Experimental study on the water–rock interaction mechanism in a groundwater heat pump reinjection process

Abstract

Groundwater heat pump (GWHP) is a clean new energy technology. However, recharge clogging has always affected the operational efficiency of GWHP systems. The mechanism of the water–rock interaction inducing the chemical blockage of aquifers in particular is not clear enough. In this study, a sand column device was designed to simulate the recharge of GWHP, and the geothermal water and aquifer sand of the actual GWHP project were collected. Moreover, we have characterized the sand using SEM-EDS, XRD and FT-IR; meanwhile, the evolution of the hydrochemical components, the relationship between TDS and mineral dissolution and the concentration variation trend of [Na+ + K+] and [Mg2+ + Ca2+] were analysed. The results showed that the maximum reduction of the albite content in the column, except for P4 and P6, was 13.97%, while the calcite content in the P3–P4 and P7–P10 segments increased by 1.2%. The anhydrite content was reduced in the whole interval. Therefore, the precipitation and dissolution of minerals might occur in the process of recharge, which was more significant in the front of the column. In addition, the water–rock reaction induced by GWHP recharge is a process that also involves the cation exchange adsorption of Na+ with Mg2+ and Ca2+. HIGHLIGHTS A sand column was used to explore the water–rock interaction mechanism in a GWHP recharge process.; The sand samples were characterized after reinjection using SEM, XRD and FT-IR.; The concentration values of Na+, Cl− and in recharge water were linearly correlated with TDS.; The water–rock interaction mechanism involved the dissolution and precipitation of minerals and cation exchange adsorption.;

Keywords

• cation exchange adsorption
• dissolution and precipitation
• heat pump recharge
• mineral composition
• water–rock interaction