We imaged the pore-scale distribution of air and water within packed columns of glass spheres of different textures using x-ray microcomputed tomography after primary drainage and after secondary imbibition. Postimbibition residual air saturation increases with roughness size. Clusters larger than a critical size of about 15 to 40 pores are distributed according to a power law, with exponents ranging from τ=2.29±0.04 to 3.00±0.13 and displaying a weak negative correlation with roughness size. The largest cluster constitutes 7 to 20% of the total residual gas saturation, with no clear correlation with roughness size. These results imply that activities that enhance grain roughness by, e.g., creating acidic conditions in the subsurface, will promote capillary trapping of nonwetting phases under capillary-dominated conditions. Enhanced trapping, in turn, may be desirable in some engineering applications such as geological CO2 storage, but detrimental to others such as groundwater remediation and hydrocarbon recovery.
|Number of pages||11|
|Journal||Physical Review. E, Statistical, Nonlinear and Soft Matter Physics|
|Early online date||22 Jul 2020|
|Publication status||Published - Jul 2020|