Three-Dimensional Distribution of Lithofacies, Bounding Surfaces, Porosity, and Permeability in a Fluvial Sandstone--Gypsy Sandstone of Northern Oklahoma

Where it was studied at two sites in north-central Oklahoma, the Gypsy sandstone of the Pennsylvanian Vamoosa Formation provides significant insights into the controls on reservoir quality in a meandering river deposit. At an outcrop site west of Tulsa, a three-dimensional architectural framework, based on erosional surfaces, allowed the recognition of a channel-fill sequence consisting of six channel sand bodies and representing at least three channel belts. Belts are vertically stacked and are incompletely separated by low-permeability flood-plain deposits, which are locally eroded. Porosity and permeability are primarily related to depositional facies. Within channel belts, mudclast lags associated with erosion surfaces at the base of channels have the potential to act as vertical permeability baffles between channel sand bodies, as do mud-draped lateral accretion surfaces within channel sand bodies. At a subsurface site 31 km (19 mi) to the west of the outcrop site, nine wells were drilled and cored through the Gypsy interval. At this site, it was possible to identify and correlate three channel belts comprising amalgamated channel sand bodies. Although lower level architectural elements could be recognized in cores, they could not be correlated with confidence given a 100-m (330-ft) well spacing.