Morphometry, bathymetry, gravity analyses and active tectonics of the petroliferous Gulf of Mannar in the Indian sector

The Gulf of Mannar has been producing natural gas in the Sri Lankan portion. This indicates that a detail geoscientific study is to be undertaken from the Indian section of the gulf, which can have a far-reaching implication in the Indian petroleum geoscience. In this work, morphometric and gravity studies were made from the gulf/basin near the onshore area, and bathymetric studies from the offshore portion of the Mannar basin within the Indian sector. Five watersheds were delineated based on study of eight geomorphic parameters on remote sensing images form the onshore area. Out of these watersheds 4 and 5 are found to be presently tectonically most active. Well-bore stability issue is to be considered while drilling these portions in future. We further prepared a regional contour map for the offshore study area, analysed the free air gravity data from the onshore area, and deduced the First Vertical Derivative (FVD) and Tilt Derivative Ratio (TDR). Bathymetric height gradually increases along the north-south trend from the coast region of the study area towards the central region, while the gravity magnitudes display a very sharp gradient (around 150 mGal). The gravity anomaly shows positive values at continental shelf (0–160 mGal), which includes parts of watersheds 1 and 3 and attains negative magnitude (up to −20 mGal) towards the basin area. Negative gravity anomaly in the offshore area may indicate presence of hydrocarbon but more studies are needed for confirmation. Apparently, almost a negative correlation (except watershed 1) between surface elevation and free air gravity magnitudes has been found.