The critical salinity concentration (CSC) was used to compare the ability of nonionic polyacrylamides (PAM) and cationic polyacrylamides (CPAM) to stabilize montmoriilonite clay dispersed in sandpacks. The method consists of injecting brine at decreasing salinity levels until clay release is detected by a continuous increase in pressure drop.
As expected, because of the neutralization of negative clay surface charges by adsorbed macromolecules, CPAM have a higher stabilizing power than PAM, lowering the CSC of NaCl from 27 500 to only 500 ppm, and the CSC of KCI from 5000 to 1000 ppm. However, because of their ionicity and very high adsorption level, CPAM strongly reduce sandpack permeability. Likewise, a low-molecular-weight PAM may be preferred because of its good stabilizing power associated with a minimal loss of core permeability.