Foraminifera Biostratigraphy Study of Neritic–Bathyal Sandstones, Deep Offshore, Niger Delta, Nigeria

Abstract

One of the factors needed to unravel hydrocarbon accumulations, volumetric computation and reservoir performance in a field is to have the proper view and understanding of the environment of depositions and the age of deposited sediments. Some fossils such as the foraminifera species from three wells namely (AO-01, AO-03, and AO-04) in ‘‘AO’’-Field, deep offshore, Niger Delta were studied to evaluate the paleoenvironment, age of sediments and the penetrated formations in the field. Well logs and biostratigraphy data were analyzed using the SPDC Zonation Scheme and Niger Delta Cenozoic Chronostratigraphic chart. The biostratigraphic analysis was conducted for well AO-01, AO-03, and AO-04 in the depth intervals (6810-3270) ft., (6989 – 9900) ft., and (4970 – 8670) ft respectively. The index fossils were identified and their respective foraminifera zones were conducted based on the SPDC zonation scheme and the Niger Delta Cenozoic Chronostratigraphic Chart. The environment of deposition was determined by plotting the fauna abundance against the depth intervals where the recovered index fossils were encountered. Results of the analysis show that the wells drilled within the field are rich in their preserved Benthonic and Planktonic foraminifera species which are relevant in the finding of hydrocarbon deposits. The forams recovered from the wells are the Ammonia becarii, Bolivia scalprata miocenica, Bolivia scalprata retiformis, Cibicorbis inflate, Cyclammina minima, Epistominella vitrea, Hanzawaia strattoni, Haplophragmoides compressa, Lenticulina inornata, Praeglobobulimina ovata, Quinqueloculina microstate, Rectuvigerina spp., Saccammina complanata, Textularia spp. and Valvulina flexilis and other foraminifera such as Brizalina beyrichi, Heterostegina costata, Uvigerina spp. were exclusively discovered in well AO-03 and AO-04 but absent in AO-01. The sediments identified in the field fall within the inner neritic to middle bathyal. However, the study generally presents the step-by-step technique for an improved interpretation of the environment of deposition and aid in the successes of hydrocarbon exploitation.