Sedimentological and reservoir characteristics of a fluvial-dominated delta-front sequence: Ferron Sandstone Member (Turonian), East-central Utah, USA

Abstract

Abstract Exposures of the Ferron Sandstone Member (Turonian) of the Mancos Shale Formation in east-central Utah offer an opportunity to examine the dimensions of delta-front reservoir elements and their associated heterogeneities. Field mapping within the Ferron Sandstone has demonstrated that distributary mouth-bar facies have maximum lengths of 8–9 km and maximum widths of 4–6 km. Distributary channel width-to-thickness ratios commonly have values between 10:1 and 20:1. Distal bar sandstone thicknesses and shale lengths are dependent upon their location within the mouth-bar. Distal bar shales are shortest within the proximal region of the mouth-bar, where amalgamation of distal bar sandstones is greatest. 850 field minipermeameter measurements were obtained from the various facies elements of a distributary mouth-bar sandbody. The data display significant correlation between facies elements and permeability structure. Trough cross-bedded upper mouth-bar facies exhibit the highest means and lowest coefficient of variation. Muddy and bioturbated distal bar facies exhibit the lowest means and highest coefficient of variation. The permeability distributions appear to be related to the degree of heterogeneity, and show increasing left-skewness with increasing heterogeneity. Fluid flow simulations of two geological models of a distributary mouth-bar were conducted to assess the effect of permeability contrasts on predicted reservoir behaviour. One of the models depicts a lithologically homogeneous mouth-bar, while the other depicts a mouth-bar that is composed of two internal facies elements (lower and upper mouth-bar). Results of the simulations show that up to 30–45% difference in predicted water breakthrough can occur between the two models.