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# Difference between revisions of "Differential-pressure pipe sticking"

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− | Differential-pressure [[ | + | Differential-pressure [[Stuck_pipe|pipe sticking]] occurs when a portion of the drillstring becomes embedded in a mudcake (an impermeable film of fine solids) that forms on the wall of a permeable formation during drilling. |

− | ==Differential sticking== | + | == Differential sticking == |

− | |||

− | <gallery widths=300px heights=200px> | + | If the mud pressure, ''p''<sub>''m''</sub> , which acts on the outside wall of the pipe, is greater than the formation-fluid pressure, ''p''<sub>''ff''</sub> , which generally is the case (with the exception of underbalanced drilling), then the pipe is said to be differentially stuck (see '''Fig. 1'''). |

+ | |||

+ | <gallery widths="300px" heights="200px"> | ||

File:Devol2 1102final Page 434 Image 0001.png|'''Fig. 1—Differential-pressure sticking.''' | File:Devol2 1102final Page 434 Image 0001.png|'''Fig. 1—Differential-pressure sticking.''' | ||

</gallery> | </gallery> | ||

Line 10: | Line 11: | ||

The differential pressure acting on the portion of the drillpipe that is embedded in the mudcake can be expressed as: | The differential pressure acting on the portion of the drillpipe that is embedded in the mudcake can be expressed as: | ||

− | [[File:Vol2 page 0434 eq 001.png]]....................(1) | + | [[File:Vol2 page 0434 eq 001.png|RTENOTITLE]]....................(1) |

The pull force, F<sub>''p''</sub>, required to free the stuck pipe is a function of the differential pressure, Δ''p''; the coefficient of friction, ''f''; and the area of contact, ''A''<sub>''c''</sub>, between the pipe and mudcake surfaces. | The pull force, F<sub>''p''</sub>, required to free the stuck pipe is a function of the differential pressure, Δ''p''; the coefficient of friction, ''f''; and the area of contact, ''A''<sub>''c''</sub>, between the pipe and mudcake surfaces. | ||

− | [[File:Vol2 page 0434 eq 002.png]]....................(2) | + | [[File:Vol2 page 0434 eq 002.png|RTENOTITLE]]....................(2) |

− | From Ref. 1.<ref name="r1" />, | + | From Ref. 1.<ref name="r1">Bourgoyne, A.T., Millheim, K.K., Chenevert , M.E. et al. 1986. Applied Drilling Engineering. Richardson, Texas: Textbook Series, SPE.</ref>, |

− | [[File:Vol2 page 0434 eq 003.png]]....................(3) | + | [[File:Vol2 page 0434 eq 003.png|RTENOTITLE]]....................(3) |

where | where | ||

− | [[File:Vol2 page 0434 eq 004.png]]....................(4) | + | [[File:Vol2 page 0434 eq 004.png|RTENOTITLE]]....................(4) |

− | In this formula, ''L''<sub>''ep''</sub> is the length of the permeable zone, ''D''<sub>''op''</sub> is the outside diameter of the pipe, ''D''<sub>''h''</sub> is the diameter of the hole, and ''h''<sub>''mc''</sub> is the mudcake thickness. The dimensionless coefficient of friction, ''f'', can vary from less than 0.04 for oil-based mud to as much as 0.35 for weighted [[ | + | In this formula, ''L''<sub>''ep''</sub> is the length of the permeable zone, ''D''<sub>''op''</sub> is the outside diameter of the pipe, ''D''<sub>''h''</sub> is the diameter of the hole, and ''h''<sub>''mc''</sub> is the mudcake thickness. The dimensionless coefficient of friction, ''f'', can vary from less than 0.04 for oil-based mud to as much as 0.35 for weighted [[Drilling_fluid_types#Classification_of_drilling_fluids#Water-based_fluids|water-based mud]] with no added lubricants. |

+ | |||

+ | == Pipe sticking force == | ||

− | |||

'''Eqs. 2 and 3''' show controllable parameters that will cause higher pipe-sticking force and the potential inability of freeing the stuck pipe. These parameters are: | '''Eqs. 2 and 3''' show controllable parameters that will cause higher pipe-sticking force and the potential inability of freeing the stuck pipe. These parameters are: | ||

− | |||

− | |||

− | |||

− | |||

− | Although hole and pipe diameters and hole angle play a role in the pipe-sticking force, they are uncontrollable variables once they are selected to meet well design objectives. However, the shape of drill collars, such as square, or the use of drill collars with spiral grooves and external-upset tool joints can minimize the sticking force. | + | *Unnecessarily high differential pressure |

+ | *Thick mudcake (high continuous fluid loss to formation) | ||

+ | *Low-lubricity mudcake (high coefficient of friction) | ||

+ | *Excessive embedded pipe length in mudcake (delay of time in freeing operations) | ||

+ | |||

+ | Although hole and pipe diameters and hole angle play a role in the pipe-sticking force, they are uncontrollable variables once they are selected to meet well design objectives. However, the shape of drill collars, such as square, or the use of drill collars with spiral grooves and external-upset tool joints can minimize the sticking force. | ||

+ | |||

+ | == Indicators of differential stuck pipe == | ||

− | |||

Some of the indicators of differential-pressure-stuck pipe while drilling permeable zones or known depleted-pressure zones are: | Some of the indicators of differential-pressure-stuck pipe while drilling permeable zones or known depleted-pressure zones are: | ||

− | |||

− | |||

− | |||

− | ==Prevention or mitigation of differential stuck pipe== | + | *An increase in torque and drag |

− | Differential-pressure pipe sticking can be prevented or its occurrence mitigated if some or all of the following precautions are taken: | + | *An inability to reciprocate the drillstring and, in some cases, to rotate it |

+ | *Uninterrupted [[Drilling_fluids|drilling-fluid]] circulation | ||

+ | |||

+ | == Prevention or mitigation of differential stuck pipe == | ||

+ | |||

+ | Differential-pressure pipe sticking can be prevented or its occurrence mitigated if some or all of the following precautions are taken: | ||

− | * Maintain the lowest continuous fluid loss adhering to the project economic objectives. | + | *Maintain the lowest continuous fluid loss adhering to the project economic objectives. |

− | * Maintain the lowest level of drilled solids in the mud system, or, if economical, remove all drilled solids. | + | *Maintain the lowest level of drilled solids in the mud system, or, if economical, remove all drilled solids. |

− | * Use the lowest differential pressure with allowance for swab and surge pressures during tripping operations. | + | *Use the lowest differential pressure with allowance for swab and surge pressures during tripping operations. |

− | * Select a mud system that will yield smooth mudcake (low coefficient of friction). | + | *Select a mud system that will yield smooth mudcake (low coefficient of friction). |

− | * Maintain drillstring rotation at all times, if possible. | + | *Maintain drillstring rotation at all times, if possible. |

Differential-pressure-pipe-sticking problems may not be totally prevented. If sticking does occur, common field practices for freeing the stuck pipe include: | Differential-pressure-pipe-sticking problems may not be totally prevented. If sticking does occur, common field practices for freeing the stuck pipe include: | ||

− | * Mud-hydrostatic-pressure reduction in the annulus | + | |

− | * Oil spotting around the stuck portion of the drillstring | + | *Mud-hydrostatic-pressure reduction in the annulus |

− | * Washing over the stuck pipe | + | *Oil spotting around the stuck portion of the drillstring |

+ | *Washing over the stuck pipe | ||

Some of the methods used to reduce the hydrostatic pressure in the annulus include: | Some of the methods used to reduce the hydrostatic pressure in the annulus include: | ||

− | |||

− | |||

− | |||

− | ==References== | + | *Reducing mud weight by dilution |

+ | *Reducing mud weight by gasifying with nitrogen | ||

+ | *Placing a packer in the hole above the stuck point | ||

+ | |||

+ | == References == | ||

+ | |||

+ | <references /> | ||

+ | |||

+ | == See also == | ||

− | + | [[Stuck_pipe|Stuck pipe]] | |

− | |||

− | |||

− | + | [[Mechanical_pipe_sticking|Mechanical pipe sticking]] | |

− | [[ | ||

− | [[ | + | [[PEH:Drilling_Problems_and_Solutions]] |

− | + | == Noteworthy papers in OnePetro == | |

− | == | + | == External links == |

− | == | + | == Category == |

+ | [[Category:1.4 Drillstring design]] [[Category:YR]] |

## Latest revision as of 12:06, 26 June 2015

Differential-pressure pipe sticking occurs when a portion of the drillstring becomes embedded in a mudcake (an impermeable film of fine solids) that forms on the wall of a permeable formation during drilling.

## Contents

## Differential sticking

If the mud pressure, *p*_{m} , which acts on the outside wall of the pipe, is greater than the formation-fluid pressure, *p*_{ff} , which generally is the case (with the exception of underbalanced drilling), then the pipe is said to be differentially stuck (see **Fig. 1**).

The differential pressure acting on the portion of the drillpipe that is embedded in the mudcake can be expressed as:

The pull force, F_{p}, required to free the stuck pipe is a function of the differential pressure, Δ*p*; the coefficient of friction, *f*; and the area of contact, *A*_{c}, between the pipe and mudcake surfaces.

From Ref. 1.^{[1]},

where

In this formula, *L*_{ep} is the length of the permeable zone, *D*_{op} is the outside diameter of the pipe, *D*_{h} is the diameter of the hole, and *h*_{mc} is the mudcake thickness. The dimensionless coefficient of friction, *f*, can vary from less than 0.04 for oil-based mud to as much as 0.35 for weighted water-based mud with no added lubricants.

## Pipe sticking force

**Eqs. 2 and 3** show controllable parameters that will cause higher pipe-sticking force and the potential inability of freeing the stuck pipe. These parameters are:

- Unnecessarily high differential pressure
- Thick mudcake (high continuous fluid loss to formation)
- Low-lubricity mudcake (high coefficient of friction)
- Excessive embedded pipe length in mudcake (delay of time in freeing operations)

Although hole and pipe diameters and hole angle play a role in the pipe-sticking force, they are uncontrollable variables once they are selected to meet well design objectives. However, the shape of drill collars, such as square, or the use of drill collars with spiral grooves and external-upset tool joints can minimize the sticking force.

## Indicators of differential stuck pipe

Some of the indicators of differential-pressure-stuck pipe while drilling permeable zones or known depleted-pressure zones are:

- An increase in torque and drag
- An inability to reciprocate the drillstring and, in some cases, to rotate it
- Uninterrupted drilling-fluid circulation

## Prevention or mitigation of differential stuck pipe

Differential-pressure pipe sticking can be prevented or its occurrence mitigated if some or all of the following precautions are taken:

- Maintain the lowest continuous fluid loss adhering to the project economic objectives.
- Maintain the lowest level of drilled solids in the mud system, or, if economical, remove all drilled solids.
- Use the lowest differential pressure with allowance for swab and surge pressures during tripping operations.
- Select a mud system that will yield smooth mudcake (low coefficient of friction).
- Maintain drillstring rotation at all times, if possible.

Differential-pressure-pipe-sticking problems may not be totally prevented. If sticking does occur, common field practices for freeing the stuck pipe include:

- Mud-hydrostatic-pressure reduction in the annulus
- Oil spotting around the stuck portion of the drillstring
- Washing over the stuck pipe

Some of the methods used to reduce the hydrostatic pressure in the annulus include:

- Reducing mud weight by dilution
- Reducing mud weight by gasifying with nitrogen
- Placing a packer in the hole above the stuck point

## References

- ↑ Bourgoyne, A.T., Millheim, K.K., Chenevert , M.E. et al. 1986. Applied Drilling Engineering. Richardson, Texas: Textbook Series, SPE.

## See also

PEH:Drilling_Problems_and_Solutions