THE STUDY OF FORAMINIFERA BIOSTRATIGRAPHY AND PALEOENVIRONMENT FOR ENHANCED HYDROCARBON RECOVERY ‘AO’-FIELD, DEEP OFFSHORE, NIGER DELTA

Understanding the depositional environment and the preservation history of a Formation is crucial in unravelling reservoir quality and prolific hydrocarbon deposits. The determination of the depositional environment is achieved through the detailed description of distinct responses, signatures and conditions preserved in a deposit that are characteristics of that environment. For ‘AO’ field, deep offshore, Niger Delta, understanding the environment of deposition and chronostratigraphical relationship is a necessity due to its distinct hydrocarbon potentials. Using biostratigraphic data at depth interval 1500- 4050 m, three wells (AO- 01, AO-03, and AO-04) have been studied to unravel the Foraminifera assemblages and subsequent paleoenvironment. On the basis of sequence stratigraphic principles with age dating of the zonal boundaries, the identified foraminifera species assemblage were grouped into four (Inner Neritic, Middle Neritic, Outer Neritic-Upper Bathyal and Upper Neritic-Middle Bathyal) biozones reflecting differences in biofacies compositions. To determine the environment of deposition, the fauna abundance were plotted against the depth of occurrence where the recovered index fossils are dominant this fostered the comparison of biofacies at fixed stratigraphic intervals. Results show that the wells are rich in well-preserved Benthonic and Planktonic foraminifera species which are good indicators of potential hydrocarbon deposits. The Foraminifera species recovered are; Ammonia becarii, Bolivia scalprata miocenica, Bolivina 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. The chronostratigraphic rock record of sediments in the studied interval transition from the Middle Miocene to late Miocene while the paleobathymetry of the wells are interpreted to represent Inner Neritic to Middle Bathyal of the Niger Delta. The high dominance of the Inner Neritic to Upper Bathyal biofacies reflect a deep water system with expanding diversity with increasing water depth. This study is particularly applicable for the understanding and predicting potential hydrocarbon rich deposits.