Bogra Fault

Bogra Fault one of the structural elements which have been active at different times and are located in the Western Foreland Shelf. Local influences such as rejuvenation of the Bogra fault might have favoured development of specific environments in relatively small areas. Movements along the Bogra fault led to the deposition of a huge sedimentary pile within the bogra graben. The Upper Miocene sequence encountered in Bogra-XI well drilled on the relatively uplifted block or at least in the range of the Bogra fault is 122m structurally higher than that in Kuchma-xi well. Additionally the 183m thick lowermost position of the Upper Miocene sequence in Kuchma is missing in the Bogra section due to non-deposition.

Seismic sections and particularly the results of biostratigraphic investigations on samples from Bogra-xi well and Kuchma-xi well provide evidence of the rejuvenation of the Bogra fault in Palaeogene and Neogene times. The down thrusted block, ie the Bogra Graben shows thicker development of the Sylhet Limestone than the uplifted segment. This implies vertical movements along the fault and subsidence within the Bogra Graben during deposition of the Sylhet Limestone. The Bogra Fault was active during Middle and Upper Miocene times as indicated by the increased thickness of Upper Miocene deposits within the Bogra Graben. The Upper Stable Shelf ie up dip of the Bogra Fault system is immature for hydrocarbon generation. On the other hand, the Lower Stable Shelf south of the Bogra Fault system offers several prospective plays, some of which have so far not been tested adequately by wells. The Tertiary strata deposited in the halfgraben south of the Bogra Fault contain coals. [Sifatul Quader Chowdhury]