Carbonate reservoir development in a graben structure (example of Sirt Basin, Libya)

The Sirt Basin formed by intracratonic rifting, with possible phases of stability and of structural reversal. Sedimentation was controlled by tectonic and eustatic influences, locally inducing high sedimentation rates, with the distribution of the various lithologies being governed by ridge-and-trough paleotopography. ; The oil field studied can be separated into 3 paleogeographic areas : 1) a northern area where peri-reef deposits prevails. 2) a central area dominated by protected middle shelf deposits ; and 3) a southern area of dolomitised inner platform deposits, probably intermittently emerged. Lateral facies variations occur throughout the area, whereas argillaceous levels are concentrated in the central area. Discontinuity surfaces are mostly developed in the southern area and decrease in frequency northwards as the sequence thickens. Most of them are related to temporary subaerial exposure in the south, with local solution processes within the northern build-ups. Discontinuities always record breaks in the sedimentation and related processes can significantly improve the reservoir potential of underlying sediments.