AUFFANT, ARIEL D., JANICE GILLESPIE, Department of Geology, California State University, Bakersfield, CA; and MICHAEL S. CLARK, Chevron USA, Bakersfield, CA

Abstract: Stratigraphic and Depositional Analysis of Gas-bearing Scallez Sands, Pliocene San Joaquin Formation, Coles Levee Field, San Joaquin Basin, Bakersfield, California

Thickening trends evident in net isopach maps of the middle Scalez sand zones of the San Joaquin Formation at North and South Coles Levee fields, San Joaquin basin, California indicate shallow-marine deposition in a tectonically active setting. Net thickness of "First Sub-Scalez" (range from 5 ft to 50 ft), "Scalez Marker Zone", and "Above Scalez" (range from 10 ft to 100 ft) sandstones was determined from spontaneous potential (SP) signature of wells penetrating the Scalez sand zones.

These sands were deposited in shallow marineenvironments during periods of fluctuating sea level on the Bakersfield Arch. The "First Sub-Scalez" and "Above Scalez" sandstones appear to represent shoreline regressions separated by mudstones of the "Scalez Marker Zone". Correlation of spontaneous potential logs in the northwest part of the study area reveals a greater percentage of coarseningupward sandstones, which may indicate shoreface or foreshore deposition. By contrast, thinner, fining-upward sandstones indicate an ephemeral distal alluvial plain or tidal flat environment.

Understanding the architecture and depositional environments of the Scalez will aid exploitation of this and other Pliocene dry gas sands at North and South Coles Levee. Similar sandstones have produced 60 BCF of gas at Coles Levee. Furthermore, well number 46-36S produced an average of 600 BOPD for many years from fault traps at adjacent Elk Hills field. Similar traps of Scalez reservoirs at Coles Levee may ultimately prove productive.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California