【作者】 程晶晶；

【导师】 孔力；

【作者基本信息】 华中科技大学 ， 控制科学与工程， 2011， 博士

【摘要】 多频核磁共振测井仪器是目前最先进的测井技术手段之一。未来几十年中它在我国石油勘测行业有着较大需求。为突破国际大公司的技术封锁,研制开发具有我国自主知识产权的多频核磁共振测井仪具有非常重要意义。多频核磁共振测井系统工程实现中重要关键技术之一是微弱信号获取与处理问题。本文主要讨论核磁共振回波信号提取及其回波串衰变信号构建过程中的干扰噪声滤除方法和高效数据采集等相关问题。本论文的主要工作内容有如下几个方面：(1)要求工作在高温环境中的微弱信号放大器的设计与实现,是多频核磁共振测井系统中关键的环节和难点。针对测井回波信号具有一定频带宽度,传统低噪声窄带点匹配方法已不能满足设计要求,本文提出一种适用于相对较宽频带的微弱信号噪声匹配方法,并设计研制出具有高信噪比高增益的前置放大器。测井实践结果表明,它不仅完全达到各项设计技术指标要求,而且为后续信号处理过程奠定良好的基础。(2)噪声滤除的最大化与信号损失的最小化是一个矛盾体的两个方面。如何做到两者之间的平衡,是滤波器选择截止频率的常遇问题。文中基于信号损失和残余噪声功率和最小准则,讨论广义信噪比最大为前提的最佳滤波截止频率确定问题,根据核磁共振测井仪回波信号的特征,建立小波滤噪方法分解尺度选择的量化指标。其结果已应用于实际反演算法,并取得较好效果。(3)针对在实际测井工作中发现测井环境温度会造成回波串衰减率测量偏差问题。在计算说明环境温度与跃迁能量之间关系的基础上,以正演所得的双峰孔隙度回波模型为对象,基于Bloch方程建立回波串温度误差模型,从理论上也得到此项误差的存在机理。论文给出一种消除温度偏差的近似方法。(4)为提高核磁共振测井低孔渗储层测量的准确性,需用较小的回波间隔并增加测量时问,但由此造成数据处理时间的减少,强化了T2谱测量的实时性要求,基于压缩感知的检测方式,设计专用核磁共振回波信号检测系统,以可靠性较高的硬件电路结构和低的功耗满足了测量的实时性要求。理论计算和实验表明,该实时采集处理系统不仅适合于对测量结果有高质量要求的回波信号检测过程,而且同时满足核磁共振测井过程的实时性及低功耗要求。更多还原

【Abstract】 Multi-frequency NMR logging method is one of the most advanced logging techniques nowadays. In following decades, it would still be wide used in oil exploration. To break through the technique blockade, it is of great importance to develop multi-frequency NMR logging instrument. In the NMR logging system development, the weak signal’s capture and process is very crucial. In the dissertation, the echo’s extraction and high efficient acquisition and noise filtering method in the echo string construction were discussed deeply. The main content of this paper was as below.(1) The design and implementation of weak signal amplifier which is required to work in high temperature environment is a key process in multi-frequency logging system. Because echo signal has a wide bandwidth, traditional point noise match method could not meet design target. Due to this, a wide band noise match method was proposed and a high gain high SNR amplifier had been designed. Logging experiments showed, it not only met the design specification but also provide a good foundation for the follow-up signal process.(2) Noise filtering maximum and signal loss minimum are the two aspects of a paradox. The tradeoff between the two issues is common problem to choose a filtering cutoff frequency. Based on the signal loss and residual noise power sum minimum principle, the choice of best filtering cutoff frequency was analyzed to get generalized SNR maximum. The quantitative standard to choose wavelet decomposition scale was established according to the echo’s characteristics. The result had been applied in inversion algorithm and get good performance.(3) The measurement deviation caused by the difference between calibration and logging temperature was analyzed. Based on the relation between environment temperature and transition energy, the temperature error mechanism was described. In addition, the model of temperature error was built through Bloch equation based on the twin-peak porosity model. Furthermore, a approximate temperature error suppression method was proposed according to the characteristic and mechanism of temperature deviation.(4) To improve the accuracy in ultra-deep NMR logging, short echo interval and long acquisition time should be adopted. Because of this, the signal process time decreased. To meet the real time requirement of T2 spectra measurement, a detection method based on compressed sensing was proposed to design a capture system dedicated for NMR echo signal. Experiments showed that the detection system gained good performance in NMR logging system which requires high quality result and has rigid demand in real time and low cost.更多还原