井场噪声形成机理、建模及其对低频EM-MWD系统的影响研究

The electromagnetic measurement while drilling tool is a system that transmits data from down hole to the surface using electromagnetic wave as a carrier, which is an important tool for drilling with air or gasified drilling fluids. However, the electromagnetic signal coupling between the well head and the ground electrode is severely affected by formation resistivity and wellsite noise, which become a major bottleneck restricting electromagnetic measurement-while-drilling system development. This project deals with the electromagnetic carrier signal detection、processing and decoded in complex ambient noise of well site and channel noise, and is devoted to studying three key issue: the characteristics of electromagnetic wave transmission channel、the model of ambient noise in well site with different dill rig、the method of detection and processing electromagnetic signal from the downhole transmitter. Firstly, the characteristics of electromagnetic wave transmission channel are researched and analyzed in details, which is concerned with the carrier frequency, formation resistivity, well structure and casing size. Secondly, the statistical properties and spectrum of the well site are analyzed in details. Then, the model is constructed to describe the ambient noise in well site by analysis of the mechanical rig, electric drill rigs, top drive and rotary noise sample. Thirdly, in order to solve the problem of the electromagnetic carrier signal with complex noise, an optimal nonlinear detector structure is derived with the rotary noise as a reference signal. Finally, the model verification and validation is applied based on trial data and simulation data. The aim of this study is to obtain the characteristics of electromagnetic wave transmission channel, determine the model of drill site noise and detect the weak electromagnetic signal in the complex noise. The proposed theories and models are the theoretical basis of seismic-while-drilling, logging-while-drilling and other fields.

电磁随钻测量方法是解决气体钻井、雾化钻井、泡沫钻井、充气钻井、堵漏和常规钻井液钻井的随钻测量问题的重要技术手段。然而这种以耦合井架与地面电极间的电磁信号为获取信息的方式极易受到地层电阻率和井场噪声的严重影响，成为制约电磁随钻测量系统发展的主要瓶颈。本项目以机械钻机、电动钻机和复合驱动钻机的井场噪声为研究对象，开展复杂随钻电磁信道传输特性、时变与起伏的井场噪声形成机理与模型的构建、井场噪声处理方法及对EM-MWD系统的影响研究等方面的应用基础科学研究，构建井场噪声模型，探索纳入了时变起伏的井场噪声的统计特性的处理与检测方法，以期解决电磁随钻系统探测距离短的难题。本项目旨在认知不同钻机、不同钻进状态下，转盘启停时的井场噪声的形成机理和统计特性，构建近似的噪声模型，从信号提取的视角提升随钻测量系统的传输深度，为电磁随钻测量系统、中继器系统、随钻地震以及随钻测井等领域奠定理论基础。

地层电阻率和井场噪声是制约电磁随钻测量系统发展的主要瓶颈。项目以机械钻机、电动钻机和复合驱动钻机的井场噪声为研究对象，开展了复杂井筒电磁信道传输特性、时变与起伏的井场噪声模型、复杂噪声背景下地面接收电磁信号的处理方法等方面科学研究，项目取得的主要成果包括：（1）收集国内重点区块的地层电阻率信息，综合钻井泥浆、层厚、套管、井眼尺寸、地层倾角、井斜、岩石各向异性和地层层理等因素，构建了电磁信号传输受地层电阻率影响的衰减模型；基本掌握井筒中电磁随钻信号的衰减规律；能够评价不同区块EM-MWD系统的适应性。（2）采集了使用不同钻机时的井场噪声，分析不同钻进状态时噪声源的种类、构成，研究了井场噪声的频率相关性、时间相关性、空间相关性以及噪声的分布特性和谱特性，提出了将Bootstrap方法应用于井场噪声处理，建立不同钻机、不同钻进状态时的近似的井场噪声模型；（3）提出了将井场噪声的先验知识纳入井场噪声统计特性，修正了常规的LMS算法，确定合适的迭代因子 μ，使得该方法能有效地降低井场噪声对电磁随钻测量系统接收信号的影响，从而增强EM-MWD系统对井场电磁环境的适应能力，提高地面接收机的接收灵敏度，拓展测量深度。通过以上研究，从信号处理的视角，基本阐明了不同钻机、不同钻进状态下，转盘启停时的井场噪声的形成机理、统计特性和谱信息；构建了近似的井场噪声模型，评估了井场噪声模型对EM-MWD系统的影响，为提升随钻测量系统的传输深度奠定了理论基础。