Hector George Barnett , Mark Ireland, Charles K Dunham, Cees van der Land

The ability to safely store non-hydrocarbon fluids in the subsurface, such as carbon dioxide or hydrogen, will likely be vital in all pathways to decarbonise global energy systems. Storage of these fluids will require monitoring programmes to identify dynamic changes during the injection and storage phases and to identify unintended migration. Seismic monitoring is widely adopted in monitoring plans. We investigate the changes in seismic response for different non-hydrocarbon fluids and different saturations.
The bulk elastic properties of subsurface rocks are influenced by the fluids present within the pore space and impact the seismic response of the rock. We undertake fluid substitution modelling, calculating new rheological properties of reservoir intervals after substituting brine for either hydrogen or carbon dioxide, varying the water saturation from 100% to 0%, and determining the new elastic properties. We investigate three proposed reservoirs for carbon dioxide storage on the UKCS, the Triassic Bunter Sandstone Formation, the Permian Leman Sandstone Formation and the Triassic Helsby (Ormskirk) Sandstone Formation. The workflow is stochastic and as such allows for the investigation of the impact of geological uncertainty on the results. The newly determined elastic properties are then used for modelling the seismic response and wedge models.