Unique Properties Of Permeability Curves Of Concern To Reservoir Engineers
Authors: Higgins R.V. , Boley D.W. , Leighton A.J. 
Published: December 2007

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Abstract
With the advent of the modern electronic computer, relative permeabilities of reservoir rock to oil and water are used much more than previously in calculating the performances of water floods. Also, appreciably more fluid mechanics are employed in computer problems than before. As a result, small differences in permeability curves often show marked differences in waterflood predictions than some of the earlier procedures would detect. Hence, better advantage can be taken, than previously, of accurate relative permeability curves.
This paper points out areas where hidden, yet relatively large, inaccuracies can exist in the use of certain permeability curves that previously were not easily discernible. This paper shows the following.
There are many possible combinations of relative permeability curves that will result in virtually the same recovery vs injection, but require different times and rates to recover the oil. This can occur even with different mobility ratios. There are permeability curves obtained by the use of nonviscous oil [less than 2 or 3 cp], when employed for calculating the performances of water floods of viscous oils, which can lead to serious inaccuracies. As far as viscous oils are concerned, the sections of the permeability curves from the breakthrough saturation region to the nearly watered-out end [high water saturation] affect recovery nearly as much as do the terminal values of the permeability curves. Stated in another way, the wettability characteristics in the middle portion of the permeability curve affect recovery nearly as much as other portions of the permeability curve. This is not true for nonviscous oils in water-wet reservoir rock. The difference in magnitude may be of the order of 20 per cent of the recoverable oil.
Each of the foregoing is illustrated by one or more examples.

Introduction
Waterflood calculations using the effective permeability to oil at the interstitial water saturation and the effective permeability to water at the irreducible oil saturation are used in prediction methods. Welge has presented a method that uses relative permeability curves and presents an example using two phases - gas and oil.