STRUCTURAL MODELLING BASED ON SEISMIC REFLECTION PROFILES AND HYDROCARBON POTENTIAL, TRIPURA FOLD-THRUST BELT

Abstract

Tripura region is a part of the Assam-Arakan fold belt. It has a complex tectonic history and thus structurally very critical to understand the geometry and kinematics of the structures.. As other fold-belts, it contains thrusts and thrust-related folds. Field work in this area is quite difficult due to inhospitable and hostile conditions and in part due to political instabilities. So, the details of the structures in this region are yet to be fully understood. Tripura fold-thrust belt is known to be rich in hydrocarbon. So the area needs to be studied in more detail to explore more and more hydrocarbon and not to let any pooi skipped due to improper understanding of the structures by making the proper location of wells. This needs the cross sections of the area to be prepared in the tectonic transport direction, as the structures are better quantifiable when viewed in dip direction. Cross-sections can be prepared from surface map data and/or seismic data. When seismic data are poor and detailed surface mapping is difficult in an area then, the one and only solution for this is, modelling and balancing sections knowing kinematics of fault-related folds. This needs constructing cross-sections from incomplete data by interpolation and extrapolation and several iterations. The testing of any of the interpretations is done by validating the sections. The structures must follow the rules of kinematics and geometric principles. Both forward modelling and reverse modelling are involved to model the structures and construct a balanced cross-section. Modelling and restoration of sections reveals many interesting facts about the structures like evolution, fracture formation and fluid migration paths, possible traps and shortening which are crucial for structural analysis and hydrocarbon exploration. Structures in Tripura region are mostly Detachment folds having straight limbs and broad hinges which follow parallel fold geometry. The folds are asymmetrical and having a very low amplitude (1.5-2 km) on long wavelengths (10-11 km). A total shortening of 2-3% is accommodated by folding within the sections. The detachment lies within or at the base of the lower Bhuban formation. These folds form the structural traps for most of the hydrocarbon reserves in this region.