The Effect of Vapor-Pressure Lowering upon Pressure Drawdown and Buildup in Geothermal Steam Wells

Abstract

The equilibrium vapor pressure of liquid water in an unsaturated porous medium is less than the steam table value. This phenomenon is incorporated into a finite difference model for the production of stem in vapor dominated geothermal reservoirs. In the model the steam is assumed to be produced by boiling of immobile liquid water in the vapor dominated zone. Assuming radial symmetry, plots of pressure buildup and drawdown are obtained both with and without vapor presume lowering. The results show that whereas pressure drawdown is virtually unchanged, the pressure buildup curve is significantly different when the vapor pressure lowering effect is included. The pressure plateau predicted by the model without vapor pressure lowering is eliminated, and the response is similar to that expected for noncondensable gas.