Evaluating the impact of fractures on the long-term performance of the In Salah CO2 storage site

The In Salah Gas Joint Venture CO2 storage project has been in operation in Algeria since 2004 and is currently the world's largest onshore CO2 storage project. CO2 is injected into a saline aquifer of a gas reservoir several km away from the gas producers. Current focus in the project is on implementing a comprehensive monitoring strategy and modelling the injection behaviour in order to ensure and verify safe long-term storage. A key part of this effort is the understanding of the processes involved in CO2 migration within relatively low-permeability sandstones and shales influenced by fractures and faults. We summarise our current understanding of the fault and fracture pattern at this site and show preliminary forecasts of the system performance using Discrete Fracture Models and fluid flow simulations. Despite evidence of fractures at the reservoir/aquifer level, the thick mudstone caprock sequence provides an effective flow and mechanical seal for the storage system; however, quantification of the effects of fracture flow is essential to the site verification.