A Method for Improving the Measurement Accuracy of Nuclear Magnetic Resonance Fast Relaxation Signal

doi:10.11938/cjmr20233082

Abstract

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

CLC Number:

TE112.6

MA Yingying, ZHANG Gong, LIAO Zhongshu. A Method for Improving the Measurement Accuracy of Nuclear Magnetic Resonance Fast Relaxation Signal[J]. Chinese Journal of Magnetic Resonance, 2024, 41(2): 162-172.

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模型名称		模型一				模型二
测量方法		理论标准	T_E=0.1 ms	T_E=0.8 ms	MCTEM	理论标准	T_E=0.1 ms	T_E=0.8 ms	MCTEM
高信噪比（100）	孔隙度/%	8.00	8.21	5.64	6.26	8.00	8.20	5.59	6.28
高信噪比（100）	绝对误差/%	0.00	0.21	2.36	1.74	0.00	0.20	2.41	1.72
低信噪比（10）	孔隙度/%	8.00	8.21	5.65	6.50	8.00	8.21	5.25	6.11
低信噪比（10）	绝对误差/%	0.00	0.21	2.35	1.50	0.00	0.21	2.75	1.89

样品编号	体积/mL	模型T₂/ms	采集参数
样品编号	体积/mL	模型T₂/ms	等待时间/ms	扫描次数	回波间隔/ms	回波个数
1号	1.0	0.7、11.0	4000	1	0.1、0.8、0.9、1.0、1.1、1.2、1.3、1.4、1.5	2000
2号	1.0	0.7、21.0	4000	1	0.1、0.8、0.9、1.0、1.1、1.2、1.3、1.4、1.5	2000