A decoupled CFD-mechanical model for estimating the deflections from CO₂ sequestration in low & high buoyancy flow regimes

This work evaluates the caprock deflections at various timeframes induced by underground injection of CO2 in all flow regimes for cap integrity considerations in CO2 sequestration. The pressure profiles in the various regimes are not known a-priori and depend strongly on the pumping scenarios followed and are hence obtained numerically via CFD numerical simulations that were performed with the software Ansys-Fluent. Following a decoupled approach for time effectiveness, pressure profiles are approximated by logarithmic functions and integrated into a mathematical model assuming elastic medium storage, cap and surface rocks while the formulation is in the spirit of the Germain-Poisson-Kirchhoff thin plate theory. Elastic solutions are developed for the axisymmetric flexure deflections of the cap layer during CO2 internal pressurization of the aquifer for the low buoyancy and high buoyancy regimes. The novelty of the model lies in the fact that is capable for estimating fast and accurately the deflections created in the various flow regimes with a simplified approach, effectively avoiding the time consuming fully coupled FEA-CFD and could be used as a convenient tool for evaluating cap rock integrity. The results of the analysis indicate that for the set of data used, most uplift magnitudes are not capable for creating fractures on the cap rock compromising the cap integrity when the solution is mapped in the high-buoyancy regime. On the other hand, if the solution is mapped in the low-buoyancy regime the pressure-induced, could cause poro-elastic deflections over time which could lead eventually to fracture creation.