SCALED PHYSICAL MODEL OF SECONDARY OIL MIGRATION

A scaled physical model was constructed to simulate gravity- and capil lary-controlled flow of oil into a water-saturated sand during seconda ry hydrocarbon migration. The model provided both visualization of the flow patterns and estimates of hydrocarbon transport rates and effici encies. The dimensions and physical properties of the model were desig ned so the balance of gravity, capillary, and viscous forces was the s ame in the model as in the geologic system. The physical model was a s and pack between glass plates; the pack was 52 cm high, 100 cm long, 2 .5 cm thick, and inclined at a 5-degrees dip; its porosity was 42%, an d its permeability was 7.0 x 10(-10) m2 (710 d). It modeled a geologic carrier bed 27 m thick with 20% porosity and 9.9 x 10(-14) m2 (100 md ) permeability overlying a source rock. A dyed oil was injected into t he lowest corner at a rate of 1 cm3/day, and it exited the highest cor ner at atmospheric pressure. Oil movement was followed both visually a nd by ultrasonic velocity measurements. The behavior of fluids in the model led us to the following conclusions for oil transport through wa ter-wet, homogeneous carrier beds. The rate-limiting step in charging a trap is not secondary migration, but rather the rate of oil release from the source rock. High hydrocarbon loss may occur during vertical migration (when the carrier bed lies above the source) because of exte nsive dispersion. Losses during lateral migration are probably minimal because flow is concentrated below the top seal.