any significant reduction in the permeability in contrast the same suspension caused a gradual blocking of the sandstones with initial permeability k lt 140 md it is also evident that the number of pore volumes of the suspension required to significantly reduce the permeability of these sandstones decreased with the initial brine permeability of the core for example the 140 md sandstone became blocked after 230 pore volumes and the 5 md sandstone became blocked after only 3 pore volumes the data indicate that the suspension could be selectively placed in the higher permeability k 800 md sandstone as the particles would limit flow into adjacent lower permeability k lt 140 md sandstone layers zones we also note from fig7 that the same suspension caused a rapid reduction in the permeability of the high permeability limestone core this effect is caused by a rapid destabilisation flocculation of the ludox cl12 particles due to their interaction with dissolved bicarbonate carbonate ions in the pore fluid of the limestone core this is consistent with the observation that in the absence of gelant the particles flocculate in the presence of 0 0015 mol l carbonate see example 3 fig4 however when the same particles.