A hydromechanical approach to assess CO2 injection-induced surface uplift and caprock deflection

• A semi-analytical solution is proposed to assess CO2 injection in deformable medium.
• Good agreement is found between the proposed solution and the finite element method.
• Geomechanical interactions between a caprock and adjacent regions are examined.
• The surface uplift measured at In Salah can be reproduced by the proposed solution.

This study focuses on the derivation of a semi-analytical approach for the evaluation of surface uplift and caprock deflection induced by underground injection of CO22. The adopted methodology includes the development of a mathematical model that incorporates the deformable behaviour of the storage reservoir and the flow of two immiscible fluids (CO22 and brine) within the aquifer while the surface rock or the caprock layer is modelled as a thin plate. Governing equations are solved for the axisymmetric flexural deflection due to a constant rate of CO22 injection. Both developed solutions are applied to a representative CO22 storage case solved numerically by the finite element method, and good agreement between results is observed. When benchmarking to the In Salah surface uplift, the developed semi-analytical approach can capture a high rate of surface uplift caused by the pressure build-up during the early stage of CO22 injection. The required calculation time is very short compared to a classical finite element approach. This method can be employed as a design tool for the analysis of uncertainty in parameters such as the injection rate, porosity, rock properties and geological structures. This semi-analytical approach also provides an efficient means of estimating the influence of high injection rates of CO22 on surface uplift.