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
- While jetting, the drill string was not rotated in order to effect a trajectory change (slide drilling)
- After jetting, the drill string was rotated to drill ahead