Multi-dimensional Nuclear Magnetic Resonance Characterizations of Dynamics and Saturations of Brine/Crude Oil/Mud Filtrate Mixtures Confined in Rocks: The Role of Asphaltene

摘要

We propose multidimensional one-dimensional (1D) and two-dimensional (20) nuclear magnetic resonance (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 characterized by standard petrophysical techniques. Electron spin resonance (ESR) quantitatively measured levels of the paramagnetic vanadyl ions V0~(2+) and organic radicals trapped in the used crude oils with and without asphaltene. Size-exclusion inicrochromatography with a high-resolution inductively coupled plasma—mass spectrometric detection technique has demonstrated the trapping of metalloporphyrine (MP) by asphaltene nanoaggregates. These two latter techniques have shown that around 2/3 of VO~(2+) is trapped in MP embedded 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. We employed 2D NMR D—Tz experiments for different in situ successive rock saturations in monophasic, biphasic, and triphasic conditions. The D-T2 experiments of imbibition drainage of petroleum fluids on a sandstone rock have also been performed for different temperatures and pressures. In all of the multiphasic cases, the characteristic features of the D-T2 spectrum allow for 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 the presence of asphaltene. On the basis of a theoretical relaxation treatment, we propose an interpretation of this relationship with a nonlinear scaling T2 → √T2 affecting mainly the local dynamics of the long hydrocarbon chains. The leveling off, D ≈ C~(te), of this relationship for large T2 values is new and explained in terms of surface dynamics of the short hydrocarbon chains on asphaltene nanoaggregates. This result is consistent with the bilogarithmic frequency dependence of the nuclear magnetic relaxation dispersion (NMRD) profiles observed for the same crude ofl in the presence of asphaltene.