Structural Deformation and Depositional Processes: Insights from the Greater Ughelli Depobelt, Niger Delta, Nigeria

Abstract

The growth and development of the structural and depositional systems in the hydrocarbon rich Niger Delta, off the Atlantic Coast of Nigeria, West Africa, involves a complex interaction of extension, contraction and subsidence such that at any given point in time up-dip extensional system are kinematically linked to down-dip contractional systems via a transitional zone. On the regional tectonostratigraphic zonation are local structural and depositional systems associated with individual extensional faults and thrust-cored folds, local subsidence and withdrawal associated with shale diapir growth. The research is a case study of growth faults and associated deltaic sedimentation in the Greater Ughelli Depobelt of the Niger Delta. Using 3D seismic, a range of well log suites and biostratigraphic data, a regional sequence stratigraphic framework of the study area was produced. Six Maximum Flooding Surfaces MFS’s and five Sequence Boundaries SB’s were defined within the confines of available data. With the aid of these regional horizons/markers (MFSs and SBs) and events pattern in the seismic volume, a structural interpretation model and framework for the study area was also undertaken. Structural analysis show that fault activity began well before 31.3 Ma and continued beyond 20.7 Ma, and has greatly influenced the creation of accommodation space and sediment accumulation. Generally, due to structural deformation and structurally induced accommodation creation, stratigraphic thickness is observed to have increased in the basin ward direction, and at different stages in the structural evolution of the study area, ‘local depocenter’ have migrated to the NW (29.3 Ma-22.2 Ma) and then to the SE (22.2 Ma-20.7 Ma) resulting also in lateral changes in stratigraphic thicknesses in these directions