Stratigraphic Architecture and Facies Distribution Within the Wall Creek Member of the Frontier Formation, Western Powder River Basin, Wyoming

Abstract

Understanding facies distributions and stratal architectures is critical for accurate prediction of hydrocarbon production from reservoirs formed by ancient deltaic deposits. In practice, prediction of facies and architecture commonly relies largely on values calculated from petrophysical logs or interpreted from geophysical properties. Integration of sedimentary data and geometric relationships from outcrop analogues provides a powerful means to improve understanding of the heterogeneity within deltaic reservoirs. Excellent exposures of the Wall Creek member (WCM) of the upper Cretaceous Frontier Formation on the western margin of the Powder River Basin (PRB) provide a unique opportunity to study the lateral and stratigraphic complexity of a tide and wave influenced low accommodation delta system. Within the outcrop study area, the WCM exhibits a complex stratigraphic architecture and facies distribution that changes vertically and laterally at scales relevant to the resource development of this unit. The thickest section of the WCM is 32m thick and observed along the Wall Creek Road (WCR), near the center of the study area. The WCM thins dramatically both to the north and south of the WCR, comprising ∼18m in northernmost sections and ∼20m in southernmost section included in this study. Associated with the thickness changes are strong along strike facies variations including changes of grain size, lithology, bedding thickness, sedimentary structures and ichnofauna. These lateral facies variations integrated with paleocurrent data indicate that the WCM has been deposited as a complex system of wave and tidally influenced delta lobes. The thickest section in the study area is the sediment fairway of one delta lobe that gradually thins to the south. The thinner sections to the north are the distal portions of a second delta lobe that was sourced from a source to the northwest. In addition to lateral variations, the WCM reveals a temporal change from wave and storm-dominated asymmetrical deltas in the lower portion of the WCM, to tidally influenced delta systems being the primary delta type in the upper part of the stratigraphic succession. Results from this outcrop analysis reveal a better understanding of the complex facies distribution and architecture in a mixed tidal and wave influenced delta, and can be applied directly to active exploration and production efforts involving the Frontier Formation to the east within the PRB.

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