Flow Of A Disperse Emulsion Of Crude Oil In Water In Porous Media

Abstract

Abstract It has been suggested that oil migrates through reservoir sands in the form of a fine, disperse emulsion of oil in water, and that oil accumulations occur where the stream enters finer-grained rock such as silt or shale. In order to investigate the possible mechanisms, stable emulsions of oil in water were prepared without the use of wetting agents. They consisted of droplets 1/2 to 1-1/2 microns in diameter, in a concentration of 20 to 40 parts of oil per million of water. These emulsions passed freely through filter paper and ordinary passed freely through filter paper and ordinary sand. A plastic tube containing glass beads of 200-microns diameter included a bed 1/2-cm thick of crushed beads 37 to 88 microns in diameter. When the emulsion was passed through this tube, up to 80 percent of the oil was screened out at the coarse-fine interface. The amount removed depended on the contrast in grain size, the nature and the preferential wettability of the media. Similar results occurred when quartz sand was used as the coarse, and crushed sand as the fine medium. This screening did not occur as a result of capillary effects., because the pores were many times the diameter of the droplets. The oil collected as a result of flocculation of the droplets into strings and clusters., and the oil saturation in the pores consisted of masses of droplets with very little coalescence. Possibly electrostatic forces are more important Possibly electrostatic forces are more important than capillary in the behavior of fine, disperse, oil-in-water emulsions. our current ideas on multiphase flow in porous media may not apply to disperse emulsions. Introduction The physical mechanisms of the migration of oil, including the expulsion of oil from the source rock, its migration, and its accumulation in the reservoir rock, are very poorly understood. Most authorities believe that the expulsion of water from compacting shale causes regional flows of water within the pores of the enclosing sediments, and the water somehow carries the oil with it. Hydrocarbons heavier than decane have such a low solubility in water that it is inconceivable that large quantities could have migrated as true solutions. Most subsurface waters have near normal oil-water interfacial tension, so that migration in "solubilized" form as suggested by Baker is improbable. Conventional reservoir mechanics require that oil occupy more than 15 percent of the pore volume in order to exist as a continuous, mobile component. No doubt migration in the continuous phase has occurred frequently, especially secondarily when previously formed oil accumulations have been shifted by tilting of the reservoir rocks. However, such movements should leave residual oil saturations and staining in the flow paths.