What is PETGEM?

Electromagnetic methods (EM) are an established tool in geophysics, with application in many areas such as hydrocarbon and mineral exploration, reservoir monitoring, CO₂ storage characterization, geothermal reservoir imaging and many others. In particular, the marine Controlled-Source Electromagnetic method (CSEM) and the 3D magnetotelluric (MT) method have become important techniques for reducing ambiguities in data interpretation in exploration geophysics. In order to be able to predict the EM signature of a given geological structure, modelling tools provide us with synthetic results which we can then compare to real data. In particular, if the geology is structurally complex, one might need to use methods able to cope with such complexity in a natural way by means of, e.g., an unstructured mesh representing its geometry. Among the modelling methods for EM based upon 3D unstructured meshes, the High-order Nédélec Finite Elements (FE), a type of Edge Finite Elements, offer a good trade-off between accuracy and number of degrees of freedom, i.e. size of the problem.

In the multi-core and many-core era, parallelization is a crucial issue. Nédélec FE offer good scalability potential. Its low DOF number make them potentially fast, which is crucial in the future goal of solving inverse problems which might involve over 100,000 realizations (e.g. within a inversion routine). However, the state of the art shows a relative scarcity of robust high-order edge-based codes to simulate these problems.

On top of that, Parallel Edge-based Tool for Geophysical Electromagnetic Modelling (PETGEM) is a Python tool for the scalable solution of the EM modeling on tetrahedral meshes, as these are the easiest to scale-up to very large domains or arbitrary shape. It supports distributed-memory paralelism through petsc4py package.

As a result, PETGEM tool allow users to specify high-order edge-based variational forms of H(curl) for the simulation of electromagnetic fields in realistic 3D active-source (e.g. CSEM) and 3D passive-source (e.g. MT) surveys with accuracy, reliability and efficiency.

PETGEM is developed as open-source under BSD-3 license at Computer Applications in Science & Engineering (CASE) of the Barcelona Supercomputing Center (BSC). Requests and contributions are welcome.