Hydrocarbon prospects across NarmadaeTapti rift in Deccan trap, central India: Inferences from integrated interpretation of magnetotelluric and geochemical prospecting studies K.K. Abdul Azeez * , T. Satish Kumar, Sharana Basava, T. Harinarayana, A.M. Dayal National Geophysical Research Institute (Council of Scientific and Industrial Research), Uppal Road, Hyderabad 500 007, India article info Article history: Received 2 April 2010 Received in revised form 7 November 2010 Accepted 9 January 2011 Available online xxx Keywords: Deccan flood basalt Magnetotelluric Geochemical Hydrocarbon abstract As the Mesozoic sediments contribute most of the oil and gas reserves of the world, we present an integrated interpretation approach using magnetotellurics (MT) and surface geochemical prospecting studies to demarcate hydrocarbon prospective Gondwana (Mesozoic) formations underneath the Deccan flood basalts of Late Cretaceous age across NarmadaeTapti rift (between Bhusawal and Barwah) in Central India. The MT interpretation shows deep (w5 km) basement structure between southern and central part of the MT profile however, it gradually becomes shallower to either ends of the profile with a predominant basement depth reduction in the northern end compared to the southern end. The geophysical results suggest thick (2e3.5 km) Mesozoic sediments in the area characterized by deep basement structure. The geochemical analysis of the near surface soil samples indicate higher concen- trations of light gaseous hydrocarbons constituents over the area marked with thick sub-basalt Mesozoic formations. Analyses of the geochemical data imply that these hydrocarbons are genetically related, generated from a thermogenic source and these samples fall in the oil-producing zone. The temperature edepth estimations in the region supports favorable temperature conditions (80e120  C) for oil generation at basement depths. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Delineation of sub-basalt hydrocarbon prospective zone has been a very challenging task as the seismic technique, the highly effective and most preferred tool for hydrocarbon exploration, is hampered by its inherent weakness in resolving the low velocity structures (such as sediments) underlying a heterogeneous high velocity layer. Hence, though a significant part of the global hydro- carbon reserves are estimated in sub-basalt sediments, these prospective hydrocarbon targets are poorly explored (Rohrman, 2007). In such complex geological settings, where seismic inter- pretation is limited, alternative/complementary sub-surface infor- mation can be obtained from other geophysical methods, such as gravity, magnetic, and electromagnetic. More success has been found with an integrated approach in which integrated sub-surface models are derived from the joint interpretation of different geophysical data sets, such as seismic, gravity, magnetic, and mag- netotellurics (Young and Lucas, 1988; Chakravarthi et al., 2007; Pandey, et al., 2009). Though not often, geophysical and geochem- ical prospecting methods are used together to reduce the inherent risk in exploration as the later seeks surface or sub-surface evidence of vertical migration of hydrocarbons (Eventov, 2000). The central Indian shield is a major basalt covered region resulted from the Late Cretaceous/Tertiary Deccan volcanism. Prior to this volcanic activity, the region has experienced intense tectonic changes since Precambrian time, creating major graben structures and Mesozoic (Gondwana) sediments concealed under Deccan volcanism (Biswas, 1982, 1987). The signatures of these sub-basalt sediments are mapped in seismic studies along a few profiles across central India (Kaila et al., 1985; Kaila, 1988). The seismic studies were primarily focused to understand the deep crustal structure in central Indian region and some of the seismic observations, particularly at shallow depths, are contradicted based on important ground geological observations (Nayak et al., 1986). The magnetotelluric (MT) method, with its remarkable improvements in data acquisition, processing, and numerical modeling in the recent years, is a viable tool for hydrocarbon exploration (Unsworth, 2005). This technique is extremely useful in * Corresponding author. Tel.: þ91 40 23434711; fax: þ91 040 27171564. E-mail addresses: azeez@ngri.res.in (K.K. Abdul Azeez), satishthadoju@gmail. com (T. Satish Kumar), bsharan@gmail.com (S. Basava), thari54@yahoo.com (T. Harinarayana), dayalisotope@yahoo.com (A.M. Dayal). Contents lists available at ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo 0264-8172/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpetgeo.2011.01.003 Marine and Petroleum Geology xxx (2011) 1e10 Please cite this article in press as: Abdul Azeez, K.K., et al., Hydrocarbon prospects across NarmadaeTapti rift in Deccan trap, central India: Inferences from integrated interpretation of magnetotelluric and geochemical prospecting studies, Marine and Petroleum Geology (2011), doi:10.1016/j.marpetgeo.2011.01.003