关键词: 核磁共振, 测量精度, 多次微变回波间隔测量方法, 快弛豫组分

Abstract:

Nuclear magnetic resonance (NMR) technology can directly detect hydrogen signals in hydrogen-containing fluids, such as water and hydrocarbon. It can provide quantitative characterization of the fluid content and surrounding environment, thus finding extensive application in oil and gas exploration field. However, when measured samples containing ultra-fast 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 Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence can be obtained for the fast relaxation components. To address this problem, 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 fast 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 fast relaxation components in T₂ spectrum caused by long echo interval. MCTEM method could enhance the measurement accuracy of fast relaxation signals effectively.

Key words: NMR, measurement accuracy, multiple micro echo interval measurement, fast relaxation components