TOUGH uses the "Multiple INteracting Continua" (MINC) method to approximate modeling fluid and heat flow in fracture-porous media. As described in [Pruess, 1992], "The method is applicable to flow processes in which an important aspect is the exchange of fluid, heat, or chemical species between fractures and unfractured rock. ... MINC can only be applied to media in which the fractures are sufficiently well connected so that a continuum treatment of flow in the fracture network can be made." If the fractures are not sufficiently connected, a discrete representation of the fracture should be used with a different porous material for flow in the fracture. A detailed explanation of MINC is provided in [Pruess, 1983].

As described in [Pruess, 1992], "The method is an extension of the double-porosity concept, originally developed by [Barenblatt, et al., 1960] and [Warren and Root, 1963]. It is based on the notion that fractures have large permeability and small porosity (when averaged over a reservoir subdomain), while the intact rock (the rock "matrix") has the opposite characteristics. Therefore, any disturbance in reservoir conditions will travel rapidly through the network of interconnected fractures, while invading the matrix blocks only slowly."

MINC is implemented in TOUGH as a mesh processor of the mesh. Additional cells and connections are created so that matrix blocks are "discretized into a sequence of nested volume elements which are defined on the basis of distance from the fractures. Continuum #1 represents the fractures, continuum #2 represents matrix rock in close proximity to the fractures, continuum #3 represents matrix rock at larger distance, etc. In response to an imposed disturbance in the fracture system, fluid and/or heat can migrate in the matrix blocks outward towards the fractures, or inward away from the fractures.

For a complete description, the user is referred to [Pruess, 1992] and [Pruess, 1992], copies of which are available in the help section of http://www.petrasim.com.

To activate the MINC option in PetraSim, select Properties->Global Properties... or . Go to the MINC tab, Figure 14.1. Select "Enable Multiple Interacting Continua (MINC)". Then, the input data corresponds to that given in the TOUGH2 User's Guide,.

Figure 14.1. Activating MINC in PetraSim

Once the MINC option is activated, the user will need to specify the fracture material data on the Fracture tab of the Material Data dialog. This will be the data used for the fractures. The Matrix data will be used for the rock matrix.