Combining basin modelling with high-resolution heat-flux simulations to investigate the key drivers for burial dolomitization in an offshore carbonate reservoir

Abstract

The Eocene El Garia Formation in the offshore Hasdrubal Field was originally a nummulitic limestone in which subsequent burial dolomitization has significantly enhanced permeability. Identification of the reservoir's petrophysical property distributions requires knowledge of the spatial extent of its dolomitization, in turn requiring understanding of the processes that caused the dolomitization. Some of this understanding can be derived from measurements but others need to be simulated. In this study, the former are used as guides and we focus on the latter, evaluating the character of the dolomitizing fluid's movement and temperature patterns by using basin modelling to develop heat-flux simulations to represent the time of dolomitization. Basin modelling reconstructs the region's geology at the time of dolomitization, while heat-flux simulations recreate the appropriate conductive and convective heat and mass transport through these systems. Potential key drivers are rock mass and fault-zone permeability, and the position and shape of any salt domes. The results suggest that salt dome shape and position is the dominant control, the salt dome localizing convective systems which also use convenient faults so that hotter upwelling fluids pass through the Hasdrubal reservoir and are instrumental in the development of burial dolomitization.