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

Jyoti Shanker Pandey*, Ørjan Strand, Nicolas von Solms, Stian Almenningen , Geir Ersland*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

The current literature lacks visualization studies that could improve our understanding of fluid migration and hydrate rearrangement during CO2 injection into a CH4 hydrate. CO2 injection into a CH4 hydrate has been proposed as a novel technique to store CO2 while generating CH4. However, to improve this process, a better understanding of the pore-level processes is needed. This experimental study is the first to provide pore-level visualization (using a high-pressure micromodel) when liquid CO2 (0.1–0.5 mL/h) is injected into gas-saturated CH4 hydrates (SH = 0.81–0.99, P = 59–69 bar, and T = 3.3–4.5 °C). CO2 injection leads to invasion/displacement of the liquid phase within the gas-saturated CH4 hydrate, resulting in thickening of the hydrate film and crystallization of the liquid phase. After injection, the crystalline hydrate phase with and without the liquid phase was observed and no residual gas phase was observed, indicating that the gas phase was consumed during hydrate formation. The gas-phase saturation and low injection rate controlled the hydrate formation mechanism, delayed liquid-phase crystallization to the hydrates, and contributed to a slower pressure buildup in the micromodel. The resulting CH4/CO2 mixed hydrates were dissociated by stepwise depressurization. During depressurization, several dissociation and reformation events were observed below the CH4 hydrate stability pressure. The process was supported by continuous mobilization and mixing of the liquid and gas phases. The reforming process enhanced the CO2 concentration in the hydrate phase. The entire hydrate system dissociated closer to the equilibrium pressure of pure CO2 hydrates, suggesting the presence of hydrate mass below the stability pressure of the CH4 hydrate. The results demonstrate the effects of the CO2 injection scheme on the evolution of morphology in the CH4 hydrate system, which is relevant to the proposed production method (CO2 injection into CH4 hydrate reservoirs is followed by a slow depressurization) to improve CH4 gas recovery without the loss of hydrate mass.
Original languageEnglish
JournalEnergy & Fuels
Volume36
Issue number18
Pages (from-to)10552–10571
ISSN0887-0624
DOIs
Publication statusPublished - 2022

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