横向各向同性地层随钻多极子测井声场的分波分析与特性研究  

Theoretical calculation and mechanism analysis for component waves of acoustic logging while drilling in transversely isotropic formations

作　　者：饶博 唐晓明 苏远大[1,2,3] RAO Bo;TANG XiaoMing;SU YuanDa(School of Geosciences,China University of Petroleum(East China),Qingdao 266580,China;Key Laboratory of Deep Oil and Gas,China University of Petroleum(East China),Qingdao 266580,China;Qingdao National Laboratory for Marine Science and Technology,Qingdao 266580,China)

机构地区：[1]中国石油大学(华东)地球科学与技术学院,青岛266580 [2]中国石油大学(华东)深层油气重点实验室,青岛266580 [3]青岛海洋科学与技术试点国家实验室,青岛266580

出　　处：《地球物理学报》2022年第8期3198-3212,共15页Chinese Journal of Geophysics

基　　金：国家自然科学基金(41821002,42074137);国家重点研发计划(2019YFC0605504);中国石油重大科技项目(ZD2019-183-004)联合资助.

摘　　要：随钻声场在各向异性地层中的传播一直是随钻声波测井的重要课题.该问题中钻铤与井孔和地层的相互作用极大地影响着声场,特别是系统中的模式波的传播特征.因此,本文采用分波计算法来详细地研究在横向各向同性(VTI)地层中随钻多极子声波的传播规律,将声场全波分解成来自波数域中的奇异点(包括支点和极点)的分波的贡献,以此模拟分析了声场中各个分波的传播特征,包括模式波在频域中的频散、激发响应及时域中的分波波形.结果表明:在快速VTI地层中,钻铤的存在使得单极伪瑞利波和二阶四极地层螺旋波的频散大为降低,可以此来测量地层垂直向横波速度;慢速VTI地层中仅存在单一四极地层螺旋波,其低频速度为地层垂直向横波速度.值得注意的是,在各向异性参数满足δ>ε+c_(44)/2c_(33)的地层中,上述模式波的低频截止速度均小于地层的垂向横波速度,这一结果与已知的裸眼井情况一致.The acoustic wave propagation in the presence of a drill collar and an anisotropic formation has always been an important topic of acoustic Logging While Drilling(LWD).In this subject,the interaction between the drill collar and the borehole and the formation greatly affects the wave propagation characteristics,especially those of the guided wave modes in the system.To tackle the problem,this work uses an analytical wave separation method to calculate the detailed propagation characteristics of each wave component of the multipole LWD wavefield in a Vertical Transversely Isotropic(VTI)formation,analyzing the wave amplitude excitation,velocity dispersion,and the time-domain waveform characteristics.The results show that in a fast VTI formation,the presence of drill collars greatly reduces the dispersion of monopole pseudo Rayleigh waves and second-order quadrupole screw waves,allowing for measuring the formation vertical shear-wave velocity using these wave modes.In a slow VTI formation,only a single formation quadrupole wave is excited,whose low-frequency velocity is the formation vertical shear-wave velocity.Worthwhile to mention is that,in formations whose anisotropic parameters satisfy the condition δ>ε+c_(44)/2c_(33),the low-frequency cut-off velocity of the above-mentioned LWD acoustic wave modes are all lower than the formation vertical shear-wave velocity.This result is consistent with that obtained in an open-hole condition.

关 键 词：横向各向同性 随钻声波测井 频散 分波 横波速度 

分 类 号：P631[天文地球—地质矿产勘探]