Coupling OpenFOAM and PhreeqC to quantify local disruptions of hydrochemical equilibria due to bubble formation and stripping of CO2

Scaling refers to the accumulation of solid precipitates on the surfaces of pipes, heat exchangers, and other equipment across various industrial processes, notably within geothermal systems. This process can lead to decreased efficiency and increased maintenance needs, highlighting the importance of accurate prediction and control methods.

Hydrogeochemical models tend to overestimate the extent of scalings, especially if the scalings are caused by a disruption of the lime-carbonic acid equilibrium due to degassing in the geothermal fluid. This is because the models are not capable to describe diffusion-limited crystal growth, partial volume effects, and local saturation states adequately. In this study we introduce a novel approach by coupling a multiphase CFD-model (OpenFOAM) for the description of the gas phases in the produced geothermal fluids with PhreeqC to simulate the hydrochemical effects of the stripping of CO2 by the gas phase. This results in a model with high spatial and temporal resolution which allows to quantitatively differentiate between processes in the fluid and the processes taking place at the solid interfaces (pipe walls or matrix).

The code is validated with published experiments in bubble columns. The coupling results in a highly flexible model which can account for different hydrochemical conditions, different matrix, and varying gas composition using a well established thermodynamic database. Transfer to other hydrochemical conditions is therefore facilitated.