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<p>To investigate the mechanisms governing hydrochemical evolution in coastal geothermal waters under prolonged exploitation, this study examines the Baoquan hot spring—a representative granitic fracture-controlled geothermal system in Weihai’s coastal area—through integrated hydrochemical and isotopic analyses spanning 2000, 2014, and 2020. The results indicate that the exploitation induced a significant decline in total dissolved solids (TDS), which decreased by 73.83% over 20 years, accompanied by a shift in hydrochemical facies from Cl-Na·Ca type (2000) to Cl-Na type (2014–2020). Concurrently, the reservoir temperature decreased by approximately 20&#xa0;°C, while the proportion of cold-water mixing increased from 52.94% to 63.21% (2014) to 63.53%–64.2% (2020). Quantitative mixing models revealed a reduction in seawater mixing ratios from ~ 40% (2000) to ~ 10% (2020). Mg<sup>2+</sup> depletion signatures indicate that seawater predominantly mixes with geothermal fluids prior to reservoir heating. Mineral precipitation (e.g., anhydrite [CaSO<sub>4</sub>] and dolomite [CaMg(CO<sub>3</sub>)<sub>2</sub>]) was identified as the primary cause of progressive clogging within mixing microchannel. Sustained extraction enhanced recharge driven by hydraulic pressure gradients, while seawater-geothermal water interactions intensified seawater mixing channel clogging. These processes collectively resulted in an annual decline in seawater mixing ratios alongside increased freshwater recharge volumes. Multi-end member water mixing and mineral clogging play important roles in controlling the reservoir temperature and geochemical characteristics of the Baoquan hot spring.</p>

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Impacts of geothermal exploitation on hydrochemical evolution in coastal granite fissure systems: evidence from Baoquan hot spring

  • 期刊论文

  • 发表日期：

    2025年10月14日

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  • Changqin Hu,
  • Xingfang Yuan,
  • Xiaocui Wang

摘要

To investigate the mechanisms governing hydrochemical evolution in coastal geothermal waters under prolonged exploitation, this study examines the Baoquan hot spring—a representative granitic fracture-controlled geothermal system in Weihai’s coastal area—through integrated hydrochemical and isotopic analyses spanning 2000, 2014, and 2020. The results indicate that the exploitation induced a significant decline in total dissolved solids (TDS), which decreased by 73.83% over 20 years, accompanied by a shift in hydrochemical facies from Cl-Na·Ca type (2000) to Cl-Na type (2014–2020). Concurrently, the reservoir temperature decreased by approximately 20 °C, while the proportion of cold-water mixing increased from 52.94% to 63.21% (2014) to 63.53%–64.2% (2020). Quantitative mixing models revealed a reduction in seawater mixing ratios from ~ 40% (2000) to ~ 10% (2020). Mg2+ depletion signatures indicate that seawater predominantly mixes with geothermal fluids prior to reservoir heating. Mineral precipitation (e.g., anhydrite [CaSO4] and dolomite [CaMg(CO3)2]) was identified as the primary cause of progressive clogging within mixing microchannel. Sustained extraction enhanced recharge driven by hydraulic pressure gradients, while seawater-geothermal water interactions intensified seawater mixing channel clogging. These processes collectively resulted in an annual decline in seawater mixing ratios alongside increased freshwater recharge volumes. Multi-end member water mixing and mineral clogging play important roles in controlling the reservoir temperature and geochemical characteristics of the Baoquan hot spring.