井筒内钻井液连续脉冲信号传输频率相关摩阻模型

随钻测量的连续脉冲信号在井下传输的能量损失大部分来自于钻井液内部及其与管壁之间的摩擦。引入复频率概念,考虑到钻井液流体非牛顿流动特性,应用拉普拉斯变换,对脉冲信号在井筒内传输过程的衰减情况进行了频域分析,建立了钻井液连续脉冲信号传输频率相关摩阻模型;应用现场工程数据,分析了频率相关摩阻的影响因素及影响规律。结果表明,连续脉冲信号在低频段内衰减强度小,传输距离更远;在高频段内,连续脉冲信号传输稳定性更好。频率相关摩阻主要由脉冲信号频率特性和钻井液流体性质决定,在低频段内,其对脉冲信号衰减强度的影响更为显著;钻井液黏度越小,频率相关摩阻越小。

Frequency-dependent friction model for consecutive pulse signal of drilling fluid transmitting in borehole

The major energy loss of consecutive pulse signal of drilling fluid always comes from the friction of drilling fluid with the shell of pipe during underground transmission. In the consideration of the non-Newtonian characteristics of drilling fluid and the concept of complex frequency, a frequency-dependent friction model for consecutive pulse signal of drilling fluid transmission was set up using the Laplace transforms. The frequency domain of the pulse transition signal of drilling fluid in borehole was also discussed. The influencing factors and the disciplines of transient friction loss were analyzed with the practical data from similar projects. The analysis results showed that the attenuation of the pulse signal was smaller and the transmitting distance was longer in the low-frequency stage. Conversely, the signal transmitting was more stable in the high-frequency stage. The transient friction loss was only affected by the frequency of signal and the characteristics of drilling fluid. The influence of transient friction loss on the attenuation was more remarkable in the low-frequency stage. Thus, the lower viscosity of drilling fluid could result in the less transient friction loss.