Stabilization of Montmorillonite Clay in Porous Media by High-Molecular-Weight Polymers

Abstract

Summary A dynamic method is proposed for checking the stability of clay in porous media for different brine conditions and the stabilizing effect provided by several anionic and nonionic high-molecular-weight polymers. The method consists of injecting brine at decreasing salinity levels into clayey sandpacks until unstabilized permeability reduction is reached from the dislodging of clay particles that become trapped in pore restrictions. The last stable state before clay destabilization is characterized by a critical salinity concentration (CSC). As expected, montmorillonite clay 5% dispersed in a sandpack is more stable in the presence of KC1 than NaCl brines, giving CSC values of 5, 000 and 27, 500 ppm, respectively. Polyacrylamides are much better clay stabilizers than carboxymethyl cellulose (CMC) or xanthan gum (XG), lowering the CSC of KC1 to 1, 000 to 2, 000 ppm and the CSC of NaCl to 6, 000 to 7, 000 ppm. A low-molecular-weight shear-degraded polyacrylamide is shown to keep good stabilizing power without inducing the high permeability reduction values obtained after adsorption of high-molecular-weight products. In addition to preventing clay migration, polyacrylamides are also shown to inhibit clay swelling.