The nuclear magnetic resonance (NMR) and the dielectric dispersion are excellent techniques to study the petrophysical properties of hydrocarbon bearing rocks. The superiority of these measurements rises from their sensitivity to the different interactions occurring in the porous medium which include grain – fluid and fluid – fluid interactions. Therefore, an integration between both measurements helps in evaluating different petrophysical properties such as mineral composition, porosity, permeability, wettability and fluids distribution.
In this study, we have explored the dielectric and the NMR responses to pores structure, permeability, and saturation profiles for two sandstone samples (Berea and Fontainebleau) and two Indiana limestone samples with different permeability values which were undergone a centrifuge drainage. Initially, routine core analysis was performed on the samples including porosity, permeability XRD and Scan Electron Microscope (SEM). The rock samples were studied at 3 saturation points, dry condition, 100 % water saturation (Sw=1) and irreducible water saturation (Swirr). To reach the Swirr conditions, the sample was undergone a drainage cycle with model oil using the centrifuge.
The results showed an excellent correlation between NMR, dielectric measurements and the petrophysical properties. The small pores and the lower permeability (21 md) of one of the carbonate rock compared to the sandstone samples (74 md for Fontainebleau and 100 md for the Berea) affected the sweep of the water during the centrifuge process which resulted in a variation in the saturation profile confirmed by the NMR saturation profile and spatial T2 techniques and higher Swirr value (43%) in the carbonate sample while the sandstone samples showed uniform fluid distribution and less Swirr (26% and 9.51% for the Berea and Fontainebleau samples respectively). Consequently, a significant variation between the dielectric measurements of the inlet and the outlet was observed in the carbonate sample with low permeability. Overall, this study provides a new workflow of integrating the dielectric and the NMR techniques to assess the impact of petrophysical properties such porosity, permeability, and pore sizes on the saturation profile across the sample resulted from the centrifuge displacement which consequently affect the dielectric and NMR responses. Ultimately, this work would help in improving the characterization of carbonate and sandstone formations by integrating the dielectric and NMR measurements.
