Subsurface Modeling of Digboi‒Dilli Ghat Oil Bearing Structures (India) Using 2D Move

The first discovery of commercial hydrocarbon in India was in 1889 in a structural trap at Digboi in Assam. Ever since the discovery, geologists have mapped and modeled the subsurface structure of this 50 km long anticlinal fold-thrust belt. However, never before, the existence of a hanging wall syncline north of Jaipur anticline, near the Kusijan oil and gas field, was considered. In this paper, we have proposed a structural model for the regional fold-thrust structures that successfully explains the existence of this syncline adjacent to the Naga thrust. Trishear Fault Propagation folding followed by a complex breakthrough pattern of the thrust at later stages is proposed as most suitable model to explain the outcrop pattern and sub-surface data. We have prepared two northwest-southeast trending balanced structural cross sections using this kinematic model. Total shortening percentages across the southern and northern cross sections are estimated to be 44 and 30 respectively. A complementary play with locations of prospective boreholes is suggested. Based on the dip data in the hanging wall structures of Naga thrust, we predict medium- to small-scale concealed imbricate structures in the sub-thrust. These zones of local thrust imbrications may prove to be prospective leads for concealed petroleum traps.