变内径钻柱中微波传输衰减规律

摘要

With the drill string hole being regarded as an ultra-long irregular lossy cylindrical waveguide,the optimal frequency point for microwave transmission was calculated according to the electromagnetic wave coupling theory,the attenuation law and efficient transmission distance of microwave channel were obtained and the microwave mode in the waveguide was analyzed.Furthermore,the channel model and signal attenuation model were established by the microwave transmission equivalent circuit method.The power attenuation coefficient per unit of length was proposed to simplify the analysis on effective transmission distance for the ultra-long drill string.The optimal frequency points of 139.7 mm (5.5 in) and 127 mm (5 in) API drill pipes are 2.04 GHz and 2.61 GHz,respectively,and there are several inner diameter varying sections and break points in the drill string hole along the axial direction.The microwave transmission suffers a lot of reflections.The channel impedance change is a key factor affecting the transmission quality.The lab and field tests reveal that the attenuation model established in this paper is accurate,and it is helpful for guiding the design of microwave transmission measurement while drilling system.%为确定钻柱内孔微波传输的最佳工作频点,获取微波信道的衰减规律及有效传输距离,将钻柱内孔视为超长不规则有耗圆波导,采用电磁波耦合理论计算了微波传输最佳工作频点,分析了波导中的微波模式,采用微波传输等效电路法建立了信道模型及信号衰减规律模型.针对超长钻柱,提出单位长度功率衰减系数从而对有效传输距离进行简化分析.研究表明,139.7 mm(5.5 in)和127.0 mm(5 in) API标准钻杆最佳工作频点分别为2.04 GHz和2.61GHz,钻柱内孔沿轴向存在多个内径渐变段和突变点,微波传输存在大量反射过程,信道的阻抗变化是影响传输性能的主要因素.室内及现场测试结果表明,建立的微波传输衰减规律模型计算结果准确,可用于微波传输随钻监测系统的设计.