Depressurized dissociation of methane-hydrate-bearing natural cores with low permeability

Depressurization is a promising technique for producing natural gas from methane hydrate reservoirs. However, current studies focus mainly on artificial sediments with high permeability. Research on low-permeability conditions such as those of natural cores is scarce; therefore, there is little information on the natural core dissociation characteristics. This report presents the dissociation characteristics of low-permeability methane-hydrate-bearing cores. We used a natural core obtained from the eastern Nankai Trough. From dissociation experiments at the low-permeability core, we clarify differences during the depressurization process: the pressure propagated slowly, and dissociation was driven mainly by sensible heat consumption. The dissociation process was divided into four stages similar to that of the artificial core. We also compared our experimental results with those using two dissociation models for the divided dissociation stage. One of these previously proposed dissociation model were applied to a constant production pressure stage. The other model was a simple sensible heat consuming model, and it described the dissociation during the depressurization process toward constant production pressure. By comparing our experimental results with the theoretical results from the two dissociation models, it was clearly demonstrated that both models can accurately describe the experiment results of the divided dissociation stage. (C) 2011 Elsevier Ltd. All rights reserved.