Angular unconformity in Pennsylvanian strata from 3-D seismic interpretation, Goldsmith Field, West Texas

Abstract

The Pennsylvanian unconformity, which is a detrital surface, separates the beds of the Permian-aged strata from the Lower Paleozoic in the Central Basin Platform. Seismic data interpretation indicates that the unconformity is an angular unconformity, overlying multiple normal faults, and accompanied with a thrust fault which maximizes the region's structural complexity. Additionally, the Pennsylvanian angular unconformity creates pinch-outs between the beds above and below. We computed the spectral decomposition and reflector convergence attributes and analyzed them to characterize the angular unconformity and faults. The spectral decomposition attribute divides the broadband seismic data into different spectral bands to resolve thin beds and show thickness variations. In contrast, the reflector convergence attribute highlights the location and direction of the pinch-outs as they dip south at angles between 2° and 6°. After reviewing findings from RGB blending of the spectrally decomposed frequencies along the Pennsylvanian unconformity, we observed channel-like features and multiple linear bands in addition to the faults and pinch-outs. It can be inferred that the identified linear bands could be the result of different lithologies associated with the tilting of the beds, and the faults may possibly influence hydrocarbon migration or act as a flow barrier to entrap hydrocarbon accumulation. The identification of this angular unconformity and the associated features in the study area are vital for the following reasons: 1) the unconformity surface represents a natural stratigraphic boundary; 2) the stratigraphic pinch-outs act as fluid flow connectivity boundaries; 3) the areal extent of compartmentalized reservoirs' boundaries created by the angular unconformity are better defined; and 4) fault displacements are better understood when planning well locations as faults can be flow barriers, or permeability conduits, depending on facies heterogeneity and/or seal effectiveness of a fault, which can affect hydrocarbon production. The methodology utilized in this study is a further step in the characterization of reservoirs and can be used to expand our knowledge and obtain more information about the Goldsmith Field.