(411h) Fundamental Investigation into the Thermal Decomposition of Methane Hydrates and the Impact of CO2 Sequestration

Authors: 
Castaldi, M. J., City College of New York
Fundamental investigation into the thermal decomposition of methane hydrates and the impact of CO2 sequestration

Fundamentals of the hydrate formation and dissociation in a large-scale laboratory reactor were studied using a thermal stimulation and thermal stimulation combined with CO2 sequestration method. Methane hydrate production can be coupled with simultaneous CO2 sequestration by converting injected CO2 into hydrate phase. Carbon sequestration makes this process carbon neutral to some extent. A Large-Scale Hydrate Vessel (LSHV) of internal volume 59.3 liters was used to duplicate the permafrost conditions in which hydrates form naturally. Methane hydrate formations were achieved and the formation of hydrates in LSHV was confirmed by comparing the Pressure-Temperature data with the pure CH4 hydrate equilibrium curve. A testing matrix was developed and executed to study the effect of heating rate (20 W & 100 W) and CO2 injection rate (155 ml/min and 1000 ml/min) on methane recovery and CO2 sequestration at a constant initial hydrate saturation (50 % by pore volume). In addition to these tests, 2 baseline tests were conducted where no CO2 was injected during the dissociation for comparison purposes. Results from those tests show that at 100 W heating rate the number of moles of CH4 recovered increased by addition of CO2 at 155 ml/min whereas, it decreased the CH4 production by adding CO2 at 1000 ml/min; relative to baseline tests where no CO2 was injected. Similar results were obtained for 20 W heating tests. The number of moles of CO2 sequestered increased from a value of 13 moles at 155 ml/min to 40 moles at 1000 ml/min. The motivation for this work comes from the need to utilize unconventional natural gas resources. Natural gas extraction from the hydrates can also enable sequestration of carbon dioxide helping reduce the carbon footprint and contribute to reducing overall greenhouse gas emissions. Currently, the conventional gas extraction and recovery methods are cheaper than the gas hydrate recovery methods and it is expected that this will change as, more efficient methods are being developed in gas hydrate field. It is required to focus the research on a lab scale experiments to provide economically feasible guidelines for large-scale production tests.