508 K
6 pp.
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TitleUse of Computed X-ray Tomographic Data for Analyzing the Thermodynamics of a Dissociating Porous Sand/Hydrate Mixture
Author(s)Freifeld, Barry M.; Kneafsey, Timothy J.; Tomutsa, Liviu; Stern, Laura A.; Kirby, Stephen H.
Publication DateFebruary 28, 2002
Report NumberLBNL--49859
Unique IdentifierACC0256
Other NumbersR&D PROJ: G30801; OSTI ID: 793798
Research OrgErnest Orlando Lawrence Berkeley National Laboratory (LBNL), CA (US)
Contract NoAC03-76SF00098
Sponsoring OrgUSDOE Assistant Secretary for Fossil Energy (DOE/FE); Office of Natural Gas and Petroleum Technology (US)
Other Information4th International Conference on Gas Hydrates, Yokahama (JP), 05/19/2002--05/23/2002
Subject03 Natural Gas; CAT Scanning; Gas Hydrates; Mixtures; Thermal Conduction; Thermal Conductivity; Thermodynamics; Sand; Separation Processes; Mathematical Models; Dissociation Heat
Related Web PagesNon-medical Uses of Computed Tomography and Nuclear Magnetic Resonance
AbstractX-ray computed tomography (CT) is a method that has been used extensively in laboratory experiments for measuring rock properties and fluid transport behavior. More recently, CT scanning has been applied successfully to detect the presence and study the behavior of naturally occurring hydrates. In this study, we used a modified medical CT scanner to image and analyze the progression of a dissociation front in a synthetic methane hydrate/sand mixture. The sample was initially scanned under conditions at which the hydrate is stable (atmospheric pressure and liquid nitrogen temperature, 77 K). The end of the sample holder was then exposed to the ambient air, and the core was continuously scanned as dissociation occurred in response to the rising temperature. CT imaging captured the advancing dissociation front clearly and accurately. The evolved gas volume was monitored as a function of time. Measured by CT, the advancing hydrate dissociation front was modeled as a thermal conduction problem explicitly incorporating the enthalpy of dissociation, using the Stefan moving-boundary-value approach. The assumptions needed to perform the analysis consisted of temperatures at the model boundaries. The estimated value for thermal conductivity of 2.6 W/m K for the remaining water ice/sand mixture is higher than expected based on conduction alone; this high value may represent a lumped parameter that incorporates the processes of heat conduction, methane gas convection, and any kinetic effects that occur during dissociation. The technique presented here has broad implications for future laboratory and field testing that incorporates geophysical techniques to monitor gas hydrate dissociation.
508 K
6 pp.
View Document 

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