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AAPG Bulletin

Abstract

(Begin page 169)

AAPG Bulletin, V. 85, No. 1 (January 2001), P. 169-189.

Copyright ©2001. The American Association of Petroleum Geologists. All rights reserved.

Monterey Formation porcelanite reservoirs of the Elk Hills field, Kern County, California

S. A. Reid,1 J. L. McIntyre2

1Occidental of Elk Hills, Inc., P. O. Box 1001, Tupman, California, 93276; email: [email protected]
2Occidental of Elk Hills, Inc., P. O. Box 1001, Tupman, California, 93276; email: [email protected]

AUTHORS

Stephen Anthony Reid is a senior geological advisor for Occidental of Elk Hills, Inc. He received his B.S. and M.S. degrees from California State University, Northridge. His work on the Miocene reservoirs of Elk Hills has focused on the identification of trapping characteristics of Stevens turbidite systems and on development of reservior models for Monterey Formation porcelanite reservoirs.

Jana McIntyre works as a development geologist for Occidental of Elk Hills, Inc. She has worked on several Miocene Monterey Formation turbidite and porcelanite reservoirs at Elk Hills and is currently working on shaly sandstone reservoirs of the Pliocene Etchegoin Formation. She received her geology degrees from the University of California at Davis (B.S.) and Oregon State University (M.S.).

ACKNOWLEDGMENTS

We appreciate the contributions of the following individuals in preparing this reservoir model: Tor Nilsen for Monterey facies identification; JoAnn Conard for fracture descriptions; Drew Dickert, Greg Lord, and Bob Horton for observations on microscopic textures; and Tom Hampton for reservoir engineering comments. Jim Rogers, Mark Longman, Richard Behl, and Ray Sorenson provided helpful suggestions on improving the initial manuscript. We also thank the management of Occidental of Elk Hills, Inc., for permission to publish this article.

ABSTRACT

Oil and gas production from Monterey Formation porcelanite at the Elk Hills field in California's San Joaquin basin occurs from intervals that have quartz-phase mineralogy. However, characteristics differ from chert and porcelanite reservoirs of the coastal California Monterey Formation in that matrix porosity is more typical of the opal-CT phase, petroleum storage is mostly in the matrix, and natural fracture patterns are dominantly small scale. Several Elk Hills reservoirs located on two large anticlines produce from porcelanite. The 29R AB and 31S D are the most productive porcelanite reservoirs, each having cumulative oil production of about 40 million bbl. Although interbedded with siliceous shale, sandstone, and dolomite, most of the porous reservoir rock is laminated porcelanite. Porosity averages between 20 and 25% and is evenly distributed throughout the porcelanite as extremely small pores ranging in size from 1 to 10 µm. Matrix permeability averages 0.8 md, but flow of oil and gas is enhanced through fractures parallel with and perpendicular to bedding. Higher than anticipated porosity may be in part due to migration of hydrocarbons into the porcelanite reservoirs while still in opal-CT-phase mineralogy. The dissolution of opal-CT and precipitation of quartz occurs in place, and the resulting quartz-phase mineral structure mimicks the porous opal-CT framework.

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