--> --> Undeveloped petroleum potential of the western-most Santa Barbara Channel, offshore California

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Undeveloped petroleum potential of the western-most Santa Barbara Channel, offshore California


Offshore seismic surveys (now in the public domain) led to the discovery of several potential oil fields in the western-most Santa Barbara Channel. The surveys and wells also help to better understand this tectonically and stratigraphically complex area. It is at the western edge of the Transverse Ranges tectonic block, where the overall rotation may have created compressional structures, and it includes a portion of the transition zone from the Santa Barbara Channel to the Santa Maria basin to the northwest. Offshore wells and seismic lines extend the control provided by onshore data, with unconformities, volcanics and local depocenters documenting the opening of the Santa Maria basin (from the Upper Oligocene). The exploratory wells in the area also discovered ten accumulations of heavy oil in the Miocene Monterey formation. Only one of the two largest structural highs was developed, Point Arguello field (200 MMBO), with much political opposition. The second large (undeveloped) structure is known as Sword. These structures illustrate aspects of the inter-basin transition zone, with very different structural orientations and ages. Sword is part of a persistent pre-Monterey structural high, whereas Point Arguello is a post-Monterey inversion structure typical of the Santa Maria basin. Both Sword wells encountered oil in quartz-phase chert and dolomite in the Monterey. These zones have high matrix porosities, but fractures provide most of the permeability. Both wells tested 8 to 10 degree API oil at potentially economic rates (2000 to 3000 BOPD) on artificial lift. Conservative estimates for the undeveloped fields (226 MMBO) indicate a very large resource technically within reach of facilities at Point Arguello, but low oil prices and politics suggest they will be waiting many more years.