| Abstract |
China is rich in, especially low-medium temperature geothermal resources. There are more than 3000 natural geothermal springs and 3500 geothermal wells distributed in the country. The direct use of geothermal energy reached 18,900 GWh in 2007, with an annual increase rate of 13%, which ranked first in the world. The space heating area in China has reached 30 million m2 by using geothermal water, and 40 million m2 by using geothermal heat pumps. Due to the heavy exploitation of geothermal water and irrational layout of exploitation, overdevelopment of geothermal resources has occurred in China, and induced some corresponding environmental geothermal issues, including water level (pressure) declining continuously, cold water intrusion and temperature and TDS drop, waste water pollution, etc. Aiming sustainable development of geothermal resources, this paper explores the concept of sustainable yield of geothermal wells and reservoirs. The prerequisite of calculating sustainable yield is to determine a rational maximum allowable drawdown of the production wells in the geothermal reservoir, within a time frame. For a new discovered reservoir, which has not been heavily extracted, it is essential to build a conceptual and numerical model to carry out sustainable yield evaluation based on interference pumping test and water level response observation. Whereas for a developed geothermal reservoir, it is essential to evaluate sustainable yield in view of long-term water level response and the constraints of unacceptable environmental geothermal issues. It is believed that the sustainable development of geothermal resources can be achieved, i.e. the water level and temperature will be maintained in the allowable limits at the end of time frame, if the production is based on sustainable yield. Three case studies have been presented in this paper, one is for a heavily developed sedimentary geothermal reservoir with continuous water level decline, the second is for a new discovered sedimentary geothermal reservoir, and the third is for an overexploited fractured geothermal reservoir with temperature and TDS drop. |