Characterizing Petroleum Fractions for Compositional Reservoir Simulation
Hassan S. Naji
King Abdulaziz University, Saudi Arabia
In compositional reservoir simulation, equations of state (EOS) are extensively used for phase behavior calculations. Proper characterization of petroleum fractions, however, is essential for proper EOS predictions. In this paper, the most common characterization methods for pure, undefined, and plus fractions are presented. A set of equations for predicting the physical properties of pure components is proposed. The equations require the carbon number as the only input. They accurately calculate properties of pure components with carbon numbers in the range 6-50 while eliminating discrepancies therein. Correlations for characterizing the undefined petroleum fractions assume specific gravity and boiling point as their input parameters. If molecular weight is input instead of boiling point, however, the same molecular weight equation is rearranged and solved nonlinearly for boiling point. This makes their use more consistent and favorable for compositional simulation.
Most experimental studies of hydrocarbon mixtures group components with a carbon number higher than six in one component referred to as the plus fraction or C7+. Splitting (re-extending) and lumping (grouping components into several pseudo-components) methods of C7+ enhance EOS predictions. The widely-used splitting and lumping methods are revised. A worthwhile aspect of the paper, however, is that it proposes a new splitting method. The new method compared well with other methods for all tested data sets. Another aspect of the paper is that all coding has been done in an object-oriented manner. Whereas most phase behavior coding has been developed using the traditional FORTRAN language, which is a natural choice from the view point of continuity in downstream data processing. This natural choice may not necessarily be the optimal one. In fact, the use of an object-oriented language offers flexibility in programming and allows the different parts of the code to be described easily as if they were real world objects.
AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain