Pressure Interference Data Analysis for Two-Phase (Water/Steam) Geothermal Reservoirs

Abstract

A previously published approximate solution by Garg is used to develop a practical procedure for analyzing pressure interference (drawdown) data from a hot-water geothermal reservoir which evolves into a two-phase system as a result of fluid production. The observation well is assumed to remain in the single-phase (liquid) part of the reservoir. A numerical geothermal reservoir simulator is employed in a series of calculations to test the limits of applicability of the interpretation procedure. The numerical results suggest that the accuracy of the computed reservoir transmissivity depends somewhat on the size of the induced two-phase region. Even if the two-phase zone is extensive, the method can still be used to provide a good first approximation for the reservoir transmissivity; forward modeling with a numerical reservoir simulator may then be employed to refine the latter estimate for transmissivity. Numerical results also show that the observation well pressure buildup data will obey the superposition principle after the return of the reservoir to Single-phase conditions.