Sea Level and Paleotectonic Controls on Distribution of Reservoir Sandstone of Lower Cretaceous Muddy Sandstone, Hilight Field, Powder River Basin, Wyoming

David M. Wheeler, Edmund R. Gustason

To date, over 74 million bbl of oil have been produced from stratigraphic traps at Hilight field. Production is primarily from thin but stratigraphically complex fluvial and shallow marine sandstones of the Lower Cretaceous Muddy Sandstone. The deposition and preservation of these reservoirs were controlled by the interplay between sea level and tectonics.

The Muddy Sandstone in Hilight field was deposited during a late Albian sea level rise. It onlaps an erosional surface, developed during the preceding sea level drop, including a dendritic valley system cut deeply into the underlying Skull Creek Shale. In this area, the Muddy consists of four members that are bounded by transgressive disconformities. These members were deposited during stillstands in the overall rise of sea level. The lower two members consist of fluvial and fluvial-estuarine deposits which fill the valley system; the upper two members consist of fluvial-deltaic and barrier island deposits.

Three northeast-trending lineaments transect Hilight field. These lineaments are interpreted to represent basement faults that experienced recurrent movement during Muddy deposition. Relative structural downdrop controlled the orientation of drainage that cut the Hilight valley system. Recurrent movement provided structural and topographic lows within which relatively thick fluvial-deltaic and barrier island sandstones were deposited and preserved. Thinner sequences were deposited and subsequently eroded on adjacent structural and topographic highs.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.