Sensor transportation apparatus

A sensor transportation apparatus for conveying a sensor assembly through a wellbore, the sensor transportation apparatus comprising:

• at least one engagement structure to connect the sensor transportation apparatus to the sensor assembly,
• at least one axle, at least one wheel, a bearing connected to the axle between the wheel and the engagement structure, a shaft seal to prevent or reduce debris from the wellbore entering the bearing, and
• a lubrication delivery system to provide a lubricant to the bearing at a pressure which is greater than an ambient wellbore pressure, wherein the lubrication system comprises:
• a spring bellows formation, and the apparatus comprising a housing to contain the lubricant, the housing in fluid communication with the bearing, the spring bellows formation sealingly mounted to the housing with at least a portion of the spring bellows formation received within the housing to provide a bias force so that the pressure in the lubricant is greater than the ambient wellbore pressure of a wellbore fluid surrounding the device;
• a flexible member, an outer surface of the flexible member in communication with wellbore fluids surrounding the apparatus in use;
• and
• a liquid contained in a sealed chamber defined, at least in part, by the interior of the spring bellows formation and an inner surface of the flexible member.