Characterisation of a dolomitised offshore carbonate reservoir using basin modelling, digital rock models and high-resolution heat flow simulations

Abstract

Carbonate reservoirs host more than half of the world’s remaining conventional hydrocarbon reserves. However hydrocarbon production from carbonates is very challenging because they often have complex distributions of porosity and permeability that are the result of depositional and diagenetic processes. Indeed, 80% of North American and many Middle and Far Eastern carbonate reservoirs are found in dolomitised rocks where dolomitisation is a main control on reservoir quality. In this thesis, three main contributions relating to carbonate diagenesis in general and dolomitisation in particular were made by combining digital rock models, basin modelling, geomechanical simulations and high-resolution heat-flow simulations. Data from an Ypresian (early Eocene) dolomitised carbonate reservoir located in the offshore Tunisia was used. First, the diagenetic sequence and the corresponding porosity and permeability evolution before and during dolomitisation were investigated using digital rock models. Secondly, published fluid inclusion micro-thermometry data was combined with insights of the burial and thermal history obtained from basin modelling to identify the possible time of dolomitisation. A structural restoration was carried out to reconstruct the basin geometry up to the time when dolomitisation occurred. Finally the basin scale hydrogeology at the time of dolomitisation was investigated using high-resolution heat-flow simulations. The fault permeabilities in these simulations were based on geomechanical considerations and simulations. The resulting flow patterns and temperature distributions in the basin were qualitatively compared against oxygen isotope data that served as proxy for temperature.