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.