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.