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International audience; In the presence of a large excess of asphaltenes in oil phase, an interfacial tension anomaly (a small bump of the order of 1 mN/m), is found to correspond to the optimum formulation where the fastest water-in-oil emulsion breaking is observed. This correspondence, also observed for other systems, indicates that strong interaction should occur between asphaltenes and demulsifiers. Therefore, the optimum formulation would correspond to a situation where there is enough demulsifier to remove the asphaltenic interfacial gel by orogenic displacement, but not too much to cause adsorption of large asphaltenic/demulsifier complexes which would slow down emulsion drainage.

International audience; In this work, two asphaltenes derived from the same set of source rocks, C1 from a crude oil and C2 from an oil sand, were studied, concerning their adsorption/occlusion properties. From the adsorbed components, saturated and aromatic hydrocarbon distributions are distinctly different for these two asphaltenes. For example, some n-alkanes and alkyl-branched alkanes were found adsorbed in C2 asphaltenes, whereas only some cyclic compounds, particularly terpanes were detected from C1 asphaltenes. This difference is due to their different evolution processes in oil reservoirs, and the exchangeability between asphaltene-sorption compounds and those from outside of the bulk phase is different for these two asphaltenes. However, from the asphaltene-occlusion compounds, saturated hydrocarbons show almost the same distribution features. This is consistent with the fact that these two asphaltenes were derived from the same set of source rocks, therefore, occluded almost the same original oils from the source rocks. The experimental results suggest that substantial microporous units exist inside the macromolecular structures of asphaltenes and the asphaltene-derived adsorption/occlusion phenomena extensively occur in oil reservoirs. It seems that asphaltene occlusion should have taken place before asphaltene was detached from kerogen.

International audience; Seven asphaltene samples and six octylated asphaltene (OA) derivatives were analyzed using laser desorption ionization-time-of-flight (LDI-TOF) mass spectrometry (abbreviated as MS) and vapor pressure osmometry (VPO) techniques. Molecular weight distributions (MWDs) that were determined using MS spanned, for all asphaltenes samples and their octylated counterparts, a similar range, from ∼100 Da to ∼10 000 Da. For asphaltenes, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) afforded values in the 1900 ± 200 and 3200 ± 400 intervals, respectively. Consistently heavier values were observed for the OA derivatives (Mn ≈ 2300 ± 200 and Mw ≈ 3600 ± 200). To select the adequate laser power for these measurements, experiments at different laser powers were performed, to increase volatility and reduce fragmentation to a minimum. Several other experiments were performed to validate these results. First, good agreement between the measured and calculated Mn values was observed for OA materials (calculated from asphaltene Mn and n, the number of octyl groups introduced, as determined from elemental analysis); second, Mn values, as measured by VPO and MS, were determined to be equal, within an average standard deviation of ±27.0%. These results and calculations strongly suggest that the MWD, the molecular weight range, and the molecular weight averages determined using the present MS technique are reasonable estimates of the molecular weight properties of asphaltenes and not the result of artifacts such as fragmentation, polymerization, incomplete volatilization, etc., which may be occurring during the MS experiment.