Reinjection Experiment for a Sandstone Aquifer in Pingyuan, China

Abstract

For the purpose of sustainable development of geothermal resources, especially for the sandstone aquifers with very little geothermal water recharge in China, reinjection has been becoming an effective means for sustainable and environmentally friendly geothermal utilization. It is efficient for waste water disposal, as well as to provide additional recharge to geothermal aquifers. Therefore, reinjection counteracts fast pressure (water level) drawdown induced by heavy development, and extracts more thermal energy from the reservoir rocks, together with a larger production capacity. Meanwhile, reinjection can also mitigate land subsidence and be used to maintain geothermal manifestations (artesian wells, natural hot springs). But due to scaling, clogging and corrosion, the reinjection rates decrease dramatically in sandstone aquifers. A reinjection experiment in sandstone aquifers of Neogene Guantao Formation, which are widely distributed in North China Plain, has been successfully conducted in Pingyuan County, Dezhou City, Shandong Province, China. The distance between the production and reinjection wells is 232 m, the depth to sandstone aquifer is 1130.70`1393.30 m, and the TDS of geothermal water is 5221.8 mg/l. The experiment has continued for 54 days, with the largest reinjection rate of 70 m3/h, accompanying the water level increase in reinjection well of 28.65 m, and the water level increase in production well of 3.55 m. This paper describes the geological and geochemical conditions of the experiment site, and mainly explores the technical solutions for rapid aquifer clogging, which often accompanies sandstone aquifer reinjection. It involves reinjection well drilling techniques, as well as filtering, oxygen free and re-pumping for the reinjection well at an interval of reinjection for 7 days.