Robert A. Bridges¹, James W. Castle¹

(1) CU, Clemson, SC

ABSTRACT: Application of Outcrop Analogs to Reservoir Characterization of Shallow-Marine and Coastal-Plain Reservoirs: An Example from the San Joaquin Basin, California

Recognition of lithologic facies in outcrops and comparison with cores is providing an architectural framework for constructing three-dimensional computer realizations of heavy-oil sands in the Temblor Formation (Miocene), West Coalinga Field, California. Detailed outcrop, core, and permeability studies are helping to predict subsurface geological heterogeneity and fluid-flow patterns in shallow-marine and coastal-plain reservoirs. Approximately 4470 feet of cores and 2300 feet of nearby outcrops have been described and interpreted. Chevron Production Company is providing core petrophysical data and geophysical logs.

The following depositional environments are interpreted from lateral and vertical facies patterns: incised valley-fill, estuarine, tide- and wave-dominated shoreline, and shallow-marine subtidal. Sharp basal contacts, pebble lags, and upward-fining sand trends are characteristic of the incised valley-fill facies, which were deposited during marine transgression. Laterally discontinuous valley-fill sands have a mean permeability of 3.5 darcies. Interbedded fine-grained sand, silt, and clay characterize the estuarine deposits, which are heterogeneous and highly variable in permeability. Tide- and wave-dominated shoreline deposits consist of multiple upward-coarsening sequences of fossiliferous sands, with a mean permeability of 2 darcies. Shallow-marine subtidal deposits consist of indurated, homogenous, bioturbated sands having a mean permeability of 2.5 darcies. The overall facies-stacking pattern indicates two major transgressive-regressive sequences in the Temblor Formation, reflecting the combined influence of sediment supply and relative sea-level variations in a tectonically active setting. The contrasts in geometry and permeability between the facies are being incorporated into 3-D geological computer models for steam-flood simulations of West Coalinga Field.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado