Microscopic observations of oil displacement in water-wet and oil-wet systems

Laboratory studies of the behavior of crude oil and brine in a waterflood were conducted using micromodels packed with graded sand. Flow mechanisms and residual oil patterns were observed and photographed through a microscope. The wettability of the micromodels, which possessed many of the overall characteristics of reservoir rocks, ranged from strongly water wet to strongly oil wet. Observations of waterflooding showed that each fluid moves through individual networks of interconnected pores during the period of oil production. The size of trapped oil pockets behind the water front depends upon the wettability of the system. The rapid development and growth of water fingers ahead of the front resulted in early water breakthrough in the oil-wet systems. The length of these fingers ahead of the front depended upon the wettability of the system. When additives were used to stimulate residual oil production, 3 distinctly different types of residual-oil flow mechanisms were observed. These can be described as slug flow, globular flow, and extraction.