TI地层声学各向异性随钻评价方法的数值研究

采用三维有限差分方法模拟偶极子声源在含钻铤的各向异性地层井孔中激发的声场,研究地层各向异性对偶极模式波频散特征的影响,并提出从随钻四分量偶极子声波数据中提取地层快、慢横波慢度及其各向异性的方法。结果表明,偶极子声源在各种地层井孔中均可激发对横波慢度的方位各向异性敏感的偶极模式波:对于快速地层,F2模式的低频部分对地层横波慢度及其方位各向异性最为敏感;对于中速和慢速地层,弯曲波较高频率部分对地层横波慢度较为敏感。采用各向同性地层建模的方法可以较为准确地提取地层的快、慢横波慢度,提取结果的误差小于4%。

Numerical study of anisotropy evaluation method by acoustic logging while drilling in TI formations

The acoustic field excited by dipole sources in a fluid-filled borehole with a collar surrounded by anisotropic and the corresponding isotropic formations was simulated by a three-dimension finite difference method. The effects of formation anisotropy on dispersions of borehole modes were investigated. The results show that the dipole source can excite dipole modes which are sensitive to the formation anisotropy in all types of formations. For fast formation, the low-frequency part of F2 mode is most sensitive to shear velocities and anisotropy of the formation, while for intermediate speed and slow formations, the higher frequency part is more sensitive to shear velocities. A method of extracting formation fast and slow shear slowness and anisotropy parameters from four-component dipole waveforms is proposed, and is verified using numerical data. The error of extracted result is less than 4%.