Elastic reverse time migration in VTI medium based on P/S wave-mode decoupling and upgoing/downgoing wavefield decomposition
LI Yingyan1, ZHANG Lele2, CHEN Gang1, LI Wei1, ZHANG Fang1, SONG Siyu1
1. Research Institute of Exploration and Development, Xinjiang Oilfield Company, PetroChina, Karamay, Xinjiang 834000, China; 2. Unconventional Petroleum Research Institute, China University of Petroleum(Beijing), Beijing 102249, China
Abstract:Elastic reverse time migration in VTI media can effectively reveal the underground stratum structure,and thus has become one of the popular imaging methods. In this paper,firstly,the Christoffel equation in VTI medium is constructed,and the polarization direction vectors of P-wave and S-wave are obtained by solving the equation. According to the Helmholtz decoupling principle,the anisotropic elastic wavefield is projected onto the polarization direction,and the wavefield decoupling formula of P/S wave in VTI medium is obtained. Then,the normalization term in the P/S wave decoupling formula is approximated by the first-order Taylor expansion,and an efficient P/S wave decoupling method suitable for any complex medium is obtained and applied to the reverse time migration of elastic waves. In addition,low-frequency noise and imaging artifacts seriously affect the imaging quality of reverse time migration. The former is caused by the imaging of the same path wavefield,and the latter is caused by the correlation between the upgoing wavefield of source and the downgoing wavefild of the receivers. Therefore,the upgoing/downgoing wavefield separation imaging conditions are introduced to the VTI elastic wave inverse time migration,a set of imaging processes including P/S wave-mode decoupling and upgoing/downgoing wavefield separation,which effectively suppresses the low-frequency noise and crosstalk artifacts,and improves the imaging quality. Finally, the imaging results of simple and complex models validate the effectiveness of the method.
李映艳, 张乐乐, 陈刚, 李维, 张方, 宋斯宇. 基于P/S波解耦和上下行波分离的二维VTI介质弹性波逆时偏移[J]. 石油地球物理勘探, 2023, 58(3): 651-659.
LI Yingyan, ZHANG Lele, CHEN Gang, LI Wei, ZHANG Fang, SONG Siyu. Elastic reverse time migration in VTI medium based on P/S wave-mode decoupling and upgoing/downgoing wavefield decomposition. Oil Geophysical Prospecting, 2023, 58(3): 651-659.
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