3D beam‐based prestack redatuming for efficient subsalt velocity analysis

Abstract

Accurate velocity model building is a key in achieving high quality subsalt images. To reach this goal, we propose a target oriented and efficient velocity analysis methodology. Our methodology comprises of two steps. In the first step the surface data is downward extrapolated to a new datum plane using a beam based redatuming algorithm. In the second step we switch to a Kirchhoff or fast beam migration algorithm to perform the actual velocity analysis. The redatuming process has the advantage that it not only regularizes the subsurface data, but also reduces the data to a shorter recording times and a narrower offset range. Most importantly the resulting wave field at the new datum plane is generally much simpler in nature as supra salt sediment and top salt reflected as well as refracted arrivals have been removed-hence revealing the weaker subsalt events. A fast migration method can therefore be used to scan the subsalt velocity to determine the best image quality. As the beam based redatuming converts the irregular surface data into regular data at the datum level, it can also be used as a regularization tool.