Abstract

Sub-coal imaging is one of major exploration objectives in Lakwa-Sonari field. Apart from coal, Sonari field has a high velocity zone above coal that causes structural distortion of sub-coal sequences. High impedance contrast of Barail coal causes a low illumination of underneath source rock and Lower Barail Sands (LBS). So, successful sub-coal imaging demands a reliable estimation of interval velocity model from poorly illuminated reflection signal and a migration algorithm to reduce coal generated wavefield distortion. In this work formation dependent constraint dix inversion and full azimuth reflection tomography is used for initial modelling and refinement of depth interval velocity. The final velocity model has coal imprints and clearly brought out high velocity zone above coal in Sonari field. Multidimensional local angle domain wavefiled decomposition, specular and diffraction imaging is then carried out for migrated wavefield separation. Specular stack shows enhance reflection continuity of sub-coal sequences and diffraction stack delineates sub-surface discontinuities. Final image has improved continuity of sub-coal source rock Kopili, Lower Barail Sands (LBS) and Basement. Sub-coal structural changes in Sonari is also clearly addressed and verified with well data.