Evaluation of Travel Time Approximation Methods of Prestack Time Migration for Improving the Subsurface Image: A Case Study from Cauvery Offshore Basin, India

In this paper, curved-ray travel time approximation, paired with the Constrained Velocity Inversion (CVI) technique, is used in prestack time migration to enhance subsurface imaging in the Cauvery Offshore Basin, India. Traditional travel time approximation approaches based on 2nd-order and 4th-order provide travel time errors at far offset in the migrated gathers. The curved-ray travel time approximation was adopted to overcome this limitation. Travel time approximations for curved ray migration require interval velocities usually inverted from RMS velocities using simple Dix inversion during Prestack time migration. However, Dix-type inversion could create pitfalls in interval velocities because data-driven RMS velocities are sensitive to noise in seismic gathers. This study applied CVI to estimate interval velocities instead of dix-type inversion, ensuring a stable and geologically plausible solution. These interval velocities are reviewed, and formation-based smoothing is applied before estimating travel time using curved-ray approximation for Prestack time migration. Thus, it provides an option to do quality analysis for interval velocities before application prestack time migration. From a comprehensive comparison of results, curved-ray travel time approximation with CVI-based migration has provided a better subsurface image than with 2nd-order/4th-order travel time approximation-based migration in identifying geological events such as dipping events, faults, and fractures.