The Isothermal Decompression Analysis System (IDAS) is a device to conduct experimental work on natural gas hydrate specimens as they step-wise dissociate under controlled pressure and temperature conditions. The IDAS originally was designed by G. Brass and M. Kastner. Figure 1 is a schematic of the original system with modifications made by us prior to Leg 164. The IDAS was not used for its intended purpose during Leg 164, because there were insufficient hydrate specimens for such experimental work, although the instrument was used to store a large hydrate sample (Paull, Matsumoto, Wallace, et al., [1996], Fig. 2, p. 60) at high pressure under helium for post-cruise research.
In theory, the IDAS is operated as follows. Gas hydrate samples are placed into a Parr 500-mL pressure vessel equipped with three ports with valves. The vessel is sealed and placed into a constant temperature bath. Pressure in the vessel is raised to a prescribed amount (<400 atm) by injecting helium from a gas booster system through the first port. The reason for using helium is that helium does not form a clathrate. After closing the valve of the first port, pressure in the vessel is lowered by opening the valve of the second port and releasing gas. Gas hydrate within the vessel will begin to dissociate when the pressure drops below that of the appropriate hydrate-liquid-gas equilibrium curve. Aliquots of gas are released from the valve of the second port through a gas intake system and into a manifold for gas analyses. Aliquots of liquid are released from a tube at the base of the pressure vessel through the valve of the third port and into a closed tube of ~5-cm3 volume. Liquid within this tube then can be released into an ~500-cm3 bottle for water analyses.
1Paull,
C.K., Matsumoto, R., Wallace, P.J., and Dillon, W.P. (Eds.), 2000. Proc. ODP,
Sci. Results, 164: College Station, TX (Ocean Drilling Program).
2School of Earth
Sciences, James Cook University, Townsville, QLD, 4811 Australia. Jerry.Dickens@jcu.edu.au
3Department of
Geology, University of North Carolina, Chapel Hill, NC 27599, U.S.A. (Present
address: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss
Landing, CA 95039-0628, U.S.A.)
Date of
initial receipt: 16 April 1998
Date of acceptance: 2 December 1998
Ms 164SR-245