Oyedele KF, Oladele S, Ogagarue DO and Bakare K
This study combined seismic, well logs (from BK-1 and BK-2 wells), paleobathymetric and biostratigraphic tools in the evaluation of Bobsaa field in the shelf setting of the Niger Delta, Nigeria. This was done to determine the lithostratigraphy, chronostratigraphy, possible reservoir sands, age and depositional environment of the study area for opportunities that will support exploration program. Different Formations, lithologies, lithofacies, sediment types, depositional sequences and their environments of deposition were identified from log signatures of the two wells. High resolution biostratigraphic data consisting of microfauna abundance and diversity chart aided in the delineation of the Maximum Flooding surfaces (MFSs), paleobathymetric interpretation and in age determination. The locally recognized cycles were correlated with the globally recognized eustatic cycle chart. Depositional sequences, system tracts, system boundaries and candidate MFSs were identified based on their diagnostic characteristic log patterns in the studied wells and age-dated with marker species. Sequence Boundaries (SBs) were recognized from logs, age-dated where possible, and constrained by age control sensu. Interpretation showed that the lithology is dominated by alternating sand and shale, occurring approximately in a ratio 70:30 within the logged intervals. From the log successions, prograding delta deposits and channel deposits were interpreted. Four MFSs and four SBs were recognized from BK-1 well while two MFSs and three SBs were recognized from BK-2 well. All the MFSs and SBs fall between Late Miocene to Middle Miocene interval. Biostratigraphic analysis showed four foraminifera Zones: Globorotalia merotumida/plesiotumida/Ammobaculites agglutinans Zone; Globorotalia acostaensis/Uvigerina subperegrina Zone; Globorotalia mayeri/Spirosigmoilina oligocaenica Zone and Globigerinoides subquadratus/Uvigerina sparsicostata Zone. The results suggest sediment deposition within the Coastal Deltaic and Shallow marine environments for the two wells. The integrated interpretation of different datasets in the study area has enabled the sub-division of the stratigraphic column of the wells into sequences, systems tracts and sedimentary cycles. These sequences may have potential to serve as excellent source rock and seals while the systems tracts may depict excellent seals and stratigraphic traps.
Share this article