Scaling potential during (CO2) degassing in geothermal installations

Abstract

Several geothermal doublets in the Netherlands co-produce CO2 and to a lesser extent methane with the targeted hot water. This occurs since the produced water degasses upon pressure release at the surface. As the gas is no longer dissolved, a new chemical equilibrium must be formed which may cause mineral precipitation (scaling) within the geothermal installation. A geochemical evaluation of geothermal water was performed to match and predict the scaling potential for Dutch geothermal doublets. We had the unique opportunity to use water and gas composition data of actual geothermal projects, providing us with case studies for the different target reservoirs in the Netherlands. The performed simulations indicate that doublets containing dissolved CO2 have high scaling risks for carbonate precipitation. It is therefore advisable to take measures to keep the CO2 in solution or re-introduce CO2 or another pH decreasing agent during degassing.