Experimental study on chemical plugging of weakly consolidated sandstone by geothermal tailwater recharge based on artificial cores

ABSTRACT Flowchart of experimental and simulation study on chemical clogging in weakly consolidated sandstone during geothermal tailwater recharge, including artificial core reinjection tests, X-ray diffraction, ion concentration measurements, PHREEQC simulation, and resulting clogging reaction pathways and permeability evolution. Clogging in weakly consolidated sandstone reservoirs hinders geothermal tailwater recharge, with chemical clogging being particularly complex due to multiple influencing factors and in reservoir reactions. This study conducts experimental and simulation research on this issue. Artificial cores made from natural rock samples are used in recharge experiments. After various recharge durations, the internal mineral compositions of the cores and ionic concentrations in the effluent are measured. Results show that potassium feldspar, kaolinite, quartz, and calcite cause chemical clogging. By analyzing composition and concentration changes, potential reaction pathways are deduced: the dissolution of albite promotes the precipitation of potassium feldspar; the OH− generated from potassium feldspar precipitation raises the solution pH, facilitating its transformation into kaolinite; Ca2+ and CO32- in the solution react to form calcite; and quartz is generated as a product of certain chemical reactions. The PHREEQC simulation validates these pathways. Based on these findings, the tailwater recharge process can be optimized by implementing targeted strategies. Pretreating geothermal tailwater can mitigate early-stage potassium feldspar precipitation, while subsequent reduction of Ca2+ and Mg2+ concentrations can inhibit the formation of quartz, kaolinite, and calcite within the reservoir.