Characterization of dual porosity system in suthern Qinshui basin coal with micro-CT and nano-scale SEM technology

Abstract

Coal has long been exploited as a combustive source of energy, but coal bed methane is a recent development and has been attracting global interest only in the couple past decades. Developing of coal bed methane reservoirs demands better understanding of the fluid flow behaviour in coal reservoirs. Coal seam is a naturally fractured reservoir and contains a high amount of mainly localised organic matter. This results in dual-pore system where pores in organic matter are often too small to be efficient flow paths, whereas much larger fractures (known as cleats) are believed to be main conducts from which gas in organic matters can flow out. Intermediate rank coal samples were collected from Southern Qinshui Basin (China). The coal fractures were scanned using micro computed tomography (micro-CT), while scan electron microscopy (SEM) was implemented to scan the coal matrix. Matrix data was used to reconstruct the 3D nano-scale pore structure using the Markov Chain Model. The permeability of the segmented cleat system and nano-pore system were then simulated using the Lattice-Boltzmann method. The simulation results for fracture/cleat were validated by comparison with analytical solution for Poiseulle flow in a single crack, and pore permeability simulation is under investigation.