This paper evaluates the reliability of the most common empirical correlations used for determining reservoir fluid properties whenever laboratory PVT data are not available: bubblepoint pressure, solution GOR, bubblepoint OF W, isothermal compressibility, dead-oil viscosity, gas-saturated oil viscosity and undersaturated oil viscosity.
The reliability of the correlations has been evaluated against a set of 195 crude oil samples collected from the Mediterranean Basin, Africa, the Persian Gulf and the North Sea. About 3700 measured data points have been collected and investigated. All measured data points are reported in the paper. For all the correlations, the following statistical parameters have been calculated: a) relative deviation between estimated and experimental values, b) average absolute percent error, c) standard deviation.
Oil samples have been divided into the following four different API gravity classes: extra-heavy oils for °API< 10, heavy oils for 10<°API≤ 22.3, medium oils for 22.3<°API< 31.1, light oils for °API> 31.1.
The best correlations both for each class and for the whole range of API gravity have been evaluated for each oil-property.
The functional forms of the correlations that gave the best results for each oil property have been used for finding a better coiTelation with average errors reduced by 5-10%. In particular, for extra-heavy oils, since no correlations are available in literature (except for viscosity), a special investigation has been performed and new equations are proposed.