Modelling Studies of the Evolution of Vapour-Dominated Geothermal Systems

Numerical experiments, based on linear stability results, are invoked to model the evolution of two-phase vapor-dominated zones within geothermal systems. A reservoir model with all boundaries impermeable to fluid flow and a uniform heat flux at the bottom boundary is used. The results obtained show that different steady-states are accessible along different quasi-static paths from the same initial vapor-dominated steady-state. Thus, the realization of a steady-state with a two-phase vapor-dominated zone overlying a single-phase hot water region can indicate that the geothermal system undergoes a process of slow cooling. A steady-state with a two-phase vapor-dominated zone overlying a single-phase vapor region can be formed either as a result of slow heating or as a result of a reduction in permeability. A steady-state with an upper vapor-dominated part and a lower liquid-dominated part can occur if permeability of the system has been gradually increased