Chemical flooding of oil reservoirs .9. Dynamic adsorption of surfactant onto sandstone cores from injection water with and without polymer present

The effect of polymer on the adsorption of surfactant at the solid/liquid interface related to low tension polymer water flood (LTPWF) of sandstone oil reservoirs was studied by means of dynamic laboratory experiments. An alkylpropoxyethoxy sulfate was used as surfactant, xanthan and a copolymer of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate (An 125) were used as polymers, crude oil and n-heptane were the oils, and synthetic seawater was used for brine. All experiments were conducted at 50 degrees C and 1 atm. Long-term adsorption experiments were performed by circulating the chemical solution through clay-containing reservoir cores for several weeks, and short-term experiments were conducted by injecting chemical slugs of constant concentration, but different size, through model sandstone cores. Various adsorption regimes of the surfactant were detected at different contact times between the reservoir core material and the circulated chemical solution, and it was observed that xanthan behaves as a sacrificial adsorbate towards the surfactant by decreasing the surfactant adsorption. In the slug experiments, using model cores, xanthan appeared to decrease the surfactant adsorption when using small surfactant dug sizes, but no measurable effect of xanthan or AN 125 on surfactant adsorption was observed for large slug sizes. A dynamic reversible adsorption model appeared to predict the propagation of the surfactant slug through the porous medium, but the adsorption level was not fitted. (C) 1997 Elsevier Science B.V.