Online Journal for E&P Geoscientists

Al-Shehhi, Fatma ^*1; Brandenburg, Aly ¹
(1) Exploration, Petroleum Development Oman, Muscat, Oman.

In Oman old structural lineaments can be re-activated multiple times over geological time. This structural re-activation can not only generate new structures and traps for oil and gas, but can result in the leakage of hydrocarbon from traps and remigration of hydrocarbons into shallower levels (Filbrandt et al 2006). It also influences the development and re-activation of fracture systems which are important controls on productivity, especially within tight reservoirs.

Petroleum Development Oman (PDO) has acquired an extensive grid of 3D seismic over the Block 6 area over the past years. The regional 3D has been merged and used to interpret shallow events of Cretaceous and Tertiary age. Several events could be interpreted at Natih E, Base Tertiary and Umm er Radhuma. These have been used to generate horizon semblance displays and isochrons to delineate structural style and timing of deformation.

Two main phases of deformation can be clearly recognised; one during Late Cretaceous with a maximum horizontal stress orientation of NW-SE and one during Tertiary with an apparent maximum stress orientation NE-SW. This is consistent with observations in North Oman.

The presence of salt in the subsurface is observed to have a significant impact on the style of recent deformation, and how the overburden rocks respond to the far field stress regime. The outlines of the salt ridges and salt withdrawal basins can be clearly seen in the isochron maps for the Upper Cretaceous. The Khuff syncline at the eastern Salt withdrawal edge running sub parallel to Oman coastline and Jurassic rift orientation is also clearly active in that period. Lower Tertiary isochrons show much less salt related subsidence. The central Oman appears as a structurally high area with significant reactivation during both Cretaceous and Tertiary.