While flowing through a porous medium, a reactive fluid dissolves minerals thereby increasing its porosity and ultimately the permeability. The reactive fluid flows preferentially into highly permeable zones, which are therefore dissolved most rapidly, producing a further preferential permeability enhancement. Thus, the reaction front may be unstable. However, other factors, such as diffusion, suppress the instability of a reaction front. This study presents a numerical model to evaluate the interactions between mechanisms that determine the shape of a reactive front. That is, a method is developed to solve a set of nonlinear equations coupled with fluid flow, species transport, and rock-fluid reactions and includes the effects of grain dissolution and the alteration of porosity and permeability due to mineral-fluid reactions. The numerical model enables us to evaluate how a dissolution reaction affects the porosity structure and fluid pressure variation, from which local Darcy flux can then be evaluated. In addition, the model is used to examine how upstream pressure gradient affects the morphological instability of the species concentrations and the aquifer porosity. Simulation results indicate that, although stable for small upstream pressure gradients, the growth of a planar front becomes unstable for large upstream ones. Moreover, the diffusive, advective and resultant species fluxes of both these mechanisms are computed and presented to further elucidate the behavior of the morphological instability for a planar concentration and porosity front that results from the interactions between diffusion and advection.
- Reactive transport