Improved characterization of the plus fraction for wax precipitation from petroleum fluids

Abstract

Wax formation is a serious problem in the gas and oil industry because it can block oil production facilities and transportation pipelines. It is, therefore, of great importance to have a reliable tool to predict wax formation under various operational conditions. The hydrocarbon plus fractions that comprise a significant portion of naturally occurring hydrocarbon fluids create major problems when determining the thermodynamic properties and the volumetric behavior of these fluids by equations of state. In this work, an effort has been made to further improve the characterization of the plus fraction, splitting the plus fraction into a single carbon number (SCN) and generating the mole fraction, on the basis of the relationship between the three-parameter gamma distribution, experimental molar fraction, molecular weight, and SCN data obtained from literature and industrial contact. The three-parameter gamma distribution is used to fit the trend of the computational analysis. The method has been used to predict wax appearance temperatures (WATs) for a great number of systems and to compare with some methods generated previously. The average deviation of the calculated WAT is 1.47 K for the system with the experimental data. There are some correlations generated to calculate the physical-chemical properties as a function of SCN. Those correlations have been originally developed to work with light oil. The developed approach, along with some of the correlations, is tested for calculating WAT to identify the applicability in this work.

Determination of Diffusion Coefficient for Alkane Solvent–CO2 Mixtures in Heavy Oil with Consideration of Swelling Effect

“…Properties of such plus hydrocarbon fractions have significant effects on estimating properties of the reservoir fluid even when they are present in small quantities, while treating plus fraction as a single pseudocomponent may lead to serious errors. , Proper characterization of the heavier components is crucial when the CEOSs are used to describe the complex phase behavior of reservoir fluids, especially for those with considerable amount of plus fractions. Characterization of heavy oil usually consists of three steps: (1) splitting (extending) the plus fraction into SCN fractions with known molar amounts and molecular weights; (2) estimating the properties of each SCN fraction, such as critical pressure, critical temperature, acentric factor, specific gravity, and boiling point; and (3) lumping (grouping) the SCN fractions into pseudocomponents and determining their properties. , …”

Prediction of Sanchez‐Lacombe equation of state characteristic parameters for plus fractions

“…The components of a hydrocarbon fluid mixture can be classified into two main categories: pure components and an undefined petroleum fraction. The undefined petroleum fractions are those heavy components lumped together and identified as the plus fraction . In the S‐L EOS the characteristic parameters are P* , T* , and r which are determined for pure components.…”

“…The undefined petroleum fractions are those heavy components lumped together and identified as the plus fraction. [21] In the S-L EOS the characteristic parameters are P * , T * , and r which are determined for pure components. In other equations of state there are empirical correlations to determine the plus fraction parameters, [22] but no empirical correlation exists for the determination of the S-L EOS characteristic parameters for plus fractions.…”

“…Minor changes in plus fraction properties, such as mole fraction, molecular weight, or specific gravity, can have a significant effect on phase equilibria and fluid properties. [21] The effect of the plus fraction would be even greater if its mole composition in fluid increases. [23] By increasing the molecular weight and the specific gravity of the plus fraction, the density of the hydrocarbon fluid will increase and also cause a change in the critical temperature and the critical pressure of the phase envelope of the fluid.…”

“…Phase behaviour of reservoir fluids is very sensitive to the properties of the plus fraction. Minor changes in plus fraction properties, such as mole fraction, molecular weight, or specific gravity, can have a significant effect on phase equilibria and fluid properties . The effect of the plus fraction would be even greater if its mole composition in fluid increases .…”