THE APPROACH
THE INTRODUCTION: Describe off-shore oil reserves.
THE BODY
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- Geographical distribution of off-shore oil reserves.
- Differences from on-shore oil reserves.
THE CONCLUSION: Importance of these resources.
THE INTRODUCTION:
Off-shore oil reserves are found beneath the seabed, predominantly along continental shelves and coastal sedimentary basins that were once ancient shallow seas teeming with marine life.
THE BODY:
Geographical distribution of off-shore oil reserves:
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- Continental shelves and margins:Most off-shore oil reserves are concentrated along sedimentary basins near the edges of continents. These regions were ancient seas, rich in plankton and algae, whose remains got buried and transformed into oil through heat and pressure.
- Major off-shore fields:
a) Persian Gulf:Home to supergiant fields like Safaniya and Marjan (Saudi Arabia, Iran, UAE), formed in thick marine sediments and structural traps.
b) North Sea:Off the coasts of UK and Norway; oil is contained in Jurassic and Cretaceous sandstones and chalk deposited in ancient marine deltas and shallow seas.
c) Gulf of Mexico:The USA and Mexico exploit huge off-shore reserves in deep-water sediments formed by river deltas and structural traps.
d) Brazil (Campos and Santos Basins):Located in deep Atlantic waters, these are among the largest off-shore oil provinces, formed in sediment-rich rift basins.
e) West Africa (Nigeria, Angola), Caspian Sea (Azerbaijan, Kazakhstan), South China Sea (Malaysia, Vietnam):All feature sizable off-shore oil reserves, typically along faulted continental margins and structural or stratigraphic traps.
f) India:Mumbai High and Krishna-Godavari Basin are key off-shore fields, formed in Tertiary period sedimentary traps.
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- Geological setting:Off-shore reserves require thick deposits of organic-rich sediments, appropriate burial and maturation conditions, plus a geological trap (folds, faults, or impermeable cap rocks) to accumulate oil.
Differences from on-shore oil reserves:
On-shore oil reserves: The prolonged sedimentation and deposition of organic matter within the ocean basin, combined with subsequent tectonic activity and folding, created the geological conditions and traps necessary matter for the formation of these hydrocarbon reservoirs.
Example: The closure of the Tethys Sea led to the formation of significant oil and natural gas reserves in the Middle East, North Africa, and parts of Central Asia, such as the Persian Gulf and the Caspian Sea.
Other examples: Assam reserves, Oil reserves of Venezuela.
| Feature | Off-shore oil reserves | On-shore oil reserves |
|---|---|---|
| Location | Below seabed (continental shelf/slope) | Land surface, sedimentary basins |
| Exploration & extraction | Requires advanced rigs, subsea equipment, remote logistics; higher costs and risks | Land drilling rigs and pipelines; easier access, lower cost |
| Scale & reservoir size | Often larger, less exploited, deeper, with thicker sediment covers | Can be supergiant fields on land, but more fragmented and shallower |
| Environmental risks | Oil spills threaten marine ecosystems; weather disruptions are frequent | Oil spills impact land, groundwater, and local populations |
| Maintenance & operations | Remote, complex, weather-dependent; platform maintenance is challenging | Simpler, ground-based, weather has less impact |
THE CONCLUSION:
Off-shore oil reserves are concentrated around sediment-rich continental margins, differing from on-shore occurrences in location, infrastructure, cost, and operational challenges.
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