C-wave depth migration with topography CREWES Research Report — Volume 23 (2011) 1 Converted wave prestack depth migration from topography: a comparison Saul E. Guevara and Gary Margrave ABSTRACT Pre-stack depth migration is applied to PP and PS waves of a synthetic dataset, obtained using 2D elastic finite difference modeling with a geological model having structural features and topography. Two methods of migration, Kirchhoff and PSPI are applied directly from the topography. Correct depths were obtained however with different character in the images, which can be related to the migration algorithm and to the wave mode used. Also, statics correction to a horizontal datum followed by migration was compared with migration directly from topography, which showed that the statics significantly degrades the images. INTRODUCTION Converted-waves have promise to contribute important information to the hydrocarbon resources industry, as shown by many authors (e.g. Stewart et al., 2002). Simultaneously, structurally complex areas are of increasing interest to the industry. This work is intended to explore the improvement of the subsurface information content provided by imaging converted waves (known as PS waves or C-waves, and in the following identified with this last term)., which are recorded with the multicomponent method. Methods used currently by the industry for C-wave processing in time domain are based in relatively simple approximations (e. g. Tessmer and Behle, 1988); however, these have allowed successful applications (Stewart et al., 2002). Experience has shown that although it is possible to obtain a time image of the PP wave without too much knowledge of the geology, it is not so easy with C-waves. Thus, some authors have identified the close relation between the geological properties and the C-wave image, even for simple models (e.g. Thomsen, 1999). Besides that, identification of events of P- and C-waves coming from the same reflector is required, which can be easier in the depth domain. Therefore the depth migration methods present very attractive features for C- waves. Additionally prestack depth migration has been identified as more appropriate in complex areas and it has interesting properties related to AVO analysis. On the other hand many processing algorithms assume a flat surface. Elevation static corrections has been an usual method applied to approximatly adjust the data to a flat datum, however it has an implicit error and is less accurate in rough topography areas (Cox, 1999). Instead of static corrections, methods like migration from the rough surface or wave equation datuming (e. g. Beasley and Lynn, 1992) have been developed.. A test of migration algorithms is presented in this work. Synthetic data from a geological model with topography and complex structure are analysed. Methods specific to elastic wave migration have been proposed in the literature (e. g. Hokstad, 2000), however this work is an extension of the methods used for P-waves. Two depth migration