Model Answer
0 min readIntroduction
India possesses significant reserves of crude oil and natural gas, crucial for its energy security. These hydrocarbons are found within sedimentary basins formed over millions of years. As of 2023, India meets approximately 53% of its crude oil demand through domestic production, highlighting the importance of exploring and exploiting these resources. The country’s petroliferous basins are categorized based on geological formations and potential for hydrocarbon accumulation. Understanding the distribution of these basins and the specific geology of key oil-producing areas like the Assam basin is vital for effective resource management and future exploration strategies.
Distribution of Petroliferous Basins in India
India has 26 sedimentary basins, covering approximately 300,000 sq km. These basins are categorized into eight major categories based on their geological setting and hydrocarbon potential:
- Continental Basins: These basins are formed by the stretching and thinning of continental crust. Examples include the Vindhyan Basin, Gondwana Basin, and Kachchh Basin.
- Coastal Basins: Formed along the margins of the Indian subcontinent, these basins are associated with rift valleys and passive margins. Examples include the Mumbai High, Krishna-Godavari, and Cauvery basins.
- Onland Basins: These are basins located on the mainland. Examples include the Assam-Arakan Basin, Cambay Basin, and Rajasthan Basin.
- Offshore Basins: These basins are located in the offshore areas of India. Examples include the Bombay High, Krishna-Godavari offshore, and Kerala-Konkan offshore basins.
Here’s a table summarizing the major petroliferous basins in India:
| Basin Name | Location | Dominant Hydrocarbon | Key Fields |
|---|---|---|---|
| Assam-Arakan | Northeast India | Crude Oil & Natural Gas | Digboi, Naharkatiya, Moran |
| Mumbai High | Offshore Western India | Crude Oil | Mumbai High North, Heera |
| Krishna-Godavari | Eastern Coast of India | Natural Gas | Rava, KG-D6 |
| Rajasthan | Western India | Crude Oil | Mangala, Bhagyam |
| Cauvery | Southern India | Crude Oil & Natural Gas | Nannilam, Karaikal |
| Cambay | Gujarat | Natural Gas & Condensate | Ankleshwar, Balol |
Geology of Oil-Fields of Assam Basin
The Assam Basin is one of the oldest and most prolific oil-producing regions in India. It’s a foreland basin formed due to the tectonic loading of the Himalayas. The basin is characterized by thick sequences of sedimentary rocks deposited during the Mesozoic and Cenozoic eras.
Stratigraphy
- Pre-Tertiary Basement: Composed of Archaean and Proterozoic crystalline rocks.
- Tertiary Sediments: The main reservoir rocks are found within the Tertiary sediments, particularly the Oligocene and Miocene formations. These sediments consist of sandstones, shales, and conglomerates.
- Sandstone Reservoirs: The Barail Formation (Oligocene) is a crucial reservoir rock, known for its high porosity and permeability. The Tipam Formation (Upper Miocene) also contains significant oil reserves.
- Shale Caps: Overlying shale formations act as effective seals, preventing the upward migration of hydrocarbons.
Structural Geology
The Assam Basin is characterized by a series of anticlines and synclines formed due to regional folding and faulting. These structural traps are crucial for the accumulation of oil and gas.
- Anticlinal Traps: Oil accumulates in the crests of anticlines, where permeable reservoir rocks are capped by impermeable shale layers.
- Fault Traps: Faults can create barriers to hydrocarbon migration, leading to the formation of fault-bounded traps.
- Fractured Reservoirs: Fractures in the reservoir rocks enhance permeability and improve hydrocarbon flow.
Oil Accumulation Process
The oil in the Assam Basin originated from organic-rich shales deposited in a deltaic environment. These shales underwent thermal maturation at depth, generating hydrocarbons. The hydrocarbons then migrated upwards through permeable pathways until they encountered structural traps, where they accumulated.
Key Oil Fields
- Digboi: The oldest oilfield in India, discovered in 1867. Produces from shallow sandstone reservoirs.
- Naharkatiya: A major oilfield with significant reserves in the Barail Formation.
- Moran: Another important oilfield producing from the Oligocene and Miocene formations.
Conclusion
The distribution of petroliferous basins in India is diverse, reflecting the complex geological history of the subcontinent. The Assam Basin, with its unique geological characteristics and established oilfields, remains a crucial contributor to India’s energy production. Continued exploration, coupled with advanced technologies like seismic imaging and enhanced oil recovery techniques, is essential to unlock the full potential of these basins and ensure India’s energy security. Further research into unconventional hydrocarbon resources within these basins is also warranted.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.