Physics of large-scale subsea releases of CO₂

With offshore CCS projects gaining momentum, extensive research has focused on understanding chronic reservoir leaks (bubble trains and swarms) and their environmental impacts.

However, predicting the fate of large-scale acute releases which could persist for weeks in the case of damaged pipelines (bubble plumes), critical for large-volume CO₂ CCS, remains limited. This study investigates the unique features of large-scale subsea CO₂ releases, particularly their multiphase buoyant behavior.

We extend previous work of a detailed 3D CFD model for transient bubble plumes with mass transfer to include dispersed immicible liquid dropplets and their evaporation dynamics (phase change). The phase diagram of CO₂ for relevant operating conditions puts new demands on the physics that needs to be represented in such models.

Using this extended model we analyze and show examples of how ocean depth, temperature and stratification influence plume dynamics and nearfield dissolved CO₂ characteristics in contrasting environments like those found in the Gulf of Mexico, Australian North West Shelf, Timor Sea and the North Sea.

In contrast to onshore pipelines, there is a lack of data and observations of large acute releases of CO₂.

Thus, first principles based modelling will play an important role in pre-FEED and FEED studies of CCS projects in the coming years.

In presenting the model we highlight where more observations/experimental data is needed.