Capillary Displacement and Fluid Trapping in Fractures
2014 (English)Conference paper, Abstract (Other academic)
Multiphase flow in disordered media is a common phenomenon, attracting extensive attention in the field of water resources. A fundamental process for multiphase flow is immiscible displacement, i.e., the displacement of one fluid by another immiscible one. Immiscible displacement in fractured media results in a fluid phase distribution and fluid-fluid interfaces which cast decisive influence on a range of macroscopic flow and transport parameters and such as relative permeability and mass transfer rate.
When displacement in a fracture occurs slowly, capillary forces will dominate over viscous forces in the absence of gravity. Capillary force in a rough-walled fracture is proportional to the local fluid-fluid interface curvature, which can be represented by two principal components, one in the direction perpendicular to the fracture plane (aperture-induced curvature) and one parallel to the fracture plane (in-plane curvature). Capillary displacement has been shown to be controlled by the competition between aperture variability which tends to roughen the interface and in-plane curvature which tends to smooth it. The aperture field of a real fracture typically exhibits aperture variability, influence of which on fluid displacement has not yet been well understood.
Here we present a numerical study systematically investigating the critical role of aperture variation and spatial correlation on fluid trapping and phase structure. We consider a single fracture with normally distributed random apertures. The aperture fields (2048×1024) are generated by a power spectrum based, inverse fast Fourier transform algorithm. The aperture correlation scale is related to the cutoff wave length (or the inverse of cutoff wave number). We consider cutoff wave numbers of 16, 32, 64 and 256. To simulate fluid displacement in the fracture, we use a newly developed invasion percolation (IP) model  which has been shown to well reproduce displacement patterns and phase structures observed in experiment. We focus on analyzing macroscopic saturations and trapping structures.
Figure 1 shows two example patterns of fluid displacement with non-wetting invasion from the left edge. The upper pattern corresponds to the breakthrough phase distribution for an aperture field with cutoff wave number 16, while the lower one corresponds to the final fluid distribution for an aperture field with no spatial correlation.
Monte Carlo simulation results show that for aperture field coefficient of variation equal to 0.25, the case with cutoff wave number 64 produces the lowest average macroscopic saturation. This suggests that macroscopic saturation and total trapped mass are not monotonically dependent on the spatial correlation scale. They exhibit complex dependence on the aperture variability and correlation scale.
Place, publisher, year, edition, pages
immiscible displacement, trapping, invasion percolation
Oceanography, Hydrology, Water Resources
IdentifiersURN: urn:nbn:se:uu:diva-239457OAI: oai:DiVA.org:uu-239457DiVA: diva2:774615
XX International Conference on Computational Methods in Water Resources (CMWR 2014), 10-13 June 2014, Stuttgart, Germany