CLARK, W. J., S. D. STURM, C. A. HINSON, L. W. EVANS, N. S. SAGAR, GeoQuest Reservoir Technologies, Inc., Denver, CO; and D. N. BURCH, The Discovery Group, Denver, CO

Abstract: Reservoir and Sweet Spot Characterization of Tight Gas Sandstone -- The Siberia Ridge Field, Wamsutter Arch

Siberia Ridge Field is located on the Wamsutter Arch in the eastern Green River Basin. Since discovery in 1975, 67 BCF has been produced from 133 wells from the Cretaceous Almond Formation. Completion data indicates most production is derived from the "Bar" sequence at the top of the formation. The purpose of this study was to characterize and define sweet spots within this low-permeability sandstone reservoir by integrating geologic, petrophysical, geophysical, and fracture attributes.

The Almond Formation was subdivided into 8 reservoir zones based on semi-continuous coals and carbonaceous shales. Discontinuous, tidally dominated deposits characterize the lower Almond, whereas the upper zone (Almond "Bar") is comprised of amalgamated shoreface sequences dissected by a northeasttrending fluvial sequence. Analysis and mapping of petrophysical properties identified better reservoir quality within the fluvially deposited rocks.

Understanding of the field was accelerated by the acquisition of a 36 mile 3-D Survey in 1995. The Almond dips toward the NE at about 150 to 200 ft per mile. Attribute mapping reveals that discrete northeast and northwest fracture domains within the field coincide with regional lineament trends. In Siberia Ridge, these inherent linear features controlled the distribution of lithofacies and thickness changes throughout Almond deposition.

Sweet spots were defined based on a statistical analysis of total gas production over various time intervals. Hierarchical analysis of integrated geophysical, stratigraphic and petrophysical datasets indicate these sweet spots are coincident with coal thickness, fracture domains and increased permeability (KH) associated within the fluvially dominated "bar" facies.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana