关键词: 核磁共振, 测量精度, 多次微变回波间隔测量方法, 快速弛豫组分

Abstract: Nuclear magnetic resonance (NMR) technology can detect hydrogen signals in the hydrogen-containing fluids, such as water and hydrocarbon, directly. It can provide quantitative characterization of the fluid content and surrounding environment, thus finds extensive application in oil and gas exploration field. However, when measuring samples contain ultra-short relaxation components, such as shale oil and gas, the reliability of measurement results tends to be very low because only a small number of front-end signals in CPMG pulse sequence can be obtained for the fast relaxation components. Thus, a multiple micro echo interval measurement (MCTEM) method was proposed in this research. In the measurement stage, the proposed method acquired more NMR front-end signals. In the inversion stage, multiple echo data were adopted for the joint inversion. It contributed to forming an accurate short relaxation T₂ spectrum. MCTEM method was validated through numerical simulations and rock physics experiments. It was concluded from the results that MCTEM method could improve the problem of peak disappearance for short relaxation components in T₂ spectrum caused by high echo interval. MCTEM method could enhance the measurement accuracy of short relaxation signals effectively.

Key words: NMR, Measurement accuracy, Multiple micro echo interval measurement, Fast relaxation components