Ledges are occurred while drilling in sequential formations which have soft, hard formations, and naturally fractured formations. Stabilizers in BHA and tool joint easily wear soft formations and naturally fractured formations, however, the hard formations are still in gauge (hole size not change). If there are a lot of ledges in the wellbore, the drillstring can get stuck under ledges.
Warning signs when you get stuck due to Ledges
• Hard and soft streak formations are drilled. You can easily observe from changes in ROP.
• Mud logging samples show soft and hard rocks.
• There is potential for fractured formations to be drilled.
Stuck identification for Ledges
• Erratic over pull is observed.
• It can be happened while tripping or drilling and it is also related to micro doglegs.
• Circulation can be established without any restriction.
What should you do for this situation?
1. If the drillstring is stuck while moving up, jar down with maximum trip load. Torque can be applied with caution while jarring down.
2. If the drillstring is stuck while moving down, jar up with maximum trip load without applying any torque in drill string.
3. If the drill string is free, you may need to consider back reaming to clear some ledges.
1. Minimize big stabilizers.
2. Minimize changes in inclination and azimuth.
3. Back reaming operation should be performed when the suspected formations are drilled. Carefully watch the over pull while reaming.
4. Slow down tripping sleep when entering possible problematic formations.
Drilling formulas Stuck Pipe Prevention Book => Stuck Pipe Prevention Book