Hydrate formation from CO2 saturated water under displacement condition

Hydrate formation during the process of displacing pore fluid is of great significance for CO2 subsea storage and gas production from natural gas hydrates. In this work, the nucleation kinetics of CO2 hydrate under displace-ment condition was investigated using CO2 saturated water and sea sand. For comparative analysis, similar experiments were also conducted under static conditions. The experimental results show that the changes of temperature and pressure under displacement condition are not necessarily the same as those under static condition. The induction time and the temperature increase are 206.8-723.0 min and 0.1-2.3 K, respectively, at experimental temperatures of 270.8-273.7 K and pressures of 4.3 and 5.0 MPa, which are smaller than those obtained from static experiments under the same conditions. The two variables exhibit the stochastic character of a lognormal distribution. The flow disturbance not only can promote hydrate nucleation and shorten induction time, but also homogenize the temperature field, reducing the randomness of hydrate nucleation and temper-ature increase. But the flow may entrain some hydrate crystals, resulting in a low hydrate saturation. Thus, the permeability of the static experiment (11.6-18.8 mu m2) is smaller than that of the displacement experiment (13.3-21.5 mu m2) at the same temperature and pressure conditions. Relatively, the experimental results of permeability are in agreement with the predicted values of Masuda model and Dai model.