Impact of Lithofacies Architecture and Distribution on Fluid Flow: Examples from the Cretaceous Ferron Sandstone, East-Central Utah

Stephen H. Snelgrove, Craig B. Forster, Ann Mattson, and Marjorie A. Chan

Detailed outcrop studies of the Cretaceous Ferron Sandstone reveal the spatial relationships between facies in a fluvial-deltaic system. Outcrop data include detailed and regional geological mapping, gamma ray transects, and core plug transects. These data are supplemented by laboratory measurement of plug porosity and mini-permeater measurement of plug permeability, petrographic analysis of plugs, "behind-the-outcrop" coreholes, detailed mini-permeameter measurements on these cores, and wireline logs. Prograding delta front clinoforms within the seaward-stepping Kf-1 parasequence show a systematic decrease in permeability from the proximal delta front (k_avg approx. ~20 md) to the distal delta front (k_avg < 2 md). This trend correlates with, and i likely a consequence of, similar trends in sedimentary structures and grain size. Grain size and sandstone:shale ratio both decrease in the depositional dip direction. In the proximal delta front clinoforms are commonly bounded by thin (< 10 cm), discontinuous siltstone and mudstone that act as baffles to flow, partially segregating clinoforms from each other. Vertically stacked wave-modified delta deposits within the Kf-2 parasequence set contain the cleanest sands. These sands also have the highest permeability (k_avg > 100 md). Individual parasequences are up to a few 10s of meters thick, are areally extensive, and are often isolated from one another by nearly continuous mudstone and siltstone up to a meter thick. Multiphase flow simulations illustrate how lithofacies architecture and the juxtaposition of related lithofacies impact reservoir efficiency.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California