Fault Leakage Risk Assessment via Coupled Probabilistic Modelling During CO2 Sequestration
Authors: Sorgi C. , De Gennaro V. , Welsh P. 
Published: August 2024

ABSTRACT:
Some of the potential risks associated with CO2 sequestration include leakage, induced seismicity, groundwater contamination, reservoir integrity, health and safety risks, long-term liability, economic viability, and operational challenges. Ensuring the safe storage of CO2 over the long term requires an accurate management of the risks based on quantitative prediction (modelling) of the containment of the storage complex before, during and after the injection operations. In this paper we propose to use numerical results of dynamic subsurface modelling to assess in a quantitative manner containment risks via coupled dynamic flow and geomechanics analysis. By combining advanced coupled modelling, probabilistic analysis, and interactive 3D visualization, the approach described provides a holistic, objective, and innovative representation of simulations results, allowing to effectively explain and communicate the main findings to stakeholders (engineers, project managers and authorities), facilitating informed decision-making and risk mitigation strategies.

1. INTRODUCTION
Modelling is crucial in CO2 sequestration risk management to assess potential exposure to emissions, such as groundwater contamination or atmospheric release. It is widely acknowledged that various risks associated with CO2 sequestration, such as fault reactivation, cap rock failure, and well integrity, can be mitigated through coupled dynamic flow and geomechanics analysis. However, this field often involves intricate theoretical models and extensive simulations, resulting in complex datasets that pose challenges in translating them into operational recommendations. To tackle these complexities while addressing real-world scenarios, it is critical to utilize simplified outputs.
Numerous contributions in literature have addressed the containment integrity evaluation by means of numerical modelling during CO2 sequestration, e.g. Rutqvist (2012), Tenthorey et al. (2014), Vilarrasa et al. (2014), Mustafa et al. (2022), Pan et al. (2023). Simple staggered coupling scheme (also called One Way Coupling - OWC) is generally used in petroleum engineering to run these numerical simulations. In this scheme the two problems (mechanical equilibrium and hydraulic flow) are solved separately using two different numerical codes and same or different spatial discretization. The coupling is ensured via the transfer of information (pressure and/or temperature and/or saturation) between the codes at predefined time steps. The major disadvantage of such approach is its inability to capture the correct physics and material balance. In particular, OWC scheme can't account for permeability changes induced by porosity changes (compaction or swelling) and it doesn't respect mass conservation. On the other hand, explicit or implicit staggered coupled schemes (also called Two Way Coupling - TWC), e.g. Zienkiewicz et al. (1988), show significant advantages in assessing the driving mechanisms associated to depletion and induced rock compaction or pressurization and consecutive rock swelling.