Integrated petrographic and petrophysical study of the Smackover formation, Womack Hill field, Clarke and Choctaw counties, Alabama

Abstract

The objective of this study was to describe depositional and diagenetic characteristics of the Oxfordian (Jurassic) Smackover formation in Womack Hill field, Alabama, as part of an integrated reservoir description program. In order to understand the distribution of reservoir units, this study utilized an integrated array of data from core lithological descriptions, borehole logs, core reports, thin section petrography, porosity and permeability measurements on core plugs, and mercury injection capillary pressure (MICP) measurements. These data made it possible to establish reliable measures of reservoir quality by comparing pore geometry with pore type; then determining which pore types correspond with highest porosity-permeability paired values. Pore aperture (throat) median sizes measured by mercury capillary pressures were tested for correspondence with porosity, pore type, permeability, and saturation in order to establish quality rankings for the reservoir units.This study aims to bridge the gap between petrological and petrophysical studies, merging the data into a comprehensive model. This model, instead of mapping facies based solely on lithology, or flow units based only upon permeability, depicts petrofacies, with each petrofacies having distinct porosity, permeability, and capillary pressure ranges. These characteristics are related to specific lithologies, pore types and diagenetic processes. The resulting combinations are grouped into good reservoir quality rock, intermediate reservoir quality, or baffles, and poor quality reservoir material, or barriers. These zones were then put into a stratigraphic context, allowing for a better understanding of the effects of pore categories, original depositional texture, and diagenetic influences on the distributions of the reservoir quality zones. By incorporating these quality zones, or petrofacies units, with core lithological descriptions and petrophysical data curves, such as porosity and permeability on a cross section, a much more comprehensive model of the field emerges. While in this study, mapping these petrofacies between wells was not possible; this method resulted in the identification of several zones of potentially bypassed pay.