans Spring field is on an east - west structural high that separates the productive central Railroad Valley sub-basin from the as yet unproductive southern sub-basin. Gravity, regional and detailed conventional 2-D seismic data coverage was employed to define the structure. This geophysical data further suggested that the structure had remained relatively undeformed, providing seal and trap integrity, during the post Oligocene extensional structural development of Railroad Valley. The location also met a critical criterion of being along a potential hydrocarbon migration pathway for oil generated by the Mississippian Chainman shale source rocks.

The discovery well found reservoir development in a moderately welded and altered rhyolitic ignimbrite, with an IPF 1253 BOPD. The trap is an angular unconformity, with truncation to the west that has been modified and complicated by cut and fill channeling and faulting.

Definition of the structural configuration, fault geometries and offsets has been greatly enhanced with the acquisition of a 3-D seismic survey. However, the data volume does not as yet provide an unambiguous solution to stratigraphic variations.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada