Discrete microbubbles flow in transparent porous media

The coal seam gas and underground coal gasification industry has caused concerns with the risk of potential groundwater contamination. Gases leaked from coal seams are thought to be a source of groundwater pollution. However, the basic principles and controlling parameters for gases seepage from deep ground formations to the surface are not fully understood. Microbubble transport, as a possible mechanism for gases transport in the subsurface, is investigated here through a laboratory-scale experiment. Microbubbles were generated from a bubble diffuser and released into a 2D artificial transparent porous medium. The point source of bubble injection was used to simulate the release of gases from geological faults/fractures. The medium's transparency enabled a clear visualization of the bubble pathways. Images captured by cameras were used to facilitate analyses on the bubble transport behavior affected by advection and dispersion.