Assessment of CO2 Storage Capacities and Identification of Operational Risks Using Large Basin-Scale Multi-Physics Simulation
Authors: Kachuma D. , Ramsay T. , Gross H. , Kloucha C. , Hamon F. , Gacem M. , Jellema R. , Noushabadi M. J. 
Published: October 2023

Fast and accurate subsurface simulations are required to strategically plan for robust CO2 Capture and Storage (CCS) developments and reduce operational risks. The impacts, however, of multiple coupled physical phenomena that arise due to CO2 injection have been found to be challenging for many conventional reservoir simulators to support. The objective of this paper is to highlight the steps taken to demonstrate a large-scale feasibility assessment of CO2 sequestration in a basin-scale saline aquifer located in Abu Dhabi.

The GEOS simulator was used to perform this study because of its ability to encompass the main uncertainties associated with assessing CO2 storage potential. The assessment of these uncertainties led to an improved understanding of operational risk in very large scale and long timeline models through fully coupled multi-physics simulation. This study evaluated the risks and uncertainties arising from both standalone dynamic flow simulations & coupled flow-geomechanical simulations.

For standalone dynamic flow simulations, uncertainties linked to changes in injection rate and maximum allowed borehole pressure were explored. Several CO2 injection scenarios with various well counts, rate targets and pressure constraints were developed to estimate the notional injection capacity, CO2 plume movement, and the CO2 footprint after 2000 years. After consolidating the dynamic flow simulation results, geomechanics properties were incorporated into a fully coupled flow-geomechanical model. Disparate CO2 injection scenarios were explored and the effect on caprock integrity, overburden & surface subsidence were observed. The geomechanical impact on the notional storage capacity were then derived.

The results of the dynamic flow simulations showed the evaluation of notional CO2 storage capacity in an aquifer over a long duration. It was also observed that the CO2 remained trapped within the structure for a period of up to 1000 years. Several trapping mechanisms such as structural trapping, residual trapping, and dissolution trapping were investigated. It was demonstrated that the residual trapping mechanism was the most proficient in maintaining CO2 containment within the formation.

The results of the coupled flow-geomechanical simulations showed that depletion, having occurred in specific areas, can be reversed with CO2 injection as well as marginal uplift of the surface. An investigation into the impact of CO2 injection on cap rock integrity showed that a nominal injection rate would be within the acceptable limits of safe injection. A sensitivity analysis of higher injection rates up to three times the reference value, showed that in the absence of maximum bottom hole pressure constraints, cap rock integrity and CO2 containment may be compromised. Through the determination of mechanical stresses and deformations around the injectors, GEOS has demonstrated that it may facilitate complex, large-scale, and long timeline challenges associated with critically important CCS operations.