Geological and Seismic Delineation of D2000 and D4000 Petroleum Reservoirs Within Afenmai Field, Niger Delta Basin, Nigeria

Abstract

Afenmai Field is an old petroleum discovery within Central Swamp Depobelt on the eastern part of the Nigerian Niger Delta basin. Eight wells were drilled within the field, and Wells 006 and 008 respectively encountered petroleum in the D2000 Sand and D4000 Sands. This study was conducted to firm up the reservoirs’ spatial extent as well as their pore fluid distribution, which has hitherto been unattended to. To achieve this, the reservoirs were correlated within a framework of parasequence sets that was created from sequence stratigraphic interpretation of combined lithologic, geophysical and foraminiferal data. The reservoir tops were then tied at Well 008 to seismic reflections within a 3D seismic volume, and mapped through the volume. Root mean square (RMS) amplitude was extracted from the seismic volume along mapped reservoir surface. The depth maps produced reveal a southward concave, major synthetic structure building fault across the entire field. A series of en echelon synthetic faults are revealed on the NW and SE of the upthrown block of the major synthetic structure building fault. The D2000 Sand constitutes a rollover anticline with entrapped saturated petroleum in a four-way anticlinal closure that lacks fault support. The western, eastern and northern parts of the reservoir are yet to be penetrated by a well. Petroleum is entrapped in a three-way closure within the D4000 Sand in the western part of the upthrown block of the major synthetic structure building fault. Average RMS amplitude characterise the petroleum reservoir at Well 008 location and immediate vicinity. The values become low westward within the delineated reservoir. Opportunity for productive drilling exists within the undrilled part of the delineated reservoir, westward of Well 008. Opportunities for productive drilling also exist within the undrilled western, eastern and northern parts of the delineated D2000 reservoir sand.