Detection of asphaltene flocculation using NMR relaxometry

We present a preliminary study of the detection of flocculation by NMR relaxometry. For this purpose, various asphaltene solutions in the presence of solvents inducing aggregation and flocculation were prepared. The asphaltenes were extracted from one crude oil and various fractions of toluene and n -heptane were prepared to vary the solvent quality. We measured the transverse magnetization decays at 60 MHz using standard CPMG sequences. We show first that asphaltene aggregates have a well-defined signature typically at relaxation times in the order of 1 ms. In general, the signal can be split into two parts characterizing the asphaltene aggregates and the solvents. The asphaltene signature becomes bimodal near the flocculation threshold. The solvent relaxation rate varies linearly with the asphaltene concentration and this effect can be associated with viscosity variations. To cite this article: A. Prunelet et al., C. R. Chimie 7 (2004).