Reservoir assessment of the Xiongxian geothermal field, Hebei province, China

Abstract

The Xiongxian geothermal reservoir is a low-temperature sedimentary sandstone and dolomite system. According to long-time pressure and temperature monitoring data, the reservoir temperature for the sandstone is in the range of 40-92°C and for the dolomite in the range of 60-118°C, which is suitable for space heating, swimming pools and greenhouses. No reliable evidence shows that the reservoir temperature has declined in the past few years. Because of increasing production since the 1980s, the water level has dropped continuously and the total drawdown has reached more than 40 m. Based on the available geological and geophysical information, a conceptual reservoir model was set up that explains the heat source, recharge zone, reservoir size, etc. Lumped parameter modelling is used for simulating pressure response data and predicting future water level variations. The simulation results indicate that the reservoir behaves as an open system with recharge water coming from an outer system or through the permeable faults around the Niutuozhen uplift. The prediction results show that by keeping a production rate of 70 l/s for the next 15 years, the water level will be relatively stable and finally reach equilibrium with the surrounding recharge system. In addition, several reinjection wells will be drilled in the next few years, which can slow the pressure drawdown and allow the withdrawal of more heat energy from the formations. The Monte Carlo volumetric method was used for estimating the thermal power potential of the Xiongxian geothermal system; the calculation results show that the recoverable thermal power has a potential between 48 and 300 MWt for the next 100 years with 90% probability.