AN EXPERIMENTAL-STUDY OF SECONDARY OIL MIGRATION

Experiments using long glass columns packed with glass beads or sand have been done to investigate secondary oil migration under hydrostatic conditions. Different combinations of bead sizes, oil densities, oil-water interfacial tensions, and column orientations have been tested. In some experiments, the oil was replaced by air. The observations included the oil migration pathway, the minimum oil column height needed for migration, and the rate of advance of the migration front. Migration was found to take place along restricted pathways and an imbibition front often formed at the bottom of the oil zone. The minimum oil zone height needed for migration can he predicted accurately if the values of the drainage and imbibition capillary pressures are known for the saturations at which the oil just becomes disconnected. In most experiments, the migration front advanced at a constant rate, which depended on the fluid properties, bead size, initial oil height, and pore structure. Migration rate is dependent on buoyant and capillary forces, but the dependence on capillary forces becomes weaker as the oil length increases. Column orientation also has been found to affect migration efficiency.