Basin and Petroleum System Modeling of the Sur and Northern Offshore Santa Maria Areas, Offshore Central California

The Sur basin (also called the Partington basin) is an undrilled, asymmetrical basin offshore central California. It is the northwestern extension of the offshore Santa Maria basin, and therefore shares similar stratigraphy and tectonic history. Although some successful petroleum discoveries have occurred in the southern offshore Santa Maria area, the Sur basin and northern offshore Santa Maria areas have never been commercially explored. Peters and others (2008) collected tarball and seep samples from the central California coast and suggested that some may have originated from seeps within the Sur and northern offshore Santa Maria areas. In this study, we used three-dimensional (3D) basin and petroleum system modeling to evaluate whether a mobile petroleum charge exists in these areas. A 3D geologic model of the Sur and northern Santa Maria areas was constructed by converting travel time isopach maps to depth via well data available in the nearby southern offshore Santa Maria area. Because Type IIS kerogen generated significant amounts of heavy sulfur-rich crude oil in the southern offshore Santa Maria area, Type IIS kerogen kinetics was used to simulate petroleum generation from the Miocene Monterey Formation in the 3D basin model. The Monterey Formation was split into the lower calcareous-siliceous, the carbonaceous marl and the clayey-siliceous members. Other stratigraphic inputs for the model included the Lower Foxen, the Upper Foxen, the Lower Sisquoc and the Upper Sisquoc Formations. The model results suggest that the Miocene Monterey Formation source rock is thermally mature and generated volumetrically significant accumulations of low-maturity petroleum in minor anticlines sealed by the mudstone of the Sisquoc Formation or by the clayey-siliceous member of the Monterey Formation. The model results also suggest the potential for unconventional shale oil opportunities.  

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California