AVO and Anisotropy from Logs and Walkaways

Abstract

AVO (Amplitude Versus Offset) is the seismic technique used for mapping lithology, and modelling is an important step for successful AVO interpretations. Shear velocity measurements are essential, since AVO attempts to exploit the elastic (as opposed to acoustic) nature of seismic wave propagation. A property of seismic wave propagation not often considered is anisotropy. This is probable because the magnitude of the anisotropy has been difficult to measure, and its effect on AVO is not widely known. New technology is helping to improve AVO modelling. Dipole source shear logging tools can now measure very slow shear velocities, increasing the range of applicability of AVO, and new borehole seismic techniques can measure anisotropy. When integrated, these new measurements provide more detailed information about the elastic moduli that govern wave propagation, and bring the possiblity for greater reliability in AVO interpretation. The effect of anisotropy on AVO is found to be significant and may lead to misinterpretations of AVO anomalies.