Fluid leakage assessment of the overburden structure at the Sleipner CO2 storage site

Abstract

Carbon capture and storage (CCS) has been proposed as one of the alternatives for climate mitigation. CCS is a process where CO2 is trapped from large point sources, transported to a storage location and injected into storage reservoirs. One of the alternatives for CO2-storage is underground geological storage. Characterizing such an underground reservoir is crucial for safe storage, where leakage from the reservoir is considered the biggest hazard. Knowledge of the geology and in particular the flow of fluids in the area is of special interest.

In this thesis the overburden of the Sleipner CO2-injection field, located in the North Sea, has been mapped for vertical curvilinear features in seismic data. Their distribution and origin has been assessed and interpreted.

The vertical features are thought to be fluid flows, found across the data set (ST98M11) interpreted in this thesis. The fluid flows in the data set have similar characteristics, both in size and the seismic amplitude anomalies seen in connection to them. Concerning the distribution of these fluid flows, they seem to have the highest occurrence rate in the southwestern corner of the data set, which might be seen in context with the seal defined for the Sleipner reservoir thinning out to the south west. The origin of the fluid flows seem to be connected with the underlying layer of mud diapirism and polygonal faulting, as well as being influenced by an intermediate layer of Pliocene age.