Improved Fault and Reservoir Channel Delineation of a Gas Field in the Onshore Niger Delta Basin

A discovered and unitized gas field of the Nigerian Delta, through an initial 2D seismic survey and drilled well, is being studied. Imaging of the crest of the structure remained very poor. Uncertainties about the lateral extent of the reservoirs, pinchout, distribution of reservoir properties, and fault positions along the reservoirs were some challenges that were not yet fully understood in the study area. Hence, some of the risks associated with the field were fault and seal integrity, sand development, overpressures and reservoir rock properties. There were also exploration challenges in the data set of the field, such as the discrimination of hydrocarbon-bearing sands from shales and, more importantly, the separation of gas sands from brine-saturated sandstones. In order to address these issues, new 3D prestack seismic data were acquired with long offset cable and high fold of coverage, giving better resolution and structural interpretation across the reservoirs of interest. The current challenge was, therefore, to use the newly processed anisotropic 3D prestack seismic data to de-risk the reservoirs’ variability and heterogeneity and select locations for new development wells. Full, near, mid and far sub-stacks were generated to aid structural interpretation. Using anisotropic 3D seismic reflection data calibrated to well data, closely spaced, low displacement, planar, normal growth faults were mapped within the Tertiary Agbada Formation. A series of seismic horizontal time slices and computed seismic attributes were used to interpret the configuration of these faults. The closely spaced faults display an east-west trend. Accurate interpretation of the faults has enabled precise location of the faults and their orientation, style, and density, intending to reduce drilling risks and hazards.