Compartmentalization of Carbonate Reservoirs by Cenozoic Reverse Faulting in the Northern Oman Mountains (UAE)

Liesbeth Breesch¹, Rudy Swennen¹, and Benoit Vincent^2
1K.U.Leuven, 3001 Heverlee, Belgium
²Institut Français du Pétrole, Rueil-Malmaison, France

The objective of this study was to document similarities and differences in diagenetic processes influencing reservoir rocks and the importance of syntectonic focused fluid flow on both sides of a major reverse fault in the Northern Oman Mountains. In Wadi Ghalilah, Early Cretaceous Thamama Group limestones are overthrusted by Late Triassic Ghalilah Formation limestones. A detailed petrographical and geochemical analysis of calcite-filled fractures was carried out. This made clear that hanging wall and footwall carbonate rocks experienced a completely different diagenetic history. Early diagenesis was quite similar since in both fault blocks most fractures are pre-burial extensional in origin, formed by a crack-seal mechanism, and the calcite infill is host-rock buffered. These veins predate burial and tectonic deformation and consequently do not provide any information about syntectonic fluid flow. The fractures post-dating tectonic stylolitisation in the footwall, by contrast, show evidence of syntectonic migration of saline formation waters at temperatures of 80 to 110°C. These fluids probably were sourced from the subsurface via the reverse fault, which acted as a fluid conduit during deformation. At the same time, however, this fault functioned as a permeability barrier towards the hanging wall, since no evidence of syntectonic fluid flow is present here. In this way compartmentalization of the hanging wall and footwall block was realized. The occurrence of compartmentalization of reservoirs by faults is of main importance in hydrocarbon exploration for the distribution of reservoir properties and prediction of production volumes.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece