Laboratory tests and field pilot of foam-assisted deoxidized-air flooding in a low-permeability sandstone reservoir

Foam-assisted deoxidized-air flooding is a promising technique for improving oil recovery, particularly in low-permeability oil reservoirs. However, significant differences in displacement efficiency have been observed. A comprehensive program including field pilot analysis in Wuliwan oil reservoir, a low-permeability reservoir in China, and laboratory experiments was initiated to investigate the displacement mechanism of foam-assisted deoxidized-air flooding. We carried out a series of laboratory experiments of foam-assisted deoxidized-air flooding with different gas–liquid ratios at different water cut stages, while using nuclear magnetic resonance technology to monitor the distribution of crude oil in pores. The results revealed that increasing gas–liquid ratio enhanced oil recovery during the high water cut stage, but reduced it during the middle water cut stage. The differences in oil recovery at different water cut stage appear to be linked to changes of the displacement mechanism. We indeed observed that oil was produced from a wide range of pores at the high water cut stage, but only from the macropores at the middle water cut stage. The field pilot analysis supported our conclusion based on the experimental findings, that foam-assisted deoxidized-air flooding using an appropriate gas–liquid ratio can efficiently lower water cut and enhance oil production at different water cut stages. The combination of laboratory and field pilot tests used here can serve as a template for future studies in other oil reserves.