G. Chauveteau (Institut Français du Petrole) | K. Denys (Institut Français du Petrole) | A. Zaitoun (Institut Français du Petrole)
In previous papers we investigated high-molecular-weight polyacrylamide adsorption under high shear rates in low-permeability media and found that, above a critical value ?c , adsorbed macromolecules can reduce the permeability by factors over hundred, suggesting a mechanism of pore throat bridging. New lab experiments have been designed specifically to elucidate the mechanism at the origin of this “bridging adsorption”. Polymer injections were carried out over a wide range of shear rates in homogeneous high-permeability granular packs having hydrodynamic pore throats too large to be bridged by polymer macromolecules. When polymer is injected at low shear rate (?c) the adsorbed layer thickness eHS (calculated from permeability reduction values) does not depend on injection rate. When the injection occurs at higher shear rates (?>?c), eH increases slowly up to reach maximum values eHM increasing with injection shear rate. These eHM values were found to be large enough to explain the very high reductions in permeability obtained previously in low-permeability packs.
These results show that polymer adsorption in porous media can be increased significantly by the hydrodynamic forces normal to the pore wall, as soon as they become high enough to “push” additional macromolecules into the already adsorbed polymer layer. This mechanism increases both polymer adsorption density and adsorbed layer thickness. We propose to refer to this mechanism as a “flow-induced adsorption”. This new interpretation is consistent with all results previously attributed to “bridging adsorption” and the new results reported in this paper. It provides an important conceptual tool to model polymer placement in water shutoff and to design conformance treatment.