Carbon dioxide (CO2) capture and storage are evolving as a direct method for emissions reduction, where CO2 is captured either directly from the atmosphere or from an emitter source, such as a power plant, and injected into saline water-bearing formations. Research studies conducted based on steady-state models show that CO2 flows in its supercritical form during normal operations and is expected to remain in this phase in the flow path segments upstream of the geologic formation, where it is to be sequestered by physical and chemical processes. The supercritical state is dependent on the pressure and temperature conditions along the flow path and the fluid composition, i.e., as the heterogeneity of the composition increases, the phase envelope enlarges. Although the overall fluid composition is assumed to be held constant, pressures and temperatures vary throughout the flow path. Contrary to the steady-state assumption for normal operations, the pressure and temperature profiles are expected to vary considerably during transient events, such as start-up, ramp-up, and depressurization; the magnitude of the transient variation depends largely on the system dimensions and initial flowing conditions. The aim of this paper is to provide an integrated view of system behavior for two distinct flow scenarios and field configurations (onshore Illinois Basin-Decatur Project and offshore Northern Lights Consortium Project, with their accompanying pipeline and well systems) and operational parameters (start-up time, depressurization, injectivity, and ambient conditions).

First, transient simulation models are built for the scenarios, history is matched with field data, and then predictions for different operational cases are performed. The simulation results are analyzed to detect the operating limits for the system. For more extreme ambient conditions and for compositions containing impurities, the CO2 mixture can exhibit multiphase flow, where a flowing liquid phase in parts of the system and a supercritical phase flowing through other parts of the system are expected. Operations such as start-up or depressurization result in substantial changes in pressure, temperature, and fluid phase behavior, creating dispersed multiphase flow and slugging in the pipeline–well system. Finally, the effect of well storage on pipeline segment behavior is considerable and should be considered in front-end engineering and design (FEED) to ensure more complete modeling of such systems. With practical implications on design practices, these findings are valuable for the engineering community when designing CO2 storage and sequestration facilities.

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