Dynamic CO2 Storage Capacity for a Fault-Bounded Structure in the Trøndelag Platform, Offshore Mid-Norway
Authors: Abdelkareem Sherif Shaban , Grimstad Alv-Arne , Bergmo Per Eirik , Gaol Calvin Lumban , Jahanbani Ghahfarokhi Ashkan , Lothe Ane Elisabet , Ringstad Cathrine , Ganzer Leonhard 
Published: June 2023

Abstract
The latest report of the UN International Panel on Climate Change (IPCC) has affirmed once again the urgent need for carbon capture and storage (CCS) to realize the international climate ambitions. Deployment of CCS technologies is a fundamental key to reach the 1.5°C climate target since the estimated global technical geological CO2 storage capacity is 1000 gigatons, which is higher than the CO2 storage needs through 2100.
In this study, the dynamic carbon dioxide storage capacity for a potential CO2 storage site in the Trøndelag platform is investigated. The Garn formation of the selected site in the Norwegian Sea has promising geological characteristics and is here considered to be the main storage formation. A conceptual geological model has been built based on the available geological data which have been mainly extracted from the literature. Three main realization models representing different porosity and permeability ranges are constructed.
Dynamic reservoir simulation studies for each realization are run with an injection rate of 2 million tonnes per year for 50 years and continued for 70 years of post-injection. Sensitivity analyses investigate different parameters’ effect on the CO2 plume, pressure development, and CO2 storage capacity. The sensitivity parameters include relative permeability, injection rate, number of injection wells, perforation length, boundary conditions, fault transmissibility and capillary pressure effects.
The results after 120 and 240 years of total simulation time, show the clear effect of saturation functions on plume migration and CO2 dissolution into the water phase. The porosity and permeability variations within a specific range have a minor effect on the pressure development and dissolved/trapped CO2 amounts but mostly affects the CO2 plume shape, extent, and migration speed. Doubling the injection rate using one well will increase the dissolved and trapped CO2 amounts by more than 70% and 90% by the end of simulation, respectively. While injecting the doubled CO2 amount using two wells will lead, up to 130 % and 115 % rise in the dissolved and trapped CO2 amounts, respectively. For both cases with the double injected amount, the increase in the average field pressure during injection is about twice the increase in the base case. A sharp rise in the average field and near-wellbore pressures has been noticed when the boundary conditions are closed demonstrating the importance of hydraulic communication with the wider connected pore volume, represented through analytical Carter-Tracy aquifers in the base case scenarios to represent the semi-open full volume of the Garn Formation. Without the external pore volume, a sharp increase in formation pressure led to an automatic shutdown of the injection well which caused a reduction in the injected CO2 amount. Increasing the perforation length of the injection well, eliminating fault transmissibility as well as including a non-zero capillary pressure showed no significant effect on CO2 plume, and pressure development after 120 years of simulation, while a slight change in the dissolved and trapped CO2 amounts is observed. The effect of these sensitivity parameters may be obvious if the simulation time is increased.
This study mainly confirms that this structure in the Trøndelag Platform can store up to 200 Mt of CO2 as predicted in previous work. This makes the selected structure a potential CO2 storage site in the Norwegian Sea for future CCS projects.