核磁共振测井地层界面响应特征研究

Studies on NMR logging responses at formation boundary

核磁共振(NMR)测井是在仪器运动状态下实现对地层NMR信号的观测.研究垂直方向的速度对NMR测井响应特征的影响,能够为仪器设计和资料解释应用提供重要依据.本文给出NMR测井在地层界面的响应方程.对单界面、对称双界面和不对称双界面等地层模型进行模拟分析,以此为基础,深入讨论NMR测井响应的影响因素.结果表明,运动状态对NMR响应有显著影响,主要影响因素有:天线长度、测速、等待时间、累加次数、信噪比、层厚等.随着天线长度、测速、累加次数和等待时间的增加,纵向分辨率明显降低.文章最后为提高核磁共振测井纵向分辨率提出了建议.

The formation signal is measured by Nuclear Magnetic Resonance （NMR） logging tool in the moving state. Researches on the effect of vertical logging speed on NMR logging responses can provide a sound basis for tool design and data interpretation. The logging response equation at the formation boundary was proposed in this paper. The logging responses at the single, symmetrical, and asymmetrical boundaries were simulated. And the factors affecting NMR logging response were discussed. It is suggested that the NMR logging responses were greatly affected by tool moving. The main factors are. antenna length, logging speed, waiting time, running average, signal to noise ratio and thickness of formation. With the increase of antenna length, logging speed, running average and waiting time the vertical resolution decreases. Suggestions about how to improve NMR logging vertical resolution were proposed in the last part of paper.