Michael S. Clark2,
Karla E. Tucker3
(1) Texas A&M University, College Station, TX
(2) Chevron USA Production Company, Bakersfield, CA
(3) Chevron Production and Technology Company, La Habra, CA
Abstract: Characterization of Miocene Temblor Formation, West Coalinga Field, San Joaquin Basin, California: Insights into the Stratigraphic Geometry of a Transgressive Reservoir
The Temblor Formation at West Coalinga field, California is a prolific heavy-oil reservoir (12°-22° API gravity) that is part of a shallow-marine, unconformity-bound megasequence, up to 215 meters (700 feet) thick, deposited in the tectonically active San Joaquin basin during Miocene transgression. Upper and lower onlap surfaces bounding this megasequence are evident in outcrop and 3D-seismic. Two additional unconformities marked by decreasing dinoflagellate abundances subdivide the reservoir part of the megasequence into three depositional sequences. Abundant fresh-water algae, brackish-water dinoflagellates, pollen, spores and terrestrial-derived organic matter elsewhere in the megasequence section indicate fresh water input into the basin. Sharp increases in apatite abundance above two of the unconformities may indicate transgressive deposits resting on the sequence boundaries. Alternatively, river run-off increased influx of phosphorus derived from weathering of an exposed shelf. Although upwelling associated with Miocene transgression is a probable phosphorus source, river flow is a more likely source in nearshore settings.
Basal Temblor production data, well log correlations, and stacking patterns indicate that onlap at the base of the megasequence controls production of heavy oils, as well as lateral migration of steam injected into the reservoir. Onlap and truncation geometries may also control vertical steam migration between different reservoir levels. Identification of time-significant surfaces bounding flow units provides the basic framework for determining reservoir heterogeneity and continuity in the Temblor. Integrating this analysis with new reservoir characterization tools, such as 4D-seismic and flow simulation models, facilitates well placement and steam management in a complex reservoir.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana