A Case Study of Heat Depleted Tail Geothermal Water Reinjection in Sandstone Geothermal Reservoir

Abstract

Geothermal energy has been widely using for space heating in northern China to replace coal burning to resolve the severe atmospheric pollution problems there. However after thermal energy been extracted, the tail geothermal water with high salt contents was mostly directly discharged to drainages or rivers, caused surface water pollution and pressure drop of geothermal reservoir. Reinjection of the cooled tail geothermal water back into the reservoir is necessary. A case study of reinjection to sandstone reservoir in a 52,000m2 space heating program which has been successfully operating for three years. Several key technologies adopted in the practice ,which are (1) Using heat exchanger to shorten the circulation path avoiding air contamination; (2) Coarse and fine two stage filters to remove the suspending solids avoiding physical blockage; (3) Gas deprive instrument to remove the separated gases avoiding gas blockage; (4) Thrust the injection pipe-end deep under well water’s surface avoiding air entering; (5) Longer well screen to ensure sufficient injection space; (6) Large diameter borehole with gravel pack to provide a high permeable zone around the screen, while restraining the reservoir rock from collapsing near borehole.