Thermal Physical Characteristics Of Rocks And Distribution Of Geothermal Fields In Beijing

The Beijing area is rich in geothermal resources,and the development and utilisation of geothermal resources can promote the transformation of existing energy sources into green and low-carbon ones.Rock thermal properties are the basic parameters of geothermal research,and understanding the distribution characteristics of geothermal resources is the first task for geothermal resource development.This paper presents a detailed analysis of the thermal properties of rocks and the distribution of geothermal resources in Beijing.Seventy-six rock samples from the study area were tested for thermal properties,and the average thermal conductivity of each stratum was calculated as a summed average based on the distribution of different lithologies within the stratum.The overall thermal conductivity of the rock strata ranged from 2.497 to 5.024 W/（m·K）,with the largest thermal conductivity of 5.024 W/（m·K）for the Jixian Formation,which has good thermal storage properties;the overlying strata have low thermal conductivity and together form a good thermal storage cover combination.The distribution of rock specific heat parameters ranges from 1.440 to 2.126 MJ/（m³·K）and rock thermal diffusivity parameters range from 1.117×10^-6～2.322×10^-6m²/s.The geothermal geological data is used as the basis for determining the characteristics of heat sources,thermal reservoirs,cover layers,channels and geothermal fluids in the study area,and defining the formation conditions of geothermal resources in the study area.To establish the thermal column of the rock stratum and combine it with the temperature measurement data of the geothermal wells to calculate the geothermal heat flow,the geothermal temperature gradient of the thermal reservoir cover section and the temperature of the top plate of the thermal reservoir in the study area.Geothermal heat flow values range from 42.4 to 86.8 mW·m^-2,with an average heat flow value of63.66 mW·m^-2;the geothermal gradient in the cover section is distributed between 8.15and 30.88°C/km,with an average geothermal gradient of 24.70°C/km.The temperature distribution of the top plate of the Jixian system thermal reservoir ranges from 37.40 to92.60°C,with an average temperature of 72.84°C,showing excellent conditions for the endowment of geothermal resources,with the southern Daxing area featuring shallow burial and high temperature as a favourable geothermal potential area.By analysing the correlation between geothermal geological features and the geothermal field,it is found that the burial depth of the Moho surface,tectonics,lithology and groundwater are important factors controlling the distribution of the geothermal field.The results of the study can provide data support and theoretical reference for the subsequent continuous research analysis and development and exploitation of geothermal resources in the study area.