Abstract The widespread Western Interior Plains aquifer system of the central United States provides a significant potential for sequestration of CO 2 in a deep saline formation. In Kansas, several severely depleted Mississippian petroleum reservoirs sit at the top of this aquifer system. The reservoirs are primarily multilayered shallow-shelf carbonates with strong water drives. Fluid flow is strongly influenced by natural fractures, which were solution enhanced by subaerial karst on a Mississippian–Pennsylvanian regional unconformity. We show that three-dimensional (3-D) seismic volumetric reflector curvature attributes can reveal subtle lineaments related to these fractures. Volumetric curvature attributes applied to a 3-D seismic survey over a Mississippian oil reservoir in Dickman field, Ness County, Kansas, reveal two main lineament orientations, N45°E and N45°W. The northeast-trending lineaments parallel a down-to-the-north fault at the northwestern corner of the seismic survey and have greater length and continuity than the northwest-trending lineaments. Geologic analysis and production data suggest that the northeast-trending lineaments are related to debris-, clay-, and silt-filled fractures that serve as barriers to fluid flow, whereas the northwest-trending lineaments are related to open fractures that channel water from the underlying aquifer. The discrimination of open versus sealed fractures within and above potential CO 2 sequestration reservoirs is critical for managing the injection and storage of CO 2 and for evaluating the integrity of the overlying seal. Three-dimensional seismic volumetric curvature helps to locate fractures and is a potentially important tool in the selection and evaluation of geologic sequestration sites.

Abstract During the Carboniferous a carbonate shelf covered areas of the central U.S, including Kansas, with the outer shelf and shelf margin intermittently extending through southern Kansas and northern Oklahoma. The regional setting resulted in deposition of relatively laterally continuous carbonate and siliciclastic facies belts. Areally sparse subsurface well data and surface exposures have led to the interpretation that most structures on the craton are simply shallow draped anticlines and associated synclines primarily reflecting general aspects of regional structure and depositional and erosional heterogeneity. Models that assume a broad continuous shelf relegate local structure to being minor or non-existent. However, our recent examination of subsurface data, 3-D seismic, and rock properties for oil fields from the Middle Mississippian shelf margin, Middle Pennsylvanian mid-shelf, and Late Pennsylvanian lower shelf indicate that regional- and kilometer-scale structures (e.g., faults, fractures, lineaments) segmented the shelf and shelf-margin areas in Kansas, primarily along Precambrian structures that were reactivated throughout the Phanerozoic. Movement on faults resulted in segmentation expressed as rhombic-shaped structural blocks (1-10s km) with subtle variations in relief (generally meter to ~ 70 m) and slope (near zero to upwards of 2-3 m/km). Regional, down-to-basin block faulting produced linear shelf edges and segmentation of the ramp and shelf profile repeatedly during the Carboniferous. The association of stratal packages and rock properties with structural elements argues that structure exerted continued, but episodic, influence and affected sediment accommodation, depositional patterns, paleotopography, weathering intensity, diagenesis, and later fluid movement, including hydrocarbon emplacement. Results from our study of the “stable” shelf carbonates of the Midcontinent indicate that tectonic events may have had far-reaching effects and caused structural deformation in the interiors of cratons. Sedimentologic and stratigraphic analyses in such settings can benefit by evaluating the possible influence of subtle faulting and fault reactivation on depositional and diagenetic patterns that can significantly influence rock properties and reservoir development.