Abstract：The particular advantage of Nuclear Magnetic Resonance(NMR) log is that it can distinguish the irreducible fluid porosity from the free fluid porosity,provided more reliable irreducible brine saturation.T2 cutoff is the key parameter when using nuclear magnetic resonance logging data to calculate irreducible brine saturation.T2 cutoff is determined by NMR experiment.Through the NMR experiment of core samples from Yingge-sea Basin,the paper studied the relationship between NMR T2 cutoff and capillary pressure.The studied results showed that T2 cutoff decreased exponentially when displacement pressure increased.Therefore,T2 cutoff is related to the height of gas column.The size of T2 cutoff needs to be determined by gas column in process of NMR logging data,especially when the reservoir has high irreducible brine saturation,the selection of T2 cutoff needs to be more careful.
