Geological storage of CO2

The ULTIMATECO2 (Understanding the long-term fate of geologically stored CO2) project will increase knowledge of specific processes that could influence the long-term fate of geologically stored CO2 and provide predictions for long-term storage site performance.

The initiative has employed detailed laboratory, field and modelling studies of the main chemical and physical processes involved and their long-term impacts. They include trapping mechanisms, fluid-rock interactions, and effects on the mechanical integrity of fractured caprock and faulted systems. Other effects include leakage due to mechanical and chemical damage in the vicinity of the well.

ULTIMATECO2 assessed the overall long-term behaviour of storage sites at the regional scale regarding efficiency and security, as well as far-field brine displacement and fluid mixing. This will enable more accurate predictions of the effects of geological storage of CO2 by addressing the uncertainty associated with numerical modelling.

Researchers used typical geological environments suitable for storage demonstration sites in deep saline sandstone formations. One site was located onshore in West Lorraine, France, while the other was offshore in the North Sea, United Kingdom.

3D trapping models were calculated for the two sites at short (injection) and long-term (post-injection) timescales and showed the importance of structural and dissolution mechanisms. The presence of impurities was also investigated through modelling.

In addition, innovative models were developed to incorporate damage zones and deformation bands in the representation of fault models. Experiments also evaluated the effects of acid leaching on the transport properties and mechanical integrity of pre-fractured (by freezing) Opalinus clay samples.

The consortium developed a coupled geochemical-geomechanical model to assess the long-term fate of CO2 in the subsurface by addressing induced flow and potential failure during CO2 injection. It also studied the behaviour of faulted caprocks and the geochemical interactions between clay and cement with CO2.

ULTIMATECO2 will develop recommendations for operators and regulators, enabling a demonstration of the assessment of long-term storage site performance. Scientific knowledge on the long-term efficiency and safety of CO2 storage will be disseminated to not only operators of demonstration sites but also other stakeholders. These include policymakers, storage developers, investors, the scientific community and the wider public.