Numerical Analysis of Transient Steam-Water Two-Phase Flow in Geothermal Production Wells with Multiple Feed Zones

Abstract

Geothermal production wells sometimes show oscillations of wellhead pressure and flow rate when they are completed with multiple feed zones. This instability of the production leads to problems of power plant operation, such as lack of steam supply and unstable turbine inlet pressure. In the worst-case scenario, steam production of the well may cease. Its mechanism, however, has not been well understood. In this study, we developed a numerical model of transient steam-water two-phase flow in a geothermal production well. This wellbore model is coupled with a reservoir model so we can treat flow rate change with time from the reservoir into the wellbore and deal with a well with multiple feed zones. We use a homogeneous model for steam-water mixture flow in a wellbore and related conservation equations. The simulation results show that the oscillation of flow rate in a wellbore begins to appear as the temperature difference of the fluids between feed zones becomes large. This also shows that the oscillation is generated by interactions among pressure, pressure drop, and specific enthalpy in a wellbore.