| T2 cutoff value is one of the most important parameter in T2 spectrum. NMR measurement results of samples such as movable fluid saturation,irreducible water saturation will be scientific and accuracy when T2 cutoff value select scientifically and accurately.Centrifugal method was general method used at home and abroad to calibrate T2 cutoff value, and most experts and scholars at home and abroad selected 100 psi as best centrifugal force calibrating T2 cutoff value glutenite and carbonatite cores. Most foreign scholars believed that T2 cutoff value of sandstone cores was about 33 ms and domestic scholars generally believed that T2 cutoff value of domestic sedimentary reservoirs cores was less than 33 ms. In majority study abroad most T2 cutoff value of carbonatite cores distributed between 90 ms and 100ms, and never saw author relevant reports yet about T2 cutoff value of vulcanite reservoir cores.Large number of core analysis results showed that 100 psi as the best centrifugal force of calibrating T2 cutoff value might be not suitable for glutenite cores have low porosity and low permeability and special lithological cores such as carbonatite cores and vulcanite cores.This paper selected a certain number of representative cores of glutenite have low porosity and low permeability,carbonatite and vulcanite, and carried on best centrifugal force calibration experiments. each of cores were carried on NMR measurement after each of six or seven different centrifugal force, author can got that 200 psi was suitable to be best centrifugal force calibrating T2 cutoff value for glutenite cores, and 400 psi was suitable for carbonatite and vulcanite cores in this paper, and corresponding lower limit of valid throat is 0.1μm for glutenite and 0.05μm for carbonatite and vulcanite.Under best centrifugal force, author selected a lot of representative Glutenite,carbonatite and vulcanite cores and carried on centrifugal experiments and NMR T2 measurement, and determined T2 cutoff value of each cores, This paper also selected a certain amount of representative fresh oil-bearing sandstone for calibrating T2 cutoff value, and analyzed influence of T2 cutoff value with original wettability of core. In this paper, T2 cutoff value of glutenite cores mostly distributed between 10 and 30 ms, carbonatite cores were about 100ms. T2 cutoff values of vulcanite cores changed great with lithology, and average T2 cutoff value of rhyolite cores was 87.91 ms, tuff was 52.02 ms, and volcanic breccia was 36.28 ms.On the basis of ensuring T2 cutoff value, author analyzed relationship between NMR irreducible water saturation in different cores and porosity,permeability, and established analytic method of irreducible water saturation,movable fluid saturation of vulcanite core. NMR results of some Daqing oilfield vulcanite cores and gas test results of corresponding reservoir and CT results were compared in this paper.
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