CONSTRAINING SUBSURFACE FRACTURE NETWORKS FROM SEISMIC ATTRIBUTES: TEAPOT DOME, WYOMING

Anomalous trends in complex seismic attributes in a 3-D seismic reflection data volume are used to map subsurface fracture trends in the Late Cretaceous-Paleogene Teapot Dome anticline in south-central Wyoming. Teapot Dome is a doubly-plunging basement-involved Laramide anticline located on the western edge of the Powder River Basin in Wyoming. Linear low-coherence seismic anomalies are well-developed on reflections from the tops of the Upper Cretaceous Frontier Formation, Lower Cretaceous Dakota Group, Jurassic Sundance Formation, Triassic Chugwater Group, and Pennsylvanian Tensleep Formation. These linear coherence anomalies dominantly trend NE-SW, sub-parallel to the inferred maximum stress orientation during the Laramide orogeny and parallel to joint systems mapped at the surface. The low coherence anomalies correlate with similar anomalous trends in other seismic attributes, including a decrease in average seismic wavelet energy, a decrease in maximum wavelet amplitude, a decrease in instantaneous frequency, and either a negative or positive phase shift. The seismic attribute anomalies are associated with one of two distinct waveform character changes. The first is a decrease in period and amplitude in the near zero-phase seismic wavelet compared to adjacent traces. The second is formation of a doublet in the seismic pulse and an increase in period and decrease in amplitude compared to adjacent traces. The changes in instantaneous attributes and waveform character are consistent with scattering of seismic energy through relatively narrow (< 30 m) sub-vertical hinge-perpendicular fracture swarms. The resolution of the seismic data constrains the vertical offset of reflection horizons across the inferred fracture swarms to be less than 10 m, indicating that the hinge-normal fractures are joints, small offset (sub-seismic) dip-slip faults, or strike-slip faults. The fracture systems extend in a coherent manner from the surface to the base of the hanging-wall, indicating that fracture-induced reservoir partitioning, if present, is consistent throughout the hanging-wall. The study demonstrates that fracture systems in fault-related folds that have vertical displacements below the typical seismic resolution can be reliably imaged through seismic wavelet attribute analysis.