Seismic Mapping of the Fenchuganj Structure, Surma Basin, Bangladesh.

English Abstract:

The Surma Basin is a sub-basin of the Bengal Basin occupying the northeastern part of Bangladesh. It is the prime hydrocarbon producing region of Bengal Basin. The Fenchuganj structure is located along the eastern margin of the Surma Basin. This present work comprises the seismic, gravity, magnetic and well data for interpreting the subsurface geology, structural configuration and tectonics of the Fenchuganj structure. The research also involves integrated interpretation of gravity and magnetic data to delineate the subsurface structural condition of the Surma Basin and its surrounding region. In order to interpret the study area, five seismic sections have been considered. Based on the analysis of the sections and correlation with well data, four reflecting horizons are marked, viz., top of Lower gas sand, Bhuban Formation, Bokabil Formation and Tipam Formation. Time and depth contour maps of these four horizons are constructed using the two way travel time of the sections and T-Z curve of the study area. Preparation of subsurface geological maps and interpretation of subsurface features suggest that the Fenchuganj structure is a reversibly faulted, NNE-SSW trending assymmetrical anticline with sharp dip in eastern flank than western. The seismo-stratigraphic study of the area furnish three formations- Bhuban, Bokabil, and Tipam. An attempt has been made to analyze the gravity and magnetic data to configure the subsurface structural features of the Surma Basin and adjoining areas. It is an east-west trending oval shaped basin and is characterized by significant gravity low. The upward continuation and second vertical derivative (VZZZ) methods have been used to enhance residual gravity effects. Regional and residual anomaly maps for gravity field continued to 7.5km, 10km and 15km have been prepared. The three regional anomaly maps show almost similar structural configuration of the basin. Residual anomaly maps are characterized by some positive effects, possibly related with positive density contrast. Considering the findings of this study, the further investigation (3-D seismic survey, advanced software interpretation) can give more valuable information about real subsurface structure and hydrocarbon occurrence in this area.