EFFECTS OF SIMULATOR MESH GEOMETRY ON A SIMPLE THREE DIMENSIONAL TOUGH2 MODEL

As graphical user interfaces for the TOUGH2 simulator become more advanced, modelers must choose between traditional rectangular grids and multi-dimensional meshes with variable element and layer dimensions. The use of meshes with layers of varying thickness and non-rectangular elements refined around sources and sinks is essential in the creation of larger scale models that can be run in a reasonable amount of time. However, the modeler should consider the implication of non-rectangular and non-horizontal meshes, especially if the mesh does not honor the geometric requirements of the TOUGH2 simulator and other IFDM simulators.

A simple model simulating geothermal production was created using the TOUGH2 EOS1 Fluid Property Module using the PetraSim graphical user interface. Cooler fluid was injected into a centrally located injection well and water was pumped from two nearby extraction wells. Four simulation meshes were created using various meshing techniques to compare the use of horizontal and non-horizontal cell layers and rectangular and polygonal mesh elements. Flow rates and energy production for the two production wells were compared for all four models to determine whether either of the layer characteristics had a significant effect on the fluid flow within the simulation. The results showed that for this example, the orientation of cell layers has more of an effect on model results than the shape of the model element. This is most likely because flow between wells is non-horizontal and follows the general orientation of the cell layers in the non-horizontal layer models.