Abstract: A method for holographic imaging an object having density and/or magnetization is described, the object being located in an examined medium using potential field data including but not limited to gravity and/or magnetic total field and/or vector and/or tensor data. The potential field sensors may measure the gravity and/or magnetic total field and/or vector and/or tensor data at least one receiving position with respect to the examined medium. At least one component of the measured potential field in at least one receiver location (potential field data) may be used as at least one artificial source of the potential field data. Artificial sources may produce a back-propagating (migration) field. An integrated sensitivity of the potential field data to density and/or magnetization perturbation may be calculated. A spatial weighting of at least one of the back-scattering (migration) fields may form a potential field holographic image.

Abstract: The method and apparatus for determining the conductivity of anisotropic formations surrounding a borehole. The method comprises measuring the gradient of the magnetic field by an electromagnetic logging tool in a borehole in the subsurface formation. The instrument comprises one or several closely positioned parallel receiver coils and one or several closely positioned parallel transmitter coils with the magnetic moment direction of the transmitter coils parallel or different from the magnetic moment direction of the receiver coils. In a preferred embodiment a gradient induction instrument consists of a tri-axial transmitter array and up to 27 pairs of receiver coils, measuring some or all magnetic gradient components: formula (I).

Abstract: A method for measuring the resistivity of geologic formations is described. An electromagnetic field may be generated using at least one stationary long-range transmitter. The frequency of the electromagnetic field may be between and/or including the ULF/ELF range. At least one component of the electromagnetic field may be measured by land, marine, and/or airborne receiver. A conductivity distribution may be determined based on the at least one measured component. The determined conductivity distribution may be correlated with geological formations and/or hydrocarbon deposits.