LAUSR

Abstract In this study, a series of laboratory experiments were performed to firstly analyze the characteristics of the pore structure in low-rank coal (R o 1000 nm), with a poor development of mesopores (100–1000 nm). The fractal features of adsorbed pores and seepage pores were defined and calculated using fractal dimensions D 2 (2.563–2.926) and D 4 (2.683–3.263), respectively. D 2 has a positive correlation with moisture content, while D 4 has a positive correlation with R o and fixed carbon and a negative correlation with the volatile content. Both D 2 and D 4 have a weaker association with the ash yield and no apparent relationship with coal macerals, indicating that coal-forming materials and environments have little influence on the pore structure fractal characteristics. D 2 has a strongly correlation with the BET surface area (R 2  = 0.9026) and the average pore diameter (R 2  = 0.9841), again proving that D 2 can be used to characterize the pore structure fractal dimension of adsorbed pores. D 2 shows a negative correlation with the Langmuir volume (V L ), but no apparent relationship with the Langmuir pressure (P L ), indicating that the pore structure of absorbed pores has little effect on methane desorption during the process of CBM exploitation. D 4 has weak positive correlation with permeability. Overall, fractal analysis is beneficial for better understanding the pore structure, methane adsorbability and seepage ability of low-rank coal.