Geothermal field and its relation with coalbed methane distribution of the Qinshui Basin

The average geothermal gradient in the Qinshui Basin, Shanxi Province, North China, estimated from temperature logging data of 20 boreholes is 28.2 +/- 1.03 degrees C/km. The thermal conductivities of 39 rock samples are measured and 20 heat flow values are obtained. The estimated heat flow ranges from 44.75 mW/m(2) to 101.81 mW/m(2), with a mean of 62.69 +/- 15.20 mW/m(2). The thermal history reconstruction from the inversion of vitrinite data, using Thermodel for Windows 2004, reveals that the average paleo-heat flow at the time of maximum burial in late Jurassic to early Cretaceous is 158.41 mW/m(2) for the north part, 119.57 mW/m(2) for the central part and 169.43 mW/m(2) for the south part of the basin respectively. The reconstruction of the buried history of the strata indicates that the age for the end of sedimentation and the beginning of erosion for the basin is 108-156 Ma, and that the eroded thickness of the strata is 2603 m in the north, 2291 m in the central, and 2528.9 m in the south of the basin respectively. The "higher in the north and the south, lower in the central" distribution pattern of the paleo-heat flow coincides with the distribution of the coal-bed methane spatially and temporally, which shows that the coal-bed methane is controlled by the paleo-geotemperature field in the basin.