Carbon capture and storage

Carbon Capture and Storage (CCS) is a process that helps reduce carbon dioxide (CO₂) emissions and stop them from entering the atmosphere. It’s mostly used by big industries to lower their impact on the environment. CCS has three main steps: capturing, transporting, and storing CO₂:

1. Capture: CO₂ is separated from other gases made by factories, power plants, and refineries. This includes facilities that process coal, natural gas, cement, oil, and steel.
2. Transport: CO₂ is compressed into a thick liquid-like state to make it easier to move through pipelines to a storage site.
3. Injection and storage: CO₂ is pumped deep underground, more than a kilometre down, into porous rock formations called reservoirs. These rocks, like sandstone or limestone, have small spaces (called pores) where the CO₂ can be stored safely as tiny droplets. These reservoirs, called deep saline formations, are filled with very salty water, and provide a secure way to store CO₂ forever.

This technology is an important way to help reduce pollution and protect the environment. The individual technological components of CCS are well understood and being used in successful projects in Norway, Australia, Algeria, Canada, and the United States of America. 

What is carbon dioxide and how is it linked to climate change?

Climate scientists are almost certain that human-made CO₂ is a major cause of climate change.

Carbon dioxide (CO₂) is a gas that is colourless, odourless, non-flammable, and non-toxic. It is heavier than air and can dissolve in water. Each CO₂ molecule is made of one carbon atom and two oxygen atoms. CO₂ is part of your breath—you exhale it every time you breathe. It’s not harmful to inhale as long as you’re also getting enough oxygen. CO₂ is also created when fossil fuels like coal, oil, and natural gas are burned.

CO₂ plays an important role in nature and industry. Trees and other green plants absorb CO₂ from the air to grow, releasing oxygen back into the atmosphere during photosynthesis. Humans use CO₂ in many ways. It’s used to make wine, add bubbles to soft drinks, power fire extinguishers, keep things cold in refrigeration, and even as a key ingredient in baking soda. CO₂ is the main greenhouse gas released by human activities.

Greenhouse gases cause global warming because they trap heat from the sun, stopping it from escaping Earth's atmosphere. Climate scientists are almost certain that human-made CO₂ is a major cause of climate change. Since the Industrial Revolution, we have been burning more and more fossil fuels like coal, oil, and gas to create energy. Burning these fuels releases CO₂ into the atmosphere which adds to the greenhouse effect and leads to global warming. Before the industrial revolution, CO₂ levels were about 280 parts per million (ppm). Now, they have risen to 424.61 ppm in 2024—an increase of around 50%. 

What is geosequestration?

Storing CO₂ deep underground is called geosequestration.

CO₂ is converted from a gas into a supercritical fluid before it is injected underground, because in this state it takes up to 400 times less space than as a gas and behaves like both a liquid and a gas. The CO₂ remains as a supercritical fluid below about 800 metres underground where heat and pressure are high enough.

Supercritical CO₂ is injected into porous rocks like sandstone, which act as natural storage reservoirs. These reservoirs, called saline aquifers, are filled with salty water and are perfect for storing CO₂. To keep the CO₂ safely trapped, these reservoirs are ideally covered by a layer of solid, impermeable rock like shale or salt, called caprock. This works like a natural seal, ensuring the CO₂ stays deep underground, just like natural gas deposits that have been trapped underground for millions of years. CCS injection sites are carefully chosen after advanced seismic studies and thorough testing. This ensures that CO₂ reservoirs are much deeper and not connected to any freshwater or water used for industry.

The formations called saline aquifers contain very salty water that could not be used for drinking or other purposes.

There are four ways CO₂ can be trapped in a sandstone formation within a saline aquifer:

1. Local trapping: CO₂ bubbles are trapped in the tiny pore spaces of the sandstone.
2. Dissolving: CO₂ mixes with the salty water in the sandstone.
3. Mineralisation: CO₂ reacts with the rock to form solid minerals.
4. Physical trapping: A layer of rock, such as shale, acts as a seal to stop the CO₂ from moving upward toward the surface. CO₂ naturally occurs in underground reservoirs. For example, natural oil and gas reservoirs, which sometimes contain CO₂, can stay sealed for millions of years.

Deep underground rock formations are considered excellent storage sites for CO₂. Ideal sites have:

• A reservoir unit, usually sandstone, where CO₂ can be injected.
• Rocks in depleted oil and gas fields or deep formations filled with saline water.
• An impermeable sealing layer, like shale, to prevent CO₂ from escaping to the surface.
• Geological stability, meaning the rocks won’t be deformed or faulted. 

CCS projects in Western Australia

As of February 2025, the only active CCS project in WA is Chevron Australia's Gorgon Project on Barrow Island which is one of the world's biggest CO₂ injection projects. The project pumps CO₂ into a deep underground reservoir, more than 2 km below the surface, helping to reduce the Gorgon gas plant's greenhouse gas emissions by about 40 percent. Across Australia, there are other projects focused on CCS and you can find more details about them on the CO2CRC website.