北京城区地热田某地热井热水地球化学研究

地热的开采会引起热储压力的降低 ,从而引起热流场的改变。热储压力的降低可能导致温度较低的地下水的流入 ,也可能导致深部更高温度热流体的补充 ,从而引起地热流体化学特征的变化。地热流体中一些组分的浓度依赖于热流体温度的高低。不同温度的水发生混合会破坏地热系统的化学平衡 ,从而改变地热流体的化学成分。因此 ,地热流体的化学监测可以提供许多有关地热系统变化的宝贵信息。由于长期开采 ,北京城区地热田的压力明显下降 ,并引起了地热水化学成分的细微变化。根据 1984年以来一眼地热井的地热水化学监测资料 ,研究了地热水的化学成分、地球化学温标的变化规律以及地热活动的总体强度和水 /岩平衡矿物中的示温矿物的变化趋势 ,说明地热的开采既引起了地热田水补给的加强 ,又导致了地热田热补给的加强

LONG-TERM GEOCHEMISTRY CHANGES OF GEOTHERMAL WATER FROM A GEOTHERMAL WELL IN THE URBAN GEOTHERMAL FIELD, BEIJING

The abstraction of geothermal fluid often causes pressure drawdown of the geothermal reservoir and changes of flow fields. The lowering of the pressure of geothermal reservoir may lead to the inflow of water with lower temperature, and also may lead to the recharge of geothermal fluid with higher temperature. This will cause changes of the chemical components of the geothermal fluid. The content of some components of geothermal fluid are highly dependent on temperature. The mixing of water with different temperatures may cause changes of the status of chemical equilibrium and changes of chemical components of geothermal fluid. Therefore, chemical monitoring of geothermal fluid may give important information about the changes of geothermal systems. Long term exploitation in the urban geothermal field has caused large pressure drawdown of the reservoir in the city of Beijing. Based on the long-term monitoring, a study including chemical components of geothermal water, geothermometers, the general strength of geothermal activity and water/rock equilibrium indicates that the production of the geothermal field has caused certain increase of both water and heat recharge into the geothermal reservoir.