Seafloor and buried mounds on the western slope of the Niger Delta. (May 2017)

• Record Type: Journal Article
• Authors: Benjamin, Uzochukwu Kingsley; Huuse, Mads
• Is Part Of: Marine and petroleum geology. Volume 83(2017)
• Page Start: 158
• Page End: 173
• Publication Date: 2017-05
• Subjects: Submarine mound -- Deepwater Niger Delta -- Gulf of Guinea -- Seafloor fluid flow -- Seismic amplitude anomaly -- Geohazard -- Subsurface sediment entrainment; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2017.02.023
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: Seafloor mounds are potential geohazards to offshore rig emplacement and drilling operations and may contain evidence of underlying petroleum systems. Therefore, identifying and mapping them is crucial in de-risking exploration and production activities in offshore domains. A 738 km 2 high resolution three-dimensional seismic dataset was used to investigate the occurrence, seismic characteristics and distribution of features interpreted as seafloor and buried sediment mounds, at water-depths of 800–1600 m, on the western Niger Delta slope. Fifteen seafloor mounds and eighteen shallowly buried mounds were identified. The seafloor mounds are characterised by lower seismic amplitude anomalies than the surrounding seabed sediments, and overlie vertical zones of acoustic blanking. The buried mounds in contrast are characterised by high amplitude anomalies; they also directly overlie sub-vertical zones of acoustic blanking. Seismic evidences from the features, their distribution patterns and tectono-stratigraphic associations suggest that their formation was controlled by the juxtaposition of buried channels and structural highs and their formation caused by focused fluid flow and expulsion of entrained sediments at the seabed. Considering the acoustic and geometrical characteristics of the mounds and comparing them with mound-shaped features from around the world, we conclude that the mounds most likely comprise heterolithic seafloor extrusions of muds and sands from the Agbada Formation with gas and possibly oil in some of the pore space giving rise to the acoustic characteristics. Highlights: Fifteen seafloor mounds and eighteen shallow buried mounds have been documented for deepwater western Niger Delta. Seismic evidence shows that the mounds are related to seabed fluid flow. Heterogeneous siliciclastic mound models have been proposed for the mounds. The mode of formation of the mounds may have implications for the under-filling of hydrocarbon reservoirs in the study area. The mounds constitute potential geohazards to offshore operations.