Outcrop-to-Subsurface Correlation of the Blackhawk Formation, Uinta Basin: Shoreline Trends, Parasequence Distributions, and Gas Production

Jeffrey A. May¹, Donna S. Anderson¹, Roger W. Falk¹, and Anne Grau^2
1EOG Resources, Inc., Denver, CO
²Newfield Exploration, Denver, CO

Whereas superb outcrops of the early Campanian Blackhawk Formation along the Book Cliffs in eastern Utah have been the topic of over 100 papers, little has been published on its subsurface distribution to the north and northeast. Dense drilling in Natural Buttes Field, eastern Uinta Basin, combined with recent wells to the west, provide dip and strike control on subsurface configuration. Depositional and chronostratigraphic relationships identified from outcrop tie directly to well logs.

Members of the Blackhawk - Spring Canyon, Aberdeen, Kenilworth, Sunnyside, Grassy, and Desert - represent 4th-order sequences. Their paleogeographic distributions and parasequence stacking patterns reflect changes in accommodation and sediment supply. During early Blackhawk time, accommodation constantly increased, albeit at varying rates. The Spring Canyon and Aberdeen members thus display progradational to retrogradational stacking. During late Blackhawk time, accommodation increase slowed and was periodically punctuated by decreasing accommodation. Consequently, the Kenilworth, Sunnyside, Grassy, and Desert members display progradational to retrogradational parasequence sets separated by one or more high-frequency sequence boundaries. In addition, shoreline trends rotated to the north-northeast, contrary to some published projections.

The stratigraphic framework helps explain variability in Blackhawk gas production. Greatest production comes from the Natural Buttes area, where tight, distal portions of the upper two parasequences of the Grassy Member are present in a pressure cell. Surprisingly, laterally adjacent incised-valley deposits - with better porosity and permeability - are wet. Much lower gas production comes from fluvial-to-shoreface parasequences of the Sunnyside, Kenilworth, and Aberdeen members, which occur in the deeper central and western Uinta basin.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas