Seismic Stratigraphic Investigation of the Ukpokiti Field Channel Complex, Oml 108, Offshore Nigeria, Northwestern Niger Delta

• Main Author: Stewart, Toby Latwan
• Other Authors: Harry Roberts
• Format: Others
• Language: en
• Published: LSU 2004
• Subjects: Geology & Geophysics
• Online Access: http://etd.lsu.edu/docs/available/etd-05202004-143653/

Detailed seismic stratigraphic analyses and mapping show that a well defined Ukpokiti Field Channel complex (late Miocene) found on the up-thrown side of a major back-to-back fault system in the West Niger delta inner-continental shelf probably formed during a single eustatic fall. The channel (>500 msec, 10 km wide) shows several tributaries entering the trunk axis from what was probably a surface of subaerial exposure. Slumping is prominent on the north flank of the trunk channel. No channel unconformity is evident in the down-thrown block. This investigation seeks to resolve the lack of down-dip correlative seismic expression across the major structural boundary and place the Ukpokiti Field channel complex within a sequence stratigraphic framework, thereby explaining the channel genesis. Seismic sequence analysis was performed in the LSU Subsurface Laboratory with the Landmark Graphics© software suite using standard workstation interpretation procedures. Ukpokiti Field reservoir interval appraisals, preloaded digital well logs, poststack synthetic seismograms, and multiple horizon maps were interpreted during the course of the study. Results show the down-thrown correlative channel base to be a depositional surface. Three internal channel fill seismic facies patterns (fluvial deposition, marine inundation, and deltaic progradation) are evident in both structural blocks. On the basis of available biostratigraphic age control, the channel base probably represents an incised valley created at the 6.3 Ma sequence boundary. The internal seismic facies units probably represent a single shoreline regression interval. Shoreline and fluvio-marine deposition occurred after incision. Next, estuarine and pro-delta deposition occurred when the channel was flooded. Last, deltaic deposition filled the valley. Observed slumping is probably a product of instability due to the rapid progradation of deltaic deposits in the final stage of channel evolution. The channel produces no resolvable lowstand basinfloor fan within the study area.