CO2 storage in depleted oil and gas fields

We have started a new CO2 Storage research programme with a vision to develop cost effective and low risk CO2 storage in depleted oil and gas reservoirs, tailored for offshore Denmark.

Denmark has an ambition of reducing carbon emissions by 70% in 2030. One of the tools to help deliver on this goal is access to CO2 storage capacity. The existing oil and gas fields provide an opportunity to accelerate the permanent storage of CO2 thanks to:

  • A significant well described reservoir storage capacity
  • Decades of accumulated knowledge of subsurface behaviour
  • A reservoir seal which has been proven gas tight over geological time
  • Existing infrastructures that may be re-utilised
  • Distance to shore and inhabited areas

The centre finalized a CO2 storage state-of-the-art study in early 2021, identifying knowledge and technology gaps. This gap analysis has been a starting point for defining the scope for the research programme. 

The CO2 Storage research programme is split into three themes:

Chalk

The CO2 storage State-of-the-Art study revealed that there are some concerns about using chalk reservoirs for CO2 storage. These concerns may be overcome with increased knowledge on the topic.

The research projects within the chalk theme are looking into the suitability of chalk as a storage reservoir for CO2. The question is addressed from several different angles and the aspiration is that by the end of 2022 the projects will jointly be able to clarify if there are any showstoppers preventing chalk from being used for CO2 storage.

As most of the existing oil and gas fields in Denmark are chalk fields, proving the use of these particular reservoirs can have a large impact on the storage potential offshore Denmark.

Monitoring

Monitoring of CO2 injection is key for public acceptance of the CO2 Capture and Storage (CCS) concept. When injecting CO2 into the subsurface two things have to be monitored; how does the CO2 plume move in the subsurface reservoir and how are potential leaks at the seabed detected. The monitoring theme within the CO2 Storage Programme covers both types of monitoring.

The theme stretches from the development of a subsea CO2 detection sensor to a novel use of existing data to reduce requirements for seismic data acquisition. In addition to this, the feasibility of a completely new and different approach to both monitoring of CO2 plume movement and CO2 leak detection is being investigated.

Wells

One of the benefits of re-using depleted oil and gas reservoirs for CO2 storage is that existing infrastructure can be re-used for the injection. The re-use will reduce both the overall cost of the CO2 injection project and the environmental impact.

The wells are an important part of the existing infrastructure even though the wells were initially not designed for a CO2 operating environment. Therefore, the Wells theme of the programme is looking into how existing wells can be re-used, both by developing a CO2 corrosion prediction model and by preventing corrosion with the use of coatings.

When injecting CO2 into a reservoir with several existing wells, the majority of these wells will have to be abandoned prior to the injection start. The abandonment barriers will have to be able to withstand the new reservoir fluid with CO2. In the DUC part of the Danish North Sea, the reservoir chalk is overlain by a thick layer of shale and this shale can form a long-lasting barrier against CO2. Research within the Wells theme will investigate how this shale formation can be utilised as part of the abandonment barriers for existing wells. Finally, several novel barrier materials for well abandonment in a CO2 environment will be evaluated for feasibility to find alternatives which can support abandonment methods.