The Influence Of Geothermal Features And Radioactive Heat Production Of Rocks To Potential Of Geothermal Resources In Eastern Area Of Liaoning Province

The conflict between economic development and environmental protection becomeincreasingly sharp, many countries have proposed the development of a green and lowcarbon economy. Meanwhile, with the development of society, traditional energy sourceslike oil, gas, coal and others caused serious damage on the environment, and resourceshave been gradually depleted. The demand for clean energy is increasing day after day.Geothermal resources, as a renewable energy, gradually replace energy in other forms(especially fossil fuels), and has become an important part of future energy. Comparedwith traditional energy sources, geothermal resources have many advantages, such as:huge reserves, renewable and environmentally friendly. Geothermal resources are not onlyclean and in suit access, but also inexhaustible. Thus, geothermal resources graduallyattracted attention around the world in recent years. It is likely that the study ofgeothermal resources will catch up with the solar and wind energy.There are many sources of geothermal. But in medium-low temperature geothermalfield (areas that geothermal flow and geothermal gradient are both low), it is said that the"low" heat zone developed a large amount of geothermal resources, which has no reliablecertification. During the study of geothermal resources in Eastern Liaoning Province, theheat flow values are found to be closed to the average heat value of crust, the geothermalgradient is only2.0℃/100m,and the w hole area belongs to "low " tem perature zone.B utits geothermal resources are well developed with the highest temperature of output wateris up to70℃. In order to explain this phenom enon of "low " zone but "high" heatresources, this paper starts with the geological background of Eastern Liaoning. By thestudy of regional geophysical field characteristics, geothermal features, faults and theradiogenic heat amount of major rock bodies in the study area, the impact of heat of radioactive elements of rocks and the basic rules of geothermal development in theEastern Liaoning are summarized.Rock types in the study area are complex. More than1,200rock samples arecollected for understanding the regional geophysical field and geological structure of deepcrust. There are1128rock samples were carried on the analysis of density, magneticsusceptibility and resistivity. The calculation results of precision gravity and aeromagneticELder deconvolution are reflected that geothermal resources are usually develop at thepositions of distort part of gravity gradient belt and the magnetic gradient belt.Typically168rock samples were analyzed to test the content of radioactiveelements238U,232Th and40K by the method of laser fluorescence. The heat productionrates of radioactive elements in major rock samples in the study area are calculated bycombining rock density values. The results present that granite of Late Triassic and EarlyCretaceous both has high content of radioactive elements, and the average values of heatproduction rates were4.36μW/m3and3.72μW/m3, while the common values are5.0μW/m3and3.2μW/m3. The average value of heat production rates is low inPaleoproterozoic granitic rocks samples, its average is about1.6μW/m3. Combined thefield exploration, inversion analysis of gravity and magnetic data and the profiles ofmagnetotelluric sounding, present the total amount of heat production in Yanshan graniticpluton (about0.3TW) is much higher than the Paleoproterozoic granites (about0.03TW).From the test results of radioactive elements and the calculation results ofheat-generation amount, we come to conclusion that the heat production of radioactiveelements in the study area laid a good foundation for geothermal resources. The model offlower faults controlled thermal is proposed in this paper according to the characteristicsof development of main heat-controlled faults. The heat-controlled model of flowerstructures is dominated by both positive and negative control style. The groundwater flowthrough "petals" fracture into passages, and the gathered groundwater in "scape" trunkfracture would be leaded to the deep (under10km) via a strong regional broken fault, andthen migrated upward after heated. The heated groundwater formed hot spring or thermalreservoir through the "petals" fracture path. This heat-controlled model of flowerstructures could better explain the phenomena that geothermal resources developed at theboth side of the main fault in study area. The migration patterns and possible depths ofmigration of groundwater are proposed on the basis of faults’ development characteristicsin different depths levels. Large-scale (regional tectonic fault) heat-controlled faultsprovide good geothermal flow path for geothermal resources. Downward movement of groundwater can flow along with good brittle broken fracture zone. In the strong brokenarea, the maximum migration depth could reach to the brittle-ductile transition zone.When the groundwater reaches the ductile deformation zone of crust, it cannot passthrough due to the lack of pore in the ductile deformation zone and poor liquidity. Thegroundwater are heated to200-300℃near the brittle-ductile transition zone, and drivenupward by the pressure system of underground hot water, then flow into the shallowformation or to the surface forming the hot springs.The rules of geothermal resources’ development in the study area are summarizedby integrating geological, geophysical, data of rocks’ radioactive. Clear the basic rules ofdevelopment of geothermal resources in the study area, and the favorable area forgeothermal development. Three types of geothermal fields in the study area are proposed,in which one is related to the faults structure and another is associated with intrusions, thelast one is related to Mesozoic faulted basin. The geothermal fields, which are related tothe faults, mainly distributed in the Yalu River fault, Zhuanghe-Huanren fault, Hai&Ximu City-Xiuyan fault, Han-Pian Ridge faults etc.,. And geothermal belt nearby.Geothermal fields, which are related to intrusions, developed mainly in or adjacent thegranite bodies of Indosinian and Yanshan period. The development of “high fever” rockbody has the function of “reheated” to underground geothermal water. Geothermal fields,which are related to Mesozoic faulted basin developed mainly in the Jurassic basin.