Lithofacies and depositional environments study of the “B3” reservoir sand (3899-3950) m, well-05, Biwa field, Niger delta, Nigeria

Abstract

The “B3” reservoir sandbodies, in Biwa field, Niger Delta, were investigated for lithofacies and depositional sequence. Textural analysis, sedimentary structure and bioturbation intensity were used to study the core data for the various lithofacies types and were integrated with the gamma ray log in the cored interval for the determination of lithofacies association and depositional sequence. The study revealed five lithofacies types. Integration of the lithofacies with well log data from base to top of reservoir sandbodies helped to group the sandbodies into facies association that occur together and are considered to be genetically or environmentally related. Two facies associations interpreted from the cored intervals include: Braided Channel-Point Bar, and a well developed shoreface succession comprising the three main domains of Upper Shoreface, Middle Shoreface, and Lower Shoreface and capped by a Shelf Mudstone subfacies. The braided channel facies association shows a fining upward sequence, capped by an overbank deposit of mudstone lithofacies, while the Upper, 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 association of the sand bodies in the study interval can be interpreted as a deposit of braided channel, capped by a prograding shoreface deposits. This observation implies a fluvial dominated process as observed in the cored interval of “B3” reservoir sandbodies, Biwa Field.