Statistical Evaluation of PVT Correlations Solution Gas-Oil Ratio

Abstract

Abstract The predictive accuracy of three commonly used correlations for the solution gas-oil ratio is tested against new data from 385 PVT tests. To perform an unbiased evaluation, this study is made using strictly PVT data which are not used in the development of any of the chosen correlations. The performance of each correlation is compared over selected ranges of oil API gravity. The comparison indicates the relative strengths and weaknesses of each correlation and should aid in the selection of a satisfactory correlation for certain conditions. The best over-all performance is obtained using the Vazquez-Beggs correlation, based on consistently low values of absolute per cent error and standard deviation. Introduction The prediction of physical fluid properties is one of the main concerns in the handling of the different stages of oilfield operations such as in the determination of pressure losses occurring in multiphase flow situation, the design of surface operation facilities, and the design of reservoir performance operations. Some of these properties are solution gas-oil ratio, oil FVF, and oil viscosity. The purposes of this study are to (1) ascertain the accuracy of the existing solution gas-oil ratio prediction correlations, and (2) define the areas of application of each correlation. The correlations included in this study, as described below aTe the Standing(l), Lasater(2), and Vazquez-Beggs(3) correlations. Standing Correlation In 1947, Standing presented the results of a laboratory study of the PVT behaviour of 22 different crude oil natural gas mixtures from California oil fields. His correlation, which was derived from 105 experimental data points, can be expressed as: Equation (Available In Full Paper) Lasater Correlation Lasater in 1958 presented a correlation of bubble point pressure derived from data on black oil systems produced in Canada, western and mid-continental United States and South America. The correlation is based on 158 experimental measured bubble point pressures of 137 independent systems and is expressed as: Equation (Available In Full Paper) The effective molecular weight (EMWGT) is related to API gravity as shown in Figure 1. Lasater found a satisfactory correlation of bubble point pressure factor (BPPF) with gas mole fraction (GMF) as shown in Figure 2. Equation (Available In Full Paper) Vazquez-Beggs Correlation In 1976, Vazquez and Beggs developed an empirical correlation for gas evolution using data from more than 600 PVT analyses from fields all over the world. The correlation is derived from 5008 experimental data points, and is defined as: Equation (Available In Full Paper) Data Acquisition and Preparation To perform an unbiased evaluation, this study is made using strictly PVT data which are not used in the development of any of the previous chosen correlations. The data bank used in this study (385 points) are obtained from four different unpublished sources. In these sources, the flash separation data are used in conjunction with the values of the flash and differential process to calculate the solution gas-oil ratio.