3D pore structure characterization and permeability anisotropy visualization simulation of fusain

The Jurassic‒Cretaceous coal seams in northern China are rich in fusains, and the pore size of the residual plant tissue in fusains is much larger than the limit value of seepage pores and even larger than that of some microfractures in coal. Therefore, understanding the 3D pore structure and permeability of fusains is helpful for determining the physical characteristics of inertinite-rich coal reservoirs. The porosity of the fusain varies widely, the pore structure has obvious directivity, and this study summarizes three pore types. Based on the visual distribution module of fluid migration, three types of seepage models of fusains were established, including the tubular cell structure seepage model, the broken cell wall pore seepage model, and the complete cell structure surface barrier seepage model. The results of the physical simulation verify the rationality of the three seepage models and show that the degree of fusification and cell pore fragmentation strongly affect the permeability of the fusain. For a low-rank coal reservoir with a rich fusain, the overall pore permeability is high, which is conducive to the seepage production of coalbed methane and is an important reference value for high-permeability layer selection.