The Impact of Sedimentology and Diagenesis on the Hydraulic Flow Units Quality of Lower Cretaceous Aradeiba-Bentiu Sequence Reservoir Rocks of Laloba Oilfield, SE Muglad Basin, Sudan

Abstract

<title>Abstract</title> The Muglad Rift Basin in Sudan has been discovered to have two significant main hydrocarbon reservoirs: the Aradeiba Formation and the Bentiu Formation. This study endeavours to investigate the impact of diagenesis and depositional lithofacies on reservoir characteristics to improve prediction and deepen the current understanding of reservoir quality. However, this research incorporates fundamental characterisation and examination of cored intervals of the Laloba Oilfield in the Muglad Basin. An analysis of three cored intervals of a well in the Laloba Oilfield in the Muglad Basin of Sudan comprised petrographic, petrophysical, and diagenetic aspects, thereby providing in-depth insight into the reservoir properties of the analysed intervals. Moreover, gamma-ray well log analysis of seven wells performed to emphasise the facies groups. Six principal lithofacies have been identified: fine laminated sandstone (Fl); siltstone and mudstone, ripple marked siltstone (Sr); trough cross-bedded sandstone (St); planar cross-bedded sandstone (Sp); massive sandstone (Sm); and intra-formational conglomerate-size mud clast (Sco). The lithofacies observed exhibit characteristics that reflect a fluvial depositional environment comprising both channel-fill and overbank deposits. The average porosity and permeability values were 24.9% and 1286.5 mD, respectively. Furthermore, the entire studied interval was classified into three hydraulic flow units (HFUs) based on cross plots of the reservoir quality index (RQI), the normalised porosity index (NPI), and the flow zone indicator (FZI). The good, intermediate and bad reservoir quality types are respectively corresponding to HFU-1, HFU-2 and HFU-3. The reservoir quality of the sandstone units from Aradeiba (upper part, Core-1) and Bentiu (Core-3) are grouped under HFU-1, which is greatly affected by the dissolution of k-feldspar particles, leading to enhanced porosity and permeability (visual porosity). However, the HFU-2 and HFU-3 samples are characterised by high cementation of authigenic kaolinite and high mechanical compaction (point grain contact, long grain contact, and concave-convex grain contact), which have lowered and degraded the reservoir properties. Generally, integrated core data analyses provide insight into the impact of depositional and diagenetic processes on reservoir quality, thus improving reservoir quality prediction.