Pore-Filling Clays and Their Impact on Reservoir Quality Parameters in Pennsylvanian Sandstones of the Anadarko Basin, Oklahoma

Abstract

The role of clay minerals in sandstone reservoirs has increasingly gained importance over the last few decades owing to the fact that clays readily occlude primary porosity and permeability, influence different petrophysical parameters, and react with drilling fluids thus affecting various oil recovery practices. Pennsylvanian sandstones of the Anadarko Basin in Oklahoma remain under-researched in that regard. By conducting a thorough analysis of clay parageneses, this study aims to shed more light on sandstone reservoir characteristics and ultimately achieve a better constraint of the basin’s burial history.

Approximately 552 feet of core from two discrete wells specifically targeted a Pennsylvanian sandstone succession in the Anadarko Basin were analyzed using thin-section petrography, scanning and automated electron microscopy (SEM-EDS and QEMSCAN^®), and X-ray diffractometry (XRD). The sandstone succession is comprised of interlaminated shaly sandstones to massive homogenous sandstones bounded by thick black shale intervals. Preliminary interpretation of QEMSCAN^® data points to quartz and feldspar as the major mineral constituents of these sandstones. Carbonate cementation is widely present while pore-filling clays are dominantly of illitic and chloritic mineral chemistry. Measured porosity ranges from 5 to 10% and is in good agreement with 3D porosity results obtained from the conventional core analyses. XRD clay mineralogy further refined the pore-filling clay constituents, identifying detrital illite, mixed-layered illite-smectite (I-S), chlorite, and minor kaolinite minerals. Preliminary SEM-EDS investigation revealed authigenic I-S and chloritic minerals effectively filling porosity at certain depth intervals. Yet, more work is needed to deduce possible patterns linking stratigraphical facies, burial depths, and rock geochemistry with prevalent clay diagenesis trends.

Further data analyses and identification of distinct stratigraphical units, in concordance with the detailed quantification of porous clay content, will have a decisive impact on reservoir porosity calculation from density-based wire-line logging as well as future research seeking to reconstruct the stratigraphic distribution of reservoir properties in Pennsylvanian sandstones of the Anadarko Basin.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018