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Asphaltene Densities and Solubility Parameter Distributions: Impact on Asphaltene Gradients

Rogel, Estrella, Ovalles, Cesar, Bake, Kyle D., Zuo, Julian Y., Dumont, Hadrien, Pomerantz, Andrew E., Mullins, Oliver C.
Energy & Fuels 2016 v.30 no.11 pp. 9132-9140
case studies, coal, equations, gravity, models, oil fields, particle size, petroleum, shale, solubility
Analysis of spatial gradients of the concentration of asphaltenes in reservoir crude oils has become an important tool for oilfield reservoir characterization. Modeling these gradients requires knowledge of asphaltene properties. For example, the commonly employed Flory–Huggins–Zuo (FHZ) equation requires the asphaltene particle size, solubility parameter, and density. Asphaltenes from various sources, particularly including sources beyond conventional crude oil, can have widely varying compositions such as the H/C ratio. Here, we measured the solubility parameters and densities of five asphaltenes that span a large range of H/C ratios, including asphaltenes from coal, petroleum, and shale, and then performed a sensitivity analysis to examine how that range of compositions impacts the magnitude of asphaltene gradients as predicted by the FHZ equation. Two case studies are included in the sensitivity analysis, one in which the asphaltene gradient is driven primarily by gravity, and another in which the asphaltene gradient is driven primarily by solubility. The results shows that the sensitivity of the modeled asphaltene gradients to the measured range of asphaltene solubility parameters and densities is low such that, for both case studies, varying these parameters across the entire measured range does not impact the assignment of the state of asphaltene aggregation determined by the fitted asphaltene particle size. These results suggest that asphaltene gradients can be modeled using the FHZ equation with default values for the asphaltene solubility parameter and density, and local calibration of those parameters will negligibly impact the analysis.