Carbon capture, utilisation and storage (CCUS) prevents carbon dioxide (CO2) from being released into the atmosphere. The technology involves capturing CO2 produced by industrial plants and then recycling the CO2 for utilisation (CCU) or compressing it for transportation and then injecting it deep into a rock formation at a carefully selected and safe site, where it is permanently stored (CCS).
Carbon dioxide is produced when fossil fuels including coal, oil and natural gas are burnt in power plants or factories. It is also released in the production process of oil and gas, ending up in the atmosphere. The purpose of CCUS is to “capture” the CO2 before it’s released to the atmosphere and permanently store it deep underground. Capture rates of around 90 percent of total CO2 emissions produced by power plants, heavy industries and refineries are technically achievable. Further research is underway to improve capture rates above 90%.
In order to capture CO2, a capture plant is attached to an industrial process, such as a power station or fertiliser plant.The capture plant uses technologies such as solvents or membranes to capture CO2 before it is cooled and compressed so it can be transported as a liquid.
The captured CO2 is transported in liquid form to the storage location by ship or pipeline – in the same way that natural gas, oil and many other fluids are transported around the world.
The CO2 must be stored in a geologically secure location. It will be injected into a porous reservoir (e.g., the pore spaces within the rock) rather than a cavity in the earth. The target formation must exhibit several characteristics to be an effective storage location. It must be:
- Porous with good permeability.
- Below 800m in depth so that the CO2 remains in dense liquid-like (‘supercritical’) state, although typical storage depths are 2-3 km.
- In a stable geological environment.
The geological formations that meet the above criteria are typically depleted oil or gas reservoirs and deep saline formations.
CO2 storage in these geological formations further benefits from ‘trapping mechanisms’ that work to create additional storage security to trap the CO2 within the formation’s fluids and minerals. These trapping mechanisms include ‘structural’ trapping (the presence of an impermeable caprock beneath which the CO2 is trapped), ‘residual’ trapping (CO2 bubbles trapped behind pore throats), ‘solubility’ trapping (dissolution of the CO2 into the formation water) and ‘mineral trapping’ (CO2 precipitating in the formation to form carbonate minerals). Click here for more information on the chemistry of storage and the trapping mechanisms at work to ensure CO2 is permanently stored.
The storage area is monitored during and after CO2 injection to ensure the CO2 storage is effective and being appropriately managed. Typically, monitoring techniques include a combination of injection well (‘downhole’) measurements of pressure and temperature, seismic measurement using sound waves to provide images of the CO2 and observation wells to take measurements at other locations in the formation.
In summary, geological carbon storage imitates how nature has stored oil, gas and CO2 for millions of years. It builds on decades of oil and gas industry expertise, ensuring that CO2 remains trapped below the surface just as oil and gas have naturally remained trapped.
Captured carbon dioxide can be re-used or recycled in several commercial applications.
The most common is to use CO2 for enhanced hydrocarbon recovery – whether oil or gas – to boost the amount of oil or gas recovered. Carbon dioxide enhanced oil recovery (CO2-EOR) involves the injection of compressed carbon dioxide into an oil reservoir. The CO2 acts like a solvent and causes the oil to expand and flow more easily to production wells. In CO2-EOR, a large portion of the injected CO2 remains below the ground. If the CO2 that returns to the surface is separated and reinjected to form a closed loop, this results in permanent CO2 storage.
Carbon dioxide can also be used as a feedstock for new products. In this process, the CO2 is reintroduced into the production process and treated as a carbon resource, rather than a post process emission. The major processes are biological CO2 transformation by algae into new organic compounds, the chemical transformation for building blocks in the chemical industry or synthetic fuels in the transport sector, and the production of synthetic building materials.
CCUS is Here
CCUS is not experimental and is already being deployed, storing millions of tons of CO2. Globally, more than 260 million tonnes of CO2 have been captured and injected deep underground since the 1970s. One project – the Sleipner CCS operation in Norway has captured and injected about one million tonnes of CO2 per year since 1996. As of June 2020, 21 large scale CCUS facilities are operating, another three are in construction and 35 in various stages of construction.
Australia is home to the world’s largest commercial scale CO2 injection project in saline formations at Gorgon LNG on Barrow Island off the north-west coast of WA. At full capacity, Gorgon will safely and permanently store four million tonnes per year of CO2.
More Australian projects are under development including:
- Santos plans for a commercial CCS storage hub in the Cooper Basin to store ~1.7 Mtpa with potential to store up to 20Mtpa.
- The CarbonNet Project is investigating the potential for a commercial-scale (5Mtpa) CCS network. The network would bring together multiple CO2 capture projects in Victoria’s Latrobe Valley, transporting CO2 via a shared pipeline and injecting it into deep underground, offshore storage sites in Bass Strait. The HESC Project (hydrogen from coal) in Latrobe Valley if approved could be a foundation CO2 source for CarbonNet.
- CTSCo is examining the feasibility of a commercial-scale (~1 Mtpa) CCS project in Queensland’s Surat with FID on a $150M carbon capture plant at Millmerran power station set for late 2020.
Numerous world-leading agencies, including The International Energy Agency (IEA), the Intergovernmental Panel on Climate Change (IPCC) and the International Clean Energy Ministerial (CEM), have acknowledged that CCUS must be part of the portfolio of low emission technology options if global emissions reduction targets are to be achieved at the lowest cost. CCUS is internationally acccepted within the United Nations Framework Convention on Climate Change (UNFCCC) as a mitigation solution, capable of delivering environmentally safe mitigation outcomes. It has been an eligible project level activity in the Kyoto Protocol’s Clean Development Mechanism since 2011, and institutional arrangements to operationalise it as an international offset have been in place since 2012.
The Global-CCS-Institute_Key-Messages_2020 answer common questions and provide facts on CCUS.