This situation could happen when drilling into unconsolidated formations such as gravel, sand, pea, etc. Since bonds between particles are weak, particles in the formations will separate and fall down into the hole. If there are a lot of unconsolidated particles in the annulus, the drilling string can possibly be packed off and stuck.
Warning signs when you get stuck due to unconsolidated formation
• This situation could happen either while drilling or tripping. There is more of a chance that the situation can happen while drilling.
• Slight loss may possibly be seen while drilling.
• Drilling torque and pump pressure abnormally increases.
• Abnormal drag can be observed while picking up a pipe.
Indications when you are stuck due to unconsolidated formation
• Observe a lot of particles of gravel, sand, pea over shale shakers.
• Increase in mud weight, rheology and sand content in drilling mud.
• When it happens, the annulus may be completely packed off or bridged off; therefore, circulation is very difficult or impossible to establish.
• Most of the time this situation happens while drilling a surface section where formation bonding is not strong. Moreover, it can occur suddenly.
What should you do for this situation?
1. Attempt to circulate with low pressure (300-400 psi). Higher pump rate is not recommended because it will cause more cutting accumulation around a drill string and your drill string will become harder to get free.
2. If you are drilling or POOH, apply the maximum allowable torque and jar down with the maximum trip load.
3. If you are tripping in a hole, jar up with the maximum trip load without applying any torque.
4. When the pipe is freed, circulate to clean wellbore prior to drilling ahead.
1. Use high vis/weight sweep to help with hole cleaning.
2. Ensure that fluid loss of drilling mud is not out of specification. Good fluid loss will create good mud cake, which can help seal the unbounded formation.
3. Control ROP while drilling into unconsolidated zones and take the time to clean the wellbore if necessary.
4. Slow tripping speed when BHA is being passed unconsolidated zones to minimize the formation falling down.
5. Minimize surge pressure by starting/stopping pumps slowly and working the string slowly.
6. Spot gel across suspected formations prior to tripping out of a hole. Gel could prevent some particles from falling down into the wellbore.
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.