Modeling of super-dispersion in unsaturated porous media using NMR propagators

• We present an overview of a new model to interpret dispersion in porous media.
• The model can reproduce various shapes of NMR propagators (asymmetric, bimodal).
• The model predict the PFG-NMR signal directly.
• Model fitting is performed using the PFG-NMR signal instead of the propagator.

We present a general model (SMIM) specifically designed for the interpretation of NMR velocimetry data. Extending the well-known concept of Mobile/Immobile tracer particles applied in dispersion theory, we reproduce two mechanisms responsible for non-Gaussian behavior: immobile molecules trapped in non-flowing zones, and unexpectedly long but rare displacements. From the derived analytical expressions of the NMR signals fitted to the recorded data, we can determine a generalized dispersion coefficient in the case of super dispersion. Using NMR velocimetry data collected in a homogeneous 30 μm grain pack and 10 < Pe < 35, we quantified the observed weak super dispersion in saturated conditions, and the strong super-dispersion observed during steady-state oil–water two phase flow.

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