Extended Analysis for Gas Condensate Systems

Abstract

Abstract Equation of State (EOS) predictions for gas condensate systems require extended analysis beyond the heptanes plus fraction. In the absence of experimental data, several schemes have been proposed to extend these compositional data based on the observation that a single straight line relationship exists between log of mole percent and molecular weight for these pseudo-components or Single Carbon Number (SCN) fractions. An examination of compositional analysis for gas condensate systems showed a discontinuity in the relationship between mole percent and molecular weight at C13. As a result two straight lines are needed for a more accurate description of mole percent; one from C8 to C12 and the other from C13 and beyond. An average absolute deviation of less than 6.0 % between the predicted and experimental mole percent was obtained using parameters from two straight lines. From a single straight line relationship this difference was as high as 36.0 %. When applied this new universal observation gives an improved prediction of the mole percent of the last fraction. As a result a more accurate description of molecular weight for this fraction can be achieved for use in equation of state predictions. The change in slope at C13 indicates that for gas condensate systems a partial analysis is required up to C12 and splitting schemes can be applied from C13+ and beyond using a single straight line relationship. Beyond C12, experimental data shows that the mole percent of the isomers present are too small to cause any further change in slope.