VSP-CDP TRANSFORM IN ANISOTROPIC MEDIA

VSP reflection imaging techniques require accurate velocity models to effectively image the data. VSP to COP transform is usually applied in media described by homogeneous isotropic flat layers. In the presence of transversely isotropic layers (shales for example) or in the presence of fractures. isotropic velocity models may be inadequate and rcftections events may be positioned incorrectly. We propose a VSP to COP transform algorithm that treats properly the anisotropy of the medium and positions events in their proper reflection place. The algorithm, conceptually similar to the conventional ones. is based on anisotropic ray tracing in heterogeneous models described by a set of homogeneous layers. The anisotropic parameterS (elastic constants) that described such models can be estimated tomographically. By using anisotropic ray tracing, we calculate the reflections points and the traveltimcs of the corresponding events. Using these positions and traveltimes. reflection data in the (t,z) domain are transformed into data in the (x.z) domain, yielding an image of the medium of inter cSL