横向各向同性地层井孔声场分析与剪切模量和渗透率反演

项目名称： 横向各向同性地层井孔声场分析与剪切模量和渗透率反演

项目编号： No.40874062

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 金属学与金属工艺

项目作者： 胡恒山

作者单位： 哈尔滨工业大学

项目金额： 43万元

中文摘要： 沉积岩常呈现横观各向同性（TI）。本项目研究TI地层中井孔声波和井外弹性波的传播特性，并从声波测井响应反演地层的剪切模量和渗透率。取得的主要成果有: （1）采用横观各向同性地层模型，针对井轴垂直于横观各向同性平面（即VTI）的情形，通过理论研究，获得了弯曲波的低频极限速度公式，阐明了除一类特殊地层外，弯曲波速度的低频极限速度都等于沿井轴向传播的地层横波速度，而在这类特殊地层中，弯曲波速度的低频极限速度低于沿轴向传播的地层横波速度。 这就给出了利用弯曲波测量TI地层横波速度的理论依据和适用条件，是对井孔声学理论的发展。（2）分别针对弹性地层和孔隙地层，在VTI模型下，基于复变函数理论的解析算法计算出了井孔声波的全波和各个构成分波，同时采用离散波数法计算出了全波， 两种算法获得的全波一致。（3）推导出了井轴平行于横观各向同性平面或与之以任意角度斜交（TTI）情况下井孔波场计算的时域有限差分算法和完全匹配层吸收边界条件，并基于计算获得的波场对TTI情况波的传播特性进行了研究。（4）考察了波场对井孔几何参数、流体密度和地层参数的敏感性差异，提出了利用声波测井响应反演渗透率和两个剪切模量的算法。

中文关键词： 声波测井；各向异性；剪切模量；孔隙地层；渗透率

英文摘要： Sedimentary rocks usually exhibit transverse isotropy (TI)。We investigate the acoustic wavefield in a borehole embedded in an elastic TI solid in order to invert shear moduli and permeability from acoustic logs. Major achievements are as follows. (1) The propagation velocity of the flexual wave in the low frequency limit is analytically obtained in a TI formation whose axis of the symmetry parallels to the borehole. In such VTI conditions the low frequecny flexual wave speed approcahes the shear wave speed along the direction of the borehole axis, excluding in a special type of TI formation whose parameters satisfies the equation given in the report. The flexual wave travels at a speed slower then the shear speed in TI formations of the said special type. This result lays the theorectical foundation for inversion of the shear speed from the flexual wave, and tells its limitation.(2) Full waveform and its component wave packages are obtained through the discrete wavenumber method and complex analysis method. The waveforms obtained by the two different methods agree each other. Besides, these analytically obtained full waveforms agree with thoses from finite difference simulation. (3) For boreholes whose axis deviates from the axis of symmetry of the TI formation, the finite difference time domain (FDTD) technique with perfectly matched layers on each computation boundary is employed to simulate the three-dimentional elastic wavefield.The algorithm is further extended to simulate the acoustic wavefield in a borehole embedded in a formation with anisotropy in both permeability and tortuosity. (4)The sensitities of the wave propagation properties to the formation and borehole parameters are investigated, and inversion methods are proposed to obtain the shear moduli and permeabilities.

英文关键词： Acoustic logging; anisotropy; shear modulus; porous medium; permeability