The hydrate saturation in hydrate reservoir is usually very high,
according to the geological exploration results (Lpa et al. ,
2019). Thus, when the \(S_{h}\) reached about 35%, opened the outlet
value of the reactor immediately, so the pressure in the reactor was
controlled by the back pressure pump, this was the preparation for the
gas–seawater flow. At 274.15 K, the phase equilibrium pressure of
methane hydrate in seawater was 3.18 MPa (Lafond et al. , 2012),
the back pressure in this study is 3.5 MPa or 4.0 MPa, which are all
above the methane hydrate phase equilibrium pressure. The hydrate
reservoir was usually in the state of water saturation
(Almenningen et al. , 2018; Chong et al. , 2017). Therefore,
to better simulate the academician state of hydrate in marine
environment, the seawater was injected into the reactor using
high–precision water injection pump at the flow rate of 0.5 ml/min. The
seawater flow rate was low enough so that it can be considered that
there was no hydrate decomposition during this process (Chen et
al. , 2019c). After that, the gas and seawater were injected into the
reactor at the same time using pumps. The temperature of injected
methane gas and seawater was 273.95 K, which was slightly below the
reservoir temperature, for the purpose to avoid the influence of heat
injection on hydrate dissociation. The hydrate formation datas are
showns in Table 1, it was obviously that all experimental conditions
were inside the hydrate
thermodynamic stable area to avoid the dissociation of hydrate due to
other reasons (depressurization, temperature rise).
Results and discussion
Methane gas and seawater were injected into the hydrate–bearing
sediments to simulate the gas and seawater ascending in the seafloor
sediments. Thus, gas–water two phase flow is a method to verify the
sealing effect of hydrate reservoir. The water–saturated hydrate
samples were made by injecting water into hydrate samples, as shown in
Fig. 2. Furthermore, the gas–seawater flow rate ratio was constant at 4
for all Cases. The real–time characteristics of hydrate reservoir state
was investigated using MRI visualization
technology.