北京南口—孙河断裂带水热系统特征与成因分析

中低温对流型地热资源在华北地区广泛分布,是一种清洁的替代能源.与活动断裂带相关的水热型地热资源是中低温地热系统的重要组成部分.本文基于高精度重力测量、微动测深及钻孔温度测量等数据,从热源、通道、储层和盖层四个方面探讨了南口—孙河断裂带水热系统特征.低重力异常揭示的燕山期花岗二长岩、闪长岩岩体范围为23.8 km~2和14.3 km~2,放射性测井数据计算得到其生热率均值为3.14μW·m~(-3),侏罗系火山岩生热率均值为1.65μW·m~(-3),隐伏岩体和火山岩均难以构成地热系统的附加热源.重力异常显示南口—孙河断裂带宽度约500~800 m,断裂带切割蓟县系雾迷山组白云岩热储层.钻井温度曲线显示断裂带内水热活动强烈,说明该断裂带是导水、导热的重要通道.断裂带南西侧马池口一带第四系松散层与侏罗系火山岩形成了热储盖层,微动测深显示火山岩最大厚度约1500 m.综上源、通、储、盖四个要素分析,该地热系统为热传导一对流复合型,来自京西北山区的大气降水经远距离径流深循环吸收地层热量后沿南口—孙河断裂上移到达裂隙发育的白云岩地层中形成热水.总之,沿南口—孙河断裂带具备了良好的地热地质条件,可达到规模开采的条件.

Characteristics of hydrothermal system and its origin of Nankou-Sunhe fault in Beijing

The low-medium temperature geothermal resources,as a clean and alternative energy source, are widespread in North China. The hydrothermal system which is related to active faults is an important component of low-medium temperature geothermal system. Based on the data of high precision gravity measurement, microtremor survey and borehole temperature logging, we discussed the characteristics of the hydrothermal system in Nankou-Sunhe fault zone, including heat source, channel, reservoir and cap rock. The negative gravity anomaly reveals that the area of buried Yanshanian granodiorite-adamellite mass is about 14.3~23.8 km². The heat production of the buried rock is 1.65~3.14 μW·m^-3. Thus, the buried mass rock is not enough to provide additional heat to the geothermal system. The width of gravity gradient belt of Nankou-Sunhe fault is about 500~800 m. The fault zone cut through the carbonate reservoir of Wumishan Formation of Jixian System and is characterized by strong hydrothermal activity. The fault zone is considered as an important channel of deep geothermal water. The Quaternary and Jurassic volcanic rocks,located in the southwest of the fault zone, constitute the cap rocks of thermal reservoir. The microtremor survey results show that the Jurassic volcanic rocks have a maximum thickness of around 1500 m. Based on the analysis of four factors of geothermal system, i.e., heat source, channel, reservoir, and cap, the genetic model of the geothermal system of Nankou-Sunhe fault can be considered a conduction and convection mixed thermal system. The precipitation from the northwest mountainous area of Beijing is heated by the strata when it moves from surface to the deep ground. The hot water carried by high pressure through the Nankou-Sunhe fault to the dolomite strata and formed hydrothermal system with good geothermal conditions and economic production.