Reverse time migration of multiples for subsalt imaging

Some hydrocarbon reservoirs are trapped beneath salt bodies, where seismic imaging is greatly challenged due to poor illumination. Multiple reflections have different propagation wave paths from primary reflections and thus can be used to complement the illuminations where primary reflections from beneath the salt are not acquired. Consequently, migration of multiples can sometimes provide better subsalt images compared to conventional migration which uses primaryreflectionsonly.Inthispaper,weproposetomodifyconventionalreversetimemigrationsothatmultiplescanbeused asconstructivereflectionenergyforsubsaltimaging.Thisnew approach replaces the impulsive source wavelet with the recorded data containing both primaries and multiples and uses predicted multiples as the input data instead of primary reflections. In the reverse time migration process, multiples recorded on the surface are extrapolated backward in time toeachdepthlevel,andtheobserveddatawithbothprimaries and multiples are extrapolated forward in time to the same depth levels, followed by a crosscorrelation imaging condition. A numerical test on the Sigsbee2B data set shows that awidercoverageandamorebalancedilluminationofthesubsurface can be achieved by migration of multiples compared with conventional migration of primary reflections. This exampledemonstratesthatreversetimemigrationofmultiples might be a promising method for complex subsalt imaging.