Experimental Research On Characterizing Behavior Of A Thermal Tracer By ERT

As a substitute for salt tracers,thermal tracers have been widely used in the monitoring and investigation of groundwater environment due to their advantages of little pollution and wide application.Traditional thermal tracer monitoring methods,such as temperature sensor method,have the advantage of high precision,but can not give continuous and complete geological information of the section.To this,in recent years,the resistivity method(ERT)in the field of underground heat affected zone monitoring,much attention has been paid to become a research hotspot,however due to the environmental heterogeneity and underground there is material exchange between solid and liquid,unable to get a more accurate temperature,the corresponding relationship between the resistivity of the need to strengthen the control mechanism research and application conditions.Therefore,this paper carried out an experimental study on characterizing the transport process of heat tracer based on ERT method through laboratory scale experiments,and comprehensively and quantitatively evaluated the applicability of characterizing the transport process of heat tracer based on ERT method from two perspectives of different research scales and different homogeneity of media.Firstly,by monitoring the variation of resistivity and temperature in the homogeneous sand column under static water conditions,the relationship between resistivity and temperature in different porous media was determined and fitted.Then,the effectiveness of describing the transport of heat tracer in one-dimensional homogeneous sand column based on the ERT method was studied to explore whether the ERT method can describe the one-dimensional flow of heat tracer in homogeneous media.On the basis of the above studies,a comparative study of heat transport and salt transport in a two-dimensional fracture-matrix system based on the ERT method was carried out to explore the transport process of heat tracers under heterogeneous conditions.The conclusions of this study are as follows:(1)Through the resistivity response experiment of temperature change,it is found that the resistivity and temperature have an exponential relationship,with a strong correlation and the correlation coefficient greater than 0.996.(2)Through one-dimensional homogeneous sand column experiment,the results of ERT method and distributed temperature optical fiber sensor are compared.It is proved that ERT method can accurately describe the one-dimensional flow of heat tracer in sand column,and the results show that the higher the temperature of water injection,the smaller the resistivity error.(3)Through two-dimensional heterogeneous sand box experiments,it is proved that the ERT method can identify the migration process of salt tracers and heat tracers,and describe the existence of cracks in the fracture-matrix system.The experimental results show that the conductivity is linearly correlated with temperature/concentration.The resistivity response of salt-heat combined tracer is more significant than that of single salt or heat tracer.In this paper,ERT method was used to describe the transport process of heat tracers,and its effectiveness was quantitatively analyzed.The similarities and differences between it and salt tracers were compared,which provided a new idea and theoretical basis for monitoring the change of heat tracers or underground temperature.