Liquid nitrogen fracturing efficiency as a function of coal rank: A multi-scale tomographic study

Abstract This study explored the potential of liquid nitrogen fracturing in three different coal ranks. X-ray computed tomography results in micro- (μ-CT) and macro (medical-CT) scales revealed a poor performance of LN2 fracturing in anthracite. In contrast, porosity evolution for bituminous and sub-bituminous coal in microscale was 14 % and 119 %, respectively. The porosity enhancement in macroscale for these coals was also significant. Interestingly, in both coals, thoroughgoing fracture planes originated from the initial cleat network following freezing. Furthermore, connectivity analysis through skeletonization and Euler number analysis suggested that sub-bituminous connectivity increased by 20-fold for small pores (