Cuttings in the wellbore are not efficiently removed from the annulus because the drilling fluid does not sufficient carrying capacity and/or there is not enough flow rate to create good annular velocity. When pumps are off, cuttings fall down due to gravitational force and pack and annulus. Finally, it results in stuck pipe. Typically, the wells classified as vertical or near vertical wells have an inclination of less than 35 degrees.
Note: In order to clean annulus effectively, the annular velocity must be more than the cutting slip velocity in a dynamic condition. Moreover, mud properties must be able to carry cutting when pumps are on and suspend cutting when pumps are off.
Cutting While Pump On
Cutting Falling Down While Pump Off
Warning signs of cutting setting in a vertical well
- There is an increase in torque /drag and pump pressure.
- Observe over pull when picking up and pump pressure required to break circulating is higher without any parameter changes.
Indications when you are stuck due to cutting bed in a vertical well
- When this stuck pipe caused by cutting settling happens, circulation is restricted and sometimes impossible. It most likely happens when the pump is off (making connection) or tripping in/out of hole.
- Pipe rotation is limited or impossible.
What should you do for this situation?
- Attempt to circulate with low pressure (300-400 psi). Do not use high pump pressure because the annulus will be packed harder and it will not be able to free the pipe anymore.
- Apply maximum allowable torque and jar down with maximum trip load. Do not try to jar up because it will create a worse situation.
- Attempt until the pipe is free, then circulate and work the pipe until the wellbore is clean. High-vis sweep is recommended to pump in order to clean excessive cutting. Check cutting at shale shakers, torque/drag and pump pressure in order to ensure hole condition.
Preventive Actions
- Ensure that annular velocity is more than thee cutting slip velocity. You can learn more about cutting slip velocity calculation via these links (Cutting Slip Velocity Calculation Method 1,Cutting Slip Velocity Calculation Method 2)
- Ensure the mud properties are in good shape.
- Consider pump hi-vis pill. Try weighted or unweighted and see which one gives the best cutting removal capability.
- If hi-vis sweep is pumped, ensure that sweep must be returned to surface before making any connection. For a good drilling practice, it is recommended that there should not be more than one sweep in the wellbore.
- Circulate hole clean prior to tripping out of a hole. Ensure that good reciprocation while circulating is achieved.
- Circulate few minutes before making another connection in order to clear cutting around the BHA.
- Record drilling parameters and observe trend changes frequently.
- Maximize hole cleaning.
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].
