PRE-FEASIBILITY REPORT

The L-II PML Block, covering an area of 1524.08 Sq.Km, is located in the central part of Cauvery On-land, extending from Tulsapattinam and Vadatheru in the South, Flank on the East and Mattur-Pundi in the West. On the North is the contiguous areas of L-I block. The total area of L-II PML block is 1524.08 sq.km. PML has been granted for seven years w.e.f. 31.12.2012 to 30.12.2019.

GEOLOGICAL SEETING OF THE BLOCK

The L-II PML block encompasses three sub-basins of Cauvery Basin namely Tanjore, and Southern Part of Tranquebar Sub-basin.

Tanjore Sub-basin

The Tanjore Sub-basin is in the western most part of the Block. The Tanjore sub-basin is a NNE- SSW elongated half graben bounded on the East by the Pattukottai-Mannargudi ridge which separates it from Nagapattinam sub-basin and Eastern Ghat Metamorphics in the West.This sub-basin is an asymmetrical rift graben with the deepest part along the western margin forming a half graben morphology. The Vadatheru High is a elongated horst block in the southern part of the block, where presence of hydrocarbon is established. Parallel to this two more horst blocks are mapped at shallower level than Vadatheru Horst. These high trends are also expected to be the good locales for hydrocarbon exploration targets. In Vadatheru and Neduvasal fields are established areas for hydrocarbon in Basement Play in the Tanjore Sub-basin.

Nagapattinam and Southern Part of Tranquebar sub-basins.

Nagapattinam Sub-Basin : The Nagapattinam sub-basin is bounded by Pattukottai-Mannargudi ridge in the West and and Tirupundi highs to the East. Towards the North and North-East the sub- basin is bounded by the Karaikal High and towards south it opens in the Palk Bay Sub-basin. A prominent low called the Nagapattinam low separates the Karaikal High Flank area from the southern part of the sub-basin. A Cretaceous cut and fill feature runs across the sub-basin from West to East, almost along the Karaikal High. The ambient tectonic trend in the northern part of the sub-basin is NE- SW, with some NW-SE cross faults. But, the fault trends in the Eastern flank of Mannargudi high is NNW-SSE. The faults have played a key role in the structure building and in hydrocarbon migration and accumulation. Hydrocarbon has been established from different Formations ranging in age from Late Jurassic to Tertiary. The established hydrocarbon plays are Andimadam (Late Jurassic to Early Cretaceous), Bhuvanagiri and (Late Cretaceous), Kamalapuram and Niravi Formations (Tertiary). The Nagapattinam Sub-Basin hosts some of the main producing oil and gas fields of Cauvery Basin such as Kuttanallur, Nannilam Kamalapuram, Vijayapuram, Pallivaramangalam, Tiruvarur, Adiyakkamangalam Kizvalur, Nairmanam, Periyakudi, Kovilkalappal, North Kovilkalappal, Tirukkallar and Tulsapattinam.

Southern Tranquebar sub-basin : The L-II PML area also consists of the Southern part of the NE-SW oriented Tranquebar sub-basin. The portion of this sub-basin falling within the PML is bordered by the Karaikal High towards South and SE, and Portonovo horst in the North and plunge of Kumbakkonam horst on the West. On the West part of the South Tranquebar sub-basin, hydrocarbons have been established in Basement, Bhuvanagiri and Nannilam Formations in Pundi and Mattur fields in different plays.

In most of these sub basins, the shales within Andimadam Formation are the effective source rocks and have proclivity to generate both liquid and gaseous hydrocarbon. Basement controlled faults are thought to be the main conduit for migration of hydrocarbon. Top seal for Andimadam, Bhuvanagiri, Nannilam, Kamalapuram and Niravi Formations are provided by shales within Andimadam, Sattapadi, Kudavasal, Protonovo Karaikal and Shiyali Formations respectively.

Exploratory efforts are being carried out to evaluate the hydrocarbon potential of Late Jurassic, Cretaceous and post Cretaceous sequences before the completion of the PML cycle in December 2019 to convert maximum PML areas into long term ML. Several prospects for different plays have been identified in L-II PML block and are in the process of approval to be lined up for drilling in Tanjore, Nagapattinam and South Tranqeubar subbasin.

Technical Justification for exploration activities

Search for Hydrocarbons in this L-II PML Block led to discovery of Hydrocarbons in Narimanam, Tirivarur, Khizhavalur, Adiyakamangalam, Pallivaramangalam, Vijayapuram, Kamalapuram, Nannilam and Kuthanallur fields in North Nagapattinam; Pundi and Mattur fields towards the South of Kumbakonnam-Madanam high area; Kovilkalappal, Thirukallar, Periyakudi and Thulsapattinam fields in the south Nagapattinam area and Vadatheru and Neduvasal fields in Tanjore sub-basin. The Cauvery Bsin is a very complex poly-history basin with rifting history upto Albian and establishment of passive margin set up from Turonian onwards. Therefore the hydrocarbon play within the sedimentary sequences and the entrapment mechanisms are also complex ranging from structural, strati-structural and stratigraphic traps. The earlier focus of exploration in the block was on shallower Cretaceous and Tertiary plays. However, in the recent past two main plays namely Early Synrifts and Basement Play have come to the focus of exploration subsequent to the discovery of Periyakudy field in Nagapattinam Sub-basin in 2010 from within Early Synrifts (L-II PML) and discovery of hydrocarbons from Basement in Madanam, Pandanallur and Tirunagiri fields in the North Tranquebar Sub-basin of Block-I.(L-I PML). These discoveries have opened up vast vistas of exploration in the block as there are huge pile of early synrift sediments in the South Tranquebar, Tanjore and Nagapattinam Sub-basins. The deeper synrift plays falls in the high pressure-high temperature (HPHT) category and the Government has offered greater incentives for wells falling under this category. As on date there are 6 HPHT locations in the block which are lined up for drilling in near future. If successful, leads from these wells will be used to identify more locations under this category.

Efforts are being made to establish the extension of the established plays to other parts of the block and also to relook basement exploration on the Karaikal high and plunge areas in addition to discovering new plays to unlock the yet to find potential in this block before completion of the PML cycle so as to convert maximum PML area into long term ML. The drilling schedules are also planned accordingly and high priority wells are lined up for drilling. 40 locations are envisaged to be drilled in the coming years, based on the leads obtained from the drilling of available locations and from the interpretation projects planned both at Basin and various institutes of ONGC. These locations are likely to establish and accrete more reserves and will facilitate in opening up further areas for future exploration in L-II PML block.

TECHNO-ECONOMIC JUSTIFICATION FOR LOCATIONS

A. RIG PROPOSED TO BE DEPLOYED

The location is proposed to be drilled by E-760, E-1400 (BHEL Rig) and Type-III rigs, which are having capacity to drill to depth of 3000m, 4000m & 5500mrespectively.

B. INVESTMENT ANTICIPATED

The anticipated pre-drill cost of the wells planned & proposed which includes the PML fees, EIA, Stacking of the location, land acquisition, site preparation, G & G, PML fees, etc & the drilling cost works out to be around Rs 1498 crores.

JUSTIFICATION FOR ENVIRONMENTAL CLEARANCE

The exploratory efforts in the 7 years period of L-II PML granted from 31.12.2012 to 31.12.2019 for this block has been very encouraging. As on 01.09.2017, 16 exploratory wells have been drilled in L-II PML block. One well TVW-1 (TVWAA) is under drilling. Out of the 16 wells drilled, 4 wells are hydrocarbon bearing, 1 well needs further testing and HF and 9 wells are dry. Two wells namely NKK#11 and PM#8 are under evaluation for testing. These wells have shown encouraging indications during logging and drilling and are under evaluation for testing. These wells are likely to accrete some reserves.

As on 01.04.2017, total accretion in this L-II PML block has been 9.65 MMt. New pool has been discovered in Bhuvanagiri Formation in North Kovilkalappal field. In Periyakudi field, about 600m of hydrocarbon column has been encountered. This field has been monetized and put on production. Hydrocarbons have been established in Cauvery Basin right from Basement to as younger as Oligocene Formations. However a large part of this L-II PML block remains under explored especially for the deeper Synrift plays. With greater understanding of the basin from the various studies being carried by Basin group and other agencies, locations will be drilled to evaluate the hydrocarbon potential of L-II PML block.

In view of the above it is proposed to obtain the environmental clearance at the earliest so that the evaluations of the block could be carried out. The total area proposed for environmental clearance amounting to 1524.08 SKM (present area after all relinquishments.)