Adsorption characteristics, isotherm, kinetics, and diffusion of nanoemulsion in tight sandstone reservoir

Nowadays, nanoemulsions have shown a high application potential in improving hydrocarbon recovery from tight reservoirs. However, the adsorption characteristics, isotherms, kinetics of nanoemulsions onto reservoir rocks surface and the diffusion behavior into reservoir matrix are still not been systematically clarified. In this work, nanoemulsion was prepared by diluted microemulsion method using two nonionic surfactants, isopropanol, limonene and 2.0 wt% KCl solution. The static adsorption capacity measurement under different influencing factors were carried out, and the adsorption process was characterized through equilibrium isotherms and kinetic studies. Also, the diffusion behavior of nanoemulsion in the sandstone reservoir matrix were evaluated by core flooding experiments. Results indicated that the nanoemulsion was successfully synthesized and the droplet size mainly distributed between 8 and 18 nm. It had been found that the optimal static adsorption experimental parameters for 0.1 wt% nanoemulsion were 1:8 solid–liquid ratio and 50/60 mesh rock powder. Equilibrium adsorption results indicated that Langmuir model yielded a better fit which means that single-layer coverage of the surfactants composed of nanoemulsion onto the rock surfaces was more probable. Meanwhile, it was concluded that the pseudo-second order model could better describe the kinetic behavior of nanoemulsion adsorption onto the rock surfaces, which revealed that the adsorption rate was positively correlated with the nanoemulsion concentration. Dynamic adsorption experiments showed that the adsorption amount is inversely proportional to the core permeability, while the diffusion coefficient increases with the increase of permeability. Moreover, the advantage of nanoemulsions over sole surfactant is that the oil nucleus in the nanoemulsions enable control the release of the attached surfactants, and there is a competitive adsorption relationship between oil nucleus and rock surface for the free surfactants in the solution, which offers a possibility for reducing the surfactant adsorption loss and extending the invasion distance in the reservoir matrix. The findings obtained in this study can help for better understanding of the interaction mechanism between nanoemulsions and reservoir rocks, and provide guidance for selecting appropriate nanoemulsions for the enhanced oil recovery (EOR) project in tight sandstone reservoirs.