Active-source and natural-field EM data differ in their sensitivity to subsurface conductivity structures. Generally, the former offer higher spatial resolution and have a greater sensitivity to near-surface conductivities. The latter are more sensitive to broader structures and, for MT data, offer deeper depth penetration. The applied joint inversion algorithm, based on 2D NFEM and 1D active-source EM codes, combines the strengths of both data sets, resulting in more reliable models. Further, joint inversion allows for the galvanic distortion affecting MT data to be taken into account, and for MobileMT data the electric reference field can be constrained better. Three North American case studies are discussed to demonstrate the benefits of joint inversions: Dighem/ZTEM/MT data acquired for copper porphyry exploration, HeliTEM/ZTEM data for uranium and VTEM/MobilMT data for VMS exploration.

Keywords:
upstream oil & gas, ztem data, witherly, exploration geophysicist 10, static shift, dighem data, unconformity, conductivity structure, structural geology, applied geoscience
Subjects:
Reservoir Characterization, Exploration, development, structural geology, Seismic processing and interpretation
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