ABSTRACT: Internal Architecture and Permeability Structure of a Distributary Channel within a Strongly Progradational, Fluvial-Dominated Deltaic System, Cretaceous Ferron Sandstone, East-Central Utah

BARTON, MARK D., Bureau of Economic Geology, University of Texas at Austin, Austin, TX, and NOEL TYLER, University of Texas at Austin, Austin, TX

The influence of facies architecture on permeability structure within an individual distributary channel sandstone was determined in a large distributary channel (500 ft wide and 70 ft thick) in a fluvial-dominated deltaic unit of the Cretaceous Ferron Sandstone, Utah. The channel complex is composed of a series of vertically stacked macroforms on the order of 100 to 500 ft wide and tens of feet thick. The channel fill is sand rich and is dominated by trough cross-bedding. Grain size (fine to very coarse) displays overall an upward-fining trend but with notable variation. Minipermeameter data were collected along a series of equally spaced (50 ft) vertical transects. In addition, a large grid (24 by 30 ft with 1 ft sample spacing) and a series of vertical and horizontal transects at 0 25 ft spacing were constructed in order to examine fine-scale permeability variation. Grain size, stratification type and discontinuities, and geometric attributes of component facies were mapped in the channel deposit by inspection and from photomosaics.

Permeability varies considerably within the channel fill (less than 0.1 md to greater than 1000 md). Both lateral and vertical variations are controlled by the internal geometry of bounding elements. Sources of permeability variation correlate with grain size and the presence of bounding elements. In general, increases in permeability correspond well with increases in grain size except at bounding elements where the lowest permeabilities within the channel fill are recorded. Permeability decreases across bounding elements, a decrease that in some cases approaches four orders of magnitude over the distance of several feet. In addition, these bounding elements also serve to define the boundaries of distinct permeability groupings.

Permeability structure within the distributary channel fill is defined by the bounding elements that separate macroforms. Hence, permeability zonation approximates macroform geometries, and individual zones are on the order of 100 to 500 ft in width and several tens of feet thick. In a similar fashion, zones of relatively homogeneous permeability distribution are defined by higher-order bounding elements that exist internally within the macroform and are on the scale of 10 to 100 ft in width and up to 10 ft thick.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)