Abstract:  During the oil drilling process, the near-bit vibration signal can reflect the drill string movement and the drilling tool's working condition. By analyzing near-bit vibration data, the down-hole working conditions can be judged in a timely manner, which can reduce bit wear and improve drilling quality.In this paper mainly starting from the signal processing of multiple groups of near-bit vibration signals in terms of time domain analysis, frequency domain analysis and time-frequency analysis, the mean, variance and the mean square values of the vibration signals are thus obtained, as well as the power spectral density and the short time Fourier transform. Then compared with normal drilling data, the general characteristics of stick-slip conditions are found out. When stick-slip occurs, The mean, variance, and mean square values of the X-axis and Y-axis vibration data all increase, especially X-axis values. The spectrum of the power spectral density of the X-axis and the Y-axis increases, and the amplitude increases, which can be more intuitively observed from the three-dimensional time-frequency chart of the short-time Fourier transform. The results show that the power spectral density and short-time Fourier transform can timely determine the down-hole stick-slip conditions, prevent early damage to the drill bit, optimize the drilling process, and reduce the drilling cost.

Key words: drill string vibration, stick slip, power spectrum density, short time Fourier transform 

摘要： 通过分析近钻头振动数据能够及时判断井下工况，可减少钻头磨损，提高钻井质量。从信号处理的方向出发，通过对多组近钻头振动测量数据进行时域、频域以及时频域分析，得到振动信号的均值、方差、均方值，以及功率谱密度和短时傅里叶变换，与正常钻进时数据进行对比分析，找出粘滑工况的一般特征。在发生粘滑时，Ｘ轴和 Ｙ轴振动数据的均值、方差和均方值均变大，Ｘ轴尤为剧烈；Ｘ轴和 Ｙ轴的功率谱密度频谱增多，幅值增大，整体偏移横轴；短时傅里叶变换的三维时频图能够更加直观的观察到这一特征。研究结果表明，通过功率谱密度和短时傅里叶变换能够及时判断井下粘滑工况，预防钻头早期损坏，优化钻井过程，降低钻井成本。

关键词: 钻柱振动, 粘滑, 功率谱密度, 短时傅里叶变换