Vibrationless moineau system

Abstract

A method of operating a Moineau system to substantially eliminate vibrations, the method includes rotating a first rotational member, and rotating a second rotational member. Each of the first rotational member and the second rotational member includes a plurality of lobes. A first rotational speed of one of the first rotational member and the second rotational member is selected based on 1) a second rotational speed of the other of the first rotational member and the second rotational member and 2) the number of lobes of one of the first rotational member and the second rotational member to maintain eccentric force of one of the first and second rotational members below a predetermined threshold.

What is claimed is: 
     
       1. A method of operating a Moineau system including a first downhole motor mechanically linked in series to a second downhole motor to substantially eliminate vibrations, the method comprising:
 rotating a first rotational member of the first downhole motor; 
 rotating a second rotational member of the first downhole motor coupled to a third rotational member of the second downhole motor, each of the first rotational member and the second rotational member including a plurality of lobes; and 
 selecting a first rotational speed of one of the first rotational member and the third rotational member based on: 1) a second rotational speed of the other of the first rotational member and the third rotational member, and 2) the number of lobes of one of the first rotational member and the second rotational member to reduce eccentric force of one of the first and second rotational members. 
 
     
     
       2. The method of  claim 1 , wherein operating the Moineau system includes operating a downhole motor coupled to a drill string extending into a formation. 
     
     
       3. The method of  claim 1 , wherein coupling the first downhole motor to the second downhole motor includes connecting the first downhole motor to the second downhole motor through a dampening member. 
     
     
       4. The method of  claim 1 , wherein selecting the first rotational speed of the one of the first rotational member and the second rotational member maintains eccentric forces on the one of the first and second rotational members below about 2 g. 
     
     
       5. The method of  claim 1 , wherein reducing eccentric force comprises maintaining eccentric force below a predetermined threshold. 
     
     
       6. The method of  claim 1 , further comprising: inputting a fluid flow at a selected flow rate into a housing of the Moineau system, the selected flow rate establishing the second rotational speed of the third rotational member of the second downhole motor coupled to the second rotational member of the first downhole motor. 
     
     
       7. The method of  claim 1 , wherein operating the Moineau system comprises inputting a fluid flow at a selected flow rate into the first downhole motor and the second downhole motor. 
     
     
       8. A vibrationless Moineau system comprising:
 a first downhole motor including a first stator having a first number of stator lobes, and a first rotor having a first number of rotor lobes; and 
 a second downhole motor connected in series with the first downhole motor, the second downhole motor including a second stator mechanically linked to the first rotor, the second stator having a second number of stator lobes, and a second rotor having a second number of rotor lobes, wherein the first and second downhole motors are selectively operated to reduce eccentric forces on at least one of the first rotor and the second rotor. 
 
     
     
       9. The vibrationless Moineau system of  claim 8 , wherein the first rotor is operatively connected to the second stator through a dampening member. 
     
     
       10. The vibrationless Moineau system of  claim 8 , wherein a rotational speed of the second stator is selected based upon a rotational speed of the second rotor and one of the second number of stator lobes and the second number of rotor lobes. 
     
     
       11. The vibrationless Moineau system according to  claim 8 , further comprising: a bypass conduit having a first end fluidically connected to the first downhole motor and a second end fluidically connected to the second downhole motor. 
     
     
       12. The vibrationless Moineau system according to  claim 11 , wherein the first end of the bypass conduit is fluidically connected uphole of the first downhole motor. 
     
     
       13. The vibrationless Moineau system according to  claim 11 , further comprising: a valve fluidically connected with the bypass conduit, the valve being selectively controllable to allow fluid to pass from the first end to the second end. 
     
     
       14. The vibrationless Moineau system according to  claim 8 , further comprising: a drill bit operatively connected to the second rotor. 
     
     
       15. The vibrationless Moineau system according to  claim 8 , wherein the first and second downhole motors are selectively operable to maintain eccentric forces on the second rotor below about 2 g. 
     
     
       16. The vibrationless Moineau system of  claim 8 , wherein the second downhole motor is arranged downhole of the first downhole motor. 
     
     
       17. A resource exploration system comprising:
 a surface system; and 
 a downhole system including a downhole string operatively connected to the surface system, the downhole string including a vibrationless Moineau system comprising: 
 a first downhole motor including a first stator having a first number of stator lobes, and a first rotor having a first number of rotor lobes; and 
 a second downhole motor including a second stator mechanically linked in series to the first rotor, the second stator having a second number of stator lobes, and a second rotor having a second number of rotor lobes, wherein the first and second downhole motors are selectively operated to reduce eccentric forces on at least one of the first rotor and the second rotor. 
 
     
     
       18. The resource exploration system according to  claim 17 , wherein the first and second downhole motors are selectively operable to maintain eccentric forces on the second rotor below about 2 g. 
     
     
       19. The resource exploration system according to  claim 17 , further comprising: a bypass conduit having a first end fluidically connected to the downhole string and a second end fluidically connected to the second downhole motor. 
     
     
       20. The resource exploration system of  claim 17 , wherein the second downhole motor is arranged downhole of the first downhole motor.