Improving Accuracy and Speed of NMR Flow Propagators Measurements in Permeable Rocks

摘要

There are two distinct drawbacks to the measurement of fluid flow in porous media using Nuclear MagneticResonance (NMR) flow propagators. First, spin relaxation impairs the quantitative nature of the data. Second, the experimentscan be considerably time consuming since both the Pulsed Field Gradient (PFG) strength g and observation time A need tobe varied independently. Here we present two separate solutions to these problems and show how they can be applied to thestudy of fluid flow in permeable reservoir rocks. The accuracy of the measurements can be improved using a combinationof ζ — T_2andT_1—T_2correlations. Under certain ideal conditions it is possible to use these data remove both theT1and T2 relaxation weighting from flow propagators [Mitchell et al. J. Magn. Reson. DOI:10.1016/j.jmr.2008.05.001 (2008)].Statistical analysis of the resultant probability density distributions yields observed mean displacements <ζ> equal to theexpected mean displacements <ζ>_0. If speed is more important than accuracy, then the rapid Difftrain pulse sequence can beused to acquire multiple propagators with a range of observation times simultaneously. Difftrain has been validated for use instudies of fluid flow in reservoir rocks [Mitchell et al. J. Magn. Reson. 191 267-272 (2008)] and facilitates the observation ofdynamic flowing systems, such as deposition or erosion.