河北牛驼镇与天津地热田水化学和氢氧同位素特征及其环境指示意义

摘要

本文分析了河北牛驼镇和天津两个中低温地热田水化学、氢氧同位素分布特征及其反映的地热水赋存环境.结果表明: 两个地热田系统存在明显差异, 从浅部第四系地下水到雾迷山组地热水存在各自的混合线.不同层位的浅层地下水、地热水物理混合作用明显.地热田蓟县系雾迷山组和奥陶系高温地热水与碳酸岩含水介质发生的水-岩相互作用, 造成了δ18O发生飘移; 馆陶组和明化镇组地热水主要是浅部第四系地下水与雾迷山组和奥陶系地热水发生混和作用的结果.牛驼镇地热田雾迷山组和奥陶系地热水中Cl–和HCO–3含量增高的同时, SO2?4含量随之减小(0.20~1.30 mg/L), 明显低于天津地热田雾迷山组及奥陶系地热水中的 SO2?4含量(273~394 mg/L), 指示牛驼镇地热田雾迷山组和奥陶系地热水发生了明显的脱硫酸作用.水化学、氢氧同位素分布特征揭示了牛驼镇地热田雾迷山组和奥陶系地热水处在还原环境中, 与浅部第四系地下水水力联系弱, 主要以侧向径流补给为主, 而天津地热田奥陶系和雾迷山组地热水与浅部第四系地下水水力联系较强, 同时存在垂向和侧向径流补给.牛驼镇和天津两个地热田均具有巨大的地热资源开发潜力, 但在开发过程中要坚持资源环境并重的原则, 保障地热资源的持续利用.%Based on hydrochemical characteristics and existing environments of low to medium temperature geothermal fields, the authors revealed an obvious difference of the mixing lines from Quaternary groundwater to Wumishanian geothermal water between Niutuozhen and Tianjin geothermal fields. The water-rock interaction between high temperature geothermal fluid and carbonate rock from the Ordovician and Wumishanian Formation (OAWF) geothermal reservoir may cause δ18O shift. The geothermal water from the Minghuazhen and Guantao Formation is formed by mixing with Quaternary groundwater and geothermal water from the OAWF in Niutuozhen. Cl–and HCO–3of the geothermal water from the OAWF in Niutuozhen increase with decreasing SO2–4 (0.20~1.30 mg/L), which is obviously lower than SO2–4 (273~394 mg/L) in the geothermal water from the OAWF in Tianjin, indicating that the sulfate reduction has occurred in the geothermal water from the OAWF in Niutuozhen. The process of sulfate reduction could enrich the δ2H of the geothermal fluid from the OAWF in Niutuozhen by releasing H2S. The hydrochemical and δ2H-δ18O characteristics prove the relatively reducing environments and weak hydraulic connection with Quaternary groundwater for geothermal water from the OAWF in Niutuozhen. The geothermal water from the OAWF in Niutuozhen has also been mainly recharged by lateral infiltration of precipitation, whereas the geothermal water from the OAWF in Tianjin has strong hydraulic connection with Quaternary groundwater and has been recharged by vertical and lateral infiltration of precipitation. The geothermal water development in Xiongan New Area and Tianjin has great potential. However, researchers must adhere to the principle of paying equal attention to resources and environment in the development of geothermal water and ensure the sustainable development and utilization of geothermal resources.