Physical properties of coalbed methane reservoirs and favourable exploration areas in the northern Qaidam Basin, NW China

Coal and coalbed methane (CBM) resources are abundant in the northern Qaidam Basin, northwestern China. Physical properties of a total of 57 coal samples were characterised utilising methods of low-temperature nitrogen adsorption, mercury porosimetries, and microfracture statistics. The results show that transitional pores, mesopores and macropores (10-10(4) nm in size) of the coal reservoir were found the most developed. Additionally, as maximum vitrinite reflectance (R-o,R-max) increases, the volume of micropores shows an increasing trend while the volume of transitional pores and other pores shows a decreasing trend. Microfracturing density of the coal reservoirs is generally more developed in deformed coal and higher brightness coal, which is also influenced by R-o,R-max and macerals. Centred on multi-level fuzzy optimisation, the Yuqia Coalfield is found to be the most suitable for CBM exploration and development in the northern Qaidam Basin, followed by the Saishiteng Coalfield, Quanji Coalfield, and Delingha Coalfield.