Converting heterogeneous complex geological models to consistent finite element models: methods, development, and application to deep geothermal reservoir operation

Static geological models representing complex geological systems are the prerequisite of dynamic model simulations applied for assessing subsurface processes. The corner point grid approach has been applied to represent the complexity in geometry, hydraulic connectivity, and heterogeneity found in these static geological models. Due to the occurrence of faults, pinch-outs, and eroded geological layers, corner point grids easily degenerate, which leads to model inconsistencies. This study introduces a workflow for converting heterogeneous geological models to consistent finite element models, accounting for regular and irregular hexahedral blocks of the corner point grid by converting to a set of hexahedra, prism, pyramid, and tetrahedral elements, based on the individual degeneration situation. Heterogeneous geological data such as permeability or porosity can be transferred layer-wise or on a block-wise basis. Additionally, well trajectories can be accurately mapped to the converted finite element mesh, to place the corresponding source terms. The developed workflow is tested on dedicated test cases and applied to convert a real complex field site from the North German Basin for use in a deep geothermal reservoir operation. The field application demonstrates the robustness and applicability of the newly developed conversion workflow and the suitability of the converted mesh for dynamic finite element reservoir model simulations.