基于法向阻抗分量的P⁃P波反射系数近似表达与纵横波阻抗反演  

P⁃P wave reflection coefficient approximate expression and P⁃&S⁃wave impedance inversion based on normal impedance component

作　　者：王升荣 孙成禹[1] 蔡瑞乾 杜燚镜 WANG Shengrong;SUN Chengyu;CAI Ruiqian;DU Yijing(School of Geosciences,China University of Petroleum,Qingdao,Shandong 266580,China)

机构地区：[1]中国石油大学(华东)地球科学与技术学院,山东青岛266580

出　　处：《石油地球物理勘探》2023年第4期933-941,共9页Oil Geophysical Prospecting

基　　金：国家自然科学基金面上项目“基于石油勘探面波与P‑导波的近地表纵横波速度一体化反演”(42174140);“深度偏移地震数据特征剖析与深度域直接反演方法研究”(41874153)联合资助。

摘　　要：弹性阻抗(EI)的提出是基于Zoeppritz方程有关近似垂直入射的P‑P波反射系数近似表达式,对地层性质和观测系统有特定的假设条件,如阻抗界面两侧的弹性系数差异小、入射角较小等,在实际应用中具有一定的局限性。此外,EI不同于声阻抗,没有确定的量纲,不是一个物理量,无法直接解释其物理含义。为此,从阻抗本身的物理定义入手,将应力矢量的两个分量和速度矢量的两个分量分别相除取反,构成阻抗张量,该阻抗张量具有明确的量纲。针对P波入射的情形,利用阻抗张量的法向分量(T)近似表达反射系数,并发展了相应的反演方法。数值算例结果表明:T反演、EI反演的结果基本一致,且均与理论值吻合较好,但在低速层处,T反演的横波阻抗相对较平稳,振荡较小;相对于EI而言,由于T的定义式中没有指数运算,因此反演结果对速度、密度和角度的敏感度降低,反演结果相对稳定。实际地震资料测试结果表明,反演结果与实际钻井资料吻合较好,同相轴强弱反映了明显的阻抗差异;两套薄储层呈清晰的低泊松比异常。由于所提方法仅使用两个角度的数据进行反演,故对入射角范围较窄的观测系统尤为适用。法向阻抗分量扩展了叠前地震反演的内涵,是对地震阻抗反演的有益补充。The proposal of elastic impedance(EI)is based on the P‑P wave reflection coefficient approximate expression for near‑vertical incidence,which is related to the Zoeppritz equation.However,specific assumptions are required for the formation properties and geometry system,such as small differences between the impedance interfaces and small incidence angles,which limit the practical application of EI.Additionally,EI is different from acoustic impedance and does not have a definite dimension,which means that it is not a physical quantity and cannot be directly interpreted physically.Therefore,according to the physical definition of impedance,the two components of stress vectors and two components of velocity vectors are divided and inverted to form the impedance tensor,which has a definite dimension.For the case of P‑wave incidence,the normal component(T)of the impedance tensor is used to approximately express the reflection coefficient,and a corresponding inversion method is developed.Numerical examples show that the results of T inversion and EI inversion are basically consistent and are in good agreement with the theoretical values.However,for the low‑velocity layer,the S‑wave impedance by T inversion is relatively stable and oscillates less compared with EI inversion.In addition,as the exponential operation is not included in the definition of T,the sensitivity of the inversion result to velocity,density,and angle is reduced,and the inversion result is relatively stable.The test results of actual seismic data show that the inversion result is in good agreement with the actual drilling data,and the impedance differences are evident in seismic events,indicating two sets of thin reservoirs with a clear low Poisson’s ratio anomaly.Since the proposed method only uses data from two angles for inversion,it is particularly suitable for geometry systems with a narrow range of incidence angles.The normal impedance component extends the connotation of prestack seismic inversion and is a beneficial supplement to s

关 键 词：阻抗 阻抗张量 法向阻抗分量 反射系数 

分 类 号：P631[天文地球—地质矿产勘探]