Shale gas

Geography glossary

Also called: Fracking, Hydraulic fracturing · Topic: Primary Activities: Gathering, Pastoralism, Agriculture and Mining · NCERT: Beyond NCERT

Meaning

Shale gas is natural gas trapped inside shale, a fine-grained sedimentary rock. Shale's tiny pores are poorly connected, so the gas cannot flow out on its own. It is freed by horizontal drilling and hydraulic fracturing ("fracking").

It matters because the US shale boom made the USA the world's largest oil and gas producer and a major gas exporter. India has shale potential in four basins, but it has produced very little.

Explanation

Why the gas is "locked in"

  • Shale forms when fine mud settles in layers and hardens into rock.
  • Its pores (tiny empty spaces) are very small and poorly connected.
  • The gas sits inside these pores.
  • It cannot move through the rock to a normal well.

  • So an ordinary vertical well brings up little or no gas.

  • This makes shale gas an unconventional gas. Special methods are needed to get it out.

How it is freed: horizontal drilling + fracking

  • Step 1: Horizontal drilling
  • A well is drilled straight down to the shale layer.
  • Then it is turned sideways and runs for kilometres inside the thin shale layer.

  • This puts far more rock in contact with the well.

  • Step 2: Hydraulic fracturing ("fracking")

  • Water, sand and chemicals are pumped down under very high pressure.

  • The pressure cracks the rock.

  • Step 3: Gas flows

  • The sand keeps the cracks open. Sand used this way is called a proppant.

  • Gas, or "tight oil" (oil held in the same kind of tight rock), flows through the cracks and up the well.

  • Chain in one line: tight rock → drill sideways → crack it with high-pressure fluid → prop cracks open with sand → gas or oil flows out.

Conditions it needs

  • Shale rock that holds gas or oil, spread over large areas.
  • Plenty of water, because each well needs millions of litres.
  • Open land for many well pads, roads and pipelines.
  • Simple, workable geology, where the shale layers are not badly folded or broken.
  • The USA has all four. India lacks most of them, which is why its output is small.

Concerns

  • Water use: each well needs millions of litres of water.
  • Groundwater contamination: fracking chemicals and gas can leak into aquifers (layers of rock that hold underground water).
  • Induced earthquakes: these are small earthquakes caused by human activity. They come mainly from pumping wastewater deep underground, not from the fracking itself.
  • Methane leaks: methane, the main gas in natural gas, is a strong greenhouse gas.

Where it occurs

World: the US shale boom

Field Location Main output
Marcellus Appalachian Basin (Pennsylvania, West Virginia, New York) Gas
Permian West Texas and south-east New Mexico Oil and gas
Bakken North Dakota and Montana (extends into Canada) Tight oil
  • Result: the USA became the world's largest oil and gas producer. It also became a major LNG exporter. LNG (liquefied natural gas) is gas cooled into a liquid so ships can carry it.

India: potential shale basins

Basin State(s)
Cambay Gujarat
Krishna–Godavari (KG) Andhra Pradesh
Cauvery Tamil Nadu
Damodar Jharkhand–West Bengal
  • A 2013 shale gas policy allowed ONGC and Oil India to explore for shale gas.
  • Output has been very small.
  • Limits: water shortage, crowded land and difficult geology.

Don't confuse with

  • Conventional natural gas: this gas sits in porous, permeable rock (rock whose pores connect), so it flows to a normal vertical well. Shale gas sits in tight rock and needs horizontal drilling and fracking.
  • Tight oil: this is oil, not gas, taken from the same kind of tight rock by the same fracking method. The Bakken field is mainly tight oil, while Marcellus is mainly gas.
  • LNG (liquefied natural gas): this is not a source of gas. It is a form used for shipping, where gas is cooled into a liquid. Shale gas, once produced, can be turned into LNG for export.
  • Open-pit mining: this digs solid ore out of a huge step-shaped pit at the surface, as for copper or iron ore. Shale gas is taken out through deep wells, and no pit is dug.

Prelims Hooks

  • Fracking fluid = water + sand + chemicals, pumped in under high pressure. The sand keeps the cracks open.
  • Field–location matches: Marcellus is in the Appalachian Basin (Pennsylvania), Permian is in West Texas–SE New Mexico, and Bakken is in North Dakota–Montana.
  • Field–output matches: Marcellus produces gas, Permian produces oil and gas, and Bakken produces tight oil.
  • India's shale basins: Cambay is in Gujarat, KG in Andhra Pradesh, Cauvery in Tamil Nadu, and Damodar in Jharkhand–West Bengal.
  • India's shale gas policy came in 2013. It allowed ONGC and Oil India to explore.
  • Trap: induced earthquakes from shale activity come mainly from deep wastewater injection. Shale is a sedimentary rock, not igneous.

Mains Points

  • Shale changed world energy geopolitics (GS-III): the shale boom turned the USA into the largest oil and gas producer and a major LNG exporter. Gas-importing countries now have more choice of supplier, and big exporters have less power over them.
  • Why India has not had a shale boom (GS-III):
  • The Cambay, KG, Cauvery and Damodar basins have shown little output since the 2013 policy.
  • Water shortage: each well needs millions of litres, and much of India is water-stressed.
  • Crowded land: densely farmed and settled land leaves little room for many well pads.

  • Difficult geology makes drilling costly and uncertain.

  • Environmental cost (GS-III): fracking brings water stress, groundwater contamination, induced earthquakes and methane leaks. Shale gas burns cleaner than coal, but methane leaks can cancel much of that climate benefit. India therefore needs strict rules on water, wastewater disposal and leaks before it scales up.

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