The structural complexity of many fields in the Tertiary Niger delta implies considerable scope for the application of three-dimensional seismic methods. The first such survey by Shell Petroleum Development Company of Nigeria Limited was acquired over the complexly faulted Nun River field in 1987.

The interpretation of the Nun River three-dimensional seismic survey has provided a detailed structural framework of reservoir previously unattainable with two-dimensional seismic and well data. This detailed information has led to the confident identification of highly prospective, partially tested and untested closures, highlighted by stacked amplitude anomalies.

New interpretation and mapping techniques on interactive seismic interpretation workstations have been used to enhance the structural interpretation. These techniques include dip and azimuth displays for delineation of fault patterns, and slices through three-dimensional seismic data parallel to faults (fault slices) to evaluate juxtaposition and fault seal. Generally, only the strike of the major faults has remained the same, whereas the complexity and discontinuity of the faulting have increased, resulting in fewer isolated blocks and a more open structure. This increased knowledge of reservoir compartmentalization and communication will result in a more optimum development of the field.

The importance of clay gouge forming a seal along fault planes may also be evaluated using three-dimensional seismic. Clay gouge present within a fault plane may prevent cross-fault migration of hydrocarbons even where fault slices indicate that permeable sandstones are juxtaposed across a fault.