ZWEIGEL, PETER,ANE E. LOTHE, and ERIK LINDEBERG, IKU Petroleum Research, Trondheim, Norway

Abstract: Offshore underground CO2-disposal - 'Reservoir geology' of the Neogene Utsira Formation, Sleipner Field, North Sea

Underground deposition of industrial emitted CO₂ in offshore aquifers is currently considered as a large-scale option to reduce the amount of greenhouse gases released to the atmosphere. Disposal of CO₂ by oil companies may be necessary to fulfil environmental requirements, e.g., to be allowed to produce gas from CO₂-rich reservoirs, as in the case of the Sleipner Field in the North Sea.There, Statoil and license partners started in 1996 to inject CO₂ into sands of the Utsira Formation. This project serves as a test case for offshore underground CO₂-disposal in general, and for possible future use of the wide-spread Utsira Formation in particular. The Utsira Formation is a sand-unit of Miocene and/or Pliocene age that occurs in the northern North Sea. It is highly permeable, which facilitates injection and migration of CO₂. The Utsira Formation is overlain by the shaly Pliocene Nordland Group that is down-lapping onto it. This potential cap-rock is generally considered to be impermeable for CO₂. However, it contains silty, and possibly sandy intervals of so far unknown geometry. The Utsira Formation has been affected by faulting, which may have deformed its cap-rock, too. A reliable geological model of the 'reservoir' and the cap rock is crucial to be able to predict the retention time of CO₂ by simulations.The sensitivity of how various reservoir parameters affect the migration and distribution of CO₂ in the Utsira Formation will be illustrated. These parameters will include permeability of the sand, imperfections, lithology and deformation of the cap rock.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England