Insights to controls on dolomitization by means of reactive transport models applied to the Benicàssim case study (Maestrat basin, E Spain)

Partially dolomitized carbonate rocks of the Middle East and North America host large hydrocarbon reserves. The origin of some of the dolomites has been attributed to a hydrothermal mechanism. The Benicàssim area (Maestrat basin, E Spain) constitutes an excellent field analogue for fault-controlled stratabound hydrothermal dolomitization: dolostone geobodies are well exposed and extend over several kilometers away from seismic-scale faults. This work investigates the main controls on the formation of stratabound vs. massive dolomitization in carbonate sequences by means of 2D reactive transport models applied to the Benicàssim case study. Simulation results suggest that the dolomitization capacity of fluids is maximum at temperatures around 100ºC and minimum at 25ºC. It takes on the order of hundreds of thousands to millions of years to completely dolomitize kilometer-long limestone sections with solutions flowing laterally through strata at velocities of meters per year. Permeability differences of two orders of magnitude between layers are required to form stratabound dolomitization. The kilometer-long stratabound dolostone geobodies of Benicàssim must have formed under a regime of lateral flux higher than meters per year during about a million years. As long-term dolomitization tends to produce massive dolostone bodies not seen at Benicàssim, the dolomitizing process there must have been limited by the availability of fluid volume or the flow driving mechanism. Reactive transport simulations have proven a useful tool to quantify aspects of the Benicàssim genetic model of hydrothermal dolomitization