ABSTRACT: Facies-Related Permeability Trends in the Frontier Formation along the Moxa Arch, Green River Basin, Wyoming

H. Scott Hamlin, Robert L. Buehring

In the western part of the Green River basin, the Frontier Formation comprises marine and nonmarine sandstone and shale facies, which record early Late Cretaceous foreland-basin sedimentation. Diporiented fluvial channel-fill sandstone and strike-aligned marine shoreface sandstone are enclosed in coastal-plain and nearshore-marine shale and sandy shale. The Frontier sandstone facies form a major low-permeability gas play in the Green River basin. Frontier reservoirs typically lie in laterally extensive but shale-rich sandstone "benches" that contain variable amounts of clean sandstone in which porosity and permeability are best developed.

Studies of core show that the clay plus silt (mud) component of Frontier reservoirs is an important control on porosity and permeability and that detrital mud content is related to depositional environment. Unlaminated mixtures of sand and mud typify bioturbated shoreface facies, whereas in channel-fill facies mud occurs as rip-up clasts, drapes, and interlayers. Shaly sandstone facies generally have permeabilities less than 0.5 md (commonly less than 0.1 md). Clean sandstone, having permeabilities between 0.1 and 10.0 md, is most commonly found in units having well-developed cross-stratification or planar lamination.

Gross sandstone thickness can be obtained from the gamma-ray log alone, but net clean sandstone in the Frontier is most reliably interpreted using SP, gamma-ray, and resistivity logs in conjunction. More sparsely distributed core and porosity-log data are used to calibrate log responses. For this study logs from more than 700 wells and cores from 15 wells form the database for regional and field-scale sandstone mapping. Netclean-sandstone maps reveal facies-related trends, which can be extended into sparsely drilled areas, and therefore are useful in guiding strategies for development in low-permeability gas-bearing Frontier sandstones.

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