Rotary valve for steering a drill string

1. A drill string, comprising:

a rotary valve disposed within a bore of the drill string comprising a first disc attached to a driving mechanism and a second disc axially aligned with and contacting the first disc along a flat surface;

each disc comprises a port adapted to align with each other periodically when the discs rotate relative to one another;

wherein the aligned ports are adapted to direct fluid to at least one nozzle disposed in a working face of a drill bit of the drill string;

wherein a jack element substantially coaxial with an axis of rotation is disposed in the bore of the drill string and comprises a distal end extending beyond the working face of the drill bit.

2. The drill string of claim 1 , wherein the fluid passed through the at least one nozzle is adapted to steer the drill string.

3. The drill string of claim 1 , wherein the driving mechanism is a turbine, a generator, a jack element, or a motor.

4. The drill string of claim 1 , wherein the second disc is fixed to a bore wall of the drill string or to a jack element.

5. The drill string of claim 1 , wherein the jack element and the driving mechanism rotate opposite each other.

6. The drill string of claim 1 , wherein the jack element is adapted to be stationary with respect to a formation and the drill bit is adapted to rotate around the jack element.

7. The drill string of claim 1 , wherein the nozzle is adjacent to the jack element.

8. The drill string of claim 1 , wherein a plurality of fluid ports are formed in the second disc.

9. The drill string of claim 8 , wherein the fluid ports direct fluid to a plurality of nozzles.

10. The drill string of claim 9 , wherein the plurality of nozzles are positioned at different angles with respect to the axis of rotation.

11. The drill string of claim 1 , wherein a portion of the drilling fluid is passed through the fluid ports.

12. The drill string of claim 1 , wherein the flat surface comprises a material selected from the group consisting of chromium, tungsten, tantalum, niobium, titanium, molybdenum, carbide, natural diamond, polycrystalline diamond, vapor deposited diamond, cubic boron nitride, TiN, AlNi, AlTiNi, TiAlN, CrN/CrC/(Mo, W)S2, TiN/TiCN, AlTiN/MoS2, TiAlN, ZrN, diamond impregnated carbide, diamond impregnated matrix, silicon bounded diamond, and/or combinations thereof.

13. The drill string of claim 1 , wherein the rotary valve is disposed within the drill bit.

14. The drill string of claim 1 , wherein the driving mechanism operates at different speeds.

15. The drill string of claim 1 , wherein the speed of the driving mechanism is controlled by a closed loop system.

16. The drill string of claim 1 , wherein the rotary valve is in communication with a telemetry system.

17. The drill string of claim 1 , wherein a rotor connects the first disc to the driving mechanism.

18. A method for steering a drill string through a formation, comprising the steps of:

providing the drill string with a rotary valve disposed within its bore comprising a first disc attached to a driving mechanism and a second disc axially aligned with and contacting the first disc along a flat surface;

providing a drill bit with a jack element substantially coaxial with an axis of rotation and being disposed in the bore of the drill string and comprising a distal end extending beyond the working face of the drill bit;

passing fluid through the bore from the surface;

selectively passing at least a portion of the fluid through ports formed in each of the discs into a nozzle disposed in the drill bit by rotating the discs relative to another by the driving mechanism such that the ports periodically align;

steering the drill bit by directing a fluid pulse formed by the aligning of the ports against the formation in a selected azimuth proximate the drill bit thereby eroding the formation along the selected azimuth.

19. The method of claim 18 , wherein the eroding of the formation occurs proximate a distal end of a jack element.