Outcrop Quantification of Flow-Unit and Seal Properties and Geometries, Ferron Sandstone, Utah

Abstract

River-dominated deltaic sandstones of the Upper Cretaceous Ferron Member of the Mancos Shale provide the opportunity to quantify the 3-D architecture and permeability structure of fluvial, deltaic, and shorezone sandstones that are analogous to large oil and gas reservoirs of the Gulf Coast. Current investigations, working within a previously established stratigraphic framework, are aimed at quantifying flow-unit character as well as delineating bounding and sealing surfaces that cause inefficient drainage and the abandonment of conventionally recoverable hydrocarbons in reservoir analogs. Measured sections at 1-mi spacings establish the facies framework within which windows are selected for detailed study. Average permeabilities are highest in distributary-channel facies. Distributary sandstones are, however, also characterized by the highest degree of permeability heterogeneity. Lateral permeability heterogeneity, a response to lateral accretion and channel-flooring scours, is pronounced. In contrast, associated shoreface sandstones have lower average permeabilities, simple upwardly increasing permeability profiles, and a high degree of lateral continuity. Vertical heterogeneity, provided by laterally continuous mud layers, is dominant. Communication between distributary channel and associated shoreface sandstones is likely to be hindered by low-permeability (less than 5 md) zones that consistently occur at the base of channel sandstones and along the toesets of lateral accretion surfaces.