CO2 Leakage Risk through Remobilized Cenozoic Sediments in the Northern North Sea

Abstract

Climate change is one of the biggest challenges faced today. One of the possible solutions to mitigate this challenge is the secure storage of CO2 in the subsurface. Remobilized Cenozoic sediments contain large sand volumes in the North Sea. Previous storage in in similar sediments above the Sleipner field has proven to be safe. This thesis assesses the possibility of CO2 storage within remobilized sediments of the Miocene-Oligocene age in the northern North Sea. To perform such evaluation, seismic images below, within, and above remobilized sediments are analyzed. This is done to identify potential fluid escape structures, migration pathways, and potential hydrocarbon accumulations that can tell us something about the sealing capacity of Miocene-Oligocene sediments. The results show many occurrences of shallow bright spots above the remobilized sediments. These are mostly located in the northern part of the dataset and often above deeper oil reservoirs. This proves that there is sealing capacity in the sediments above Miocene-Oligocene. Chimneys are observed from the Jurassic up to the Eocene. Further extensions of these features are difficult to determine. Chimneys are also observed in the interval above Miocene but do not seem to connect directly to chimneys below Eocene. Moreover, such occurrences are typically found in close proximity to one another. There is little evidence for hydrocarbons within the remobilized sediments. Therefore, these suggest that there is limited evidence for gas accumulations in Oligocene/Miocene sediments. Possible reasons for this are effective sealing by smectite-rich clay or poor sealing capacity that allows gas to escape and not accumulate. It is therefore not quite clear whether these remobilized sediments are suitable for CO2 storage. Further research, including high quality seismic data processing and well data is needed to further evaluate their safety as a storage cite.