Application of Calcareous Nannofossil to Petroleum Exploration; A Case Study of Offshore Depobelt, Niger Delta

Calcareous nannofossil biostratigraphic studies were carried out on ditch cutting samples obtained from wells X-1 and X-2, offshore deep water area, Niger Delta. The focus of these studies, using the pipette strew preparation methodology, was to establish a nanno fossilbiozonation, age, and correlation across the study intervals. Lithologically, the study sequences composed of shales, siltstones / mudstones which are grey, with intercalation of thin-bedded sandstones. Fairly diverse nannofossil assemblages were recovered. Calcareous nannofossils zones were established based on first and last occurrences of readily identifiable marker species and their relative abundances. These zones aided the age assignment of Early Pliocene through to Middle Miocene to the studied sections. Marker species and assemblage diagnostic types such as Calcidiscus leptoporous, Ceratho- lithusrugosus,Coccolithuspelagicus, Coronocylcusnitescens, Discoastervariabilis Reticulofenestrapseudoumbilica, Sphenolithusabies, Sphenolithusheteromorphus and Sphenolithusmoriformis have been used in the designation of the zonal ages ranging from NN15 through to NN5 based on the classic zonation scheme of Martini (1971). The recognition of such a disparate array of zones in the study wells, suggests that poor preservation of nannofossils or poor recoveries which could be linked to the Middle Miocene (Serravallian) Carbonate Crash as alluded to by Fadiya and Salami (2012) may be affecting zoning of intervals.