Eight rigid/nonpolarizable water models and three methane potentials were tested respectively for lattice parameters of sI full-occupancy methane hydrates. The results show that the combination of TIP4P/2005 water model and DACNIS united-atom methane potential can reproduce the lattice parameters which are closest to the experimental values and achieve the balance between relatively accurate results and computational time. And then we report extensive calculations of the isothermal compressibility and thermal expansion of the full-occupancy sI methane hydrates, CO2 hydrates and their mixture hydrates by rescaling energetic parameter for methane-water interaction. The results show that with the increase of CO2 percentage, the compressibility and expansion of hydrates increases and bulk modulus decreases accordingly. The effect of hydrate volume variations perhaps cloud not be neglected during the recovery methane from methane hydrates in deep oceans by using CO2 to replace methane, especially on the phase equilibrium and the mechanical stability of sediments.

Eight rigid/nonpolarizable water models and three methane potentials were tested respectively for lattice parameters of sI full-occupancy methane hydrates. The results show that the combination of TIP4P/2005 water model and DACNIS united-atom methane potential can reproduce the lattice parameters which are closest to the experimental values and achieve the balance between relatively accurate results and computational time. And then we report extensive calculations of the isothermal compressibility and thermal expansion of the full-occupancy sI methane hydrates, CO2 hydrates and their mixture hydrates by rescaling energetic parameter for methane-water interaction. The results show that with the increase of CO2 percentage, the compressibility and expansion of hydrates increases and bulk modulus decreases accordingly. The effect of hydrate volume variations perhaps cloud not be neglected during the recovery methane from methane hydrates in deep oceans by using CO2 to replace methane, especially on the phase equilibrium and the mechanical stability of sediments.

One of the main challenges in deep-water diJlling is gas-hydi-ate plugs, which make the diJlliilg unsafe. Some oil-based clfilling finds (OBDF)that would be used for deep-water dlfilling in the South China Sea were tested to investigate the characteristics of gas-hydi-ate formation, agglomeration and inhibition by an experimental system under the temperature of 4 o C and pressure of 20 MPa, which would be siiullar to the case of 2000 m water depth. The results validate the hydiate shell formation model and show that the water cut can greatly fiNuence hydi-ateformation and agglomeration behaviors in the OBDF. The oleophobic effect enhanced by hydiate shell folmation which weakens or destroys the interfacial films effect and the hydi-ophilic effect are the dominant agglomeration mechanism of hydi-ate particles. The formation of gas hydrates in OBDF is easier and quicker than in water-based drilling fluids in deep-water conditions of low temperature and high pressure because the former is a W/O dispersive emulsion which means much more gas-water interfaces and nucleation sites than the later. Higher ethylene glycol concentrations can inhibit the formation of gas hydi-ates and to some extent also act as an anti-agglomerant to filhibit hydi-atesagglomeration in the OBDF.