3D Seismic Curvature and Curvature Gradient for Fractured Reservoir Characterization at Teapot Dome (Wyoming)

摘要

Curvature is a popular attribute that has been widely used to delineate faults and fracture zones in seismic structural interpretation; however, our observations from 3D prestack, depth-migrated seismic data at Teapot Dome (Wyoming) indicate that many faults do not correlate with any curvature anomalies, while many curvature anomalies do not correlate to any faults. Instead, the major faults are typically located at the maximum absolute gradient of curvature. Inspired by these observations, we extend the curvature algorithm and construct a new curvature gradient algorithm by calculating the maximum change in curvature along the bedding. We then extract both maximum curvature and maximum curvature gradient attributes to describe the Teapot Dome fractured reservoirs. Our results indicate that the maximum absolute curvature gradient is more descriptive of the northeast-trending transfer faults and the northwest-trending thrust faults that are seismically visible; whereas the maximum curvature is more descriptive of the folded but unfaulted crestal portion of anticlines. These observations from seismic data, along with image logs, cores, and outcrops reported from previous studies, lead to our interpretation that curvature may be more indicative of tensile fractures whereas curvature gradient may be more indicative of shear fractures. Although tensile fractures can be directly observed on image logs, cores, and outcrops, they usually fall below the limit of seismic resolution. In contrast, shear faults give rise to significant offset of reflectors such that they are easily recognizable on seismic images. We propose using a combination of curvature and curvature gradient attributes for discriminating reservoir fracture facies (tensile versus shear fractures), evaluating reservoir storage capacity and caprock integrity, and modeling reservoir fracture networks at teapot Dome.