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We present a model framework for dynamic simulation of the flow of CO2 and other components in an injection well coupled with a near‐well reservoir. With a partitioned approach, we employ numerical methods adapted to the governing equations in each domain. In both well and reservoir, accurate thermodynamics are used. This model can be used for various design and operational considerations for CO2‐injection wells, that is, the quantification of pressure and temperature transients, and phase composition, including the appearance of a water‐rich phase. We study cases where the flow in the well and the near‐well reservoir is dynamically coupled. The rock properties are seen to strongly affect the well dynamics, both regarding magnitude and transient evolution of the bottom‐hole pressure. We consider a variation of this case where water is co‐injected with CO2, showing that this is a potential method to mitigate salt precipitation. We also consider intermittent injection, representing the case of direct injection from ships transporting CO2. Finally, we observe that in the present cases, a coupled model (as opposed to a well‐only model) is necessary in order to capture the dynamics in the well during injection. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A hierarchy of relaxation two-phase flow models is considered, formulated as hyperbolic relaxation systems with source terms. The relaxation terms cause volume, heat, and mass transfer due to differences in pressure, temperature, and chemical potential, respectively, between the two phases. The subcharacteristic condition is a concept closely related to the stability of such relaxation systems. It states that the wave speeds of an equilibrium system never can exceed the speeds of the corresponding relaxation system. The work of Flåtten and Lund [Math. Models Methods Appl. Sci., 21 (2011), pp. 2379-2407] is extended, with analytical expressions for the wave velocities in each model in the mentioned hierarchy. The subcharacteristic condition is explicitly shown to be satisfied using sums of squares, subject only to physically fundamental assumptions. [ABSTRACT FROM AUTHOR]

Abstract: A model for two-phase pipeline flow of CO2 with phase transfer is presented. Two different relaxation models for phase transfer are developed. The system of equations is solved by splitting it into a hyperbolic conservation law and a relaxation ODE, solved by a multi-stage (MUSTA) finite volume scheme and the backward Euler method, respectively. The stiffened-gas equation of state is used for calculating thermodynamic properties. Simulation results from a depressurisation case of a CO2 pipe, causing phase change and cooling, are presented, showing that statistical rate theory predicts solutions close to those of an equilibrium model with instant phase transfer. [Copyright &y& Elsevier]