Facies and Reservoir Quality of Zarqa Formation (Turonian-Late Senonian), in Heglig and Unity Fields, Muglad Rift Basin, Sudan

By

 Saida O. Mohammed¹, Osman M. Abdullatif²

(1) University of Khartoum, Khartoum, Sudan (2) KFUPM, Dhahran, Saudi Arabia

 The sedimentology and reservoir characteristics of Zarqa Formation in the Muglad rift basin were investigated using cores, wire line logs as well as petrographic analyses. The subsurface lithofacies analysis reveals that Zarqa formation comprises three major units, fluvial- dominated, fluvial-lacustrine and lacustrine-dominated facies units. The fluvial unit is composed of stacked fining upward facies sequences of fine to medium grained channel sandstone and overbank/floodplain siltstone and claystone facies. The fluvial/lacustrine unit consists of mixed interbedded fine to medium sandstone and claystone facies. The lacustrine-dominated unit consists mainly of claystone and siltstone facies interbedded with high sinuosity meandering stream facies. The three units of Zarqa Formation reflect the fluvial and lacustrine system response to base level change change as controlled mainly by tectonism and climate. In part, autocyclic controls such as channel processes , discharge rates and sediment load also played a role in that respect.

Zarqa Formation sandstones are mostly arkosic arenite, mainly fine to medium grained, poorly to moderately sorted, subangular to angular and cemented by calcite and argillaceous cement. Secondary porosity is introduced as a result of partial or complete dissolution of carbonate, feldspar and clay cements. Heavy and clay minerals composition indicates the control of climate, tectonism, source rocks, environments and diagenesis.

Reservoir quality of Zarqa Formation is controlled by the macro scale facies architecture, geometry and dimensions of sandstone bodies and claystone/siltstone barrier and baffle units. Sediments detrital sources, compaction, diagenetic alteration and dissolution are influential on micro-scale.