Injection of Superheated Water Vapor into a Porous Reservoir Saturated in the Initial State with Methane and Its Hydrate

Abstract

The work presents a mathematical model of the process of pumping of superheated water vapor into a semi-infinite natural porous reservoir, which in its initial state is saturated with a gas (methane) and its gas hydrate, in a flat-one-dimensional approximation. The most general case is considered, when four zones of different composition of the saturating phases and three moving boundary surfaces separating these zones appear in a natural reservoir: between the first and second zones, on which condensation of superheated water vapor occurs; between the second and third zones, where displacement of condensed methane water takes place; and between the third and fourth zones, where the dissociation of the gas hydrate occurs. In the considered formulation of the problem, the first zone of the porous reservoir is saturated with superheated water vapor, the second zone is saturated with condensed water, the third zone is saturated with methane and still water (released during the dissociation of gas hydrate), and the fourth zone of the reservoir is saturated with methane and its gas hydrate. On the basis of a numerical solution, the hydrodynamic and temperature fields that arise in the porous reservoir are studied. It is shown that solutions with the indicated areas and boundaries exist only at relatively low values of injection pressure and reservoir permeability. It is established that an increase in both the injection pressure and the reservoir permeability leads to a noticeable increase only in the coordinates of the boundary separating the second and third regions; in this case, the coordinate of the methane hydrate decomposition front is practically independent of the indicated parameters. An increase in the values of these parameters leads to the confluence of the boundaries of methane displacement and gas hydrate decomposition. The dependence of the limiting value of the injection pressure on the permeability at which these boundaries merge is obtained.