Assessment of geothermal resources in Xianyang, Shaanxi province, China : lumped parameter modelling and predictions

Abstract

The Xianyang geothermal field, located in Shaanxi province in the People´s Republic of China, is rich in low-temperature geothermal resources, having considerable flow-capacity, with the Wei River northern bank fault playing a key role in geothermal activity. Today more than 30 wells, ranging in depth from 1602 to 4080 m, have been drilled in the region with temperatures ranging from 55 to 120°C. The geothermal water is suitable for district heating and balneology. Since the first well was drilled in 1993, geothermal space heating has been developed to take the place of coal boilers and so far approximately 3 million m2 of geothermal space heating have been established , which is equivalent to reducing 120,000 tons of CO2 emissions annually; these numbers are continually increasing. A conceptual reservoir model was set up that explains the heat source, recharge zone and reservoir size, based on the available geological and geophysical information. Lumped parameter modelling is used for simulating pressure response data and predicting future water level variations. The results of a 20-year prediction show that the water level of Sanpu 1, Sanpu 2 and WR 3 will drop 1.1, 5.0 and 2.0 m per year according to pessimistic closed models, respectively, if the present production rate is maintained. In contrast, predictions with open models shows an optimistic future in which the water level of Sanpu 1, Sanpu 2 and WR 3 will remain stable at 0.36 MPa, 0.05 MPa and 53 m under the ground, respectively. A prediction with 30% injection results in a tendency where the water level decline slows down. The permeability of the Xianyang reservoir is estimated to be in the range of 6-24 mD according to simulation parameters. The results of pressure interference calculations indicate that over the past ten years considerable interference should have occurred between wells.