A novel computational method for determination of water saturation in oil reservoirs using discrete wavelet transform and nuclear magnetic resonance (NMR) T2 log

Nuclear magnetic resonance (NMR) technique is the most innovative tool to determine water saturation. Notwithstanding a solid foundation in theory, current NMR methods have some practical limitations to determine water saturation. The main problem with using the current method is to measure the cut-off value of transverse relaxation time from a large number of water-saturated core samples. Determining the cut-off value in the core laboratory is costly and time-consuming. Hence, this study is aimed at providing a new method for determining water saturation using wavelet transform and the transverse relaxation time log. In this study, the transverse relaxation time log was first decomposed repeatedly by wavelet transform to eliminate the porosity effect, thus achieving immovable fluid relaxation time. Then, water saturation was calculated at each depth using the current NMR method with different cut-off values, referred to as bound water saturation. Finally, by establishing a relation between bound water saturation and immovable fluid relaxation time, water saturation was calculated at each depth, referred to as irreducible water saturation. The results achieved from this study demonstrated that irreducible water saturation closely matches bound water saturation in various oil reservoirs.