Reflection seismic interpretation of deepwater fold-thrust structures, Niger Delta

Structural and stratigraphic interpretation of 2D and 3D seismic data sets across the zone of compression referred to as the eastern fold-thrust belt (EFTB) suggests that the EFTB is characterized by a regional imbricate fan-thrust system and fault propagated folds. The imbricate fan-thrust system is subdivided into three distinct imbricate fan-thrust subsystems.; The EFTB is interpreted to be the compressional downdip part of an active deformation cell. This deformation cell is characterized by an up-dip area of extensional deformation, a translational middle area, and a down-dip area of compressional deformation (FTBs). An estimated 26% shortening is accommodated by these thrust and fold structures. It is anticipated that the amount of extension updip, which is the focus of future studies, will approximately equal to the estimated amount of compression within the EFTB.; Seismic facies analysis of one of the thrust blocks within the EFTB reveals the existence of alternating depth intervals of high and low amplitude seismic event packages. These are interpreted as channel-levee systems alternating with thin shale drapes (beds). They represent confined gravity flow subsystems within basin floor fan complex. The seismic facies at deeper stratigraphic levels are interpreted as unconfined gravity flows also part of the basin floor fan complex.; In terms of prospective hydrocarbon traps, both structural and stratigraphic traps could exist. The structural traps will probably include simple four-way dip closures (anticlinal folds) or thrust fault-assisted closures. Estimated shale gouge ratio (SGR) across the thrust plane ranges between 10% and 50%. Areas of 20% SGR and above have a high probability of sealing and trapping hydrocarbon. The existence of a deformed thrust plane zone however introduces a risk factor to these prospective thrust assisted closures. Channel-levee systems of deepwater environments proximal to the EFTB, or other basins analogous to the Niger Delta, are associated with prolific hydrocarbon fields. It is therefore probable that the interplay of sand and shale bodies within the interpreted multi-story channel-levee system will enhance chances that stratigraphic traps could significantly contribute to the hydrocarbon prospectivity in this fold-thrust belt.