Background to the Study

Sedimentary basins that provide most of the world’s CO2 storage potential also host fossil fuel, groundwater and geothermal energy resources, as well as providing options for gas storage and permanent disposal of waste fluids.

There is a need to define key factors that affect interaction of such resources with CO2 storage, to provide policy makers and regulators with guidance on the allocation of pore space and resource interaction management, and to clarify the potential impact of interaction on storage capacity and availability.

Storage could affect resource exploitation through fluid displacement and pressure effects beyond the extent of the CO2 plume, as well as through direct interaction of the plume and its reaction products. Interactions could have beneficial effects, for instance by reservoir re-pressurisation, or negative effects by sterilising resources through contamination with CO2 or its reaction by-products. This dual potential could be the case in regards to groundwater, where an increased pressure footprint caused by CO2 injection could beneficially increase the recovery of groundwater resources, or conversely if CO2 or the associated brine migrates out of the storage formation, there could be an adverse potential for it to reach adjacent potable groundwater resource and cause contamination, either directly or through any substances that may have been mobilised by CO2.

The exploitation of resources, such as hydrocarbon production, may enhance CO2 storage by de-pressurising reservoirs/aquifers and by providing re-usable boreholes and infrastructure as well as sub-surface data. This enhanced potential for storage may be durable in some cases, but temporary in others - such as circumstances where offshore oil and gas infrastructure has to be de-commissioned on completion of production, thereby limiting availability. Storage potential could also be negatively impacted, e.g. in locations where seal integrity has been compromised by poor well completions or by the fracturing of seals during shale gas production.

There may also be direct competition for the use of pore space by the proponents of other forms of sub-surface storage or disposal.

When considering locations of overlap, it is important to consider whether the overlap is geographical or whether the actual pore space is in competition. For example, in a recent IEAGHG study on potential impacts on groundwater (2011/11), regional maps showing areas of geographical overlap of potential CO2 storage locations and potable groundwater resources have been produced. However, in some areas where there is overlap, it is known that there are impermeable layers separating the two potential resources.
Similarly for locations of geothermal resources and potential CO2 storage resources, there may be some areas of pore space conflict, but if looking at purely geographical overlap, there is the possibility for misinterpretation as geothermal energy for power production usually takes place at much greater depths than the optimum for CO2 storage. For district heating generation projects, they are more likely to take place at similar depths, though this may not necessarily cause a conflict as the 2 technologies still have different requirements, such as CCS projects needing a caprock, which is not the case for geothermal projects.

In areas of geographical overlap, but no conflict of pore space, it may be potentially possible to have more than one activity, though this may need to be considered on a site specific basis and any planning and monitoring programme would need to take this into account.

It may also be possible, in some circumstances, for two activities to work in synergy with each other, such as CO2 storage with hydrocarbon production, such as in enhanced oil and gas recovery or with geothermal energy.

CO2CRC, a consortium based in Australia and New Zealand, was commissioned by IEAGHG to undertake a study considering what subsurface resources may interact with CO2 storage and how this can be managed.

Key Messages

• Other subsurface resources may exist at similar depths and localities and therefore interact with CO2 Storage. These include oil and gas, coal, natural gas storage, saline aquifer minerals, geothermal energy, potable groundwater and waste water disposal.

• Interaction of CO2 storage with other resources can be positive or negative depending on the geology, existing resources, economic potential and the regulatory environment.

• CO2 storage operations may be feasible, both adjacent to other resource uses or at different stratigraphic levels in the same locality, particularly if there is no detrimental pressure connection.

• Resource use interactions can occur at the same time or sequentially.

• Regulatory agencies should consider the following stages when evaluating resource development in relation to geological storage of carbon dioxide:

o Identify all resources within region/ basin, map their distribution and assess their quality.
o Establish priority of use between the various resources and CO2 storage.
o Assess proposed CO2 storage project - site characterisation, MMV plans, contingency and mitigation planning.
o Review injection plans and achievability; assess if they might lead to conflict
o Review abandonment plan, longer term MMV, liability transfer arrangements.

• Delays in establishing CO2 storage regulations could not only inhibit CO2 storage project development, they could lead to future, detrimental resource interactions.