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Determination of dissociation rate of MH sediment<br />
To evaluate the dissociation rate by the thermal stimulation method, the temperature gradient<br />
was added to the bottom of artificial MH sediment. MH was dissociated to one direction, and<br />
the speed of movement of the dissociation front was measured. Artificial MH sediment was<br />
made in the dissociation experimental apparatus, and experimented upon without taking it out.<br />
To prevent heat flow to the side in the pressure vessel, a thick acrylic cylinder was installed as<br />
heat insulation. The speed of movement of the MH dissociation front was measured by the<br />
temperature change in the sample. The propagation process of the MH dissociation regime<br />
was analyzed, and the relation between the moving rate and the temperature gradient was<br />
analyzed.<br />
In addition a dissociation rate measurement device was developed that was able to measure<br />
the dissociation rate of artificial MH sediment with increasing the temperature and pressure<br />
gradients. The existing device used for the measurement of the dissociation front speed has<br />
the advantage that the temperature distribution can be measured precisely in the necessary<br />
side insulation. However, the fact that the interface of the vessel and the sample easily<br />
becomes the channel <strong>gas</strong> is an unfortunate fault. Therefore, the method of increasing the<br />
confined pressure to the core sample with the sealing sleeve was adopted. Moreover, because<br />
the MH sediment is unconsolidated, it is necessary to reproduce the change in sediment frame<br />
structure/ permeability of the <strong>gas</strong> according to the MH dissociation. Therefore, the core holder<br />
type of dissociation experimental apparatus that was able to add the confined pressure was<br />
developed.<br />
Figure 8. Core Test Apparatus.<br />
(for dissociation test)<br />
The pressure decreasing method has been adapted for the artificial core sample. The<br />
drawdown pressure was set at 20, 40, 60, 80 and 90% to the initial pressure of 10MPa at<br />
286K, as the dissociation rate was increased in the drawdown. Also, the internal temperature<br />
of the core sample reached to 273K and indicated ice formation at high drawdown pressure.<br />
The data has now been analyzed, but both the dissociation rate and the recovery ratio are high<br />
compared with those of the thermal stimulation method explained previously. The equipment<br />
developed for the dissociation test is shown in Figure 8.<br />
New Energy Resources in the <strong>CCOP</strong> Region - Gas Hydrates and Coalbed Methane 95
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