基于地震正交各向异性的裂缝介质岩石力学建模研究  

Geomechanical model of fractured media based on seismic anisotropy with orthorhombic symmetry

作　　者：赵小龙 张金淼 桑淑云 ZHAO Xiao-long;ZHANG Jin-miao;SANG Shu-yun(CNOOC Research Institute Limited,Beijing 100028,China)

机构地区：[1]中海油研究总院有限责任公司,北京100028

出　　处：《地球物理学进展》2020年第3期1109-1115,共7页Progress in Geophysics

基　　金：国家自然基金企业创新发展联合基金(U19B2008)资助.

摘　　要：岩石力学模型是描述地层原地应力状态的基础,而常规各向同性模型难以刻画地层本征横观各向同性(VTI)和天然高角度裂缝的耦合作用,建立更为准确的正交各向异性模型变得尤为重要.本文利用VTI介质中发育单组垂直缝的Schoenberg裂缝等效模型,简化了一般正交各向异性介质的表征参数,推导了由背景VTI介质弹性参数和裂缝参数的各向异性杨氏模量、泊松比和水平地应力的精确方程.借鉴Thomsen弱各向异性近似思路,舍去裂缝弱度参数高阶扰动项,推导了正交各向异性介质岩石力学近似方程,由裂缝弱度表示的近似方程更为直观地反映了裂缝对背景介质力学性质的影响,杨氏模量和泊松比值随裂缝法向弱度的增大而显著减小.选取页岩实验数据进行数值实验,结果表明本文方程与实际物理规律相吻合,随裂缝弱度的增加,形成相同应变所需的水平地应力值降低,且近似方程与模拟结果相对误差小于5%,有助于提高岩石力学参数估算和地应力预测精度.Geomechanical model is the foundation in characterization of subsurface in-situ stresses.However,it is difficult to describe the coupling effect of Vertical Transversely Isotropic(VTI)layer and natural high-angle fractures using conventional isotropic model.Therefore,building a more accurate orthorhombic model is crucial.Based on the Schoenberg effective fracture model for vertically fractured in VTI,the parameterization of general orthorhombic media is simplified.Then,the exact equations of anisotropic Young's modulus,Poisson's ratio and horizontal principal stresses are derived in terms of VTI parameters and fracture weaknesses.Reference on Thomsen weak anisotropy approximation,the approximate geomechanical models have been derived through omitting the highorder fracture weaknesses.The proposed approximate equations,which represented by fracture weaknesses,provide a better intuitive understanding of the effect of fracture on background anisotropic media,the increase of fracture weakness leads to a significant decrease in Young's modulus and Poisson's ratio.For verifying the validity and accuracy of the proposed equations,a published experimental data from shale sample is chosen to calculate exact and approximate results which demonstrate the horizontal stresses decrease with increasing fracture weakness following the physical laws,and the relative error of approximation is less than 5%.The proposed geomechanical model helps to improve the accuracy of predicting anisotropic modulus and in situ stress.

关 键 词：地应力 各向异性模量 裂缝等效介质 正交各向异性 

分 类 号：P631[天文地球—地质矿产勘探]