横波各向异性分析方法及其在复杂储层中的应用

S-wave anisotropy analysis method and its application on complex reservoir

(中国石油大学(华东),山东青岛266555)

Wei Zhoutuo,China University of Petroleum (East China),Qingdao 266555,China

裂缝和井周的不均衡地应力均可引起地层的横波各向异性。分析井周地层的横波各向异性特征,可以指示地层的裂缝和不均衡地应力信息。从各向异性地层中的横波分裂现象入手,基于波形反演理论,利用正交偶极子阵列声波资料,分析和评价了裂缝性和低孔、低渗储层的横波各向异性,利用计算得到的各向异性参数评价了裂缝性地层中裂缝的发育程度、方位以及低孔、低渗地层的地应力分布状态。利用单极子横波各向异性大小和快、慢弯曲波波形频散曲线关系,分析了引起横波各向异性的原因。结合常规测井资料、岩心及FMI成像资料对分析结果进行了验证和对比,两者吻合得较好。应用结果表明,横波各向异性参数可以有效地评价裂缝的发育程度、走向及有效性,并能准确地确定地应力分布状态和最大水平应力方位。

Fractures and wellside unequal in-situ stress may lead to the S-wave anisotropy of formations.The analysis of the characteristics of S-wave anisotropy for wellside formation can indicate the fractures and unequal in-situ stress.Starting from S-wave splitting in the anisotropic formation,based on waveform inversion theory,we used the orthogonal dipole array acoustic data to analyze and evaluate the features of fractures and the S-wave anisotropy of low-porosity & low-permeability reservoir.Then,the calculated anisotropic parameters were used to evaluate the development and azimuth of fractures and the distribution of in-situ stress in low-porosity & low-permeability formation.Meanwhile,the relation between S-wave anisotropy of monopole and waveform dispersion curve of fast and slow bending wave was utilized to analyze the cause for S-wave anisotropy.Finally,combined with conventional logging data,core and FMI imaging data,the analysis result was verified and contrasted,and the result shows the two matches well.Application indicates that S-wave anisotropy parameters can effectively evaluate the development,trend and feasibility of fractures,exactly identify the distribution of in-situ stress and the azimuth of maximum horizontal stress.