Effect of chemical clogging on the permeability of weakly consolidated sandstone due to reinjection at different temperatures


 While utilizing hydrothermal resources, it is necessary to reinject wastewater into the reservoir through reinjection wells to extract heat without mining groundwater. Chemical clogging is a serious problem in the process of reinjection. The precipitation of minerals can lead to reservoir clogging and the reduction of permeability. Therefore, to study the effect of chemical clogging on permeability, the weakly consolidated sandstone of the Neogene Guantao Formation geothermal reservoir in northern Shandong (Eastern China) was taken as the research object. A long-term thermal-hydro-mechanical-chemistry (THMC) coupling reinjection experiment was carried out. The results showed that when the temperature of wastewater was higher than 45 °C, there was a temporary phase of permeability enhancement in the first 10 min of reinjection. However, wastewater with higher temperatures would cause more chemical clogging eventually. XRD and ion analysis results showed that the precipitation of minerals was mainly potash feldspar, illite, calcite, and other carbonate minerals during reinjection. According to the characteristics of low-TDS wastewater in the Guantao Formation, it is recommended to adopt low-temperature wastewater reinjection and reduce the concentration of Ca2+ and Mg2+ in wastewater before reinjection.