The Aeromagnetic Definition of Wrench Faults and Their Influence on Hydrocarbon Entrapment and Production Fairways

Inden, Richard F.¹, William C. Pearson², John C. Horne³, Mary P. Frush^1
1 LSSI, Inc, Denver, CO 
² Pearson Technologies Inc, Lakewood, CO 
³ Orion International Limited, Denver, CO 

The identification of inherited PreCambrian wrench fault systems and structures is key to effectively locating hydrocarbon entrapments in all Rocky Mountain basins. These structural features are readily interpreted from patterns detected on a number of displays derived from the state of the art processing of high-resolution aeromagnetic data. Integration of these data with subsurface data strongly indicates that these faults are instrumental in controlling 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 on which hydrocarbons are entrapped.

Virtually all 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, or 2., to 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. These features are of critical importance in controlling not only present structural configurations, but also the updip productive limit of many stratigraphic entrapments, whether being caused by diagenetic pore throat entrapment, or a change in facies.

In basins such as the Williston, Big Horn, Powder River, Piceance, Uinta, and Greater Green River Basins, fields are located on mostly northeast trending wrench faults, or on orthogonal structures limited by these cross-cutting wrench faults. In the Williston Basin, the locations of major fields such as Little Knife, the Dickinson-Eland Wausortian mounds and Newport Fields are controlled by regional faults and paleostructures active during and after deposition. Numerous other examples of fields in the basins mentioned above will be used to illustrate the relationships between aeromagnetic structural evaluations and hydrocarbon entrapment.