Assessment of geothermal resources in Xi'an, China

Abstract

The Xi’an geothermal field, where about 70 geothermal wells had been drilled by the end of 2001, is located in the province of Shaanxi in central China, The Xi’an geothermal reservoir is a low-temperature sandstone reservoir with conduction-dominated heat flow. Temperature of the hot water produced from the Xi’an geothermal system ranges from 40 to 104?C. The production rate has increased rapidly since large-scale exploitation began in 1994, and correspondingly the water level has declined rapidly, with an average annual drawdown of 10 m. The reservoir’s main geological features are described, and the present utilization of the Xi’an geothermal field are reviewed. A simple lumped parameter model was used to simulate the water level of well XA-1, by using the LUMPFIT software, and to estimate the properties of the system based on the model parameters. LUMPFIT was also used to predict the potential of the system under various production scenarios with and without injection. Another program, VARFLOW, was also employed to simulate the existing data and to predict future performance of the system. The potential was determined by specifying a maximum allowable pump setting depth of 150 m. On this basis, the potential of the Xi’an geothermal system is estimated to be about 5 million tons per year until 2010. The possible risk of thermal breakthrough during reinjection, is evaluated in order to determine the minimum distance between production wells and reinjection wells. A tracer test is suggested to study the flow paths of the injected water.