Abstract

Seismic exploration in the Paleozoic Basins of Texas focuses on subtle features embedded in high velocity rocks. The 3-15 m thick chert intervals of the Devonian Thirtyone Formation of the Central Basin Platform, West Texas, commonly fall below the classical 1/4 wavelength (20-50 m) limit to seismic resolution. In the Fort Worth Basin, the microfaults, joints, and fractures so important to gas production may have little to no vertical offset. Although we may not be able to resolve such subtle features on the vertical section, we can often detect them on horizon amplitude extractions. Modern multi-trace seismic attributes such as coherence, coherent energy gradients, and a suite of vector dip attributes, including inline dip, crossline dip, reflector curvature, and reflector rotation greatly facilitate this process by avoiding the need to interpret discrete horizons and enhance subseismic lateral variations in reflectivity. In this presentation, we will define the mathematical and physical basis of these attributes, and show how they are often coupled to each other through the underlying geology. Next, we will apply these attributes to the analysis of complex faulting, deposition, and karsting from Paleozoic plays in Texas. We will show that while seismic coherence is a powerful tool for mapping faults and stratigraphic features, it often fails in providing any insight into reservoir heterogeneity when the reflections are consistently strong. Instead, we find that coherent energy gradients best image subtle channels, while dip/azimuth and curvature allow us to see subtle faulting and fracturing that is below seismic resolution.