India's Hydrocarbon Outlook – 2022-2023

70 DGH: 3 DECADES OF UNLOCKING INDIA'S HYDROCARBON POTENTIAL 20 exploratory wells, 16 wells in Ganga sub- basin and 4 wells in Punjab sub-basin were drilled. In Ganga sub-basin, 2 wells were drilled in Madhubani depression, 5 wells in the Gandak depression, 9 wells in Sarda depression. Ganga- Punjab basin is delimited in north and north-east by theHimalayanuplandalongHimalayanFrontal Thrust (HFT), where the folded and faulted outer Himalayan belt (Siwalik) structurally terminates against the Indo-Gangetic alluvial sediments. Southern limit is delineated by the Yamuna lineament along Bundelkhand massif, Vindhyan basin and Delhi-Sargodha Ridge. Munghyer- Saharsa Ridge mark the eastern boundary and Indo-Pakistan international border of Punjab and J&K is the Western limit. Delhi-Aravalli ridge is considered as the boundary between Ganga sub-basin and Punjab sub-basin. Ganga-Punjab basin hosts the Proterozoic and Tertiary sediments over the granitic basement. Ganga sub basin is a poly-history basin, marked by rifting during Meso-Proterozoic, platformal deposition during Neo-Proterozoic, passive margin sedimentation during Paleocene to early Eocene and opening up of foreland-basin during early Eocene, followed by deposition of Molasse sediments forming Siwalik Supergroup during Neogene. Among the most important structural elements that have been identified in this foreland basin, Aravalli Horst trends in northeast-southwest direction. There are transverse ridges and their associated spurs, which divide the Indo- Gangetic plain into prominent basinal lows. Structurally, Ganga sub-basin is subdivided into three depressions viz., (i) Sarda, (ii) Gandak and (iii) Madhubani, each separated by intervening basement ridges. Sarda Depression is aligned east-west and has a sediment thickness of more than 7,000m. Two prominent sub-depressions, Puranpur low and Bahraich low can be identified within it from GM data. Gandak Depression, located east of the Sarda has a sediment thickness of the order of 7,000-8,000m and Madhubani Depression lying east of the Gandak has a narrow graben with sediment thickness of more than 6,000m. Current views on the age of Ganga-Punjab basin are based on the recent biochronological data sets. Since long, the sediments of Ganga sub- basin were considered to be of Proterozoic age but studies by M/s ONGC extended the age of the sediments to Paleozoic age. Since Proterozoic sediments are present in the north (Himalayan Foothills) and south (Vindhyan basin), the sediments in the intervening Ganga basin are also expected to be of Proterozoic Eon. In Ganga sub-basin two speculative plays have been identified i.e. Neo-Proterozoic unconventional play and Middle Miocene conventional play. Whereas in Punjab sub-basin only one hypothetical play i.e. Middle Miocene Play is envisaged as only Tertiary sediments, resting directly over metamorphic basements. Ganga sub-basin Neo-Proterozoic play is unconventional tight gas play like Vindhyan play. Play fairway was delineated combining the thickness of Ujhani, Tilhar and Karnapur formations, which have source aswell as reservoir sequences. Intermediate shales and the tight reservoirs can act as seals, while both vertical and short lateral migration are envisaged. Middle Miocene play (Lower Siwalik) has been considered as a conventional play, where source rock indicates richness of organic matter and hydrocarbon generation potential, however initial geochemical results are inconclusive on maturity of organic matter. In absence of structural traps due to reduced tectonic activity, stratigraphic traps are primary exploration targets. Prospectivity The Ganga-Punjab basin has a total hydrocarbon inplace of 123 MMTOE, which is entirely undiscovered and potential for intense exploration. The basin has been assessed earlier during 1995-96 study along with 14 other basins. During 2017 Hydrocarbon Resource Assessment Study, Aerial Yield has been used on analogy of Vindhyan basin (Pre- Cambrian sequences) and Duarmara gas field of Assam (Tertiary sequences). The study has incorporated 19 wells of Ganga subbasin and 4 wells of Punjab subbasin. Besides, 2,251 LKM 2D seismic data and 706 LKM seismic refraction data from Punjab sub-basin along with 3D seismic data from Ganga sub-basin have been used. Other non-seismic data namely Aeromagnetic survey (130,700SKM), GM data (76,000 stations), MT