Tracer test of reinjection into a metamorphic rock geothermal reservoir in Xishan area, Taiyuan City

The geothermal resources hosted in metamorphic rock in Hekou Town, Xishan area, Taiyuan City, are characterized as a medium-low temperature, mountain-type geothermal field, with geothermal water temperature of 40-42 ℃, and the hydrochemical type of Cl•SO₄—Na. In the study area, the connectivity of the two geothermal wells is not clear. To extend the operational lifespan of the geothermal field, a scientifically grounded production–reinjection scheme must be developed. Understanding the flow dynamics and recharge potential of geothermal fluids in the region is essential for identifying the causes of thermal breakthrough. In this study, the GJDR-1 geothermal well was used as a recharge well and a KI tracer delivery well to monitor the water level and recharge water temperature. A reinjection tracer test was conducted targeting the metamorphic rock reservoir. The GJ-WEMC geothermal well served as the production well and a tracer observation well to monitor the tracer composition and water temperature. By integrating the results of the tracer test with existing geothermal geological data, the protection radius of the geothermal well was calculated. The results indicate a hydraulic connection between the production and reinjection wells. Under natural conditions, the recharge capacity of metamorphic rock thermal reservoir in this area is estimated to be 9.2m3/h. Thermal breakthrough phenomenon will occur when the well spacing is approximately 488 m, whereas a spacing of more than 1140 m is recommended to avoid such effects. The well spacing, reinjection temperature, and reinjection rate will affect the thermal breakthrough.