A multiple front propagation model for gas migration through clay

A model for the migration of gas through clay is described, in which gas propagates as a set of independent paths. The paths are constructed stochastically from sections of capillary-like tubes which inflate when the gas pressure exceeds a threshold value. The paths partially deflate when they break through the clay, but their inflation is still sufficient to significantly increase the resultant slow flow of gas. The model also includes gas flows for path content and gas puffs at breakthrough, and describes expelled water in a simple manner.