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Sub-Basalt Geology Deepwater Offshore India

Fainstein, Roberto *1; Kalra, Rajesh 1
(1) WesternGeco International Limited, Mumbai, India.

This paper describes the geophysics imaging of sub-basalt features offshore India, these off the west coast Kerala-Konkan Basin and the southern tip off India. Data originates from regional 2D seismic lines and modern 3D surveys these were integrated with joint regional investigations comprising gravity, magnetic, electro-magnetic and MT data to form the basis for the geological assessment of the key components of Deepwater petroleum systems, both along the Tertiary overburden above basalt and, below it, the critical imaging of the Mesozoic lithology. The modern marine 3D surveys conducted with long spreads and processed with state-of-art migration algorithms brought in remarkable improvements for imaging resolution and coherence of sub-basalt structures these were interpreted by pairing images of pre-stack time and depth migrated lines.

Kerala-Konkan basin is a vast deepwater un-explored frontier region that lies south of the Mumbai Offshore area the main productive oil province of India. The Mesozoic strata of Kerala-Konkan basin is buried under the late Cretaceous flood basalts of the Deccan Traps event that occurred at the Cretaceous-Tertiary boundary. Regional lines cover outer shelf, slope, rise and ocean basin providing insight on the nature of continental and oceanic crust layers of the Mesozoic lithology under basalt. To focus on risked prospect plays with upside drilling potential coherency amongst sub-basalt strata needs be represented by interpretable structural prospect closures, and by stratigraphic channels and pinch-outs which are delineated by pattern recognition and seismic attributes analyses.

Interpretation mapping of the PSTM/PSDM paired images provides for correct placement of structures in depth. Furthermore this methodology focuses faults paths displacements and rectifies horizons continuity. For the purpose of seismic interpretation the sub-basalt velocity model derived from data provides for better confidence on the structural dynamics of the seismic section.

This paper presents remarkable sub-basalt imaging results from modern data sets in the deepwater realm of the Kerala-Konkan Basin. These were integrated with ancillary geophysical regional line interpretations for the purpose of understanding the nature of sub-basalt hydrocarbon prospects.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California