IGMAS+ in a nutshell

Introduction

Modern geophysical interpretation requires an interdisciplinary approach and software capable of handling multiple inhomogeneous data like seismic, FTG gravity, magnetic and magnetotelluric in complex geological environments.

We are proud to introduce IGMAS+ (Interactive Gravity and Magnetic Application System), a geo-modelling software for 3-D joint inversion of potential fields and its derivatives under the condition of constraining data and independent information.

3-D gravity and magnetic modelling appreciably improves the results of distinct depth imaging projects. This regards especially to areas of strong lateral seismic velocity and density contrasts and corresponding imaging problems. Typical areas where grav/mag modelling has been successfully used are sub-salt and sub-basalt settings.

What makes IGMAS+ highly efficient and user-friendly is that it allows adjusting the geometries and physical properties of modelled subsurface bodies interactively, i.e. while the corresponding calculated and measured potential field components are visualized together with independent observations.

See our main publication list, as well as related publications and citing instructions.

History

Brief history of IGMAS+

The software has been around for about 40 years, initially developed on a mainframe and then transferred to the first DOS PCs, before it was adapted to Linux in the ’90s and finally implemented as a cross-platform Java application with GUI called IGMAS+.

Starting from 2009, a consortium of national and international oil companies and the Norwegian Geological Survey (NGU) supported the software development. The Gravity research Group at the University of Kiel was coordinating the project and giving scientific input while the software company Transinsight (Dresden) delivered the professional programming resources and support.

Java was chosen to be the programming platform to allow platform independency. The software has proven to be very fast, accurate and easy to use once a model has been established. Later, the DGMK (German Society for Petroleum and Coal Science and Technology) funded its research project number 771 entitled “TiPOT3D - Towards an integrative interpretation of potential fields and corresponding gradients by the aid of three-dimensional modelling and visualization” (S. Schmidt et al., 2018) and supported the software development on behalf of DEA, Deutsche Erdoel AG (Hamburg), EMPG (Hannover), ENGIE E&P Deutschland (Lingen) and Wintershall Holding GmbH (Kassel).

Since 2019 IGMAS+ has been maintained and developed in The Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences by the staff of Section 4.5 – Basin Modelling and ID2 – eScience Centre.

 
 
 
 
 
Dissertation at the TU Clausthal
Naturwissenschaftliche Fakultät der Technische Universität Clausthal
1976 – 1976 Clausthal-Zellerfeld
Analystical solution of the volume integral for polyhedra (Götze, 1976).
 
 
 
 
 
IGAS/IGMAS at the TU Clausthal and the University of Bonn
1982 – 1987 Clausthal-Zellerfeld / Bonn
Until 1976 the analytical solution of the volume integral of homogenous polyhedra for the gravity field was derived and implemented on a Telefunken mainframe (TR4, later TR440) in the ALGOL language. Later the code was rewritten to FORTRAN 4 and then to FORTRAN 77. With the derivation of the magnetic field components of a homogeneous polyhedron the “M” was added to IGAS (Interactive Gravity Application System): IGMAS stood from then on for “Interactive Gravity and Magnetic Application System”. In 1988 the formulas were published in GEOPHYSICS (Götze and Lahmeyer, 1988) and shortly afterwards the calculations could be performed on a PC.
 
 
 
 
 
IGMAS+ at the FU Berlin
Freie Universität Berlin / Collaborative Research Center 267 (SFB 267)
1987 – 2004 Berlin
In the time around 2000 the original FORTRAN 77 code of IGMAS was extended by implementations of C++ routines and from then on, the name changed from IGMAS to IGMAS+. This was preceded (1995) by a complete revision of the numerical formulas for the calculation of the gravitational and magnetic fields of polyhedra as well as the gradients in gravimetry and magnetics. Due to the activities of the Collaborative Research Center 267 in the Central Andes, IGMAS was mainly used for interdisciplinary modelling at lithospheric scales but also in several oil industry projects.
 
 
 
 
 
IGMAS+ supported by Wintershall
2007 – 2011 Kiel / Kassel
Financial support in the frame of the research project TIMBA (Towards the integration of multidisciplinary geophysical data in a shelf area - the Büsum-Nord area as an example). During this time the software was extended, and two new tools were added, which enhanced the GIS functionality of IGMAS+ and enabled the modelling of aero gravimetric data.
 
 
 
 
 
IGMAS+ at Transinsight / CAU Kiel
2009 – 2014 Dresden / Kiel
Implementation as a cross-platform Java application with GUI called IGMAS+. A consortium of national and international oil companies first and foremost STATOIL/EQUINOR (Trondheim/Stavanger) and the Norwegian Geological Survey (NGU) supported the software development. The Gravity Research Group at the University of Kiel was coordinating the project and giving scientific input while the software company Transinsight GmbH delivered the professional programming resources and support. Implementation of spherical modelling.
 
 
 
 
 
IGMAS+ supported by DGMK
2014 – 2017 Kiel / Hamburg / Hannover / Lingen / Kassel
Financial support in terms of the research project “TiPOT3D - Towards an integrative interpretation of potential fields and corresponding gradients by the aid of three-dimensional modelling and visualization” (S. Schmidt et al., 2018) on behalf of DEA, Deutsche Erdoel AG (Hamburg), EMPG (Hannover), ENGIE E&P Deutschland (Lingen) and Wintershall Holding GmbH (Kassel).
 
 
 
 
 
IGMAS+ at GFZ Potsdam
2019 – Present Potsdam
Maintained and developed by the staff of Section 4.5 – Basin Modelling and ID2 – eScience Centre.

Background

Science and algorithms behind IGMAS+

In IGMAS+ the analytical solution of the volume integral for the gravity and magnetic effect of a homogeneous body is based on the reduction of the three-folded integral to an integral over the bounding polyhedrons (in IGMAS polyhedrons are built by triangles).

Later, the algorithm has been extended to cover all elements of the gravity and magnetic tensors as well. Optimized storage enables extreme fast inversion of material parameters and changes to the model geometry and this flexibility makes geometry changes easy. Immediately after each change, model geometry is updated and the field components are recalculated. Hence, this highly interactive modelling technique makes IGMAS+ very user-friendly. Whilst operating ideally in real-time topology is conserved.

Because of the triangular model structure, IGMAS+ can handle complex structures (multi Z surfaces) like the overhangs of salt domes very well. It handles remanent and induced magnetisation of geological bodies and was applied to the interpretation of borehole gravity and magnetics.

Reduction of the three-folded integral to a surface integral over the bounding polyhedrons (H.-J. Götze).
Reduction of the three-folded integral to a surface integral over the bounding polyhedrons (H.-J. Götze).

Modelling is constrained by structural input from independent data sources, such as seismic data, and is essential toward true integration of 3D thermal modelling or even Full Waveform Inversion. Geophysical investigations may cover huge areas of several thousand square kilometres but also models of Applied Geophysics at a meter scale. Due to the curvature of the Earth, the use of spherical geometries and calculations is necessary. IGMAS+ can be used for both flat (regional) and spherical models (global) in 3D.

3D flat modelling by voxels and triangulated polyhedrons of a simple salt structure (S. Schmidt).
3D flat modelling by voxels and triangulated polyhedrons of a simple salt structure (S. Schmidt).
3D flat model of the central Western South American margin, modelled gravity, and modelling constraints.
3D flat model of the central Western South American margin, modelled gravity, and modelling constraints.
A regional 3D spherical model of the Central Andes and the Pacific margin visualized with the help of the [NASA WorldWind](https://worldwind.arc.nasa.gov/) (C. Plonka)
A regional 3D spherical model of the Central Andes and the Pacific margin visualized with the help of the NASA WorldWind (C. Plonka)
Local flat 3D gravity modelling of a saltdome in the Gifhorn Trough (Northern Germany) based on historical torsion balance measurements (Goltz, G., 2001: Lokale Schwerefeldbestimmung und -modellierung mit Hilfe der Ableitungen des Schwerepotentials. Dissertation, FU Berlin, Berliner Geowissenschaftliche Abhandlungen, Reihe B, Bd. 39, p. 135.).
Local flat 3D gravity modelling of a saltdome in the Gifhorn Trough (Northern Germany) based on historical torsion balance measurements (Goltz, G., 2001: Lokale Schwerefeldbestimmung und -modellierung mit Hilfe der Ableitungen des Schwerepotentials. Dissertation, FU Berlin, Berliner Geowissenschaftliche Abhandlungen, Reihe B, Bd. 39, p. 135.).

Functionality

Brief summary of recent functionality

  • Algorithm kernel

    • Algorithms: polyhedron formula for triangulation, mass points and FFT for voxel cubes
    • Gravity field components Gx, Gy and Gz
    • Borehole gravity (both vertical and horizontal)
    • Geoid
    • Full tensor gravity gradient
    • Invariants
    • Magnetic field components Bx, By and Bz
    • Remanent and induced rock magnetisation
    • Full tensor of magnetic gradients
  • Model input

    • Import regular or irregular horizon data, reformat these data into multi-z capable triangulated geometries.
    • Voxel cube / Voxet
    • Import or create axes parallel voxel cube, assign physical parameter functions to cells, using densities and/or susceptibilities
    • Convert cell-velocities or cell-porosities into densities (pre- or user defined functions)
    • Hybrid modelling by handling both voxel and polyhedral models at same time
    • Simultaneous use of triangulated and gridded (voxel) data allows direct import of 3-D seismic property models as well as the definition of spatially varying density functions
    • Automated edge detection function for 3-D models
  • Geometry and parameter editor

    • Interactive modification: removal and insertion of vertices interactively, updating of physical model parameters (density, susceptibility)
    • Triangulated geometry: functionality that allows to divide polygons parallel or vertically to model sections to break down the modelled geometry
    • Interactive geometry changes automatically affect the voxel cube
    • Optimisation (inversion) of physical parameters, including grouped voxel cell effects
  • Visualisation

    • Multiple undockable views (cross sections, maps, stereographic 3-D and head-tracking for Graphic walls or caves)
    • Object browser including object property editor for all model elements
    • Geocode and visualize bitmaps of arbitrary shape and position
    • 3-D prints
  • Miscellaneous

    • Multi-core processor support for speedup
    • Multi-language support
    • Cross-platform: Windows, Linux, and MacOS – 32/64-bit
    • Gocad® / Geosoft® compatibility
    • Extensive User Manual

Outlook

Future activities

We hope that with the IGMAS+ software we have taken an important step towards an integrated, interdisciplinary interpretation of complex geological structures on the macro, meso and micro scale.

IGMAS+ related publications comprise various applications from the different fields of interpretation. This publication record shows that IGMAS+ has also been used very successfully in academic qualification work and teaching.

An important field of activity in the future will be the determination of parameters for model sensitivity and -uncertainty, a stronger consideration of petrological boundary conditions and the integration of 3-D thermal modelling into a combined workflow.