The study of deepwater depositional elements using seismic geomorphic and stratigraphic techniques in ''ACE'' Field, Niger Delta
This study analyzed well log data from “ACE” Field in deep-offshore settings of the Niger Delta, identified the deepwater depositional elements from 3D seismic data and characterized the geomorphology and stratigraphy of the identified depositional elements. These were with a view to investigating the occurrence of depositional elements, their formative processes and reservoir potential in the study area. The dataset included processed 3D seismic data (1160 inlines and 1117 crosslines), geophysical well logs (Gamma Ray, Density, Sonic, Neutron, Resistivity) and checkshot data for one well. A synthetic seismogram was generated to tie the well data to the seismic data. Lithofacies within the well were identified and their gross depositional environments were predicted from the gamma ray log motifs. Seismic interpretation involved the picking of faults based on abrupt termination of events and change in reflection pattern. Horizons inferred to be candidate sequence boundaries corresponding to depositional surfaces indicative of documented depositional elements were mapped across the seismic volume. The mapped horizons served as input for generating seismic surfaces and attribute maps that gave planform images of identified depositional surfaces and their associated depositional elements. Seismic stratigraphic analysis was also carried out to determine the seismic sequences in the study area and their associated seismic facies. The well log analysis revealed that the studied interval was predominantly characterized by thick sequences of shale, deposited in a low-energy environment, interbedded by relatively thin hydrocarbon bearing turbidite sands. Twenty-nine (29) faults with approximate E-W trends and steep dips were mapped in the study area. Seismic sequence analysis revealed five (5) seismic sequences (Sequence A through to Sequence E) with their characteristic seismic facies. The depositional elements delineated included a submarine incised valley, an erosional channel belt and a leveed channel. Other features include; erosional scallops, erosional and fault-scarped terraces, linear grooves as well as scours of mass transport deposits (MTDs). The meandering laterally migrating channel-fills observed within the submarine incised valley, the isolated channel-fills within the erosional channel and the levee deposits were found to be characterized by high amplitude sandprone deposits. The study concluded that the depositional elements within the study area were formed from repeated erosive turbidity flows and other mass transport processes. The fill-deposits assessed within the depositional elements had good reservoir potential and hydrocarbon exploration significance.