Geological controls on prediction of coalbed methane of No. 3 coal seam in Southern Qinshui Basin, North China

In order to better understand the geological controls on coalbed methane (CBM) in Southern Qinshui basin (SQB), North China, geological surveys and laboratory experiments, including coal petrology analysis, proximate analysis and methane adsorption/desorption, were conducted. Results show that the coals from the SQB contain 0.59-3.54% moisture, 3.5-15.54% ash yield, 73.62-88.92% fixed carbon and 2.14-4.04% hydrogen, with C/H ratios in the range of 19.96-36.25. The vitrinite reflectance (R-o,R-m) ranges from 1.95 to 3.49%. The coals are composed of 18.5-97.4% vitrinite and 2.4-81.4% inertinite. The geologic structures, coal-bearing strata and coal depositional environment were studied by both field geological research and laboratory tests. A positive relationship is found between CBM content and basin hydrodynamics, in which CBM easily concentrates in the groundwater stagnant zone because of the water pressure. Furthermore, integrated geographical information system (GIS) and analytical hierarchy fuzzy prediction method (AHP) were used to evaluate the CBM resources in the SQB. The results show that the amount of CBM associated with the No. 3 coal seam in the SQB is 3.62 x 10(11) m(3). The CBM resource concentration (gas-in-place per square kilometer) in the SQB is in the range of (0.72-2.88) x 10(8) m(3)/km(2), with an average of 1.21 x 10(8) m(3)/km(2), which decreases from Zhengzhuang coal district to Shitou fault and from Fanzhuang coal district to the margins of the basin. The best prospective targets for CBM production are likely located in the southwest/northwest Zhengzhuang and central Hudi coal districts. (C) 2011 Elsevier B.V. All rights reserved.