Numerical simulation of phenol migration for underground coal gasification

Taking the western UCG site in China as the example, the mathematic model of groundwater flow and phenol migration after gasification were established, and numerical simulation was conducted. The results indicate that no obvious phenol pollution is found in the neighboring upper aquifer during the prediction period of 20 years. Molecule diffusion is the main path of phenol migration toward the upper aquifer. Phenol migration in the coal seam occurs near the UCG cavity, and elliptic shape area with long axis of 500 m and short axis of 300 m is found. Low permeability of coal seam, lower hydraulic gradient, and the absorption by the surrounding strata make big contributions to prevent phenol migration in the coal seam. In addition, the water head difference, the destroy extent of the confining strata, and molecule diffusion are the key factors for groundwater pollution evalution. Groundwater pollution should be prevented by the combination way of site selection, process pressure control, and cavity pollution disposal.