India's Hydrocarbon Outlook – 2022-2023

77 DGH: 3 DECADES OF UNLOCKING INDIA'S HYDROCARBON POTENTIAL TheHimalayas are divided into five physiographic zones. The Foothills or the Sub-Himalaya (Paleogene- Neogene-Quaternary) has molasse sediments deposited in the Himalayan Foreland Basin (HFB). The Lesser Himalaya have the metamorphosed Proterozoic rocks in north, overlying the Tertiary rocks along the Main Boundary Thrust (MBT). The Higher Himalaya consists of the crystalline thrust sheets with Main Central Thrust (MCT) occupying the highest tectonic level. The MCT marks the southern boundary of the Greater Himalaya against the low-grade metamorphic rocks of the Lesser Himalaya. Tethyan Himalayan sediments are exposed on the back slope of the Greater Himalayan basement rocks. Topographically, the Tethyan Himalayan rocks form low-dipping mountains of high altitude and resemble the Tibetan plateau. The southern boundary of the Tethyan Himalayan metasediments is believed to be represented by the South Tibetan Detachment Fault/Thrust (STDT). The Tethyan Himalaya is made up of the Neoproterozoic-Eocene succession and it rests non-conformably over Central Crystallines. The Indus-Tsangpo Suture Zone representing rocks associated with the Suture lie between the Indian and Asian plates. The stratigraphic sequences comprise of a basement of igneous and metamorphic rocks over which the Proterozoic carbonate deposition took place. These formed the floor for the subsequent Cenozoic deposition to the extent of 10Km and also for the deposition of Palaeozoic-Mesozoic succession in the adjacent Potwar Plateau which are the extension of the litho-tectonic elements of the Jammu sub Himalayas. Based on earlier studies from 2D seismic multi-channel reflection data in Poonch-Rajauri area of J&K with Kohat- Potwar Plateau of Pakistan, Siwalik and Murree sequences are envisaged to be underlain by Eocene carbonates and Mesozoic-Paleozoic strata. Reflection events corresponding to these strata were observed to be of similar seismic characters and thickness of different sequences matched at both the places. Pre-Tertiary sedimentation took place in the Punch-Rajauri area and also to the north of major normal fault and is likely to have continued in the concealed Jammu-Pathankot-Dasuya graben in Punjab Plains. The stratigraphic sequence of foreland basin sediments in the Punjab plains comprises of granitoids and metamorphic rocks as their basement, overlain by Middle to Late Proterozoic sediments, dominantly made up of carbonates and unconformably followed by the Cenozoic sediments. Neo-Proterozoic- Infra-Cambrian-Paleozoic play are within the oil generation window and source rocks are shallow marine. Subathu rocks are within the oil generation window and source rocks are shallow marine to lagoonal. Dharamshala and Siwalik have Vaishnodevi limestone/shale and Subathu shales beingpotential source rocks/ facies, representing mostly fluvial with marine influences in the basal part of Lower Dharamsala. In general, fault closures along thrust plane form the likely entrapment while sandstone and limestone are the reservoir facies/rocks. Prospectivity The Himalayan Foreland basin has a total hydrocarbon inplace of 45 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 method is used on analogy of Kohat Potwar Basin (Pakistan). The basin has 10,000m envisaged sedimentary thickness. Amongst various datasets, semi-detailed geological mapping and reconnaissance traverse (300 LKM), aeromagnetic survey, 2D refraction seismic (3,696 LKM), GM data (14,913 stations), Magneto-Telluric data (5 profiles) and geochemical survey (analysis of adsorbed gas of 6,013 samples) have been incorporated. The 2017 resource reassessment study has incorporated 4,542 LKM of 2D seismic data, 29 drilledwell information. Gravity, 2Dseismic ,Wells and reports are of good quality while magnetic and geochemical data is of fair quality with no availability of 3D data. Reliability of the data is good. Potwar Basin of Pakistan has been used as analogue. Areal Yield method was adopted to assess the hydrocarbon resources. Main challenge faced was in seismic data mapping in thrust fold belt. Improved seismic is required for understanding of complex structures.