A logging tool assembly comprises an elongate sensor assembly, a plurality of sensor transportation apparatuses for transporting the elongate sensor assembly through a wellbore, and an orientation structure. The sensor transportation apparatuses are spaced apart along the elongate sensor assembly. Each sensor transportation apparatus comprises an engagement structure to connect the sensor transportation apparatus to the elongate sensor assembly and prevent relative rotation between the sensor transportation apparatus and the elongate sensor assembly, and one or more pairs of wheels arranged to rotate on an axis of rotation substantially perpendicular to a longitudinal axis of the elongate sensor assembly. The axes of rotation of the pairs of wheels of said transportation apparatuses are parallel. The orientation structure is connected to the elongate sensor assembly to prevent relative rotation between the orientation structure and the elongate sensor assembly. The orientation structure comprises at least one radially extending orientation projection. In a transverse outline of the logging tool assembly a said orientation projection extends between the pair of wheels so that the shortest distance between a centre of gravity of the elongate sensor assembly and the wellbore wall is when the pair of wheels of the transportation apparatus is in contact with the wellbore wall.

A control apparatus controls driving of an oil feeding unit. The oil feeding unit includes a piezoelectric body that deforms in response to a voltage applied thereto, and a reservoir to store lubricating oil. The capacity of the reservoir changes in accordance with deformation of the piezoelectric body so as to discharge lubricating oil from the oil feeding unit. The control apparatus includes N driving circuits 71a to 71n configured to apply voltages to the piezoelectric body (where N is an integer equal to or greater than two). The N driving circuits 71a to 71n are connected in parallel to the piezoelectric body. During oil feeding, the control apparatus uses a predetermined number of the driving circuits selected from the N driving circuits. The predetermined number is smaller than N.

A sensor transportation apparatus to convey an elongate sensor assembly through a wellbore, the sensor transportation apparatus comprises a pair of axles and a pair of wheels corresponding with the pair of axles with each wheel mounted on a respective said axle to rotate about an axis of rotation perpendicular to a longitudinal axis of the elongate sensor assembly. A protection structure extends longitudinally around each wheel to prevent a side of the wheel from contacting a wall of the wellbore. Each wheel extends above and below the protection structure to contact a side of the wellbore.

A sensor transportation apparatus to convey a sensor assembly through a wellbore. The apparatus comprising has an engagement structure to connect the sensor transportation apparatus to the sensor assembly, and one or more wheels arranged to rotate about an axis of rotation substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly. An orientation structure defining a form having a transverse outline which has a rotational center, wherein the rotational center is offset from a centroidal axis of the elongate sensor assembly.

A logging tool assembly comprises an elongate sensor assembly, a plurality of sensor transportation apparatuses for transporting the elongate sensor assembly through a wellbore, and an orientation structure. The sensor transportation apparatuses are spaced apart along the elongate sensor assembly. Each sensor transportation apparatus comprises an engagement structure to connect the sensor transportation apparatus to the elongate sensor assembly and prevent relative rotation between the sensor transportation apparatus and the elongate sensor assembly, and one or more pairs of wheels arranged to rotate on an axis of rotation substantially perpendicular to a longitudinal axis of the elongate sensor assembly. The axes of rotation of the pairs of wheels of said transportation apparatuses are parallel. The orientation structure is connected to the elongate sensor assembly to prevent relative rotation between the orientation structure and the elongate sensor assembly. The orientation structure comprises at least one radially extending orientation projection. In a transverse outline of the logging tool assembly a said orientation projection extends between the pair of wheels so that the shortest distance between a centre of gravity of the elongate sensor assembly and the wellbore wall is when the pair of wheels of the transportation apparatus is in contact with the wellbore wall.

A rolling bearing device includes a first bearing section including a first outer ring, a first inner ring, and a plurality of balls, each of which is made of metal, and a second bearing section including a second outer ring, a second inner ring, and a plurality of balls, each of which is made of metal. The first inner ring and the second inner ring are electrically connected to each other, and the first outer ring and the second outer ring are electrically insulated from each other. The first outer ring is provided with an input contact for an electric signal, and the second outer ring is provided with an output contact for the electric signal.

A sensor transportation apparatus to convey a sensor assembly through a wellbore. The apparatus comprising has an engagement structure to connect the sensor transportation apparatus to the sensor assembly, and one or more wheels arranged to rotate about an axis of rotation substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly. An orientation structure defining a form having a transverse outline which has a rotational centre, wherein the rotational centre is offset from a centroidal axis of the elongate sensor assembly.

A sensor transportation apparatus to convey a sensor assembly through a wellbore. The apparatus comprising has an engagement structure to connect the sensor transportation apparatus to the sensor assembly, and one or more wheels arranged to rotate about an axis of rotation substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly. An orientation structure defining a form having a transverse outline which has a rotational center, wherein the rotational center is offset from a centroidal axis of the elongate sensor assembly.