核磁共振测井回波信号噪声抑制设计

Design of Noise Reduction in NMR Well Logging

受物理机理与井眼环境的影响,核磁共振测井回波信号固有灵敏度低,因此噪声抑制成为贯穿仪器设计全过程的关键问题。以中海油田服务股份有限公司自主研发的核磁共振测井仪器EMRT(Elis Magnetic Resonance Tool)为例,基于原始回波信噪比的理论分析,分别从前置放大电路结构改进、采集模块有效分辨率提高和回波信号数字滤波算法设计等方面论述噪声抑制的方法及应用。EMRT在测井中的CHI值曲线表明:以上方法有效解决了核磁共振测井中的低灵敏度信号的检出问题。

Limited by physical mechanism and borehole condition, the intrinsic sensitivity of NMR echo signal is weak. So noise reduction becomes a key issue throughout the entire design process. Based on the principle analysis of original echo signal, taking NMR well logging tool EMRT （Elis Magnetic Resonance Tool）developed by China Oilfield Services Limited for example, this paper discussed the methods and applications of noise reduction in three aspects, including an improved structure of preamplifi- er circuit, the enhancement of efficient resolution in acquisition module and the design of digital filter algorithm. From the curve of CHI recorded while logging, the methods above was proven to effectively solve the issue of detection of low sensitivity echo signal in NMR well logging.