Pore-throat size distributions in Permo-Triassic sandstones from the United Kingdom and some implications for contaminant hydrogeology

Pore-throat size distributions (PSDs) from mercury injection capillary pressure (MICP) tests have been used to characterise 153 samples of Permo-Triassic sandstones from the United Kingdom. The PSDs have been parameterised using the Brooks-Corey and van Genuchten functions. Pore-throat sizes are in the range 0.01–427 μm, and dominant pore-throat sizes range from about 0.1–90 μm. Values of λ, the Brooks-Corey poresize distribution index, range from 0.002–2.27, and values of m, the van Genuchten pore-size distribution index, range from 0.03–0.92. A number of classes of sandstone can be recognised on the basis of trends in the fitted parameters. The van Genuchten function provides the most effective method for classifying different sandstones. Additionally, a cross-plot of gas permeability against displacement pressure (derived from the van Genuchten function) shows that the data fall into two distinct subpopulations. The frequency distribution of a larger population of sandstone permeabilities can be modelled using the mean and standard deviation of the two sub-populations identified in the MICP study, assuming that the sub-populations are approximated by log-normal distributions. The distribution of sandstones with small porethroat sizes is critical to the fate of pathogens and immiscible phase contaminants in the aquifer.