Viscosity Correlations for Gulf of Mexico Crude Oils

Abstract

SPE Members Abstract New empirical viscosity correlations for estimating dead oil, saturated oil and undersaturated oil viscosities have been developed as a function of commonly available field data. Results show that these viscosities can be predicted with average absolute errors ranging from 2.91% for undersaturated oil viscosity to 14.47% for saturated oil viscosity. Introduction Reservoir fluid properties form the basis of many petroleum engineering calculations. The evaluation of oil and gas reserves, fluid flow through porous media, multiphase flow in pipe, surface and subsurface equipment design, and production system optimization all depend heavily upon reservoir fluid physical properties. These properties may be measured experimentally in a PVT (pressure-volume-temperature) laboratory or they may be estimated by using empirical correlations. The most accurate method for determining the behavior of these fluids is a laboratory PVT analysis; however, the evaluation of exploratory wells and the advanced design of equipment often requires an estimate of the fluid behavior prior to obtaining a representative reservoir sample. Also, experimental data is often unavailable in reservoirs which do not warrant the cost of an in-depth fluid study. Empirical correlations are often used for these purposes. Correlations are also needed for the calculation of multiphase flowing pressure gradients which occur in pipe. These calculations require the prediction of fluid properties at various pressures and temperatures. Even though laboratory measurements of these properties may be available as a function of pressure, they are usually measured under isothermal conditions. The behavior of these properties as a function of temperature is usually predicted by using empirical correlations. The accuracy of empirical correlations is often limited because reservoir fluids consist of varied and complex multi-component systems. It is also difficult to describe these complex systems with simple parameters such as gas gravity, oil gravity and gas-oil ratio because these parameters depend upon the process by which the oil and gas are separated. Empirical viscosity correlations have been published for crude oils from several geographic locations around the world. These correlations often do not adequately predict the behavior of crudes from the Gulf of Mexico. In 1984, Sutton and Farshad evaluated the accuracy of several published viscosity correlations for application in the Gulf of Mexico. A total of 31 different crude oil systems from the Louisiana and Texas gulf coast were used in their analysis. The errors encountered were rather high for dead and saturated oil viscosity. P. 249