Quantitative risk assessment of plugged and abandoned wells for an onshore CO 2 storage pilot: a stochastic approach for evaluating leakage magnitude and exposure potential

An essential path towards full-scale CO2 injection is via storage pilot projects intended to demonstrate proof-of-concept in different regions, jurisdictions, and geological provinces. long-term storage integrity is imperative for any CO2 storage project and must be addressed through risk assessment techniques, as several factors are inherently uncertain. This paper presents preparatory work in advance of a proposed onshore storage pilot in the Moravia region, South-East Czech Republic, where such risk assessment methods were developed and applied for the Žarošice oil and gas field. The focus of this paper is to evaluate abandoned wellbores as future leakage pathways. A novel approach has been developed based on stochastic leakage modelling coupled with a ground-level CO2 gas dispersion model to predict possible exposure to humans, animals, and plants in the vicinity of the injection site. Threshold levels for CO2 were used to describe the degree of severity of different exposure levels. A key aspect has been to quantify and propagate uncertainty throughout the model-chain of the analysis. By using this approach, value may be gained by managing and reducing uncertainties, to guide planning of risk-reducing measures and actions, determine safe operating conditions and use the inherent uncertainty to facilitate well-founded decisions in a transparent way.