Exploring the Dynamic Capillary Pressure and its Influence on Co2 Plume Migration: A Comprehensive Carbon Capture, Storage and Utilization Simulation Study in Saline Aquifer

Abstract Over the past few decades, numerous reservoir simulation studies have explored the flow behavior of injected Carbon di-oxide (CO2). A common assumption in these studies is that capillary pressure remains largely unaffected by CO2 injection. This paper investigates the dynamic nature of capillary pressure examining factors such as pressure and temperature, which significantly impact CO2 plume migration. Several CO2 trapping mechanisms are involved in CO2 sequestration in saline aquifers. These include residual, hydrodynamic, solubility, and mineral trapping. Injected CO2 will gradually move towards the top of the reservoir until it encounters the cap rock and gets trapped in the pore space under a very low permeability seal layer due to capillary trapping, where the mobility of the injected CO2 is constrained in the rock pores by capillary pressures. CO2 can leak through the seal layers if there are fractures, diffusion, or capillary breakthrough. This paper will study in detail the factors that can affect CO2 movement due to changes in capillary pressure of the seal layers over time because of changes in interfacial tension. In most reservoir simulation studies, capillary entry pressure is considered very high in the seal layers, and it is treated as static in the simulation model. Sensitivity runs were carried out where reservoir pressure and temperature in the aquifer were altered to capture changes in capillary pressure and, in turn, the flow behavior of the CO2 plume. It was observed that CO2 movement in the reservoir is impacted by changes in capillary pressure in the seal layers as the pressure in the reservoir changes over time. The temperature effect on capillary pressure is also considered in the study. It was found that with an increase in reservoir pressure due to CO2 injection, interfacial tension between gas and water decreased, causing are duction in capillary pressure. The reduction in capillary pressure caused the injected gas to enter the shale barriers more easily, leading to faster vertical movement of the gas. When the CO2 gas plume sizes and shapes were compared, the CO2 footprint was found to be different in size and shape due to the reduction in capillary pressure (caused by the reduction in CO2-brine interfacial tension). Additionally, when different values of reservoir temperature were assumed in the model, it caused changes in CO2-brineinterfacial tension, which modified the shape of the CO2 plume. This paper discusses in detail the novel approach of using dynamic capillary pressures, which are calculated on the fly based on reservoir pressure and temperature. The ability to capture this behavior greatly helps in understanding the actual flow migration of CO2 plumes in the reservoir, significantly impacting the success of a CCUS project.