Differentiation And Geological Controls Of Modern Geothermal Field In Bide-Santang Basin

This paper organized the borehole temperature measurement datas of Bide-santangbasin systematically, analyzed the modern geothermal field distribution characteristics, andthen discussed the geological controls of modern geothermal field distribution and theinfluence of stratum temperature on coal and CBM development.Based on temperature measurement data from135boreholes and the thermal physicalparameters tests of coal and rock samples, analyzed the modern geothermal gradient, theterrestrial heat flow and the stratum temperature distribution characteristics of the researcharea. It is revealed that the modern geothermal gradient in the research area is between1.46~3.34℃/hm, averages2.35℃/hm; The Shuigonghe Syncline’s average geothermalgradient is the highest with the value of2.72℃/hm, and the Agong Syncline’s averagegeothermal gradient is the lowest with2.18℃/hm. The terrestrial heat flow in the researcharea is between52.8~63.5mW/m2, averages59.4mW/m2, which is slightly lower than theaverage heat flow of Yangzi area in South China. According to the deep stratumtemperature, it is predicted that the first level heat damage will occur when the coal seamdepth is beyond800m.The modern geothermal field distribution in research area is basically consistent withthe regional tectonic-thermal setting in South China. Regionally, Nayong mining area’smodern average geothermal gradient is higher than Zhijin mining area, both of which areall belongs to the normal geothermal field category. Geothermal temperature variation issignificantly controlled by tectonic characteristics, which is illustrated by the consistencybetween isotherm distribution direction and the structural trace strike. Geothermal gradientis relatively high in anticline arching region, while which is relatively low in synclinedepression region. Vertically, geothermal temperature increases with the increase of depth,the geothermal gradients of different areas transform from dispersion to consistency withthe depth increased, and the transformation depth is about300m.The methods of geothermal gradient and grey sequence are applied and compared inprediction of deep formation temperature, and the result shows grey sequence predictionmodel GM(1,1) has higher accuracy. Some exploration areas possess the favorablegeothermal field conditions for CO2foam fracturing or CBM gas injection development,stratum temperature controls the selection of CBM development technology and methods.