Tilted orthorhombic imaging of full-azimuth OBC data offshore Trinidad

Until quite recently it was common practice to apply isotropic imaging for depth migration projects, but now most projects are performed using TTI anisotropic imaging. This has greatly improved results both in terms of image quality and better well ties. It is now understood that anisotropy is found everywhere, and depth imaging and velocity model building workflows and algorithms have progressed to the point where TTI anisotropy is now standard procedure. Today’s new challenge is azimuthal anisotropy, which is seen on seismic projects around the world, and which is of great interest because it is usually related to fractures or stress. However azimuthal anisotropy is normally ignored for several reasons. For example, azimuthal anisotropy is often perceived to be insignificant. Wide-azimuth data that can resolve azimuthal anisotropy is often not available. Also, resolution of azimuthal anisotropy adds significantly to the complexity of velocity model building. In this paper we describe how significant azimuthal anisotropy was discovered in the Columbus basin, offshore Trinidad, in the course of velocity model building work on the BP Trinidad and Tobago ISS OBC project and how orthorhombic model building and imaging is being applied to produce a superior image.