This paper takes the Dongba Sag in the Tianzhu geothermal field in Beijing as an example,in which the thermal groundwater is of the highest temperature and the highest total dissolved solids.Data of the geothermal wells and related geological survey in the recent years were used to better examine the mechanism of the relative high temperature and total dissolved solids by analyzing the geological conditions of the geothermal filed,such as faults,geothermal reservoirs,cap rocks,hydrochemistry and occurrence of the thermal groundwater.The results show that the northern section of the Taiyanggong fault,Liangxiang-Qianmen fault and Louzizhuang fault are big faults,and they deeply cut the Jixian geothermal reservoir.The Jixian geothermal reservoir in the Dongba Sag is approximately 1,000 m lower than two sides of the sag.Thus,the Dongba sag is a relatively closed area like a “black box”.This kind of geological structure leads to a very weak lateral recharge,and the south of Dongba Sag is in a closed reduction environment.The results also show that the deep heat source can flow up into the northern section of Taiyanggong fault along the fault.The high temperature geothermal fluid in the deep part of the sag is ruptured in the geothermal reservoir in the southern Dongba Sag.As a result,the geothermal fluid is of high temperature,high dissolved solids and week yield to wells.This work is of positive significance for the development of geothermal resources in our country.%以北京地区地热流体中温度和矿物质含量较高的东坝凹陷南部地区作为实例,在完整的地热钻孔及相关地质资料基础上,通过对研究区断裂构造、热储层、热储盖层、地温场、流体水化学特性和富水性等地热地质条件进行分析,研究造成该区地热流体中温度、矿物质含量升高的主要原因.研究表明:受太阳宫断裂北段、良乡一前门断裂和楼梓庄断裂的切割作用,东坝凹陷南部地区热储层下落近千米,形成了一个较为封闭的“黑箱子”区域.这种独特的地质结构导致东坝凹陷南部地区接受东南城区地热田侧向补给较少,长期处于较为封闭的还原环境;太阳宫断裂北段存在深部的热源通道,地层深部的高温热流顺断裂上涌在东坝凹陷南部地区的热储层富集,因此该区地热流体表现出温度高、矿物质含量高、富水性差的特征,该研究对我国今后地热资源的开发具有积极的借鉴意义.
展开▼
