Evaluation of the Coupling of a Full-Dimensional Multiphase Model with a Vertical Equilibrium Model for the Simulation of Underground Gas Storage

Abstract:

Modeling underground gas storage requires simulations on a large domain over the whole time of plant operation and beyond, including local features such as fault zones and a representation of the transient saline front. The boundary conditions and resulting pressure reversal are affected by external fluctuations in energy demand and supply (e.g. power to gas) over a wide range of time scales. In addition, often a large number of simulation runs need to be conducted to quantify parameter uncertainty (e.g. Monte Carlo simulation). Within acceptable computational time this cannot be achieved by full three-dimensional multiphase multicomponent models due to limited computational resources. In contrast to that, less computational resources are required by numerous simplified mathematical models. One class of these models is based on the assumption of vertical equilibrium. However, this assumption may be invalid in the area around the well during injection and extraction of gas and at the tip of the plume and in general only holds after a certain timescale in the rest of the domain. In addition, simplified models do not provide the accuracy desired for some parts of interest in the domain, like fault zones, the displacement front or geological heterogeneity especially around the injection zone. The individual benefits of simplified models such as a vertically integrated model and more complex and thus more accurate models such as a full-dimensional multiphase model are combined by coupling both model types in one domain. The boundary between the models is adapted during the simulation to capture transient processes. Stability, applicability and efficiency of the coupled model for different injection scenarios and domain features will be analyzed and discussed. Physically/mathematically motivated coupling criteria to govern the movement of the boundaries between the models will be presented and compared. It will be shown how the coupled model maintains a high degree of accuracy where necessary while being at the same time efficient to be applied for real case scenarios of underground gas storage.