Direct Visualization of CH₄/CO₂ Hydrate Phase Transitions in Sandstone Pores

This paper reports the formation and dissociation pattern of hydrate crystals with varying compositions CH4 CO2 in porous media. Direct visualization was carried out using a high-pressure, water-wet, silicon wafer-based micromodel pore network resembling sandstone rock. Hydrate were formed under reservoir conditions (P = 45–65 bar T 1.7–3.5 °C) from either two-phase system consisting liquid water CH4–CO2 gas mixture or three-phase water, CH4-rich gas, CO2-rich liquid. A stepwise pressure reduction method later applied to visualize multiple events occurring between equilibrium pressures pure hydrates hydrates. The results showed that liberated initial became trapped immobilized by surrounding undissociated when saturation high. Mixing led rapid reformation during reduction; reformed dissociated at lower close demonstrate possibility producing local while simultaneously reforming other parts sediments. is relevant for proposed production where injection reservoirs followed depletion enhance recovery.