Where Do I Start with Subsurface Flow Modeling?
Before beginning with modeling, it is important to be aware of the following questions:
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Which goal do I pursue with the simulation?
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What accuracy is required from the results?
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Which physical effects play a role?
The first question refers to the results that the simulation should deliver. The system under consideration is often very complex in structure and the physical processes involved. Not everything is relevant for the specific task. Together with the second and third question, the simulation model can then be reduced to the most essential.
Often a 2D or 2D axial symmetric model, sometimes even a 1D model is sufficient. Especially in subsurface flow problems, one has to deal with very large areas. The question is to what extent small-scaled structures are relevant for the result and therefore have to be represented in the geometry. The physical effects to be considered also depend on how accurate the results should be: Does gravity play a role or do I have to take temperature fluctuations into account? These questions should be answered before starting the simulation.
The accuracy of the results also depends on the accuracy of the input quantities. Especially in geophysical questions the exact structure, the material and its properties are not exactly known. Therefore the result cannot be more exact than the accuracy of these and it is not necessary to represent every smallest detail in the model.
Regardless of the above answers, it is always advisable to make the models successively more complex. Complex 3D models are always significantly more computationally demanding and often make high demands on the meshing, whereas in 2D models the focus can be placed on the physical processes and effects. This implies using a simplified model as a starting point in the project. Complexities can then be introduced gradually so that the effect of each refinement of the model description is well understood before introducing new complexities.