Fig. 3 . Characteristics of pressure at reactor inlet and reactor outlet flux
In Case 2, the inlet pressure reached about 10.0 MPa twice at the gas–water flow rate of 2–0.5 ml/min, and finally the inlet pressure dropped the same as outlet pressure. The inlet pressure increased before 163 min (turning point 1), and the seawater accumulated in the reservoir because the slope of outlet flux was decreased gradually. The inlet pressure increase indicating capillary sealing effect (Liu , 2007) appeared in the hydrate reservoir, and the reservoir permeability decreased which was caused by the hydrate saturation increase in the sediments (Mahabadi et al. , 2019). But the capillary sealing effect of hydrate reservoir was not stable, the hydrate hydrate saturation was not high enough, the hydrate–containing sealing layer was broken through at 163 and 194 min, respectively, and caused inlet pressure decrease, the whole process is shown in Fig. 4. The break through (BT) pressure were 6.68 MPa, 6.46 MPa, respectively, and the reason of this phenomenon are the large pressure difference on both sides of hydrate reservoir (Liu , 2007) and the incompletely formation of hydrate–containing sealing layer.