1. Field of the Invention
The invention relates generally to the field of well logging instrument conveyance devices. More specifically, the invention relates to devices used to move a well logging instrument through the interior of a pipe string so that the well logging instrument can be deployed in a wellbore.
2. Background Art
Well logging instruments are used, among other purposes, to make measurements of physical properties of Earth formations that have been penetrated by a wellbore. Well logging instruments typically include one or more types of sensors to make the measurements of the physical properties. Signals from the sensors may be communicated to the Earth's surface by various forms of signal telemetry, and/or may be stored in various types of recording device disposed within the well logging instrument.
As the well logging instrument is moved along the wellbore, a record of the signals generated by the sensors is made with respect to time and/or depth of the sensors within the wellbore. There are a number of different devices known in the art for moving the well logging instrument along the wellbore. The instrument may be affixed to the end of an armored electrical cable, which is unwound from w winch or similar spooling device to extend the instrument into the wellbore by the action of Earth's gravity. The instrument is withdrawn by rewinding the cable onto the winch. The well logging instrument may be moved along the wellbore by coupling it to the end of a coiled tubing, and unspooling and spooling the coiled tubing to move the instrument into and out of the wellbore. The instrument may also be coupled to the end of a threadedly coupled pipe, called a pipe “string.” The pipe string with the instrument attached to the lower end thereof is extended into the wellbore by threadedly coupling segments of pipe end to end. The pipe string is withdrawn from the wellbore by threadedly uncoupling segments of pipe.
U.S. Patent Application Publication No. 2004/0074639 filed by Runia discloses another device for moving the well logging instrument along the wellbore. The system comprises a tubular conduit or pipe extending from the Earth's surface into the wellbore containing a body of wellbore fluid. A well logging instrument string is included that is capable of passing from a position within the conduit to a position outside the conduit at a lower end part thereof and capable of being suspended by the conduit in said position outside the conduit. In some embodiments the well logging instrument may include a pressure pulse device arranged within the conduit in a manner that the pressure pulse device is in data communication with the logging tool. The pressure pulse device is capable of generating pressure pulses in the body of wellbore fluid, the pressure pulses representing data communicated by the logging tool string to the pressure pulse device during logging of Earth formation by the logging tool string.
In using the device disclosed in the Runia '639 publication it has been found desirable to be able to control the speed of movement of the well logging instrument inside the conduit, particularly when the conduit is disposed in a vertical or nearly vertical wellbore. Conversely, it is necessary to provide some mechanism to move the well logging instrument along the interior of the conduit when the wellbore is highly inclined form vertical such that Earth's gravity is incapable of moving the well logging instrument sufficiently.