Experimental investigation and development of correlation for static and dynamic polymer adsorption in porous media

Part of the injected polymer during polymer flooding is lost in porous media by adsorption, mechanical entrapment, and hydrodynamic retention. Therefore, having a clear understanding of polymer losses/retention is very important for designing a technically and economically successful polymer flooding project. Polymer losses are traditionally modeled using Langmuir Isotherms, requiring costly and time-consuming dynamic corefloods to obtain fitting parameters. This research suggests a faster and low-cost method for first-order approximation of polymer adsorption in porous media without conducting corefloods. The proposed technique uses the results of polymer adsorption on the crushed core in the static test that can be used in a lookup table in the simulator instead of Langmuir Isotherms Equation. Mercury injection (MICP) was used to find a cut-off molecular size based on the hydrodynamic size of the polymer calculated using the Flory-Fox equation. Brunauer-Emmett-Teller (BET) tests are used to measure the specific surface area of the crushed core. These three tests determine the equivalent weight of crushed core to be used for static adsorption tests that would represent the specific surface area of the core. Seven high permeability Bentheimer core plugs from outcrops were used to perform polymer corefloods to determine polymer adsorption, followed by seven static adsorption tests performed at similar conditions to compare the results. Polymer adsorption tests showed that 1-h residence time, 0.5 solid-to-liquid ratio, and pre-saturating crushed core with brine before starting static adsorption were important to map static to dynamic polymer adsorption. Other important observations were the increase in polymer adsorption with increasing polymer molecular weight, polymer concentration, and NaCl salinity in order of descending significance of the effect. The proposed method gave a reasonable statistical correlation between static and dynamic polymer adsorption with a coefficient of determination (R-2) of 0.97, and Pearson's correlation coefficient (r) of 0.98. The maximum deviation between static and dynamic result was 34% for cores of similar flow zones, and 48% for cores of dissimilar flow zones.