OSCILLATORY INSTABILITY OF ONE-DIMENSIONAL 2-PHASE HYDROTHERMAL FLOW IN HETEROGENEOUS POROUS-MEDIA

We derive a general analytical solution for one-dimensional steady sta te two-phase hydrothermal flow in porous media. The solution indicates that saturation jumps associated with discontinuities in material pro perties of porous media, such as permeability and thermal conductivity , and phase change boundaries are common in these systems. Using linea r stability analysis, we then show that the saturation jump associated with discontinuities in permeability or thermal conductivity of porou s media can be unstable under infinitesimal perturbation. We also prov ide a simple numerical example to show that saturation waves attribute d to the instability can propagate away from the discontinuity as rela tively undamped oscillations. Because rapid spatial changes in materia l properties are likely in nature, we suggest that two-phase hydrother mal systems may often exhibit oscillatory behavior. When observational data on oscillations become available, such data may yield informatio n on permeability and/or thermal conductivity structures of two-phase hydrothermal systems.