基于水化学的沂源盆地地热田成热模式探讨

Study on Thermal Model of Geothermal Field in Yiyuan Basin Based on Hydrochemistry

沂源盆地地热田为低温水热型岩溶热储地热系统,盖层为古近系、白垩系、石炭系,热储层为寒武纪、奥陶纪碳酸盐岩,区内发育的深大断裂如上五井断裂、韩旺断裂、傅家庄断裂等为沟通深部热源的良好通道。为掌握地热田热水的补给来源、热源、地热水年龄,进一步分析其形成机理,采集地热水样品进行了地热水水文地球化学分析、气体及其同位素分析。结果表明,该地热田地热水水化学类型为HCO_(3)·Cl·SO_(4)^(-)Na·Ca型、HCO_(3)-Ca·Mg型,矿化度小于1g/L;地热水补给来源为大气降水,具深循环特征;热源以壳源为主;地热水年龄10.51ka B.P.,为古地下水。结合地下水循环机理,将其地热水形成机理总结为小型断陷盆地深循环承压型。

The geothermal field in Yiyuan basin is a low-temperature hydrothermal karst thermal reservoir geothermal system.The caprock is Paleogene,Cretaceous and Carboniferous.The thermal reservoir is Cambrian and Ordovician carbonate rocks.The deep and large faults developed in the area,such as Wujing fault,Hanwang fault and Fujiazhuang fault are good channels for communicating deep heat sources.In order to master the supply source,heat source and age of geothermal water in geothermal field,and further analyze its formation mechanism,geothermal water samples have been collected for geothermal water hydrogeochemical analysis,gas and isotope analysis.It is showed that hydrochemical types of geothermal field are HCO_(3)·Cl·SO_(4)^(-)Na·Ca type and HCO_(3)-Ca·Mg type,and the mineralization degree is less than 1g/L.The recharge source of geothermal water is atmospheric precipitation,which has the characteristics of deep circulation.The heat source is mainly shell source.Geothermal water age is 10.51B P.Ka,and belongs to ancient groundwater.Combining with groundwater circulation mechanism,the formation mechanism of geothermal water has been summarized as the deep circulation pressure type of small faulted basin.