Quantifying the Matching Relationship of Sizes Between Partially Hydrolyzed Polyacrylamides and Regular Nuclepores

Water-soluble polymers have been extensively utilized for enhanced oil recovery (EOR) due to their strong thickening power to aqueous displacement fluids. However, the typical EOR polymer, high-molecular-weight (MW) partially hydrolyzed polyacrylamide (HPAM), often encounters injectivity challenges, particularly in low permeability reservoirs, which is attributed to the lack of a quantitative matching relationship of sizes between polymer and porous media. In this study, the radius of gyration (R _g) and the hydrodynamic radius (R _h) of five HPAMs with various MW ranging from 4.8 × 10⁶ to 15.4 × 10⁶ g·mol⁻¹ were determined via light scattering. Subsequently, by employing polycarbonate nuclepore membranes to mimic regular micro- and nano-pore throats, the flow and matching relationship of these HPAM solutions in porous media were investigated. It was found that the R _g of HPAM gradually magnifies from 89 to 161 nm with an increase in polymer MW, while R _h ranges from 53 to 92 nm. The matching relationship between R _g/R _h and nuclepore size (R _p) can be described as follows: when R _p/R _g < 2.01 or R _p/R _h < 3.7, injection difficulties emerge for HPAM solution; conversely, when R _p/R _g > 2.48 or R _p/R _h > 4.77, there is no blockage caused by the HPAM solution.