Secondary Migration of Oil: Experiments Supporting Efficient Movement of Separate, Buoyant Oil Phase Along Limited Conduits: GEOLOGIC NOTE

Abstract

Experimental data suggest that the secondary migration of oil in porous, permeable sediments probably occurs, in most circumstances, along restricted pathways or conduits. These conduits are formed after the oil has reached a high enough saturation in the reservoir rock for the buoyancy of the oil to overcome the capillary pressure in the pore throats. The oil probably moves vertically until it reaches the top of the reservoir interval. The oil then moves updip along the top of the reservoir interval via a narrow, restricted pathway until it reaches the trap and begins to accumulate. Depending on the area of the original oil saturation at the bottom of the reservoir unit and the structural geometry, multiple conduits may form, along which the oil may flow. Because these conduits are limited in diameter, the amount of oil lost during secondary migration could be limited to the irreducible oil saturation left behind in the conduit, provided no small-scale traps exist along the path to the main trap. Rates of oil movement are very rapid in a geologic context, suggesting that the timing of primary migration is a good indicator of the timing of secondary migration.