Pore Structure Reconstruction and Gas-Water Dual-Flow Simulations Combined with CT Scans and NMR Measurements on Coal...

To accurately investigate the three-dimensional coal pore structures and their relationships with gas-water migration at different stages of coalbed methane (CBM) drainage, this study conducts computed tomography (CT) scans, nuclear magnetic resonance (NMR) measurements, and single water and gas-water flow simulations on two coal particle samples. The following conclusions were drawn: two coal samples exhibit strong heterogeneities, with diffusion pores dominated for sample CN01 and diffusion pores and fractures as the main components for sample CN02. For sample CN01, the total porosity corresponding to saturated fluid is 10.38%, the residual porosity corresponding to bound fluid is 8.74%, and the effective porosity is 1.64%, indicating poor pore connectivity and fluid mobility. For sample CN02, the total porosity corresponding to saturated fluid is 6.54%, the residual porosity corresponding to bound fluid is 3.28%, and the effective porosity is 3.26%, indicating good pore connectivity and fluid mobility. The shape factor, corresponding to the complexity of the pore structure, is positively correlated with the pore diameter, indicating that the pore structure of CN01 is much more complex compared with that of CN02. During the seepage simulation process, the magnitude of the relative water permeability in different directions reflects the corresponding pore-throat arrangement pattern and bedding development degree. A higher relative water permeability can result in a more uniform pore-throat arrangement and a better bedding development. It is also concluded that the CN02 sample has greater productivity potential, as it has a higher decline of relative water permeability in each direction.