Sequence stratigraphy and depositional sequence interpretation: A case study of “George” Field, offshore Niger Delta, Nigeria

Abstract

The seismic sequence stratigraphic analysis revealed four depositional sequences (DS-1, DS-2, DS-3 and DS-4). The accompanying systems tracts were interpreted and mapped in the study area based on the log motifs of the reference well and the spatial distribution of the recognized constrained surfaces: maximum flooding surfaces (MFSs), sequence boundaries (SBs) and transgressive surfaces (TSs) on the seismic data. Depositional systems in the study area comprise lowstand systems tracts (LSTs), transgressive systems tracts (TSTs) and highstand systems tracts (HSTs). The LSTs are represented by coeval facies dominated by deposition basinward of the shelf-edge during maximum regression and are characterized by shallow-water deposition from gravity flows and/or traction processes within the shelf-edge or canyon-head delta. The sediments associated with lowstand systems tracts recognized in the study area are the fluvial channel sands and slope fans (SF). The transgressive sand units were interpreted as shoreface sands deposited in the shelf region during rising sea levels. Highstand systems tracts are characterized by intervals of coarsening and shallowing upwards, with both fluvial and deltaic sands prograding laterally into neritic shales. In the study area, the units are very thick. The highstand and lowstand system tracts exhibit blocky log patterns and are associated with the reservoirs while the transgressive system tracts serve as seals to the reservoirs. The environment of sediments deposition in this area is delta plain, shelf, slope to toe of slope. Keywords: Sequence stratigraphic analysis, Depositional systems, Log motifs, Systems tracts, Environment of sediments deposition