Subsalt imaging using TTI reverse time migration

Abstract

TTI depth imaging technology is routinely applied to image structures that lie beneath dipping, anisotropic overburden in the Canadian Foothills (Vestrum and Vermeulen, 2004), the North Sea (Hawkins et al., 2002), and offshore West Africa (Ball, 1995). Until now, ray-based migration algorithms served as the only choice for TTI imaging because upgrading ray-based imaging algorithms for TTI is straightforward and incurs minor additional computational cost. Unlike ray-based algorithms, TTI wave-based algorithms are difficult to formulate, and their implementations are often unstable and computationally intensive. Unfortunately, ray-based algorithms perform poorly in comparison to wave-based algorithms in imaging structures beneath a complex overburden such as the salt canopy in the Gulf of Mexico. However, the use of TTI imaging in this area is impeded by the lack of appropriate check shots and offset VSPs that can constrain anisotropic parameters.