Numerical modelling of two-phase flow through heterogeneous porous media into water column
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This research focuses on the development of the self-consistent numerical model to predict the two-phase plume dynamics developed through porous media into the fluid media flow field. The engineering background of this study is the dynamics of upward migration of CO2 plume through superimposing complex structures and residues in seabed sediments into the ocean bottom boundary layer. A model called as ‘An arbitrary Navier-Stokes-Darcy multi-fluid flow model (AnsdMF) was developed to automatically incorporate the fluids flow through the complex geoformations, where either the nonlinear convection dominates or Darcy’s law dominates, into the turbulent ocean. The model was developed on the basis of OpenFOAM platform. This study is part of the research of EU project STEMM-CCS*. Sub-models are developed for mass transfer in porous media with an effective interfacial area using data from laboratory experiments. The models are calibrated with data from the experimental laboratory of CO2 gas dispersion through standard sediments. A method of reconstruction of complex sediment by using the data from field observations is proposed and applied for the model setting of the complex structured sediments for simulations of field experiments carried by STEMM-CCS project. The developed model (AnsdMF) is then applied to investigate the fluid pathways within geoformation structures without chimneys (NC), with unconnected chimneys (UCC), and connected chimneys (CC). It is found from the investigation that the CC provides fast pathways to gas dispersion, 3.8 times faster than that through a UCC and 12.8 times faster than that through an NC. In comparison with the results from Darcy model, the similar velocity pattern identified inside the sediments when no cracks were present, with the maximum velocity of 2.0 x 10-4m/s in the case of AnsdMF model as compared 1.1 x 10- 4m/s. The difference is from the contributions of nonlinear convection modelled by AnsdMF model. The developed model (AnsdMF) is then applied to simulate the field experiment carried out by STEMM-CCS project to predict the dynamics from CO2 injection, dispersion, and dissolution in sediment, and finally leakage into ocean bottom boundary layer. In comparison with the data obtained from the field, it shows that the model has successfully predicted CO2 plume developments in complex sediments, including dissolved/undissolved CO2 inside the sediments and the rates of CO2 leakage. It is found that the role of the ‘chimney’ structure on CO2 dispersion is clearly demonstrated, through which, the injected CO2 disperses to the seafloor within 16 minutes. The results show that total 150 Kg of gas is stored inside the sediments while the peak dissolution rate of 0.2g/s in the first hour of gas injection (at a rate of 5.7 Kg/sec) confirming most of the dissolution of CO2 into porewater occurred within this time period. The rest of the gas found the migratory path through overlying clay in the fracture or pockmarks reach to a leakage rate of 5.5 Kg/day. The leakage rate into the ocean bottom boundary layer starts from a single stream of bubbles at ~2.1 Kg/Sec and settles at ~5.1 Kg/Sec after 2 hours of gas release. The leakage and gas release rates found in a similar range results in a relative to the constant volume of the plume in sediments with a gas dissolution ratio of 0.038. When the gas injection rate increases from 29 Kg/day to 143 Kg/day, the horizontal size of gas plume also increases from 4.92m to 6.51m. *STEMM-CCS: Strategies for Environmental Monitoring of Marine Carbon Capture and Storage. European Union’s Horizon 2020 research and innovation programme under grant agreement No. 654462.