随钻电磁波测井环境影响分析

Analysis of environment influence in electromagnetic logging while drilling

本文在随钻电磁波测井原理的基础上,给出了三线圈系电磁波测井视电阻率的计算方法。采用基于加权余量法的矢量有限元方法进行分析,计算得到了地层环境对随钻电磁波测井仪器测量结果的影响,其中包括泥浆电阻率、侵入带、围岩和地层介电常数的影响。计算表明:衰减电阻率受泥浆电阻率的影响比相移电阻率小;在侵入深度较浅时,视电阻率主要反映原状地层电阻率,在侵入深度较深时反映侵入带电阻率;介电常数的影响与测量仪器的频率和地层电阻率有关,当介电常数增大时,两接收器之间的相位差和幅度比也随之增大;围岩的影响主要与地层电阻率和围岩电阻率对比度有关。

On the basis of the principle of electromagnetic logging while drilling, the paper gave the calculation procedure of apparent resistivity for triple coil electro-magnetic log and adopted vector finite-element method based on weighted remainder method to carry out analysis, which resulted in influence on formation environment on measured results by electromagnetic logging apparatus while drilling, including the influence of mud resistivity, invaded zone, surrounding bed and dielectric constant of formation. The calculated results showed the influence of mud resistivity on attenuation resistivity is smaller than on phase-shift resistivity; when the invasion depth is shallower, the apparent resistivity mainly reflects the resistivity of original formation and the resistivity of invaded zone when the invasion depth is deeper; the influence of dielectric constant is relative to the frequency of measurement apparatus and resistivity of formation, when dielectric constant increases, the phase difference and ratio of amplitude between two receivers increase too; the influence of surrounding bed is mainly relative to contrast of resistivity between the formation and the surrounding bed.