Abstract
Capillary trapping prevents the migration of CO2 in reservoirs due to buoyancy. The residual gas saturation is strongly influenced by the gas saturation after gas injection. In this study, we have investigated the effect of stratified structure of heterogeneous porous media on gas permeation and entrapment. Experiments were carried out at a laboratory condition for a nitrogen-water system with the packed beds of glass beads with various diameters which modeled stratified porous media. In the case of parallel structure, the injected gas selectively percolated into permeable layers. The gas permeation can hardly occur for the less permeable layers because of the capillary entrance pressure. In the case of serial structure, the interface of porous structure hindered the migration of gas across it, because of the capillary entrance pressure. When the gas percolated in the permeable layers, capillary fingering was developed in the layers. However, when the tip of finger reached the interface, fingers grew in tangential directions until the pressure built up to overcome the capillary entrance pressure. As a result, high gas saturation was achieved in the permeable layers of both upward and downward gas injections.
Highlights
Global warming becomes one of the worldwide issues
Several researchers have carried out the core flooding experiments with sandstone for a supercritical CO2 and water system and found that the residual gas saturation increases with an increasing initial gas saturation [21]-[23]
We have investigated the effect of stratified structure of heterogeneous porous media on gas permeation and entrapment
Summary
Global warming becomes one of the worldwide issues. Its solution may include the carbon dioxide capture and storage (CCS) technology that is one of the possible options to mitigate the global warming of the earth. The residual gas saturation, which is defined as the volume ratio of trapped CO2 to the pore space, is affected by various factors, such as the property of rock, the viscosities and densities of fluids, the velocity of water injection, and so on [20]. It is influenced by the gas saturation after the gas injection, hereafter we refer it as the initial gas saturation. The most of the CO2 injected into the porous rock is trapped at the same place by capillarity for low initial gas saturations.
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