The present invention relates to drilling pipes for making a drill string, in particular adapted to deviation drilling, i.e. drilling performed in such a manner that the drilling direction at the beginning is substantially vertical, while the direction is later changed towards one side, so that the direction of drilling finally is under a larger or smaller angle with the vertical direction, up to 90°•

Such drilling allows drilling into several mutually separate sources from one point , and is used for offshore drilling.

Deviation drilling causes, however, and in particular when the deviation angle from the vertical direction is large, problems with respect to transporting of the cuttings. Moreover, the friction against the bore hole becomes large, and the weight on the drill bit may be insufficient. General¬ ly the weight of a conventional drill string will be a probl¬ em when the more or less horizontal portion of the bore hole has a large length.

The problem of transporting the cuttings will increase with the deviation angle and the length of the hole. A large devi¬ ation angle means that the cuttings have a short v/ay to " all" until they reach the "bottom" of the hole.

The weight of the drill string will generally be proportio¬ nal to the frictional forces and frictional torques which occur between the drill string and the wall of the hole. In long holes having a large deviation angle said forces and torques will be of importance, and they will determine the • possible length of drilling until the -friction becomes too large.

The object of the present invention is to provide a drilling pipe which makes it possible to reduce the frictional forces and the frictional torques and which simultaneously keeps the pressure losses and the operational and handling conditions within acceptable limits.

According to the invention the above is achieved with a drilling pipe as specified in the accompanying claims.

The tube itself may for instance be made by being drawn around a forming tool having the desired pitch and geometry. Another alternative is to use a roll forming tool.

Because of the helical shape the tube itself will have a small contact surface against the wall of the bore hole, so that the friction and the adhesion against the wall of the bore hole will be small compared with the use of tubes which initially are straight.

In the following the invention will be explained by means of an example of embodiment shown in the accompanying drawing.

The drawing shows a drilling pipe according to the invention, said drilling tube comprising a helically shaped tube 1 and two heads 2 and 3 _» one on each end of the tube 1. Through each head is an aperture which communicates with the tube 1.

The joining of the tube 1 and the heads may be performed in any suitable manner, for instance by use of a threaded connection or by welding.

Both the tube 1 and the heads 2 and 3 may be made of aluminium, but also other materials, for instance steel, may be used.

It is not a presupposition that the tube 1 has helical shape along its entire length. On account of the joining to the heads 2 and 3 it is, to the contrary, appropriate that the tube 1 has a straight portion at each end which is parallel to the main axis of the tube, in the manner shown in the drawing.