Tohidi, Bahman¹, Ben Clennell², Jinhai Yang¹, Maria Llamedo³ 
(1) Heriot-Watt University, Edinburgh, United Kingdom 
(2) CSIRO Petroleum Division, Perth, Australia 
(3) PDVSA, Caracas, Venezuela

ABSTRACT: Experimental Investigation of Marine Gas Hydrate Formation and Production

We report on the results of our experiments on forming gas hydrates in unconsolidated porous media and producing gas using step-depressurisation. In the tests packed glass beads of 0.1 mm in diameter were used, and certain overburden pressures were exerted to simulate natural conditions. Two different procedures of gas injection were applied to form gas hydrates in the porous media. In the first method gas was injected into the system after initial water injection. Whereas in the second method gas was injected first, followed by water injection. Methane and a natural gas were used in the tests. 
The results on gas production showed that upon depressurisation water is produced first, until the gas phase becomes mobile. The results could have significant implications on the feasibility of depressurisation techniques in producing gas in open systems with highly active aquifers. 
The tests with the natural gas demonstrated the effect of gas fractionation due to hydrate formation. In the tests, although the system was cooled-down to temperatures much lower than the hydrate stability zone of the natural gas, some gas was present inside the porous media. This could be explained with the fact that hydrate formation removes heavier hydrocarbons from the gas phase. Therefore, further cooling is required to convert the remaining gas phase (which is mainly methane with some nitrogen) into hydrates. The depressurisation tests support the above phenomenon, as upon depressurisation gas is produced at much higher pressures than natural gas dissociation pressure at the system temperature.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.