Nonlinear Effects in Two-Phase Flow to Wells in Geothermal Reservoirs

Abstract

Numerical and quasi-analytic solutions for nonlinear two phase (steam/water) flow to a well have been developed. Simulations of pressure, saturation and flowing enthalpy transients for constant well discharge are compared for different relative permeability functions. The semilog pressure response tends to become a straight line as the rate of change in saturation diminishes and the total kinematic viscosity stabilizes, although noticeable curvature persists for low pressures. During recovery, values of liquid saturation rise significantly above initial undisturbed levels, in some cases producing an all liquid zone surrounded by two phase conditions. Nonlinear effects are also prominent in variations in the enthalpy of the flowing fluid mixture, which equals the observable discharge enthalpy at the well face. Analysis of both pressure and enthalpy data from two phase well tests can yield useful information on reservoir properties such as permeability, porosity, and relative permeability.