Deep-Water Reservoir Quality Prediction of the Norphlet Formation (EGoM) Using Clay Coat Analysis and Sandstone Petrography

Abstract

The Norphlet Formation is an extensive eolian conventional play in the eastern Gulf of Mexico (EGoM) that has proven to be highly economical. This study aims to identify the clay coat prevalence between linear and isolated barchan dune facies within the Jurassic Norphlet Formation to improve predictions of reservoir quality within eolian sandstone facies/systems. This work will test the hypothesis that isolated barchan dune facies will contain a greater proportion of mobilized dune sand particles, which will result in a decrease in the prevalence of clay coatings and an increase in quartz cement. Understanding clay coatings on sand grains is essential for reservoir studies because the clay coats helps combat porosity loss with increasing depth and degree of diagenesis. The thickness variability of the Upper Tight Zone of the Norphlet and underlying reservoir facies across the extent of the Norphlet erg is controlled by subsidence of the dune into the underlying Louann Salt, but there is little information regarding how variation of in dune morphology may have influenced clay coat development. Cores will be logged from the Hatter’s Pond and Flomaton field’s in Alabama available from the Geological Survey of Alabama. Hatter’s Pond eolian sandstones are interpreted to be linear dunes whereas Flomaton eolian sandstones are interpreted to be of isolated barchan dune type. Cores will be logged in order to identify dune facies, determine eolian cross-bed thickness, and identify the boundary between the cemented Upper Tight Zone and the underlying porous reservoir facies. Core intervals will be selected for sampling from thin-section analysis available from the Geological Survey of Alabama. Optical petrography and image analysis software will be used to measure the frequency and distribution of clay coats in thin-section. The percentage of grain boundary that is coated with clay will be determined for all clay-coated grains observed in each thin-section. Scanning Electron Microscopy (SEM) technology will be utilized to determine clay coat crystal morphology, asses clay minerology, and measure clay coat thicknesses. Observations of clay coats will be compared to sandstone grain size, framework grain composition, and previous detrital zircon provenance. A statistical analysis will be performed to place various clay coat attributes within a specific reservoir facies. The results of this study will determine if the specific dune type and associated migration behavior impact overall reservoir quality and exert control on the thickness of the Upper Tight Zone. This is imperative to petroleum geology of the Gulf Coast region because this knowledge can help guide exploration efforts in the Norphlet Formation while decreasing drilling risk.

AAPG Datapages/Search and Discovery Article #90351 © 2019 AAPG Foundation 2019 Grants-in-Aid Projects