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The Yowlumne oil field is a stratigraphic trap formed by Miocene Stevens turbidite sandstones pinching out across the San Emidio Nose. In 1989, ARCO initiated a detailed reservoir study aimed at maximizing total oil recovery. The extent of the reservoir sands and their internal geometry are described using three-dimensional 
seismic
and well data.
The presence of sand is shown in the seismic data by thickening in the upper Stevens interval, decreased seismic amplitudes and development of mounded seismic character. The increased spatial resolution provided by the seismic data allows the interpretation of internal sand boundaries between the 25-40 ac well spacing. Geometry of sand bodies on the order of 50-200 ft thick are revealed by weak reflections cutting diagonally across the gross sand interval. Boundaries between sand bodies occur as marine shale, contorted beds, and sand on sand contacts.
The Yowlumne sands occur as narrow channelized sands in the southeast part of the field, which fan out north of a paleoslope break. The oldest deposits are detached fans in the northern part of the field and narrow channelized deposits in the southeastern part of the field. Subsequent fan lobes extend farther up depositional slope. Both fan and channelized deposits generally migrated westward through time overlapping older deposits.
The integration of the three-dimensional seismic and well data provide a new description of the sands, which will be combined with reservoir data
and incorporated into a full-field reservoir model.
AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)