CWP-683 A comparison of shot-encoding schemes for wave-equation migration Jeff Godwin & and Paul Sava Center for Wave Phenomena, Colorado School of Mines ABSTRACT In the last decade the seismic imaging industry has begun collecting data volumes with a substantial amount of data redundancy through new acquisition geometries including: wide-azimuth, rich-azimuth and full-azimuth geometries. The increased redundancy significantly improves image quality in areas with complex geology, but requires con- siderably greater computational power to construct an image because of the additional data and the need to use advanced imaging algorithms. One way to reduce the compu- tational cost of processing such datasets is to blend shot-records, using shot-encoding, together prior to imaging which reduces the number of migrations necessary for imag- ing. The downside to doing so is that blending introduces strong, non-physical, cross- talk noise into the final image. By carefully choosing the shot-encoding scheme, we can reduce the additional noise inserted into the image and maximally reduce the num- ber of migrations necessary. To find an optimal encoding scheme, we develop a theory of blended imaging that describes all shot-encoding schemes, and design a new class of encodings that use amplitude weights instead of phase-shifts or time-delays. We are able to use amplitude encoding to produce blended images of the same quality as pre- vious encoding schemes at a similiar computational cost. Additionally, we compare the results of amplitude encoding with the results from well-known shot-encoding schemes from previous work including decimated shot-record migration. In our comparison, we find that no single shot-encoding scheme is always better than others, and that deci- mated shot-record migration has some advantages over blended imaging. Overall, this work questions the potential for shot-encoding in standard seismic imaging workflows because blended imaging does not appear to justify its use by sufficiently reducing the cost of imaging, given the quality of the blended image. Key words: imaging, wave-equation, simultaneous source, blended 1 INTRODUCTION Today’s seismic exploration challenges include imaging areas with complex geology, such as salt domes and overthrust re- gions. The major issues for imaging areas with complex ge- ology are poor data quality and lack of seismic illumination due to the severe deformation of the seismic wavefield. One approach to resolve these issues is to obtain large amounts of redundant information from various acquisition directions via wide-azimuth or full-azimuth seismic surveys (Michell et al., 2006; Shoshitaishvili et al., 2006; Howard, 2007; Kapoor et al., 2007; Ting and Zhao, 2009). However, wide-azimuth surveys require significantly more time to acquire and even greater amounts of time to process due to the large amounts of data. Subsequently, the cost of acquiring and processing a wide-azimuth survey is significantly more expensive than the cost of a conventional survey. Additionally, the cost of imaging in complex geology is much greater because advanced imag- ing algorithms such as reverse-time migration must be used to better honor the kinematics of complex wavefields. There- fore, both the financial and computational cost of today’s large surveys is increasing at a rapid pace, but recent technological advances may allow us to reduce these costs by using better processing technologies and faster computers for imaging. One such technology is acquisition using simultaneous or delayed sources (Womack, 1990; Hampson et al., 2008; Berkhout et al., 2008; Beasley, 2008; Blacquiere et al., 2009). As the name implies, simultaneous sources are triggered at the