Coupled Semi-Analytical Solution For CO₂ Injection-Induced Surface Uplift and Caprock Deflection

This study focuses on a specific problem related to the surface uplift induced by the injection of CO₂ at depth. The adopted methodology includes the development of a mathematical model that incorporates the deformable behaviour of storage media and the flow of two immiscible fluids (CO₂ and water) within the aquifers while the surface rock or caprock layer is modelled as a thin plate. Governing equations are solved for the axisymmetric flexural deflection due to a constant rate of injection of CO₂. Comparison of the results with the surface uplift measurements (In Salah project), show good agreement. The results show that this semi-analytical solution is capable of capturing the pressure build-up during the very early stage of injection, resulting in a high rate of surface uplift. Compared to a FEM simulation, the calculation time required using the semi-analytical solution is very short; it can be employed as a preliminary design tool for risk assessment using parameters such as the injection rate, porosity, rock properties and geological structures. This semi-analytical solution provides a convenient way to estimate the influence of high injection rates of CO₂ on the surface uplift. The methodology in this development can easily incorporate other pressure distributions; thus advances in hydrology researches can also benefit this approach.