Uncertainty analysis of the mud infill prediction of the Olokola LNG terminal

For a proposed liquefied natural gas export facility, Olokola LNG (OKLNG), located at the western limits of the Niger Delta in Nigeria a 10 km long and 17 m deep approach channel is designed for tankers to reach the terminal at the shoreline. Mud is expected to be deposited in the channel because of the persistent swell climate which mobilizes mud on the seabed. In order to assess operational costs and dredging requirements predictions of the infill rates are required which realistically include possible uncertainties. An extensive study on the sediment characteristics in the OKLNG area was conducted. Indications were found that the sediment in the water column at OKLNG is unflocculated or poorly flocculated. If confirmed, this would be very unusual and in fact unknown to the best knowledge of the consulted experts for this thesis and in the studied literature. Cohesive sediment in the marine environment is typically flocculated. In terms of identifying and reducing uncertainties, the sediment state in the water column was found to be the most important uncertainty for the prediction of the mud infill; it has a large influence on the sedimentation mechanism and quantities. Because of this large uncertainty, and in the absence of definitive data, it was decided to investigate the implications of both unflocculated (scenario 1) and flocculated (scenario 2) sediment. If the sediment is found to be unflocculated, the infill rate is a factor 10 higher than when it is flocculated. Next the sediment concentrations near the bottom are not precisely known, while this information is required to properly predict the mud infill of the channel. All other uncertainties are of minor importance in comparison to the mentioned two.Hydraulic EngineeringCivil Engineering and Geoscience