In-situ Viscosity of Hydrolyzed Polyacrylamides and Surfactant Worm-Like Micelle Solutions in Microscale Capillaries

Hydrolyzed polyacrylamides (HPAMs) are shear-thinning polymers and have wide application in enhanced oil recovery (EOR), whereas worm-like micelles (WLMs) are known as "living polymers", which can be constructed by the self-assembly of surfactant molecules. Here, a series of experiments were conducted on the fluid behavior of HPAMs and worm-like micelles in microscale capillaries with radii from 1 to 10 pm. The results show that the size of capillary has a decisive effect on the in-situ viscosity of the polymer aqueous phase. It was observed that the shear thinning effect of HPAMs is more pronounced in smaller size of capillaries, where the non-Newtonian polymer flow turns into the Newtonian flow. Evidences from filtration with a microporous filter and transmission electron microscopy (TEM) reveal that the polymer network was broken down when entering into the capillary. Conversely, WLMs can maintain their bulk viscosity to a wide extent. We assume that surfactant molecules may reassemble their aggregates and recover their network in-situ. The results suggest that WLMs have a much lower viscosity, but display similar thickening power compared with large polymers in the low or ultra-low permeability reservoirs.