Using pressure recovery at a depleted gas field to understand saline aquifer connectivity

A key uncertainty facing Carbon dioxide Capture and Storage (CCS) in saline aquifers is long term injectivity, which is primarily a function of the connected aquifer pore-volume within which formation brine can be displaced as the CO2 is injected. Protracted injection testing to interrogate and prove the far-field connected pore-volume would increase the lead-in times for commissioning of storage sites and would significantly increase appraisal costs. Here we use natural gas production and subsequent reservoir recharge legacy data from the Esmond gas field in the UK sector of the southern North Sea to gain an understanding of the dynamic behaviour of the Bunter Sandstone, a major saline aquifer. Results suggest that Esmond has a connected pore volume of 1.83x1010 m3, suitable for injecting CO2 at a rate of up to 2 million tonnes per year for at least 55 years. 3D seismic data suggest that Esmond reservoir properties are likely to be replicated across the wider Bunter Sandstone aquifer, notably around the Endurance structure which was, until recently, proposed for a full-chain CCS project.