Study On Monitoring Of Shallow Ground Temperature Field And Influencing Factors Of Regional Geothermal Field In Nanjing City

During the process of urbanization,a large number of people flooded into the city and caused a series of environmental problems.Shallow geothermal energy,which is a kind of widely distributed and economical renewable and clean energy,has great potential for development and broad prospects for development and utilization.Using this clean and renewable energy can effectively alleviate the shortage of energy and environmental pollution.Building a new type of urbanization is of great significance.In the process of developing and utilizing shallow geothermal energy,a long-term effective shallow ground temperature monitoring station can be established to monitor and evaluate the shallow ground temperature field distribution characteristics in real time.This paper compares the effectiveness and rationality of different monitoring technologies by conducting shallow ground temperature monitoring in Nanjing,and analyzes the characteristics and influencing factors of regional shallow geothermal energy.The main research results are as follows:(1)Based on the distribution of drilling monitoring points in Nanjing,three different monitoring tools have been selected including DTS,FBG,PT100,whose calibration are carried out in laboratory.After the field test,eliminating the water disturbance and the influence of the temperature difference of the adjacent casing,and the compensation effect of the temperature compensation box on the DTS thermometer was tested to ensure the accuracy of the temperature measurement;(2)Based on laboratory calibration and field test,and combining the advantages and disadvantages of each monitoring tool,the drilling monitoring plan of Nanjing City was formulated:1)DTS cable with large tensile strength and corrosion resistance was arranged at all drilling monitoring points to obtain the continuous temperature of the full depth range;2)SG06,SG27 arranged DTS cable and FBG sensor for comparison and calibration of DTS in the deep range;3)Using high precision PT100 at certain intervals in adjacent casing to measure the temperature of 25m range,and the DTS temperature is calibrated to ensure the accuracy of DTS temperature measurement.Finally,a set of methods for data processing and correction is developed for the characteristics of the collected DTS ground temperature data.(3)According to the measured underground temperature data of Nanjing,the distribute regulation of underground temperature and the occurrence of regional geothermal field in Jiangning District and Qixia District are studied,including constant temperature layer and geothermal gradient.The distribution characteristics of geothermal temperature in vertical depth in different seasons and mean temperature in different seasons are analyzed.And compare the difference between the underground temperature of the urban area and the suburb of Qixia District.(4)Based on the hydrogeological and geothermal physical parameters,the numerical simulation study area is determined and the parameters are partitioned.The finite element software FEFLOW is used to establish the hydrothermal coupling model to simulate the underground temperature field migration,and the influencing factors of the underground temperature field in different depth ranges are summarized.