Non standard boundary conditions

The fluid and energy transport in high energy geothermal systems is deeply governed by the conditions set at the boundary of the computational domain. In particular, it is well known that the modelling of the interaction between the porous medium model and the atmosphere plays an important role. A boundary condition has been studied during the ongoing PhD of Laurence Beaude to model the soil-atmosphere interaction based on mole and energy balance equations set at the interface between the atmosphere and the porous medium.
The model takes into account two coupling processes: on the one hand, the vaporization of the liquid phase and the convective molar and energy transfer in the atmosphere, on the other hand, a liquid outflow condition.  Both coupling processes are combined in a single boundary condition assuming that the liquid phase does not accumulate at the surface. The radiation and the precipitation recharge are also considered.

This model has been prototyped in a 2D code in combination with both the cell-centred Two Point Flux Approximation and the Vertex Approximate Gradient scheme. It has been assessed numerically on a drying test case as well as on geothermal test cases representing a simplified 2D cut of the Bouillante geothermal reservoir. The results confirm the essential role played by the boundary condition at the soil-atmosphere interface in geothermal simulations.

 Simulation of the 2D cut of the Bouillante geothermal reservoir with three components (water, air and salt)

Illustration of a non-isothermal compositional two-phase Darcy flow simulation using the atmospheric boundary condition: temperature (in Celsius), gas saturation and salinity of the liquid phase (in g/kg) at t=1000 years of the 2D cut of the Bouillante geothermal reservoir with three components (water, air and salt).

The model and its numerical validation are published in a preprint submitted to Computational Geosciences and have been presented at the Stanford Geothermal workshop in 2018, at the Finite Volume for Complex Application international conference in Lille, France in june 2017 and at the CMWR conference in Saint-Malo, France in june 2018.

This model is planned to be implemented in ComPASS in 2019.

Dernière mise à jour le 12.06.2018