The Effects of Viscosity and Wettability on Oil and Water Relative Permeabilities
Authors: Donaldson Erle C. , Lorenz Philip B. , Thomas Rex D. 
Published: December 2007

This paper was prepared for the 41st Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Tex., Oct. 2–5, 1966. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
Outcrop cores and crude oils were used to examine the effects of viscosity and wettability on relative permeabilities. Wetting was evaluated from capillary pressure curves. Changes in wettability were produced by using different crude oils and additives. As the system became less waterwet, k(ro) decreased, but k(rw) was not affected. Cores cleaned with solvents were less waterwet than natural cores. Apparent values of k(ro) exceeding unity are due to capillary end effects.

Introduction
It is well established that waterflooding is the most important method of secondary recovery but leaves large quantities of unrecoverable oil. It is possible that specific additives may effect changes in wettability that will bring about improvements in the displacement efficiency of waterfloods. Although previous investigators have studied the effects of floodwater additives, many of these studies were conducted with refined oils and artificial cores. Crude oils and outcrop core samples were used to secure better representation of natural systems.
Gatenby and Marsden have shown that wettability tests determined by capillary pressure measurements agree qualitatively with those determined by imbibition tests. Imbibition tests with crude oils are complicated by an induction period as well as viscosity and permeability. The centrifugal method of determining capillary pressures was used because it yields results in a few hours that may require several days by the imbibition method.
Oil and water relative permeability values are basic to the calculation of waterflood performance in the field as well as in the laboratory. The unsteady-state method of core analysis was used, because it is representative of the actual oil depletion process occurring in a field waterflood and is a rapid method of analysis.

LABORATORY PROCEDURES

Cores and Solutions
Outcrop core samples: The core samples were cut from an outcrop of the Torpedo sandstone using a portable drilling rig equipped with a 1 1/2" × 40" diamond bit. The cores were taken from the formation in a pattern that was as close together as possible for uniformity of the core samples.