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Abstract To study the evolution rules and behaviors of heat transport in a sandstone geothermal reservoir caused by cooled water reinjection, this research focuses on the quantitative relationship among reinjection parameters and the thermal breakthrough time of production wells. The permeation, tracer, and reinjection tests were conducted in a simulation model using a large sand tank in conjunction with the numerical simulation method based on COMSOL Multiphysics. Subsequently, sensitivity analysis and nonlinear fitting were performed to investigate the effects of fluid viscosity and density on the reinjection process, and to analyze the impact of reinjection parameters on the thermal breakthrough time of production wells, along with their underlying mechanisms and law. The results indicate that the migration velocity of reinjection water is greater in coarse sand layer compared to that in medium sand layer, and the thermal breakthrough time t is linearly correlated with reinjection rate (Q) raised to the power of − 0.85, temperature difference (ΔT) raised to the power of − 0.21, and spacing between the production and reinjection wells (R) raised to the power of 1.4. The correlation equation and analysis show that when the temperature difference between production and reinjection ΔT is more than 30 ℃, the influence of ΔT on the thermal breakthrough time of production well becomes weak, because ΔT exerts an effect on the thermal breakthrough time of production well t by influencing the relative position of the 18.5 ℃ isotherm in the temperature transition region. The error in reinjecting high-temperature fluid into low-temperature fluid may be corrected by introducing a viscosity correction coefficient α μ.

To study the evolution rules and behaviors of heat transport in a sandstone geothermal reservoir caused by cooled water reinjection, this research focuses on the quantitative relationship among reinjection parameters and the thermal breakthrough time of production wells. The permeation, tracer, and reinjection tests were conducted in a simulation model using a large sand tank in conjunction with the numerical simulation method based on COMSOL Multiphysics. Subsequently, sensitivity analysis and nonlinear fitting were performed to investigate the effects of fluid viscosity and density on the reinjection process, and to analyze the impact of reinjection parameters on the thermal breakthrough time of production wells, along with their underlying mechanisms and law. The results indicate that the migration velocity of reinjection water is greater in coarse sand layer compared to that in medium sand layer, and the thermal breakthrough time t is linearly correlated with reinjection rate (Q) raised to the power of − 0.85, temperature difference (ΔT) raised to the power of − 0.21, and spacing between the production and reinjection wells (R) raised to the power of 1.4. The correlation equation and analysis show that when the temperature difference between production and reinjection ΔT is more than 30 ℃, the influence of ΔT on the thermal breakthrough time of production well becomes weak, because ΔT exerts an effect on the thermal breakthrough time of production well t by influencing the relative position of the 18.5 ℃ isotherm in the temperature transition region. The error in reinjecting high-temperature fluid into low-temperature fluid may be corrected by introducing a viscosity correction coefficient αμ. [ABSTRACT FROM AUTHOR]

• Injection salinity can cause the variation of thermal diffusion in aquifer. • Thermal breakthrough is mainly affected by injection salinity and porosity. • Injection temperature/hydraulic gradient cause hot and cold storage disparity. When brine aquifer is used as thermal energy storage medium, pore structure and permeability of brine aquifer may change owing to the difference of salinity and temperature between the reinjected water and underground. Consequently, heat transfer characteristics and thermal energy storage performance in brine aquifer may vary correspondingly. In present work, heat transfer in brine aquifer is investigated, which considers the effect of reinjected water salinity, temperature, effective porosity and hydraulic gradient. Based on the temperature variation of pumping water, thermal energy storage efficiencies are analyzed under different conditions. The results indicate that the heat transferred from reinjection well to pumping well decreases with the reduction of reinjected water salinity, temperature difference and effective porosity of brine aquifer. The occurrence of thermal breakthrough delays when reinjected water salinity and effective porosity reduce, while thermal breakthrough is almost unaffected by reinjected water temperature and hydraulic gradient. The effective porosity of brine aquifer has the greatest influence on performance of thermal energy storage. When effective porosity of brine aquifer increases from 0.33 to 0.43, cold storage efficiency and heat storage efficiency decreases about 56.56% and 40 %, respectively. Reducing reinjected water salinity and hydraulic gradient result in the increase of thermal energy storage efficiency. Reinjected water temperature has opposite effect on heat and cold energy storage efficiency. Sensitivity analysis indicates that the sensitivity of heat energy storage efficiency to considered parameters is greater than that of cold energy storage efficiency does. [ABSTRACT FROM AUTHOR]