Coupled LBM-DEM Three-phase Simulation on Gas Flux Seeping from Marine Sediment

Abstract:

One of the main issues of the geological storage of CO₂ under the seabed is a risk of CO₂ leakage. Once CO₂seeps into the ocean, it rises in water column dissolving into seawater, which results in the acidification of seawater and/or returning to the air. Its behaviour significantly depends on flow rate and bubble size (Kano et al., 2009; Dewar et al., 2013). As for porous media, bubble size is generally predicted through simple force balance based on flow rate, surface tension and channel size which is estimated by porosity and grain size. However, in shallow marine sediments, grains could be mobilised and displaced by buoyant gas flow, which causes distinctive phenomena such as blow-out or formation of gas flow conduit. As a result, effective gas flux into seawater can be intermissive, and/or concentrated in narrow area (QICS, 2012; Kawada, 2013). Bubble size is also affected by these phenomena. To predict effective gas flux and bubble size into seawater, three-phase behaviour of gas-water-sediment grains should be revealed. In this presentation, we will report the results of gas-liquid-solid three-phase simulations and their comparisons with experimental and observation data. Size of solid particles is based on grain size composing marine sediments at some CCS project sites. Fluid-particle interactions are solved using the lattice Boltzmann method (LBM), while the particle-particle interactions are treated by coupling with the Discrete Element method (DEM).

References:

Dewar, M., Wei, W., McNeil, D., Chen, B., 2013. Small-scale modelling of the physiochemical impacts of CO₂leaked from sub-seabed reservoirs or pipelines within the North Sea and surrounding waters. Marine Pollution Bulletin 73(2), 504-515.

Kano, Y., Sato, T., Kita, J., Hirabayashi, S., Tabeta, S., 2009. Model prediction on the rise of pCO₂ in uniform flows by leakage of CO₂purposefully stored under the seabed. Int. J. Greenhouse Gas Control, Vol. 3(5), 617-625.

Kawada, R. 2014. A study on the mechanism which determines the size of bubbles seeping from sand sediment. Graduation thesis. Faculty of Engineering, The University of Tokyo. (in Japanese).

QICS, 2012. QICS: Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage. <http://www.bgs.ac.uk/qics/home.html> (accessed Aug.06.14)