Reverse time migration: An evolving imaging technology for solving difficult geological problems
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Reverse-time migration (RTM) based on directly solving the two-way wave equation provides a natural way to deal with large lateral velocity variation and imposes no dip limitations on the images. It is considered to be a method of choice for imaging complex subsurface structures and can adapt to different acquisitions, such as marine streamer, land, OBC/OBN (ocean bottom cable/node), VSP (vertical seismic profile), etc. . In this review paper, we will introduce the applications of RTM and focus on the latest RTM developments: anisotropy RTM and RTM 3D angle gathers.
Wide-azimuth data provides better illumination in complex areas and better noise cancellation. The additional azimuthal information in the datasets has also revealed anisotropy effects that are not apparent in narrow-azimuth data. Motivated by the surge of anisotropic data processing, a TTI (tilted transversal anisotropy) RTM technique was commercialized and has been used worldwide. Recently, more complicated imaging method, tilted orthorhombic RTM has been developed which further enhances our ability to image complex faulting geology.
3D angle domain common-image gathers (ADCIGs) retain the localized subsurface information with respect to azimuth and reflection angle and take care of anisotropy in the migration medium. The gathers from RTM greatly help to derive anisotropy parameters and subsalt velocity fields. They also provide a universal solution for imaging and model building for VSP, OBC/OBN and other unconventional acquisitions. In addition to tomographic applications, 3D ADCIGs can be used to evaluate subsurface illumination and stack optimization for WAZ data.
AAPG Search and Discovery Article #90160©2012 PAPG/SPE Annual Technical Conference, 3-5 December 2012, Islamabad, Pakistan.