Sedimentologic and petrophysical assessment of the lower cretaceous Abu-Gabra tight reservoir formation, Laloba oilfield, Bamboo sub-basin, Muglad Rift basin, Sudan

The Abu-Gabra Formation is considered the main source rock and secondary reservoir in several oilfields in the Muglad Rift basin. Its lithology comprises claystone, siltstones and fine to coarse sandstones. This study evaluates the Abu-Gabra Formation as a reservoir in the Laloba oilfield based on two core intervals available in one well in the studied field. These involved; (a) subsurface facies analysis based on two conventional cores descriptions and (b) petrographic analyses including thin sections, scanning electron microscope (SEM), QEMSCAN, and X-ray diffraction (XRD). The facies analysis revealed seven major lithofacies including laminated to massive mudstone and siltstone, fine laminated sandstone and siltstone, ripple laminated sandstone and siltstone, turbulent laminated sandstone and siltstone, trough cross-bedded sandstone, planar cross-bedded sandstone and massive sandstone. These lithofacies are deposited in deltaic to lacustrine depositional systems. The sandstone type is feldspathic arenite to subfeldpathic arenite. The sandstone reservoir quality is significantly impacted by the microscale textural change and diagenetic processes. The clay minerals especially kaolinite and illite observed in considerable percentages on the XRD, SEM, and QEMSCAN analyses. The porosity and permeability are greatly reduced by the burial diagenesis that represented in illite increase with depth. In contrast, the k-feldspar dissolution relatively enhances the reservoir quality. The average porosity values of the studied intervals are 10.16 and 12.31%, respectively, for core-1 and -2. Also, the permeability values are relatively low (0.69mD, core-1, and 7.81mD, core-2). The challenges of reservoir heterogeneity found in this study may enhance the understanding and prediction of reservoir quality of equivalent intervals of the Abu-Gabra Formation in the Muglad Rift basin.