BRITTON, ALLEN W., Core Laboratories, Bakersfield, CA, and GARY L. NOLEN, Core Laboratories, Houston, TX

ABSTRACT: Influence of Mineralogy and Texture on Porosity and Permeability of Diatomites

Accurate porosity and permeability values are fundamental inputs into any formation evaluation program. While conventional core material is the best source of representative formation material for physical properties determination, economic constraints and/or wellbore problems often require the substitution of sidewall core samples instead. Unfortunately, the process of physically taking a percussion sidewall core severely alters pore geometry; resulting in nonrepresentative porosity and permeability values being reported.

A study was begun in January 1992 on conventional and sidewall core samples from the Mobil Oil Corporation "Belridge V" 8360A-2 well. The purpose of this study was threefold: to evaluate the factors controlling matrix porosity and permeability of diatomaceous (opal-A and opal-CT) reservoirs; to quantify pore geometry alteration induced in diatomite percussion sidewall-core samples; and to apply the results of this investigation to the problem of accurately determining porosity and permeability in diatomaceous reservoirs using percussion sidewall-core samples.

Equations relating the influence of mineralogy and texture on porosity and permeability are presented and evaluated. Comparisons are made with porosity and permeability values determined from conventional core samples, traditional core analysis, and values generated by mineral and textural analysis. Pore geometry alteration induced in sidewall core samples is investigated and corrections are presented. Finally, the results of this study are applied in an attempt to explain and predict porosity and permeability (air and liquid) in diatomite reservoirs.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.