gas hydrate - CCOP

Figure 7. One-dimensional development simulation system.
Experimental studies of gas hydrate dissociation by depressurization
After hydrate formation, the production simulation test begins. The hydrate dissociation
experiments by depressurization have been carried out by setting the stable pressure of backpressure
regulator. During the experiment runs, the inlet and outlet pressure are kept the same.
When the system pressure decreases from 8Mpa to 3MPa, the gas production rate and
accumulated gas produced are given in Figures 8 and 9 respectively.
It can be revealed from Fig. 8 that the gas production rate can be divided into four stages:
1) First stage: The gas production rate increases sharply with decreasing pressure. The
main reason is that there exists free gas in the vessel after hydrate formation. When the
pressure in the vessel begins to decrease, the free gases expands and flows out of the
vessel;
2) Second stage: After gases production rate peaks, the production rate begins to decrease.
This suggests that with the further decrease of the pressure, the effects of free gases on
the gas production rate become negligible. The hydrates begin to dissociate;
3) Third stage: The gas production rate keeps a constant level. This is because the natural
gas hydrate dissociation is a nearly stable process;
4) Last stage: The gas production rate decreases to zero.
From the accumulated gas production curve given in Figure 9, it can be found that the
cumulative gas produced for hydrate production is similar to a conventional gas reservoir, i.e.
in the first stage; the gas is produced quickly, and becomes stable at a later stage.
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 71