Thermal Structure And Genesis Of Tangdong Geothermal Field In Zhaoyuan,Shandong Province

The Tangdong Geothermal Field in Zhaoyuan City is located in the middle of the Jiaodong Peninsula.The intersection of several fault zones provides conditions for the formation of the geothermal field.The area has large reserves of geothermal resources and considerable development potential.Conducting research on thermal structure and hot water formation in this area will provide a scientific basis for the rational development and utilization of geothermal resources in the area,and it is also of great significance for promoting local social and economic development.Based on the data of geology,hydrogeology and geothermal geology in the study area,field investigation and ground temperature measurement were carried out.In this paper,the history of the area and the chemical analysis data of the collected water samples are fully utilized to systematically analyze the genesis of the underground hot water in the area.At the same time,according to the data of rock thermophysical properties collected in the study area,the conceptual model of thermal structure in the study area is constructed scientifically,and the genetic mechanism of geothermal resources in the area is further described.The main conclusions are as follows:（1）Based on the meteorological data and hydrogeological data in the area,the main sources of underground hot water supply in the area are analyzed,and the thermal storage temperature and hot water circulation depth in the area were reasonably calculated.Base on the analysis of hydrogen and oxygen isotope data of groundwater in the study area,the main source of geothermal water supply in this area is precipitation in the Luoshan area,which is mainly supplied by 585.1-882.35m in the northern part of the study area.According to the silica temperature scale and the calculation results of the silicon enthalpy model,the thermal storage temperature in this area is 103.82～131.32℃,the hot water circulation depth is3717.42 meters,and the cold water mixing ratio of underground hot water is 61.01%.（2）Based on the geological conditions and drilling data in the area,a conceptual model of the thermal structure of the area was established.Through analysis of the thermal conductivity and radioactive elements of the rock samples in the area,the results show that the average value of the thermal conductivity of the rocks in the area is 3.49 W/（m·k）;the elements potassium,uranium,and thorium are used to calculate the radioactive heat generation rate of the rocks.The results show that the average heat generation rate was1.15μW/m³.According to the temperature measurement data,the geothermal gradient in this area was calculated to be 28.87℃/km,and the shallow heat flow value is calculated by using the geothermal gradient,and the geothermal heat flow value in this area is determined to be101.47 m W/m².According to the relationship between the shallow heat generation rate and the seismic wave,the deep heat generation rate data is calculated.The heat generation rate data is used to calculate the heat energy generated by the decay of radioactive elements in the shallow and deep layers,and then the"stripping method"is used for the mantle The heat flow is solved,and the crustal heat flow（Q_c）in the area is about 20.56 m W/m²,and the mantle heat flow（Q_m）is about 80.91 m W/m².The thermal structure type in this area is determined to be the"cold crust and hot mantle"type.（3）The conceptual model of geothermal field in the area was further improved by combining the previous research results of the geothermal formation mechanism in the area.The cap rocks in the area are mainly Quaternary sedimentary layers with a thickness of 3～10meters.The lithology is mainly cohesive soil and sandy soil.The heat storage is mainly the fractured zone heat storage dominated by Mesozoic monzogranite.The water inflow of a single well in the thermal reservoir in the area is about 1798.56m³/d.Based on the topographic and geological conditions of the area,the analysis shows that the atmospheric precipitation in the northern mountainous area infiltrates through the F₁ and F₂ faults to a depth of about 3,800 meters and mixes with the geothermal fluid.The mixed underground hot water flows up through the F₃ fault and passes through Small faults formed by the intersection of fault zones are exposed on the surface to form hot springs.