In this work, we visualize pore-scale hydrate phase transitions during CO2 injection into CH4 hydrate-saturated porous media. A total of six visualization experiments were performed using a water-wet, high-pressure silicon wafer-based micromodel with a pore network resembling a cross-section of sandstone. Liquid CO2 was injected at a constant volumetric rate of 0.2-0.5 mL/hour into the pores already saturated by CH4 hydrates at P = 59-69 bar and T = 3.3-4.5°C. The initial saturation of CH4 hydrates was high (SH = 0.81-0.99), while the rest of the pore space was saturated by liquid water and CH4 gas. The results showed that the hydrate phase changes were influenced by the initial liquid distribution and the amount of CO2 injected. A low CO2 injection rate formed massive hydrates surrounded by CO2-rich fluid, while high CO2 injection rates and ultimate injection volumes led to the formation of massive hydrates without residual fluid saturation. Later, stepwise depressurization was performed to visualize the dissociation and reformation patterns of the resulting hydrates. Multiple hydrate dissociations and reformations were observed between the stability pressure of pure CH4 hydrates and pure CO2 hydrates. Migration of pore water and mixing of fluids caused localized hydrate reforming at lower pressures. This is the first pore-scale visualization of CO2 injection into CH4 hydrate-saturated porous media and demonstrates the feasibility of combining CH4/CO2 exchange with pressure reduction to produce CH4 gas.
|Number of pages||1|
|Publication status||Published - 2021|
|Event||ACS Fall 2021 - Atlanta , United States|
Duration: 22 Aug 2021 → 26 Aug 2021
|Conference||ACS Fall 2021|
|Period||22/08/2021 → 26/08/2021|