Sequence Stratigraphic Analysis of Well Bobo-3, Deep Offshore, Niger Delta Basin, Nigeria

Abstract

Sequence stratigraphic analysis was carried out on well Bobo-3, deep offshore, Niger Delta Basin, Nigeria. This is done in order to delineate sequence stratigraphic units using vertical sequence of depositional environments. Palynological analysis was carried out on 82 ditch cutting samples using the standard acid technique in order to zone the studied section of the well. Open hole geophysical log data was also provided for the studied interval (10700-15600 ft) belonging to the Agbada Formation. Lithologically, the section varies from alternation of sand and shale units with carbonaceous debris, mica flakes, ferruginised materials and glauconite at some interval as accessory minerals. Palynological zonation included three taxon range zones; Belskipollis elegans, Crassoretitriletes vanraadshooveni, and Pachydermites diederixi, which Are correlatable with the pantropical biozones. The studied section is dated as early to middle Miocene based on the independent palynological evidences. The deduced paleoenvironments of the strata penetrated by the well range from outer neritic through bathyal to abyssal. The successions were differentiated into highstand systems tracts (HST), lowstand systems tracts (LST) and transgressive systems tracts (TST) and chronostratigraphic surfaces such as maximum flooding surface (MFS), sequence boundary (SB), and transgressive surface (TS). Three HST, three LST, three TST, two MFS and three SB were recognized. The MFS and SB were dated 15.9 Ma, 15.0 Ma and 16.7 Ma, 15.5 Ma, 13.1 Ma, respectively by correlation of the established pollen zones with the Niger Delta Cenozoic chronostratigraphic chart. The sandstone and shale units of the systems tracts are potential hydrocarbon reservoirs and seal rocks respectively.