Coalbed methane system potential evaluation and favourable area prediction of Gujiao blocks, Xishan coalfield, based on multi-level fuzzy mathematical analysis

Abstract Coalbed methane (CBM) resources are abundant in Gujiao blocks, Xishan coalfield, China. However, there is little previous geological research regarding coalbed methane. Using a quantitative and qualitative index, the hydrocarbon source rocks and preservation conditions of No. 2, 8 and 9 coalbed methane systems in Gujiao blocks were evaluated through a multi-level fuzzy method. On this basis, the comprehensive favourable area of three CBM systems and multi-layer commingled production were predicted. The results showed that the comprehensive score trend of hydrocarbon source rocks in Gujiao blocks gradually increases from southeast to northwest. The comprehensive score trend of preservation conditions increases gradually from north to south. The No. 2 coalbed methane system of the Shanxi formation is given priority over level II, which is distributed in the central and southern study area. The No. 8 coalbed methane system of the Taiyuan formation is given priority over level III, followed by level IV. The No. 9 coalbed methane system of the Taiyuan formation is given priority over level II and level III, which is distributed in the central and southern study area. Most of the area is suitable for individual CBM exploitation of No. 8 coal. The favourable area for the No. 2+8 coal layer is located in parts of the central, south-western and south-eastern study area. The favourable area for No. 8+9 coal layer is located in the Dongqu well field and the southern Tunlan well field. The favourable area for No. 2+8+9 coal layer is located in the eastern Yang Zhuang well field.