Two geothermal fields with calcite scaling in some wells in Iceland were selected for the study of calcite scaling potential. An allowable supersaturation was found by comparing the degree of calcite supersaturation and actual scaling status in the selected wells.The saturation index,0.37～ 0.48, was the boundary between calcite scaling and no scaling. The information about changes in chloride concentration shows that mixing different waters is the main cause to form calcite scaling in the geothermal wells selected in this study.In this case, the content of chloride can be used as an index of scaling.
