Seasonal Thermal Energy Storage Characteristics Of Underground Aquifer Under Multiphysics Effect

The coupling effect of natural fluid flow makes the evolution of hydrodynamic field and temperature field in aquifers used for high temperature thermal energy storage more complicated and studies are needed for its action mechanism.Based on coupling of multiphysics,theoretical analysis and numerical simulations were carried out in this paper to study parameter sensitivity of evolution characteristics of hydrodynamic field and temperature field in aquifers used for high temperature thermal energy storage,to obtain preferred scheme of well group arrangement for large-scale aquifer thermal energy storage in the absence of natural regional groundwater flow,and to analyze influence of natural regional groundwater flow on temperature and fluid flow distribution in aquifers and give allowable natural regional groundwater flowrate for aquifer thermal energy storage system consisting of doublet wells.（1）Multi-cycle operation simulations and analysis were carried out for a typical aquifer energy storage system consisting of doublet wells,sensitivity of evolution of hydrodynamic field and temperature field to hydrogeological conditions and design/operating parameters was analyzed,and evolution mechanism of hydrodynamic field and temperature field in aquifers for thermal energy storage was revealed:for thermal energy storage with a temperature of greater than 30℃ under basic conditions studied in this paper,permeability should be in the range from1.27×10^-10 m² to 6.35×10^-12 m²;thermal dispersion of less than 20 m is preferable;thickness of the aquifer should keep the dimensionless value of R_th/H₁ be about 4;well distance should be not less than 3.5R_th to control thermal interaction strength at later operation stage of the system;difference between aquifer ambient temperature and thermal energy storage temperature should be controlled within 45℃;pumping/injection flowrate should be controlled in the range of 50 m³/h to 90 m³/h.（2）Water transport and heat transfer characteristics of systems consisting of single doublet wells and systems consisting of two doublet wells were compared,preferred scheme of well group arrangement for large-scale aquifer thermal energy storage was explored,and contour map of thermal recovery ratio and comprehensive performance parameterη_e under different combination of RR₁（distance between lanes）and RR₂（distance of wells within a lane）were given:when the value of RR₁ is large,thermal recovery ratio of the system increases with the decrease of the value of RR₂;when the distance between warm well and cold well drops below 3 R_th,the thermal recovery ratio of the system is significantly reduced if continuing to reduce RR₁ and RR₂;considering thermal recovery ratio of the system and the effective utilization of underground space,the comprehensive performance of the system is good when theη_eis in the range of 0.2 to 0.4,i.e.,the value of（RR₁,RR₂）is between(1.75R_th,R_th)to(4.5R_th,1.5 R_th)for the system studied in this paper.（3）Effect of natural regional groundwater flow on promotion,deflection,and suppression of water transport and heat transfer in aquifers used for thermal energy storage were analyzed,allowable natural regional groundwater flowrate of aquifers for thermal energy storage with a temperature of greater than 30℃ was obtained,and guidelines for site selection and design of medium-high temperature aquifer thermal energy storage systems were given:cold well should be located in the upstream of the natural regional groundwater flow;in order to ensure service life time and performance of the system,allowable natural regional groundwater flowrate in the aquifer is 19 m/y,and the value is preferable to be less than 10 m/y;permeability of the aquifer should be lower than 1×10^-10 m²,longitudinal thermal dispersion should be less than 10 m,and well distance should not be lower than 4R_th;injection heat temperature is better not more than 60℃,and feasible pumping/injection flowrate should be about 20%smaller than that without natural regional groundwater flowrate under the basic hydrogeological conditions studied in this paper.