Abstract:
State-of-the-art software used for numerical modelling of non-isothermal, two-phase flow in geothermal systems does not allow for the accurate tracking of the water table over time. Current approaches use either a fixed water table or an air/water model where the location of the water table is inferred from the air mass fraction in shallow blocks – an approach which often suffers from convergence issues and whose accuracy is dependent on grid resolution. The present paper first describes the current approaches used in geothermal and groundwater contexts, and then discusses two new methods for tracking the movement of the water table, based around the TOUGH2 code. The methods use a fully saturated, water-only, model where the top surface of the grid moves at each time step as required from a mass balance calculation (derived either through iteration or a flux approximation). Further development and extension of the two methods, plus other mass balance approximation methods, will be explored in order to extend water table tracking to two-phase, non-isothermal flow.
