The Influence of Basement Linears on Valley-Fill Depositional Patterns and

Hydrocarbon Entrapment

By

John C. Horne

Orion International Limited, Denver, CO

Richard F. Inden

LSSI, Denver, CO

William C. Pearson

Pearson Techologies, Inc, Lakewood, CO

Structurally and stratigraphically entrapped hydrocarbons in valley-fill reservoir facies in the Greater Green River, Wind River, and Powder River basins are influenced strongly by basement linears. Many of the valley-fill depositional patterns and their associated reservoir facies exhibit direct relationships to basement linear features in these basins.

Major northwest-oriented regional basement linears controlled the distribution and orientation of Dakota and Muddy lowstand valley-fill deposits in the western part of the Greater Green River basin. In the Moxa arch area, basement linears developed a northwest-northeast orthogonal pattern. During the Late Mid-Turonian sea-level drop, fluvial valleys that formed on the lowstand surface incised into the more easily eroded fractured basement linears. Frontier valley-fill reservoir facies accumulated in these orthogonally oriented valleys. Production trends from these valley-fill deposits reflect the orthogonal depositional patterns resulting from the influence of basement linears.

Similar to the association between basement linears and valley-fill deposits observed in the Greater Green River basin, relationships exist between basement linears and the location of Muddy formation valley-fill deposits in the Wind River and Powder River basins. The location of several stratigraphically influenced Muddy sandstone producing fields are controlled by basement linears.

In the Greater Green River, Wind River, and Powder River basins, production in valley-fill reservoirs commonly ends abruptly or changes trend at basement linear discontinuities. Consequently, these linears are important controls on the productive limits of many valley-fill stratigraphic entrapments. These relationships indicate basement linears were active associated with the accumulation of valley-fill deposits in these basins.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming