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MINC and MIM

Hi All,

I'm comparing MINC to mobile-immobile (MIM) models, most of which focus on transport (i.e., with the diffusion as the process connecting the two domains). MINC appears to function with respect to flow only, with no differentiation in terms of transport. Is that accurate? If not, how is transport from one domain to the other (e.g., from fracture to matrix) governed?

Thank you,

Amy

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  • Amy,

    MINC captures effects in multi-continua system purely by geometry. It thus operates on ALL processes implemented in TOUGH2; specifically, advective and diffusive transport is included (i.e., MINC can be formulated as a MIM). By setting appropriate parameters for the individual continua, you can engage/disengage individual processes (i.e., fluid flow, transport, conductive heat transfer, etc.).

    Stefan

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  • Stefan,

    Thank you for replying. What parameters for transport would one need to change to formulate MINC as a MIM for a model of isothermal, multiphase (aqueous and gas) transport (of methane)?

    Also, if a system is dual permeability, can you still have transient storage, like in a double porosity formulation?

    Amy

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  • Amy,

    I assume that you only want diffusive transport into the immobile phase, even though this is a simplification of the actual physics taking place, specifically if you include a compressible gas phase. If you want no flow and no advective transport (just diffusion), set absolute permeability of the immobile continuum to zero (MINC automatically generates zero nodal distances from the mobile to the immobile continua, so the zero permeability will  be used even if you select upstream weighting).

    Not sure I understand your second question. Dual permeability generally refers to the matrix (immobile) continuum to be globally connected - seems to contradict your conceptual NIM model.  Please clarify your NIM and dual-permeability concepts.

    Stefan

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  • Stefan,

    At present I'm wrapping my head around code capabilities and trying to compare MINC to MIM models-- the conceptual model is waiting in the wings.

    What I really need to know is how transport occurs from the mobile zone to the immobile zone and back in MINC. In MIM, there's an exchange function accounting for mass transfer between continua based on concentration differences between the continua and an exchange parameter. In MINC, there's not. Why not? Is using MINC essentially the same as changing material properties in regular (i.e., non-MINC) grid cells, but with additional options (e.g. for nesting grid cells)?

    Thank you very much for your help.

    Amy

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      • Stefan Finsterle
      • Finsterle GeoConsulting
      • Stefan_Finsterle
      • 4 yrs ago
      • Reported - view

      Hi Amy,

      The exchange between mobile and immobile zones is handled using exactly the same equations as between any other elements, i.e., there is no need for a separate exchange function with new parameters.  As stated previously, MINC calculates appropriate volumes, interface areas, and nodal distances to capture storage and exchange between effective fracture (mobile zone) and matrix (immobile zone) continua within a single grid block, i.e., its all in the geometry (note, it is not just "nesting" as the somewhat misleading "sugarcube" figure suggests; try to understand what the proximity function is, and you will be ready to use MINC!).

      Good luck!

      Stefan

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  • Hi Stefan,

    One follow-up question, regarding what is meant by "global" flow in the manual: if a a dual-porosity (not dual-perm) formulation is used in MINC and a solute goes in one side of a matrix element, could it then come out the other side of that element (given appropriate flow conditions)? Or is the only option to get stored and then come back into the fracture?

    Thank you,

    Amy

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  • P.S. This is assuming the matrix element in question in not linked up to other matrix elements, but rather surrounded on all sides by fractures.

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  • Amy,

    In any dual-continuum approach, there is no such thing as matrix being "surrounded" by fractures. The fracture and matrix are overlapping, interacting continua at the same point in space. The fracture continuum has one set of primary variables, so does the matrix. Fluids and heat are exchanged between these two continua (f to m or m to f) according to the prevailing gradients, and accounting for the fact that the surface area and nodal distances between the two continua are adjusted according to fracture spacing and geometry. But there is no "through flow", i.e., it only "gets stored and then comes back into the fracture".

    I hope this is clearer, as I am afraid the sugar-cube picture keeps misleading many MINCers! The sugar-cube model is correct if you picture that one pair of dual-porosity elements (one f and one m element) represent all these sugar cubes together, and if you can wrap your head around the possibility that in certain cases (large fracture spacing) these two elements may represent less than one sugar cube!

    Stefan

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  • Hi Stefan,

    Is the math used to describe both flow and transport in these systems available? I've read the following, which have excellent text-based descriptions of the MINC method and math pertaining to the proximity function:

    Pruess, K. (1983), GMINC-A mesh generator for flow simulations in fractured reservoirs, Berkeley, CA.

    Pruess, K. (2010), Brief Guide to the MINC-Method for Modeling Flow and Transport in Fractured Media,

    Pruess, K., and T. N. Narasimhan (1982), a Practical Method for Modeling Fluid and Heat Flow in Fractured Porous Media, , (February), 37.

    However, I need to see how MINC handles the flow and transport equations to understand what's going on. 

    Thank you very much!

    Amy

    P.S. Would you mind if I ask a question to test my understanding? Say we have two interacting continua with the volume fractions 50% fracture and 50% matrix. Fracture porosity is 20% and matrix porosity is 10%. What is the porosity of the full domain? The way I was thinking, it would be the mean of the two, 15%. However, if I'm interpreting your response correctly, porosity should be additive, and the domain porosity would be 30%. Is the latter correct? Thank you again.

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  • Hi Stefan,

    I've figured out almost all of my MINC questions, but the one in the postscript of my previous post about total porosity is still bugging me. Can you help? I'm wondering what the total porosity of a system (i.e., modeled domain) would be if, for example, the fracture porosity is 20%, the matrix porosity is 10%, and volume fractions of the two interacting continua are 50%/50%. Thank you!

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  • Vf*phif+Vm*phim=0.5*0.2+0.5*0.1=15%

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