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The Orcutt Oil Field: How Stratigraphic Relationships Reflect the Structural and Tectonic History

G. N. Hummel
BreitBurn Energy, Los Angeles, CA, [email protected]

The Orcutt Oil Field, located in the Santa Maria basin in Santa Barbara County, California has produced approximately 160 million barrels of oil since its discovery in 1901. The field lies in the easterly portion of the Santa Maria basin. The Orcutt structure is one of a series of anticlines in the basin, formed by deep-seated thrust faults and caused by convergent margin tectonics. Previous studies have suggested a clockwise rotation of the basin in the early Miocene.

Detailed stratigraphic work in the field has determined that the Orcutt structure was active during the late Miocene through medial Pliocene deposition of the Sisquoc Formation and during the late Pliocene deposition of the Cebada and Foxen Formations. These formations thin markedly over the current structure suggesting that early structural movements on the Orcutt and Casmalia anticlines influenced deposition in the basin. The Cebada and Foxen Formations pinch out on the sides of the current structure and may have never been deposited over the structure or have been removed by erosion.

Structural mapping and stratigraphic relationships suggest that the structure was initially thrust north-northeast during the medial Pleistocene and then subsequently relaxed and rotated. This activation and reactivation of faulting has provided conduits for fluid migrations within the field, limited fluid migration, and offset oil-water contacts.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009