Diagenesis and petrophysics of dolomite in the “Middle” Cretaceous of the Sorrento Peninsula (Southern Apennines).

The characterization and modeling of carbonate reservoirs is generally regarded as one of the most challenging tasks in petroleum exploration and production. The diagenetic history of carbonate rocks can be often very complex. This is mainly due to the composition of carbonate sediments. They are made of few minerals but extremely unstable, and therefore with a very high diagenetic potential. As a consequence, the evolution of porosity and permeability in carbonate rocks can follow very different pathways whose prediction can prove very difficult. Dolomitization is certainly one of the most intensively studied topics in carbonate diagenesis, not only because more than 50% of carbonate reservoirs are dolomitic (SUN, 1995), but also because of the variability of dolomitization processes (MACHEL, 2004). The porosity and permeability changes induced by dolomitization result from a complex interplay of: 1) original texture and composition of the rock; 2) composition, temperature and volume of the dolomitizing fluid; 3) kynetics of the replacement reactions (LUCIA, 2004). This complexity, added to the variety of circulation schemes that can be realized in a dolomitized zone, makes very challenging the prediction of the geometric distribution of dolomite and of its petrophysical characters. Therefore a full understanding of dolomitization processes is fundamental both for oil exploration and production. We present results concerning a study of dolomitized bodies in lower Albian carbonates of the Sorrento Peninsula. Our analyses involved the geometric reconstruction of dolomitized bodies, integrated facies and petrographic analysis, geochemical and petrophysical characterization. Different dolomites generations have been recognized and assigned to petrophysical classes on the basis of their porosity, permeability and connectivity. Structural analysis has been performed on selected outcrops to investigate the relations between the fracture patterns and the lithological and petrophysical characters of each specific rock unit.