Carbon dioxide capture and storage in subsurface geological formations is a potential solution to limit anthropogenic CO2 emissions and combat global warming. Depleted gas fields offer significant CO2 storage volumes; however, injection of CO2 into these reservoirs poses some potential challenges for the injectivity, containment and well/facility integrity due to low temperatures caused by isenthalpic expansion of CO2. A key injectivity risk is due to possible formation of hydrates at the low expected temperatures. This study aims to address main causes of CO2 hydrate formation and its impact on permeability of porous media. This review highlights the current state of knowledge in the literature while emphasizing the need to bridge existing gaps in derisking CO2 injection into (depleted) low-pressure gas reservoirs. In summary, according to the existing literature, the potential for hydrate formation is assessed to be credible. Current industry solutions exist to manage this risk; however, they are costly and energy intensive. Future research will be needed to provide capabilities to manage this risk more efficiently.@en

Injection of high-pressure CO2 into depleted gas reservoirs can lead to low temperatures promoting formation of hydrate in the near wellbore area resulting in reduced injection rates. The design of effective mitigation methods requires an understanding of the impact of crucial parameters on the formation and dissociation of CO2 hydrate within the porous medium under flowing conditions. This study investigates the influence of water saturation (ranging from 20 % to 40 %) on the saturation and kinetics of CO2 hydrate during continuous CO2 injection. The experiments were conducted under a medical X-ray computed tomography (CT) to monitor the dynamics of hydrate growth inside the core and to calculate the hydrate saturation profile. The experimental data reveal increase in CO2 hydrate saturation with increasing water saturation levels. The extent of permeability reduction is strongly dependent on the initial water saturation: beyond a certain water saturation the core is fully blocked. For water saturations representative of the depleted gas fields, although the amount of generated hydrate is not sufficient to fully block the CO2 flow path, a significant reduction in permeability (approximately 80 %) is measured. It is also observed that the volume of water + hydrate phases increases during hydrate formation, indicating a lower-than-water density for CO2 hydrate. Having a history of hydrate at the same water saturation leads to an increase in CO2 consumption compared to the primary formation of hydrate, confirming the existence of the water memory effect in porous media.@en

Understanding the kinetics of CO2 hydrate formation and the resulting saturation of the hydrate in porous rocks is crucial for processes such as the storage of CO2 in underground formations. Nevertheless, to date, there is no established procedure that utilizes a medical CT scanner for quantifying gas hydrate saturation in core samples during the growth stage. This study proposes a methodology for estimating hydrate saturation using a medical CT scanner during the injection of CO2 into porous media. This method uses the mean area obtained from the image analysis to calculate the dynamic profile of water and the CO2 hydrate along the length of the sandstone core. To demonstrate the technique, core flooding experiments were conducted to form gas hydrates in semibrine-saturated sandstone cores.@en