S. A. Reid1, J. L. McIntyre1
(1) Occidental of Elk Hills, Inc, Tupman, CA
ABSTRACT: Geologic Controls on Petroleum Production From Monterey Formation Quartz-Phase Porcelanite Reservoirs, Elk Hills Field, Kern County, California
Quartz-phase porcelanite reservoirs produce significant volumes of petroleum at the Elk Hills field in California's San Joaquin basin. Porcelanite occurs within the highly siliceous upper Monterey Formation and represents the final product of a diagenetic process that converts diatom-rich deposits to microcrystalline quartz. Reservoir intervals contain predominantly porcelanite that is finely laminated with siliceous shale and interbedded with sandstone and dolomite. Typical porcelanite composition is 60 to 90 percent microcrystalline quartz, 10 to 40 percent detritus, and minor amounts carbonate, pyrite and organic material. The highly porous matrix contains microcrystalline quartz in clusters 1 to 5 microns in diameter, and microcrystalline quartz cement that binds clusters and coats the walls of pores. Between the quartz clusters are oil-bearing pores ranging in size from 0.2 and 2.0 microns in diameter. Effective porosity averages between 20 and 25 percent, but matrix permeability averages only 0.8 md because of small, irregular-shaped pores and highly tortuous flow paths. Reservoir intervals contain natural fractures that occur parallel with and perpendicular to bedding. Fracture frequency and associated permeability is difficult to estimate, but fractures are believed to contribute to depletion of the porcelanite matrix. Cumulative oil production at Elk Hills from quartz-phase porcelanite and associated rock types is over 80 million barrels. Wells are subject to formation damage during drilling because of small pore throat diameter and high clay content, and require stimulation to effectively produce.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado