DOWNHOLE VIBRATION TOOL FOR DRILL STRING

1 . A friction reduction tool for vibrating a drill string or coiled tubing to be lowered into a wellbore and into which a drilling fluid is pumped, the friction reduction tool comprising:

a housing for connecting the friction reduction tool to the drill string or the coiled tubing;

a force converter within the housing and having a first end and a second end, the force converter comprising a stator extending from the first end to the second end, a helical rotor at least partially within the stator and extending from the first end to the second end, and a rotational cavity passageway for conveying the drilling fluid between the stator and the helical rotor; and

a valve assembly within the housing and connected to the second end of the force converter;

wherein the helical rotor has a bore which extends through the helical rotor and which defines an alternative passageway for the drilling fluid; and

wherein the rotational cavity passageway and the alternative passageway are in fluidic communication with the valve assembly.

2 . The friction reduction tool of claim 1 , wherein the ratio of the volume of drilling fluid pumped through the rotational cavity passageway to the volume of drilling fluid pumped through the alternative passageway is from 1:1 to 19:1.

3 . The friction reduction tool of claim 1 , wherein the diameter of the bore is less than 90% a minor diameter of the rotor.

4 . The friction reduction tool of claim 1 , wherein the valve assembly comprises a valve to: (i) increase an effective cross-sectional flow area for the drilling fluid pumped through the housing, and (ii) decrease the effective cross-section flow area.

5 . The friction reduction tool of claim 1 , wherein the valve assembly comprises a valve mounted within the housing that moves along a central axis of the housing between a first position that restricts passage of the drilling fluid through a vent in the housing to an exterior of the housing and a second position that allows passage of the drilling fluid through the vent.

6 . The friction reduction tool of claim 5 , wherein the valve comprises a sleeve and one or more rotational cams that cause the sleeve to slide in an axial direction along the central axis of the housing between the first position and the second position

7 . The friction reduction tool of claim 1 , wherein the valve assembly is structured to periodically vent the drilling fluid that is conveyed through the rotational cavity passageway and/or the alternative passageway.

8 . The friction reduction tool of claim 1 , further comprising a drive assembly within the housing, the drive assembly connecting the valve assembly to the force converter and structured to convert eccentric motion of the force converter to concentric motion.

9 . A drill telemetry system for transmitting downhole measurements to the surface, the drill telemetry system comprising:

a measurement while drilling (MWD) downhole tool for generating a pulsed signal in a drilling fluid;

a drill bit connected to the MWD downhole tool;

a friction reduction tool comprising a force converter having a stator extending from the first end to the second end, a helical rotor at least partially within the stator and extending form the first end to the second end, and a rotational cavity passageway for conveying the drilling fluid between the stator and the helical rotor;

wherein the helical rotor has a bore which defines an alternative passageway for the drilling fluid;

wherein the MWD downhole tool and the alternative passageway are in fluidic communication; and

wherein the friction reduction tool is structured to transmit the pulsed signal to the surface.

10 . The drill telemetry system of claim 9 , wherein the MWD downhole tool and the alternative passageway are in fluidic communication via the drill string.

11 . The drill telemetry system of claim 9 , wherein the diameter of the bore is less than 90% a minor diameter of the rotor.

12 . The drill telemetry system of claim 9 , wherein the friction reduction tool further comprises a valve assembly connected to the force converter.

13 . The drill telemetry system of claim 12 , wherein the valve assembly comprises a rotary valve to: (i) increase an effective cross-sectional flow area for the drilling fluid pumped through the housing when venting the drilling fluid and (ii) decrease the effective cross-section flow area when not venting.

14 . The drill telemetry system of claim 12 , wherein the valve assembly comprises an axial valve mounted within the housing that moves along a central axis of the housing between a first position that restricts passage of the drilling fluid through a vent in the housing to an exterior of the housing and a second position that allows passage of the drilling fluid through the vent.

15 . A method for transmitting downhole measurements to the surface, the method comprising:

pumping drilling mud through a drill string, the drill string comprising:

a measurement while drilling (MWD) downhole tool;

a friction reduction tool comprising a force converter having a stator extending from the first end to the second end, a helical rotor at least partially within the stator and extending form the first end to the second end, and a rotational cavity passageway for conveying the drilling fluid between the stator and the helical rotor; and

drill piping connecting the MWD downhole tool to the friction reduction tool;

wherein the helical rotor has a bore which defines an alternative passageway for the drilling fluid; and

wherein the MWD downhole tool and the alternative passageway are in fluidic communication via the drill piping;

measuring a parameter of interest with the MWD downhole tool to provide a measurement;

generating a pulsed signal in the drilling mud based on the measurement; and

conveying the pulsed signal through the friction reduction tool to the surface.

16 . The method of claim 15 , wherein the pulsed signal is attenuated by less than 90% during the conveying.

17 . The method of claim 15 , wherein the pulsed signal comprises a pattern of one or more pressure pulses in the drilling fluid.

18 . The method of claim 17 , wherein the pattern of one or more pressure pulses comprises a positive pressure pulse, a negative pressure pulse, a continuous carrier wave, or combinations thereof.