Buoyancy and interfacial force effects on two-phase displacement patterns:An experimental study

Modeling secondary migration of oil currently is difficult because the phys ics governing the movement is complex and information on heterogeneity of c arrier beds is always incomplete. To better understand the basic physical p rocess of secondary migration, we discuss displacement patterns based on re lative magnitudes among buoyancy, interfacial, and viscous forces using the results of one-dimensional vertical oil-water displacement experiments. Oi l was injected at a constant rate from the lower inlet of a glass tube pack ed with sorted glass beads. The injection pressure and oil outflow rate wer e measured while we observed the displacement pattern. Runs were done using different grain sizes and injection rates. Two displacement patterns were recognized during the experiments: type A co nsisted of stable, pistonlike displacement and type B consisted of capillar y fingering. The difference coincided with the relative magnitudes of the d riving forces, which can be characterized by the dimensionless modified Bon d (Bo') and Capillary (Cn) numbers. Type A pattern was produced for high Ca /Bo' ratios and type B pattern for low Ca/Bo' ratios. A flow regime diagram showing the regions of the two displacement patterns was constructed in Ca /Bo' space, including the effects of gravity. Our results also showed that excess pressure for the nonwetting phase fluid to intrude into a porous med ium was rate dependent.