Effect of Oil Viscosity on Water/Oil Relative Permeability

Katayoun S Nejad, Eirik Asbjørn Berg, Jon Knut Ringen
STATOIL

This paper was prepared for presentation at the International Symposium of the
Society of Core Analysts held in Austin, Texas, USA 18-21 September, 2011

Abstract:
This work presents an investigation on the effect of oil viscosity on residual oil saturation and water relative permeability endpoint. A number of water/oil relative permeability measurements were performed using steady state, unsteady state and centrifuge methods. Experiments were conducted on core material from viscous/heavy oil fields. Viscous crude oil and refined lab oils were used to study the effect of oil viscosity on residual oil saturation, Sorw, and the corresponding relative permeability to water, Krw(Sorw). Results were compared with field data from the Statoil SCAL database and literature data.

Data indicates that there is a correlation between the oil viscosity and residual oil saturation and water relative permeability end point. Increasing oil viscosity reduces the Krw(Sorw) and increases Sorw. Micromodel experiments also show a different fluid distribution during water / oil displacement and distribution of residual oil depending on the oil viscosity.

The remaining oil saturation from laboratory measurements might be systematically too high due to experimental artefact, capillary end effect and early termination of the experiment, especially when using heavy/viscous oil. Similarly the Krw(Sorw) may be systematically too low. We suggest using history matching (core flood simulating) or extrapolated Kro-curves to residual oil when reporting the measured lab data. The effect of wettability on the observed results is also discussed.

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Objectives
The name of this organization is the Society of Core Analysts (SCA) and was founded in 1986. This organization is a Chapter-at-Large of The Society of Petrophysicists and Well Log Analysts (SPWLA) and is established with two objectives:

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