Search

We present a theory and experiments that relate the NMR longitudinal T1 and transverse T2 relaxation times to the viscosity η for heavy crude oils with different asphaltene concentrations. The nuclear magnetic relaxation equations are based on a one-dimensional (1D) hydrocarbon translational diffusion in a transient porous network of slowly rotating asphaltene macroaggregates containing paramagnetic species VO2+. For heavy crude oils with viscosity η above a certain threshold ηc, the effective 1D confinement causes a transition from the usual Stokes–Einstein relation for the translational diffusion coefficient D ∝ 1/η below ηc to a wetting behavior D ∼ Cte close to the asphaltene aggregates above ηc. The theory is compared successfully with the universal viscosity dependencies of relaxation times T1 and T2 observed over a large range of viscosities. The theory reproduces the relaxation features of the 2D correlation spectra T1–T2 and D–T2 for heavy crude oils when varying the asphaltene concentration. Thi...

Asphaltenes cause many problems in crude oil transportation, refinery, and production. A clear understanding of asphaltene behavior in crude oils is thus crucial for improving crude oil production. Here, we used noninvasive multiscale NMR techniques such as low field NMR 2D D–T2, T1–T2, nuclear magnetic relaxation dispersion (NMRD) techniques as well as high field two-dimensional (2D) NMR DOSY for probing the dynamics and interaction of maltenes with asphaltene aggregates in crude oil. We prepared different asphaltene concentrations ranging between 0 wt % (pure maltenes) and 9 wt % (native crude oil) by using a dilution procedure that maintains the asphaltene aggregates structure initially present in native crude oil. We showed by multiscale NMR techniques that changing asphaltene concentration induces a drastic modification of hydrocarbon dynamics. In native crude oil, we observe anomalous relation between the diffusion coefficient (D) and the transverse relaxation time (T2) that we can reproduce theoret...

International audience; A coupling of thin layer chromatography with laser ablation ICP SF MS was developed for the fractionation of Ni, V, Fe and S in crude oil and its fractions (saturate, aromatic, resin and asphaltene). The detection limits were 18 ng g -1 and 23 ng g -1 for nickel and vanadium, respectively, and a sample could be characterized in terms of the metal distribution as a function of species polarity within 10 min. The method was used to characterize the metal distribution in crude oils of different origins and their different fractions. © 2012 Elsevier B.V. All rights reserved.

International audience; A method was developed for the direct analysis of petroleum samples. A silica gel plate, commonly used in thin layer chromatography, was impregnated for 30 min with a sample solution and analyzed by laser ablation-ICP MS. The use of a doubly focusing sector field mass analyzer allowed the demonstration of the absence of carbon-related polyatomic interferences. Matrix suppression effects, common in nebulization-based sample introduction, were absent which enabled quantitation by external calibration. The detection limits were in the low ng g -1 range. The method was validated by the analysis of NIST 1084a and 1085b certified reference materials (wear metals in lubricating oils) and applied to the analysis of crude oil and asphaltene samples.

International audience; Microchromatography using permeation through gels with the increasing exclusion limit (5000, 400000 and 20000000 Da) was combined with high resolution (R = 4000) ICP MS to measure the distribution of Co, Cr, Fe, Ni, S, Si, V and Zn as a function of the molecular mass fraction of crude oil and oil vacuum distillation residue. The accuracy of the simultaneous multielement determination was verified by the flow-injection-ICP MS analysis of certified reference materials (wear-metals in lubricating oils: SRM 1084a and SRM 1085b). The method allowed the acquisition of chromatograms with high sensitivity competitive existing methods, showing element- and sample origin-dependent morphology.

International audience; A method for the determination of silicon in organic solutions was developed using a double focusing magnetic sector ICP MS operating at a resolution of 4000. The signal-to-background ratio was improved 10-fold over standard sample introduction systems by the use of micro-flow injection total consumption sample introduction. The detection limits down to 1 ng g -1, the calibration graph linear over 4 orders of magnitude and precision to within a few percent were obtained. The effects of the sample matrix and of the chemical form of silicon on the sensitivity were investigated and alleviated when necessary by heating the spray chamber and sample dilution. Normal phase HPLC-ICP MS and size-exclusion ICP MS were proposed to gain an insight into the purity of the silicon standard compounds, their reactivity with different petroleum-related matrices and speciation of silicon. © 2010 The Royal Society of Chemistry.

International audience; A double-focusing sector field ICP MS was optimized for the direct simultaneous determination of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sn, Ti, V in organic solutions. Polyatomic interferences originating from the carbon-rich matrix were completely eliminated at a resolution of 4000 allowing the detection limits at the low pg g-1 level to be obtained (typically one order of magnitude lower than using a quadrupole ICP MS). A method for the routine comprehensive trace element analysis of xylene solutions of oil samples using external calibration was developed. It was validated by the analysis of three certified reference materials and applied to the analysis of 2 gas condensate samples and 4 oil samples of different origins.