MAPPING THE MIDDLE PALEOZOIC THROUGH 3-D SEISMIC ATTRIBUTES IN THE CENTRAL ARKOMA BASIN, OKLAHOMA

Seismic attribute analysis and mapping reveals that Hunton Group strata do occur in the central and southern Arkoma Basin of eastern Oklahoma and that they were not completely removed by pre-Woodford erosion as previously believed. Well and isochron data through the Viola-Woodford interval (Ordovician-Devonian) show isolated ~40 m thick lenses of Hunton rocks, on average measuring 3 km in diameter. This distribution could be explained in two different ways; (1 Hunton occurrences could represent isolated erosional remnants reflecting incomplete removal of the Hunton Group during Middle Devonian time (pre-Woodford unconformity) or 2) due to karsting and collapse of stratigraphically lower units (Arbuckle Group?), lenses of Hunton rocks could have sagged into sinkholes where they were preserved beneath regional base level. Using formation tops from a well data set correlated with attribute and structure maps from a 3-D seismic data set provided by BP America, we identify three seismic characteristics in the middle Paleozoic interval that correlate well with; 1) absent Hunton seismic markers, indicating that Hunton rocks were completely removed, 2) the Hunton contacts, indicating where a seismically visible section of Hunton rocks remains, 3) absent Hunton but with a thin horizon included within lower carbonate strata that is interpreted to be an incipient karst zone and this character is consistently adjacent to areas containing Hunton rocks. The bases of the Sylvan Shale and the top of the Woodford Shale, the respective lower and upper adjoining units, form chronostratigraphic surfaces. As such, anomalous thicknesses of these units are depositionally related; thick Woodford sections often correlate to thin or absent Hunton rocks, possibly indicating back-filled pre-Woodford channels. Conversely, when there is little or no Woodford thickening over Hunton lenses and when adjacent areas show thinning and partially karsted Viola rocks we propose that collapse of Viola strata is responsible for the Hunton rocks preservation. A combination of these models may be necessary to account for areas where we see thinning both in the Woodford and Viola, suggesting that a Hunton lens is structurally lowered due to karsting, but due to its resistive nature, the lens forms a depositional high, causing the Woodford to thin over it.