A review of hydrocarbon habitats in Bangladesh

Bangladesh, with approximately 25 trillion cubic feet (TCF) of gas initially in place and 15.52 TCF of initial recoverable reserves, and an average success ratio of 3:1, has emerged as a new hydrocarbon exploration frontier. The country occupies the major part of the Bengal Basin and is essentially located in a convergent-margin basin that owes its origin to the Early Cretaceous rifting of the Indian Plate away from Antarctica, the formation of the Indian Ocean (part of Palaeo-Tethys), and ultimately the collision of the Indian Plate with the Eurasian Plate. The Bengal Basin is filled with approximately 20km of mostly Tertiary siliciclastic sediments comprising a spectrum of facies including deep- to shallow-marine, deltaic and fluvial types. The presence of thick sequences of reservoir-quality sandstones coupled with organic-rich shales, and of different kinds of traps including broad anticlinal structures, makes the basin highly prospective for hydrocarbon exploration. Of the exploration wells (52 onshore; 12 offshore) so far drilled in Bangladesh, a total of 22 reported commercial discoveries of natural gas from sandstones in the Miocene-Pliocene Surma Group. The hydrocarbon potential of older sequences, especially the Eocene Sylhet Limestone and the Oligocene Barail Group, are not adequately known at present. However, initial indications (e.g. the presence of suitable source rocks, high-pressure zones, "dim" and "flat" spots and velocity sag in reef complexes in the Sylhet Limestone) tend to favour the hydrocarbon prospectivity of these sequences.