Relationship Between Lithofacies and Reservoir Quality in Giant Oil Field: Long Beach Unit, Wilmington Field, California

Roger M. Slatt

Long Beach unit is part of the giant Wilmington oil field, Los Angeles basin. Detailed examination of six cores totaling more than 1,500 m, 900 core-plug porosity and permeability measurements, and 85 grain-size analyses from the major producing interval (the more than 300-m thick Ranger zone) provided an excellent data set for relating reservoir quality to lithofacies.

The late Miocene-early Pliocene Ranger zone was deposited by a variety of submarine mass-gravity flow processes in lower middle to upper middle bathyal (500-2,000 m) depths. Three lithofacies have been defined: (1) thick-bedded and consisting of sets of individual beds, more than 0.6 m thick, containing moderately to poorly sorted, very fine to medium-grained and interbedded with thin-bedded shale, (2) thin-bedded sand consisting of individual beds, less than 0.6 m thick, containing moderately to poorly sorted, very fine to medium-grained sand interbedded with thin-bedded shale (more shale interbeds than the thick-bedded sand), and (3) shale beds, ranging from less than 0.1 m to several meters in thickness, that are laterally discontinuous for long distances.

Primary sedimentologic characteristics exert major control on reservoir properties of these unconsolidated sands, as indicated by the following average values.

Table

The thicker bedding, slightly coarser average grain size, and fewer shale interbeds of thick-bedded sand compared to the thin-bedded sand reflect deposition of the former from higher energy flows. The coarser average grain size of beds comprising the thick-bedded sand lithofacies and equivalent sorting of beds of both lithofacies account for the higher permeability of thick-bedded sands, yet equivalent porosities of both lithofacies.

This abstract and supporting data are the sole proprietary work product of ARCO Oil and Gas Company, a Division of Atlantic Richfield Company, and the writer. No other parties necessarily concur with or endorse any of the data, analyses, or conclusions presented herein.

AAPG Search and Discovery Article #91024©1989 AAPG Pacific Section, May 10-12, 1989, Palm Springs, California.