Undergauge hole can happen when drilling in hard and abrasive formations where it wears down a drill bit. When the bit is undergauge because the abrasive formation wears a bit and stabilizes, a hole size becomes smaller. When the new BHA is run in hole, the new bit/BHA gets stuck into the undergauge hole section. Additionally, if coring is performed with a smaller core bit than the next bit, the new bit can get stuck at the top of the coring section.
Warning signs when you get stuck due to Undergauge Hole
- Drilling into abrasive formations.
- A bit and stabilizers are undergauge.
Stuck identification for Undergauge Hole
- This type of stuck pipe occurs only when tripping in hole.
- Sit down weight suddenly increases.
- The bit gets jammed off bottom.
- Circulation can be established.
What should you do for this situation?
- This stuck pipe always happening while the drill string is being moved down, therefore you need to jar up with maximum trip load without applying any torque in the drill string.
- Properly gauge bit/stabilizer after it is pulled out so you will know the possibility right away.
- Do not stage weight in order to pass the tight spots. The more weight you put on top, the harder to free the pipe.
- If the undergauge bit/stabilizer is observed, you need to ream down at least 1-2 stands off the bottom.
- Reaming at least 1-2 stands above the top of the coring section.
- Trip in hole with controlled speed prior to going to possible problematic areas.
John Mitchell Drilbert Engineering, 2002. Trouble-Free Drilling Volume 1: Stuck Pipe Prevention. Edition. Drilbert Engineering Inc.
Fanarco.net. 1999. Stuck Pipe Prevention Self-Learning Course. [ONLINE] Available at: http://www.fanarco.net/books/drilling/stuck-pipe.pdf. [Accessed 21 June 2016
Steve Devereux, 2012. Drilling Technology in Nontechnical Language, 2d Ed.. 2 Edition. PennWell Corp.