A multiphase (oil/gas/asphaltene/water) multicomponent hydrodynamic model is proposed to represent the phenomenon of asphaltene deposition in producing wells. The model is based on the assumption that asphaltene particles are thermodynamically formed at a given set of p-T-x conditions during the flow, and both molecular diffusion and shear removal are two competing mechanisms that define the radial diffusion and later deposition of asphaltene particles for either turbulent or laminar flows in a well. Predictions of the model are presented for the case of two problematic (plugged) wells from the southwest producing area of Mexico, where measured pressure-temperature-depth production profiles related to deposits are available.

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Properties of petroleum fractions of unknown composition, the so-called undefined petroleum fractions, are estimated using an approach based on group contribution methods. Using liquid density and molecular weight as experimental data and classical thermodynamics as framework, functional groups were assigned to each undefined fraction by minimizing its free energy. Thus, methods requiring molecular structures were used directly in phase equilibrium simulations of petroleum fluids. The proposed procedure also allows the critical properties of such undefined fractions to be calculated employing no specific correlations. The obtained results show reasonable accuracy concerning phase equilibrium experiments.

Application of an approach recently published [Carreoń-Calderoń et al. Ind. Eng. Chem. Res. 2012, 51, 14188− 14198] to heavy petroleum fluids allows calculation of critical properties and molecular pseudostructures of their undefined fractions. This approach is based on group contribution methods, where classical thermodynamics is used as framework to assign functional groups to each undefined fraction by minimizing its free energy. The calculated properties are employed to determine parameters entering into cubic equations of state and their respective mixing rules requiring molecular structures. Thus, phase equilibrium simulations of heavy petroleum fluids were performed employing neither specific correlations nor parameters, reducing the impact of fluid models over the thermodynamic characterization. The results are in agreement with experimental results of petroleum fluids heavier than 14°API.

A set of algebraic equations to predict upper onset-of-precipitation and bubble-point pressures of asphaltene-containing reservoir fluids in wide temperature ranges are proposed. In developing the equations, laboratory data of 11 Mexican and 12 more live oils have been analyzed, and a correlation of these data with temperature has been found. A modified least-squares regression method has been used to develop two versions of the proposed equations. In one version, a single pressure/temperature data point is required to predict the entire onset/bubble-point curves at any temperature. For oils with no experimental precipitation data available at all, a second version of the proposed expressions employs standard chromatographic data of the reservoir fluid to provide a reasonable prediction. The average absolute deviations in calculated onset and bubble-point pressures by the proposed equations are 2.53 and 0.45MPa by the one-point correlations, respectively, and 3.96 and 1.62 MPa by the compositionally-based correlations, respectively. The developed expressions are simple and can be used to provide reasonable predictions of upper onset and bubble-point pressures of asphaltenic live oils in cases where laboratory data are scarce.