Simulation of end-member scenarios of density-driven flow: prediction of dolostone geobody dimensions using COMSOL

Abstract

Abstract Density-driven flows occur in nature and are initiated by density contrast. Salinity and temperature differences are remarkably effective in initiating density-driven flow, which may instigate convective flow. In turn, convective flow is seen by many authors as key for solute and mass transport, which are important processes controlling dolomitization. Two key dolomitization models rely on the application of density-driven flow concepts: (1) dolomitization by shallow or deep reflux of hypersaline brines in coastal ramp settings; and (2) fault-related dolomitization by the inflow of deep-seated fluids. These dolomitization scenarios are evaluated in this paper to infer plausible architecture, geobody dimensions and rock property distributions of dolomitic reservoirs. Since dolomitization processes may also alter porosity and permeability of the host lithology, changes in these properties are also discussed. This contribution focuses on the application of numerical models to assess the applicability of specific dolomitization models/mechanisms in different geological scenarios. We discuss end-member results of flow simulations using the numerical code COMSOL. This software has been chosen to model these processes as it provides a multiphysics framework for solving coupled systems, as in the case of brine reflux and geothermal convection. Our results provide a useful insight to the dynamic propagation of the limestone–dolomite front through fingering effects. The dolomite geobodies/patterns generated with the help of numerical simulation compare favourably with dolomite geobodies seen in outcrops. This study shows that during the dolomitization process the shape, the extent of propagation of the limestone–dolomite front and the rock properties (porosity and permeability) of the dolomitized reservoir are mainly influenced by the ‘contaminant’ source initiating dolomitization: that is, the magnesium-rich brine density in the case of brine reflux and the heat flux intensity in the case of geothermal reflux circulation.