Micromechanical investigation of fines liberation and transport during coal seam dewatering

The reduction of subsurface hydrostatic pressure to allow natural gas desorption is an integral step in the production of coal seam gas (CSG). During this dewatering stage, viscous stresses can cause the liberation and transport of fines, which are predominantly comprised of inorganic clay groups such as smectite, illite and kaolin, from within the coal matrix. Dislodged particles migrate in production fluid through fractures towards the wellbore where capture and deposition can deteriorate the reservoir's permeability. Once in the wellbore, these particles can adversely affect the performance of mechanical equipment such as pumps. This study uses direct numerical simulation of a synthetic coal fracture to help elucidate the particle detachment process. This is approached using a coupled lattice Boltzmann-discrete element method to capture both physical and physicochemical interactions based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Preliminary testing with the developed model suggests that particles move almost freely along the bounding surface regardless of electrostatic interactions, and that Hele-Shaw predictions of particle lift in particular can be inadequate. Further, larger-scale simulations indicated that the DLVO parameters can significantly impact the vertical position of propagating fines with variations in eroded mass of over 100% observed for the range of tested salinity levels