平均入射角道集PP波与PS波联合反演  

Joint PP-and PS-wave inversion of gathers with average incident angles

作　　者：石瑛[1] 芦俊[1] 杨震[1] 杨春[2] 

机构地区：[1]中国地质大学(北京)能源学院,海相储层演化与油气富集机理教育部重点实验室,北京100083 [2]中国地质大学(北京)地球物理与信息技术学院,北京100083

出　　处：《地球物理学报》2015年第12期4617-4627,共11页Chinese Journal of Geophysics

基　　金：中央高校基本科研业务费专项资金(2652013093);北京高等学校青年英才计划项目(YETP0661);国家高技术研究发展计划(863计划)课题(2013AA064201);国家自然科学基金项目(41574126;41425017)资助

摘　　要：在界面两侧地层的弹性参数弱反差的假设难以成立的情况下,本文提出用平均入射角道集进行PP波与PS波的联合反演.首先,在PP波与PS波AVA(amplitude versus angle,振幅随入射角变化)道集的基础上,分别选择小入射角范围与大入射角范围的AVA道集进行局部加权叠加,以获得由两个角度组成的平均入射角道集,并作为后续反演的输入数据.然后,再通过最小二乘原理建立了PP波与PS波联合反演目标函数,推导了模型修改量的向量公式,建立了平均入射角道集联合反演的流程.模型数据与实际数据的测试结果表明:在信噪比较低、地层弹性参数反差较大、层厚较薄的情况下,该反演方法的精度在很大程度上超过了基于近似反射系数的反演方法,为复杂油气藏勘探提供了新的思路.To coal reservoirs,the AVO method is not widely applied.The main reason for this phenomenon is that the offset is not large enough to provide wide incident angles for the inversion and the elastic parameters are hard-contrast at the top and bottom interface of the coal seam.Therefore,the conventional inversion method based on Aki-Richard equations is not applicable.To solve this problem,we propose a joint PP-and PS-wave inversion method based on the exact Zoeppritz equations,which can invert gathers of PP-and PS-waves with average incident angles.An average incident gather consists of two incident angle traces of PP-and PS-waves.The small and large incident angle traces are derived by weighted stacking PP-or PS-wave AVA gathers in the areas with relatively smaller and larger angles,respectively. We deduce the formula about the average reflection coefficients and the four combined variables of the elastic parameters,which shows that the strata elastic parameters can be inverted by PP and PS reflection coefficient equations at two average incident angles.We use three types of stratamodels with fluid to compare the average and theoretical reflection coefficients.It is shown that both the PP and PS average reflection coefficients are high-precision events after weighted stacking.We establish the target function for the joint inversion by the least square method.Compared to the conventional inversion method,the initial model input for the inversion does not need to be precise.We use the exact Zoeppritz equations to calculate PP and PS reflection coefficients during the forward modeling and adopt the first-order approximations during solving the model updating variations.We test the inversion method on the model consisting of a hard-contrast thin coal seam.The initial model is linear without any interface and the synthetic records are noisy,however the performance of the inversion is satisfied.We apply the inversion method to the field data.In the situation that the offset area is limited,the inversion method can inver

关 键 词：平均入射角 联合反演 PS波 反射系数 最小二乘 

分 类 号：P631[天文地球—地质矿产勘探]