Mechanisms and mitigation strategies of reinjection blockage in the Yangbajing geothermal field, Tibet

Reinjection is critical for the sustainable utilization of geothermal resources. However, in high-temperature reservoirs, it triggers water–rock interactions that cause formation damage and a severe decline in productivity. This study integrates laboratory experiments and numerical simulations to investigate water–rock interactions during geothermal reinjection and proposes optimized reinjection strategies to mitigate reservoir clogging. A site-specific numerical model of the Yangbajing geothermal field was developed to simulate the evolution of water–rock interactions in the geothermal reservoir under reinjection conditions, supported by high-temperature and high-pressure water–rock reaction experiments. The thermodynamic parameters in the TOUGHREACT simulator were calibrated using the experimental data to improve the accuracy and reliability of the model. The results demonstrated that quartz and feldspar were the dominant minerals undergoing dissolution in the production wells, whereas illite and mica were the primary precipitated phases. Conversely, in the injection wells, mica is the main mineral undergoing dissolution, and quartz, feldspar, and illite constitute the major precipitated phases. These mineral dissolution–precipitation dynamics near geothermal wells induce a 10% decrease in reservoir porosity and permeability. Furthermore, sensitivity analyses involving adjustments to key simulation parameters revealed that low-temperature and low-flow reinjection mitigated the extent of mineral dissolution–precipitation during geothermal reinjection, thereby alleviating adverse impacts on reservoir permeability and porosity. The flow rate should be maintained below 14 L/s, and reinjection should be performed at a temperature of 50℃, thereby minimizing adverse impacts on the geothermal reservoir. This study provides a systematic analysis of reinjection-induced site clogging arising from water–rock interactions, and the findings offer valuable insights for optimizing the sustainable exploitation of high-temperature geothermal reservoirs.