Numerical Studies of Gas Production from Methane Hydrates

Abstract EOSHYDR2 is a new module for the TOUGH2 general-purpose simulator for multi-component, multiphase fluid and heat flow in the subsurface. By solving the coupled equations of mass and heat balance, EOSHYDR2 can model the non-isothermal gas release, phase behavior and flow of fluids and heat under conditions typical of common natural hydrate deposits (i.e., in the permafrost and in deep ocean sediments) in complex formations, and 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 and dissociated methane, a second native and dissociated hydrocarbon, salt, water-soluble inhibitors and heat). The mass components are partitioned among the phases, and their thermophysical properties can be described at temperatures as low as -110 °C. 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 exploring different mechanisms and strategies for production from typical CH4-hydrate accumulations. The results of the tests tend to indicate that CH4 production from CH4-hydrate is technically feasible and has significant potential. 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.