Stacking Patterns and Petrographic Analysis of Slurry Beds of the Wilcox Formation, Gulf of Mexico: Implications for Flow Evolution and Depositional Setting

Abstract

The Paleogene Wilcox Formation has been an important reservoir target for over a decade in the central-western Gulf of Mexico. Although known to contain vast quantities of hydrocarbons, reservoir quality issues have created significant challenges for the exploration and development efforts of the Wilcox play. This poor reservoir quality appears to be a direct result of the Wilcox Formation being comprised of a relatively high proportion (>25% by thickness in the Stones field cored intervals) of event beds which were deposited by flows that were either transitional between fully turbulent and laminar (deposits termed here as slurry beds) or quasi-laminar (i.e. debris flows). The high clay content of these beds substantially decreases reservoir quality. Although numerous studies have focused on slurry beds and the Wilcox, key uncertainties remain regarding the depositional setting(s) of slurry beds and the character of their depositing flows. Many examples from outcrop, core, and the modern sea floor suggest that these types of beds are common in unconfined, distal portions of submarine fans. However, it has also been suggested that slurry beds may be associated with channelized environments. The apparent occurrence in quite disparate depositional settings, along with the substantial variety of observed bed types, has complicated efforts to produce generalized models of these hybrid flow types and to predict the distribution of their deposits. In order to address these issues, we provide new sedimentological observations of nearly 1200ft of core from the Wilcox in the Stones Field. We conducted Markov chain analyses of 2200 beds to investigate stacking patterns and elucidate the stratigraphic distribution of slurry beds. Our results suggest that slurry beds at the Stones field appear to have two broad genetic associations, occurring interstratified with what are interpreted to be both high-energy, channel-type deposits and low-energy lobate deposits. Additionally, they have a strong propensity to occur in packages, as evidenced by the repetitive stacking of slurry bed on top of slurry bed. Petrographic and XRD data are utilized to aid in understanding the differences in texture and clay content between the various types of slurry beds and more typical sandstones and indicate that subtle differences in clay content alone can dramatically influence the sedimentological character and the permeability of deep-water deposits.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015