Study On Spontaneous Potential And Induced Polarization Characteristics Of Rock Under Temperature Change

China is one of the countries most seriously affected by coalfield fires in the world.Coal fire combustion directly leads to a large amount of coal resources loss.Only in Xinjiang,about 4.5616 million tons of coal resources are directly lost every year due to coal fire combustion,and the threatened coal reserves are as high as 1.526 billion tons.Coal fire not only causes huge economic losses,but also causes serious damage and pollution to soil resources,surface vegetation,groundwater resources,atmosphere and other ecological environment.Therefore,it has important research significance and engineering application value to carry out coal fire prevention and control work for the protection of coal resources and ecological environment.Coal fire detection is not only an important basis for coal fire fighting,but also a difficult and hot issue in the research of coal fire prevention and control.Although many scholars at home and abroad have carried out a lot of theoretical and field application research,and achieved a lot of useful results,but the detection methods still have some limitations,therefore,the accurate detection of coal fire still needs to carry out a lot of systematic and in-depth research work,and it is extremely urgent.This thesis focuses on the spontaneous potential method and frequency domain induced polarization method,starting from the basic research of rock physics,using the research method of indoor test,theoretical analysis and numerical simulation.The variation of spontaneous potential in the process of rock heating is studied,and the process and mechanism of spontaneous potential in the process of rock heating are revealed;Through the test of complex resistivity of different rocks,the change law of induced polarization characteristics of rocks before and after burning and under the condition of temperature change is revealed,which provides the theoretical basis and interpretation basis for judging the combustion state of coal fire when the frequency domain induced polarization method is applied to coal fire detection.The main conclusions are as follows(1)The results show that the spontaneous potential can be generated during the heating process of sandstone,and the change of potential amplitude corresponds well with the change of temperature field.In the process of temperature rising,the spontaneous potential of sandstone increases with the increase of temperature,and its extreme value is determined by temperature and heating rate.Based on the results of scanning electron microscope(SEM)of sandstone,the mechanism of spontaneous potential generation and change in the process of experiment is analyzed.It is pointed out that the spontaneous potential generation in the process of temperature rising is due to the thermoelectric effect and the charge separation caused by the development and expansion of microcracks,in which the charge separation during the development and expansion of microcracks and other structures plays a leading role.(2)Four pole method is used to test the complex resistivity of limestone treated at different temperatures.The experimental results show that the complex resistivity of limestone treated at different temperatures has obvious dispersion effect,and the amplitude and phase change little in the low frequency range,and gradually change significantly with the increase of frequency.The complex resistivity amplitude of limestone treated at 400 ℃ or above is significantly lower than that of limestone treated at low temperature,and the value decreases by 103 times;Time constants of Cole Cole model parameters for high temperature limestone at 400 ℃ and above τ The value decreased significantly;The dispersivity decreases with the increase of sintering temperature.The dispersivity decreases greatly from 300 ℃ to 400 ℃.Combined with SEM test results,it is clarified that the significant difference of complex resistivity dispersion characteristics of limestone after different temperature treatment is due to the changes of porosity,permeability,connectivity and other internal structures of limestone caused by temperature.The complex resistivity test system of high temperature rock is established,and the induced polarization phenomenon of rock under high temperature is studied creatively.Through experiments,it is proved that there is induced polarization phenomenon in high temperature rock,and the spectrum response characteristics of complex resistivity of high temperature rock are obviously different from that of low temperature rock.Based on the "electric double layer" structure of ionic conductor during polarization,it is proposed that there is a "electric double layer" structure similar to ionic conductor on the surface of rock particles in high temperature rocks.(3)The detection data of frequency domain induced polarization method naturally contains the data related to apparent resistivity,that is,two or more groups of data of different geophysical methods can be obtained at the same time by one geophysical exploration operation.Therefore,this thesis studies the resistivity temperature characteristics of sandstone and limestone,and finds that the variation trend of resistivity temperature characteristic curves of different rocks is basically the same.Based on the energy band theory and SEM test results,the mechanism of rock resistivity temperature characteristic change is clarified: the change of rock resistivity in the process of heating is the result of the coupling of carrier concentration and internal structure change.(4)Taking the measured complex resistivity data as the modeling parameters,the numerical models of the variation of the buried depth and the different volume of the abnormal body are established,and the variation law of the abnormal response of the video dispersion is analyzed.The simulation results show that the two pole device can not only determine the horizontal position of the abnormal body,but also locate the bottom interface more accurately than the three pole and four pole devices.The apparent resistivity contour map of the coal seam geoelectric model shows that the two pole device has good resolution for different strata,and can effectively judge the horizontal and vertical position of the ellipsoidal coal fire anomaly body.The above research results provide theoretical basis and explanation basis for the application of spontaneous potential method and frequency domain induced polarization method in coal fire detection,and are of great significance to promote the application of spontaneous potential method and frequency domain induced polarization method in coal fire detection.This thesis has 87 pictures,8 tables and 146 references.