Facies Relationships and Statistical Measures for Reservoir Heterogeneities in the Cretaceous Ferron Sandstone, Central Utah: ABSTRACT

Abstract

The Cretaceous Ferron Sandstone of the Mancos Formation is a wave modified fluvial-deltaic system containing seven parasequence sets. The lower two sea-ward-stepping parasequence sets Kf-1 and Kf-2, are the focus of this reservoir erogeneity study. Statistical summaries of lithologic parameters are used to evaluate the distribution of permeability data for up-scaling in fluid flow simulation. The database consists of measured sections, cored drillholes, permability, petrography, and scaled photomosaics. The area is studied at two scales: (1) 2.5 x 2.9 km covering the Kf-1 and Kf-2; and (2) 0.8 x 0.8 km centered on prograding clinoforms in a parasequence within the Kf-1. Four facies are characterized in terms of sedimentary structure, grain size, bedding thickness, % sandstone, and geometry. The proximal delta front facies is > 95% fine-grained, horizontal and trough cross-stratified sandstone. The medial delta front facies is 85% fine-to very fine-grained, horizontal-stratified sandstone (15% shale). The distal delta front facies is 60% very fine-grained sandstone (40% shale) and contains the highest degree of burrowing. The mouth bar facies is > 99% medium- to fine-grained sandstone, and is dominantly trough cross-stratified. Petrographic samples from each facies indicate complex diagenesis with up to 5 stages of cementation. Highest permeabilities (attributed tomore » secondary porosity) correlate to the coarsest sandstone lithologies. Permeabilities in fine-grained sandstones are uniformly low (several md) with the exception of some secondary porosity in bedding-parallel, gypsum microfractures. These statistical measures allow quantification of reservoir heterogeneity at the parasequence level. Lithofacies maps allow visualization of these data. The Kf-1 clinoform surfaces (2-D) are generated deterministically from photomosiacs, and Kf-2 unit surfaces (3-D) are generated by kriging data points derived from photomosaics and well data.« less