The SCCS CO2MultiStore Joint Industry Project has now published findings from an innovative study of rocks beneath the North Sea, which predict that the secure and permanent storage of carbon dioxide (CO2) within a single geological storage formation can be optimised by injecting CO2 at more than one point simultaneously.
Research by scientists and prospective site operators focused on a North Sea case study – the Captain Sandstone – and used cutting-edge methods, which will, in future, reduce the effort and resources needed to characterise other extensive storage sandstones that could be suitable for CO2 storage.
The findings could help to unlock an immense CO2 storage resource underlying all sectors of the North Sea for the storage of Europe’s carbon emissions, and will inform the work of those managing and operating this natural asset.
A Working Paper summarises the knowledge gained from the process, progress and findings of the research that is applicable to the development of any multi-user storage resource.
Key conclusions from the study
- The potential capacity for subsurface CO2 storage identified by previous studies can be optimised by the operation of more than one injection site within a geological formation, based on this investigation by research scientists and prospective site operators.
- The predicted performance of two reasonable and realistic CO2 injection sites in the Captain Sandstone illustrates how security of storage can be maintained for the simultaneous operation of two sites.
- Stakeholders can have increased confidence that at least 360 million tonnes of CO2 captured over the coming 35 years could be permanently stored, at a rate of between 6 and 12 million tonnes per year, using two injection sites in the store assessed in CO2MultiStore.
- The availability of historical information, knowledge and data acquired during decades of UK offshore hydrocarbon exploration and production increases understanding and confidence for two or more prospective CO2 injection sites in a storage formation. This research has greatly benefited from the re-use of historical information and expert input from industry participants, and access to data vital to increase confidence in storage prediction.
- Storage of CO2 at more than one injection site will create widespread interacting pressure changes within the storage formation, which will determine the total amount of CO2 that can be stored. Effective appraisal of stores must include assessment of the regional changes in pressure generated by CO2 injection over the lifetime of two or more sites.
- The maximum acceptable pressure for all injection sites in a regional storage formation is ultimately defined at the location with the lowest acceptable maximum pressure limit to ensure security of storage throughout the formation. This location may be distant from an injection site.
- The pressure changes generated at one site will interact with another site and also affect any nearby hydrocarbon fields within a storage formation. Pressure changes should be monitored at each of the injection sites and at hydrocarbon fields in the vicinity. Interaction of pressure changes from injecting CO2 at a later time may be detrimental to a pre-existing site, which the second operator would address during project design. After the start-up of a second site, transmission of pressure changes can take years to significantly affect the first. In the scenario explored in CO2MultiStore the delay is five years for sites that are 45 km apart.
- CO2MultiStore has implemented methods to reduce the effort and resources needed to predict the performance of additional prospective sites in the Captain Sandstone case study, validated by the industry data, by:
- Targeted simplification of extensive geological and flow simulation models
- Initial resource-effective fluid modelling before resource-intensive predictive modelling
- Grouping formations of similar geomechanical properties
- Defining a mathematical formula to evaluate the geomechanical stability of the injection sites
- Combining simpler calculations and detailed analyses; initial regional-scale calculations followed by site-specific geomechanical assessments and construction of simplified models for flow simulation of the regional pressure response before detailed modelling
- CO2MultiStore methods are expected to reduce the cost and increase investor confidence by resource-effective characterisation, to create a good storage reservoir model as recommended by the CCS Cost Reduction Task Force (CRTF, 2013). The CO2MultiStore methods streamline the predictive process and can give a 'first pass' assessment of the suitability of a prospective site before embarking on costly detailed investigations. The methods tested are generic and can be applied worldwide.
- If development of a store with more than one injection site is planned, a regional approach should be followed to establish the maximum operating pressure at individual sites. The maximum acceptable pressure would be defined to prevent adverse effects to the store, including nearby operational hydrocarbon fields. Mandatory monitoring will demonstrate the sites are operating as predicted and to provide an early 'flag' should additional pressure management activities be needed.
- Monitoring should distinguish the pressure effects from injection at the operator’s own site, the effects of injection from another site in a storage formation, and pressure management activities. Additional monitoring by later storage sites may be required to ensure they do not adversely affect existing storage operations.
- A pro-active regional approach to management of storage has the potential to optimise the resource, increases confidence in the 'security of provision' of storage capacity and increases certainty in the relationship with other users of the storage formation.
- Managed changes in pressure due to CO2 storage operations may be beneficial to oil and gas fields in a mature hydrocarbon province. The cost of pressure management or increased pressure for a hydrocarbon field operator may be reduced by managed CO2 storage operations.
- Insights gained from this research, essential to the effective characterisation and appraisal of any CO2 storage resource with injection at more than one site, are:
- Early and continuous dialogue between geologists and engineers is vital to reliably predict performance to inform design and operation of more than one injection site within a storage formation
- The value of a storage formation model is increased by merging more than one existing geological model and re-using established knowledge and experience contained within the models gained from hydrocarbon field exploration and production
- The character of fluids and the properties of rocks at nearby hydrocarbon fields are essential data, acquired by field operators, to inform prediction of CO2 storage operations
- Records of operations throughout the lifetime of a hydrocarbon field are a key source of information to validate predictions of storage performance. The detailed history of pressure changes and concurrent well flow rates, from initiation to depletion of a field, is very important and significantly increases confidence in the prediction of the performance of injection sites
- Understanding of the Captain Sandstone storage resource has been substantially matured by integration of the expertise and knowledge of research scientists and industry in the CO2MultiStore study investigations. Injection of 360 million tonnes of CO2 modelled at the two sites is stored within one sixth of the total Captain Sandstone area. Storage of 360 million tonnes of CO2, the previous estimated minimum theoretical capacity for the sandstone (SCCS, 2009) and total calculated at twelve possible injection points (SCCS, 2011), is predicted using hydrocarbon field data at two feasible and practical injection sites.
- The CO2MultiStore findings are important in a European context as they illustrate an approach to make the vast potential, in all sectors of the North Sea, accessible and practical for CO2 storage. The methods developed in CO2MultiStore can be applied to optimise CO2 storage and give greater confidence to prediction of site performance worldwide.