井中偶极声源在横向各向同性地层中的辐射波场

研究井中声源在地层中的辐射特性对发展井下探测技术具有重要的意义,而井孔周围地层的各向异性对弹性波激发的影响不容忽视.本文从井中偶极声场积分表达式的远场渐近隐式解出发,借助相速度与群速度之间的转换关系,得到了井中偶极声源在各向异性地层中的辐射指向性与辐射波场,并深入研究了声源激发主频与各向异性对偶极辐射特性的影响.结果表明: 与各向同性情况相比,SH波在辐射波场中依然占据主导地位,但各向异性的存在导致其优势辐射频率向低频移动; qP波与qSV波的井外辐射波场均包括qp和qsv两种分量的贡献; 在特殊各向异性地层中,qP波与qSV波的qsv分量会呈现出三叉区与幅度奇异值.本文的结果可以为井外全波场的观测以及偶极声波远探测技术在各向异性地层中的应用提供理论支持.

Borehole dipole-source radiation wavefield in transversely isotropic formation

The borehole-source radiation characteristics are of significant importance in the development of downhole acoustic measurements,and the influence of formation anisotropy on the borehole elastic wave excitation should not be ignored. Using an implicit far-field asymptotic solution of dipole wavefield and simplify it based on the slowness and wave surfaces,the borehole dipole-source radiation pattern and wavefield in anisotropic formation are obtained. We further analyze the frequency and anisotropy effect on the dipole radiation characteristics. Results indicated that compared with the isotropic case,the SH wave predominates the dipole source radiation but the presence of anisotropy shifts the effective radiation to a lower frequency range. Both qP and qSV radiation wavefields include two components,qp,and qsv respectively. Moreover,the wavefront triplication and cusps of the qsv component can be observed in the special anisotropic formation. Our analysis results can provide an important foundation for observing the wavefield outside the borehole and applying SWI in anisotropic formation.