Device for directional drilling

1. A drill string section for receiving and directionally controlling a drill bit, comprising:

an outer casing adapted for abutment with a borehole or borecasing, the outer casing having a drive shaft arranged therein, the drive shaft adapted to receive a drill bit, the drive shaft having a drive shaft centre axis and further capable of parallel displacement relative to the outer casing, said outer casing further housing an adjustment mechanism, said adjustment mechanism comprising:

an outer shaft having a first axial centre axis, wherein the outer shaft is arranged to be rotated relative to the outer casing, and wherein the outer shaft is configured with an axial eccentric first bore having a first bore axis that is parallel to the first centre axis; and

an inner shaft having a second axial centre axis, wherein the inner shaft is positioned in the first bore and arranged to be rotated relative to the outer shaft, and wherein the inner shaft is configured with an axial eccentric second bore for passage of the drive shaft for driving the drill bit, wherein the second bore has a second bore axis that is parallel to the second centre axis;

wherein rotation of one or more of the inner or outer shafts alters the relative position of their respective eccentricities, thereby causing the drive shaft to undergo parallel displacement to drill a deviated section of a wellbore, wherein while inducing parallel displacement of the drive shaft, the drive shaft centre axis of the drive shaft, the first axial centre axis and the first bore axis of the outer shaft, and second axial centre axis and second bore axis of the inner shaft are parallel.

2. A drill string section according to claim 1 ,

wherein the outer casing further comprises return channels for return flow of drilling fluids.

3. A drill string section according claim 1 ,

wherein the eccentricity of the first bore is identical to the eccentricity of the second bore.

4. A drill string section according to claim 1 ,

wherein the drive shaft is arranged in the second bore rotatable relative to the inner shaft.

5. A drill string section according to claim 1 ,

wherein the drive shaft comprises a flexible element which permits a radial motion of the drive shaft.

6. A drill string section according to claim 5 , wherein the flexible element is one or more springs.

7. A drill string section according to claim 6 ,

wherein the one or more springs comprise a first radial spring and a second radial spring, the first radial spring arranged around a lower portion of the drive shaft and the second radial spring arranged around an upper portion of the drive shaft.

8. A drill string section according claim 1 ,

wherein the outer casing has a sleeve-like design with an axial extent in the axial direction of the drill string section.

9. A drill string section according to claim 1 ,

wherein the adjustment mechanism comprises

an outer rotational mechanism for reciprocal rotation of the outer casing and the outer shaft, and which is adapted for locking against reciprocal rotary motion between the outer casing and the outer shaft;

an inner rotational mechanism for reciprocal rotation of the outer shaft and the inner shaft, and which is adapted for reciprocal rotary motion between the outer shaft and the inner shaft.

10. A drill string section according to claim 9 , wherein the inner rotational mechanism comprises a first motor and the outer rotational mechanism comprises a second motor.

11. A drill string section according to claim 10 , wherein the first and second motors are electric motors.

12. A drill string section according to claim 10 , wherein the first and second motors are hydraulic motors.

13. A drill string section according to claim 12 , wherein the anti-rotational mechanism includes a spring element adapted to press the anti-rotation element outward in a radial direction.

14. A drill string section according to claim 1 ,

wherein the outer casing comprises an anti-rotational mechanism.

15. A drill string section according to claim 14 , wherein the anti-rotational mechanism comprises an anti-rotational element movably arranged in the radial direction, wherein the anti-rotation element has a T-shaped cross-section and is arranged in a cavity formed in the outer casing such that the anti-rotation element projects from a slit which extends from the cavity and through the radially outer surface of the outer casing.

16. A drill string section according to claim 14 , wherein the anti-rotational mechanism comprises an anti-rotational element, the anti-rotational element being an arcuate or curved spring element.

17. A drill string section according to claim 14 , comprising two or more anti-rotational mechanisms.

18. A drill string section according to claim 1 , wherein the outer casing includes one or more return channels for return flow of drilling fluids.