Patent ID: 8854045

Claim:
Apparatus for measuring electrical conductivity of a rock formation surrounding a wellbore, comprising: a housing adapted for operation of electronic apparatus in a wellbore; means for generating a linear frequency modulated multi-frequency sine wave at variable frequencies enveloped within pulse compressed time intervals and pulse widths; a differentially driven transmitter coil disposed at a selected location on the housing connected for receiving and transmitting the signals from the first electronic circuits; a plurality of mutually balanced fully differential receiver coils disposed at selected locations on the housing, each coil connected to second digitally-controlled electronic circuits for amplifying and filtering signals from the receiver coils; a phase-sensitive detector and low pass filter for receiving signals from the second electronic circuits and the first electronic circuits and producing in-phase and quadrature out-of-phase signals as an analog signal; an analog-to-digital converter to process the analog signal and produce a digital signal for transmission; and a programmable controller having a computer-readable medium programmed for controlling electronic apparatus in the housing.