Natural gas hydrate, as a potential energy resource, deposits in permafrost and marine sediment with large quantities. The current exploitation methods include depressurization, thermal stimulation, and inhibitor injection. However, many issues have to be resolved before the commercial production. In the present study, a 2-D axisymmetric simulator for gas production from hydrate reservoirs is developed. The simulator includes equations of conductive and convective heat transfer, kinetic of hydrate decomposition, and multiphase flow. These equations are discretized based on the finite difference method and are solved with the fully implicit simultaneous solution method. The process of laboratory-scale hydrate decomposition by depressurization is simulated. For different surrounding temperatures and outlet pressures, time evolutions of gas and water generations during hydrate dissociation are evaluated, and variations of temperature, pressure, and multiphase fluid flow conditions are analyzed. The results suggest that the rate of heat transfer plays an important role in the process. Furthermore, high surrounding temperature and low outlet valve pressure may increase the rate of hydrate dissociation with insignificant impact on final cumulative gas volume.
Methane production from hydrate reservoir may induce seabed slide and deformation of the hydrate-bearing strata.The research on mechanical properties of methane hydrate is considered to be important for developing an efficient methane exploitation technology.In this paper,a triaxial test system containing a pressure crystal device was developed with the conditions to stabilize the hydrate.A series of triaxial shear tests were carried out on artificial methane hydrate specimen.In addition,mechanical characteristics of methane hydrate were studied with the strain rates of 0.1 and 1.0 mm/min,respectively,under the conditions of different temperatures（T =-5,-10,and-20 ℃） and confining pressures（P = 0,5,10,15,and 20 MPa）.The preliminary results show that when the confining pressure was less than 10 MPa,the increase of confining pressure leaded to the enhancement of shear strength.Furthermore,the decreasing temperature and the increasing strain rate both caused the increase in shear strength.
Yongchen Song Feng Yu Yanghui Li Weiguo Liu Jiafei Zhao
An experimental device was set up to study the hydrate formation conditions.Effects of pore size,salinity,and gas composition on the formation and dissociation of hydrates were investigated.The result indicates that the induction time for the formation of hydrates in porous media is shorter than that in pure water.The decrease in pore size,by decreasing the size of glass beads,increases the equilibrium pressure when the salinity and temperature are kept constant.In addition,higher salinity causes higher equilibrium pressure when the pore size and temperature are kept constant.It is found that the effects of pore size and salinity on the hydrate equilibrium are quite different.At lower methane concentration,the hydrate equilibrium is achieved at lower pressure and higher temperature.
