3-D Prestack Time Migration – an Application to the Ravva 3-D Dataset, Offshore India

The Ravva oil and gas field is located offshore eastern India in the Krishna-Godavari Basin. Command Petroleum (India) Pty. Limited was granted operatorship of the field in October 1994 by the government of India, on behalf of a Joint Venture consortium that includes Oil and Natural Gas Corporation (ONGC) Ltd, the Indian national oil company; Videocon Petroleum Ltd; and Ravva Oil Ltd (Marubeni).

One of the first geophysical projects to be initiated in the development plan was reprocessing of the Ravva 3-D seismic dataset, acquired in early 1990 using a single streamer/single source configuration. The geography of the coastline and the shallow water depths in the area (<20 m) required a shooting direction that was predominantly in the strike direction but somewhat oblique to the main structural elements of the field.

This reprocessing project was initiated to achieve an optimum dataset for siting of the development/exploration wells over the next two to three years. Recent developments in computer hardware and the applications to 3-D seismic data processing have allowed the implementation of 3-D prestack migration to develop into a usable process for the practising explorationist.

The reprocessing project is described, with particular emphasis on the testing and analyses that led to use of 3-D prestack time migration to image the data volume. Examples show the improvements in stacking velocity definition and seismic imaging that have been achieved using 3-D seismic processing techniques that were not practicably available when the dataset was initially processed in 1990.