Microwave spectroscopic analysis of surfactant/polymer flooding: interrelationships between chemical slug properties, coalescence

Microwave absorption spectroscopy was employed to monitor the dynamic in situ oil saturation profiles during laboratory tertiary oil recovery experiments in consolidated Berea cores. Experiments were performed using Salem crude oil and 2 different low-concentration petroleum sulfonate systems. Microwave analysis revealed distinctly different oil banking characteristics for the different surfactant systems. Low-viscosity slugs were seen to channel, causing the formation of 2 oil banks, one upon surfactant injection and another upon polymer injection. The fractional oil flow showed 2 peaks with a decrease between production of the 2 oil banks. In contrast, in tests with slugs exhibiting good mobility control, the core exit oil saturation rose and remained above waterflood residual saturation coincident with the production of a single continuous oil bank. Surfactant slugs exhibiting rapid coalescence produced oil in emulsion-free form, while slowly coalescing systems produced primarily emulsified oil. These observations combined with produced fluids analyses lead to a mechanistic description of oil banking and oil reentrapment processes. 20 references.