Theoretical assessment of James' method for the determination of geothermal wellbore discharge characteristics

Abstract

A theoretical study based on two-phase critical flow models has been performed to evaluate James' empirical method for the determination of geothermal wellbore discharge characteristics. The following conclusions are obtained: the James' empirical method for the determination of stagnation enthalpy, steam quality, and total flow rate are within 8% from results predicted from one-component two-phase critical flow models of Fauske, Moody, and Levy. When the wellbore discharge contains a substantial amount of CO{sub 2}, the determination of discharge characteristics based on the modified James' method agree with those predicted based on a modification of Fauske's model to the same degree of accuracy. An extension of Fauske's theory shows that if a large amount of dissolved salts exists in the discharge, the straight-forward application of James' method for the determination of discharge characteristics will lead to serious errors. When the lip pressure is low and the discharge pipe diameter is equal to or larger than 6-inches in diameter, the pressure gradient in the approach region of the critical flow is small such that the lip pressure measurements taken within 1/4-inch from the exit would not affect the accuracy of the determination of the critical flow rate.