Multiphase deformation of Paleozoic and Mesozoic units, Nebraska Panhandle, USA

Abstract

Renewed interest in the hydrocarbon systems of the Nebraska Panhandle stems from the increasing economic viability of unconventional plays, which must be understood in terms of regional geologic structure. We present preliminary interpretations of a seismic dataset from the north-eastern margin of the Denver-Julesburg (D-J) basin. The study area is in the Alliance sub-basin, partially separated from the main D-J basin by the Morrill County High. Other local highs create similar, partially isolated basins. The regional stratigraphic succession includes two targets for exploration: (1) Pennsylvanian-Permian carbonate-dominated cyclothems and clastic sediments, and (2) the Cretaceous succession. Hydrocarbon plays have traditionally targeted the latter, but interest in the Paleozoic succession is increasing. The present study analyses a series of 2D seismic lines, dominantly oriented NE-SW, with sufficient crossing lines to build a 3D representation of the survey area. Formation tops were picked from key wells and associated velocity profiles, and then mapped across the remaining lines. The basal Cenozoic unconformity, as well as Mesozoic and late Paleozoic strata, are clearly imaged on these lines. Pre-Cenozoic units dip to the SW, consistent with the position on the margins of the D-J basin. The late Paleozoic section is subtly folded with both normal and reverse offset faults visible in the overlying Cretaceous section. Subtle folds within the late Paleozoic section may be zones of enhanced porosity due to fold-related fracturing, making them suitable as targets for unconventional exploration. In addition, folded and fractured zones may have been further deformed in subsequent tectonic events.

AAPG Datapages/Search and Discovery Article #90193 © 2014 Rocky Mountain Section AAPG Annual Meeting, Denver, Colorado, July 20-22, 2014