Fig. 7 . Pressure difference values at onset time of sealing
layer formation
Fig. 8 shows the variation characteristics of hydrate saturation in FOV
during the gas–water injection process of cases 4 and 5. The MRI images
is getting darker in Case 5 and hydrate saturation present an increasing
trend, thus, hydrate formed during the gas–water flow process and
hydrate–bearing reservoir had sealing effect. However, hydrate
saturation didn’t show an obviously increasing trend in Case 4, though
the sealing effect existed after 94 min. It could be found that there
was a significant change in the lower left corner of FOV in Case 4, so
we analyzed the change in MI value of Line 1. The small distance of MI
value (0~4.2 mm) is obviously reduced, indicating that
hydrate formed in this area and consumed the pore water. The reason for
sealing effect exists in Case 4 was also caused by hydrate formation,
but hydrate formation was not concentrated in the FOV, and thought it
was below the FOV. To further analyze the reservoir state, multi–level
MRI image (4 layers) was carried out by adjusting the position of the
reactor.