From geological to groundwater flow models: an example of inter-operability for semi-regular grids

Integrating geologic information into hydrogeologic numerical models is by no means a straightforward operation. This is especially true for finite element modeling which generally requires that the geological information be integrated into grids that are generally irregular in the horizontal (i, j) direction and regular in the vertical (k) direction. Semi-regular grids of this type are still rarely supported by geological modeling packages and the data structure can vary significantly between softwares. Nevertheless, workable solutions exist for some software packages. Here we present a solution that allows the properties of a gOcad geomodel to be transferred to a semiregular grid built in GMS, a commonly used pre-processor for groundwater flow modeling applications. The transfer is achieved first by building in gOcad a “twin grid” that has the same mesh structure as the original GMS grid. This is done using the research plug-in GridLab developed by the gOcad Research Group. Once the properties of the geomodel are transferred to the twin grid, cell or element number correspondences and property transfer to the original GMS grid is achieved using the database system Access. ASCII file format is used for most data exchange between softwares. The time required to go through the procedure is on the order of minutes, even for large grids, making it a practical solution for the lasting problem of property transfer from geological to hydrogeological models, at least until more convenient and built-in interfaces are developed.