Method and apparatus for vibrating horizontal drill string to improve weight transfer

Abstract

An apparatus for use in a horizontal section of a drill string is disclosed. The apparatus includes a motor that is connected to the horizontal section of the drill string. The motor is adapted to impart vibrations in the horizontal section of the drill string, where the vibrations are at about the lateral resonant frequency of the horizontal section of the drill string.

1 . An apparatus for use in a horizontal section of a drill string comprising:
 a motor, wherein the motor is connected to the horizontal section of the drill string; and   a mandrel, the mandrel being a hollow shaft, the mandrel having a longitudinal axis, the mandrel having an external wall and an inner wall, the external wall or inner wall including a partial cutout, the partial cutout providing an imbalance in the mandrel, such that the motor rotates the mandrel to impart lateral vibrations in the horizontal section of the drill string and wherein the vibrations are at about a lateral resonant frequency of the horizontal section of the drill string.   
     
     
         2 . The apparatus of  claim 1 , wherein the vibrations are imparted generally at the lowest lateral resonant frequency 
     
     
         3 . The apparatus of  claim 2 , wherein the vibrations are in the frequency range of 1 to 10 Hz. 
     
     
         4 . The apparatus of  claim 3 , wherein the vibrations are in the frequency range of 2 to 5 Hz. 
     
     
         5 . The apparatus of  claim 1 , wherein the motor is a mud motor or an electrical motor. 
     
     
         6 . A mud motor for use in a horizontal section of a drill string comprising:
 a rotor;   a stator engaged with the rotor adapted to cause a drive train coupled to the rotor to rotate at a rotary speed;   a mandrel mechanically connected to the drive train, the mandrel being a hollow shaft, the mandrel having a longitudinal axis, the mandrel having an external wall and an inner wall, the external wall or inner wall including a partial cutout, the partial cutout providing an imbalance in the mandrel such that when rotated by the rotor, the mandrel generates lateral vibrations in the horizontal section of the drill string in a selected frequency range of 1 to 10 Hz.   
     
     
         7 . (canceled) 
     
     
         8 . The mud motor of  claim 6  , wherein the drive train includes a drive shaft and further comprising two eccentric masses attached to the drive train. 
     
     
         9 . (canceled) 
     
     
         10 . A mud motor for use in a horizontal section of a drill string comprising:
 a rotor, the rotor being hollow;   a stator engaged with a drive train to rotate at a rotary speed, wherein drive train comprises a hollow rotor;   a rod, wherein the rod is longitudinally inserted into the hollow rotor, and wherein the cross-section of the rod is non-circular.   
     
     
         11 . The mud motor of  claim 10 , wherein the cross-section of the rod has a half-moon shape. 
     
     
         12 . A process for generating lateral vibrations in a horizontal section of a drill string comprising;
 supplying a motor, wherein the motor is mechanically connected to the horizontal section of the drill string;   operating the motor to rotate a mandrel having an imbalance, the mandrel being a hollow shaft, the mandrel having a longitudinal axis, the mandrel having an external wall and an inner wall, the external wall or inner wall including a partial cutout, the partial cutout providing an imbalance in the mandrel so as to cause the horizontal section of the drill string to vibrate laterally in reference to the longitudinal axis of the drill string as the mandrel is rotated, wherein the vibrations are at about a -lateral resonant frequency of the horizontal section of the drill string.   
     
     
         13 . The process of  claim 12 , wherein the lateral resonant frequency is the lowest lateral resonant frequency. 
     
     
         14 . The process of  claim 13 , wherein the lowest lateral resonant frequency is calculated using the formula: 
       
         
           
             
               
                 f 
                 min 
               
               = 
               
                 
                   1 
                   
                     2 
                      
                     
                         
                     
                      
                     π 
                   
                 
                  
                 
                   
                     
                       
                         q 
                         
                           r 
                            
                           
                               
                           
                            
                           μ 
                         
                       
                       - 
                       
                         
                           F 
                           2 
                         
                         
                           4 
                            
                           
                               
                           
                            
                           EI 
                            
                           
                               
                           
                            
                           μ 
                         
                       
                     
                   
                   . 
                 
               
             
           
         
         wherein q is the buoyant weight, r is the radial clearance between drilling drillstring and wellbore, F is the axial force on the drill, μ is the vibrating mass per unit length, and EI is the bending stiffness of the drill string. 
       
     
     
         15 . The process of  claim 13 , wherein the vibrations are in the frequency range of 1 to 10 Hz. 
     
     
         16 . The process of  claim 15 , wherein the vibrations are in the frequency range of 2 to 5 Hz. 
     
     
         17 . The process of  claim 12 , wherein the motor is an electric motor or a mud motor. 
     
     
         18 . The process of  claim 12 , further comprising:
 monitoring the frequency of the lateral vibrations of the horizontal section.   
     
     
         19 . The process of  claim 18 , further comprising:
 supplying a control system, wherein the control system is adapted to adjust the motor to impart the lateral resonant frequency based on the frequency of the lateral vibrations of the horizontal section determined by the monitoring step.   
     
     
         20 . The apparatus of  claim 1 , wherein the mandrel comprises two or more partial cutouts. 
     
     
         21 . The apparatus of  claim 1 , wherein the partial cutout is formed in the external wall of the mandrel. 
     
     
         22 . The apparatus of  claim 1 , wherein the partial cutout is formed in the inner wall of the mandrel.