http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Wettability of porous media by nuclear magnetic resonance relaxation methods
Wettability is a major factor which influences the distribution of multiphase fluids in reservoir rocks. However, the conventional methods for determining wetting characteristics of reservoir rocks are difficult and time-consuming. NMR (nuclear magnetic resonance) relaxation time measurements provide a quantitative, fast, and relatively easy technique for determining rock wettabilities. The use o f NMR relaxation time methods to characterize wettability of porous media is based on the observation that the surface of porous media significantly influences the relaxation times of fluids in the pores. NMR relaxation measurements o f Tx (spin-lattice relaxation time in laboratory) and Tip (spin-lattice relaxation time in the rotating frame) for H2O and D2 O in bead packs are initially investigated in this study. The apparent contradictory observations of previous investigators are explained. Both H2 O and D2 O have shorter relaxation times in water-wet porous m edia than in oil-wet m edia in the absence o f magnetic impurities. Deuteron relaxation times are less affected by magnetic impurities, but are also less sensitive to the surface wettability changes. The determination of fractional wettability by NMR relaxation time methods are also demonstrated. Carbonate core samples are treated to create preferentially water-wet and preferentially oil-wet surfaces. NMR relaxation time measurements of such cores show good agreement with the results from the Amott/USBM methods. The pore level wetdng distribution of core samples are also obtained using NMR relaxation techniques. A new approach to esdmate the surface energy of a non-polar solid surface from NMR relaxation time methods is developed. This method is based on proton Tlp measurements o f a series o f homologous hydrocarbons with different surface tensions in bead packs. The solid surface energy is also compared with the Zisman method which uses contact angle measurements to obtain a solid surface energy. The results show that the proton TV> relaxation time is analogous to the contact angle used by the Zisman method. Therefore, the NMR relaxation time method provides a measure of solid surface energies.