Schlumberger

Technical Paper: Modern Sub-Basalt Seismic Imaging - Deepwater Realm Offshore Southwest India

Society: Other
Paper Number: P241
Presentation Date: 2012
 

Abstract

This paper describes contemporaneous efforts undertaken in the seismic imaging of sub-basalt features offshore the southwest coast of India particularly focused in the Kerala-Konkan Basin. Data for this basin study originates from a modern 3D seismic survey integrated with long regional 2D seismic lines and 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 deep-water petroleum systems, both along the Tertiary overburden above basalt and, below it, the critical imaging of the Mesozoic lithology. The modern marine 3D Q-surveys conducted with long spreads and processed with state-of-art migration algorithms brought in remarkable improvements for the imaging resolution and coherence of sub -basalt structures these interpreted by pairing images of pre-stack time and depth migrated lines.

Kerala-Konkan basin lies south of the Mumbai Offshore area, the main productive oil province of India. Key to the exploration of this vast deepwater region is the assessment of its petroleum systems in Mesozoic strata buried under late Cretaceous flood basalts. Regional geology re-constructions and interpretation of its Mesozoic depositional history was done through our set of regional lines that cover outer shelf, slope, rise and ocean basin providing insight on the nature of continental and oceanic crust layers of Mesozoic lithology under basalt. To focus on risked prospect plays several 3D surveys were carried on so that sub-basalt exploratory drilling locations could be derived from mapping of structural dip and fault seismic closures under basalt and associated stratigraphic traps.

Interpretation mapping of the PSTM-/PSDM paired images provides for new enhanced domain with 3D structure and stratigraphic features correctly placed in depth. The methodology of time/depth imaging allows for significant subbasalt recognition of structural planes, focuses faults paths displacements and rectifies horizons continuity. For the purpos e of seismic interpretation the sub-basalt velocity model derived from data also provides for better confidence on the structural dynamics of the seismic section.

In this paper we present results of seismic interpretation of an “over -under” modern data set acquired in the deepwater realm of Kerala-Konkan Basin. These data were integrated with ancillary geophysical regional lines for the purpose of understanding the nature of sub-basalt hydrocarbon prospects.

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DISCover Technique Delivers Improved Imaging

A zoomed-in section of the legacy (left) and DISCover (right) data. Data courtesy of ONGC.
Efficiently delivered 3D seismic data with an enhanced bandwidth, providing increases in low frequencies for deeper penetration and high frequencies for improved resolution.