Foraminifera, Biostratigraphic and Paleoenvironmental Analysis of “X-1” Well, on the Western Sector of the Niger Delta Basin, Nigeria

Abstract

A foraminiferal biostratigraphic and paleoenvironmental study was conducted on ditch-cutting samples from well X-1 (1870–1320 m), located in the western sector of the Niger Delta Basin, southern Nigeria. The objectives were to determine the stratigraphic age, depositional paleoenvironments, sequence-stratigraphic framework, and preliminary petroleum potential of the penetrated interval. A total of 48 ditch-cutting samples were analyzed using standard lithologic (visual and microscopic) and micropaleontological preparation techniques. Lithostratigraphic analysis identified four sub-lithofacies units (X1–X4) characterized by alternating sand and shale, a typical feature of the Agbada Formation. Foraminiferal analysis revealed moderate abundance and diversity of planktonic, calcareous benthic, and agglutinated benthic forms. A total of 60 foraminiferal species were identified, comprising 21 planktonic species (42%) and 39 benthic species (58%). The co-occurrence of key taxa including Globigerinoides obliquus, Globorotalia acostaensis, Globigerinoides obliquus extremus, and Cyclammina cf. minima enabled recognition of two planktonic foraminiferal zones: the Globorotalia acostaensis Zone (N16; early Late Miocene, Tortonian) and a composite Globorotalia humerosa / G. margaritae margaritae / G. margaritae evoluta Zone (N17–N19; late Late Miocene to earliest Early Pliocene, late Tortonian–Zanclean). A composite benthic foraminiferal zone spanning the Marginulina costata Zone (NNDF 04; uppermost Miocene to earliest Pliocene), Cyclammina minima Zone (NNDF 05; latest Late Miocene), Haplophragmoides narivaensis Zone (NNDF 06; middle Late Miocene), and Ammobaculites agglutinans / Florius costiferum Zone (NNDF 07; early to middle Late Miocene) was erected, in accordance with the standard Niger Delta chronostratigraphic framework. Biostratigraphic results indicate that the studied interval penetrates sediments of Late Miocene to earliest Early Pliocene age. Paleoenvironmental interpretation, based on integrated biofacies and lithofacies data, identified four paleodepositional/paleobathymetric settings ranging from coastal delta plain to fully neritic conditions (inner neritic, middle neritic, and outer neritic). Sequence-stratigraphic analysis delineated a major maximum flooding surface (MFS) at 1390 m (~5.0 Ma), separating a transgressive systems tract (TST) below from a highstand systems tract (HST) above. The moderately well-sorted sands and enclosing shales exhibit good potential as petroleum reservoir, source, and cap rocks, respectively.