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Yowlumne is a giant oil field in the San Joaquin basin, California that has produced over 100 MMBO from a low-permeability (10-100 md), fan-shaped turbidite complex with left- and basinward-stepping geometries deposited in an active-margin basin. The Yowlumne and other “deep water,” upper Miocene sandstones in the San Joaquin basin make up a clastic facies of the Monterey Shale called the “Stevens” sandstone, which has contributed more than 15% of 12 BBO produced here since 1864.

The Yowlumne reservoir is a prograding turbidite complex of seven lobes deposited on the basin margin during Miocene orogeny. Although the fan is lens-shaped, it does not significantly incise underlying strata. Apparently, deposition resulted from confinement of prograding lobes, about 2 km wide by 4 km long, between a faulted paleohigh on the west (left) side of the fan, and another high, associated with overbank deposition and possibly differential compaction, on the east (right) side. Basinward-stepping compartments in the reservoir represent deposition during decreasing accommodation, and high sediment flux, whereas left-stepping compartments reflect the influence of Coriolis forces.

More abundant shale-bearing levee facies characterize the east (right) margin of the fan, whereas sand-rich lobe facies characterize the west. Therefore, reservoir quality decreases from the fan axis eastward towards the fan margin. Cost-effective exploitation of bypassed oil trapped against the thinning margin is facilitated by 3D-computer modeling to effectively locate highly deviated to horizontal wells, and design completions that maximize productivity from the layered, low permeability turbidite reservoir that characterizes the distal fan margin.

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