Sequence stratigraphy identification and evaluation of the Mars field offshore Benin basin, Nigeria

Abstract

The concept of sequence stratigraphy in explaining sediment accumulation and preservation trends within basin fills have become a highly successful exploration tool in the search for hydrocarbon resources. Thus, the subdivision of a basin's sedimentary deposits into time stratigraphically constrained depositional packages is imperative in unraveling its development and inherent hydrocarbon potentials. The sequence stratigraphic analysis is based on the integration of the biofacies data derived from the peaks of foraminiferal abundance and diversity with lithostratigraphic data. Paleowater depths were inferred from the qualitative evaluation of selected environmentally significant benthic foraminifera. The textural ditch cutting samples information was integrated with the biostratigraphic analysis to derive significant depositional environment. This suggest that depositional environment of the studied sections was within the shallow inner Neritic and Middle Neritic and progressively deepening towards outer Neritic/Upper Bathyal. The fossils used in this research to characterize the sequence stratigraphic biozonations are the foraminiferal, calcareous nannofossils and palynomorphs. The sequence stratigraphy recognition of the maximum flooding surfaces was carried out using the Foraminiferal biozonation in which only faunal biozones (faunal assemblage characterizing a stratigraphic interval) were recognized. The sequence boundary was picked based on the maximum flooding surfaces and unconformities are based on progressive missing section between the sequence. The integration of the textural characteristics of ditch cutting samples with palynological data and paleobathymetric information for selected environmentally significant foraminifera suggest that the well section studied was deposited between Shallow inner Neritic and Middle Neritic environments at the base, deepening progressively to Outer Neritic/ Upper Bathyal towards the top of the well. In conclusion, depositional sequences with its internal geometric elements will be reconstructed from key dated unconformities and major flooding surfaces.