Page 178 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 154

[ ] Well Programming
2.2.3

unexpected drilling break occurs it may be wise to have a policy of
closing in and circulating bottoms up across open chokes before
proceeding further.
5. Water-based muds should be used, if possible. This will reduce
well control problems caused by gas dissolving in the mud system.
If water based mud cannot be used for drilling then consider the
(logistical) possibility of killing the well by replacing the drilling
oil mud with water-based kill mud. This may involve having a sup-
ply boat on location for the duration of the HPHT hole section with
a supply of mud on board. The gas-bearing oil mud returns may be
hard or impossible to treat on the rig; if this is the case then it can-
not be pumped back down the well for killing and has to be dis-
posed of. If no other alternative is available, it may be possible to
burn it off through flare booms.
The main drawback to using water muds is the increased likeli-
hood of hydrates forming in the surface equipment as the gas
expands and cools. However, provisions should be made against
this, even if using oil muds.
This question has to be looked at from all possible angles and be
thoroughly discussed with the drilling contractor (as should all the
proposed HPHT plans and precautions).
6. Do not core long intervals in single runs. If the cores liberate gas
while pulling out of the hole, a kick could be precipitated while a
long way off bottom, which is harder to control.
7. Running a float sub in the drilling assembly will provide worth-
while safety in the event of a kick. A circulating sub run above the
BHA will improve the position if the nozzles plug. In a jet bit, do
not try to maximize HHP, but run large nozzles to help avoid plug-
ging if LCM has to be pumped.
8. If swabbing is suspected at any time while tripping, run back to bot-
tom and circulate bottoms up. Pump out of the hole if necessary, or
even as a routine precaution. Calculate swab and surge pressures
and maintain good rheology to minimize these occurrences.
9. If there are no concerns over formation fracture gradients, consid-
er bullheading an influx back into the kicking formation prior to
circulating kill mud around. This would be particularly applicable

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