Study On The Distribution Law And Control Mode Of Geothermal Field In Huainan-Huaibei Coalfield

The thermophysical properties of coal measure rock in Huainan-Huaibei Coalfield have been focused studied and the distribution laws as well as influencing factors have been expounded, what’s more, the control mode of distribution of geothermal field has been set up and the geothermal resources have been forecasted and evaluated on the basis of collecting the tested data of temperature during the exploration and mining in Huainan-Huaibei mining area systematically as well as combining drilling, and using the test on temperature of surface boreholes, test on temperature of rock in roadways, experiment on geothermal parameters, comprehensive analysis on numerical simulation and theory. The scientific gist for safe and efficient mining of coal in deep mines and the development and utilization of geothermal resource in Huainan-Huaibei Coalfield has been provided. The main results are as follows:(1) The correction of steady state approximation on simple temperature test curve and instant temperature test curve of boreholes in Huainan-Huaibei Coalfield has been made as well as the formula of correction curve of temperature which is at the bottom of mines and the correction coefficient of the temperature at each level have been established as well as the temperature values at the bottoms and the temperature value at each level have been assured, which would provide more reliable basic data for drawing contour maps of temperature at each level and geothermal gradient in every coal mine, and realizing the distribution characteristics in Huainan-Huaibei Coalfield as well as predicting temperature in different depth. What’s more, it could provide gist for correcting the simple temperature test in Huainan-Huaibei Coalfield.(2) The distribution characteristics of Huainan-Huaibei Coalfield mainly show that the geothermal gradient in Huaibei mining area is lower than that in Huainan mining area and the average of geothermal gradient in Huaibei mining area is 2.42℃/hm while the average in Huainan mining area is 2.9℃/hm; the geotemperature in north is lower than that in south and the geotemperature in east is lower than that in west in Huaibei mining area while the geotemperature in north is higher than that in south and the geotemperature in east is higher than that in west in Huainan mining area; the geothermal distribution of Huainan-Huaibei Coalfield is controlled by structure and it is in the direction along the trend of strata in the region; geotemperature increases with the depth and it shows that conduction is main; the geothermal gradient decreases with the increase of depth and it tends to be accordant as well as -400m is critical depth; the temperature of each level shows a positive correlation with buried depth well.(3) The thermal conductivity of coal measure rock in Huainan-Huaibei Coalfield range from 0.37 W/mK to 4.36 W/mK and the average is about 2.54W/mK; the thermal conductivity is different in different rocks and the thermal conductivity of fine sandstone is the highest as well as the one of medium sandstone, siltstone, mudstone and limestone is lower while the thermal conductivity of coal rock is the lowest; the thermal conductivity of fine sand in loose bed of Quaternary is 0.98 W/mK and the one of sandy clay is 1.33 W/mK; the relation between thermal conductivity, lithology, depth and density is familiar.(4) Heat generation rate of radioactivity of rocks in Huainan-Huaibei Coalfield is low and the average is 1.68μ.W/m3. The heat from radioactive element in coal measure strata provides 1.613mW/m2 for surface heat flow, which occupies 3.6% of terrestrial heat flow, and that means the heat from radioactivity of coal measure rocks make a certain contribution to surface heat flow.(5) The terrestrial heat flow value in Huainan-Huaibei Coalfield has been calculated on the basis of thermal conductivity of rocks and geothermal gradient value and the results show that the average of terrestrial heat flow value in Huainan-Huaibei Coalfield is 58.16mW/m2 and there is a difference on terrestrial heat flow between Huainan and Huaibei mining area, while the average in Huainan mining area is 63.69 mW/m2 and the one in Huaibei mining area is 54.96mW/m2; the difference of terrestrial heat flow in Huainan-Huaibei mining area is mainly influenced by regional geological structure and the deep geological background.(6) The influence of tectonic background, geological structure characteristics, thickness of loose bed, thermophysical properties of rocks, magmatism and ground water activities on current geothermal field has been analyzed systematically on the basis of geology and thermodynamics. The results show that geological structure and characteristics of lithology (thickness of loose bed) control current geothermal field a lot in the regional geological background as well as the activities of ground water and magmatism play a role in the distribution of geothermal field.(7) On the basis of analyzing controlling factors of geothermal field in Huainan-Huaibei Coalfield, four typical control modes of geothermal field have been established, which are control mode of folding type, control mode of fault, control mode of fold and fault as well as control mode of coupling of thermal-liquid-solid. The characteristics of geothermal field and redistribution of terrestrial heat flow value of different modes in the region have been simulated and the control mechanism of the distribution of geothermal field has been revealed.(8) The geothermal resources in Huainan-Huaibei Coalfield have been estimated through Geologic exploration standard of geothermal resources, and the results show that the distribution and reserve of terrestrial heat in Huainan-Huaibei Coalfield is large and developing the development and utilization of terrestrial heat is important in the study area. The current situation of development and utilization of low temperature geothermal resources in coal mines has been analyzed as well as the prospect of development and utilization of geothermal resources has been evaluated. Mine water and return air of coal mines are stable and superior residual heat resources, and they are also reproducible resources with a large quantity.