Quantitative Assessment of Calcite Scaling of a High Temperature Geothermal Production Well: Hydrogeochemistry—Application to the Yangbajing Geothermal Fields, Tibet

Wellbore scaling in high temperature geothermal fields is one of the prominent problems encountered in geothermal development, which involves complex hydrogeochemical processes. In this paper, a coupling model for quantitative assessment of wellbore scaling, including two-phase flow, hydrogeochemical reactions among water-gas-scaling minerals and wellbore adhesion, was established. The wellhead sampling for water, gas and mineral was carried out in typical geothermal wells in the Yangbajing geothermal field. The analysis results show that calcite is the dominant scaling-formed mineral. The geothermal fluid is supersaturated with respect to carbonate minerals. CO2 is the main non-condensable gas in the fluid. Finally, this paper evaluates the location and rate of calcite scaling based on the established model and measured fluid results. The results show that CO2 partial pressure has controlling effect on the precipitation of calcite. The maximum scaling thickness with 14-25 mm occurs 10-20 m above the flash depth for one-year production. Under the assumption that all the precipitation of calcite adheres to the wellbore wall, the scaling thickness is about 200 mm. The high CO2 content in the fluid results in greater thickness of scaling. © 2023 China University of Geosciences. All rights reserved.