Information on Fault Orientation from Unoriented Cores

Abstract

Unoriented core data can be integrated with other data types, such as seismic data, dipmeter data, and stratigraphic isochore or isopach data, to provide a unique solution for bedding orientation. In addition, such an integrated approach will help to identify erroneous data and interpretations. Once a unique solution for bedding orientation is obtained, this information can be used to find the orientation of faults and deformation bands as observed in core data. Although larger scale faults commonly are difficult to core due to brecciation and poor coherency of the fault rock, structural studies demonstrate that faults (with discrete slip surfaces) in sandstones are associated with numerous deformation bands in damage zones that are typically several meters wide. Within the fault zone itself, the deformation bands commonly are subparallel to the larger scale fault. Analyses of the orientation of deformation bands within the fault zone thus may yield information on the orientation of the larger scale fault. Based on such an integrated approach, it is possible to find information on faults on a subseismic scale that would otherwise be difficult or impossible to obtain. Quality control against seismically resolvable faults from the Gullfaks field, northern North Sea, demonstrates that this simple approach is valid and can provide important additional information for the structural interpreter. The results can be used to optimize well planning and enhance the understanding of fluid flow patterns in the reservoir.