Carbon dioxide injection 

Present position on land

Carbon injection for improved recovery has been applied since the early 1970s in many oil fields on land, mainly in Texas, USA, and Canada.

Output from large natural carbon sources is piped to the relevant oil fields for injection. Some industrial sources in the region also contribute carbon deliveries.

Injected carbon injection has an efficient sweeping effect in the reservoir, caused by:

• gas-oil miscibility
• compositional effect (swelling and vaporisation)
• reduced oil viscosity
• high density of carbon dioxide compared with oil
• high viscosity of carbon dioxide compared with hydrocarbon gas.

 

Present position offshore

So far no application based on carbon injection for offshore IOR has been initiated.

Reservoir evaluation and screening studies for offshore carbon injection have been carried out on several Norwegian fields, and Statoil has performed in-depth reservoir studies for Gullfaks, Volve and Sigyn.

Current studies on the Heidrun field relate to a carbon value chain for the Halten-Nordland area of the Norwegian Sea.

A lack of readily available carbon sources and the high costs of carbon capture and transport have so far meant that carbon injection into fields on the Norwegian continental shelf would be uneconomic at low to medium oil prices.

However, this picture may change in future if cheaper carbon dioxide becomes available for injection – through governmental incentives or reduced costs –  and a rise in long-term oil prices.

Challenges

Special challenges are posed for the offshore use of carbon dioxide by materials corrosion, facilities and excessive well spacing.

The use of carbon dioxide in water-alternating-gas (WAG) injection seems to be the most promising option as a tertiary recovery method for fields where the current production strategy is water flooding.

Big uncertainties also exist in estimates, while large variations in predictions for IOR from different fields reflect individual reservoir properties and field conditions.

The simulation of a carbon dioxide WAG process faces similar challenges to a hydrocarbon WAG.

Significant experience acquired by Statoil with hydrocarbon WAG on a large number of its fields, such as Gullfaks, Snorre, Statfjord and Veslefrikk in the North Sea, will provide valuable understanding of the possible application of carbon dioxide WAG.

Statoil has considerable experience of carbon separation from natural gas. It is also a leader for offshore carbon storage in sub-surface aquifers through its projects on Sleipner East in the North Sea and Snøhvit off northern Norway.