A compositional formulation for reactive transport modelling of systems involving strong coupling between geochemistry and hydrodynamics

In certain reactive transport applications, strong coupling between geochemical reactions and hydrodynamics exists. The conversion between gypsum and anhydrite [1], the precipitation of nesquehonite during CO₂ sequestration [2] or the heat generation induced by sulphide mineral oxidation [3] are examples in which the geochemical reactions can significantly alter the evolution of flow and reactive transport processes. In these instances, commonly used reactive transport modelling approaches, which rely on decoupling flow and reactive transport processes, have limitations. For density dependent flow problems, the coupling between flow and reactive transport can be accounted for through a Picard iterative approach [4]. However, this is a computationally expensive approach which solves two nonlinear problems multiple times at each timestep. More recently, a weak explicit coupling approach was developed to capture the impact of chemistry on flow by integrating water as a component and perform a volume balance calculation [5]. Our current research focuses on the development of a compositional model, in which the flow variables (pressure, density) are directly integrated in the reactive transport problem. The advantage of this approach is that it utilizes a global implicit approach as it simultaneously solves the flow and reactive transport problems including the water balance. First, we present the novel reactive transport approach, which has been implemented in MIN3P-THCm. Then, we present relevant test cases, verifying the consistency of the approach in comparison to the traditional formulations. Finally, we show that, in highly coupled systems, not considering these coupled effects may lead to significant errors in simulating system evolution, highlighting the benefits of the newly developed approach.

[1] Jowett, Cathles & Davis (1993). AAPG Bulletin, 77(3), 402-413.

[2] Harrison, Dipple, Power & Mayer (2015). Geochimica et Cosmochimica Acta, 148, 477-495.

[3] Lefebvre, Hockley, Smolensky & Gélinas (2001). Journal of Contaminant Hydrology, 52(1-4), 137-164.

[4] Henderson, Mayer, Parker, & Al (2009). Journal of contaminant hydrology, 106(3-4), 195-211.

[5] Seigneur, Lagneau, Corvisier & Dauzères (2018). Advances in Water Resources 122, 355-366