A method for designing a controlled-source electromagnetic survey, in thefield ofsurveying for and producing hydrocarbons, that will discriminate between adefined deepmarginal-interest reservoir and specified false positive resistivitystructures of concern. Areservoir model and a false positive model are constructed for each falsepositive scenario.The resistivity of the false positive model may be tuned to giveelectromagnetic data similarenough to the reservoir model when forward modeled that any differences fallin the modelnull space. A null-space discriminating ratio ('NSDR') is defined, for exampleas the peaknormalized difference of the two related modeled electromagnetic field datasets. An areacoverage display of NSDR values allows determination of such additional dataas may beneeded to distinguish the false positive body, and a survey design isdeveloped accordingly.Reduction of the number of variables affecting the area coverage displays isachieved.
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