Sequence stratigraphic analysis of the Otu Field, onshore Niger Delta, using 3D seismic data and borehole logs

Abstract

3D seismic data and wireline logs from thirteen boreholes were used to establish a sequence stratigraphic analysis of Miocene depositional systems of the Otu Field in the onshore area of the Niger Delta. The subsurface facies of the field revealed three sequences that are bounded by four sequence boundaries (SBs) which are interpreted as erosional unconformities with three maximum flooding surfaces (MFSs). Sequences delineated are composed of lowstand systems tracts (LST), falling stage systems tracts (FSST), transgressive systems tracts (TST) and highstand systems tracts (HST) revealing depositional systems deposited during different phases of base level changes. Deposits identified within the LSTs are fluvial channel sands while TSTs capped the LST facies. HSTs are composed of coarsening and shallowing upwards intervals including deltaic fluvial sands. The sequences were deposited in transitional to shallow marine environments. A seismic geomorphological study carried out on all the SBs and MFS 3 shows a relationship between depositional environments, channel type and direction of palaeo-flow in relation to faults. The reservoirs of the LST and HST and seals from marine shale of the TST and HST could form stratigraphic traps for hydrocarbon accumulation in the Otu Field. This study has integrated 3D seismic and borehole log data to develop a sequence stratigraphic framework that would be a profitable means to guide hydrocarbon exploration and production strategies.