Deformation During Multiple Phases of Extension: Complex Fault Patterns and Reservoir Compartmentalization

Alissa A. Henza, Martha O. Withjack, and Roy W. Schlische
Earth and Planetary Sciences, Rutgers University, New Brunswick, NJ

Multiple episodes of extension, commonly with different extension directions, affect many rift basins. We have used scaled experimental models with wet clay to study the fault patterns that develop during two sequential non-coaxial episodes of extension. The models show that both the angle between the two extension directions and the magnitude of the first-phase extension strongly affect fault development during the second extensional phase. In the models, fault reactivation occurs during the second extensional phase even if the angle between the two extension directions is large (i.e., 45° or greater). As the angle between the extension directions decreases, fault reactivation accommodates more deformation, and fewer and shorter normal faults form during the second extensional phase. An increase in the magnitude of the first-phase extension (and, thus, the displacement and length of the first-phase normal faults) also results in fewer and shorter normal faults during the second extensional phase. The interactions between the first-phase normal faults and the second-phase normal faults vary considerably. Newly formed normal faults cut and offset pre-existing normal faults, they emanate from the tips of pre-existing faults, and they terminate against the surfaces of pre-existing faults. Model fault patterns closely resemble fault patterns observed on 3D seismic data from the Grand Banks (Jeanne d’Arc basin) and the North Sea (Viking graben). Thus, the models may provide templates for interpreting complex fault patterns, constraining fault interactions, and estimating the magnitude of reservoir compartmentalization in regions with multiple phases of extension

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas