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Abstract: Depositional Model for the Potter Sand Member of the Reef Ridge Formation, Midway Sunset Field, Kern County, California

FEDEWA, WILLIAM T., and MICHAEL L. SIMMONS

The Potter sand of the Upper Miocene Reef Ridge Formation is one of the most prolific oil producing sands in California The sand has accounted for approximately 35% of the Midway-Sunset Field's 2.4 billion barrels of cumulative oil production and greater than one-half of the field's current daily production of 160,000+ BOPD. The Potter sand actually consists of boulders, cobbles, sands, and silts that were sourced from the Salinian block, located west of the field and the San Andreas fault. Several interpretations of the depositional setting for the Potter sand have been proposed in geological literature.

Several authors have stated that the Potter sand was deposited as a coalesced turbidite fan in a deep marine basinal setting, while others have stated the Potter sand was probably deposited in channels on the proximal portion of a submarine fan complex. Water depths during deposition have been estimated at between 270 and 300 m (885 ft -980 ft) and as deep as 1000 m (3280 ft).

A combination of data collected from electric logs, cores, and regional mapping suggest an alternative depositional model. The Late Miocene to Recent stratigraphic section in the vicinity documents the progressive infilling of an intraslope marine basin, with the Potter overlying deep marine equivalents to the Miocene Stevens sand and separated by an unconformity from very shallow marine, brackish, and continenta1 deposits of the Etchegoin, San Joaquin, and Tulare Formations. Sequence stratigraphy analysis of the Potter sand using electric log data suggest flooding surfaces within the sand, characteristic of shelf deposition. Bioturbated muddy sands with their trace fossil assemblages, cobbles and boulders, rip-up clasts, sponge spicules, and woody plant debris described in cores, suggest a very proximal location for Potter sand deposition. These data support a relatively shallow, nearshore marine fan-delta depositional model for the Potter sand.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California