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Special requirements for design of tools used for wireline NMR logging and NMR logging while drilling and for interpretation model are demanded due to the dispersion properties of NMR relaxation for crude oil. NMR longitudinal relaxation time (T_1) and transverse relaxation time (T_2) of the dead oil samples with different viscosities were measured by NMR spectrometers with a Larmor frequency of 2 MHz and 23 MHz at five different temperatures respectively. The results showed that T_1 was obviously dependent on the Larmor frequency of NMR spectrometer. The degree of T_1 dispersion became stronger with the increasing crude oil viscosity, Larmor frequency and the viscosity/temperature ratio. T_2 was independent of NMR spectrometer measuring frequency. It is suggested that the resonance frequency should be selected lower than 2 MHz when measuring T_1 in logging while-drilling and that T_1 dispersion should be corrected when Larmor frequency is higher than 2 MHz.
Special requirements for design of tools used for wireline NMR logging and NMR logging while drilling and for interpretation models are demanded due to the dispersion properties of NMR relaxation for crude oil. NMR longitudinal relaxation time (T_1) and transverse relaxation time (T_2) of the dead oil samples with different viscosities were measured by NMR spectrometers with a Larmor frequency of 2 MHz and 23 MHz at five different temperatures respectively. The results showed that T_1 was obviously dependent on the Larmor frequency of NMR spectrometer. The degree of T -1 It is suggested that the resonance frequency should be selected lower than 2 MHz when measuring T_1 in logging while-drilling and that T_1 dispersion should be corrected when Larmor frequency is higher than 2 MHz.