Regional Variations in Woodford Fm Facies and Depositional Environments in the Permian Basin: New Insights From Chemostratigraphic Data

Abstract

Despite its status as the primary source of hydrocarbons in Permian Basin reservoirs and the recent emergence of similar source rock successions as unconventional reservoir plays, the Devonian Woodford Fm is not well known. To better understand these rocks we combined integrated chemostratigraphic techniques (XRF, XRD, TOC, pyrolysis, and stable isotope analysis) with more conventional methodologies (microscopy, biostratigraphic data, and wireline log analysis) to define regional and local variations in facies and depositional setting across the region. Collectively, these data demonstrate the interplay of the two dominant sediment supply mechanisms that characterize most mudrock systems: detrital sediment flux from proximal (landward) areas and oceanic flux from distal (basinward) areas. Proximal Woodford deposits are characterized by well-oxygenated, relatively high energy, quartz and clay mineral rich, burrowed to ripple laminated mudrocks and siltstones and less common fossiliferous lime mudstones. Distal facies, in contrast, comprise organic matter rich, highly siliceous mudrocks composed primarily of biogenic silica, much lower amounts of clay minerals, and organo-genic dolomite indicative of anoxia. Updip areas in the basin display upward-deepening successions in which basal proximal facies are overlain by more TOC-rich mudrocks containing mixtures of detrital and biogenic silica. In contrast, although downdip successions display locally well-developed cyclicity, apparently the result of fluctuations in bioproductivity, they display no indications of changes in water depth or sea level controlled sediment flux. Integrated wireline log and biostratigraphic data suggest that regional facies patterns are complicated by the inherited topography of the differentially eroded and tectonically deformed underlying Siluro-Devonian carbonates. These findings demonstrate the complexities of the Woodford succession and the necessity of employing multidisciplinary methods of investigation to characterize them.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016