Outcrop analogy with the subsurface geology and hydrocarbon prospectivity of Jaintiapur and adjacent areas in North-East Bangladesh

Abstract

The availability of hydrocarbons in the eastern part of Bangladesh indicates the presence of active petroleum systems in the Bengal basin. Although extensive research has been conducted in the Surma basin, the correlation between structural configuration, tectonostratigraphic framework, and hydrocarbon potentiality in the basin including Jaintiapur area has not yet been established. In this study, the hydrocarbon prospectivity of Jaintiapur and the adjoining Dupigaon area has been characterized through outcrop analogy with the subsurface interpretation of seismic data along L13-01, PK-SY-5, and L13-03 lines. The main three megasequences have been recognized based on sequence stratigraphy in the Sylhet region utilizing outcrop, seismic, and well-log data. The exposed Tertiary and Quaternary formations of Jaintiapur and adjoining areas can be classified into eleven litho-stratigraphic units. Detailed facies analyses indicate that these rock units were deposited in fluvial, deltaic, and shallow marine environments. The subsurface lithology of the study area has been inferred from the petrophysical data obtained from Sylhet-7, Kailashtila-4, and Jalalabad-1 wells. Jaintiapur area lies in a tectonically complex province and is controlled by the Dauki Fault System. Folding and faulting represent intense tectonic deformation in the area. Detailed analyses of surface and subsurface geology indicate that faults pass along the rivers and transverse faults segment the reservoirs. A total of seven horizons have been interpreted using Petrel software. The seismic attribute analysis identifies leads and prospects based on transverse faults and amplitude anomalies with distinct bright spots at the PK-SY-5 line. From seismic interpretation, attribute analysis, and lithofacies distribution of Sylhet-7 well and its surround area in the Dupigaon, it seems that same gas bearing sand. Gas sands of the Sylhet-7 well indicate the possibility of gas/oil in the equivalent sedimentary sequence in the Dupigaon structure as this area is located close to and more down-dip towards the kitchen area.