(645b) Analytical and Pore-Network Calculations of Methane Saturation Resulting From Hydrate Dissociation in Porous Media

The capability of clathrate hydrates to store large amounts of gases has attracted significant attention from the scientific and industrial communities. Practical applications such as the storage and transportation of “energy-carrier” gases (methane, hydrogen), or “green-house” gases (carbon dioxide), mixture separation, and desalination, are among those of interest. Flow assurance, ocean-floor stability, and hydrates as a major source of well-drilling hazards are issues of major concern to the oil/gas industry [1].

The discovery of large amounts of natural gas-hydrate deposits in oceanic or permafrost sediments has rendered hydrates as a possible future energy source. Of interest to this study is the case of methane hydrate in porous media, as a source of methane for energy applications. For this purpose the hydrate needs to dissociate in order for the gas phase to be released, and subsequently to be produced through production wells. Methods that are considered in order to achieve the particular goal of hydrate dissociation include pressure reduction, thermal stimulation, hydrate-inhibitor injection or combinations of the above methods. The gas saturation that results from the dissociation of methane hydrate inside aqueous-saturated porous domains is a crucial parameter that determines if the resulting methane gas phase can be produced. To this purpose the gas phase needs either to form a percolating gas cluster that connects to the producing well, or reach the well, as a result of gas bubble mobilization due to viscous or buoyancy forces.

In this study we develop predictive tools for methane gas saturation that results from hydrate dissociation in porous media at different length scales, ranging from the single-pore scale, up to the pore-network scale [2]. Porous-medium overall, as well as, transversely-averaged, spatially specific, gas saturations are calculated. The analytical calculations are compared with the results obtained from detailed simulations using pore networks [3] and both results are found to be in very good agreement. Pore networks have been used successfully to capture the randomness of real porous media, and simulate processes involving flow, heat/mass transfer, and reactions in porous media. 

References

[1] Sloan, E. D.; Koh, C. A. Clathrate Hydrates of Natural Gases, 3^rd edition, Taylor & Francis. CRC Press, 2008.

[2] Tsimpanogiannis, I. N.; Lichtner, P. C. J. Phys. Chem. C 2013, In press.

[3] Tsimpanogiannis, I. N.; Lichtner, P. C. Phys. Rev. E 2006, 74, 056303.