Investigation of Thermo-hydro-geochemical Processes in a Standing Column Well Intersected by a Fracture

Abstract

Local thermal and chemical conditions may favor minerals' scaling

Impact of Standing Column Well Operation on Carbonate Scaling

“…Indeed, the median concentrations were systematically lower at higher temperatures, which indicates that calcite precipitation probably occurred when the GSHP system was in cooling mode. These experimental observations are consistent with the results of Eppner et al [27,28] who used a coupled geochemical model and observed numerically that recirculation of cold groundwater in a SCW promotes calcite dissolution and calcium enrichment, while recirculation of warmer groundwater during cooling mode favors calcite precipitation and calcium depletion. The fact that magnesium concentrations were also lower in cooling mode is a good indicator that dissolution and precipitation of dolomite or magnesian calcite were also active in the GSHP system.…”

“…The operation of a GSHP modifies the groundwater temperature (hotter during cooling mode, cooler during heating mode). Recently, the operation of a SCW has been simulated with a coupled thermo-hydro-geochemical model [8,27,28]. These works clearly showed that during heating mode, the continuous recirculation of cold groundwater in a SCW promotes calcite dissolution and enrichment of Ca 2+ .…”

“…On the opposite, it was observed numerically that the cooling mode promotes precipitation mostly in the above-ground equipment. This advanced model was further exploited and revealed that sealing the SCW to prevent CO 2 degassing decreased by 33.3% the precipitation rate of calcite [28], and that a constant bleed rate of 10% reduced the calcite accumulation on borehole walls due to smaller temperature variations in the SCW [27].…”

“…Based on the concentrations measured at the outlet of the groundwater treatment system (SP-2), it is clear that the continuous operation of the treatment unit could explain at least a part of these reductions. A second explanation lies in the probable impact of temperature on the equilibrium constants, which induces calcite precipitation and pH drop when the SCW is operated in cooling mode [27,28]. Degassing of CO 2 can also explain a part of the calcium reduction [28].…”