Facies architecture and depositional environments study of the “B2” reservoir sand (3764-3794) m, Well-51, Boga Field, Niger Delta, Nigeria

Abstract

The “B2” reservoir sandbody, in Boga Field, Niger Delta, was investigated for the facies architecture and depositional sequence. Textural analysis, sedimentary structure and bioturbation intensity were used to study the core data for the identification of various lithofacies types and these were integrated with the gamma ray log in the cored interval for the determination of facies association and depositional sequence. The study revealed nine (9) lithofacies types. Integration of the lithofacies with Well log data from base to top of reservoir sandbody helped to group the sandbody into facies associations that occur together and are considered to be genetically or environmentally related. Three facies associations were interpreted from the cored intervals: Fluvial channel-Point Bar, Tide-dominated estuary and a Shoreface succession comprising two domains of Middle Shore face, and Lower Shoreface, capped by a Shelf Mudstone subfacies. The channel facies association shows a fining upward sequence, capped by an overbank deposit of mudstone lithofacies, the tide-dominated estuary shows a fining upward sequence. It consists from base: medium to coarse grained sandstone (mcS) facies, and capped by a fine to silt grained tidal flats sediment (M), while the Middle and Lower Shoreface subfacies consist of coarsening upward sequence of sandstone succession of medium to coarse and fine to medium sand facies associations respectively. The facies associations of the sandbody in the study interval were interpreted as a deposit of fluvio-marine prograding shoreface overlaid by a fluvial Point bar deposits. This observation implies a fluvial dominated process as observed in the cored interval of “B2” reservoir sandbody, Boga Field.

Keywords: Fluvial, Estuary, Shoreface, Fluvio-Marine, Tide-dominated