Geologic Reservoir Description of the Miocene Upper Stevens Sandstone within Paloma Unit, Kern County, California

ANDERSON, JEFFREY A., Shell Western E&P Inc. (SWEPI), Bakersfield, CA

Paloma Unit is located 18 mi southwest of Bakersfield, California. Production is from upper Stevens, late Miocene age sands at depths ranging from 10,000 to 12,000 ft. Industry estimates upper Stevens STOOIP at over 200 MMBO within the 5230 ac Paloma Unit. SWEPI first acquired interest in Paloma during 1984, and is now operator of this unit, which is near the end of its primary producing life.

This paper describes the methods used and the resulting geologic description to characterize the Paloma upper Stevens sandstone for input into reservoir studies. Primarily, core descriptions and conventional and stressed small sample analyses were used for the geologic portion of this study.

A turbidite onlap model was developed to describe the environment of deposition and lithofacies observed in the Paloma sandstone packages. Core descriptions were instrumental in this characterization due to lack of quality well-log data. Whole-core data were used to correlate major stratigraphic packages field wide, displaying greater lateral continuity of lithologic packages in the present-day structural dip direction, whereas beds appear less continuous parallel to strike.

Valuable data were obtained from conventional and stressed small sample analysis of SWEPI PU 38-1 core. Conventional small sample analysis of the core including photomicroscopy and physical measurements provided mineralogical and textural properties used to derive a possible paragenetic sequence. Detailed conventional petrographic small-sample analyses were key to interpreting the pore network and clay types, important to understanding how the upper Stevens rocks would respond to waterflood. Stressed small sample analysis was critical in determination of the size of the Upper Stevens accumulation.

This geologic characterization of the variable upper Stevens stratigraphy at Paloma was critical in development of accurate reservoir models for advance studies and in explaining observed production responses.

AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)