Integrative Interpretation of Potential Field Data by 3D-Modeling and Visualization

Any integrative interpretation by the aid of independent geophysical disciplines benefits from modern computational techniques. Today 3D-seismic surveying and imaging of gradients of potential field (mostly aero- and/or satellite observations) are combined with on-/offshore electromagnetic surveys. In this article new algorithms and software tools for 3D-potential field and gradients of remanent and induced magnetization of complicated underground structures, the local stress field, and the distribution of stress beneath salt domes on the base of constrained 3D-models are described. E.g. the presence of salt domes causes a significant perturbation of in-situ stress, which may cause serious implications for the stability of boreholes drilled in the vicinity of salt structures. Geological structures will be approximated by extremely flexible homogeneous polyhedrons (with respect to the domain's density and/or susceptibility) and their fields and gradients are calculated by the transformation of volume integrals into a sum of line integrals. Alternatively, the approximating polyhedrons consist of variable density distributions which are recalculated from studies of seismic velocities. Magnetic modeling is possible by either applying Poisson's Theorem or a modification of the derived formulas for gravity modeling. The inversion of potential fields is performed by the CMA-ES, the covariance-matrix-adoption evolution strategy. A new robust method was introduced for the reduction of edge effects of potential field data. Although the main structure of the new software already existed for 3D-gravity modeling, it had to be extended by a tool for magnetic modeling, a borehole gravity/susceptibility modeling tool and an immersive visualization of even complicated geological underground structures by 3D-printing. Examples from the Gifhorn Trough and KTB are presented here to illustrate the user-friendly newly developed software tools.