Water scaling predication for typical sandstone geothermal reservoirs in the Xi'an Depression

Abstract

The Xi'an Depression in the Guanzhong Basin of western China has been suggested to contain geothermal resources that could aid China in achieving carbon neutrality and optimizing energy structure. However, the high concentration of total dissolved solids (TDS) and scale-forming ions in geothermal water from the depression causes severe scaling problems in harvesting geothermal energy. To reduce scale-related problems, accurate identification of scale types and prediction of scaling during geothermal energy utilization are crucial. This study starts with identifying the types and trends of scaling in the study area, using index-based discriminant methods and hydrogeochemical simulation to calculate and analyze the mineral saturation index of water samples from some wellheads and of reconstructed fluid samples of geothermal reservoirs. The results indicate that the scales are mostly calcium carbonate scales rather than sulfate scales as a result of temperature changes. Several portions of the geothermal water systems are found to have distinct mineral scaling components. Quartz and chalcedony are formed in low temperature areas, while carbonate minerals are in high temperature areas. Despite the low iron content of geothermal water samples from the study area, scaling is very common due to scaling-prone iron minerals. The findings can be used to evaluate geothermal drainage systems and guide anti-scaling during geothermal energy utilization in similar settings.

Keywords

• Xi'an Depression
• Geothermal water
• Sandstone
• Scaling
• Hydrogeochemical modeling