Abstract:

A mathematical model of the drilling fluid pressure quadrature phase shift keying (QPSK) signal was built by mathematical analyses of a variable amplitude logic control pulse function described with the Gate function according to the rotary valve control logic rule and communication principles. Frequency spectrum and transmission characteristics of the drilling fluid pressure QPSK signal in a directional well were investigated by a theoretical and numerical method. Acoustics characteristics of the pressure wave through drilling shafts in the kick-off section of a directional well were analyzed according to acoustics theory. In the condition of water-based drilling fluids, impacts of the carrier frequency, drilling shaft size, drilling fluid features and wellbore trajectory types on the signal transmission were studied. Numerical calculation results showed that the QPSK signal was fit for transmitting downhole data due to its higher signal power within the band width, and the viscosity and gas-bearing ratio of drilling fluids considerably affected the QPSK signal transmission. The effect of wellbore trajectory types on the signal transmission could not be ignored as the gas-bearing ratio of drilling fluids was over 0.5%, and signals attenuated much more in a short vertical-depth directional well than a long vertical-depth directional well on condition that the total well length was the same.

Key words: measurement while drilling (MWD), directional well, drilling fluid, quadrature phase shift keying (QPSK), mathematical model, transmission characteristic, wellbore trajectory

摘要：

根据旋转阀的控制逻辑规则，利用门函数构成可变幅度逻辑控制脉冲序列函数，通过数学分析，结合通信原理，构成了钻井液压力正交相移键控（QPSK）信号数学模型，研究了QPSK信号的频谱特性及沿定向井钻柱内压力波的传播特性。根据声学理论，分析了压力波通过定向井造斜段钻柱的声学特征；通过建立沿定向井钻柱分布的信号强度表达式，针对水基钻井液，研究了信号载频、钻柱尺寸、钻井液特性和井眼轨道类型对信号传输的影响。数值计算和分析表明，使用QPSK调制方式，带宽内信号能量比较高，适合于频带传输；QPSK压力信号在传输中受钻井液黏度和含气率的影响较大，当钻井液含气率大于0.5%时，井眼轨道类型对信号传输的影响不可忽略，总井深相同时，浅垂直深井产生的信号损失大于大垂直深井。

关键词: 随钻测量, 定向井, 钻井液, 正交相移键控, 数学模型, 传输特性, 井眼轨道