Bifurcations and Stability of Phase Transition Fronts in Geothermal Reservoirs

The stability of a layer of water above a layer of vapor, separated by a boiling or condensation surface, in a geothermal reservoir is considered. In an unperturbed state in low-permeability rocks, there is one interface, which can be either a water boiling surface or a vapor condensation surface. At relatively large permeability values, two new solutions can be formed, corresponding to other positions of the interface. The conditions for the existence and merging of stationary solutions depending on the parameters of the physical system are studied numerically. The stability of stationary positions of interfaces was studied using the normal mode method. It was found that the transition to instability precedes bifurcations of solutions and can occur both at finite and infinite wave numbers.