Tag Archives: Oil Field Knowledge

Undergauge Hole Causes Stuck Pipe

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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.

Undergauge hole is caused by abrasive formations

Undergauge hole is caused by abrasive formations

The drill string gets stuck at the undergauge section

The drill string gets stuck at the undergauge 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?

  1. 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.

Preventive actions:

  1. Properly gauge bit/stabilizer after it is pulled out so you will know the possibility right away.
  2. Do not stage weight in order to pass the tight spots. The more weight you put on top, the harder to free the pipe.
  3. If the undergauge bit/stabilizer is observed, you need to ream down at least 1-2 stands off the bottom.
  4. Reaming at least 1-2 stands above the top of the coring section.
  5. Trip in hole with controlled speed prior to going to possible problematic areas.

References

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.

 

Underbalanced Drilling – Watch This VDO To Get Clear Idea

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Underbalanced drilling is a drilling technique that hydrostatic pressure from drilling mud is less than reservoir pressure. The underbalanced drilling can be created by using low weight fluids as base oil, fresh water which has less hydrostatic pressure than the expected formation pressure. Additionally, this drilling method is achieved by using low density drilling fluids as gas, foam, combination between conversional drilling fluid and foam/air.

The main advantage of Underbalanced drilling is to minimized formation damage in reservoir. With underbalanced drilling, the reservoir fluid is allowed to flow out into the well therefore the chance of mud invasion into the reservoir is minimal. Hence, the production from the well from this technique is higher than normal wells. Conversely, drilling with conventional method (overbalanced drilling) creates near wellbore damages which affect hydrocarbon production.

The underbalanced drilling is often applied to horizontal drilling wells because long horizontal reservoir will not be damaged with drilling fluid. Only few inches of near wellbore damage in the horizontal section can drastically reduce the reservoir performance.

This video from Shell demonstrates you regarding underbalanced drilling and there is one section showing comparison between conventional and underbalanced drilling. This short VDO will definitely give you clear picture of this technique.