New Analytic Techniques for Petroleum Fluid Characterization Using Molar Refraction

Abstract

Abstract Molar refraction of pure hydrocarbons, petroleum fractions, and other compounds present in petroleum are shown to represent well the asymmetry of such fluids. Molar refraction is used to correlate density, parachor, and other properties of hydrocarbons with an accuracy that was not achieved before. Various calculations are made to demonstrate the accuracy of the proposed new analytic techniques for various reservoir fluids characterizing properties. Molar refraction characterizes the pure as well as the complex hydrocarbon mixtures and can be measured directly and accurately. It is shown that molar refraction is a more appropriate property to correlate the asymmetry of hydrocarbon fractions than the other existing methods. Plenty of the molar refraction data have been reported in the API Data Book for all the hydrocarbons and non-hydrocarbon compounds making it possible to extend the applicability of the proposed technique to high molecular weight ranges. Introduction The molar refraction which can be measured in the laboratory is a direct measure of the London dispersion forces which affect the PVT behavior of pure fluids and mixtures. The molar refraction, R, is defined by the following equation: (1) where n is the index of refraction and v is the molar volume. The molar refraction of a substance can also be expressed in terms of the polarizability by using Clausius-Mosotti equation. (2) where N0 is the Avogadro number and is the polarizability. If a substance has a permanent dipole moment, then the polarizability is the sum of two terms: (3) where 0 is the distortion polarizability related to the displacement of the electronic cloud of a molecule with no permanent dipole moment in an electrical field and is the orientation polarizability which arises from the tendency of the permanent dipole moment to be oriented in the direction of the applied field. The orientation polarizability, , is related to the dipole moment and is inversely proportional to the absolute temperature. (4) In this equation, k is Boltzmann constant and T is the absolute temperature. Substituting Eqns. (3) and (4) into Eq. (2), we get the following equation for the molar refraction. (5) We may assume methane as a reference substance for which the dipole moment is zero (= 0), and obtain the molar refraction of other substances with respect to methane. P. 507^