Two-way wave equation depth migration using one-way propagator extrapolation

Abstract

Two-way wave depth migration (TWDM) can achieve a wider imaging angle in media with significant lateral velocity changes and better imaging results for complex structures with high dip angles than in conventional one-way wave depth migration. Conventional one-way wave migration uses a boundary condition to approximately solve the second-order wave equation, leading to limited propagating angles and inaccurate imaging results, especially for complicated structures. Theoretically, a full-wave equation is of second order and requires two boundary conditions to solve it. The dual-sensor acquisition system can provide sufficient boundary conditions; however, it is challenging to acquire ideal, cost-effective, and factual seismic data, particularly in 3D seismic exploration. Overcoming these shortcomings, we propose a solution that uses conventional surface data to accurately estimate the wavefield at the second layer as another boundary condition. Based on the eigen-decomposition theory, a one-way propagator to suit arbitrary variant velocity on the surface is introduced.The conventional Fourier finite-difference (FFD) and generalised screen propagator (GSP) are utilised to perform the proposed TWDM schemes. The impulse responses proved that the proposed scheme using FFD and GSP operators had no limitation on the propagation angle. The single-shot migrated results in the flat model confirmed that the proposed schemes could achieve better amplitude-preserving performance than the conventional one-way schemes. The dip model showed that the proposed scheme was consistent with the characteristics of one-way wave propagators in imaging steep dippings. Imaging results of the Marmousi model further confirmed that the proposed scheme could obtain more accurate imaging sections for complex structures, especially for steep flanks and deep-seated anticlines. The application of actual dual-sensor seismic data demonstrated that the proposed scheme could achieve a higher imaging quality than the dual-sensor method.