Spatially resolved <scp> ²³ Na </scp> magnetic resonance dispersion measurement in porous media

Abstract Tracer tests are widely used in the petroleum industry to assess reservoir core plugs, relying on breakthrough curve analysis to evaluate bulk‐scale transport properties such as dispersion and macroscopic homogeneity. However, the conventional breakthrough curve analysis assumes uniform bulk behaviour, which may lead to misleading conclusions in the presence of structural heterogeneities. In this study, we compare conventional tracer tests with a new 23 Na magnetic resonance imaging (MRI) based tracer test to examine solute transport in brine‐saturated Bentheimer, Buff Berea, Nugget, and Bentheimer–Berea composite sandstone core plugs. 23 Na MRI permits direct observation of sodium concentration evolution in space and time and has higher sensitivity to structural heterogeneity than the conventional breakthrough curve method. Experimental data from both techniques was fit to the advection–dispersion equation to determine Péclet numbers ( N Pe ). Conventional breakthrough curve analysis may misclassify macroscopically heterogeneous samples as homogeneous due to bulk averaging effects. 1 H MRI has been used in a limited number of tracer studies. In this work, 23 Na MRI was applied in realistic media using NaCl as a native, conservative tracer. 1D 23 Na MRI provides spatially resolved concentration profiles that improve heterogeneity detection and transport characterization and can be used as an initial screening tool in special core analysis. Moreover, 23 Na MR/MRI techniques can be integrated with existing low‐field permanent magnet systems already present in many core analysis laboratories. 23 Na MRI has not previously been employed in core plug tracer tests.