Geological Evaluation of CO2 Storage in Depleted Oilfields: A Case Study in the Ula Field

Abstract

This thesis explores the geological feasibility of utilizing the Ula Field in the North Sea for CO2 storage, particularly as the Ula Formation approaches depletion. Recognizing the potential of the overlying Balder Formation, the study expands to evaluate its suitability for CO2 storage as well. Through comprehensive analysis using well log correlation, seismic interpretation, geological mapping, and seismic attributes analysis, the study aims to provide a thorough understanding of the storage capabilities of both formations.

Structural highs, predominantly a result of salt tectonics, were identified within both formations. The Balder Formation contains four structural highs, while the Ula Formation comprises six. However, two of the Ula Formation's structural highs are excluded for further consideration due to their small areas.

The total bulk rock volume (BRV) for identified structural traps of the Balder Formation is 3.49 billion cubic meters, while for the Ula Formation, it is 13.2 billion cubic meters. Consequently, the CO2 storage capacity for the Balder Formation is estimated at 32.5 megatonnes (Mt), and the Ula Formation can store 64.6 Mt, resulting in a combined total storage capacity of 97.1 Mt. These results were derived by considering the storage capacity of the interpreted structural traps without accounting for the risks of leakage.

Considering the areas with low risk, three viable locations for CO2 injection have been identified. The first is in the east, where the Ula Formation offers a substantial storage capacity of 20.3 Mt of CO2. The second area is in the west, where the Balder Formation can accommodate 6.0 Mt of CO2. The third location is an area with aligned structural highs of both the Balder and Ula formations, which coincides with the Ula Field and can store 33.2 Mt of CO2. Finally, five wells are recommended for CO2 injections, with one vertical well in the east, one vertical well in the west, and three horizontal wells in the Ula Field for CO2-EOR purposes.