The Directorate General of Hydrocarbons (DGH) divides the sedimentary basins of India into four categories based on their proven hydrocarbon potential, maturity, and commercial production status. India possesses 26 sedimentary basins covering a total area of approximately 3.4 million square kilometers across onland, shallow water, and deepwater regions.
Category I Basins (Proven Commercial Production)
These basins possess established commercial production of crude oil and natural gas. They hold the bulk of India’s producing fields.
- Basins Included: Cambay, Assam Shelf, Mumbai Offshore, Krishna-Godavari (KG), Cauvery, Assam-Arakan Fold Belt, and Rajasthan.
- Geological Characteristics: Predominantly Tertiary and Cretaceous sedimentary sequences with high organic matter maturation.
Category II Basins (Identified Hydrocarbon Accumulation)
These basins have known hydrocarbon accumulations and discoveries, but commercial production has either not commenced or is in an exploratory development phase.
- Basins Included: Saurashtra, Kutch, Mahanadi, Andaman-Nicobar, and Bengal.
- Geological Characteristics: Extensive thick marine sediments with proven reservoir rocks but awaiting commercial infrastructure.
Category III Basins (Prospective Basins)
These basins are considered prospective based on geological data, geomorphology, and seismic surveys, but no significant hydrocarbon discoveries have been made yet.
- Basins Included: Himalayan Foreland, Ganga, Vindhyan, Saurashtra Deepwater, Kerala-Konkan, and Pranhita-Godavari.
- Geological Characteristics: Dominated by thick Proterozoic to Mesozoic sequences with complex structural traps.
Category IV Basins (Uncertain Potential)
Basins with uncertain hydrocarbon potential where geological data is sparse, requiring long-term stratigraphic drilling and seismic exploration.
- Basins Included: Karewa (Jammu and Kashmir), Spiti-Zanskar, Satpura, South Rewa, Damodar, Chhattisgarh, Bastar, Cuddapah, and Bhima-Kaladgi.
- Geological Characteristics: Inland intracratonic and rift basins, heavily dominated by ancient Gondwana or Proterozoic rock systems.
Major Petroleum and Natural Gas Producing Basins
Hydrocarbon production in India is distributed across both onland fields and offshore blocks located along the western and eastern coasts.
Mumbai Offshore Basin
The Mumbai Offshore Basin is located in the Arabian Sea and remains India’s most prolific petroleum-producing region.
- Mumbai High Field: Discovered in 1974 by the oil exploration vessel Sagar Samrat, it is located 160 kilometers west of the Mumbai coast. The reservoir consists of Miocene limestone structures.
- Bassein Field: Situated south of Mumbai High, it is one of the largest natural gas fields in India, producing sweet gas with low sulfur content.
- Aliabet Oil Field: Located in the Gulf of Khambhat near Bhavnagar, it represents a shallow-water tidal oil discovery.
Cambay Basin
The Cambay Basin is a narrow elongated graben stretching across Gujarat and extending into the shallow waters of the Gulf of Khambhat.
- Ankleshwar Field: Located in the Bharuch district, it is famous for producing high-quality light crude oil rich in kerosene and gasoline fractions.
- Lunez Field: The site of the first breakthrough oil discovery in the Cambay basin in 1958.
- Other Notable Fields: Kalol, Mehsana, Sanand, Gandhar, and Kosamba fields.
Assam and Assam-Arakan Basin
This is the oldest petroleum-producing province in India, characterized by structural thrust belts and anticlinal traps.
- Digboi Oil Field: Located in the Tinsukia district of Assam, it is the birthplace of the Indian oil industry, where oil was first discovered in 1889 and the first refinery was commissioned in 1901.
- Naharkatiya Field: Located south of the Burhi Dihing river, it achieved commercial prominence in 1953, producing both crude oil and associated natural gas.
- Moran-Hugrijan Field: Situated southwest of Naharkatiya, it forms a major drilling complex managed by Oil India Limited.
- Rudrasagar and Lakwa Fields: Major producing fields located in the Sibsagar district within the Brahmaputra valley.
Rajasthan Basin
The Barmer-Sanchore graben within the Rajasthan basin has emerged as a major onshore petroleum source in the twentieth century.
- Mangala, Bhagyam, and Aishwarya (MBA) Fields: Located in the Barmer district, these fields produce heavy, waxy crude oil that requires heated pipelines for transportation.
- Raageshwari Gas Field: A major deep-seated natural gas repository providing fuel to regional industries.
Krishna-Godavari (KG) Basin
The KG Basin is a peri-cratonic basin situated on the east coast, extending across Andhra Pradesh and into the deep waters of the Bay of Bengal.
- KG-D6 Block: A deepwater block famous for massive gas discoveries in the late twentieth and early twenty-first centuries, altering India’s natural gas production trajectory.
- Ravva Field: A shallow offshore field producing both oil and gas, located near the Godavari river delta.
Cauvery Basin
The Cauvery Basin covers onland and offshore areas of Tamil Nadu and Puducherry.
- Narimanam and Kovilkalappal Fields: Major onshore fields producing sweet crude oil.
- PY-3 Offshore Block: Located in the Bay of Bengal, contributing steady quantities of crude oil.
Hydrocarbon Stratigraphy and Geomorphology
The distribution of oil and natural gas in India corresponds directly to specific geological formations, reservoir rocks, and structural traps.
| Basin Region | Source Rock Age | Major Reservoir Rock | Structural Trap Type | Primary Hydrocarbon Type |
| Mumbai Offshore | Eocene to Oligocene Shales | Miocene Limestones | Anticlinal domes and fault blocks | Paleogene Crude Oil and Free Gas |
| Cambay Basin | Paleocene to Eocene Shales | Eocene Sandstones | Faulted monoclines and grabens | Light Crude Oil and Associated Gas |
| Assam Shelf | Paleocene to Eocene Coal-Shale | Oligocene Barail Sandstones | Anticlinal structures and thrust faults | Waxy Crude Oil |
| KG Basin | Permian to Cretaceous Shales | Tertiary and Cretaceous Sandstones | Rollover anticlines and deepwater channels | Deepwater Non-Associated Natural Gas |
| Cauvery Basin | Cretaceous Shales | Paleocene Sandstones | Faulted structural blocks | Crude Oil and Associated Gas |
| Rajasthan Basin | Paleocene Volcanics & Shales | Eocene Fatehgarh Sandstones | Fault-bounded structural traps | Heavy Waxy Crude Oil |
Pipeline Infrastructure and Refineries
The distribution of petroleum products and natural gas from production fields and import terminals to consumption hubs relies on a vast pipeline network and localized oil refineries.
Major Hydrocarbon Pipelines
- HVJ (Hazira-Vijaipur-Jagdishpur) Pipeline: India’s first cross-country natural gas pipeline. It runs from Hazira in Gujarat, passes through Vijaipur in Madhya Pradesh, and terminates at Jagdishpur in Uttar Pradesh. It feeds major fertilizer and power plants across northern India.
- Jamnagar-Loni Pipeline: A major Liquefied Petroleum Gas (LPG) pipeline connecting the western coast refineries to northern consumption zones.
- Barmer-Bhogat Pipeline: The world’s longest continuously heated crude oil pipeline, designed to transport the highly waxy crude from Barmer fields in Rajasthan to the Bhogat terminal in Gujarat.
- Kandla-Bhatinda Pipeline: Transports imported crude and refined products from the Gujarat coast to the interiors of Punjab and Haryana.
Oil Refineries Distribution
India possesses a refining capacity that exceeds its domestic crude consumption, making refined petroleum a leading export item.
- Jamnagar Refinery (Gujarat): Owned by Reliance Industries, it is the world’s largest grass-roots refinery complex.
- Digboi Refinery (Assam): The oldest operating refinery in Asia, commissioned in 1901.
- Kochi Refinery (Kerala) and Koyali Refinery (Gujarat): Leading public sector refineries with massive capacities managed by Bharat Petroleum and Indian Oil Corporation respectively.
- Paradip Refinery (Odisha): A highly modern coastal refinery configured to process heavy, high-sulfur sour crude oils imported from the Middle East.
Unconventional Hydrocarbon Resources in India
To diversify energy security, exploration has extended beyond traditional crude oil and natural gas into unconventional resource categories.
Coal Bed Methane (CBM)
CBM is an unconventional form of natural gas trapped inside coal seams.
- Resource Concentration: India possesses significant CBM resources clustered within the eastern Gondwana coal basins.
- Major Blocks: Jharia and Bokaro blocks (Jharkhand), Raniganj blocks (West Bengal), Sohagpur block (Madhya Pradesh), and Korba block (Chhattisgarh).
Shale Gas
Shale gas is natural gas trapped within fine-grained, organic-rich sedimentary shale formations.
- Identified Basins: The Ministry of Petroleum and Natural Gas has identified the Cambay Basin, Gondwana Basin, Krishna-Godavari Basin, and Cauvery Basin as prime targets for shale gas exploration.
- Technical Challenges: Extraction requires high-volume hydraulic fracturing (fracking), which faces challenges due to local water scarcity in prospective regions like Rajasthan and Cambay.
Gas Hydrates
Gas hydrates are crystalline ice-like structures wherein gas molecules (predominantly methane) are trapped inside water molecule cages under low temperature and high pressure.
- Geographical Distribution: Located in the deepwater marine sediments of the Krishna-Godavari basin, Mahanadi basin, and the Andaman offshore waters.
- National Gas Hydrate Program (NGHP): An institutional initiative mapping these deepwater reserves, which are currently non-commercial due to technological extraction complexities.
Institutional Framework and Policy Initiatives
Apex Institutional Bodies
- Ministry of Petroleum and Natural Gas (MoPNG): The central ministry responsible for exploration, production, refining, distribution, and import policies of hydrocarbons.
- Directorate General of Hydrocarbons (DGH): Established in 1993, it acts as the technical regulatory body supervising upstream exploration and production activities, ensuring optimum exploitation of reserves.
- Oil and Natural Gas Corporation (ONGC): A Maharatna Public Sector Undertaking established in 1956, responsible for the majority of India’s domestic oil and gas discoveries and production.
- Oil India Limited (OIL): A Navratna Public Sector Undertaking focused primarily on exploration and production in northeastern India and Rajasthan.
Major Policy Regimes
- New Exploration Licensing Policy (NELP): Introduced in 1997, it allowed 100% foreign direct investment in exploration and introduced competitive bidding for blocks. It operated on a profit-sharing model.
- Hydrocarbon Exploration and Licensing Policy (HELP): Launched in 2016 to replace NELP. It introduced a Revenue Sharing Model instead of profit sharing, a Single License for conventional and unconventional resources, an Open Acreage Licensing Policy (OALP), and marketing and pricing freedom for produced gas.
- Strategic Petroleum Reserves (SPR): Underground rock caverns built to store emergency crude oil stocks to mitigate supply disruptions. The Indian Strategic Petroleum Reserves Limited (ISPRL) manages these reserves at three primary locations: Visakhapatnam (Andhra Pradesh), Mangaluru (Karnataka), and Padur (Karnataka).