随钻动电测井中声诱导电场的理论模拟

为防止沿钻铤传播的声信号掩盖来自地层的声信号，目前需在钻铤上刻槽以实现对地层纵、横波速度的测量.但刻槽不仅占用钻铤空间，且降低了钻铤的强度和刚度.本文探讨在不刻槽条件下，利用动电效应获得地层纵横波速度的可行性.为此，模拟了随钻声波测井信号及由岩石动电效应产生的电场信号.先视地层为黏弹性介质，模拟随钻声波测井信号，再利用围压与孔隙流体压强的关系获得了声波在地层中引起的孔隙压强，然后计算由孔隙地层动电效应产生的声诱导电磁场.对多极声源激发的声场波形及其诱导电场的波形进行比较，发现随钻声诱导电场中钻铤波的相对幅度明显小于随钻声场中钻铤波的相对幅度.此外，发现在慢速地层条件下，偶极声源激发的电场中出现了比较明显的地层横波信号.

Theoretical simulation of the electric field induced by acoustic waves during the seismoelectric logging while drilling

While it has been a common practice to carve grooves in the steel collar to attenuate collar wave in acoustic logging while drilling(LWD), the grooves decrease the strength and the stiffness of the collar as well as occupy the collar space. In this study we explore the feasibility of using electrokinetic effect to obtain the formation compressional and shear wave velocities under the non-grooved condition. The elastic wave-field in acoustic LWD is simulated firstly, using a viscoelastic formation model. The pore fluid pressure is obtained from the average normal stress or confining pressure caused by the acoustic wave in the formation. The electromagnetic field is calculated finally from the inertial body force on the fluid and the pore pressure gradient. By comparison between the waveforms of the acoustic and electric signals, it is found that the converted electric collar wave signal is much weaker than its acoustic counterpart, in terms of the collar wave amplitude relative to the other wave groups in their respective full waveforms. While the collar wave does not disappear in the converted electric signal, the electrokinetic effects can be used to weaken the adverse influence of collar wave on extracting formation compressional and shear wave velocities while drilling. An interesting discovery from our simulated waveforms is that the shear wave signal in a slow formation is quite clear in the electric full waveforms excited by an acoustic dipole source.