An Approximate Theory of Water-coning in Oil Production

Abstract

The phenomenon called water-coning is that, observed in many oilwells, in which bottom water gradually and frequently suddenly displaces a partor all of the oil production when a certain rather critical production ratefrom the well is exceeded. To follow in detail the process of the formation of a water cone asit breaks through the oil zone and enters the well bore is a problem so complexas to make a theoretical analysis practically impossible. However, ananalytical treatment of the flow system before the water has broken through and during the time thatit lies statically beneath the oil zone with an elevated or "coned"surface can be carried through under certain approximations. To present ananalysis which shows the essential characteristics of the coning mechanism is the purpose of the presentdiscussion. Physical Basis of Theory and Meaning of Approximations As will always be true for flow systems where true water-coning is at allpossible, the water will be supposed to lie beneath the oil zone because of itsdensity contrast with respect to the oil. In fact, under the usual fieldconditions, when the pay horizon is reasonably homogeneous, the water mostfrequently enters the well through the lower zones, but even when it entersfrom intermediate zones it may, in the later life of the well, displace thebottom layers of oil, thus resulting in a system wherein the oil is effectivelyfloating on the water.