COMSOL 6.4 - Well (Multiphysics Coupling)

) interface contains an optional multiphysics coupling feature on points (in 2D) or edges (in 3D). The coupling node is intended to model injection or production wells and links bidirectionally the and interfaces.

The Subsurface Flow Module license is required to use this coupling feature (see www.comsol.com/products/specifications/).

The is the default multiphysics coupling feature name.

The default (for the first multiphysics coupling feature in the model) is wellmpp1.

When nodes are added from the context menu, you can select (the default) from the list to choose specific points or edges, or select or as needed.

This section controls which individual interfaces are coupled by the current coupling feature. If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the correct physics interface again from the or lists

Select whether the well is a production or injection well: for an injection well positive mass fluxes signify inflowing fluxes and for a production well positive mass fluxes are outflowing fluxes.

Either specify the total M0 (SI unit: kg/s), the Ml (SI unit: kg/(m·s)), the p0 (SI unit: Pa), the Hp0 (SI unit: m), or the H0 (SI unit: m). The elevation D used to convert the hydraulic head to a pressure, is defined by the gravity effects in the coupled Darcy’s Law interface.

Select the checkbox to define the dw (SI unit: m). This averages the mass source on the boundary of a cylinder around the line. This option avoids obtaining an increasing pressure value at the line when meshing finer than this diameter. It makes use of the circavg operator.

If the well diameter is defined, the option to specify the N0 (SI unit: kg/(m2·s)) is also available.

The number of sections depends on the number of phases defined in the coupled Phase Transport in Porous Media interface: the number of sections is equal to the number of phases not computed from the volume constraint, which is in turn equal to the number of phases defined in the coupled Phase Transport in Porous Media interface minus one.

Specify the boundary condition for each phase not computed from the volume constraint. You can choose to enter a value for the M0,i (SI unit: kg/s), the Ml,i (SI unit: kg/(m·s)), or the s0,i (dimensionless). If the well diameter is specified, the option to specify the N0,i (SI unit: kg/(m2·s)) is also available. For a production well, you can additionally choose the option. For an injection well you can additionally choose to specify the s0,i (dimensionless).

When the s0,i is specified for a phase, a mass flow rate per unit length Ml,i is supplied for that phase, which is given by

where Vl is the total volumetric flow rate per unit length, which is computed as follows: assume that there are N phases, and that phase 1 is the phase computed from the volume constraint, that for phases i, for i = 2, ..., p, the fraction of total volumetric flow rate s0,i is supplied, and that for the phases i, for i = p+1, ..., N, the mass flow rate per unit length Ml,i is given. Then Vl can be computed from the relation

where the mass flow rate Ml,1 for the phase computed from the volume constraint is given by

Note that the total mass flow rate per unit length Ml is readily available when any of the , , or the options is chosen. Furthermore, the total mass flow rate per unit length Ml is also available as a Lagrange multiplier in case any of the , the , or the is given, as these conditions are implemented as weak constraints. For the mass flow rates per unit length Ml,i of the individual phases, it holds similarly that they are readily available when any of the , , or the options are chosen, and that for the option, implemented as a weak constraint, the mass flow rate per unit length Ml,i is computed as a Lagrange multiplier.

When the option is specified for a phase si, an outflowing mass flow rate per unit length Ml,i is supplied for that phase, which is given by

where κri denotes the relative permeability of phase i.