Comparison and Validation of Theoretical and Empirical Correlations for Black Oil Reservoir Fluid Properties
Authors: Godefroy Sophie Nazik , Khor Siew H. , Emms David 
Published: April 2012

Characterization of reservoir fluids is important for developing a strategy tomanage the reservoir production scheme effectively and efficiently. Reservoirfluid properties (e.g., density, viscosity, gas/oil ratio, bubble-pointpressure, compressibility, and formation volume factor) are crucial for bothreservoir and petroleum engineering; they are the fundamental inputs formaterial balance calculation, determination of oil reservoir volumes, andestimation of oil recovery with the use of a reservoir simulator. Ideally, thereservoir fluid properties are determined from laboratory studies on thebottomhole samples or on the recombined separator oil and gas samples. Whenonly field measurements or limited laboratory data are available, empiricalblack oil correlations can be used to determine the essential fluid propertieswithout the knowledge of fluid compositions. In the past few decades, withlarge sets of petroleum fluid data at various reservoir conditions andproperties, the development of black oil correlations forpressure-volume-temperature (PVT) analysis study has been researchedextensively. Consequently, numerous correlations that are applicable to varioustypes of oil have been proposed and published. In this paper, we compare andprovide guideline for the various correlations that were used to determine theblack oil fluid properties.

For this study, more than 30 theoretical and empirical black oil correlationsfor bubble-point pressure, gas/oil ratio and oil formation volume factor werereviewed and validated; variations of the calculated fluid properties versusinput parameters were studied and compared across the stated ranges ofapplicability. The comparison results are presented graphically. Thecorrelations of this study are also summarized in tables that can be used toguide PVT users in selecting the most appropriate black oil correlation forspecific reservoir fluids and conditions.

Introduction

The physical properties of the reservoir fluids are very important input datain reservoir engineering calculations. Well characterized reservoir fluidproperties are crucial for a good estimate of oil or gas reserves, productionforecasts and the efficiency of enhanced oil recovery (EOR) methods. It is notalways the case that reservoir fluid samples are available and thoroughlystudied to characterize the reservoir fluid properties in the most accuratemanner. In situations where no samples are available, one must rely onempirically derived correlations to estimate the physical properties ofreservoir fluid. This paper reviews the existing black oil correlations thathave been published in the literature and elaborates how they are used in ourin-house consolidated pressure-volume-temperature (PVT) library.

There are many parameters to be considered for reservoir characterization andmodeling; however in this paper we focus and discuss on those publishedcorrelations for bubble-point pressure, gas/oil ratio and oil formation volumefactor. The decision was made as these parameters are more influential in theaccuracy of fluid properties calculation and facilities planning than otherssuch as fluid compressibility, viscosity, density and etc.

In the first part of this paper, we present a literature review of variouscorrelations for bubble-point pressure, gas/oil ratio and oil formation volumefactor. For each correlation, the origin of oil used for the developedcorrelation is presented, its range of applicability and any related potentialissues are discussed. In the second part, the studied correlations that havebeen used in our in-house consolidated PVT library are summarized, compared anddiscussed, together with their applicability.