Abstract:Irreducible water saturation is one of the fundamental parameters for characterizing reservoir formations, and the key factor for determining reserve calculation and fluid type identification. CT analysis on 125 whole cores shows that volcanic rocks have the complex porous structure and possess strong heterogeneity. As a result, accurate Swi can be only measured on whole cores. A new testing method for whole cores is proposed by combining Nuclear Magnetic Resonance(NMR) with centrifugal tests. Using T2 spectrum of whole core demarcated by a T2 cutoff, this new method measures irreducible water saturation. The T2 cutoff is measured on 25mm or 38mm diameter core samples which drilled from the whole core. Experiments on 52 volcanic rocks show that although the measured T2 cutoff values vary greatly among different volcanic rock types, but there is little difference between the values in the same group of volcanic rocks sub-classified by lithology. And NMR method can provide reliable measurements when it is applied to Sw measurement of volcanic rocks if the T2 cutoff is measured on cores from the same group sub-classified by lithology. The new method overcomes the problems involving size and shape restricts, long test cycles, and viscous fingering defects of conventional methods. Comparing with conventional method, the results of the new method well coincide with the experimental results on homogeneous rocks, and are more accurate with fractured samples.