ABSTRACT: Seismic Stratigraphy of the Muddy Sandstone, Powder River Basin, Wyoming

Brian W. Horn

The Upper Albian Muddy Sandstone of Wyoming and Colorado contains a complex suite of marine to continental facies, some of which contain reservoir-quality sandstones that produce hydrocarbons throughout the Powder River basin, Wyoming. Predicting the presence or absence of different reservoir and nonreservoir sandstone facies is difficult, inasmuch as these facies commonly overlap, cross-cut, and/or display lateral and vertical transitions to other facies suites. Eustatic sea-level fluctuations and structural basement block movements regulated Muddy Sandstone facies changes locally and regionally causing the juxtaposition of different facies suites in a variety of stratigraphic relationships.

Seismic modeling indicates that two of these depositional facies (alluvial valley fill and marine bar complexes) can be identified on seismic data. The Recluse and Steinle Ranch fields are examined to determine which exploration tools are most effective in differentiating depositional facies in the Muddy Sandstone. Each field shows a distinct seismic response predicted from seismic models depicting the geometry of various depositional facies and the presence of producing sandstones. An integrated approach using a basin-wide depositional model, seismic modeling, subsurface mapping from well log, and seismic data is utilized in this analysis.

Basement block faults and/or salt dissolution structures are interpreted to influence depositional patterns of these facies suites including the development and preservation of different depositional facies containing reservoir quality sandstones on a local to regional scale. Whereas these two fields are considered to be stratigraphic traps, these traps ultimately appear to be structurally controlled. Integrating all of these available exploration methods, new strategies for future Muddy exploration can be developed.

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