Where shallow casing strings or conductor pipe are set, fracture gradients will be low. It may be impossible to close the BOP on a shallow gas kick without breaking down the formation at the shoe. If a shallow gas kick is taken while drilling top hole then the kick should be diverted.
Drilling shallow sand too fast can result in large volumes of gas cut mud in the annulus and cause the well to flow, also fast drilling can load up the annulus increasing the mud density leading to lost circulation and if the level in annulus drops far enough then well may flow.
When drilling top hole a diverter should be installed and it is good practice to leave the diverter installed until 13 3/8" casing has been run.
1. Stop drilling
2. Pick drill string off bottom to predetermined shut in point. Stop the mud pump. If flow is excessive begin next step immediately and strip drill string to close in predetermined point once well is secured.
3. Close upper annular and open choke line fail-safe valves.
4. Ensure well is shut in and begin recording shut in pressures.
5. Pass word to the OIL COMPANY REP and DRILLING CONTRACTOR REP of the well condition.
6. Pick up circulating kill assembly if it is to be used.
7. Check space out then close upper pipe rams.
8. Adjust BOP closing pressure as required for stripping and landing drill string on upper pipe rams.
9. Close hang off rams with reduced pressure. Reduce annular pressure.
(Note: there will be pressure trapped between annular and rams)
10. Land drill string on upper pipe rams, adjust BOP closing pressure and down weight on upper pipe rams to prevent the hydraulic effect on the drill string
11. Close wedge locks and adjust compensator to support drillstring weight to BOP plus 20,000 lbs.
12. Bleed off any trapped pressure between the annular and rams.
13. Open annular.
14. Complete recording of shut in pressure build up and pit gain.
15. Decide kill programme.
SHUT-IN PROCEDURE WHILE TRIPPING ON A FLOATING RIG
1. Set slips below top tool joint.
2. Install full opening safety valve, torque connection and close safety valve.
3. Close upper annular and open choke line fail-safe valves.
4. Ensure well is shut in and begin recording shut in pressures.
5. Pass word to the OIL COMPANY REP and SENIOR DRILLING CONTRACTOR REP of the well condition.
6. Make up the top drive or circulating kill assembly.
7. Open safety valve.
8. Complete recording of shut in pressure build up and pit gain.
9. Decide kill programme.
The objective of the various kill methods is to circulate out any invading fluid and circulate a satisfactory weight of kill mud into the well without allowing further fluid into the hole. Ideally this should be done with the minimum of damage to the well.
If this can be done, then once the kill mud has been fully circulated around the well, it is possible to open up the well and restart normal operations.
Generally, a kill mud which just provides hydrostatic balance for formation pressure is circulated.
This allows approximately constant bottom hole pressure which is slightly greater than formation pressure to be maintained as the kill circulation proceeds because of the additional small circulating friction pressure loss.
After circulation, the well is opened up again and the mud weight may be further increased to provide a safety or trip margin.
There are three ‘constant bottom-hole pressure’ kill methods in common use today which are:
• Driller’s Method
• Wait & Weight Method (also known as the ‘Engineer’s Method’)
• Concurrent Method
These three techniques are very similar in principle, and differ only in respect of when kill mud is pumped down.
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