Non-Hyperbolic Moveout Multi-Parameter Anisotropic Tomography

Abstract

Application of anisotropy has proved to be mandatory for the improvement of imaging quality, at the point that nowadays the introduction of TTI anisotropy has become a standard for PSDM projects. These advancements pose new challenges to migration velocity analysis, and the time domain approaches commonly used for the estimation of anisotropic velocity parameters are no longer enough to satisfy imaging accuracy requirements. A depth-domain estimation technique is proposed, which is completely based on PSDM and on the classic CIG (Common Image Gather) flattening principle. One of the key aspects is the use of a robust automatic non-hyperbolic moveout picking algorithm, which is applied on the depth migrated CIGs and provides the correct description of the complete residual moveout: this allows the joint tomographic inversion of two anisotropic velocity volumes, which are able to properly account for the non-hyperbolic residual moveout behavior at both short and long offsets. The method has general validity and it can be applied to any imaging project; it is also particularly stable when applied to multi-azimuth acquisitions. This approach can obtain a good anisotropic focusing velocity if the data contains sufficiently large offsets, although still one or more wells are needed to constrain vertical velocity.