Effect of Edge Water on the Recovery of Oil

Abstract

In many fields edge water is one of the most important factors governing theproduction of oil. Possibly this fact is not appreciated by many producersexcept in so far as it may bring about a loss in production from wells drilledon the flanks of structures. In the light of artificial flooding as practicedin New York and Pennsylvania, and of the beneficial effect of naturalwater-flooding on many wells and leases in the Mid-Continent and elsewhere, itseems reasonable to suppose that very few phases of the petroleum industry holdgreater promise for future benefit than the study and control of the naturalwater drive. Rate Of Water Encroachment The rate of movement of water in artificially flooded areas has been referredto as so many feet per unit of time, usually from an injection well towardsurrounding producing wells. This definition is vague when used in reference tothe movement of natural edge water, inasmuch as such factors as sand thickness, steepness of dip and horizontal extent are not considered. In the ultimateanalysis, only the vertical component of movement affects the production of oilin the natural drive, and in order to define the rate of water encroachmentmore exactly, such a term as acre-feet per unit time might be used. Thus, whereone well is located to each 10 acres a vertical movement of 5 ft. in the waterlevel in a year would be defined as an encroachment of 50 acre-feet per year, and where one well is located to each 20 acres, as 100 acre-feet per year. Sucha definition as this is entirely arbitrary, but it takes into consideration toa certain extent the influence of well spacing, and consequent sand drainage, on the rate of water movement. The rate of movement is considered to be an important function of waterencroachment, for it is believed that the efficiency of recovery by naturalwater flood depends a good deal upon the rate of movement. In general, rapidencroachment is thought to effect a poor recovery because of the differentialin favor of the movement of water through a sand body and the consequenttendency to trap oil in the sand.