An arrangement for generating a resistivity image having a drill bit with cutters configured to be placed within a wellbore, the cutters configured to create further sections of the wellbore upon rotation, the drill bit having an end with threads for engagement, at least one section of drill string connected to the drill bit through a matching set of threads for engagement, a receiver toroid connected to the at least one section of drill string along at least a portion of the drill string, a transmitter toroid connected to the at least one section of drill string and located at least a portion of the drill string away from the receiver toroid, at least one stabilizer connected to the at least one section of drill string, a power source connected to the transmitter toroid and the receiver toroid, an electrode arrangement placed at the drill bit, wherein the electrode arrangement is electrically connected to the drill bit through a non-linear circuit element and a computer arrangement connected to the receiver toroid.

An arrangement for generating a resistivity image having a drill bit with cutters configured to be placed within a wellbore, the cutters configured to create further sections of the wellbore upon rotation, the drill bit having an end with threads for engagement, at least one section of drill string connected to the drill bit through a matching set of threads for engagement, a receiver toroid connected to the at least one section of drill string along at least a portion of the drill string, a transmitter toroid connected to the at least one section of drill string and located at least a portion of the drill string away from the receiver toroid, at least one stabilizer connected to the at least one section of drill string, a power source connected to the transmitter toroid and the receiver toroid, an electrode arrangement placed at the drill bit, wherein the electrode arrangement is electrically connected to the drill bit through a non-linear circuit element and a computer arrangement connected to the receiver toroid.

Various embodiments include methods and apparatus structured to balance electrode pairs (112, 312) of a tool (105, 305) providing voltage equivalence between the electrode pairs. An electrically conductive wire (113, 313) coupling the electrodes of an electrode pair can be arranged such that resistance of the electrically conductive wire does not adversely affect the voltage equivalence. The electrically conductive wire can also be structured to provide temperature independent balancing by arranging the electrically conductive wire with respect to a measuring node (116, 316). Additional apparatus, systems, and methods are disclosed.

Various embodiments include methods and apparatus structured to balance electrode pairs (112, 312) of a tool (105, 305) providing voltage equivalence between the electrode pairs. An electrically conductive wire (113, 313) coupling the electrodes of an electrode pair can be arranged such that resistance of the electrically conductive wire does not adversely affect the voltage equivalence. The electrically conductive wire can also be structured to provide temperature independent balancing by arranging the electrically conductive wire with respect to a measuring node (116, 316). Additional apparatus, systems, and methods are disclosed.

An apparatus for detecting an electromagnetic signal originating in a wellbore includes an antenna comprising a pair of spaced apart electrodes in the ground spaced apart by a first distance having a midpoint at a second distance from the wellbore. The system includes at least one of a shielded electrical cable connecting each electrode to an input of a detector circuit, wherein the shielding is connected to produce common mode noise rejection; b) a second spaced apart electrode pair antenna spaced apart by one half the first distance and having a midpoint spaced √2/2 times the second distance from the surface of the wellbore, c) a second electrode pair antenna having a common midpoint with and being orthogonal to the at least one electric dipole antenna; and d) wherein the at least one electric dipole antenna is disposed in a second wellbore, the second wellbore having substantially no electrically conductive pipe therein.

An apparatus for detecting an electromagnetic signal originating in a wellbore includes an antenna comprising a pair of spaced apart electrodes in the ground spaced apart by a first distance having a midpoint at a second distance from the wellbore. The system includes at least one of a shielded electrical cable connecting each electrode to an input of a detector circuit, wherein the shielding is connected to produce common mode noise rejection; b) a second spaced apart electrode pair antenna spaced apart by one half the first distance and having a midpoint spaced √2/2 times the second distance from the surface of the wellbore, c) a second electrode pair antenna having a common midpoint with and being orthogonal to the at least one electric dipole antenna; and d) wherein the at least one electric dipole antenna is disposed in a second wellbore, the second wellbore having substantially no electrically conductive pipe therein.

A measurement device can be provided for a tubular string of a drilling subsystem. The measurement device can include a transmitter and a receiver. A cover can be applied to at least one of the receiver or the transmitter. While at least one of the receiver or the transmitter is covered by the cover, an amount of crosstalk can be measured. The cover can be removed from the measurement device. Subsequent to removing the cover from the measurement device, an air-hang response of the receiver and the transmitter can be measured in an air-hang configuration of the tubular string. A corrected air-hang response of the measurement device can be determined by subtracting the amount of crosstalk from the air-hang response.

A system and method for estimating porosity distribution in a region of interest of a geologic formation from a resistivity image log representative of the geologic formation is disclosed. A normalization factor representative of a rock matrix based on a first resistivity value and an image point factor based on a second resistivity value are calculated and compared to identify points in the resistivity image log that correspond to the secondary porosity. The normalization factor and image point factor are recalculated based on a different first resistivity value and a different second resistivity value as necessary to identify additional points in the resistivity image log that correspond to the secondary porosity until a termination criterion is met. The method may further include a porosity calibration operation and one or more artifact corrections.

Methods, systems, devices, and products for making formation resistivity measurements including reducing the resistivity of the fluid proximate the electrode using ionizing radiation to induce a transient increase in electrical conductivity of the fluid for the resistivity measurement. The fluid may include oil-based mud. Methods include making the downhole measurement using the electrode during the transient increase. An electrode may be disposed on a pad having a bremsstrahlung assembly disposed thereon. Methods may include mitigating effects of an electrical resistivity of the fluid on the formation resistivity measurement by using the radiation to induce a transient increase in electrical conductivity of the fluid for the formation resistivity measurement. Methods may include using the ionizing radiation to generate at least one of: i) free ions; and ii) free electrons.

Methods, systems, devices, and products for making formation resistivity measurements including reducing the resistivity of the fluid proximate the electrode using ionizing radiation to induce a transient increase in electrical conductivity of the fluid for the resistivity measurement. The fluid may include oil-based mud. Methods include making the downhole measurement using the electrode during the transient increase. An electrode may be disposed on a pad having a bremsstrahlung assembly disposed thereon. Methods may include mitigating effects of an electrical resistivity of the fluid on the formation resistivity measurement by using the radiation to induce a transient increase in electrical conductivity of the fluid for the formation resistivity measurement. Methods may include using the ionizing radiation to generate at least one of: i) free ions; and ii) free electrons.