Numerical studies of gas production from methane hydrates

EOSHYDR2 is a new module for the TOUGH2 general-purpose simulator for multicomponent, multiphase fluid and heat flow in the subsurface. By solving the coupled equations of mass and heat balance, EOSHYDR2 can model the nonisothermal gas release, phase behavior, and flow of fluids and heat under conditions typical of common natural hydrate deposits (i.e., in permafrost and in deep ocean sediments) in complex formations, and it can describe binary hydrocarbon systems involving methane. EOSHYDR2 includes both an equilibrium and a kinetic model of hydrate formation and dissociation. The model accounts for up to four phases (gas phase, liquid phase, ice phase, and hydrate phase) and up to nine components (hydrate, water, native CH4 and CH4 from hydrate dissociation, a second native and dissociated hydrocarbon, salt, water-soluble inhibitors, and a heat pseudocomponent). The mass components are partitioned among the phases. The thermophysical properties of the various mass components can be described at temperatures as low as -110degreesC. Dissociation, phase changes, and the corresponding thermal effects are fully described, as are the effects of salt and inhibitors. The model can describe all possible hydrate dissociation mechanisms (i.e., depressurization, thermal stimulation, salting-out effects, and inhibitor-induced effects). Results are presented for four test problems of increasing complexity that explore different mechanisms and strategies for production from typical CH4-hydrate accumulations. The results of the tests indicate that CH4 production from CH4-hydrates could be technically feasible and has significant potential. In particular, thermal stimulation is capable of producing substantial amounts of hydrocarbons, and its effectiveness can be enhanced when coupled with depressurization and the use of inhibitors.