Can Absence of Edge-Water Encroachment in Certain Oil Fields Be Ascribed to Capillarity?

Abstract

In several oil fields the amount of edge water invading the wells after the field is almost exhausted is very small. This may be due to different causes, some of which are briefly mentioned in this paper. The writer's object is to show that capillarity can not hold the oil outside the depleted area around the well and can not prevent the edge water from moving toward the well. In the depletion zone two conditions are possible when the formation is an unconsolidated sand, (1) the funicular and (2) the pendular. In the former, oil and generally gas flow freely. In the latter, gas flows freely and may be followed by oil. If the oil-bearing formation is consolidated and the interstices are pores with narrowings, Jamin effect would not stop the flow altogether because the gas would diffuse through the films of oil which shut off the pores in the narrowings. Light oils would evaporate from one film and condense on the next nearer to the well and thus move toward the well. It can be proved, however, that if a certain number of gas bubbles could stop the flow of oil, the number of bubbles necessary to fulfill this condition would not be formed, so that oil would move toward the well, ultimately followed by edge water, unless it is held back by other causes.