Evaluation of fault leakage rates in the context of subsurface hydrogen and carbon storage

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Temporary storage of hydrogen or permanent storage of carbon dioxide in the subsurface requires a profound understanding of associated risks for leakage, bearing environmental, political, and economic risks that are still to be quantified. Risks are highest for leakage along wells or faults. The latter (Fig. 1) might already be hydro-dynamically conductive, or conductivity might be triggered by an increase in fluid pressures due to CO2 or H2 injection. Fluid pressure increase, and thus effective stress decrease, depends on the vicinity of the faults to the injection well. Drilling an injection well near a known fault is rather discouraged, while it remains unknown if faults can act as leakage pathways over engineered time scales on the order of < 10,000 years.In this context, we will investigate the impact of multiphase flow effects on fault leakage from geological reservoirs used for fluid storage, focusing specifically on CCS and hydrogen. This research will ground on recent data that has been obtained from multiscale 4D X-ray imaging at the Swiss Light Source. This PhD project will provide new and detailed insights into the multiphase fluid dynamics in rough fractures. Using novel data from synchrotron experiments will support more accurate predictions of the potential fluid leak rates from subsurface reservoirs. These are urgently needed to improve our confidence in subsurface fluid storage over long periods of time. This research can be divided into the following objectives:1. Develop a robust understanding of multiphase flow in rough fractures, based on 4D flow data. The data will be analysed towards displacement to obtain relative permeability and capillary pressure curves at a given effective stress but with varying surface roughness, aperture heterogeneity, and flow rates (capillary numbers).2. Represent fracture flow phenomena at the Darcy scale in physical models for fractures and fracture networks. This will support caprock leakage risk assessments by improving our confidence in the determination of leak rates by bringing together fracture network data (from previous research by the PI/co-Is) and upscaled fluid displacement models from this research.