Mains Practice Questions

Introduction:

Offshore petroleum basins are submarine sedimentary regions where hydrocarbons accumulate within porous rocks beneath the seabed. They account for nearly 30% of global crude oil and 27% of natural gas output. Their occurrence is closely associated with continental margins, rifted shelves, and sedimentary troughs, shaped by geological and environmental processes over millions of years.

Body :

Global Spatial Distribution:

• Offshore petroleum basins are unevenly distributed across the globe, mainly along passive continental margins and shallow continental shelves where thick sedimentary sequences prevail.
  • Atlantic Margins:
    • North Sea Basin (UK–Norway) – one of the oldest and most productive offshore zones.
    • West African Shelf (Nigeria, Angola) and Brazilian Basins (Campos, Santos) – host deepwater oil fields along the South Atlantic rifted margins.
  • Gulf of Mexico Basin:
    • Shared by the USA and Mexico, it features prolific deepwater fields contributing significantly to global output.
  • Middle East and Indian Ocean Region:
    • Persian Gulf (world’s richest petroleum basin) and Arabian Sea shelf (Mumbai High, KG Basin) are key to Asia’s energy security.
  • Asia-Pacific Region:
    • South China Sea, Timor Sea, and North West Shelf of Australia contain vast gas reserves.
    • Polar and Arctic Basins:
    • Barents Sea and Beaufort Sea are emerging frontiers with untapped hydrocarbon potential.

Geological Factors Influencing Formation

• Tectonic Setting: Most basins occur on passive continental margins formed by rift-induced subsidence, such as the Atlantic coasts of Africa and South America.
• Sedimentation: Continuous marine sediment deposition (5–10 km thick) provides suitable source and reservoir rocks.
• Source and Reservoir Rocks: Organic-rich marine shales generate hydrocarbons, while sandstone or limestone layers act as reservoirs.
• Structural Traps: Anticlines, fault traps, and salt domes (e.g., Gulf of Mexico) ensure hydrocarbon entrapment.
• Thermal Maturation: Appropriate temperature–pressure conditions during burial convert organic matter into oil and gas.

Environmental Factors

• Marine Productivity: Warm, shallow, low-oxygen seas promote organic matter accumulation.
• Sea-Level Changes: Fluctuations influence sedimentation rates and reservoir formation.
• Coastal Geomorphology: Determines basin morphology and sediment influx.
• Climatic Conditions: Affect erosion and organic deposition patterns.

Conclusion:

Offshore petroleum basins are products of complex geological evolution and favourable marine conditions concentrated along continental margins. As terrestrial reserves decline, exploration is extending to deepwater frontiers like the Guyana-Suriname and Mozambique Channel. Balancing energy security with marine environmental sustainability will define the next phase of global offshore petroleum development