Calculation of Bubble Pressure for Crude Oils: The Effect of q-Weibull Distribution for Splitting the Heavy Fraction

Abstract

Thermodynamic calculations involving crude oils require a proper characterization of the heavy-fraction in order to describe the phase behavior. Bubble pressure is a key property, and its calculation depends on splitting the heavy-fraction of the crude oil through a distribution function to obtain properties such as molecular weight and specific gravity. Small changes in these properties can significantly affect phase behavior calculations. The exponential and gamma distributions are the most used for splitting but they fail in characterizing many oils. Alternatively, the q-Weibull distribution is proposed to the splitting step instead of the exponential and gamma distributions in order to calculate the molecular weight and specific gravity. These three distributions are critically tested and compared for 13 oils with extended composition selected from the literature, stressing the effect of the characterization methods on the calculation of bubble pressure for reservoir fluids.