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Gunk Plug Squeeze Procedures | Bentonite Diesel Oil

The use of a gunk plug or squeeze may be considered if conventional LCM pills are unsuccessful in reducing or curing formation losses. The traditional gunk plug or squeeze involved dispersing Bentonite in diesel oil and spotting the resulting gunk plug across the thief zone. The gunk squeeze involves closing the annular BOP and squeezing the gunk plug into the thief zone in an attempt to cure the formation losses. This gunk plug procedures should not be used for curing losses in the reservoir section due to resultant formation damage.

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A gunk plug can be formulated using any mineral or synthetic base oil, because the primary function of the oil is to prevent hydration while displacing a concentrated suspension of Bentonite down the drill string to the thief zone.

Bentonite Diesel Oil Slurry | Gunk Plug Applications:

Bentonite Diesel Oil slurries can be useful in the following situations:

  • They can assist in controlling severe mud loss in areas where conventional LCM ineffective.
  • They can be very helpful in vugular and cavernous thief zones

Avoid Bentonite Diesel Oil slurry contamination with water or water based mud in the Pump lines as it will hydrate and forming a dense plastic plug which will plug the lines 

Gunk Plug Squeeze Procedures

The procedure for a typical bentonite diesel oil / gunk plug and squeeze that is mixed at the cement unit is as follows:

  1. Flush the cement pump and associated lines with base oil to remove all traces of water.
  2. Make sure the cement mix tank is clean and dry.
  3. Fill the cement mix tank with 25 bbl base oil.
  4. Switch on the mix tank agitator.
  5. Add 300 ppb Bentonite to form a concentrated suspension in base oil.
  6. Keep circulating the mix tank to disperse and suspend the Bentonite.
  7. Displace a 10 bbl base oil spacer into the drill string.
  8. Displace the gunk plug pill into the drill string.
  9. Displace a 10 bbl base oil spacer into the drill string.
  10. With the drill bit just above the thief zone, pump the gunk pill down to the bit with a pumping rate 4 bbls/min.
  11. When plug exits drill string, close annular preventer and pump fluids into annulus while displacing the plug from the DP. Drillpipe/ annulus ratio is 2:1, about 600 l/min from drill pipe and 300 l/min from the annulus.
  12. After displacing (bentonite oil diesel) half the plug, reduce the pump rate by half.
  13. After displacing 3/4 of the plug, attempt a ‘hesitation squeeze pressure’ with 100-500psi.
  14. Under displace plug by one barrel, POOH, allow 8-10hrs set time
  15. Close the annular blowout preventer and squeeze the gunk pill into the thief zone.
  16. Pull up into the casing shoe and maintain pressure for approximately 4 hours.

It is recommended that plastic plug volume shall equal, or be greater than, the hole below the loss zone

What Will Happen After The Squeeze

During the squeeze, the base oil is pushed into the thief zone and the Bentonite is then hydrated by water from the water-based mud, which will form a thick, putty-like material that is designed to seal the thief zone.

The gunk plug or squeeze will only be effective if the exact location of the thief zone is known, which can be determined by running logs (e.g. wellbore temperature log), and the diesel spacers must be large enough to prevent Bentonite hydration before the gunk pill has left the drill string.