Empirical PVT Correlations For Colombian Crude Oils
Authors: Frashad F. , LeBlanc J.L. , Garber J.D. , Osorio J.G. 
Published: December 2007

The pdf file of this paper is missing the tables and figures.

Empirical PVT correlations are presented for estimating bubblepointpressure, solution gas-oil ratio, oil formation volume factor, and isothermal compressibility. To develop the above correlations, the data base consisted of ninety-eight PVT laboratory analyses for Colombian crude oils. The gas-oil ratios, gas gravities, oil gravities, and formation volume factors involved in the development of the correlations are the result of one, two and three-stage flash separation as recorded from PVT samples analyzed in the laboratory.

The effect of separator conditions on the prediction of the bubble-point pressure, solution gas-oil ratio and oil formation volume factor is studied. Anew correlation that corrects the separator solution gas-oil ratio for separator conditions is provided. Improved correlations for estimating the bubble-point pressure, based on the corrected separator solution gas-oil ratio, are developed. In addition, total solution gas-oil ratio and oil formation volume factor correlations based on separator data are presented. Since the stock-tank gas-oil ratio and stock-tank gas gravity are not usually measured in the field, these correlations represent a realistic form of estimating PVT properties.

Although the correlations presented are based on Colombian crude oils and gases, consideration should be given to their applicability to all types of gas/oil mixtures with API gravities ranging between 18 to 44.9 (single stage separation), 14.3 to 29.0 (two stage separation) and 40.3 to 44.1 (three stage separation).

Introduction

An accurate knowledge of Pressure-Volume-Temperature (PVT) properties is essential in reservoir and production engineering calculations. Estimation of reserves, determination of oil reservoir performance, recovery efficiency, production optimization and design of production systems are some of the areas which require precise determination of a fluid's physical properties at different conditions of pressure and temperature.

Ideally, the physical properties of the reservoir fluids are determined experimentally in the laboratory. However, due to economical and/or technical reasons, quite often this information cannot be obtained from laboratory measured values. In this case, PVT properties must be estimated from empirically derived correlations.

Several correlations have been proposed for determining the PVT properties of reservoir fluids. Some of the most widely used correlations are: Standing's, Lasate, Calhoun, Trube's, Chew-Connally's, Beal's, Glaso's, Vazquez-Beggs, Beggs-Robinson's, Dokla-Osman, Petrosky-Farshad, and Petrosky-Farshad. These correlations are based on reservoir fluid samples from certain specific regions of the world.

Because of the varying compositions of crude oils from different regions, prediction of PVT properties from empirical correlations may not provide satisfactory results when they are applied to hydrocarbons behaving differently from the fluid samples on which the correlations were based. Previous studies have shown that extrapolation of empirical PVT correlations should beundertaken with caution.

P. 311