Permeability damage due to the water sensitivity of three types of sandstone cores was studied. X-ray diffraction showed that the cores contain varying amount of clays and that the Aramco sandstone cores have a higher ratio of smectites (6% relative abundance among clay families) than the other two types of sandstone. Chemical analyses were carried out to determine the base exchange capacity and exchangeable cations in the untreated clay extracted from the cores. To assess further the effect of exchangeable ions, ageing in NaCl, MgCl2 and CaCl2 was carried out to alter the exchangeable ions prior to displacement runs.
The critical salt concentration (CSC)* and the amount of permeability drop were used as a criterion for measuring water sensitivity. The displacement runs showed that water sensitivity can be expressed as a function of the exchangeable cations. The maximum drop in the permeability observed was 86% and the CSC was 0.63 wt% (0.149 M) established when displacing the Aramco cores with aqueous LiCl solutions of decreasing concentrations. Varying the cations in the displacing solution had a large effect on water sensitivity; the permeability drop was reduced to 13.5% and the CSC to 0.13 wt% (0.006 M) when displacing the Aramco cores with aqueous BaC12 solutions of decreasing concentrations. Changing the anions in the displacing solution had a minor effect when compared to changes in the cations.