Friday, 22 December 2017

VOLUMTRIC STRIPPING - SWABBED KICK

VOLUMTRIC STRIPPING


The options available if there are a swabbed influx OR if the well starts flowing during a trip:

a)      If well is not flowing, trip back to bottom keeping a careful check on returns. Then circulate influx out of hole.

b)     If well is flowing and is shut in and the gas is percolating with the bit a long way off bottom and tight hole conditions have been experienced, then consider doing a volumetric bleed.

c)      If well is flowing and is shut in and the gas is percolating with the bit a long way off bottom and tight hole conditions have been experienced, then consider bullheading.

d)     If well is flowing and is shut in and the gas is percolating and no problems are anticipated in stripping back to bottom, then consider volumetric stripping to get bit to bottom. Circulate influx out using first circulation of Driller's Method.

Note:         A swabbed kick well can be most effectively killed with bit on bottom. So every effort must be made to get bit safely back on bottom.

Example of Volumetric Stripping

Well details


volumetric stripping

Shut in procedure for a swabbed kick while tripping

Fast shut-in

1.      Stab safety valve (kelly cock).

2.      Close safety valve.

3.      Open HCR fail safe valves.

4.      Close annular.

5.      Read casing pressure and if possible read drill pipe pressure.

6.      Stab inside BOP (Gray valve).

7.      Open safety valve.

8.      Do stripping calculations, prepare stripping sheet.

9.      Reduce annular pressure and start stripping drill pipe.


Note:    The above procedure (steps 1 through 5) assumes there is no float or non-return valve in the drill string.

Calculating safety margins and working margins:






Note

  • If the gas is not migrating while stripping, only theoretical bleed off will be seen in strip tank.
  • If gas is migrating then any excess bleed off is due to migration.

When excess bleed off is ± 2.3 bbls, then build in another 50 psi working pressure. Refer to Volumetric Stripping chart




Step 1 :Allow casing pressure to increase to calculated Pchoke pressure while stripping first stand, then hold casing pressure constant by bleed off at choke.

Note: The casing pressure may not rise straight away because the gas has to be compressed. It may take 2 - 3 stands before a pressure build up is seen.

Step 2, 3 and 4 : With theoretical bleed already calculated, record actual bleed, when the difference between the actual and theoretical bleed is 2.3 bbls allow annulas pressure to increase by Pw (50 psi).


graphical of volumetric stripping operations

With bit on bottom 

Casing pressure reads 560 psi, gas influx has expanded by 9.45 bbls and if it was possible to read drill pipe pressure it would read zero with drill pipe full of mud. The influx should now be circulated out using auto choke.

Note:    No kill mud will be required as this is a swabbed kick.


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