Prediction of Calcite Scaling at the Oguni Geothermal Field, Japan: Chemical Modeling Approach

Abstract

Both calcite-scaled wells and non-scaled wells exist at the Oguni geothermal field and its vicinity. The chemical compositions among all pre-flashed waters exhibit no significant difference. The most important factor on calcite saturation at the Oguni field seems to be the degree of steam loss in addition to the reservoir temperature. The calcite saturation index (log of pre-flashed water increases with steam loss in the reservoir. anhydrite saturation index, however, is little affected by steam loss. The change in the anhydrite saturation index during production may be empirically used as an indicator of calcite scaling. The anhydrite saturation index equal to -0.3 seems to correspond to the threshold for calcite scaling at the Oguni field. Calcite scaling may be decreasing in Oguni wells because the anhydrite saturation indices change to this criterion during production.