The Sleipner CO2 injection project was the world's first industrial offshore CO2 Capture and Storage (CCS) project with more than 16 Mt CO2 injected since 1996. Key monitoring insights from Sleipner are the dual interpretation of seismic and gravimetric monitoring surveys to quantify the free CO2 mass changes and plume geometry development as a function of time. The learnings from Sleipner have contributed to making guidelines for monitoring future CCS injection projects, showing that selection of monitoring technology and the timing and extent of monitoring surveys should be case specific and risk based, while also taking into account the long term nature of CCS projects.
Furre et al. (2017) studied this question.