To study the likelihood of and controls on a potential CO2 leak from the storage reservoir to the marine ecosystem in a typical North Sea setting.
To calculate risks of leakage, we need to track the fate of CO2 underground – particularly how it becomes permanently trapped in order to assess what the chances are that some fraction of the CO2 might escape. We therefore need to understand how CO2 moves underground. CCS storage sites will be chosen because the risk of CO2 escaping from the storage site (typically at depths greater than 800 m below the surface) into the surrounding rocks is low. However, if CO2 does escape from the storage site, we need to understand what proportion could reach the marine sediments and ultimately the environment. Quantifying this is challenging because of the widely differing characteristics of the geology and sediments and because the properties of CO2 change from liquid to gas as it moves towards the surface due to a decrease in temperature and pressure.
The tasks within this work package are:
Task 1.1 Flow Review (BGS):
A literature review of natural CO2 leakage has been completed. This will help us to determine flow rates in different geological settings. Information from natural (Figure 1) and modelled leaks through and around existing boreholes will also be compiled.
Task 1.2 Review of geological storage water content (Heriot Watt University):
This involves researching the pressure-temperature- grain size arrangements for CO2 escape from storage reservoirs at North Sea depths. This will determine under what conditions water may form within the storage reservoir geology if a CO2 leak occurred, and how this may be enhanced.
Task 1.3 CO2 movement: (Durham University)
This will examine the mechanisms of CO2 ascent with particular focus on the possibility of self-fracturing pathways towards the surface caused by pressure changes during CO2 injection.
Task 1.4 Geochemical and phase models (Bristol University)
This will examine fluid flows, CO2 states (from liquid to gas), chemical reactions with below surface formations and shallow sediments of differing composition enabling us to carry out mass balance calculations.
Task 1.5 Box model construction (University of Edinburgh)
This will provide a 1D box model which will provide information on the most important processes affecting CO2 in marine sediments
Task 1.6 Geological models (University of Edinburgh)
Geological models of the marine sediment and water in rock layers will be constructed for two typical North Sea CO2 storage sites.
Task 1.7 Knowledge Exchange (University of Edinburgh)
We will explain our results through the Knowledge Exchange programme to stakeholders, statutory bodies and publics, and write up results for publication.
 A mass balance calculation allows us to calculate how and where CO2 has been distributed within the formations and sediments.