Genesis and consequences of fracturing in the cretaceous carbonate reservoirs of North Oman

Abstract

North Oman is underlain by Cretaceous Natih and Shuaiba carbonates, which are important hydrocarbon reservoirs. Fracturing, especially fracture clusters, contributes significantly to reservoir performance. The fractures in the Natih are strongly affected by mechanical layering, whereas the Shuaiba is less obviously layered, except in the NW, where Upper Shuaiba is present. The fracture network of the Lower Shuaiba in the central and SE region of north Oman is dominated by fault–related fractures and associated corridors. Late Cretaceous deformation created NW-WNW strike-slip faults and associated fractures, as well as activation of salt diapirs. Tertiary deformation (NE shortening) resulted in the creation of abundant NE oriented background fractures, and more importantly NE fracture corridors that act as conduits to flow. Salt diapirs, when reactivated during Tertiary events, result in more intense fracturing locally. Field scale analyses of the fracture networks for Ghaba North and Lekhwair A North (both Shuaiba), based on BHI logs, reveal a change in dominant fracture orientation between the SE and the NW parts of north Oman. The NE fracture corridors play a major role in connecting the NW-WNW fractures seen in Lekhwair A North, and the current NE oriented maximum horizontal stress may also play a role.