An Update to Viscosity Correlations for Gas-Saturated Crude Oils

Abstract

For live crude oils, dissolved gas acts to reduce viscosity from the value observed for dead oils. The reduction in viscosity can significantly impact pressure drop and flow rate and must be properly accounted for by any viscosity model. This article provides a detailed review of existing correlation methods and offers state-of-the-art solutions necessary for oil field operations in 2007 and beyond. A total of 21 methods for calculating saturated oil viscosity have been identified from the literature. A large database consisting of data from oil PVT reports and literature sources has been compiled in order to evaluate these methods. This data represents over 12,000 measurements from 1849 samples. The gases dissolved in the oils contain varying amounts of non-hydrocarbons and the oils provide a representative crossection of the expected range in API gravity and Watson characterization factor found in crude oils from producing regions located around the world. A detailed analysis of correlation performance has been conducted which reveals inaccuracies in many of the previously published methods. As a result, a new method is proposed which is consistent across a wide range of parameters and offers increased accuracy over existing methods. Introduction Viscosity is the single most important parameter for calculating the pressure drop of fluids flowing through pipe or porous media. The viscosity of the crude oil is affected by the composition of the oil (specific gravity and characterization factor), solution gas-oil ratio, pressure and temperature. Three distinct areas are identified: dead or gas free, saturated, and undersaturated. Fig. 1 shows the viscosity behavior of a crude oil with each area identified. Starting from a dead condition, free gas in contact with the oil dissolves into the oil with increasing pressure until all of the gas is in solution at the bubblepoint. As the gas dissolves in the oil, the density and viscosity of the oil are reduced. Above the bubblepoint, viscosity increases in the undersaturated region due solely to the effect of pressure on the oil. Bergman and Sutton5,6 have provided a detailed review of the dead and undersaturated regions including accurate methods to determine viscosity in each region.

A novel approach to oil production optimization considering asphaltene precipitation: a case study on one of the Iranian south oil wells

“…As the first step, the fluid properties model of the well should be made. In order to determine the best relation to predict: (a) the formation volume factor, bubble point pressure and solution gas oil ratio (among different relations such as Standing 1971;Lasater 1958;Vazquez and Beggs 1980;Glaso 1980;Petrosky et al 1993;Al-Marhoun 1992) and (b) oil viscosity (between relations such as Beal (1946) Petrosky et al 1993;Bergman and Sutton 2007), some regression operations have been done using experimental data given in Table 8. The regression operations have been carried out using prosper software from the Integrated Production Modelling software (IPM group).…”

Viscosity Predictions of Viscous Oil from a Kuwait Oil Field by Low-field NMR

“…For consistency, T 2 distributions were obtained by applying the same processing parameters in the inversion for both the log and lab data. Since viscosity data was acquired on dead oils, a small correction of the measured viscosity due to the presence of gas (Յ 20 scf/stb) can be made by applying a GOR correction (Bergman & Sutton, 2007) since PVT analysis revealed saturated conditions for almost all wells. Due to the lack of corresponding log and oil sample data, some of the most nearby wells were chosen for direct comparison to oil samples that are represented in the same oil layer.…”

Oil Viscosity Impact on Invasion Zone Structure and Resistivity Measurements

“…The most popular correlations for predicting oil viscosity are described in publications of Beal [Beal, 1946] and Chew [Chew et al, 1959]. During the pressure decrease to the "bubblepoint" the gas fraction begins to separate from the oil.…”

“…There are many correlation functions for viscosity calculation [Katz, 1942;Beal, 1946;Standing et al, 1947;Lasater, 1958;Chew et al, 1959;Beggs et al, 1975;Vazquez et al, 1976;Glaso et al, 1980; Khan et al, 1987;Al-Marhoun et al, 1988;Petrosky, et al, 1990;Kartoatmodjo et al, 1991;Labedi, 1992;De Ghetto, et al, 1994;Bergman, et al, 2008]. The above-mentioned equations can be utilized in various parts of the world.…”