In this study, effects of surfactant adsorption and desorption on oil production were investigated in laboratory scale by using Sodium Dodecyl Benzene Sulfonate and Berea sandstone. The maximum adsorption-desorption values were measuredas57.7mg/100g and 47.9mg/100g of rock, respectively. Based on those measurement results, numerical reservoir simulations were performed with a commercial simulator, STARS, to discuss about effects of the degree of surfactant adsorption reversibility. Reservoir heterogeneity was also taken into consideration by comparing to that of homogenous reservoir. The numerical simulation results showed that the reservoir heterogeneity reduced oil recovery factor by up to 7.4%comparing to homogenous reservoir, but the effects of reversibility of surfactant adsorption on oil recovery are different due to reservoir types.

After primary or secondary recovery, Speight (2016) proposed that considerable amount of residual oil is still left in reservoir from 50% to 67% of Original Oil in Place (OOIP). This is due to the high capillary pressure, unfavorable rock-fluid condition and inaccessible from reservoir heterogeneity.

Surfactant flooding is one of potential Chemical Enhanced Oil Recovery (CEOR) techniques which is able to reduce reservoir capillary pressure and then lower interfacial tension (IFT) between aqueous and oil phases. As a result, oil can be liberated from pore surfaces, and turning into small droplets or emulsion as addressed by Srisuriyachai (2008).When IFT is archived to ultra-low condition, residual oil can be liberated from reservoir pore spaces and consecutively improved oil recovery. However, surfactant solution injected into reservoir contacts with both reservoir fluid and formation rock surfaces. High adsorption of surfactant molecules onto internal pore surfaces in the formation rock lead to insufficient surfactant molecules to interact with reservoir fluids, so this makes surfactant flooding economically inapplicable. Meanwhile, heterogeneous reservoir types also play a vital role in reducing efficiency of surfactant injection method. According to those conditions, injected surfactant fails to establish ultra-low IFT condition. Therefore, the surfactant adsorption has been confirmed to be reversible back into reservoir system under certain conditions.