Pressure-Volume-Temperature Correlations for Heavy and Extra Heavy Oils

Abstract

Abstract The 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 OFVF, isothermal compressibility, dead-oil viscosity, gas-saturated oil viscosity and undersaturated oil viscosity, The reliability has been evaluated against a set of about 65 heavy and extra-heavy oil samples. About 1200 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 in two different API gravity classes: extra-heavy oils for °API< 10, heavy oils for 10<°API< 22.3. The best correlations for each class 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 correlation with errors reduced, on average, by 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.