Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
IGMAS+: A new 3D gravity, FTG and magnetic
modelling software tool
Summary
Hans-Jürgen Götze 1 and Sabine Schmidt 2
1 Christian-Albrechts-Universität Kiel (hajo@geophysik.uni-kiel.de)
2 Christian-Albrechts-Universität Kiel (sabine@geophysik.uni-kiel.de)
Modern geophysical interpretation requires an interdisciplinary approach and software capable of
handling multiple geophysical data types such as seismic, full tensor gravity gradiometry (FTG),
magnetics, and magnetotellurics. We introduce the IGMAS+ ("Interactive Geophysical Modelling
Application System") geo-modelling software that can be used for 3D FTG and magnetic modelling.
The software can be used in grid computer environments and allows fast distributed calculations to be
performed on standard hardware such as PC networks.
Introduction
3D gravity and magnetic modelling can significantly improve geophysical imaging of subsurface
structures in areas where lateral density and magnetisation contrasts are strong. Typical areas where
gravity and magnetic modelling have been successfully used include studies of sub-salt structures
(e.g., O’Brian et al. 2005; Fichler et al., 2007) and sub-basalt environments (e.g., Reynisson et al.,
2007; Reynisson et al., 2009).
Lahmeyer et al. (2010) noted that seismic depth imaging had become much faster in the past few
years. A 3D pre-stack migration can often be carried out in less than an hour. It is possible to perform
several iterations to improve the velocity models, and the whole process has become far more
interactive and interpretative. Seismic interpreters work closely together with structural geologists to
rapidly achieve better seismic images using the available information as constraints. The workflow and
tools for gravity and magnetic modelling need to adapt to this situation. For example, it would be ideal
if the gravity effects of velocity models could be calculated using various density-velocity relationships
and compared with measured gravity, all within the software environment of the tool used for seismic
imaging. The density model could then be optimized using the available constraints to minimise the
gravity misfit, converted to a velocity model, and used as the input for the next iteration in depth
migration.
IGMAS+
Three-dimensional interactive geological and geophysical modelling using IGMAS+ provides a means
to improve geological interpretation through integrated processing and interpretation of geoid, gravity,
magnetic, FTG, and invariant data. The software is based on twenty years of research and
development experience (www.gravity.uni-kiel.de/igmas) and has been subject to continuous
improvement to meet the changing requirements of modern software architecture such as the changes
to graphical user interfaces and the availability of grid computing environments
(www.potentialGS.com). The IGMAS+ gravity and magnetic calculations utilise an analytical solution
of the volume integral for gravity and magnetic response of a homogeneous body that is based on a
transformation of the volume integral of a polyhedral structure to a surface integral (Götze, 1984;
Götze and Lahmeyer, 1988). The algorithm has been extended to cover gravity gradient tensor
components (H.-J. Götze, personal communication, 2010).
In 2006, a consortium was set up with the goal to improve IGMAS in several stages (Alvers et al.,
2010). The consortium is currently sponsored by Statoil, Wintershall and NGU. The gravity research
group of the University of Kiel is coordinating the project and provides scientific input. The software
company Transinsight (Dresden/Germany) delivers part of the professional programming resources
and support. Java was chosen to be the programming platform to facilitate platform independence. In
order to achieve realistic geological structures, the 3D models from IGMAS+ are constructed using
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