抄録
Understanding of natural convection of miscible two phases in porous media is of great importance to problems of geological storage of carbon dioxide. We consider saltwater-freshwater fingering instabilities in a saturated porous medium. Plastic resin particles with an average diameter of 320μm or 440μm were packed 50 mm in height in a tube with the inter diameter of 32 mm. Development of the fingering due to instabilities and natural convection of freshwater and saltwater in porous media have been imaged by means of micro-focused X-ray computer tomography (CT) every three minutes. At early stages of convective mixing, ripples appear on the contour surface of the concentration of sodium iodine and grow to be fingers which extend vertically downwards with time. As fingers proceed downwards, the concentration of sodium iodine in fingers are reduced. As a result the convective mixing is rapidly suppressed. With an increase in the density difference and the permeability, the development of the natural convection occurs more quickly. The standard deviation of CT values in the particle pack was used to evaluate the critical time and the mixing time of natural convection.
