Coupled thermal-hydrodynamic-chemical modeling of calcite scaling in geothermal wells

Calcite scaling is a common and persistent issue in geothermal reservoirs, leading to flow restrictions, reduced operational efficiency, increased maintenance costs, and, in severe cases, system failure. Accurate prediction of the location, thickness, and temporal evolution of calcite scale is, therefore, essential for effective management and treatment planning of geothermal wells. This study presents a coupled thermal-hydrodynamic-chemical modeling framework to simulate calcite scaling in geothermal systems. An iterative drift-flux model was employed to resolve the temperature and pressure profiles along the wellbore, while the geochemical interactions driving calcite precipitation were modeled using PHREEQC. The simulation incorporates both crystallization and particulate scaling mechanisms, as well as the potential for scale removal from the wellbore walls. Model validation against field data from wells SNLG87-29 (Nevada, USA) and RN-15 (Reykjanes, Iceland) demonstrated strong agreement in temperature and pressure profiles. Furthermore, solubility models for calcite and CO2 were calibrated against existing experimental data. The modeling approach accurately captured the evolution of calcite scaling in well 84-7 (Dixie Valley, USA), predicting a maximum scale thickness of approximately 30 mm and a vertical distribution span of around 290 m after 75 days of operation. It also appeared that in well 84-7, a 25% increase in calcium concentration led to a 50% reduction in flow area within only 56 days, compared to 74 days in the case with the original calcium concentration. These results underscore the ability of the proposed modeling approach as an important tool for predicting and managing calcite scaling, thereby enhancing the sustainability of geothermal energy production.