The Aeromagnetic Definition of Wrench Faults and Their Influence on Hydrocarbon

Entrapment and Production Fairways

By

Richard Inden

LSSI, Denver, CO

John Horne

Orion International, LTD, Denver, CO

William Pearson

Pearson Technologies, Inc, Lakewood, CO

Entrapped hydrocarbons, as well as the reservoir facies trends and hydrocarbon migration pathways are influenced by PreCambrian wrench fault systems present in basins throughout the Rockies. Structural highs, short basement faults, and cross-cutting wrench faults are interpreted from patterns seen on magnetic displays. Integration of these interpretations with subsurface and production information indicate that wrench faults control the location of major fields because of their influence on stratigraphy and reservoir development, as well as hydrocarbon migration, and the evolution of the structural features in, and on which, hydrocarbons are entrapped.

The significant fields in the basins we’ve performed aeromagnetic interpretations in bear a direct and obvious relationship to either: 1, the juncture of basement structural highs with the cross-cutting wrench faults that are interpreted from discontinuity patterns on the various aeromagnetic displays, or 2., to certain structural features orthogonal to these wrench faults. Essentially all fields occur on the tops or immediate flanks of mapped basement structures, an indication that even subtle structures at basement level are important in the stratigraphic entrapment of hydrocarbons. Production commonly ends abruptly or changes trend at wrench fault discontinuities, which, in many instances are not apparent on seismic.

In Rocky Mountain basins, fields are located on mostly northeast trending wrench faults, or on orthogonal structures limited by these cross-cutting wrench faults. Numerous field examples from the Williston, Powder River Basin, Big Horn Basin, Piceance Basin, as well as others will be used to illustrate the relationships between aeromagnetic structural evaluations and hydrocarbon entrapment.

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