Fig. 6 . Characteristics of pressure at reactor inlet and seawater increase in reactor
As shown in Fig. 6, the turning points appeared at 94 and 54 min in Cases 4 and 5, respectively. After the turning point, the seawater won’t flow out of the reservoir outlet, the hydrate reservoir had sealing effect. The gas–water flow rates of Cases 4 and 5 were the same as Cases 2 and 1, respectively. However, hydrate–containing sealing layer formed only in Cases 4 and 5, because higher reservoir pressure provide larger driving force for hydrate formation (Ma et al. , 2020). It also indicated that higher pressure will promote the formation of hydrate–containing sealing layer than low gas–water flow rate. Because the higher pressure can enhance the mass transfer between the gas and seawater, and enhance hydrate formation during gas–water flow process. Moreover, the pressure increases rate curve had a fluctuation at the turning point, and increase rate of inlet pressure was decreased, this fluctuation also appeared in Case 3. Furthermore, there is a certain regularity in the pressure difference between the reactor inlet and outlet at the time of hydrate–containing sealing layer is formal formed, as shown in Fig. 7. The mean value of pressure different is 2.47 MPa. In this study, the pressure difference at turning point is independent of reservoir pressure, it can be used as a marker to judge the formation of hydrate seal layer during the experiment.