Improved K-values correlation for UAE crude oil components at low pressures using PVT laboratory data

Several techniques are available in the literature to estimate the K-values. In this paper, results of PVT analysis for 22 crude oil samples from different reservoirs in UAE are used. Sixty-eight single-stage flash laboratory experiments were conducted for these samples. Material balance techniques were used to extract the K-values of crude oil components. These K-values were then correlated and compared with values obtained from published correlations. Comparisons show that current correlations, while they generally give good results for light hydrocarbons in addition to carbon dioxide and hydrogen sulfide, give widely different results for nitrogen and the heptane-plus pseudo-component. Average absolute deviations in excess of 1000% were observed for nitrogen and in excess of 500% were observed for heptane-plus when current methods were used. The proposed new correlation improves significantly the average absolute deviation for both the heptane-plus fraction and for nitrogen, in addition to improving relatively the average absolute deviation for the C₁-C₆ hydrocarbons, H₂S, and CO₂. The average absolute deviation for all components was reduced to 28.6% in the new correlation compared to 240% for the Standing correlation and 156.8% for the Wilson correlation. As a test for reliability of the new correlation, bubble point pressures were calculated for 10 samples. The average absolute error for the proposed correlation was 5.2% compared with 6.9% for the Standing correlation, 16.1% for the Wilson correlation, and 7.3% for the Peng-Robinson equation of state.