ABSTRACT: Reservoir Characterization of Tensleep Sandstone (Pennsylvanian-Permian), South Casper Creek Field, Natrona County, Wyoming

Rex D. Cole, Christopher E. Mullen

Eolian facies of the Tensleep Sandstone are the main producing intervals for low-gravity oil at South Casper Creek field. Based on study of cores (N = 10) and logs, the Tensleep is divided into an upper sandstone member and a lower carbonate member, which average 160 ft (49 m) and 150 ft (46 m) in thickness, respectively. Production is mainly from the sandstone member.

Packages of eolian sandstone in the sandstone member range in thickness from 15 to 38 ft (5 to 12 m) and are separated by thin, laterally continuous interdune and erg-margin deposits, characterized by burrowed dolomitic sandstone and sandy dolomite. Eolian stratification is composed of wind-rippled grain-flow lamination (58%), wind-ripple lamination (31%), grain-flow lamination (11%), and grain-fall lamination (<1%). Cross-strata sets range in thickness from 0.1 to 29.2 ft (0.03-8.9 m), and average 1.8 ft (0.55 m). Dipmeter and oriented-core data (one well) indicate that foreset-dip azimuths are to the south and southwest.

Hydrocarbon flow units have porosity, horizontal permeability, and vertical permeability ranges of 20.7-21.6%, 638-750 md, and 468-491 md, respectively, whereas flow barriers have ranges of 11.0-17.9%, 22-259 md, and 14-117 md, respectively. Grain-flow sandstone has the best average porosity and horizontal permeability (24.4%, 1580 md), followed by wind-rippled grain-flow sandstone (22.1%, 806 md), and wind-rippled sandstone (18.3%, 293 md).

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990