Integrated Seismic-Petrologic Mapping of Ooid Bars and Associated Facies, St. Louis Formation (Upper Mississippian), Gray County, Kansas: ABSTRACT

Localized dim-spot anomalies on a large-amplitude, continuous seismic reflector correspond to porosity zones in the St. Louis Limestone. Anomalies are recognized as a decrease in wavelet amplitude on 12-fold CDP data and smaller amplitudes represent higher porosity. Mapped low-amplitude anomalies trend in a northwest-southeast direction. Continuously cored intervals from wells tied to the seismic data were studied to determine depositional environment, porosity types, and their relationships to the seismic anomalies. Porous ooid grainstones, up to 12 ft thick, encased in mud-rich skeletal wackestones and packstones document the presence of ooid shoals developed on a low-moderate energy shelf. The shoals, as seen on wireline logs and in cores, define a northwest-southeast-trending bar complex paralleling depositional strike. Primary interparticle and leach porosity totals around 10% in the ooid grainstone. Skeletal wackestones-packstones are locally cross-bedded and contain contorted shale laminations. These facies are tightly cemented and were deposited on a low-moderate energy shelf. Northwest-southeast-trending porosity zones in ooid grainstone shoals correlate with low-amplitude anomalies having the same orientation.