Abstract

Problems of accumulation of oil and gas in the Newcastle sandstone, (Upper Cretaceous) involve facies changes from shale to sandstone which are recognized most clearly in the Mush Creek and Skull Creek Area. Well sample and electric log information from 200 wells in the area has afforded details to classify five sand beds which underlie the datum bed at the top of the Newcastle sandstone. The structure on outcrops and on the subsurface datum bed is a monoclinal southwest dip of approximately 2 degrees, formed in post-Cretaceous time, Laramide orogeny. The type log describes the lithology of the five sand beds and shale inter-beds. Cross-sections and lithofacies maps of the respective sand beds illustrate the facies changes in the Newcastle sandstone. The accumulation of oil in the area is directly related to the porosity, permeability, and the thickness of each sand bed. The post-Cretaceous monoclinal south west dip on the Newcastle sandstone does not form a structural trap, and does not appear to have caused any appreciable migration of the oil in the respective sand beds. The oil accumulation is closely related to the local stratigraphic and geographic site of the origin of the oil. Recognition of litho-facies changes in the Newcastle sandstone now has been widely accepted and is being utilized in a broad exploratory program.