Characterization of a deep-water turbiditic reservoir under an active hydrodynamic regime (Niger delta)

Abstract

The Egina Field, situated in the deep-water region of the eastern Niger Delta, is characterized by a NE-SW trending anticline that contains several Middle to Upper Miocene stacked reservoirs. Notably, one of the reservoirs in the field includes three sandy intervals, which have been identified as deep marine turbidite systems. The lowest level (Interval 1) comprises a lobe complex, while the uppermost Intervals 2 and 3 consist of erosive channel complexes. These three reservoir intervals exhibit both static and partial dynamic communication. The Egina Field is affected by a coherent network of extensional and oblique-slip faults, with current activity confined to the eastern sector of the structure. Large displacement faults (throw >30m) offset individual reservoir intervals, creating lateral disconnection and acting as barriers to fluid flow across faults. Minor NNE-SSW oriented faults can locally baffle the flow of fluids, as evidenced by well tests and 4D seismic data. Nonetheless, well interference tests suggest good communication within the reservoir. Vertical communication between the stacked sand bodies is facilitated through erosional contacts between reservoir intervals, while lateral communication occurs around segmented faults, via relay ramps and fault tips, in a NE-SW direction. Across the field, ten oil-water contacts have been identified, with a general trend of deepening towards the south. This pattern has been interpreted as a tilted contact caused by an active hydrodynamic regime, where aquifer overpressures gradually decrease from north to south (31 m of difference), aligning with the regional trend. This paper describes how the geological (structural and sedimentological) heterogeneities are paramount in deep-water turbiditic reservoirs, for both static and dynamic conditions. The work presented here shows how the geological analysis can impact reservoir management, driving strategic decisions on field development, as such as the identification of infill wells opportunities or the optimizing the placement of injectors wells, to effectively support producers.