相关技术在随钻地震中的应用

随钻地震技术采用钻井期间钻头产生的振动作为井下震源,使钻头产生的连续信号记录于安装在钻柱顶部的参考传感器和布置在井轴附近已选好位置的检波器上。通过参考信号和检波器信号进行互相关实现了两个目的:1)建立了互相关函数—钻头振动通过地层传播到地面检波器的旅行时间减去钻头振动向上经钻柱到参考传感器的旅行时间的一种量度,即使钻头振动是连续的,在互相关函数中它们仍被压缩成脉冲信号;2)互相关过程加强了弱反射钻头能量。互相关既可计算钻头波传播的时间;也可减弱不相干噪声。

The Application of Correlation Technique in Seismic While Drilling

Technique of seismic while drilling uses the vibrations produced by a drill bit while drilling as a downhole seismic energy source. The continuous signals generated by the drill bit are recorded by a pilot sensor attached to the top of the drillstring and by receivers located around the borehole. Signals from the reference sensor are used as a pilot signal for cross-correlation with signals from the surface geophones. The cross-correlation method accomplishes two important objectives. First, the cross-correlation function is a measure of thetravel time of drill-bit generated energy up through the strata to the surface geophones minus the travel time from the drill bit up the drill string to the reference sensor. Even though the drill bit vibrations are continuous, in the cross-correlation function they are compressed into pulse-like events. Second, the cross-correlation process also enhances low-level, drill-bit generated signals from weak reflectors. The pilot signal is cross-correlated with the receiver signals to compute travel times of the arrivals and to attenuate incoherent noise.