【作者】 李志刚；

【导师】 管志川； 王以法；

【作者基本信息】 中国石油大学 ， 油气井工程， 2010， 博士

【摘要】 随着油气田勘探开发的不断深入,对油气井钻井质量的要求也越来越高。近钻头参数是保障井眼质量的重要内容,然而近钻头参数的测量和远传技术仍不够成熟。本文以声纵波为载波,从分析近钻头信道的声波特性着手,采用理论和实验相结合的研究方法,研究并设计实现了一套近钻头井斜角测量与无线短传系统,为国内近钻头测量和信号传输提供了新的方法和途径。根据地层特性和井下工作环境的特点,分析了在近钻头处可以使用的声波信道,认为:井下钻具具有致密、连续、一致和稳定等特点,并且直接连接井底与地面,是理想的声波传输信道。通过分析声波在固体中的基本特性,认为在钻具与钻井液、钻具与钻具以及钻具与地层的交界面上均可能出现声波的反射和折射,但由于横波和纵波不同的反射和折射特性,使得纵波更适合于井下声波通信。通过对井下各种钻具的具体结构特征的分析,发现近钻头钻具的结构特征非常复杂,国际上所常见的研究钻柱声波特性时所采用的细长杆和周期性管结构的假设,在近钻头处无法应用,需要采用新的研究方法。螺杆钻具是定向钻进时井底钻具组合的重要组件,必须首先掌握其声波特性。根据螺杆钻具的实际结构及构成情况,建立了螺杆钻具的有限元模型,采用有限元方法求解了螺杆钻具的脉冲激励响应,通过时域和频域分析的方法得到了声波在螺杆钻具中传播特性。研究发现:随着传播距离的增加,声波的幅值呈非线性衰减趋势,其波峰个数也逐渐增加,具有较为明显的频散特征。结合在实际的螺杆钻具上的实验数据发现,螺杆钻具对于声纵波具有类似于低通滤波器的声波特性,在无变径结构的12m左右的通信距离上采用6KHz以下的载波频率能够获得较好的传输波形。根据近钻头钻具组合的实际情况,并结合现场MWD等仪器的实际结构、安装和使用情况,提出了几种可能的近钻头声波传输信道的结构型式,采用有限元方法分析了这些信道结构的时域和频域特性。在研究的几种信道结构中,当以声纵波作为信号载波时,直通信道的声波反射和衰减均较小,因此可以获得较好的传输波形;而旁通信道由于分支结构的存在必然会引起声波反射,当必须采用旁通信道时,其中的第2和第3种形式的特性较好,但要获得更好的传输效果,需要在端面处加设吸声结构。另外还发现:钻具上的变径会使声波的幅值变小,并同时使其相位发生变化,因此当变径结构周期性出现并与声波波长存在一定关系时,会产生较强的反射波或波形叠加,这会对声波通信产生严重干扰,在使用中必须注意并预防。但另一方面,变径结构的这种特性也可用来削弱远处传来的反射波。根据井下声波信道的特点,针对近钻头处的工作环境和噪声特征,在分析现有数字调制解调方法、纠错控制技术和编解码技术的基础上,从节约井下系统功耗和尽量减少设备使用量的角度出发,研究并实现了基于带时延的OOK调制方法、非相干解调方法、卷积码编码及Viterbi解码算法的近钻头声波通信方法。在综合考虑近钻头处的空间、噪声和振动等环境特征的基础上,结合对井下通信方法的研究,提出了近钻头测量与无线短传系统的关键问题、设计原则和设计方案,研制了一套近钻头井斜角测量与无线短传系统,该系统能够测量距离钻头64cm的井斜角,然后利用声波将其传输至12.5m远处的接收结构中,并进一步传送给井下MWD,可由井下MWD将其传输至地面。该系统通过了地面测试,并进行了井下实验。更多还原

【Abstract】 With the development of oil and gas exploration, the quality of drilling becomes more important than ever. Information near bit is critical to assure the well s quality. However, the technology of measurement and telecommunication near bit was not mature. Using the longitudinal wave as carrier, the paper analyzes the acoustic properties of channels near bit with theory analysis and experimental methods. Also, a near bit measurement and wireless short-distance communication system is developed. It gives a new way for domestic near bit information s measurement and telecommunication.The downhole drilling tools have the characteristic such as compact, consecutive, consistent and steady. Also they connect the down hole and surface. So they are idea channel for acoustic communication. Through analyze the basic properties of acoustic wave propagated in solid, it finds that reflections and refractions will occur at the edges of tools and fluid, tool and tool, tools and formation. Due to the differences of P-wave and S-wave, the P-wave has better transmitting performance. The tools near bit are more complex than upper tools. So the hypotheses of slim pole and periodic pipe used in analyzing drill string s acoustic properties are not suitable for the near bit tools. A new research method must be developed.The screw tool is important for BHA (Bottom Hole Assembly) in directional drilling. It’s acoustic properties should be clear first. According to the real structure and construction, the FEA (Finite Element Analysis) model was build and the pulse response was resolved by FEA method. Using time-domain and frequency-domain analysis , the acoustic property of screw tool was got. The results show that the amplitude of acoustic wave will attenuate and peaks number will increase while the extension of spread. The screw tool has the low pass filter property for the longitudinal wave. The 6KHz carrier frequency is good for communication in the distance about 12m without diameter changing. Also, an experiment was executed. The experimental results show that real screw tool’s pass band is narrower than the calculated results and shift to low frequency.According to the real condition of BHA, 5 available acoustic channels and structures are introduced. Their time domain and frequency domain properties are analyzed by FEA method. In analyzed channels, when the longitudinal wave is used as carrier, the reflection and attenuation in straight channel is faint. In by-pass channels, the reflection is strong due to the branch. When the by-pass channel must be used, the 2nd and 3rd channel have more good performance. For better performance, the absorption structure should be added at the terminal. Diameter changing along the tools will make the wave s amplitude smaller and phase lagged. So the reflection will be very strong when the distances between diameter changing and wave length have an appropriate relationship. This point must be given more attention in some special tools. On the other hand this can be used to whittle the reflection.Based on the features of the down hole channels, the OOK with time space modulation, no-coherent demodulation, convolutional coding and Viterbi decoding method was applicated in near bit communication for saving the power and reducing equipments down hole.A measurement and short-distance transmitting system is designed and realized. The system can measure the inclination at 64cm far from the bit, and transmit it to the receiver 12.5m far from the transmitter using acoustic wave. The receiver can transmit the information to MWD and to surface by MWD then. It was tested on surface successfully, also in a well.更多还原