Comparison of sealing properties of Amundsen and drake formations for potential CO2 storage in North Sea

Seal evaluation for CO2 storage is different from that of a hydrocarbon trap since the oil or gas accumulation itself validates the cap-rock integrity. However, in case of subsurface CO2 storage a careful investigation is required to avoid any risk of potential seal failure. The Johansen Formation of Early Jurassic age in and around the Troll field is a potential CO2 storage reservoir in the northern North Sea. It is enveloped by Amundsen mudstone, whereas in the southeast where the Amundsen cap pinches out, the Drake mudstone Formation directly overlies the Johansen Formation. We evaluated wireline log data from 24 exploration wells using petrophysical analysis and rock physics diagnostics to obtain present day depth, thickness, temperature, volume of clay, physical and elastic properties to evaluate the seal integrity of the Amundsen and Drake Formations. The sealing properties of both the formations were found to be within acceptable range, with minor presence of brittle zones at deeper levels within the Drake Formation containing low volume of shale. These findings will help understanding the seal integrity of Amundsen and Drake Formations as cap-rocks above the Johansen Sandstone being a potential CO2 storage reservoir.