POL, JAMES C., and STEVEN R. FEKETE, ARCO Exploration & Production Technology, Plano, TX

ABSTRACT: Depositional Environment and Reservoir/Seal Characteristics of the Miocene Potter Sand, Northern Midway-Sunset Field, Kern County, California

The Miocene Potter sand is one of the primary reservoirs in the northern portion the of the Midway-Sunset field, Kern County, California. More than 1200 ft of whole core and approximately 500 sidewall cores from 31 wells were examined to help optimize steam-flood development in the area. Specific goals of this study include facies interpretation, reservoir characterization, and wireline log calibration.

The Potter sand consists of three primary lithofacies: conglomeratic coarse-grained sand, coarse to medium-grained sand, and argillaceous sandy silt. In conglomeratic intervals, cobbles reduce reservoir pore volume and must be quantified to facilitate accurate reserve calculations. Clast percentages in the two most extensively cored wells were determined by visual estimation, point counting, and computer image analysis. Results show close agreement between all three methods. Core data were subsequently used to calibrate wireline logs to develop cutoffs for picking lithofacies from logs.

Argillaceous siltstones ranging from 1 cm to 10 m in thickness are important because they compartmentalize the reservoir and act as barriers to heavy oil and steam. High clay content and bound water cause a highly conductive log response that magnifies apparent bed thickness. Neutron/density logs offer better resolution, but only core and FMS logs allow direct detection of centimeter-scale silt beds.

Gross interval isolith mapping of log-derived lithofacies indicates stacked elongate conglomeratic bodies flanked by clean sands and minor silts. The Potter sand is interpreted to have been deposited in a subaqueous coarse-grained delta-front environment.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.