The Study of Supercritical Carbon Dioxide Trapping Behaviour in Carbonate Reservoirs Through Pore-Scale Imaging Analysis

Severe climate change has urged the energy industry to revolutionalise the conventional technologies at pace to curb greenhouse gasses emission for more sustainable future. Carbon Dioxide (CO₂) storage at subsurface geological formation remains as the most effective technique to store massive quantity of CO₂ safely and permanently. Nonetheless, the flow and trapping behaviours of CO₂ at supercritical condition within geological formation are very complex, particularly for the carbonate rocks attributed to the wide spectrum of rock fabrics, pore geometries and structures. This study aims to investigate the pore interconnectivity and residual CO₂ trapping during the drainage and imbibition processes within porous media through digital rock technology. Native cores from three carbonate fields with different rock characteristics were plugged to obtain representative samples for the pore-scale coreflooding experiments. Brine and supercritical CO₂ were injected into core plugs at temperature up to 120 °C and pressure up to 3000 psi. X-ray images of the saturated core plugs were obtained through micro computed tomography (Micro-CT) facilities after injection of 10 pore volume (PV) of CO₂ and 5 PV of brine. Porosity, pore interconnectivity, fluid occupancy, saturation profiles and CO₂ ganglia size distribution were measured and studied through the pore-scale imaging analysis. The results indicate that the saturation of CO₂ after drainage and imbibition are strongly dependent on the local rock heterogeneity, specifically the presence and distribution of micropores within the rocks. All samples evidently show that micropores play critical role in pore interconnectivity. CO₂ ganglia in one sample was observed to be well connected initially but fragmented into smaller sizes after brine imbibition and, lastly, there was no CO₂ percolation within the pore network if the flow rate was too low. This paper presents a detailed study in investigating the flow and trapping behaviour of CO₂ at supercritical state, providing new insights to the important factors which influence the CO₂ trapping. Deeper understanding of the flow and trapping mechanisms is essential to formulate an effective CO₂ storage development plan, ensuring minimum injectivity and containment risk throughout the storage period.