If the pipe becomes stuck, and pulling and working the string has failed to free the pipe, spotting fluids should be used around the stuck part of the string, in an attempt to eliminate the root cause of the sticking.
Differential Sticking
Such fluids are designed to attack and break down the filter cake thus reducing the bond between the cake and the pipe.
The severity of differential sticking increases with time and therefore it is of utmost importance to take remedial action as soon as possible after occurrence of the incident.
The spotting fluid requires time to break down the filter cake. Any pill spotted should be allowed to soak for 12 hours.
Stuck Pipe In Water Based Muds
Each rig drilling shall maintain a minimum stock of the following:
- 6 drums of PIPE-LAX or equivalent to mix with diesel
- 2 drums emulsifier
- 10 sacks viscosifier
- 40 bbls of diesel
The suggested minimum stock will make 60 bbls of spotting fluid which is twice the amount required to cover a typical BHA in a 12.1/4” hole section, leaving sufficient PIPE-LAX slurry in the drill string to pump 1 bbl every 15 minutes for 4 hours.
When mixing the pill circulation of the active mud system shall be maintained throughout the mixing process, to prevent gellation of mud in the annulus.
Clean out pill tank and fill with diesel. The volume shall be equal to 100 % excess over the annular volume around the drill collars. Mix the pill in accordance with the following procedure (procedure is for 6 bbls of weighted PIPE-LAX spotting fluid).
1. Add 166 gal of diesel.
2. Add 33 gal of PIPE-LAX.
3. Add 10 gal of primary emulsifier.
4. Add 53 gal of water.
5. Mix for 15 minutes.
6. Ad 50 lbs of viscosifier (organophilic clay).
7. Mix for 30 minutes.
8. Add Barites (12 ¼” hole) or Salt/CaC03 (8 ½”/6”) until the desired gradient is achieved.
Gradient of the pill should be the same as, or preferably 0.5 - 1 ppg above, the gradient of the mud system, to minimise migration of the pill through the static mud column.
Care shall be taken to isolate oil-based spotting fluid and any contaminated mud, when it is returned to the surface.
Acid (15%-20%) can also be spotted for stuck pipe if permission is granted from Company office.