Basement–cover reservoir analogue in rift-margin fault blocks; Gulf of Suez Rift, Sinai, Egypt
A. Braathen, M.M.A. Fattah, S. Olaussen, G. Abdel-Gawad and K. Ogata
Issue: Vol 24, No 4, November 2018 pp. 449 - 468
Info: Article, PDF ( 17.69Mb )
Faults, fracture systems, weathering profiles and cover sediments of granitic basement in the rift shoulder of the Gulf of Suez Rift (Sinai, Egypt) are useful conceptual analogues for basement–cover reservoir fields. Outcrops demonstrate that fracture intensity peaks adjacent to major faults, and declines in damage zones that stretch to the background fracturing level over distances of 150 m. In the rift shoulder, smaller faults have damage zones that are 30 – 40 m wide with 1 – 5 m-wide fracture corridors. Faults show chemical alteration extending hundreds of metres into basement, with characteristics similar to saprolite in schists, mafic rocks and granitoids. Cover sandstones fill and drape top-basement relief, as recorded by metre-thick basal fluvial coarse sandstones, hosting kaolinite both as diagenetic pore fill and clastic grains. Overlying floodplain to marginal-marine deposits consist of mature quartz arenites. Strategies for production of hydrocarbons or groundwater from basement–cover reservoir couplets should consider a layered system with: (i) deep tight basement of minimal porosity (c. 1%) hosting producible fractures and faults in a plumbed system with potential thief zones; (ii) top-basement weathering profiles capping granitoids representing a volumetrically considerable reservoir; and (iii) draping cover sandstones showing good reservoir properties, and representing the most homogenous unit. Diagenetic modifications of saprolite, fault rocks and fractures potentially baffle recharge between layers.