Impact of CO2 mixing with trapped hydrocarbons on CO2 storage capacity and security: A case study from the Captain aquifer (North Sea). (15th November 2020)

• Record Type: Journal Article
• Authors: Ghanbari, Saeed; Mackay, Eric J.; Heinemann, Niklas; Alcalde, Juan; James, Alan; Allen, Michael J.
• Is Part Of: Applied energy. Volume 278(2020)
• Publication Date: 2020-11-15
• Subjects: CCS -- CO2 storage -- Mixing -- Saline aquifer -- Plume migration -- Compositional modelling; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2020.115634
• Languages: English
• ISSNs: 0306-2619

Abstract

Highlights: Mixing makes the CO2 plume lighter causing its faster migration. Faster plume migration may reduce the CO2 storage capacity in open saline aquifers. Mixing compromises the storage security as CO2 substitutes the hydrocarbon gas. The choice of modelling strategy is important to properly capture the mixing effect. Many uncertainties affect and control the mixing significance in the storage site. Abstract: Gas mixing in the subsurface could have crucial implications on CO2 storage capacity and security. This study illustrates the impact of gas mixing in the "Captain X" CO2 storage site, an open saline aquifer and subset of the greater Captain aquifer, located in the Moray Firth, North Sea. The storage site hosts several abandoned hydrocarbon fields where injected CO2 could interact and mix with any remaining hydrocarbon gas left in the depleted structures. For this study, compositional simulation of CO2 injection into the Captain X storage site reservoir model was conducted to quantify the impact of mixing. Results show mixing of CO2 with the remaining trapped hydrocarbon gas makes the plume considerably less dense and more mobile. This increases the buoyancy forces acting on the plume, causing it to migrate faster towards the shallower storage boundaries and therefore, reduces the storage capacity of the site. Mixing also compromises the storage security as it mobilises the structurally trapped hydrocarbon gas from within the abandoned fields. Informed injector placement helps to manage and reduce the impact of mixing. Correct assessment of mixing is also considerably dependent on the volume and property of the trapped hydrocarbon gas. To provide a correct long term understanding of storage capacity and security, the impact of mixing, therefore, needs to be correctly considered in all large-scale CO2 storage operations.