The CH4-flue gas replacement in naturally occurring gas hydrates has attracted significant attention due to its potential as a method of exploitation of clean energy and sequestration of CO2. In the replacement process, the thermodynamic and structural properties of the mixed gas hydrates are critical factors to predict the heat flow in the hydrate-bearing sediments and the heat required for hydrate dissociation, and to evaluate the CO2 storage capacity of hydrate reservoirs. In this study, the C-13 NMR and gas composition analyses confirmed that the preferential enclathration of N-2 molecules in small 5(12) cages of structure I hydrates improved the extent of the CH4 recovery. A high pressure micro-differential scanning calorimeter (HP mu-DSC) provided reliable hydrate stability conditions and heat of dissociation values in the porous silica gels after the replacement, which confirmed that CH4 in the hydrates was successfully replaced with flue gas. A heat flow change associated with the dissociation and formation of hydrates was not noticeable during the CH4-flue gas replacement. Therefore, this study reveals that CH4-flue gas swapping occurs without structural transitions and significant hydrate dissociations. (C) 2015 Elsevier Ltd. All rights reserved.