Identification par RMN des saturations et de la dynamique des hydrocarbures dans des roches pétrolières

Abstract : We propose multidimensional 1D and 2D NMR techniques for probing quantitatively the different saturations and dynamics of brine/crude oil/mud-filtrate mixtures confined in a rock-system that could be used potentially down-hole. The rock samples and petroleum fluids have been properly characterized by standard petrophysical techniques. Electron-spin resonance (ESR) quantitatively measured levels of the metallic paramagnetic vanadyl ions VO2+ and organic radicals trapped in the used crude oils with and without asphaltene. Size exclusion microchromatography with high-resolution inductively coupled plasma mass spectrometric detection technique has demonstrated the trapping of these metallic ions in metallo-porphyrine (MP) embedded in asphaltene nanoaggregates. These two latter techniques have shown that around 2/3 of the VO2+ are trapped in MP within asphaltene nanoaggregates while 1/3 stayed in the bulk. Standard gas chromatography (GC) and gel permeation chromatography (GPC) have extended the sensitivity to the range of the chain length distribution. The resemblance of the distributions of the longitudinal and transverse relaxation times with the GC and GPC distributions proved that the dynamics of the hydrocarbons are highly correlated with the hydrocarbon chain lengths. The central part of our study is the proposal of new 2D NMR D-T2 correlation experiments between the diffusion coefficient D and the transverse relaxation time T2 for probing progressive in situ rock saturations in monophasic, biphasic, and triphasic conditions at different temperatures and pressures. At each step of the imbibition-drainage of petroleum fluids on a sandstone rock, the characteristic features of these D-T2 correlation spectra allow, for the first time, probing the individual saturations and wettability of each confined fluid in the mixture. Finally, the anomalous relationship D∝√T2 previously observed has been confirmed at low T2 values for bulk and confined crude oils in presence of asphaltene. A non-linear scaling T2->√T2 has shown that the asphaltene molecules affect mainly the molecular dynamics (rotation and translation) of the long-chain hydrocarbons. The leveling off D≈Ct of this relationship for large T2 values is new and has been explained in terms of a mutual interaction and surface dynamics of the short hydrocarbon chains and asphaltene nanoaggregates. This result is consistent with the bilogarithmic frequency dependence of the nuclear magnetic relaxation dispersion profiles that we observed for the same crude oil.
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Lyès Benamsili. Identification par RMN des saturations et de la dynamique des hydrocarbures dans des roches pétrolières. Matière Molle [cond-mat.soft]. Ecole Polytechnique X, 2013. Français. ⟨pastel-00962339⟩

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