In Part I, a method using relative permeability curves is presented to determine in about 30 min. by the use of a desk calculator and graphs the oil recovery vs cumulative water-injection of linear and 5-spot water floods. For the linear model the determinations are nearly identical to those calculated by the electronic computer used in the Higgins and Leighton technique,1 and for the 5-spot they are within an average of 2 per cent of them. The .5-spot results by the graphical method are also within an average of 5 per cent of those for presently available experimental 5-spot water floods. However, the graphical method does not give the time or rate of oil recovery.
The study shows that the recovery for the linear vs the 5-spot differs by only a small amount after about one displaceable volume is injected. This indicates that relative permeabilities are a more dominant factor in the recovery of viscous oils than pattern efficiency. This further indicates that the concept of "dead" areas in patterns is questionable. This method, with changes in the factors, is applicable to other patterns.
Part II contains material and relationships that are not as accurate as would be obtained by the electronic computer. Part II presents specific examples relating to the effect of pressure and free gas saturation on the viscosity of crude oil mixtures before and after the start of a water flood. A method to approximate the effects of initial free gas saturation and the effect of the absolute permeability variation with depth on the recovery of oil from a 5-spot water flood is also presented and illustrated.
