Depositional model and reservoir characteristics of the Lower Tulare Formation (Plio-Pleistocene), South Belridge Field, San Joaquin Valley, California

Abstract

Understanding the depositional environments of the Plio-Pliestocene age Lower Tulare Formation, South Belridge Oil Field, offers a unique opportunity to understand the key role that complex interbedded lithologies play in planning a successful steam flood. The Tulare Formation consists of many discontinuous arkosic sands that were deposited in a prograding fluvio-deltaic system with various fluvial and lacustrine environments on the western side of a large fresh water Plio-Pleistocene lake. Sedimentation was contemporaneous with basin development and structural growth from the Miocene to the Pleistocene thus thickening the sand sequences downdip from the crest. The Tulare sands constitute a prolific reservoir with over 1 Billion barrels produced to date. This study focuses on the lower Tulare sands deposited as distributary mouth bar and fan delta deposits with interbedded silts and clays. Four coarsening-upward sequences and two ten-foot sand packages have been identified from conventional core adjacent to the study area. Two lower coarsening-upward sequences of massive sandstone with sharp basal contacts represent fan deltas. The third sequence represents lake deposits that transition into a river mouth bar. The fourth sequence contains cross-stratified sandstones, with abundant bivalves and gastropods, deposited in a river mouth bar capped by a slumped interval. A massive mudflow deposit separates the upper two sand packages. These observations indicate deposition in a fluvio-deltaic environment. The productive reservoirs have average porosity of 36%, average oil saturation of 57% and average permeability of 1400 md, with an API oil gravity of 10-13 degrees. The improved understanding of the depositional environments, sand geometries, and distribution of reservoir properties across the area of interest has enhanced reservoir characterization and will contribute to improved reservoir management. In addition, this reservoir provides an excellent opportunity to monitor effectiveness of the steam program on the basis of reservoir architecture and apply changes to improve injection efficiency.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016