Sediment transport and regional upwelling during Late Devonian Woodford deposition in Oklahoma and its influence on drilling, completions, and production.

Abstract

The Woodford Shale in Oklahoma is an organic-rich, dark grey Upper Devonian to Lower Mississippian marine mudstone that is a major hydrocarbon source rock. Since the mid-2000's, it has become a significant unconventional resource play and a prolific producer of hydrocarbons across Oklahoma. In the deep parts of the Anadarko Basin, it reaches a thickness of more than 900 ft. The Woodford is unlike many organic-rich shales, particularly those deposited in the Western Interior in that it cannot be directly linked to large, up-dip fluvial systems. Like carbonates, the Woodford is composed of a significant volume of grains such as intraclasts and bioclasts derived from both the water column and sea-floor. Much of the Woodford was deposited under strong marine upwelling conditions with a significant terrestrial input of clays and silt from eolian influx. Clay and detrital silica (silt) are found in both near-shore and more distal, upwelling-dominated facies. Upwelling facies are associated with high TOC, reworked pyrite framboids, phosphate grains and nodules, algal cysts, and a “chert” facies derived from biogenic silica (radiolarians). Terrestrial input is associated with clay, detrital silt, and terrestrial organics but are depleted in phosphate and biogenic silica. More coastal facies also contain concentrations of conodonts, large algal cysts (Tasmanites), linguloid brachiopods, fish scales, and bioturbated intervals. The upwelling facies dominated the Arkoma and portions of the southeastern margin of the Anadarko basins. Near-shore transport of sediments are apparent by the preservation of clinoforms which are oriented roughly east to west in the Arkoma Basin and west to east and locally southwest to northeast in the Anadarko Basin. Orientations of clinoforms may reflect submarine currents around the Nemaha Ridge, which separated the basins during most of Woodford deposition. The relative importance of these two sources of sediment can be linked to drilling, completions, and production.

AAPG Datapages/Search and Discovery Article #90214 © 2015 Southwest Section AAPG Annual Convention, Wichita Falls, Texas, April 11-14, 2015