A new empirical correlation for estimating bubble point oil formation volume factor Masoud Karimnezhad a, b, * , Mohammad Heidarian a, b , Mosayyeb Kamari c , Hossein Jalalifar a, b a Department of Petroleum Engineering, Technical and Engineering Faculty, Shahid Bahonar University of Kerman, Iran b Young Researchers Society, Shahid Bahonar University of Kerman, Iran c National Iranian South Oil Company, Iran article info Article history: Received 26 January 2014 Received in revised form 8 March 2014 Accepted 11 March 2014 Available online Keywords: PVT Oil formation volume factor Middle East Correlation Genetic Algorithm abstract To determine the bubble point oil formation volume factor (B ob ), which is one of the most important PVT properties, several correlations have been proposed for different regions. None of the correlations could be applied as a universal correlation due to regional changes in crude oil compositions and properties. In this paper, a new correlation is proposed to predict the B ob for Middle East crudes. Genetic Algorithm (GA) was used as the dominant tool for development of the new correlation. A total of 429 data sets of different crude oils from Middle East reservoirs were used. These Data include B ob and conventional PVT properties. Among those, 286 data sets as training data and 143 data sets as test data were randomly selected for constructing the correlation and for correlation validation, respectively. The measured mean squared errors (MSEs) of predicted B ob from the correlation in the test data were 0.0029 and the cor- relation coefficient (R 2 ) between predicted values from the model and experimental values in the test data was 0.9646. These results show a very good agreement with experimental data and are more ac- curate for Middle East crudes than those of all existing empirical correlations. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction The accurate determination of the PVT properties of the reser- voir fluids, such as bubble point pressure, solution gas oil ratio (GOR) and oil formation volume factor (B o ) is necessary for the formation evaluation of hydrocarbon reserves, reservoir perfor- mance, production operations and the design of production facil- ities (Elsharkawy et al., 1995). It is important to obtain reservoir fluid samples to determine PVT properties. In case no fluid samples are taken, correlations can be used to estimate PVT data. This is particularly true during the early development phase where fluid properties are only available from surface flow tests (Dokla and Osman, 1992). Bubble point oil formation volume factor (B ob ) is one of these properties. B ob is defined as the volume of reservoir oil that would be occupied at bubble point pressure and reservoir temperature by one stock tank barrel oil, plus any gas dissolved in the oil at this pressure and temperature. Its evaluation is an essential step in the reservoir performance calculations and the design of various stages of oil field operations (Al-Fattah and Al-Marhoun, 1994). Because laboratory determination of the PVT properties is very expensive and time-consuming, several empirical correlations have been developed for this purpose. Especially in recent decades, there has been an increasing interest in developing new correlations for crude oil of different regions in the world. A review of the published B ob correlations and their limits is presented here. Katz (1942) presented a graphical correlation to predict B ob by using U.S. mid-continent crudes. The graphical correlation used reservoir temperature, pressure, solution gas oil ratio, oil and gas gravity. The correlation was published only in graphical form and was difficult to use due to the combination of graphs and calculations. Standing (1947) published his correlation to determine bubble point oil formation volume factor of gas saturated oil. The corre- lation was based on experiments carried out on 105 samples from 22 different crude oil in California, U.S.A. The correlation assumed the oil formation volume factor (B o ) as a function of the reservoir temperature, oil gravity, gas gravity and gas oil ratio. The Standing’s correlation was first published in a nomograph form and later fitted (Standing, 1952) to produce a nonlinear equation. * Corresponding author. Department of Petroleum Engineering, Technical and Engineering Faculty, Shahid Bahonar University of Kerman, Iran. Tel.: þ98 9163639086. E-mail address: masoud_karimnezhad@yahoo.com (M. Karimnezhad). Contents lists available at ScienceDirect Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse http://dx.doi.org/10.1016/j.jngse.2014.03.010 1875-5100/Ó 2014 Elsevier B.V. All rights reserved. Journal of Natural Gas Science and Engineering 18 (2014) 329e335