Krishna-Godavari basin

Also called: KG basin · Topic: Energy Resources of India: Conventional and Non-conventional · NCERT: Class 10, Ch 5 "Minerals and Energy Resources"; Class 12, Ch 5 "Mineral and Energy Resources"

Meaning

The Krishna-Godavari (KG) basin is a sedimentary basin in Andhra Pradesh. It lies both on land and offshore in the Bay of Bengal, and it holds both oil and natural gas.

• It is built from sediment laid down by the deltas of the Krishna and Godavari rivers.
• Together with the Kaveri basin in Tamil Nadu, it is the main source of oil and gas on India's east coast.
• It matters because India imports about 88% of its crude oil and 51% of its gas [3]. Every domestic basin like this one helps India's energy security.

Explanation

How the basin formed (cause → process → result)

• Cause: rivers carry sediment to the sea.
• The Krishna and the Godavari flow east across the Peninsula into the Bay of Bengal.

• They carry huge amounts of mud, silt and sand.

• Process: the deltas build thick layers.

• Near the coast the rivers slow down and drop this load. This builds deltas (fan-shaped land made of river sediment at a river mouth).
• Over millions of years, layer after layer piles up, both on land and on the sea floor offshore.

• These layers become sedimentary rocks (rocks made from deposited and hardened sediment).

• Result: a sedimentary basin.

• A sedimentary basin is a large low area of the Earth's crust filled with thick sedimentary rock.
• The KG basin is one of these. It stretches from the delta land out under the Bay of Bengal.

How oil and gas form in it

• Petroleum is a mix of liquid and gaseous hydrocarbons (compounds of hydrogen and carbon).
• In India it is found in Tertiary sedimentary rocks. These are rock layers laid down in old seas and basins, roughly 66 to 2.6 million years ago.
• Step 1: Tiny sea plants and animals died and were buried under mud.
• Step 2: Heat and pressure acted on them for millions of years.
• Step 3: They slowly turned into oil and gas.
• Oil and gas are lighter than water, so they move upward through porous rock (rock with tiny holes, such as sandstone or limestone).

How the oil and gas are held (traps)

• Anticline trap: an anticline is an upfold, an arch-shaped bend in rock layers.
• Oil and gas rise to the top (crest) of the arch.
• A non-porous layer above, such as shale or clay, stops them from rising further. It acts like a lid.

• The fluids settle in layers by weight: gas on top, oil in the middle, water at the bottom.

• Fault trap: a fault is a crack in the rock along which the blocks have moved.

• The movement pushes a porous layer against a non-porous one.

• Oil moving up the porous layer is blocked and collects against the fault.

• Conditions the basin needs:

• Thick sediment rich in buried organic matter (the source).
• Porous rock where the oil and gas can be stored.
• A non-porous cap rock that seals them in.
• The Krishna-Godavari deltas supplied all three.

Parts of the basin

Part	Setting	Note
Onshore	Delta land of the Krishna and Godavari, Andhra Pradesh	Drilled from land
Offshore	Continental shelf and sea floor of the Bay of Bengal	Drilled from platforms at sea

Where it occurs

• Andhra Pradesh: the KG basin lies on the delta land and offshore along the Andhra coast, in the Bay of Bengal.
• Its east-coast partner: the Kaveri basin in Tamil Nadu, on land and offshore around the Kaveri delta.
• India's other oil regions, for comparison. All of them are Tertiary sedimentary basins on the edges of India:
• Assam (upper Brahmaputra valley): Digboi (1889), Naharkatiya (1953), Moran-Hugrijan.
• Gujarat (Cambay basin): Ankleshwar (1960), Kalol, Mehsana, Nawagam, Kosamba, Lunej.
• Arabian Sea offshore: Mumbai High, about 160 km north-west of Mumbai. It was found in 1974 (NCERT: 1973) and has produced since 1976.

• Rajasthan (Barmer basin): Mangala, found by Cairn in 2004.

• The Peninsular plateau between these basins is made of old, hard rocks. It holds almost no oil.

• Andhra Pradesh in the wider oil picture:
• Visakhapatnam is a coastal refinery. Coastal refineries like it mainly process imported crude.

• Visakhapatnam is also a Strategic Petroleum Reserve site of 1.33 MMT under Phase I [2]. A Strategic Petroleum Reserve is an emergency stock of crude oil stored in underground rock caverns.

• Who explores the basin:

• ONGC (set up in 1956) led the national search for oil and gas, which spread to new areas, including offshore.
• NELP (1999) opened exploration blocks to private and foreign companies through Production Sharing Contracts [6].
• HELP (2016) and OALP (2017) now govern new blocks through Revenue Sharing Contracts [4].

Don't confuse with

• Kaveri basin: this is also an east-coast oil and gas basin, but it is in Tamil Nadu, around the Kaveri delta. The KG basin is in Andhra Pradesh.
• Mumbai High: this is an offshore field too, but it is in the Arabian Sea on the western shelf. The KG basin's offshore part is in the Bay of Bengal.
• Cambay basin: this is a long, narrow basin running north–south through mainland Gujarat (Ankleshwar, Kalol, Mehsana). It is on the west side of India, not the east coast.
• Godavari valley coalfields: these hold Gondwana coal in older rocks inland. The KG basin holds oil and gas in younger Tertiary rocks near the coast and offshore. The same river gives its name to both a coal region and an oil basin.

Prelims Hooks

• KG basin → Andhra Pradesh, on land and offshore in the Bay of Bengal. Kaveri basin → Tamil Nadu. These are the two east-coast hydrocarbon basins.
• The KG basin is made of delta sediment from the Krishna and Godavari rivers. It yields both oil and natural gas.
• Offshore matching trap: Mumbai High is in the Arabian Sea, and the KG offshore is in the Bay of Bengal.
• Rock type: India's oil, including KG oil, lies in Tertiary sedimentary rocks, not in the old Peninsular rocks.
• Anticline trap: oil and gas collect at the crest of an upfold, with gas above oil above water, sealed by non-porous cap rock.
• Andhra Pradesh SPR site: Visakhapatnam, 1.33 MMT (Phase I) [2].

Mains Points

• Uneven spread of oil (GS-I/GS-III): India's oil lies in Tertiary sedimentary basins on its edges: Assam, Gujarat, the western offshore, Barmer, and the KG and Kaveri basins.
• The KG basin exists because two large Peninsular rivers dropped thick, organic-rich sediment at their deltas.

• The hard rocks of the plateau inland hold almost none. So interior refineries need pipelines, and coastal refineries depend on imports.

• Energy security (GS-III): India imports about 88% of its crude and 51% of its gas [3]. This exposes it to price shocks and to trouble at choke points such as the Strait of Hormuz [3].

• Basins like KG, which hold both oil and gas, reduce this risk.

• Policy is pushing for more exploration: HELP and OALP let companies choose blocks using data in the National Data Repository [4]. 172 blocks were awarded in OALP Rounds I–IX [5].

• Offshore challenges and regional growth: the offshore part of the basin needs costly drilling at sea and careful protection of the delta and coast. A domestic hydrocarbon base on the Andhra coast also supports coastal energy infrastructure, such as the Visakhapatnam refinery and SPR [2].

Related concepts

• Petroleum
• Anticline trap
• Oil and Natural Gas Commission
• Digboi oilfield
• Naharkatiya oilfield
• Cambay basin
• Mumbai High
• Barmer oil fields
• Field-based and market-based refineries
• Strategic Petroleum Reserve

Read more

• Petroleum: occurrence, oilfields, refineries and reserves