CO2 capture from offshore oil installations: An evaluation of alternative methods for deposition with emphasis on carbonated water injection

Capture and storage of CO₂ from gas turbine power plants can be an alternative to electrification from shore to reduce the emissions from petroleum production facilities on the Norwegian Continental Shelf. The objective of this work was to analyse and rank various options for storage using technical economic analyses. The following alternatives were considered:

• 1.

  Dissolution of CO₂ in sea water and aquifer storage of carbonated water

• 2.

  Injection of pure CO₂ into an aquifer

• 3.

  Compression of CO₂ and pipeline transport to a collection centre

• 4.

  Liquefaction of CO₂ and ship transport to a collection centre

• 5.

  Dissolution of CO₂ in sea water and injection into oil fields (carbonated water injection, CWI)

For each alternative the investment costs and operating costs were estimated, and the net present values were determined. Credit for saved CO₂ tax was included as incomes for all alternatives. The CO₂ tax is expected to increase significantly from present level to Year 2030. For Alternative 5, CWI into oil fields, incomes from incremental oil production was also included. This required more comprehensive analyses. Using both a heterogeneous and a homogeneous field scale simulation model incremental oil productions and CO₂ retention were estimated for CWI into both green and brown fields cases.

The economic calculations show that alternatives 1 – 4 have negative net present values. A higher future CO₂ tax than presently envisaged will be needed to make the alternatives economically viable. All cases related to Alternative 5 (project lifetime, heterogeneous and homogeneous reservoir models, green and brown fields) exhibit positive net present values due to incremental oil production. Most, but not all, injected CO₂ remained in the reservoir, depending on the injection period.

Oxygen in the captured CO₂, formation of gas hydrates and corrosion of well materials may cause operational problems of injecting sea water with dissolved CO₂. These aspects have been briefly discussed. Some additional measures may have to be taken to alleviate undesired effects, but none of the issues are likely to prohibit implementation of CWI.

The results obtained suggest that CWI into producing oil reservoirs offers an economic viable and safe way for disposal of CO₂ captured from offshore petroleum production plants provided that a capture plant can be installed, and that the remaining lifetime of the reservoir is so long that the benefits of improved oil recovery can be realised.