The invention relates to a self-going pipe tractor for use internally in channels, particularly oil wells.

Often, it is a need to perform inspection, maintenance and other work within pipes and channels where it is impossible to reach for people. In connection with inspection, maintenance and operation of an oil well, log equipment and devices such as plugs and valves are lowered down into the oil well.

Gradually, it has been common to drill oil wells having long horizontal or approximately horizontal courses, so that it is no longer possible to lower down necessary equipment in the entire length of the well by means of gravity alone.

It is known to use pole pipes in order to carry equipment through horizontal or approximately horizontal courses, and this is a commonly used method. Various hydraulic methods for pumping the equipment forward have also been tried.

The use of pole pipes has several disadvantages. Firstly, several kilometres of continuous pipe are required, usually in the form of a large coil or stored on a drum, requiring substantial space. Secondly, special equipment is required in order to handle pipe coil or drum during operation. Pumping is only possible when circulation can be established. Normally, this is not the case; however, upon installation

of special circulation pipes, circulation may be provided in some relations.

The object of the invention is to provide a pipe tractor which by means of its own propulsion can convey tools and equipment internally in channels.

In accordance with the invention, the object is achieved through features as defined in the following claims.

In the following, two embodiment examples of the invention are described, reference being made to the attached diagrammatical drawings, wherein:

Figure 1 shows, in side elevational view and partly in section, a pipe wherein a pipe tractor has been placed;

Figure 2 shows substantially the same as figure 1, but seen from one end;

Figure 3 shows, on a larger scale, parts of a well tractor together with motor and transmission, as seen in a side elevational view, partly in section;

Figure 4 shows, in a simplified view, a drive arrangement fo the well tractor's one end piece, as seen from one end;

Figure 5 shows, in a simplified view, a drive arrangement fo the well tractor's other end piece, as seen from the other end;

Figure 6 shows, on a larger scale, a portion of a well tractor having two motors and transmissions, as seen in a side elevational view, partly in section.

In figure 1, reference numeral 1 denotes a pipe wherein is placed a pipe tractor 2, which has an intermediate section 3 and two counterrotary end pieces 4 and 5. To each end piece

4, 5, a number of resilient arms 6 are attached, to which inclined wheels 7 have been attached, said wheels 7 being urged against the internal face of the pipe 1. A cable 8 carries electric power og control signals to the pipe tracto 2 through a tubular, centrically positioned shaft 9. Due to the inclination of the wheels 7, the pipe tractor 2 will run along the pipe when the end pieces are rotated, using mutually opposite rotational directions. Upon alteration of rotational direction of the end pieces 4, 5, the pipe tracto 2 may be brought to run along the pipe in an optional direction. When running within pipes 1 having a uniform internal cross-section, the end pieces 4, 5 will rotate with the same speed, but in opposite directions. When passing through cross-sectional changes within the pipe 1, the arms will resile more or less outwardly. In order to achieve equa transport speed on all wheels 7, the rotational speed of the end pieces , 5 may be controlled at the same pace as the resilient movements of the arms 6 by means of a variator, no shown. Equal transport speed on all wheels 7 is necessary in order to prevent rotation of the intermediate section 3.

In figure 3 , the pipe tractor 2 has been shown sectioned in side elevational view, arms 6 and wheels 7 being omitted. Th end pieces 4 and 5 are mounted on the shaft 9 by means of bearings 10 and axially secured to the shaft 9 by means of locking rings, not shown. Attachment brackets 11, 12, 13 are rigidly connected to the shaft 9 and adapted to carry an electric motor 14, a transmission shaft 15 and a drive shaft 16, as well as a cover 17. The cable 8 carries current and control signals to the motor 14 which, through a first belt pulley 18, a belt 19 and a second belt pulley 20, is adapted to drive the transmission shaft 15. Power from the transmission shaft 15 is transferred to a first gear wheel 21 meshing with a first toothed rim 22 attached within the rotary end piece 5. Also, power is transferred through a gearing 23, 24 to the drive shaft 16 and further to a second gear wheel 25 meshing with a second toothed rim 26 attached to the rotary end piece 4. The gearing 23, 24 serves to

reverse the rotational direction of the gear wheel 25 in relation to the gear wheel 21. The gear wheels of the gearing 23, 24 are of equal size and give, therefore, no change of speed. When the motor 14 rotates, the end piece 5 rotates in the same rotational direction as the motor 14, the end piece 4 rotating in the opposite rotational direction. The positioning of the components of the transmission in relation to the shaft 9 is shown as seen from the end piece 4 in figure 4 and as seen from the end piece 5 in figure 5.

Figure 6 shows an alternative transmission having two electric motors 27, 28, each carrying a gear wheel 29, 30, each driving a toothed rim 22, 26. With separate speed control of the motors 27 and 28, the number of revolutions per minute of the end pieces 4, 5 may individually adjust itself to the internal pipe circumference against which the respective wheels 7 rest, see figure 1. The pipe tractor 2 may be imagined used for operations wherein the intermediate section 3 with the cover 17 advantageously may rotate while the pipe tractor 2 is running. Such rotation of the intermediate section 3 can be achieved by giving the end piece 4 and the end piece 5 different transport speeds, e.g. by giving the motors 27, 28 different numbers of revolutions per minute, and the intermediate section 3 will then rotate with a speed proportional with the difference. If the intermediate section is to rotate many revolutions in one direction, electric power and control signals should be transferred from the cable 8 to the intermediate section 3 and the motors 27, 28 through sliding contacts. Running the motors 27, 28 in the same direction will keep the pipe tractor 2 in peace, simultaneously as the intermediate section 3 rotates.

The intermediate section 3 may contain control systems for the motors 27, 28 and additionally be adapted to carry sensors and inspection equipment as well as other equipment for use within a pipe 1.

The invention is not restricted to the embodiments shown. It goes without saying that the pipe tractor 2 e.g. may be operated by means of hydraulic motors. The travelling speed of the pipe tractor 2 depends on the internal cross-section of the pipe 1, the rotational speed of the end pieces 4, 5 and the inclination of the wheels 7; and the same travelling speed may be achieved by means of an infinite number of combinations of said quantities. The tractive power of the pipe tractor 2 depends on the accumulated friction forces between the pipe 1 and the wheels 7. The tractive power may be increased if the number of wheels 7 is increased.