Characteristics Of The Geothermal Field In Northern Beijing And The Influence Of Its Exploitation On Seismic Ground Fluid Behaviour

Beijing is one of the six capitals that have geothermal resources in the world. There are four geothermal abnormal zones in Beijing:Northern Yanqing, Northern Beijing, the urban area and Fengheying. Geologically the North Beijing geothermal abnormal zone belongs to the Xiaotangshan uplift. It includes Shahe and Xiaotangshan geothermal fields. The North Beijing geothermal abnormal zone can be defined as a mid-low temperature convective type of geothermal systems, and can also be called a convective deep recycle geothermal system in the Northern Beijing uplift region.Beijing's geothermal exploitation began from 1956. Ten geothermal fields have been exploited and utilized at present, among which, the Xiaotangshan geothermal field is the earliest one exploited and is still utilized now. This field is centered by Xiaotanshan county and expanded to east, west and south. It connects with the Shahe geothermal field to form the North Beijing geothermal field. The Tang-1 well was bored in 1974 to get hot groundwater. The number of wells reached seven in 1979 and 34 in 1990. With the exploitation of recent years, 26 new wells were bored. Now the North Beijing geothermal field becomes a big field with 3 hot reservoirs. The exploitation amount of hot groundwater is 54.5 X106m3 from 1985 to 1999. The water level descended 24.99m totally and descended averagely at a rate 1.75m /a.There are two problems in exploitation of the North Beijing geothermal field. First, the exploitation has experienced more than half century and accumulated abundant data of geology and hydrogeology. However, the scientific research does not keep up with the exploitation and utilization of geothermal fields. It is necessary to study the field systematically and fully so that the scientific basis can be provided for the further exploitation of the Northern Beijing geothermal field scientifically and effectively and serve the sustainable development of capital economy; Second, the large-scale exploitation of the field has been brought serious interference on seismic ground fluid dynamic monitor in this region and made ground fluid observation wells dried in Xiaotangshan, Dongsanqi and Taipingzhuang. It is forced to discontinue or change original observation items and types. The capabilities of seismic ground fluid precursor monitor were weakened greatly. So it is urgent to study the influence of groundwater exploitation on seismic ground fluid precursor monitor to provide scientific basis for the construction and protection of seismic ground fluid stations in our country. For the above purposes and based on collecting and sorting out previous work,this thesis makes a systematical study on the Northern Beijing geothermal field and the influence of its exploitation on seismic ground fluid dynamic monitor.The thesis collects the results of geothermal field exploitation of the Northern Beijing geothermal field in recent 50 years. It addresses the conditions of geology and hydrogeology of the research region with the application of advanced hydrogeology theory and hydrochemistry method and combination of the author's geological experiences.Then it analyzes its geotectonic framework, groundwater recycle system and features of the geothermal field, and outlines the genetic model of geothermal system. Based on all above, the author analyzes further the historical and present statusof the field exploitation, studies the influence of exploitation of geothermal field on seismic groundwater fluid monitor and proposes the countermeasures to reduce the interference of the exploitation of geothermal field.The thesis firstly introduces briefly the background of geology-hydrogeology in the Beijing region, then expounds systematically the geology formation and tectonics, hydrogeological texture, thermal water systems and geothermal field features of the Northern Beijing geothermal field.It puts forward a genetic model, and provides a foundation for the development of the Northern Beijing geothermal field and the study of its influence on seismic ground fluid precursor!Exploit...