(638g) Carbon Dioxide-Induced Liberation of Methane from Laboratory-Formed Methane Hydrates: A Pathway to Economical Carbon Sequestration | AIChE

(638g) Carbon Dioxide-Induced Liberation of Methane from Laboratory-Formed Methane Hydrates: A Pathway to Economical Carbon Sequestration


Mahajan, D. - Presenter, Stony Brook University
Horvat, K., Stony Brook University
Koga, T., Stony Brook University
The presence of vast methane (CH4) hydrate reserves around the globe are known for decades. Gas production by external stimulation techniques such as steam injection, gas depressurization or hydrate-inhibitor injection is well-established but an economical production method remains a challenge. In parallel, there is a sense of urgency to minimize carbon dioxide (CO2) levels in the atmosphere that have exceeded 400 ppm. Both CH4 and CO2 gases form structure sI hydrates and at temperatures below 10ºC, CO2 hydrates are more thermodynamically stable at lower pressures than CH4 hydrates. Considering that burying CO2 in deep formations is one of the carbon sequestration options being considered, the CH4-CO2 exchange in natural methane hydrate reservoirs may be a way to address both issues. The CH4-CO2 exchange option was attractive enough to warrant a commercial test by ConocoPhilips in 2012 in which over 24,210 m3 of CH4 was released when a 23 mol% CO2 in N2 mixture was injected in a hydrate reservoir in Alaska. Carbon dioxide was preferred over N2 in the hydrate phase, as about 70% of the N2 gas injected was recovered, while only 40% of the 1376 m3 of CO2 injected was retrieved. Thus, the CH4-CO2 exchange reaction merits further research.

In this talk, we will describe several laboratory-scale experiments to understand the CH4-CO2 hydrate exchange kinetics. Five hydrate formation-decomposition runs focused on CH4-CO2 exchange, two baselines and three with host sediments, were performed in a 200 mL high-pressure Jerguson cell fitted with two glass windows that allowed visualization of the time-resolved hydrate phenomenon. The data show that the induction time for hydrate appearance was the largest at 96 h with CH4 while with CO2, the time shortened by a factor of four. However, when the secondary gas (CO2 or CH4) was injected into the system containing preformed hydrates, the entering gas formed the hydrate phase instantly (within minutes) and no lag was observed. In a system containing host Ottawa sand (104 g) and artificial seawater (38 mL), the induction period reduced to 24 h. The CO2 hydrate formation in a system that already contained CH4 hydrates was facile and they remained stable, whereas CH4 hydrate formation in a system consisting of CO2 hydrates as hosts were initially stable, but CH4 gas in hydrates quickly exchanged with free CO2 gas to form more stable CO2 hydrates. In all five runs, even though the system was depressurized, left for over a week at room temperature, and flushed with nitrogen gas in between runs, hydrates formed instantaneously, irrespective of the gas used. The â??memory effectâ? was exhibited with either gas, a result in contradiction with that reported previously in the literature. The facile CH4-CO2 exchange observed under temperature-pressure conditions that mimic naturally-occurring CH4 hydrates show promise to develop a commercial carbon sequestration system.