Numerical Simulation of Anhydrite Scaling in Production Well at the Sumikawa Geothermal Field, Japan

Abstract

Anhydrite scale was recognized in Sumikawa production well SC-1, where it apparently caused a decrease of steam flow rate. In order to calculate scaling with time, assuming that anhydrite precipitated from geothermal fluid deposits inside of casing pipe with uniform thickness, mathematical model was developed using isothermally non-steady single liquid plug-flow model. The numerical simulation of anhydrite precipitation and production performance were made with scaling calculation coupled with wellbore simulation. The simulation of history matching with variable precipitation rate constants leaded to the rate constant, logk=-4.50. Prediction using the optimum rate constants showed that the slight difference in logk (±0.25) sensitively affected magnitude of decrease in steam rate. Consequently the developed model in this study approximately reproduced wellbore scaling. Under the situation of the local changes in fluid flow, such as with or without slits on 7″ slotted liner and boundary of the different diameter's casing, however, we failed to obtain the good matching between the measured and the calculated values.