An optimal approach for representing an open boundary in modelling CO2 storage in a regionally extensive aquifer

• Radius of Investigation integration enables finite models to mimic regionally extensive aquifers. • Generalized open-boundary representation is proposed, resolving the unresolved challenge of modelling linear extensive aquifers. • Novel boundary cell modifications overcome phase constraints and geometric limitations of traditional analytical models. • Multi-operation adaptability efficiently models interference effects from CO 2 injection, oil production, and geothermal extraction in regional aquifers. Injecting CO2 into a regionally extensive aquifer can lead to significantly less pressure buildup compared to a geologically compartmentalized aquifer. For CO2 storage in a regionally extensive aquifer, accurately modelling the impact of water being displaced outside the built geological model is crucial for assessing pressure buildup within the model. However, it remains challenging due to limitations in existing analytical aquifer models (e.g., Carter-Tracy) that assume radial symmetry and restrict fluid phase interactions. Some simplifications were commonly used to represent the open boundary, and these simplifications might inaccurately depict pressure propagation beyond the open boundary. This paper introduces an optimal approach for representing the influence of an open boundary by contrasting various current approaches. Initially, it employs the CO2 injection’s influence distance to ascertain the scope of the pressure discharge area. Subsequently, it combines boundary cell elongation with pore volume and transmissibility modifications to replicate pressure propagation beyond the modelled domain, addressing both linear and two-dimensional (2D) aquifer systems. The outcomes reveal that this approach accurately predicts pressure buildup in a model with an open boundary due to CO2 injection. Furthermore, the method can be used to accommodates interference effects from multiple subsurface operations (e.g., CO 2 injection, oil production, geothermal extraction). By overcoming the phase constraints and geometric limitations of traditional analytical and numerical models, this approach provides a versatile tool for devising injection plans and conducting risk assessments to provide reliable risk assessments and robust injection strategies for large scale CO2 storage projects.