Critical parameters influencing mixed CH4/CO2 hydrates dissociation during multistep depressurization

Insights into multistep depressurization of CH4/CO2 mixed hydrates in unconsolidated sediments

“…Therefore, CO 2 gas injection into CH 4 hydrates with these chemicals in unconsolidated sand can improve CO 2 hydrate formation at varying degrees [51], causing lower RH(CH 4 /CO 2 ) of 0.01-0.17 in Type B hydrate than that of 0.25 (without chemicals) in this work. In addition, RH (CH 4 /CO 2 ) in this work were both lower than those of Type A hydrate (1.52-2.10) and Type B hydrate (0.21-0.40) in consolidated sandstone [44,45]. The reason for this was that unconsolidated sand can provide larger surface area between gas and water, causing more thermodynamically favorable CO 2 captured in hydrate [57].…”

“…The resistivity results confirmed CO 2 hydrate retention compensated CH 4 hydrate loss. Another study demonstrated the effects of three critical parameters on production performances in sandstone [45]. In spite of these studies, dissociation characteristics of CH 4 /CO 2 hydrate during slow depressurization in unconsolidated sediments are still unclear.…”

Novel Pore-Scale Visualization during CO2 Injection into CH4 Hydrate-Saturated Porous Media

“…The experiments were performed at the core scale and included the study of morphology, measurement of gas chromatography (GC) data, and resistivity change. Fluid change composition was measured by regular GC analysis, while total saturation variation was measured by resistivity variation. ,− Figure provides an overview of the production scheme involving CO 2 injection and CH 4 production that involves mixed CH 4 /CO 2 hydrate formation and CO 2 hydrate reformation when the production pressure is between two equilibrium pressure lines.…”

“…The slow depressurization technique used here confirmed the presence of the mixed CH 4 /CO 2 hydrate (owing to multiple dissociation points) and improved CO 2 concentration in hydrate through reformation. Therefore, when applied in combination with hydrate swapping, improved CH 4 recovery and CO 2 storage efficiency were recorded . The combined method addresses the shortcomings of particular depressurization or hydrate swapping, such as low CO 2 volumetric sweep efficiency, untouched CH 4 hydrates, risk of geomechanical instability, etc.…”

“…Therefore, when applied in combination with hydrate swapping, improved CH 4 recovery and CO 2 storage efficiency were recorded. 51 The combined method addresses the shortcomings of particular depressurization or hydrate swapping, such as low CO 2 volumetric sweep efficiency, untouched CH 4 hydrates, risk of geomechanical instability, etc. CO 2 injection into the CH 4 hydrate introduces two thermodynamic stability zones that could be exploited using the slow depressurization technique.…”