Cyclic Depressurization Driven Enhanced CH4 Recovery after CH4-CO2 Hydrate Swapping

Jyoti Shanker Pandey*, Charilaos Karantonidis, Qian Ouyang, Nicolas von Solms

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


CH4/CO2 mixed hydrate forms upon CO2 gas injection into the CH4 gas hydrate reservoir. An improved understanding of the dissociation behavior of the CH4/CO2 hydrate system is necessary to increase the yield of CH4 production and CO2 storage. In this study, CH4/CO2 mixed hydrates (in bulk and unconsolidated coarse sand) were dissociated using the multistep cyclic depressurization (MCD) method. Visual and kinetic data were collected using a high-pressure reactor and gas chromatography (GC) setup to study the change in morphology and mole fraction of CH4 and CO2 in the released gas. The influence of chemicals (methionine, sodium dodecyl sulfate, and methanol) in the aqueous phase and reservoir temperature (below and above 0 °C) on recovery and storage yield was also investigated. This study reported additional CH4 recovery below the CH4 hydrate stability pressure when cyclic depressurization was implemented between CH4 and CO2 hydrate stability pressures. A rapid increase in CH4 mole fraction and a decrease in CO2 mole fraction were observed due to simultaneous CH4 hydrate dissociation and CO2 hydrate reformation. This phenomenon was accelerated at high liquid saturation. CH4 recovery potential was positively correlated with hydrate saturation and for T > 0 °C conditions. Morphology study showed the expansion of hydrate volume during cyclic depressurization, which confirmed hydrate reformation from released water from dissociation. The chemicals affected the mixed CH4/CO2 hydrate synthesis, reformation kinetics, and subsequent CO2 storage. This study demonstrates a novel application of cyclic depressurization to enhance CH4 production and improve CO2 storage. A new hydrate production method is also proposed that includes constant-rate depressurization, kinetic inhibitor-based CO2 injection, and cyclic depressurization.
Original languageEnglish
JournalEnergy & Fuels
Pages (from-to)9521−9537
Publication statusPublished - 2021

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