Geothermals, an abbreviation of geothermal resources, often refer to thermal resources in the interior of the earth which can be utilized economically by mankind. Geothermal resources available for direct use only occur in areas of strong modern volcanic activities and tectonic movements, where heat is enriched in the earth's interior.
Geothermal resources, in a broad sense, include: all products of the geothermal process, that is, natural steam, hot water and geothermal brine; secondary steam, hot water, geotheram brine arising from the water, gas and other fluids artificially introduced into geothermal reservoirs; and byproducts brought out by the above mentioned products(mineral materials with comparatively high value).
At present time five types of geothermal resources have been identified: steam-dominant type; liquid water-dominant type; geopressured type; hot dry rock type and magmatic type. The first two types , called "hydrothermal type", are the major geothermal resources that have been developed and used in China and abroad , while the latter two types, generally called"hot dry rock type", are not commonly developed now.
Geothermal resources are an integrant of mineral energy resources and have extensive usage both as energy and water resources. Their usage is determined by the temperature of the geothermal water. High temperature geothermal resources(t>150 ¡æ )are mainly used for electricity generation; moderate temperature geothermal resources (90
China is one of the earliest countries with a history of several thousand years in the world in using geothermal resources . According to the written records, the Huaqing Pool in Xi'an, Shaanxi Province began to be exploited as early as in the Western Zhou Period(c. 11th century-770 B.C.). In the following dynasties, more hot springs were built into pools for bathing and medical treatment.
Planned exploration and exploitation of geothermal resources in China started after the founding of the People's Republic of China in 1949 and has undergone 3 phases.
Before the year 1970, exploration and exploitation of geothermal resources were focused on natural outcrops. During this period, reconnaissance surveys of geothermal resources were made in some provinces, autonomous regions and municipalities of the country.To serve the development of national medical and public health undertakings and meet the needs of building convalescent hospitals, geothermal resources exploration and evaluation were conducted in some areas of important hot springs, such as the Xiaotangshan hot spring in Beijing. Based on these investigations, the Institute of Hydrogeology under the Ministry of Geology compiled the first Map of Mineral Springs of China in 1959. After that, remarkable progress was made in the development and utilization of geothermal resources when some medical and public health departments set up in succession a number of convalescent hospitals at the sites of hot springs throughout the country.
In the early 1970s, exploration and exploitation of buried geothermal resources started firstly in Beijing and Tianjin by specialized hydrogeological exploration parties under the guidance of Prof. Li Siguang, the first Minister of Geology. As a result geothermal water of 40~90¡æ was discovered at the depth of 1,000 m on the outskirts of Tianjin and in southeastern Beijing and applied for heating, medical treatment, bathe, greenhouse, aquiculture and industrial washing. Meanwhile, exploration and evaluation of the geothermal fields at Houhaoyao in Hebei Province, Dengwu in Guangdong Province and Huitang in Hunan Province were also conducted and a series of experimental geothermal power stations were set up. These efforts pushed the exploration and development of geothermal resources to a new stage.
In the 1980s, with the deepening of the reform and opening-up and the development of socialist market economy in China, new vitality has been injected into the nationwide exploration and exploitation of geothermal resources. International cooperation and scientific and technological exchanges were strengthened, and some new theories and exploration technical methods introduced into China. In 1987 and 1988 high temperature (200¡æ)geothermal resources were discovered in the Yangbajain and Yangyi geothermal fields in Tibet and the industrial Yangbajain Geothermal Power Station was set up. Exploration of geothermal fields which would influence the local economic development and evaluation of regional geothermal resources were enhanced and an understanding of regularities concerning the distribution, formation and conditions for development and utilization of geothermal resources in China was obtained. As the exploration technology was upgraded, geothermal resources at the depth down to 3,500 m or more in conduction-type geothermal fields became explorable and exploitable, and consequently moderate temperature(over 90¡æ )geothermal resources were discovered, and the field of utilization was expanded . At the same time, attention was paid to making use of the advantages of geothermal resources to develop local economy. The use of geothermal resources, like geothermal heating, geothermal cultivation, geothermal sanitariums, hot spring villas which integrated services of medical treatment, entertainment and tourism and comprehensive utilization centers of geothermal resources developed rapidly in many regions. Thus, the exploration and exploitation of geothermal resources stepped into a new stage of all-round development.
Comparing with the conventional energies, geothermal resources constitute only a small portion in China's energy development at present. According to the statistics of 1997 made by the Bureau of Management of Mineral Resources and Reserves under the Ministry of Geology and Mineral Resources, the total quantity of geothermal water that had been used was 944,000 m3 /d, producing an annual quantity of heat of 55.584 ¡Á1015 J, equal to the caloric value of 1.896 million tons of standard coal, which accounts for only 0.1% of China's annual total energy consumption of 1.305 billion tons of standard coal