Research On The Method And Model Of Multifunctional In-situ Thermal Properties Measurement

Geothermal exploration technology is one of the most important research content in geothermal development.Shallow temperature survey is a simple and efficient geophysical method.This method is widely used in the early stage of geothermal exploration abroad.However,the application of this method is less in China,mainly due to the lack of equipment for shallow temperature survey and data processing method.In this paper,the measure method for thermal properties,the research and development of equipment for shallow temperature survey and the ground temperature prediction model based on shallow temperature survey are studied.Multifunctional in-situ thermal properties measure method is put forward,and the multifunctional in-situ thermal properties tester is developed.The tester including assembly system,heating system and data collection system,can be used to measure heat conductivity,volumetric heat capacity and thermal diffusivity.It is suitable for shallow temperature survey and in-situ measurement of thermal properties.In the research and development of the tester,the ratio of length to diameter of the thermal probe and the assembly scheme is redesigned,and PT1000 platinum resistance is uesd as temperature sensor.C# is used to develop in-situ thermal properties data acquisition and processing software in the windows platform,combined with the least squares fitting straight line algorithm,the measurement of thermal properties is achieved.In order to calibrate the multifunctional in-situ thermal properties tester and verify the stability and accuracy of the thermal properties of the tester,the laboratory calibration experiment and contrast experiment are designed.Air is used as the measurement medium in calibration experiment,the best measurement voltage,test time and actual distance between PT1000 and the heating wire are determined.Fine sand and clay are used as the measurement medium in contrast experiment,thermal properties of samples with different water content are tested,thermal conductivity,volumetric heat capacity and thermal diffusion coefficient with the change of water content were analyzed,the stability and accuracy of the tester is determined.The ground temperature prediction model based on shallow temperature survey is proposed,the influence of each factor on the model is analyzed in detail,and the correction method is put forward.The influence of groundwater seepage on the prediction accuracy of the model is simulated by Tough2.The results show that the seepage velocity,the temperature difference and the thickness of the permeable layer are significantly correlated with the prediction error.SPSS is used to fit empirical formulas for prediction error with three factors.The concept and calculation method of equivalent thermal conductivity of permeable layer are presented.The maximum error is reduced to 5.1% after the application of equivalent thermal conductivity.The ground temperature prediction model is used to predict the temperature of the constant temperature layer in Dongshan hot spring area of Xiamen,and the results are compared with the measured data of the constant temperature layer.The reliability and accuracy of the model are verified.On the basis of the above work,the results of the shallow temperature survey in Houpu hot spring area in Xiamen are used to draw the temperature contour map at 2m depth and the heat flux density map at shallow layer.The ground temperature prediction model based on shallow temperature survey is used to predict the temperature of the constant temperature layer in the research area.The influence of groundwater seepage and stratum distribution are considered in the model.The geothermal characteristics of research area are described with maps and the cause of geothermal distribution is analyzed.In the research area,the geothermal anomaly area presents an elliptical temperature anomaly in North-south direction.High temperature centers appear near hp6 and hp16.F1 and F3 controls the temperature distribution of the geothermal anomaly area in the research area.Through the combination of theory and experiment method,multifunctional in-situ thermal properties measure method and the multifunctional in-situ thermal properties tester has the advantages of complete function,accurate,economical and reliable characteristics,which can be a useful equipment in the shallow temperature survey.The ground temperature prediction model based on shallow temperature survey is accurate to predict the temperature of the constant temperature layer.Finally,it forms a set of technology system of shallow temperature survey,which is developed from the instrument to the practical application to the data processing method.It provides a theoretical basis for the popularization and application of shallow temperature survey in China,and has positive significance for promoting the development and utilization of shallow geothermal energy in china.