北京市延庆地热田成因模式

Genetic model of the Yanqing geothermal field, Beijing

通过对地热流体水化学、同位素以及热储岩石热物性测试,分析了延庆地热田大地热流特征、地热流体补给来源、年龄、循环深度以及热储温度等,从源、通、储和盖四方面系统总结了地热田成因。结果显示:延庆地热田属于由正常大地热流加热的非火山型地热系统,热田内大地热流值为75.6m W/m^2,地热流体补给来源于延庆西北部山区的大气降水。热田内三个主要热储中的地热流体年龄和循环深度存在一定区别。燕山期花岗岩、白垩系砂岩和蓟县系白云岩热储中地热水年龄分别为15~21ka、28ka、48ka。花岗岩和砂岩热储中地热流体循环深度约2500m。白云岩热储中流体循环深度为2900~3600m,热储温度分布范围为80.5~98.3℃,平均热储温度90.6℃。

Objectives:The Yanqing geothermal field,as a completely independent thermal field of the ten geothermal fields in Beijing,its unclear genetic model restricts the scientific and orderly development of geothermal resources. There are three reservoirs in the geothermal field, which are Yanshanian granite, Cretaceous sandstone and Jixian dolostone, respectively. With a comprehensive consideration of geothermal geological conditions, heat flow and water flow, this paper aims at constructing a genetic model of Yanqing geothermal field.Methods:Analysis on hydro-chemistry, isotopes and thermophysical properties revealsimportant features of the Yanqing geothermal field,including the geological structure, geothermal flow, and the recharge source, age, heat storage temperature and circulation depth of geothermal fluid. Results: The heat flux of Yanqing geothermal field is 75. 6 m W/m^2. Isotopic data indicates that geothermal water is recharged from the northern mountains of Yanqing by precipitation. Three thermal reservoirs field yield different geothermal water ages and circulation depth. Ages of geothermal fluid in the Yanshanian granite, Cretaceous sandstone and Jixian dolostone geothermal reservoir are 15~21 ka, 28 ka and 48 ka, respectively. The circulation depth of geothermal water is ~2500 m in the granite and Cretaceous sandstonereservoir, but ranges from 2900 m to 3600 m in the Jixian dolostone. As the major reservoir in the Yanqing geothermal field, the ground temperature of thermal reservoir in dolostone varies between 80. 5 ~ 98. 3 ℃ with an average temperature at 90. 6 ℃.Conclusions: The Yanqing geothermal field is a non-volcanic geothermal system heated by normal geothermal heat flow. Water is recharged from the northern mountains of Yanqing with differernt thermal water ages, and then circulated at variable depths.