Sedimentological reservoir characteristics of the Paleocene fluvial/lacustrine Yabus Sandstone, Melut Basin, Sudan

Melut Basin in Sudan is regionally linked to the Mesozoic-Cenozoic Central and Western African Rift
System (CWARS). The Paleocene Yabus Formation is the main oil producing reservoir in the basin. It is
dominated by channel sandstone and shales deposited in fluvial/lacustrine environment during the third
phase of rifting in the basin. Different scales of sedimentological heterogeneities influenced reservoir
quality and architecture. The cores and well logs analyses revealed seven lithofacies representing fluvial,
deltaic and lacustrine depositional environments. The sandstone is medium to coarse-grained, poorly to
moderately-sorted and sub-angular to sub-rounded, arkosic-subarkosic to sublitharenite. On the basin
scale, the Yabus Formation showed variation in sandstone bodies, thickness, geometry and architecture.
On macro-scale, reservoir quality varies vertically and laterally within Yabus Sandstone where it shows
progressive fining upward tendencies with different degrees of connectivity. The lower part of the
reservoir showed well-connected and amalgamated sandstone bodies, the middle to the upper parts,
however, have moderate to low sandstone bodies’ connectivity and amalgamation. On micro-scale,
sandstone reservoir quality is directly affected by textures and diagenetic changes such as compaction,
cementation, alteration, dissolution and kaolinite clays pore fill and coat all have significantly reduced
the reservoir porosity and permeability. The estimated porosity in Yabus Formation ranges from 2 to 20%
with an average of 12%; while permeability varies from 200 to 500 mD and up to 1 Darcy. The understanding
of different scales of sedimentological reservoir heterogeneities might contribute to better
reservoir quality prediction, architecture, consequently enhancing development and productivity.