TED-AJ03-635 CO_2 SEQUESTRATION IN AQUIFERS : EXPERIMENTAL AND NUMERICAL STUDIES ON FLOW OF SUPERCRITICAL CO_2 IN POROUS MEDIA

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This paper describes out preliminary study consisting of experimental and numerical researches. The final goal of the study described in this paper is an understanding of the behavior of immiscible two-phase porous flow of supercritical CO_2 and water and providing with useful data to access safety and validity of the underground sequestration of CO_2. Breakthrough of supercritical CO_2 injected into a packed bed of glass beads containing water is visualized directly by utilizing magnetic resonance imaging (MRI) technique under the temperature and pressure conditions corresponding to the aquifers at the depth of about 1000m. A packed bed of glass beads with a 70-μm average diameter models a porous medium in aquifers. Through the trapped water near the center of the packed bed, there exist several paths of CO_2. Distribution of trapped water between the neighboring slices looks like each other; the scale of the structure of trapped water is much larger than pore scale. Changes of water saturation with time after CO_2 injection stopped were observed. Water saturation in the packed bed increases with time from upper part. Water moves downward swiftly due to the gravitational force. We employ a recently introduced numerical technique, known as lattice Boltzmann method (LBM), to numerically simulate immiscible two-phase flows in microscopic models of porous media. Effect of saturation and pore structure on the relative permeability is discussed for simple capillary channels. In a parallel channel with water-wetting surfaces, high velocity of water between the bubbles along the flow direction results in high relative permeability for low water saturations. At intermediate CO_2 saturations, CO_2 breaks through water along the flow direction. Though these flow patterns are referred as the annular flow, the thickness of water flow pulsates along the flow direction. At high CO_2 saturations, the stable layered flow is reproduced. Thus, the relative permeability of water decreases with saturation sharply. Effect of contraction of capillary along the flow direction is simulated in the network of pores connected with narrow channel. Flows of water and a CO_2 bubble alternate periodically through a narrow channel. The reduction of cross-sectional area results in high velocity in the channel, especially for a CO_2 bubble. Front surfaces of reduced channel get entrapped CO_2 bubbles in spite of the non-wetting surface of CO_2. For higher CO_2 saturations, steady flows are obtained.[figure]
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TED-AJ03-635 CO_2 SEQUESTRATION IN AQUIFERS : EXPERIMENTAL AND NUMERICAL STUDIES ON FLOW OF SUPERCRITICAL CO_2 IN POROUS MEDIA

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