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

COLE, REX D., Unocal Corporation, Brea, CA, and CHRISTOPHER E. MULLEN,* Unocal Corporation, Casper, WY

South Casper Creek field produces from the upper eolian sandstone facies of the Tensleep Sandstone. The productive interval averages 160 ft (49 m) in thickness and is subdivided into six mappable units, A through F. Average porosity, horizontal permeability, and vertical permeability in the productive sand facies of the reservoir ranges from 20.7-21.6%, 638-750 md, and 468-491 md, respectively. Ten main stratification types have been identified from detailed core study (N = 10) at South Casper Creek. The eolian stratification is composed of wind-rippled grain-flow lamination (58%), wind-ripple lamination (31%), grain-flow lamination (11%), and grain-fall lamination (<1%). Grain-flow laminated sandstone has the best average porosity and horizontal permeability (24.4%, 1580 md), foll wed by wind-rippled grain flow (22.1%, 806 md), wind-rippled sandstone (18.3%, 293 md), and interdune dolomitic sandstone (16.4%, 129 md). 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). Foreset dip azimuths measured from oriented-core and dipmeter data suggest that sand transport was dominantly to the south and southwest. Measured permeability was greatest at 140-160 (320-340 bipole), approximately perpendicular to the average paleowind direction, and nearly parallel to the structural axes of the field. Fractures are considered important for reservoir transmissivity. In the main reservoir, interval fractures typically are planar to slightly curviplanar, less than 0.5 mm in width, greater than 5 ft (1.5 m) long, have average dip magnitud s of about 65 degrees, and bimodal strikes. The primary strike direction of fractures in the #10-6-3 core and FMS log are N85 degrees W (slightly oblique to the structural axis), the secondary strike averages N10 degrees E.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)