Various implementations directed to a system and method for using a magnetometer in a gyro-while-drilling (GWD) survey tool are provided. In one implementation, a method may include acquiring gyroscopic data using gyroscopic sensors of a GWD survey tool while the tool is disposed at a first position within a wellbore. The method may also include acquiring first magnetic data using a magnetometer of the GWD survey tool while the tool is disposed at the first position. The method may further include determining an offset value for the magnetometer based on the gyroscopic data and the first magnetic data. The method may additionally include acquiring second magnetic data using the magnetometer while the tool is disposed at second positions within the wellbore. The method may also include determining magnetic azimuth values for the tool disposed at the second positions based on the second magnetic data and the offset value.

Various implementations directed to a system and method for using a magnetometer in a gyro-while-drilling (GWD) survey tool are provided. In one implementation, a method may include acquiring gyroscopic data using gyroscopic sensors of a GWD survey tool while the tool is disposed at a first position within a wellbore. The method may also include acquiring first magnetic data using a magnetometer of the GWD survey tool while the tool is disposed at the first position. The method may further include determining an offset value for the magnetometer based on the gyroscopic data and the first magnetic data. The method may additionally include acquiring second magnetic data using the magnetometer while the tool is disposed at second positions within the wellbore. The method may also include determining magnetic azimuth values for the tool disposed at the second positions based on the second magnetic data and the offset value.

Various embodiments include apparatus and methods to determine true formation resistivity. Such apparatus and methods may use techniques to effectively reduce or eliminate polarization horn effects at boundaries between formations of different resistivity. The techniques may use combinations of geosignals and adjustments of measurement data to evaluate true formation resistivity for formation layers investigated. Such techniques and associated analysis may be conducted real time. Additional apparatus, systems, and methods are disclosed.

Various embodiments include apparatus and methods to determine true formation resistivity. Such apparatus and methods may use techniques to effectively reduce or eliminate polarization horn effects at boundaries between formations of different resistivity. The techniques may use combinations of geosignals and adjustments of measurement data to evaluate true formation resistivity for formation layers investigated. Such techniques and associated analysis may be conducted real time. Additional apparatus, systems, and methods are disclosed.

A marine magnetism detection device and a detection method are provided. The device includes a surveying ship, an onboard laboratory magnetism measurement portion arranged on the surveying ship, an aerostat shell and an aerostat magnetism measurement portion arranged inside the aerostat shell. The aerostat shell is connected to the surveying ship via a rope, and the aerostat shell floats in air. The aerostat magnetism measurement portion includes a magnetic sensor, an electronic magnetism data acquisition unit and an aerostat transmission unit; and the onboard laboratory magnetism measurement portion includes a data recording computer and a laboratory transmission unit. The marine magnetism detection device and method of the present invention are advantageously not limited by the working sea area and can also operate with other onboard devices and dragging devices.

A marine magnetism detection device and a detection method are provided. The device includes a surveying ship, an onboard laboratory magnetism measurement portion arranged on the surveying ship, an aerostat shell and an aerostat magnetism measurement portion arranged inside the aerostat shell. The aerostat shell is connected to the surveying ship via a rope, and the aerostat shell floats in air. The aerostat magnetism measurement portion includes a magnetic sensor, an electronic magnetism data acquisition unit and an aerostat transmission unit; and the onboard laboratory magnetism measurement portion includes a data recording computer and a laboratory transmission unit. The marine magnetism detection device and method of the present invention are advantageously not limited by the working sea area and can also operate with other onboard devices and dragging devices.

A position determination device comprises data input circuitry configured to obtain magnetic field sensor data sensed by a magnetic field sensor, separation circuitry configured to separate the obtained magnetic sensor data into low frequency sensor data including frequencies below a frequency threshold and high frequency sensor data including frequencies above the frequency threshold, fingerprint combining circuitry configured to determine a combined magnetic fingerprint based on the low frequency sensor data and the high frequency sensor data, and position determination circuitry configured to determine the sensor position of the magnetic field sensor by comparing the combined magnetic fingerprint with a magnetic map.

A system and method for airborne geophysical exploration over the ground are disclosed. In one embodiment of the system, two towing bodies are towed behind an aircraft in flight in a vertically spaced-apart relation above a ground station. Respective magnetometer measurement instruments are located within each of the towing bodies and the ground station. Each magnetometer measurement instrument collects total field magnitude data to contribute to the magnetic vertical gradient data relative to magnetic crustal anomalies of geological origin and variations in an ambient magnetic field above the surface area of the survey. Each magnetometer measurement instrument also collects location, time, and inertial data substantially simultaneously with the total field magnitude data to provide position-correlated measurements thereof.

A system and method for airborne geophysical exploration over the ground are disclosed. In one embodiment of the system, two towing bodies are towed behind an aircraft in flight in a vertically spaced-apart relation above a ground station. Respective magnetometer measurement instruments are located within each of the towing bodies and the ground station. Each magnetometer measurement instrument collects total field magnitude data to contribute to the magnetic vertical gradient data relative to magnetic crustal anomalies of geological origin and variations in an ambient magnetic field above the surface area of the survey. Each magnetometer measurement instrument also collects location, time, and inertial data substantially simultaneously with the total field magnitude data to provide position-correlated measurements thereof.

Remanent ground response is induced by rapid high current in a transmit coil. The transmit coil remains at zero current for a sufficient time for the remanent ground response to be sensed in a receive coil. A rapid high voltage and a sustained low voltage establish and maintain a stable current in the transmit coil followed by a zero current period. The sequence is repeated with a stable negative and followed by positive currents and a zero current. The receive coil is repeatedly interrogated at zero current between switch closings connecting in the transmit coil. Combined ground remanence and target eddy current signals are received during the constant current periods, and the ground remanence signals sensed during zero transmit coil current are subtracted from the combined signals.