Benefits of pre-stack time migration in model building: a case history in the South Caspian Sea

A study of sub-basalt depth imaging using the local Radon attributes on the Erlend Tertiary volcanic complex - North of Shetland, UK

“…Along the PSPPSP path, a wave converts from S to P upon exiting the basalt and from P to S upon re-entering the basalt (Purnell, 1992). Dix inversion of root-mean-square (RMS) velocities and subsequent time-to-depth mapping, as suggested earlier (Robein & Hanitzsch, 2001). From inspection of preliminary results (not shown), we concluded that a major problem of building a velocity model for data such as these is the accurate mapping of the whole volcanic succession and the estimation of sediment velocities beneath the basalt structure.…”

“…The velocity model building for prestack migration in the area has two equally important tasks -the preliminary interpretation of the complicated PIVLs and the sediment velocity changes around and beneath these units. Following Robein and Hanitzsch (2001), RMS velocity analysis is initially applied to the CMP data based on the velocity approximation…”

“…Once V stac^ has been determined during pre-processing, the pre-processed subsets are migrated several times, using conventional Kirchhoff PSTM (e.g. Robein & Hanitzsch, 2001) for major wave types identified during pre-processing, as outlined by Barzaghi et al (2002). We begin with a smooth 2D model for which we search the principal reflections after PSTM has been applied with the velocity V m i g = V s t a ck-This leads in general to non-flat image gathers and requires additional (e.g.…”

Special Topic: Integration

“…Therefore, an interpretation-driven velocity model was developed for the prestack depth migration and was subsequently refined using the iterative process outlined. Improved structural imaging can be achieved by performing velocity analysis after pre-stack time migration (see for example Robein & Hanitzsch 2001). Here we extend this concept (of migration before velocity analysis)…”

“…Pre-stack depth migration of the seismic data is used to determine such velocity depth models. The idea of migrating seismic data in order to determine velocity models is not a new concept (see for example , Deregowski 1990;Robein & Hanitzsch 2001).…”