CCS Technologies for low carbon society

[1605-08-02] Three-dimensional fingering structure induced by density increase due to mixing at a vertically displacing front in porous media

○Shitong Cai¹, Tetsuya Suekane¹, Lei Wang¹ (1. Tokyo Institute of Technology)

Chairman: Kyuro Sasaki (Kyushu University)

Keywords:fingering structure, displacing front, x-ray CT, three dimension, porous media

In the process of supercritical CO₂ into oil field, fingering structure appears at a vertically displacing front even in a favorable ratio. Density increase by mixing at a vertically displacing front between the supercritical CO₂ and oil is considered as the reason induced the fingering. In this study, we focused on the fingering structure during the mixing of the two fluids. Because of the difficulty to achieve the model of the injection of supercritical CO₂ into oil in experimental condition, in our experiments, we use plastic particles packed bed as the porous medium. We use a solution of NaI (sodium iodide) and MEG (the mixture of Methanol and Ethylene glycol solutions) as supercritical CO₂ and a solution of NaCl (sodium chloride) as oil. Before mixing, the MEG-NaI is less dense than the NaCl solution which is same condition as supercritical CO₂ injection into oil. With the dissolution of MEG into NaCl solution, the density of mixture solution is increasing modeling the dissolution of CO₂. In terms of the three-dimensional images obtained from our experiments, we present that with an increase in the injection rate of MEG, the fingering development speed increases and the fingering number decreases. An enhanced dispersion is also indicated by the comparison among the various increasing injection rates, as the scale of fingering structure becomes larger when rate becomes faster. When the injection is at a high rate, the vertically displacing front develops as compact. We consider that the reason of the phenomenon is the enhanced diffusion faster than the fingering development velocity at high injection rate. At low injection rate, fingering structure depends on the peclet number.