What is Carbon Capture and Storage (CCS)?
CCS is the process of capturing and storing CO2 emissions with the aim of reducing the amount of CO2 reaching the atmosphere.
CO2 is captured as either a by‑product of industrial processes, or from waste process or flue gases, using a variety of technologies.
The captured CO2 is compressed, dried and transported to an injection site where it is sequestered underground for safe, permanent storage in suitable geological formations.
While many CCS sites are located onshore, there is significant CO2 storage potential in the rocks of the offshore continental margins.
The Australian Government has identified CCS as a priority low‑emissions technology that will play an important role in our transition to a low emissions future.
The importance of measuring and monitoring in offshore CCS
Many CCS technologies are well developed and have been used for decades by the petroleum industry.
Offshore CCS has been operational in Norway since the mid 1990s, and as CCS scales up worldwide, we are seeing rapid growth in the number of offshore CCS projects under consideration.
Assuring the safe storage of CO2 requires robust measurement, monitoring and verification (MMV) processes to be in place that would enable any CO2 leaks from a CCS site to be both quickly identified and effectively managed. In Australia, this is a regulatory requirement.
CSIRO, in collaboration with Australian National Low Emissions Coal Research and Development (ANLEC R&D), has recently undertaken several projects to assess a range of MMV methods and technologies that can be used in marine environments.
The projects took place in shallow waters off Gippsland in Victoria - an area widely recognised as a feasible option for CCS in Australia due to its proximity to industrial CO2 sources and promising geological storage potential.
CSIRO's project site overlapped with the offshore subsurface storage location proposed by CarbonNet - an initiative funded by the Australian and Victorian governments to investigate the potential for establishing a commercial scale CCS network in the region – and the research outcomes will help support informed decision making by the CarbonNet team.
Dr Nick Hoffman, Geosequestration Advisor to the CarbonNet Project notes the importance of monitoring in order to address community concerns.
"Once we selected the Pelican storage site it was clear that we would have to learn more about how to effectively monitor the storage site and the localised environment to demonstrate to all stakeholders that the CO2 was being safely and effectively stored deep underground." says Dr Hoffman.
According to CSIRO's Project Leader Dr Andrew Ross, the Gippsland project offered a valuable opportunity to evaluate the capabilities of MMV technology in real-world conditions.
"We were conducting tests in relatively shallow water, only about 20-30 metres deep," says Dr Ross.
But the area has very challenging oceanography. There are high energy currents and lots of wave action. It's about as hard as you can get for marine monitoring activities."
What should we measure, and how should we measure it?
The first key objective of CSIRO's research was to gain knowledge about the coastal subsea environment and any unique features that exist there.
This was achieved through conventional marine surveys that were conducted throughout the year to help understand any natural variability.
The surveys involved the collection of data on bathymetry, sediment, biology and oceanography to characterise the area and develop an initial baseline assessment from which change can be monitored.
Securing a greater understanding of the marine environment at a proposed CCS site is important because it reveals what degree of natural variability occurs, and helps to inform the scale of monitoring required for potential future projects.
It can also help identify possible 'false‑alarms' – natural events which could be mistaken for a CO2 release due to it having a similar signature.
"There has to be an element of pragmatism about what we can monitor," says Dr Ross.
"Theoretically you could measure everything, but we understand that some things change naturally. In a risk-based monitoring scheme we need to try and focus on monitoring change in the areas where we best understand that variability."
Deploying and evaluating state-of-the-art equipment
The second key research objective was to develop accurate, on-demand MMV methods that can measure and correctly attribute small changes in dissolved CO2 and identify gas bubbles in shallow coastal ecosystems.
Identifying the best-performing methods and technologies will enable industry to make informed decisions about what approaches to deploy in future to monitor offshore CCS sites.
"There has been some testing of this kind in Europe," says Dr Ross.
"But very little in Australia. We were really looking for the optimal solution - what can we deploy that is efficient, effective and can provide assurance without being prohibitive from a cost perspective."
Dr Hoffman agrees that applying an economic lens to the research is vital in order to secure progress.
"The technical aspects of storing CO2 in the subsurface are straightforward. The international oil and gas industry has been producing, injecting, and storing fluids for over a century and we have learned significantly from their experience and adapted and modified many of their methods. However, we are all aware that especially in Australia efforts to manage CO2 emissions have been politically contentious and subject to fluctuating societal demands to clean-up the atmosphere but at a manageable cost."
The research team deployed a network of fixed marine moorings and landers (seabed frames) near the CarbonNet site that were fitted with six acoustic sensors to monitor for bubbles and 30 geochemical sensors to measure the existing environmental variables in oxygen, pH, methane, temperature, salinity and CO2 levels.
A range of tests were then carried out to assess how good the sensors were at detecting changes in CO2 levels and how the equipment fared in the harsh marine environment. The assessment of physical conditions revealed what might be required in terms of maintenance and servicing if the technology was deployed on a long-term basis.
The team also tested an unmanned surface vehicle equipped with sensors to determine the suitability of these mobile platforms as a tool for monitoring a CCS site.
The project outcomes provide an insight into the mix of technologies and approaches that companies interested in developing marine CCS could use to set up a monitoring system. According to Dr Ross, it has helped find the delicate balance between cost and confidence.
"What we've settled on is a relatively limited set of equipment that can be deployed all the time, but a whole suite of supporting technology that could be deployed if there were any anomalies to allow you to probe what was going on."
Where to from here?
As work continues to establish a commercial-scale CCS network in Gippsland, the improved knowledge of the nearshore marine environment that is an outcome of CSIRO’s recent research will be invaluable for decision makers and industry stakeholders.
It's hoped that the findings from this project will also enable the advancement of MMV methods for offshore CCS and provide assurances about a broad range of perceived risks.
Having already moved from conceptual design to testing the technology in the field, the next step is exploring how to best operationalise those designs as part of potential future CCS projects.
"There are many areas around Australia and in other countries internationally where shallow-water environments may contain suitable CO2 storage sites," says Dr Hoffman.
"Costs are generally cheaper in these nearshore areas than further offshore, so there is an important driver to use these sites, if we can do so safely, and in full recognition of the diversity and importance of their ecosystems, and the sensitivity of local communities."