Pore scale heterogeneity in the mineral distribution and surface area of Berea sandstone

The impact of pore scale heterogeneity in chemical transport and reaction is not understood in continuum (Darcy/Fickian) models of reactive transport. This is manifested in well-known problems such as scale dependent dispersion and discrepancies in reaction rate observations made at laboratory and field scales. A potential cause is the inability of the continuum approach to incorporate the impact of heterogeneity in pore-scale reaction rates. This results in part from pore-scale heterogeneities in surface area of reactive minerals. We use X-ray micro-tomography to describe the non-normal character and statistics of reactive surface area within a porous medium, specific mineral phases and their distribution in 3-dimensions. Using in-house image processing techniques, thin sections, nitrogen BET surface area, backscattered electron imaging and energy dispersive X-ray spectroscopy, we compare the surface area of each mineral phase to those obtained from X-ray imagery. There is little correlation between the reactive surface area fraction and the volumetric fraction of a mineral in a bulk rock. Berea sandstone has a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. The observations made contribute to the incorporation of statistical descriptions of pore scale heterogeneity in reactive transport into upscaled models. (C) 2014 The Authors. Published by Elsevier Ltd.