Impact of flow regimes on coal fines generation during coal seam gas production process

This study presents the development and application of a fully coupled numerical model that integrates different flow regimes and the generation of coal fines. The Scanning Electron Microscopy (SEM) was employed to obtain coal cleat geometry at the micro-scale. Based on the real cleat geometry, the Phase Field Method (PFM) was used to simulate the two-phase flow and the combination of shear and tensile failure criteria was selected to evaluate the generation of coal fines. The results reveal that more coal fines are generated in two-phase flow than single-phase flow. For the two-phase flow conditions, residual displaced phase is observed inside the micro-roughness of coal cleat. Majority of coal fines are generated in these regions due to the substantial pressure force induced by significant pressure difference between the trapped phase and the invading phase. Coal wettability plays an important role in coal fines generation. Using the wetting phase as the injection phase will produce one order of magnitude more coal fines than that from the other way. Moreover, the change of fluid phase inside the cleat can create considerable pressure fluctuations up to several kPa, which is not favorable in managing the production of coal fines.