Porosity Structures and Capillary Migration in Granites and Limestones

Capillary flow is a main process for fluid migration in unsaturated media, being relevant for the study of pollutants and other solutes migration (e.g. salt weathering of stones) and petroleum reservoirs. To characterize the kinetics of the capillary migration (see [1]), two coefficients related to the square root of time can be defined: mass increase per unit area (Cw) and height of rising fringe (Ch). Values of Cw can be measured more objectively (with a scale) but are dependent on the porosity of the material accessible by capillarity (all other things being equal, increasing porosity in the capillary range implies higher absorbed mass). For an ideal pore network and water density=1.00 g/cm3, it can be shown (see [1]) that Ch=Cw x100/Nc(%), where Nc(%) represents porosity accessible by capillarity. Porosity after 48 hours immersion under atmospheric pressure (N48) will be considered here as estimator of porosity accessible by capillarity. The coefficient Cwx100/N48(%) will be used as a parameter for evaluation of capillary migration, represented by Cheq (equivalent height of the capillary zone). In this regard, optical and electron microscopy studies have the advantage, in relation to mercury porosimetry or BET, of allowing to relate pore structures to petrographic features, linking the observed macroscopic properties with geological processes and, therefore, the history of the rocks, as well.