Seismic Facies Analysis of Lacustrine System: Paleocene Upper Fort Union Formation, Wind River Basin, Wyoming

Louis M. Liro, Yvonna C. Pardus

We interpreted seismic reflection data, supported by well control, to reconstruct the stratigraphic development of Paleocene Lake Waltman in the Wind River basin of Wyoming.

After dividing the upper Fort Union into eight seismic sequences, we mapped seismic attributes (amplitude, continuity, and frequency) within each sequence. Interpretation of the variation in seismic attributes allowed us to detail delta development and encroachment into Lake Waltman during deposition of the upper Fort Union Formation. These deltas are interpreted as high-energy, well-differentiated lobate forms with distinct clinoform morphology on seismic data. Prograding delta-front facies are easily identified on seismic data as higher amplitude, continuous events within the clinoforms. Seismic data clearly demonstrate the time-transgressive nature of this facies. Downdip of these clinoforms, homogeneous shales, as evidenced by low-amplitude, generally continuous seismic events, ac umulated in an interpreted quiet, areally extensive lacustrine setting. Seismic definition of the lateral extent of this lacustrine facies is excellent, allowing us to effectively delineate changes in the lake morphology during deposition of the upper Fort Union Formation. Encasing the upper Fort Union lacustrine deposits are fluvial-alluvial deposits, interpreted from discontinuous, variable-amplitude seismic facies.

We highlight the correlation of seismic facies data and interpretation to well log data in the Frenchie Draw field to emphasize the accuracy of depositional environment prediction from seismic data.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.