Flow-induced-microgel adsorption of high-molecular weight polyacrylamides

Water soluble polymers are widely used in oil and gas reservoirs and usually injected into the reservoir rocks to alter their flow properties. The rheologies of the polymer solution and their adsorption or interaction with the porous system are crucial for the success of the injection. This work aims to investigate the formation of residual polymer multilayers as a result of the flow of aqueous solutions of high-molecular-weight cationic (CPAM) and non-ionic (PAM) polyacrylamides through single, circular and rectangular capillaries. Polymer solutions in de-ionized water and weak brine were injected at different flow rates into glass capillaries of circular and rectangular cross sectional area. The adsorption energy and layer thickness on glass surfaces of these polymer solutions have been investigated by Al-Hashmi and Ludcham (2010) under static conditions using colloidal force measurements. The apparent viscosity of the polymer in solution on both increasing and decreasing the shear rate are presented to indicate the thixotropic or anti-thixotropic behaviour of the solution. Also, the viscosity-time curves are presented to investigate the rheopectic behaviour of the polymer solutions. The flow CPAM in water solution through the capillaries resulted in very thick residual polymer layers, around 15 times thicker than those measured under static conditions. This solution shows both anti-thixtropic and rheopectic behaviour, which may be attributed to flow-induced-microgel formations in the bulk of the polymer solution. The same polymer solution has shown almost instantaneous adsorption from the colloidal force measurements due to electrostatic attraction of the cationic groups of the polymer to the negative glass surface. Such thick layers are not formed when CPAM in 0.34 M NaCl is used. Although it has shown strong adsorption on glass, the CPAM in 0.34 M NaCl exhibits neither anti-thixotropic nor rheopectic behaviour. Though it has shown rheopectic behaviour, the non-ionic polyacrylamide in water solution does not result in significantly thick layers, which might be due to its weak adsorption on glass. In the current study, a new mechanism is proposed to attribute the apparent formation of residual multilayer under the name of flow-induced-microgel adsorption (FIMGA). According to the new mechanism, two criteria have to be satisfied for polymer multilayer formation: the formation of sizable shear-induced-microgel structures in the bulk of the solution, and sufficiently high adsorption energy of the polymer to the solid surface. The new understanding in view of this new mechanism will contribute to more successful applications of polymers in oilfields. It will also allow faster screening of the chemicals for a specific application which may warrant different characteristics of flow and adsorption. For example, polymers used in enhanced oil recovery should have high injectivity and low adsorption. On the other hand, high adsorption and thick residual polymer layers are the key for a successful use of polymers in water shut-off in oil and gas wells. (C) 2013 Elsevier B.V. All rights reserved.