Impact of Surfactant Concentration on Chemical-Assisted Methane Flooding in Foamy Oil Reservoirs

The primary recovery factor of extra-heavy oils with foamy oil flow characteristic is only 8–12%. In previous studies, an approach of chemical-assisted methane flooding to enhance recovery in foamy oil reservoirs after primary depletion was proposed. The approach includes injecting viscosity reducer naphtha, methane and surfactant solution slugs sequentially to recreate foamy oil flow in situ. This study further investigated the effect of the surfactant concentration on the process through indoor experiments. Extra-heavy crude oil sample with typical foamy oil features, taken from Venezuela Heavy-Oil-Belt, was adopted during the experiments. To begin with, 16 groups of interfacial tension test between oil added with surfactant solution of different concentration and methane were conducted. Afterwards, 6 groups of foam stabilization test were conducted to record the foam volume and the half-life period under different surfactant concentrations. Finally, 3 groups of 2D visualized micro-flow experiments were conducted to investigate the surfactant concentration effect on the generation of dispersed gas bubbles. The interfacial tension tests showed that the oil-gas interfacial tension decreased with increase in the surfactant concentration when the concentration was below its critical micelle concentration value. The test on foam stabilization showed that an increase in surfactant concentration improves the stability of foam liquid film, delays foam drainage, and prolongs foam life. The 2D visualized micro-flow experiment results illustrated that it presents a distinct foamy oil phenomenon, at a concentration of 2wt% and above. Above understandings provide guidance for on-site implementation.