Chemical EOR process visualization using NOA81 micromodels

Abstract

The main goal for all enhanced oil recovery (EOR) processes is to gain additional oil recovery after, or in some cases along primary and secondary recovery methods. For EOR processes that use immiscible displacement to increase oil recovery, the overall displacement efficiency can be increased by improving the mobility ratio or by increasing the capillary number. Core flooding is the traditional method to study the parameters above. However, microfluidic micromodels are causing huge interest from industry. In this study, we developed procedures to fabricate microfluidic porous media micromodels using a novel polymer – Norland Optical Adhesive 81 (NOA81). NOA81 helped to overcome limitations of previous work by Xu et al. (2014) such as crude oil incompatibility and deformation with higher temperatures. NOA81 micromodels were used to investigate visually the effects of temperature and different wettability on displacement efficiency in water and surfactant flooding. In addition, the natural fractures were introduced in porous media to study water and surfactant flooding in fractured reservoirs. The temperature effect on displacement efficiency demonstrated that increasing the temperature and decreasing interfacial tension (IFT) between fluids results in higher recovery factor and can be well correlated with the capillary number. The presence of connected natural fractures showed no recovery from matrix porous media in water flooding. However, in surfactant flooding 80% oil recovery was achieved due to lowering IFT. The wettability effect demonstrated that the water-wet micromodel produced 15% less than intermediate and oil-wet micromodels in water flooding due to early breakthrough. Meanwhile, surfactant flooding achieved almost equal high recovery in both water-wet and oil-wet surfaces. It was found that after breakthrough takes place, no notable oil recovery obtained in all water flooding experiments. In contrast, surfactant flooding recovered more with more pore volume injected. Oil recovery in both water and surfactant flooding was lower in water-wet fluid displacement. There are many other interesting phenomena observed during displacement efficiency experiments such as dead-end pore displacement, microemulsion generation and complexity of fluid flow dynamics in porous media.