ABSTRACT Injectivity loss is a key source of uncertainty in geological CO₂ storage operations, particularly in saline aquifers where permeability may be reduced by salt precipitation and fines migration [1–3]. Finite element (FEM) models are commonly used to simulate CO₂–brine flow; however, uncertainty in model parameters limits their direct use for risk-based assessments. This work explores the use of Bayesian Updating with Structural Reliability Methods (BUS)[4] as a framework for probabilistic injectivity analysis, with FEM models employed as deterministic forward simulators. A one-dimensional radial FEM model based on a Black-Oil formulation is considered. Injectivity degradation is represented through an effective permeability reduction parameter, treated as uncertain. Synthetic observations of pressure or injectivity, generated from FEM simulations and augmented with measurement uncertainty, are used to illustrate Bayesian updating within the BUS framework. The resulting posterior distributions provide a basis for estimating injectivity-loss probabilities through limit-state formulations. The contribution emphasizes methodological development, with the FEM model employed to illustrate the proposed Bayesian framework. Additional simulations including thermal effects with a simplified Joule–Thomson formulation are considered as a sensitivity study. Although demonstrated using reduced-order models and synthetic data, the proposed framework is intended to support future assimilation of experimental injectivity-loss data and more detailed multiphysics simulations. REFERENCES [1] M.A.M. Yusof, Y.A.S. Neuyam, M.A. Ibrahim, I.M. Saaid, A.K. Idris, M.A. Mohamed, Experimental study of CO2 injectivity impairment in sandstone due to salt precipitation and fines migration, J. Pet. Explor. Prod. Technol. 12 (2022) 2191–2202. [2] M.A. Md Yusof, M.A. Mohamed, N.A. Md Akhir, M.A. Ibrahim, M.K. Mardhatillah, Combined Impact of Salt Precipitation and Fines Migration on CO2 Injectivity Impairment, Int. J. Greenh. Gas Control 110 (2021) 103422. [3] Y.A. Sokama-Neuyam, J.R. Ursin, The coupled effect of salt precipitation and fines mobilization on CO2 injectivity in sandstone, Greenh. Gases Sci. Technol. 8 (2018) 1066–1078. [4] D. Straub, I. Papaioannou, Bayesian Updating with Structural Reliability Methods, J. Eng. Mech. 141 (2015) 04014134.