横向各向同性弹性地层井孔中模式波的探测深度

Investigating Depth of Mode Waves in the Borehole Surrounded by Transversely Isotropic Elastic Formation

研究了横向各向同性(TI)弹性地层充液井孔中模式波的频散曲线和灵敏度曲线。结果显示:弯曲波对地层中垂直向传播的横波速度比较敏感,而斯通利波对地层中水平向传播的横波速度较灵敏;在慢速地层中,从斯通利波(或弯曲波)对不同径向位置和不同波数下水平向(或垂直向)传播的横波速度的灵敏度曲线上可知,斯通利波的探测深度在整个计算频段约为1.5个井眼半径(距井壁距离),弯曲波的探测深度相对较深,但受波数影响大:在较低波数时,其探测深度约为4个井眼半径,较高波数时约为1.5个;在快速地层中,由于受井内流体的影响较大,弯曲波在较高波数时探测深度稍有下降,但斯通利波对地层性质的敏感程度明显降低甚至消失。

The curves of the dispersion and sensitivity for the mode waves in the borehole surrounded by a transversely isotropic elastic solid are numerically simulated. The results show that the flexural wave is sensitive to the velocity of the vertically propagating shear wave （Vsv）, while the Stoneley wave is sensitive to the velocity of the horizontally propagating shear wave （VsH）. In the slow formation, the investigating depth of the Stoneley wave is about 1.5 radius of the borehole to the wall for the full calculating frequency range; the flexural wave exhibits frequency-dependent characteristic of the radial depth of investigation, and the investigating depth is deep （about 4 radius of the borehole） with low wavenumbets and shallow （about 1.5 radius of the borehole） with high wavenumbers. In the fast formation, the sensitivity of the flexural wave to the Vsv diminishes slightly, but the sensitivity of the Stoneley wave to the VSH diminishes significantly due to the influence of the fluid filled in the borehole.