An Improved Method of Using NMR T 2 Distribution to Evaluate Pore Size Distribution

Both NMR T2 distribution of core and capillary pressure can be used to characterize pore throat structures of rock to a certain degree. Theoretical analysis gives the correlation between these two sets of data. In order to utilize NMR spectra to study rock pore throat structure, the key step is to determine the transferring coefficient between T2 and pc since they are correlated. In the previous methods, the capillary pressure curve obtained by using T2 distribution has a poor match relationship with the real capillary pressure curves. In fact, due to the existence of membrane bound-water, the core space determined by T2 distribution is different from that determined by capillary pressure curves. This work proposes an improved method which uses free-water T2 distribution to construct capillary pressure curves after eliminating membrane bound-water's contribution to T2 distribution. Applying this method to some core data we make some analyses and comparisons. The result shows an improved precision and indicates that this method can provide reliable principle and methodological support to evaluation of pore structure by using T2 distribution.