声波沿钻柱的传播特性研究

发布时间：2018-04-08 09:44

本文选题：随钻测井　切入点：声传特性　出处：《西南石油大学》2017年硕士论文

【摘要】：声波传输技术是一种井下随钻测量信息传输技术。相较于目前通用的泥浆脉冲传输技术,声波传输技术具有钻柱信道性质稳定,不依赖泥浆循环以及能广泛应用于现有的各种钻井技术中等优点。因此,开展声波沿钻柱的传播特性研究,为井下声波传输技术的研发和随钻测井仪器的研制提供理论和技术支持,在推动钻井技术自动化和智能化方面具有一定价值。首先,以声学在固体中的传播理论为基础,建立了声波沿一维理想钻杆传播的数学模型,研究了声波沿钻柱传播的传播规律和频响特性;依据定常结构在截面突变时会造成阻抗不匹配这一现象,分析了钻杆+接头组合的色散特性,为井下隔声结构的设计提供了理论依据;采用有限差分法和传递矩阵法分别对周期型和非周期型钻柱结构的频响特性进行了研究,结果显示钻柱结构呈现梳状滤波器性质——通带和阻带交替出现,且钻柱结构越复杂,通带的带宽越窄;还考虑了接头两端截面渐变部分对钻柱结构频响特性的影响,结果表明,由于截面渐变部分的存在使通带的带宽增大,更有利于声波的传输。其次,结合井下实际工作环境,考虑钻井液粘滞阻尼和地层边界条件,研究了声波沿钻柱传播过程中的衰减规律并计算了声波沿钻柱传播的最大距离,表明井下声波通讯需考虑安装中继器;另外,由于地层边界对声波具有一定的反射作用,将使载波信号产生很大的畸变,建议确定声波发生器合理安装位置。最后,依据对钻柱系统的声学性质分析,设计了一套可基本实现井下声波数据传输的系统。采用组合隔声结构、双声接收装置以及确定声波发生器和接收器的合理安放位置分别对井底噪声、地面噪声和信道回波噪声进行抑制,通过计算机仿真,三种方法均能对噪声取得很好的抑制效果,对于声波信号中的其他噪声,给出了四阶带通滤波器的设计电路(在数值模拟时采用了数字滤波器);对比分析了幅移键控(ASK)、频移键控(FSK)和相移键控(PSK)三种基本信号调制方法,优选出适合井下声波通讯的二进制相移键控(BPSK)调制方法,并采用随机生成100位二进制信号对正弦载波进行模拟调制,将其施加于钻柱系统,对接收信号进行滤波和解调,误码率仅为7%,获得了较好的传输效果。
[Abstract]:Acoustic wave transmission technology is a kind of downhole measurement information transmission technology.Compared with the current mud pulse transmission technology, acoustic wave transmission technology has the advantages of stable channel property, independent of mud circulation, and can be widely used in various drilling technologies.Therefore, the research on the propagation characteristics of acoustic wave along the drill string provides theoretical and technical support for the research and development of downhole acoustic wave transmission technology and the development of logging tools while drilling, which has certain value in promoting the automation and intelligence of drilling technology.Firstly, based on the theory of acoustic propagation in solid, the mathematical model of acoustic wave propagation along one dimensional ideal drill pipe is established, and the propagation law and frequency response characteristics of acoustic wave along drill string are studied.According to the phenomenon that the impedance mismatch is caused by the constant structure when the cross section changes, the dispersion characteristic of the drill pipe joint combination is analyzed, which provides the theoretical basis for the design of the downhole acoustic insulation structure.The frequency response characteristics of periodic and aperiodic drill string structures are studied by using finite difference method and transfer matrix method respectively. The results show that the drill string structure is characterized by comb filter properties-pass band and stopband alternately, and the more complex the drill string structure is, the more complex the drill string structure is.The narrower the bandwidth of the passband is, the more the influence of the tapered section of the joint on the frequency response characteristics of the drill string structure is considered. The results show that the bandwidth of the passband increases due to the existence of the section gradient part, which is more favorable for the transmission of sound waves.It is indicated that it is necessary to install repeaters for acoustic communication in downhole, in addition, due to the reflection effect of formation boundary to acoustic wave, the carrier signal will be distorted greatly. It is suggested that the reasonable installation position of acoustic wave generator should be determined.Finally, according to the analysis of the acoustic properties of drill string system, a set of acoustic data transmission system is designed.All of the three methods can achieve a good effect on noise suppression, and for other noises in acoustic signals,In this paper, the design circuit of fourth-order band-pass filter is given (digital filter is used in numerical simulation, and three basic signal modulation methods, amplitude shift keying, frequency shift keying, FSKK and phase-shift keying, PSK) are compared and analyzed.The binary phase shift keying (BPSK) modulation method suitable for downhole acoustic wave communication is selected, and a 100 bit binary signal is generated randomly to simulate the sinusoidal carrier, which is applied to the drill string system to filter and demodulate the received signal.The error rate is only 7, and the transmission effect is better.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE921.2

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