Chapter 1 - Introduction

Abstract

Passive continental margins are basically formed by the process of continental rifting (either by active/passive rifting) and constitute nearly half of the present-day world continental margins. Several other processes such as secondary convection, mantle lithosphere delamination, magmatic accretion/crustal underplating, and sedimentation may modify the lithosphere giving rise to wide variations in structure and geometry of the passive margins. The evolutionary process of the passive margins could be broadly divided into two main phases: an initial “rift phase” which is prior to the breakup of the continent and “drift phase or post rift phase” which occurs subsequent to the onset of seafloor spreading. They represent a vast exploration domain with huge repository of sediments and host a major chunk of the world's giant hydrocarbon discoveries. The Peninsular India has nearly 7500-km-long coastline, and the coastal as well as offshore areas are characterized by vast sedimentary cover with thick pile of sediments. The continental margin extends on either side of the Indian Peninsular shield and is referred to as the Eastern Continental Margin of India (ECMI) toward the Bay of Bengal and the Western Continental Margin of India (WCMI) toward the Arabian Sea. As plate tectonic setup provides varying habitats of petroleum, all major sedimentary basins in India have been grouped by earlier workers (Biswas et al., 1993) under three main settings with further subclassification: (i) intracratonic, (ii) rifted, and (iii) orogenic settings. However, based on their status and success ratio, the Directorate General of Hydrocarbons (DGH) has divided them into four major categories: (i) proven commercial productivity, (ii) identified prospectivity, (iii) prospective basins, and (iv) potentially prospective. Further, the deepwater area beyond 400 m water depth up to the EEZ forms a separate category and is considered highly prospective. The historical background of exploration scenario in India and subsequent developments in policy as well as technological advancements have led to increased hydrocarbon exploration activity of the Indian offshore basins, and some of these aspects are highlighted in this chapter.