Flow units, connectivity, and reservoir characterization in a wave-dominated deltaic reservoir: Meren reservoir, Nigeria

Abstract

The Meren E-01 (Agbada Formation, middle Miocene) reservoir offshore Nigeria consists of a lower progradational shoreface succession terminated by a minor sequence boundary, overlain by a progradational and retrogradational shoreface succession. Deposition occurred in a wave-dominated delta front, as indicated by the presence in core of hummocky cross-beds, slumped units, and turbidites. Eight flooding surfaces were correlated, and isopach maps, sandstone-quality trend maps, and mudstone-quality trend maps were constructed for each parasequence. This work revealed a complex reservoir architecture characterized by shoreface clinoforms and a history of progradation and retrogradation cycles.Three different three-dimensional geological characterizations of the E-01 reservoir were built: a geostatistical model that used only well data; a more geologically complex facies-based model that used the sandstone-quality trend maps in addition to well data; and the most geologically complex sequence-stratigraphic model that used mudstone-quality trend maps in addition to the above data. The three models were analyzed in terms of sandstone continuity and connectivity to hypothetical injector and producer wells. Only the sequence-stratigraphic model predicted significant vertical compartmentalization through tortuosity generated by flooding-surface mudstones. Waterflood fluid-flow simulation of a downdip sector of the geologic models predicts similar recovery for the three models, but a significantly different distribution of unswept oil. Only the sequence-stratigraphic model identified parasequences with abundant unswept oil that are large enough to be economic infill prospects. History-matched, full-field fluid-flow simulations verify both the reservoir compartments predicted by the sequence-stratigraphic model and infill targets.