Reinjection into well ST0902 and tracer testing in the Xiongxian geothermal field, Hebei province, China

Abstract

The Xiongxian geothermal field is rich in low-temperature geothermal energy stored in sedimentary sandstone and dolomite reservoirs. A reinjection experiment was started in the field on November 15, 2009. The purpose of reinjection in Xiongxian is to counteract pressure drawdown and extract more geothermal energy from the reservoir rocks. This report presents the results of data interpretation from the reinjection experiment and an evaluation of the prospects for future reinjection. Through the interpretation of pumping test data on the production and injection wells involved in this experiment as well as the local reservoir region around these wells, basic hydrogeological information was obtained. Fluctuations of the water level and water temperature of these wells during the reinjection experiment were also evaluated. The analysis results indicate that the reservoir permeability is quite high, with a permeability thickness in the range of 90-120 Darcy-m. The injection well ST0902 has good injection capacity and is well connected to the reservoir. There does not appear to be a direct or open flow channel between the injection and production wells. No tracer was detected in production and observation wells during a tracer test started on January 26, 2010, which involved the injection of 22 kg of fluorobenzoic acid and recovery monitoring in several production wells nearby.

Based on some assumptions, tracer recovery was simulated and predicted. To predict the possible cooling of nearby production wells during long-term reinjection, three simple models were used to simulate possible cold-front breakthrough. The distance of 350 m between the injection well ST0902 and the production well ST0901 appears to be too short, assuming a 15 kg/s average yearly injection rate and 50 years of operation. It is important to find an appropriate balance between the injection rate and the distance between the injection and production wells when designing future reinjection projects in Xiongxian.