| Summary: | Previous studies of nanoparticles stabilized surfactant foam flooding are mainly conducted in the water-wet porous media. Hence, the purpose of this study is to investigate the foam stabilization in the oil-wet system since the applied surfactant and nanoparticles also show an effective function as wettability modifier agents. The effect of surfactant concentration beyond the critical micelle concentration (CMC) was studied during the foam static test and wettability alteration test. The static foam tests conducted were half-life, bubble size distribution, mean diameter, and lamella thickness; while the dynamic tests conducted were pressure drop, foam apparent viscosity, mobility reduction factor, oil recovery, and the effect of heterogeneity. The wettability alteration was measured by using the contact angle method. This study also investigated surfactant adsorption on clay in the presence of nanoparticles. The result shows that, the presence of nanoparticles significantly enhanced the surfactant foam in the static test where the most influential parameter was particle hydrophobicity. At CMC, the half-life of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) foam increased from 491 s and 700 s to 1360 s and 4089 s, respectively in the presence of partially hydrophobic silicon dioxide (PH SiO2) nanoparticles. In the wettability alteration test, the type of surfactant and nanoparticles which produced the lowest contact angle was an inverse sequence of the foam static test. The contact angle of the carbonate rock was reduced from 112.00o to 28.35o by using CTAB and hydrophilic SiO2. The effect of surfactant concentration beyond the CMC also shows an inverse effect between the foam static test and wettability alteration test. The effect of nanoparticles in reducing surfactant adsorption on clay was governed by particle hydrophobicity. During the dynamic test, the oil recovery of CTAB and SDS foam flooding increased from 62.07% and 66.36% to 67.03% and 71.79%, respectively in the presence of PH SiO2. Besides, the oil recovery in the heterogeneous oil-wet glass bead pack was higher from the high-permeability layer than the low-permeability layer. In conclusion, PH SiO2 nanoparticles have successfully stabilized surfactant foam in an oil-wet system. This suggests that the same nanoparticles could be utilized in the current foam enhanced oil recovery application worldwide, especially in the carbonate reservoirs.
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