Introduction
The preferred locations for CO2 sequestration in the Barents Sea are structural traps which have been proved to contain brine and no moveable hydrocarbons. In the future, depleted and abandoned gas fields can also be developed as storage sites.
Nine structures (named prospects A to I) within the aquifer systems of the Realgrunnen Subgroup have been mapped and characterized by their storage capacity, injectivity and seal quality. The storage capacity of a structural trap can be limited by the pore volume of the structural closure and by the pore volume and permeability of the connected aquifer. The evaluation of Prospect A is based on a simulation model that takes these factors into account. Evaluation of the other prospects is based on pore volumes of the structural closures and a storage efficiency factor based on the geological conditions for each prospect. Pore volumes are calculated based on mapped surfaces, porosity and net/gross maps. For the reservoirs in the Hammerfest Basin, average permeability is indicated in the tables for the Nordmela Formation (low values) and Stø Formation (high values). Provided that the CO2 will be injected in the Stø Formation, injectivity is considered to be medium to high in most prospects. The seal quality is characterized by the thickness of the primary seal (the Hekkingen and Fuglen Formations) and the faulting intensity of the reservoir. Seismic anomalies indicating shallow gas were also taken into account. Leak-off tests indicate that the typical fracturing pressures in the Barents Sea are somewhat lower than in the North Sea and the Norwegian Sea. A prospect simulation was run with a maximum pressure build-up of 30 bar. Maturation of prospects which may be of interest for petroleum exploration is considered to be low (blue colour). Prospects which have been drilled and that proved only brine or brine and residual oil, are considered more mature (green colour). The yellow colour is applied to prospects which are approaching a development plan, such as in the Snøhvit area. These prospects require more in-depth studies than what was possible in this study. In addition to the prospects, the Greater Snøhvit, Greater Askeladd and Greater Albatross areas are defined. These areas represent structural closures with several culminations. Some of the culminations are hydrocarbon-filled, and some of them have only residual hydrocarbons. There are indications in the wells that these greater structural closures have been filled with hydrocarbons at the time of maximum burial. CO2 injected in these is not likely to migrate out.
