According to Curray (1991):
Total sediment thickness beneath the [Ganges–Brahmaputra delta] southeast of the hingezone exceeds 16 km...
Considering a normal geothermal gradient and data for oil and gas formation, this suggests that at such the at some point we must have oil and gas reservoirs.
What could be a possible explanation why no such discoveries have been made so far in the region?
Reference: Curray, JR (1991). Geological history of the Bengal geosyncline. J. Assoc. Explor. Geophys. 12, 209–219.