基于81Kr定年的关中盆地深部地下水补给研究

Study on the deep groundwater recharge in Guanzhong Basin benefits for the identification of deep groundwater circulation mechanism. And it has great significance for the sustainable utilization of geothermal resources with the consideration that there are abundant geothermal resources in the thick Cenozoic strata of Guanzhong Basin. Here the research is designed to identify deep groundwater recharge sources and to reconstruct the recharge environment of Guanzhong Basin with the integrated utilization of 81Kr and other tracers. The existing sampling device for 81Kr is not feasible in obtaining deep thermal groundwater samples due to high temperature and degassing of the wellhead. In this regard, a new sampling device suitable for dissolved gas extraction from geothermal groundwater will be built to assure that the gas tightness and extraction efficiency of this device meet the testing requirements. Then the dissolved gas will be collected with the new device for 81Kr measurements in Guanzhong Basin. Deep Groundwater age will be determined using 81Kr、36Cl and 14C data. Meanwhile, the relationship between groundwater age and depth will be discussed. Furthermore, the recharge sources will be ascertained with geochemical constraints. Finally, the recharge temperature and elevation will be estimated with the data of noble gas compositions and stable isotopes. The potential findings will help understand deep hydrogeological processes in the sedimentary basins and provide scientific guidelines for the sustainable utilization of geothermal resources in Guanzhong Basin.

关中盆地沉积有巨厚的新生代地层，地热资源丰富，评价其深部地下水补给，不仅有助于探索地下水深循环机理，且对地热资源的可持续利用意义显著。本项目拟基于81Kr地下水定年与其他多种示踪剂相结合的手段，探讨关中盆地深部地下水的补给来源与补给环境。受深部地下热水温度较高及减压脱气等因素的影响，原有81Kr采样装置不可用。本项目拟搭建一套适用于深部地下热水81Kr采样的十升级溶解气提取装置,使其装置的气密性和提取效率满足81Kr测试要求。利用搭建的装置在关中盆地完成溶解气取样，获得81Kr数据。而后基于多示踪剂的分析方法，确定研究区深层地下水年龄，了解其随深度的变化规律；结合深层地下水的地球化学特征，查明其补给来源；综合惰性气体与稳定同位素数据，确定深层地下水的补给温度与高程。研究成果有助于揭示沉积盆地的深部水文地质过程，并为关中盆地地热资源的可持续开发提供科学依据。

关中盆地沉积有巨厚的新生代地层，地热资源丰富，评价其深部地下水补给，不仅有助于探索地下水深循环机理，且对地热资源的可持续利用意义显著。本项目基于81Kr地下水定年与其他多种示踪剂相结合的手段，探讨关中盆地深部地下水的补给来源与补给环境。受深部地下热水温度较高及减压脱气等因素的影响，原有81Kr采样装置不可用。本项目搭建了一套适用于深部地下热水81Kr采样的十升级溶解气提取装置,使其装置的气密性和提取效率满足81Kr测试要求。利用搭建的装置在关中盆地完成溶解气取样，获得81Kr数据。而后基于多示踪剂的分析方法，确定研究区深层地下水年龄。本项目利用冰现场冷却地热水采样分离溶解气体，和实验室激光冷却原子阱痕量探测（ATTA）技术，获得了一批Kr-81年龄数据。结果表明，该含水层地下水年龄为0.3-1.3百万年，循环更新缓慢。同时14C、36Cl、4He、地下水水位、井口温度等数据与81Kr结果一致性较好。关中盆地地热水同时接受北部北山和南部秦岭降水的补给，地下水滞留区位于渭河断裂北侧。这是我国第一批百万年尺度地下水Kr-81年龄数据。研究成果对古环境重建和地下水循环动力学研究等方面研究具有重要意义。