The effects of wettability and heterogeneities on the recovery of waterflood residual oil with low pressure inert gas injection, assisted by gravity drainage

It is shown that in the laboratory a very high percentage of the waterflood residual oil can be recovered with low pressure inert gas injection, assisted by gravity drainage, from both water-wet and oil-wet samples. A mixed wet semipermeable paste assures the production of both oil and water but it prevents gas production. Stacks of short core plugs can be produced equally as a single long core if a coarse version of the mixed wet paste is used between adjacent plugs. In water-wet cores displacement of waterflood residual oil requires a positive spreading coefficient of oil on water in air. Parallel-type macroscopic heterogeneities in the formation may have relatively little effect on the course of oil recovery, but they prevent a uniform saturation to be established in the core cross-section. Microscopic pore scale heterogeneities decrease the recovery efficiency.