Reverse-time Migration Of Marine Free-surface Related Multiples

In marine seismic exploration,the conventional reverse-time migration(RTM)algorithm suppresses surface-related multiples as noise,and imaging only with the primary.When the underground geological structure is relatively complex or the array geometry of geophones or shots are sparse due to objective factors,and the illumination of primary cannot meet the imaging requirements,more effective imaging algorithms are needed to explore the additional underground interface information contained in original seismic record.And surface-related multiples with longer propagation path and smaller transmission angle than primary,its illumination range is wider,illuminance is more balanced,which can provide additional illumination.And reverse-time migration algorithm based on two-way wave equation without being limited by the underground structure angle and migration aperture,imaging with high precision.So reverse-time migration of surface-related multiples have important research significance in improving the imaging quality.In this paper,reverse-time migration of surface-related multiples is studied.Firstly,realize the forward simulation calculation of primary and surface-related multiples based on staggered grid finite difference acoustic wave equation and elastic wave equation,and solve key problems such as boundary absorption,which provides the data basis for the subsequent imaging research.After that,for the surface-related multiples imaging with the two observation systems of sea surface excitation,seabed reception and sea surface reception,different processing schemes were studied separately: the seabed received data was subjected to a dual-detection matched filtering method for surface-related multiples separation,imaging with mirror migration of reverse-time migration.For the data received at the sea surface,SRME method is used to predict surface-related multiples and two different surface-related multiples reverse-time migration algorithms are used for imaging.In the imaging process,in order to solve the problem of low-frequency noise in the reverse-time migration profile,the Laplace operator is used to effectively suppress the generation mechanism by analyzing its mechanism.Through a series of numerical experiments from simple to complex models,the theoretical verification of the intermediate process of migration and the imaging effect has been carried out.Finally the reverse-time migration imaging results of surface-related multiples are compared with the imaging results of conventional primary reverse time migration.Numerical experiments show the feasibility,effectiveness and applicability of surface-related multiples imaging for complex models.The imaging results provide a wider imaging range and more balanced illumination of the underground interface,which verifies the theory of reverse time migration with surface-related multiples meets the requirements of high-precision imaging in seismic exploration.