中文摘要：

随钻单极源声波测井中,由于钻铤模式波的干扰而使地层纵波速度的测量变得困难.孔隙地层的声电转换物理效应给我们提供了通过测量转换电信号实现声学参数测量的可能性.针对随钻声电测井,采用Pride声电耦合方程组描述井外孔隙地层的声电耦合波场,考虑随钻环境条件下的边界条件,采用实轴积分法计算出了随钻声电测井瞬态响应的波场.计算结果表明,声电转换比与电缆声电测井量级相同,也说明随钻环境下声电效应是可应用的.但是,从得到的电场波形图中可以观察到,钻铤模式波成分虽有压制,但仍然存在.为了削弱钻铤模式波,鉴于钻铤的声波速度已知,我们尝试利用双发射源测井方法,通过控制源间距及合适的发射延迟时间对钻铤模式波进行进一步压制.结果表明,采用双源后的井内转换声场和电场波形中,钻铤模式波被有效地抑制,残余钻铤波的相对振幅明显减小,压制效果在电场波形中尤为明显,地层波的信噪比显著增强,有利于地层纵波速度的提取.

英文摘要：

Although the Logging While Drilling（LWD）acoustic technology has been developed over two decades,it still remains challenge to derive compressional-wave transit time from the LWD measurements due to the disturbance of collar waves,especially in relatively weak formation.The results from this study demonstrate feasibility of extracting acoustic parameters（e.g.,compressional-wave transit time）from the measurements of electric field induced by the electrokinetic effect.To investigate the characteristics of seimoelectric waves in LWD environments,Pride′s seimoelectric coupling equations are exploited.By applying the boundary conditions at the borehole wall and mandrel surface,the transient response of seismoelectric wave field can be simulated using real-axis integral.The results show that the seimoelectric conversion ratio in LWD is similar to that in wireline logging.Seimoelectric effect could be useful in LWD.However,it is found that considerable residual collar waves exist in the converted electric field,even most of collar waves are suppressed.To further suppress collar waves,dual transducers are proposed.The distance between transducers and their firings can vary to maximize reduction ofcollar waves.Numerical results show that relative amplitude of collar wave in the full waveforms is significantly reduced.It has shown promising that using dual-transducers in LWD deliver better quality compressional-wave transit time logs than the current LWD technologies.