Replacement of Methane from Hydrates in Porous Sediments with CO2-in-Water Emulsions

Abstract

CO2-in-water emulsions formed from polyoxyethylene sorbitan monooleate (Tween 80) and sodium dodecyl sulfate (SDS) were evaluated in terms of stabilization time and emulsion droplet distribution. A CO2 emulsion with 0.5 wt % SDS + 5 wt % Tween 80 was found to be more stable than the other emulsions. With an increase in the stirring rate or pressure or a decrease in the temperature, the size of CO2 emulsion droplets tended to be smaller, and the stabilization time of the CO2 emulsion increased. With the optimized CO2 emulsion, the CH4–CO2 replacement reaction in a hydrate-bearing quartz sand sample was performed in a three-dimensional reactor. In the emulsions, the function of Tween 80 is to make the emulsion much more hydrophilic and reduce the flow resistance of the emulsion, whereas that of SDS is to make the newly formed hydrate particles/layers more granular and looser. The results indicate that, for hydrate reservoirs located in the stability fields of both CO2 hydrate and methane hydrate, the replacement efficiency of the CO2 emulsion can reach 47.8%, higher than those of liquid CO2 and gaseous CO2. The addition of 3.35 wt % salt to the emulsion can prevent the pore spaces of sediments from being blocked.