METHODS OF DEFLECTING A WELLBORE con't

Jetting
Jetting was used as an alternative to whipstocks 
  • Jetting was only effective in softer rocks since formations have to be eroded to change the trajectory of the wellbore 
  • A bit with a larger diameter nozzle facing the side of the hole was used to erode the formation to one side of the bit                       



  • The larger nozzle was oriented in the desired direction
  • The formation was washed as the assembly was lowered into the hole 

  •  If the rocks were too soft, the entire bottom of the hole may wash out without substantially altering the hole trajectory
  • In harder formations, the bit often had to be turned slightly left and right to erode the side of the hole 
  • Penetration rate while jetting, was very slow 
  • Once a portion of the hole had been jetted and the bit worked to bottom, the assembly was rotated to continue drilling ahead   
  • Jetting created a high dogleg severity in a short interval even though surveys may not indicate it   
  • The jet deflection bit was actually the first steerable assembly 
  1.   While jetting, the drill string was not rotated in order to effect a trajectory change (slide drilling) 
  2.   After jetting, the drill string was rotated to drill ahead