Reaction Transport Modelling - Simulation of Reflux and Convection Dolomitization Models in an Isolated Carbonate Platfom

Abstract

The new approach in diagenetic studies is to integrate the classical investigative techniques with the reactive transport modelling (RTM) in order to better define the conceptual models in terms of mass balance, kinetic and thermodynamic constrains. Two synsedimentary dolomitization processes (thermal convection and mesohaline reflux) in an isolated carbonate bank (Paleozoic) were tested applying the software ‘Toughreact’ Thermal convection was able to produce a dolomitized wedge in the bank margin area, the final geometry of which was greatly affected by the permeability assumptions and particularly by the Kv/Kh ratio. A mesoaline reflux circulation was established in the bank lagoon with salinity slightly higher than normal sea water (4%) producing a poorly efficient replacement. Sensitivities on the lagoon salinity suggest that when salinity is lower than about 4,5 % the thermal convection is still active in the bank margin and a more complex dolomitization pattern develops influenced by both hydrological patterns. The tests highlight that the main control factors change depending on the specific dolomitization process. The limiting factor for the convection model is the duration of the process while the brine salinity controls the reflux. However, the most effective control is the permeability distribution that drives the hydrology.