Carbon dioxide (CO2) leakage is one of the main community concerns as to whether CO2 can be stored securely and safely underground. Ian Filby, Director of CarbonNet’s project, advises that the proposal is to inject CO2 seven kilometres offshore from the Golden Beach shoreline. Any further offshore could impact existing hydrocarbon accumulations. More concerning is the depth of injection site at only 1km. So the nearshore option is not the best option, rather it is the cheapest option. That’s not good enough!
#Note – the graphic above is parallel to the coast. Source – Basin resource management frameworks: 4D geoscience information,modelling -3MBSeismic data over the Golden Beach gas field indicates the presence of a small fault cutting the top Latrobe Group Horizon. Source – Geological Carbon Storage in the Gippsland Basin, Australia Containment Potential
Credible research documents have CO2 injected at greater depths than what can be achieved with the nearshore area of 1km depth and only moderate seal capacity. To have the injection point so close to shore requires fresh water input from the Latrobe Aquifer Storage to achieve water-washing and total dissolution of the CO2,within a foreseeable geological timescale of a million years or less. Then there is industry concern that ‘acidised solutions containing dissolved CO2 impinging on existing oil and gas facilities within a foreseeable timescale.’ (CarbonNet Project-3D Mapping and correlation of Intraformational seals within the Latrobe Group in the nearshore Gippsland Basin. Page 13) Industry is protected but what about the people onshore as expected subsurface CO2 plume could also interact with the freshwater interface and cause the onshore groundwater to become more saline?
To store the carbon dioxide requires converting the captured CO2 into a supercritical fluid (compressor station onshore) to inject into the geological formation which is the Latrobe Group reservoirs (geological formation) with the Lakes Entrance Formation acting as the regional seal. As CO2 is lighter than saline, CO2 will be buoyant and expected to migrate towards the formation top in a lateral plume. It is expected that the cap rock above the formation is impermeable to physically trap the CO2. Again, Injecting CO2 7km from offshore at a depth of 1km is the crucial point here. Most modelling has CO2 injection further offshore and into deeper formations.
Leakage of CO2 from the storage location through the subsurface into the atmosphere – this leakage could occur through isolated, catastrophic events – such as an earthquake – or through sustained, slow venting of CO2 due to improper storage site selection or preparation. Either of these forms of leakage would result in elevated CO2 concentrations at the surface or in the shallow sub-surface that could negatively impact human health and safety as well as that of plants and animals living in the area. https://hub.globalccsinstitute.com/publications/building-capacity-co2-capture-and-storage-apec-region-training-manual-policy-makers-and-practitioners/module-8-health-safety-and-environmental-risks-ccs-projects
Source Basin resource management frameworks link as above
As noted in the graphic above, the existing Golden Beach gas field sits in the moderate seal potential with the SW area being only good seal potential. Whilst there are not the same amount of exploration wells in this section as further afield, they do exist so the integrity is compromised by legacy wells already drilled in the storage area which CarbonNet have concluded the risks are low. (Page 13) All wells that penetrate the caprock are potential sites through which mobile CO2 might escape. Although these wells should be properly cemented and plugged, this may not be the case to prevent upward migration of CO2. Equally, the cement might fail either mechanically or due to corrosion. A chemical process of CO2 dissolution into brine creates carbonic acid. When this acid comes in contact with hydrated cements, corrosion can occur degrading existing well infrastructure. So, if well integrity is compromised, it may act as a conduit through which CO2 could escape.
For CO2 storage over many thousands of years, slow seepage through faults and offset baffles may be acceptable, especially where it leads to additional solution into the active aquifer which is sweeping fluids from onshore to offshore… Some faults offer orders of magnitude less permeation than others, but all faults represent a clear risk to long-term storage of buoyant fluids. The challenge is to quantify that risk, and the rate of permeation, and to evaluate whether a viable trap still exists…These preliminary calculations indicate that the meteoric water is easily able to dissolve all the permeating CO2. https://www.globalccsinstitute.com/publications/carbonnet-project-3d-mapping-and-correlation-intraformational-seals-within-latrobe-group-nearshore-gippsland-basin
Modelling of reservoir simulations of CO2 storage below certain seals is used to check permeation against porous zones, faults and thin seals. CarbonNet came up with only 0.3% of 125Mt naturally stored over 1000 years CO2 enters the desired seal.
Where their modelling becomes a total guess is the ability to predict meteoric rainfall into the future (decades, hundreds & thousands of years) given climate change and what flow rates of groundwater will recharge the aquifer to enable greater dissolution of the CO2. This subject has been confirmed by Prof Craig Simmons from the National Groundwater and Research Centre due to the many variables of future land use changes. Likewise, over extraction of groundwater from dewatering of Latrobe Valley coal mines alongside past and present oil and gas extraction offshore causing the depletion of the Latrobe aquifer and could have impacts on modelling. Local CO2 studies continue to focus on seal continuity and fault seepage.
Not only are the risks evident to the subsurface, the community would also have to contend with a pipeline transporting supercritical CO2. See Pipeline Failure. At 7km offshore of Golden Beach this community has good reason to be concerned.