Adsorption IV. An evaluation of polyethylene glycol as a sacrificial adsorbate towards ethoxylated sulfonates in chemical flooding

The feasibility of using polyethylene oxide (PEG) as a sacrificial adsorbate in surfactant flooding applying ethoxylated sulfonates in mixture with some of the corresponding ethoxylated alcohol, has been tested in different ways. Static adsorption of the surfactants has been performed using both quartz and kaolinite as adsorbents. Equilibrium times of 24 h showed decreased adsorption of the surfactants for both of the adsorbents. The sacrificial effect of PEG was greater for quartz than for kaolinite. PEG with an average molecular weight of 4000 was found to be most favorable. pH changes between 3.5 and 7.6 have small effects on the sacrificial behavior of PEG towards both of the adsorbents.Long-term dynamic adsorption studies in Berea cores were conducted by circulating the flooding solution through the cores. The addition of 0.3 wt% PEG, after the adsorption equilibrium of the surfactants had established, resulted in a fast desorption of the surfactant, about 30%. The desorption was only temporary, and a slow readsorption of the surfactant to the initial level occurred. A pressure build-up was also registered. PEG added to the surfactant solution from the beginning showed a very slow surfactant adsorption. Also in this case a pressure build-up over the core was observed. For a oil-containing reservoir core the sacrificial effect of PEG was negligible.The concentration of each of the adsorbates, i.e., the ethoxylated sulfonate and the ethoxylated alcohol, and the PEG was quantified, and the adsorption behavior of each of them is discussed. All the adsorption experiments were conducted using synthetic seawater at 80°C.