Sequence stratigraphic approach to hydrocarbon exploration: a case study of Chiadu field at eastern onshore Niger Delta Basin, Nigeria

Abstract

This study integrated lithofacies, foraminifera and seismic data to develop a sequence stratigraphic approach to hydrocarbon exploration for Chiadu field. The application of lithostratigraphic approach led to correlation of diachronous lithofacies and wrongly defined an approximately accurate extent of the reservoirs. This study necessitated the use of sequence stratigraphic framework for the purpose of establishing chronostratigraphic concept and facies prediction. The genetic sequence model of Galloway was adopted for sequence stratigraphic interpretation of the field. The structural style is dominated by closely spaced simple rollover anticline bounded by growth faults, and this includes down-to-basin listric faults, collapsed crest structures, antithetic and synthetic faults. Result of foraminifera analysis showed that the analyzed interval is very rich in calcareous benthic but decreased in planktic and arenaceous benthic foraminifera. Lithofacies analysis shows that the continental lithofacies is made up of dominantly sand with thin bands of shales, while Agbada lithofacies is made up of alternating intervals of sandstones and shales to very thick shale unit in the lower section. The facies identified using log motifs and their stacking patterns include braided fluvial, crevasse splay, fluvial point bar, distributary/tidal channels, intertidal, subtidal and storm-dominated shelf facies. The presence of water depth indicator fossils confirmed the water depths of coastal deltaic, shallow inner neritic, inner neritic, middle neritic and outer neritic were based largely on the presence of environmentally restricted benthic foraminifera species. Integration of lithofacies and biofacies data suggests depositional environments ranging from coastal deltaic to outer neritic environment. Sequence stratigraphic analysis identified three complete sequences with accompanying system tracts over the interval 7922.3–14,856.34 ft. The transgressive system tracts (TSTs) within these sequences are dominated by marine shales and thin sands. Reservoir quality sands are found in highstand system tract and shelfal lowstand system tract, while the shales of TSTs and HSTs form potential source and seal units. The delineation and correlation of sequence stratigraphic surfaces enable us to build an approximate chronostratigraphic framework, which is essential for determining facies relationships. Reacquisition and/or processing should be done to improve seismic data quality for better imaging and interpretation/mapping, especially hydrocarbon prospect at deeper horizon.