| Abstract |
Calcite scaling is widely encountered in geothermal wells and it has to be inhibited since it prevents production. As a result of a pressure drop, thermal fluids start to boil and degas of CO2 while fluids rise in a wellbore. Thermal fluid becomes saturated to calcite as a result of both CO2 exsolution and concentration increase of calcium and carbonates as a consequence of boiling. When the first gas bubble is formed, CO2 exsolution affects the ph and also carbonate species. In order to prevent calcite scaling effectively, inhibitor must be injected into the wellbore at a depth below gas breakout point where thermal fluid is still in liquid phase. Thermal fluid transforms from 100% liquid to both liquid and gas phases at the gas breakout depth when the sum of partial pressures of water vapor and non-condensable gases exceed the wellbore pressure under flowing conditions. There are a lot of ways to predict the gas breakout depth in geothermal wellbores. One of them, the easiest but primitive, is dynamic PT survey evaluation. This method is common in industry but limited with applicable flow rate. Therefore determining gas breakout depth from dynamic pressure profile is not sensitive. In this study, major chemical analysis of brines, in situ measurements (pH, CO2/H2O ratios), steam fractions at sampling conditions, dynamic wellbore temperature and pressure data were used to compute gas breakout depth in a well at Kizildere geothermal field. All calculations were performed with thermodynamic approach by using PHREEQC software. |