NMR relaxation time dependency on saturation and wettability of carbonate rocks

Summary Nuclear magnetic resonance (NMR) transverse relaxation times (T2) were measured for carbonate rocks saturated with brine and crude oil under different saturation conditions. The NMR measurements were intercalated within the stages of standard wettability core analyses, which monitor imbibition and drainage processes after restoring in situ condition. The T2 distributions are interpreted for seven core plugs in each of the following stages: 1) totally brine saturated; 2) at irreducible water saturation after drainage; 3) restored after „ageing‟ for sixty days; 4) at residual oil saturation after imbibition and; 5) at final water saturation after second drainage. Under these complex saturated rock systems, brine and crude relaxation contributions are highly overlapped. However a practical relaxation-time-domain method is proposed and fluid signals are separated. Guided by T2 monophasic results, closely related to rock pore size distribution, biphasic results reveal pore occupancy and wettability of the micro, meso and macro porosity. Finally, this work reinforces the importance of NMR technique to complement conventional wettability core analysis and its potentiality for in situ wettability measurements in borehole geophysics.