Sloan and Koh [178] summarized (a) laboratory measurements and (b) models that provide estimates of the heat of hydrate formation and dissociation, in addi­tion to equilibrium conditions (P, T, and inhibitor concentrations) of various states for many hydrate systems. Clarke and Bishnoi [17] and Kim et al. [79] studied the kinetics of hydrate formation and measured the activation energy and intrinsic rate constant of methane hydrate decomposition. Modeling by Moridis et al. [126, 138] has shown that dissociation kinetics plays a limited-to-no role in gas produc­tion from hydrate at the reservoir scale, but may be important in short-term labo­ratory studies.

Handa and Stupin [61, 202, 203] and Lu and Matsumoto (2002) investigated the effect of the properties of porous media on the hydration characteristics, and reported significant deviations between the measured hydration temperatures and those pre­dicted from the known equilibrium curve of pure methane, i. e., temperature shifts varied from -12.3 to 8°C. The implication of these studies is that the medium prop­erties and texture may play a defining role in hydrate equilibrium. The subject has not been fully addressed, and it has not been represented in numerical simulators, thus increasing the uncertainty of their predictions.

5.2.2 Thermal Properties

Laboratory measurements of thermal properties of methane HBS have been made by a number of researchers [56 60, 69, 126, 138, 164, 200, 204, 206, 207] Two thermal properties are important: thermal conductivity and specific heat. The specific heat of a GH-bearing medium can be computed using a mixing model and the specific heats of the components present, and does not pose a challenge. The thermal conductivity of pure methane hydrate differs from that of water by less than 10%. Although it is possible to make coarse estimates of the thermal conductivity of a hydrate bearing medium that has water and hydrate in the pore space by consid­ering the medium to be water saturated only [165], laboratory studies have shown that GH-bearing media have higher thermal conductivity than water-saturated media [126, 138] The difference is substantial, and thus this approximation is not valid because of the paramount importance of heat transfer in hydrate dissociation.