Background
Progression of CO2 storage in retiring oil fields is particularly valuable as it to a large extent is based on existing infrastructure and data, which reduces both capital expenditure, energy consumption and environmental impact. In addition, offshore storage in depleted oil fields is likely to meet less public resistance than onshore/nearshore storage or other initiatives involving new large-scale construction and environmental impact. However, nearly all Danish oil fields have their primary reservoirs in chalk, which to some extent will dissolve when exposed to the carbonic acid that will form in the subsurface when CO2 is injected. Some of the dissolved chalk is likely to re-precipitate elsewhere in the reservoir. These processes could seriously affect infrastructure and storage efficiency in the oil fields.

Several studies are based on CO2 injection experiments in chalk, but the focus and design of these studies have not been dissolution/precipitation processes. In addition, the extensive experience with chalk reservoirs in Denmark provides an opportunity to taking the lead on developing CO2 storage in chalk reservoirs.

Objectives
The general objective of the project is to provide the fundamental knowledge necessary to decide to further progress CO2 storage in oil/gas fields with chalk reservoirs. This will be achieved through an integration of geochemical and physical experiments, petrographic investigations and numerical modelling.

Expected results

1. Fundamental data on dissolution/precipitation in chalk during and after CO2 injection.
2. Determination of the effect of dissolution/precipitation induced by CO2 injection on the chalk and its reservoir properties.
3. A sector-scale model which can be applied to evaluate the feasibility of CO2 storage in oil/gas fields with chalk reservoirs.