AAPG Bulletin, V. 84, No. 8 (August 2000), P. 1173-1184.

Porosity Reduction During Diagenesis of Diatomaceous Rocks¹

Caren Chaika² and Jack Dvorkin³

©Copyright 2000. The American Association of Petroleum Geologists. All rights reserved.
¹Manuscript received February 10, 1998; revised manuscript received January 13, 2000; final acceptance February 15, 2000.
²Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305. Present address: Occidental of Elk Hills, P.O. Box 1001, Tupman, California 93276.
³Geophysics Department, Stanford University, Stanford, California 94305.
We are thankful to a number of sources for donations of samples and data. Core and associated data from wells at Asphalto, Cymric, and McKittrick were provided by Chevron (Steve Smith, Bruce Bilodeau, and Tom Zalan, among others). Data and core from a well at South Belridge were provided by Mobil (Bob Timmer), and the Core Warehouse at the California State University at Bakersfield provided data and core from a Shell well at North Belridge. Mineralogy, porosity, and density of all San Joaquin Valley samples were measured at Core Lab in Bakersfield, California. The Stanford Rock Physics Laboratory provided facilities for supplementary core measurements. Steve Graham and Loretta Williams gave important inputs to our understanding of the processes discussed. Reviews by Raymond Siever, Salman Block, and an anonymous reviewer greatly improved the clarity of the manuscript. The work was supported by the American Chemical Society Petroleum Research Fund Grant ACS-PRF no. 32743-AC2 and by Norsk Hydro.

ABSTRACT

With lithification and burial, diatomaceous rock transforms from opal-A to opal-CT and then quartz. This study documents two different patterns of porosity reduction and their associated mineralogical and density changes using samples from the Monterey Formation, California. Samples that have one set of properties are called group 1, and those showing other trends are assigned to group 2.