Innovative Modelling Method of Diagenetic Overprints in Carbonate Reservoirs

Abstract Modelling products of diagenetic processes in carbonate reservoirs is still a challenge since both stochastic and physicochemical simulations cannot easily reproduce complexity of features generated by those processes. An alternative way to modelling diagenetic overprints deals with an innovative methodology based on process-like simulation of the fluid-rock interaction and its effects on reservoir properties. The principle of the method is related to a lattice gas automata used to mimic the diagenetic fluid flows and to reproduce the diagenesis effects through the evolution of both mineralogical composition and petrophysical properties. This new modelling approach is well adapted to handle dolomitization processes and was applied on two case studies. In the Urgonian carbonates, (Barremian-early Aptian) characterized by a platform facies predominantly of rudists and bioclastic/ooid grainstone (S.E. France), five main diagenetic stages have been identified. The 2D modelling focuses on dedolomitization features located on parasequence boundaries. In the Venetian platform (Lias, N.E. Italy), data collected show four diagenetic stages. The main one, related to dolomitization along fractures, is called per-ascensum dolomitization. Three of the diagenetic stages have been simulated on a 3D depositional model previously filled with initial facies and original petrophysical properties. The simulations of the Urgonian series lead to generate dedolomitized bodies related to surface boundaries that match those identified on the outcrop. Calibration on actual data of diagenetic parameters used for per-ascensum dolomitization modelling of the Venetian platform also enables to reproduce and to visualize the displacement of dolomitizing fluids in the fracture network and within the stratigraphical layers. In both cases, the evolution of the mimetic diagenetic fluid effects on mineralogical composition property can be followed through space and numerical time, which helps to understand the heterogeneity of reservoir properties. This method enables the modelling of diagenetic overprints without any explicit physicochemical equation in any carbonate reservoir for which diagenetic products are generated through fluid transport.