Sub-Basalt Mesozoic Imaging Offshore India

Roberto Fainstein, Chris Koeninger, Niranjan Banik, and Rolf Broetz
Regional Technology Center, WesternGeco, Bombay, India

New technologies in data acquisition, processing and interpretation have improved understanding of deeper stratigraphy offshore India particularly Lower Cretaceous and Mesozoic imaging. New technologies such as 3D pre-stack time and depth migrations are normative for 3D volumes.

Imaging of deeper sections offshore is paramount to better understanding of the underlying syn-rift sequences that contain most of the oil bearing source rocks. Exploration is active in all of the unexplored offshore basins. From these the Kerala-Konkan Basin in the south-west coast off India is most intriguing due to its large extent and un-explored status.

In the Kerala-Konkan basin primary source rocks are under thick flood basalts cover, these which might screen seal hydrocarbon migration from lower beds into its Tertiary traps. Processing of seismic data with acquired offsets up to 8400m of 2D over-under regional lines opened up the possibility of deep penetration of seismic energy uncovering the Mesozoic layers beneath the basalt blanket hence upgrading the deep-water prospectivity of the Kerala-Konka basin. Interpretation of regional 2D lines combined with 3D datasets have provided geologic models for the structuring beneath the basalt layer that may be confirmed through seismic inversion.

Herein we describe an experiment with this modern technique applied to the imaging of Mesozoic lithology of Kerala-Konkan basin. The technique takes advantage of the acquisition of the seismic wavefield at two depth levels, both on the source as well as the receiver side, a technique known as “over-under”. Upon data processing, the migrated stacks of the 2D over-under regional lines have revealed potential Mesozoic layers beneath the basalt blanket. These deeper seismic events are interpreted and map correlated for possible new petroleum systems in the Mesozoic offshore.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery