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

May, Jeffrey A., Roger W. Falk, Donna S. Anderson, and Anne Grau
EOG Resources, 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 distribution of the Blackhawk in the subsurface to the north and northeast. Dense well spacing in Natural Buttes Field of the eastern Uinta Basin, combined with recent exploration drilling in the western Uinta Basin, provide dip and strike control on the subsurface configuration. Depositional patterns 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 was constantly increasing, albeit at varying rates. The Spring Canyon and Aberdeen members thus display progradational to retrogradational stacking of shoreface and coastal-plain deposits. During late Blackhawk time, accommodation continued increasing, though at an ever-slowing rate that 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 subsurface framework promotes understanding of the controls on Blackhawk gas production. To date, greatest production comes from distal parts of the upper two parasequences of the Grassy Member in the Natural Buttes area. Fluvial-to-shoreface parasequences of the Sunnyside, Kenilworth, and Aberdeen members have produced gas at lesser rates in the central and western Uinta basin.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah