CO2 for enhanced oil recovery in North sea chalk oil fields - can the CO2 be permanently stored?

Norway needs knowledge that facilitates large-scale CO2 storage, including the link between enhanced oil recovery (EOR) by CO2 injection, on pressure buildup as CO2 is injected and how to ensure that the CO2 is permanently immobilized. The project "CO2Chalk" focuses on processes that may facilitate or endanger large-scale permanent storage of CO2 injected to enhance oil recovery in Norwegian oil producing chalk fields. It is already well known that dissolution of the chalk by CO2 charged water can increase reservoir compaction. New knowledge on chalk-fluid interaction and compaction shows that if the wrong CO2 injection strategy is used, the reservoirs will most likely collapse and all CO2 will leak out. Alternatively, development and proper application of this new fundamental knowledge could facilitate self healing of the chalk and ensure permanent storage of up to 400 Mton of CO2 in the Ekofisk oil field alone. The project "CO2Chalk" has contributed with numerical simulation techniques, experimental techniques, new results using these techniques and a reservoir scale model building on this new knowledge. Our new, fundamental understanding of the deformation processes allow us to predict with more certainty the outcome of different CO2 injection strategies.

The proposed project focuses on processes that may facilitate or endanger large scale permanent storage of CO2 injected to enhance oil recovery in Norwegian oil producing chalk fields. Recent results based on interpretation of the geological record, theor y and nanoscale experiments have established a new, emerging understanding of the chemistry and mechanics of chalk: High porosity chalks are protected from reaction with reservoir fluids by a passivating organic material. The chalk may be activated by por e fluid changes or by fracture growth due to stress changes and become highly reactive. This may result in rapid compaction and complete collapse of the reservoir and escape of stored CO2. The project details how to develop new fundamental knowledge by co mbining experiments, geological observations and computer simulations. The research will explicitly treat the state of passivation of calcite surfaces in the chalk matrix and focus on the detailed micro and nanoscale mechanisms of deformation and fluid-ch alk reactions. The development and proper application of this new fundamental knowledge can facilitate self healing of the reservoir chalk and ensure permanent storage of hundreds of Mton of CO2.