A method for investigating well integrity, the method including pumping a magnetic fluid into an annulus of the well; magnetizing with a magnet the magnetic fluid while in the annulus of the well; moving a magnetic sensing probe through a casing of the well and recording a magnetic field generated by the magnetic fluid; and processing the recorded magnetic field to determine a distribution of magnetic particles into the magnetic fluid in the annulus.

A method may comprise measuring during a survey operation a gravitational field data using a survey accelerometer and magnetic field data using a survey magnetometer and determining during a drilling operation an azimuth of a wellbore based on the gravitational field data and the magnetic field data obtained during the survey operation. A system may comprise a drilling rig; a pipe string attached to the drilling rig; a bottom hole assembly attached to the pipe string, wherein the bottom hole assembly comprises at least one sensor; a drill bit, wherein the at least one sensor measure a revolutions-per-minute (RPM) of the drill bit; and a computing subsystem.

A method may comprise measuring during a survey operation a gravitational field data using a survey accelerometer and magnetic field data using a survey magnetometer and determining during a drilling operation an azimuth of a wellbore based on the gravitational field data and the magnetic field data obtained during the survey operation. A system may comprise a drilling rig; a pipe string attached to the drilling rig; a bottom hole assembly attached to the pipe string, wherein the bottom hole assembly comprises at least one sensor; a drill bit, wherein the at least one sensor measure a revolutions-per-minute (RPM) of the drill bit; and a computing subsystem.

An imaging device included in an assembly located in a wellbore during drilling operations may include a cylindrical housing that extends along a central axis thereof. The imaging device may include at least one gradient coil configured to produce a unique magnetic field weaker than a main magnetic field. The at least one gradient coil may create a variable field that is increased or decreased by changing a direction of the unique magnetic field with respect to a direction of the main magnetic field to allow a specific part of a rock formation to be scanned by altering and adjusting the main magnetic field. The imaging device may include at least one radio frequency coil configured to transmit radio frequency waves into the rock formation. The imaging device may include at least one magnet disposed in the cylindrical housing that resonates against the unique magnetic field.

A depth positioning method to position a production logging tool (1) and a measurement log in a hydrocarbon well (3) in production obtained by means of the tool, the depth positioning method comprises: generating (S1, S2, S3, S1′, S2′, S3′, S11, S12, S13) a set of magnetic measurements (MAG1, MAG) of a depth portion of the hydrocarbon well from a first passive magnetic sensor along the depth portion of the hydrocarbon well, the set of magnetic measurements comprising magnitude and/or direction measurements of the magnetic field that forms a characteristic magnetic field pattern representative of a surrounding magnetic environment of the hydrocarbon well all along the depth portion; comparing (S4, S4′, S14) the set of magnetic measurements (MAG1, MAG) to another set of magnetic measurements (MAG_R, MAG2), the other set of magnetic measurements being a reference set of magnetic measurements generated either by a same or similar passive magnetic sensor deployed and run in the hydrocarbon well earlier, or by a second passive magnetic sensor spaced from the first passive magnetic sensor from a defined distance (DS) deployed and run in the hydrocarbon well simultaneously; and determining (S4, S4′, S14) the maximum of correlation between the set of magnetic measurements (MAG1, MAG) and the reference set of magnetic measurements (MAG_R, MAG2), the maximum being related to identifiable characteristic magnetic field pattern over a part of the depth portion.

A downhole sensor deployment assembly includes a body attachable to a completion string and one or more arms pivotably coupled to the body. A sensor pad is coupled to each arm and movable from a retracted position, where the sensor pad is stowed adjacent the completion string, and an actuated position, where the sensor pad is extended radially away from the completion string. One or more actuators are pivotably coupled to the body at a first end and pivotably coupled to a corresponding one of the one or more arms at a second end, the one or more actuators being operable to move the sensor pad to the actuated position. One or more sensor devices are coupled to the sensor pad for determining a resistivity of a formation, the one or more sensor devices comprising at least one of a sensing electrode, a transceiver, and a transmitter.

A downhole sensor deployment assembly includes a body attachable to a completion string and one or more arms pivotably coupled to the body. A sensor pad is coupled to each arm and movable from a retracted position, where the sensor pad is stowed adjacent the completion string, and an actuated position, where the sensor pad is extended radially away from the completion string. One or more actuators are pivotably coupled to the body at a first end and pivotably coupled to a corresponding one of the one or more arms at a second end, the one or more actuators being operable to move the sensor pad to the actuated position. One or more sensor devices are coupled to the sensor pad for determining a resistivity of a formation, the one or more sensor devices comprising at least one of a sensing electrode, a transceiver, and a transmitter.

Slotted dipole antennas for use in an antenna system on a drill collar segment is presented. Dipoles may be placed in slots on the drill collar segment. A dipole consists of a ferrite rod with electric wires placed above and below the ferrite rod. Wires may be connected such that wire current forms a loop around the ferrite rod. When a group of slots are used for an antenna, wire holes are constructed between slots. Effectively a single wire may be used to go above all ferrite rods in the group and then turn to go below all the ferrite rods. Two wire segments are in a wire hole connecting two adjacent slots. Currents in the two segments are the same in magnitudes and flow in opposite directions. There is no net current in wires in a wire hole.

Slotted dipole antennas for use in an antenna system on a drill collar segment is presented. Dipoles may be placed in slots on the drill collar segment. A dipole consists of a ferrite rod with electric wires placed above and below the ferrite rod. Wires may be connected such that wire current forms a loop around the ferrite rod. When a group of slots are used for an antenna, wire holes are constructed between slots. Effectively a single wire may be used to go above all ferrite rods in the group and then turn to go below all the ferrite rods. Two wire segments are in a wire hole connecting two adjacent slots. Currents in the two segments are the same in magnitudes and flow in opposite directions. There is no net current in wires in a wire hole.

A magneto-quasistatic field may be used to align hydrogen of materials within a structure and/or to disrupt the alignment of hydrogen of materials within the structure. Realignment of the hydrogen after the disruption may cause emission of energy from the hydrogen. The characteristic(s) of the energy may be detected and used to generate image(s) of interior portion(s) of the structure.