Hydrocarbons

Hydrocarbons

Most of the hydrocarbon reserves were formed during the Cretaceous age because of 2 reasons

✓ The temperature was tropical worldwide, and

✓ Planktons were abundant in oceans 

Although, most of the Indian deposits are of Cenozoic age. 

In India, hydrocarbons occurs in 6 basins, viz.

1. Bombay high
2. Assam and Arakan basin
3. Cambay basin
4. Rajasthan basin
5. Krishna Godavari basin
6. Cauvery basin

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1. BOMBAY HIGH

• Location: Bombay high is India's largest oil producing basin. It is situated NW to the Mumbai.

• Reservoir & age: Oil mostly occurs in limestone of lower Miocene age.

• Evolution: Narmada and Tapti rivers took the organic rich stuff which accumulated  in the Saurashtra basin and diu arc. These become the potential sources of oil and petroleum.

2. Assam & Arakan basin

Assam and Arakan basin is largest basin and contains numerous oil fields, viz. Digboi, Moran, Borholla, Rudrasagar, Lakwa etc.

When Indian plate collided with Eurasian plate, horst and graben structures formed. Numerous phases of transgression and regression resulted in lots of organic matter accumulation.

• Eocene: Kopili sandstone are the source rock and kopili shales are the cap rock. 
• Oligocene: Barail sandstone is source overlain by barail shales.
• Miocene: Tipam sandstone is the source rock and girujan clay is cap rock. Digboi oil field has this reserve.

3. Cambay basin

Cambay basin is basically a failed rift and hydrocarbons are accumulated in grabens here.

Cambay shales, kalol formation and Thard formation are the potential rich rocks. These all are of eocene age. In Cambay basin, the hydrocarbons are accumulated in coal rich formations.

U. Eocene	Tarapur formation
Mid Eocene	Kalol formation
L. Eocene	Cambay shale

4. Rajasthan basin

Three major sub basins are Jaisalmer, Bikaner Nagaur and Barmer.

Jurassic: Lathi formation, Jaisalmer limestone and Baisakhi formation.
Cretaceous: Badesar and Parihar formation.
Paleocene: Sanu formation, Khuiala formation and Bandah formation.

In short, almost all formations, from Jurassic (Lathi fm) contains hydrocarbons.

5. Cauvery basin

Cretaceous sequence is rich in hydrocarbon deposits. These are accumulated in grabens. These are of age from Cretaceous to tertiary.

6. Krishna Godavari basin

Mandapetta sandstone of P/T boundary is rich source of hydrocarbons.

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