Abstract: A resistivity logging tool suitable for downhole use includes a transmitter and two spaced apart receivers. The measured signals are inverted to determine the distance to an overpressured zone in the earth formation. The overpressured zone may be a transition zone in resistivity. The direction of drilling may be controlled based on the determined distance. Optionally, seismic-while drilling measurements may be made from which a separate estimate of the distance can be obtained. The SWD® measurements may also be processed to estimate the pore pressure.

Abstract: Measurements made by a formation evaluation sensor downhole are processed to produce an image and a bitstream characterizing the image is transmitted uphole. The parameters used in the downhole processing are dynamically alterable.

Abstract: A galvanic resistivity tool with one or more measurement electrodes and guard electrodes, and one or more shielding electrodes. The potential difference between the measurement electrodes and the guard electrodes is controlled to minimize current flow between the measurement electrodes and the shielding electrodes. This provides improved focusing and avoids effects of contact impedance.

Abstract: A method and apparatus for downhole resistivity imaging uses an antenna coupled to a power source through a directional coupler. Measured reflectivity values are indicative of the antenna impedance and the formation resistivity, particularly if some compensation is made for the antenna inductance.